Model Boat Mayhem
The Shipyard ( Dry Dock ): Builds & Questions => OMRA - Offshore Model Racing Association => Topic started by: RipSlider on September 27, 2007, 08:37:46 pm
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Hello all.
Been thinking about a fast boat for OMRA events. Have read the info on their web site. As I understand it, the classes seem to be controlled by engine size.
i didn't see any mention of hull design etc, so am I right in thinking that any hull design is allowed. For example, a cat, or a tri-mirine?
Boat design at a model size, where practical issues such as people etc can be pushed massively in this area, as long as the only limits are around engine size, position of prop, allowance of a gearbox etc. So I'm wondering why all the main boats seem so similar, i.e strudder, deep V hull of a very similar hydrodynamic shape etc etc.
Here's an example: Using a single bladed ( but well balanced ) prop would immediately find a few extra mph of speed. But there not used. So this makes me think there is another, much fuller, set of rules for each class than what is on the OMRA web site?
Thanks
Steve
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steve
theres a few rules ie got to have a 2inch freeboard and got to look similar to a made boat ! think thats about it on things apart form engine etc
but being the fastest isnt really needed ! but being consistant is better
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You forgot another unwriten rule i think? no clues? oh ok ill tell yaaa dont have the surname Marles ::) Because if you do no matter how you design and build your boat they will try to bend the rules to get your boat banned :o.
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Thaks guys.
Is the bit about "must look like a real boat" a real rule or an un-written rule?
I ask because I've been thinking about how how to get a boat around the course for the most laps. And like it says above, it's about cnsistency as well as top speed.
So, there seem to be a lot of things that can be done. For example, dynamic ballasting so as to keep the boat upright even when it goes around corners and dropping drag. Or using the new wave piercing hull designs that are starting to be used, so as to go through rather than over waves ( much quicker ). Or using an aerodymanically designed lower hull so as to optimise balance when out of the water etc etc etc.
There does seem to be a whole load of "stuff" that can be done, and it would be interesting to give it a go, but if it's going to get rejected at scruitenering, then there doesn't seem to be a lot of point.
Thanks
Steve
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hi steve.please check further down these listings and you will see a thread new omra d class boat,this is the boat i am nowe racing,abit diffrent than most,and maybe the only one in the uk.what you will find is that times are changing and so are boat designs,i will use what i think will be a good boat,but i did check to make sure that it coulds be used,good luck,and give it a go,it really is fun,,,,regards kurt
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Steve you sound like you have good ideas and if you look at the sigma hull you will see a new design that just won the championship that is now been argued about by certain omra members.i think your ideas and dave marles and maybe others too are the way forward etc but my thinking is omra isnt the place to do it they are stuck in the past if you ask me.
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Mart, please see my comments on DM's thread, OMRA have done nothing wrong.
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2" freeboard, well as a scale modeller not a racer, I take it the freeboard is the distance from waterline to the weatherdeck?
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Mart, please see my comments on DM's thread, OMRA have done nothing wrong.
If OMRA have done nothing wrong then how come they are trying to ban daves sigma? or is it just a few jealous members using theire influence?, if thats the case then they should be the ones kicked out.You cant agree a set of rules and then change them to suit your own ends which has been done in the past regarding daves boats?.I think we all know who this so called model shop owner is whos against Daves boat and i have to say this man is a prat and an arrogant prat to boot.i dont care if this sounds like a personal attack either as i dont give a **** im not a member of omra and nor will i ever be while prats are running things >:(.it only takes one bad apple to ruin the barrel and you all know who he is so i think its time the good guys stood together and got him and or his mates kicked out.
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It's bad enough having this silly argument running on the other thread - we don't need it on this one as well. Any further posts relating to the OMRA squabble will be deleted.
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Thanks colin.
So just to confirm:
2" of free board ( can someone define freeboard for me please?)
governed by the engine size
exhausts need to jut out less than 2.5"
z-class need submerged props.
Apart from that, is this the total of regulations controlling the boat design?
For e.g is there anything that says I can't use 1 engine with a gearbox, in those catorgaries that can use them, to drive two props? etc etc
Many thanks
Steve
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2" of free board ( can someone define freeboard for me please?)
Steve,
The 2" freeboard rule was introduced about two years ago - after the 2005 AGM (I think). From what I remember, the rule was sent out with the minutes - in the next newsletter. I think OMRA's definition of freeboard was included as well, as the term in itself was acknowledged as ambiguous. I don't think the online info has yet been updated with the newer rules. Maybe one of the newer members here may have a more up to date copy of the rule book, or someone may have kept the newsletter. Otherwise, you can always contact through the given contacts on the website - they are always helpful.
Cat's have definitely been raced in OMRA, and gearboxes are fine in anything except the standard / unmodified "Z" class. Interesting question about multiple prop's. I have wondered once or twice about twin engines turning twin prop's (eg two 3.5cc engines in 7.5cc class). I have never seen anything which prohibits either, but I don't know if the subjects have ever come up....
Ian
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Hello all.
Been thinking about a fast boat for OMRA events. Have read the info on their web site. As I understand it, the classes seem to be controlled by engine size.
i didn't see any mention of hull design etc, so am I right in thinking that any hull design is allowed. For example, a cat, or a tri-mirine?
Boat design at a model size, where practical issues such as people etc can be pushed massively in this area, as long as the only limits are around engine size, position of prop, allowance of a gearbox etc. So I'm wondering why all the main boats seem so similar, i.e strudder, deep V hull of a very similar hydrodynamic shape etc etc.
Here's an example: Using a single bladed ( but well balanced ) prop would immediately find a few extra mph of speed. But there not used. So this makes me think there is another, much fuller, set of rules for each class than what is on the OMRA web site?
Hi Ripslider,
my understanding is that anything goes, so long as the hull complies with the basic framework requirement of the boat design rules, IE recovery handles, painter where required, no hot exhaust to be a hazard to recovery people etc., my understanding being that the idea is to encourage new design where possible. Extract from the OMRA web site:
"Provided your boat complies with all the boat rules it can be of any shape or size. There are catamarans competing successfully but they are not as popular as mono hulls and the development of any new hull is encouraged."
I have it on good authority that the wording in the OMRA rule book should read something like below. (I will confirm when my membership comes through!)
"The exact wording of the OMRA rule passed in Nov 2005 is -
"All boats (excluding 'specialised designs' such as Tunnel Hulls and Ribs) must have at least 50mm (2 inches) of freeboard, this being the measurement of the maximum distance between the chine rail and deck"
Hope this helps.
Glenn
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It's bad enough having this silly argument running on the other thread - we don't need it on this one as well. Any further posts relating to the OMRA squabble will be deleted.
You consider the topic to be silly because you're not interested it this branch of the sport. To the people involved it's not silly. Since when does being a moderator give you the right to dismiss an entire topic and the views of the participants? As someone said on the 'other thread' , if you're not interested in it don't read it.
I can recall a well known scale modeller (GG) at a regatta once when some 'functional' boats were about to take to the water saying that he 'didn't want to watch these things as he's only interested in "real boats"'.
Similar narrow-minded attitude.
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You consider the topic to be silly because you're not interested it this branch of the sport.
I'm afraid you misunderstand me completely. It's not the dispute itself which I consider to be silly but the intemperate rantings which accompany it. Martin asked that the debate be conducted in a civilised manner and some people seem to have attempted to do that. Others couldn't and in doing so have done your branch of the hobby no favours at all.
There is no right for anyone to air their dirty washing in public on this Forum. It belongs to Martin and we are all here by invitation. The Forum rules are quite clear, particularly with regard to showing mutual respect, and those people who cannot abide by them must expect to have action taken against them.
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Yes guys, Colin is quite correct.
You / we need to take the higher ground in this debate in that if you feel there is an issue with the OMRA rules, this forum is the ideal place to debate them in public. If your issue is to move forward and produce results doesn't this discussion need to be constructive producing positive points or suggestions to put forward to the powers that be?
Let me take this opportunity to remind ALL forum members, 'This is a debating chamber - not boxing ring!'
Make your point, with passion if need be, BUT NOT AGGRESSIVELY OR BY MAKING ACCUSATIONS.
We "been there and done that now" on this forum. So as Colin says, any posts that breach the forum rules will be summarily deleted.
Martin - Forum Admin
PS...... Could someone summarize the rules and the debate for the rest of us that don't know what the issue is please? :-\
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hi steve,boats must look like a boat of sorts,i know you have some very good ideas and i would try them out if i was you,but ,and this is the problem,while time and designs are changing,there is only so much you can change as the design of the boat goes,ie,it really must look like ,or as close to a boat as possible.i run a boat thats abit diffrent to most,abit wider and looks abit odd,but design wise its a boat,and you can see it is,now,if you can design something that when you look at it it looks like a boat then you can always ask omra if the said boat can be run,they will give you a answer,i had to with my new boat becouse of its design.i can see where you are coming from,but i dont think people are ready for that much change YET,best regards kurt oh.and please can we keep the omra debate to the other thread and not on steves,thankyou
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Well chaps, as my first visit to the forum for some time - it looks like I've been missing out.
The rules posted by Glenn are correct. There is nothing to stop anyone bringing new ideas into the racing scene and will certainly be welcomed in OMRA provided they comply with the (very basic) rules you have already seen. "Looking like a boat" has a very wide interpretation. You will find that the reason most boats look similar is that this is a design which works ie pointed front and somewhere flat to hang the running gear (unless you have submerged drive when rounded/sloping transoms are often seen).
Running gear is usually what is available commercially, as many competitors have neither the time nor facilities to make their own.
The same applies to hulls, the ones in use are the ones that have been proven to win - or are being experimented with.
I would be really interested to hear of different approaches to the inherent difficulties with getting a racing model to go fast whilst still being able to corner and come off waves level!
You will also learn that there are a variety of views about boat design, materials, and rules on this forum - some given by members who were actually involved in the OMRA decision making process (which IS democratic), and some that were not! There are a number of forum members who, although new to OMRA at the moment will, I'm sure become involved with the organisational process in due course and may well introduce a completely new approach to OMRA and model boat racing. If accepted by the majority, these will become the "rules" to which we will all adhere willingly.
Regards
Danny
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Danny.
Many thanks for the above.
I've not really designed a boat before, but for a living I design complex computer systems, and the thinking process seems to be the same, i.e. take a problem, pull it apart into pieces, solve each piece, make a final design out of it. Then repeate and repeat and repeat.
Just so as to not start a new thread, here are some cocepts and idea's. I would be interested in peoples idea's and opinions, especially as to whether it "looks like a boat". It does look a little like a few boats, such as the EarthChallenger, but then again, that doesn't look like a traditional boat either.
My apologies to Kurt in advance who has seen these idea's.
Ideal boat for ORMA:
Requirements:
Needs very low drag ( both hydro AND aero - Deep V hulls are aerodynamically similar to bricks)
Needs to be stable
Needs to turn easily
needs to handle waves well
Personally, i don't think I deep V is especially good for this. It's not at all aerodynamic, it has high drag when it's not planing, it is suceptible to being knocked about by waves, and they slide when it turns. Using lots of rudder dumps speed by greatly increasing drag.
What follows are only idea's, and have been purely worked on in my head. It "seems" to solve a lot of the issues above, but until I build one, I wouldn't know. And I don't really have a need to build a fast boat if I'm not going to race it. And if it's not in the ORMA, I have no where else to race it.
Here is an incredibly bad Sketchup! picture. It's just there to give you a really rough idea. Read the explaintions below to make more sense of it.
The proposed boat is somewhere between a cat and a tri hull.
At either side, there would be a sponson. There are fairly long, and would have a wave piercing hull shape at the bow end. There would be ballast added to the bows to keep them working properly.
The stern of each sponson is rounded, in order to try and reduce wave creation
The two sponsons are held together by an aerofoil. This would be an aerofoil with a significant concave in the bottom to increase lift in a WiG ( Wing in Ground ) senario. This would mean that the boat is lifted from the water at higher speeds. This gets around the need to have a hydrofoil that gives more than 4x the reduction the wetted area in order to make then useful.
The "middle bit" that touches the water is an engine compartment. This again is wave piercing. It is attached by a universal coupling to the main "wing". This means that, what ever the position of the boat, unless it is dramatically distant from the water, the prop will always be biting water and doing work.
turns can occur in two ways. The slower of the two mechanisms to to physically turn the engine compartment. This will force the boat to turn in the opposite direction. the universal joint will allow a turn to happen while still letting the compartment bouce abaout. This will not be especially fast, but it is essentially dragless
A faster turning option comes from turning the sponsons themselves. This would be done proportionally, with the outer sponson to the curve turning a greater angle than the inner one.
if these two mechanisms are used together, in some form of proportial system, it would lead to very fast, yet stable curves, with no slipping. End result is a faster turn without any slide and a reduction of drag.
Prop would be a singled bladed, balanced prop. Wettable surfaces would be covered with PTFE to drop the reynolds number a few points for faster starts. There is also scope for adding aero section above the water to the sponsons to rapidly get the boat on the plane.
OK, that's my crazy idea. I don't think it's especially hard to make, as it's all stuff that has been done before, just not together in a single place, I think, although I've seen boats with similar designs.
So, I guess my questions are:
1) Does it look like a boat?
2) Would it, or a derivation of it, be allowed in to the OMRA?
3) Would it work?
4) Does it seem like a silly idea?
Thanks
Steve
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Because it employs an aerofoil does it still get classified as a boat or does it then become an aircraft?
Glenn
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looks like two pool noodles with a smaller one in between to me ;D,sorry couldnt resist lol.right let me tell you one thing where you get the idea that a deep vee doesnt handle well in waves is beyond me,the vee is what keeps it from sliding in turns and tracking straight in those conditions in fact the deeper the vee the better it will handle in rough water.you also are not correct in saying they create drag any more than any other boats.the only part of the boat in the water when they are upto speed is probably the last 1 or 2 ".by far the most stable hull design in rough water is the deep vee that is a proven fact!!sure a hydro will go faster on flat water but any chop and you can forget it ::) cats are another matter there are two types of cats them that can and them that cant handle rough water.ive yet to see a vee that wont handle rough water if set up right its what they were designed to do O0.alsmost forgot to say a wave piercing bow will create one thing on a fast boat A SUBMARINE !!! :D.
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"single bladed, balanced prop" ???!!!
Is 'e havin' a laff?
"surfaces covered with PTFE" ???!!!
It's an interesting concept you're looking at, but if you're interested in racing you may just as well put an engine in a monohull.
The design you're proposing would be mighty fragile in a shunt!
Sounds like the sort of thing someone would use to go for the world speed record.
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Well Steve, you have some interesting ideas, so I'll try to put my views on them in order
Ideal boat for ORMA:
Requirements:
Needs very low drag ( both hydro AND aero - Deep V hulls are aerodynamically similar to bricks)
Needs to be stable
Needs to turn easily
needs to handle waves well
I'd certainly agree with 3/4 of that summary!
Personally, i don't think I deep V is especially good for this. It's not at all aerodynamic, it has high drag when it's not planing, it is suceptible to being knocked about by waves, and they slide when it turns. Using lots of rudder dumps speed by greatly increasing drag.
Certainly some boats are slab sided, but many of them, especially deep V's are almost rocket shaped when viewed from the front! You can't get much more aero/hydro dynamic than that.
A certain amount of slide is necessary in turns, otherwise the inertia would roll the boat straight over.
All planing hulls have a high drag when not planing but as they are optimised for operating on the plane, it doesn't matter unless the drag becomes so great that the hull won't come up onto the plane.
I agree that lots of rudder causes drag but a 'v' hull will 'lean' into a corner rather like a motorcycle on a bend, thus minimising the rudder force required.
The proposed boat is somewhere between a cat and a tri hull.
At either side, there would be a sponson. There are fairly long, and would have a wave piercing hull shape at the bow end. There would be ballast added to the bows to keep them working properly.
The stern of each sponson is rounded, in order to try and reduce wave creation
It appears to be a basic outrigger design with elongated sponsons.
If they are 'wave-piercing' there will be little 'lift' at the front causing 'submarining' - unless the sponsons were long enough to bridge the wave crests (which are of variable distance).
The round ends WILL be more hydrodynamic.
The two sponsons are held together by an aerofoil. This would be an aerofoil with a significant concave in the bottom to increase lift in a WiG ( Wing in Ground ) senario. This would mean that the boat is lifted from the water at higher speeds. This gets around the need to have a hydrofoil that gives more than 4x the reduction the wetted area in order to make then useful.
I think you may need a bit more research into WIGE. Have a look at
http://www.youtube.com/watch?v=nEHwRQilPRE (http://www.youtube.com/watch?v=nEHwRQilPRE)
In a racing situation, where collisions are highly likely, the aerofoil would have to be made of a durable material. Dave Marles and Ian Folkson both sell small 'wings' which also act as a lifting handle for use on multi boats. However their effectiveness is limited to the angle of the hull, which in multi racing ON FLAT WATER is usually a fairly constant 5 - 10 degrees (at a guess)
The "middle bit" that touches the water is an engine compartment. This again is wave piercing. It is attached by a universal coupling to the main "wing". This means that, what ever the position of the boat, unless it is dramatically distant from the water, the prop will always be biting water and doing work.
The engine compartment not only holds the engine, but also the tank, exhaust and radio. It would therefore need to be much larger than your diagram (unless your sponsons are HUGE). I would hazard a guess that the prop will spend far LESS time in the water compared to a 'v' hull prop as it will be being constantly lifted from the water by the sponsons - UNLESS the water is DEAD FLAT!
turns can occur in two ways. The slower of the two mechanisms to to physically turn the engine compartment. This will force the boat to turn in the opposite direction. the universal joint will allow a turn to happen while still letting the compartment bouce abaout. This will not be especially fast, but it is essentially dragless
A faster turning option comes from turning the sponsons themselves. This would be done proportionally, with the outer sponson to the curve turning a greater angle than the inner one.
if these two mechanisms are used together, in some form of proportial system, it would lead to very fast, yet stable curves, with no slipping. End result is a faster turn without any slide and a reduction of drag.
The sponsons are also responsible for maintaining straight line stability. You will need to make a mechanism that can keep them dead parallel for the straights and then proportionally turn them on bends - without weighing a ton!
Prop would be a singled bladed, balanced prop. Wettable surfaces would be covered with PTFE to drop the reynolds number a few points for faster starts. There is also scope for adding aero section above the water to the sponsons to rapidly get the boat on the plane.
Can you describe this single bladed prop? I've not heard of one available commercially. The PTFE would be unable to be sharpened which a prop's leading edge HAS to be, otherwise it would never 'bite'. The same effect of surface tension reduction can be gained by 'matting' a highly polished prop rather like the 'dimples' on a dolphins skin.
So, I guess my questions are:
1) Does it look like a boat?
A bit like a canard 'rigger' which is NOT based on a full size counterpart.
2) Would it, or a derivation of it, be allowed in to the OMRA?
If a working prototype can be made, I would suggest it would be more suitable for MPBA Circuit racing where there are classes for 'outriggers' already. They also tend to race on lakes without large waves (some of their boats are increadibly fast but VERY fragile)
3) Would it work?
As an interesting challenge, probably. As a racing model, probably not.
4) Does it seem like a silly idea?
Any idea that makes you think is never a waste and every advance in science (or anything really) started off with a silly idea!
Good luck (and keep up the 'Sketchup' practice) ;) :)
Danny
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bloody hell Danny now i really fancy a chinese O0
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Guys,
many thanks for the input. Here are somecounter-thoughts. Please please please remember that I am not trying to create a flame war, just bouncing idea's around. Other people have posted, but I'll use this as a jump off point as it has the most points.
Also, please accept my apologies in advance for poor spelling, I'm a little dyslexic ( truely a poor name for an illness for people who struggle to spell).
Steve
Well Steve, you have some interesting ideas, so I'll try to put my views on them in order
Ideal boat for ORMA:
Requirements:
Needs very low drag ( both hydro AND aero - Deep V hulls are aerodynamically similar to bricks)
Needs to be stable
Needs to turn easily
needs to handle waves well
I'd certainly agree with 3/4 of that summary!
Personally, i don't think I deep V is especially good for this. It's not at all aerodynamic, it has high drag when it's not planing, it is suceptible to being knocked about by waves, and they slide when it turns. Using lots of rudder dumps speed by greatly increasing drag.
Certainly some boats are slab sided, but many of them, especially deep V's are almost rocket shaped when viewed from the front! You can't get much more aero/hydro dynamic than that.
A certain amount of slide is necessary in turns, otherwise the inertia would roll the boat straight over.
All planing hulls have a high drag when not planing but as they are optimised for operating on the plane, it doesn't matter unless the drag becomes so great that the hull won't come up onto the plane.
I agree that lots of rudder causes drag but a 'v' hull will 'lean' into a corner rather like a motorcycle on a bend, thus minimising the rudder force required.
There are two factors here. Hydro-dynamic and aero-dynamic. Lets look at the aerodynamic first. Just becuase it's pointy, doesn't mean it's aerodynamic. In fact, as it's not passing through the sound barrier, it would be a lot better if it was rounded rather than pointy ( what shape is the nose of a 747?) Additionally, when looked at from front on, there is a LOT of space taken up. It's a big shape that is being pushed through the air. From the side, boats also are "chunky", and not the most clean of shapes. Does it matter? Boats don't go side ways. No, they don't, apart from when they turn into corners, or when there is a cross wind, which, unless it is dead calm, will happen at least SOME of the time on a circular course.
So now lets look at the hydro side. Yep, the Deep V is fairly good hydrodynamically, when it's running straight forwards. But when it goes on it's side, the wetted area becomes far greater, which adds to drag. Ideally, you want the boat to turn without increasing wetted area. there is also a good degree of debate at the moment in hydro circles as to whether a shallow V would not be more effecient anyway. ( have a look on the boat design and hydro-dynamics forums - a paper got published recently which is generating some discussion ). So what happens when the boat is on the plane., Wetted surface falls away, and the aero property's of the hull balance the falling motion of the boat. That's fine until it gets perturbed, for example by getting bounced by a way. At the point, the system (i.e the boat, the water it touches, the effect it's having on the air etc ) is disturned. Distrubance is sub-optimal. reducing this would increase average speed.
The proposed boat is somewhere between a cat and a tri hull.
At either side, there would be a sponson. There are fairly long, and would have a wave piercing hull shape at the bow end. There would be ballast added to the bows to keep them working properly.
The stern of each sponson is rounded, in order to try and reduce wave creation
It appears to be a basic outrigger design with elongated sponsons.
If they are 'wave-piercing' there will be little 'lift' at the front causing 'submarining' - unless the sponsons were long enough to bridge the wave crests (which are of variable distance).
The round ends WILL be more hydrodynamic.
Not so. The "perfect design" is one that is optimal at all speeds and in all conditions. A boat is not at top speed all the time. There is noting stopping a design having wave piercing sponsons which then moves on to a plane at a certain speed. In the concept discussed above, this is done with aerodymanic assistance. This means that at slower speeds, the boat will pierce small waves. It won't pierce all of them however, and as it speeds up, it will pass over more of them and pierce less. Also remember that waves are self similar, i.e as we shink down the scale, the physcis and dynamics of a wave don't change. A full size boat doesn't pierce ALL waves, just the ones that are smaller than some factor of the length of it's hull ( I have a feeling about a 3rd of it's length, but would have to work out why ). The same with a model boat. The boat is smaller, but so are the waves that we actually care about.
The two sponsons are held together by an aerofoil. This would be an aerofoil with a significant concave in the bottom to increase lift in a WiG ( Wing in Ground ) senario. This would mean that the boat is lifted from the water at higher speeds. This gets around the need to have a hydrofoil that gives more than 4x the reduction the wetted area in order to make then useful.
I think you may need a bit more research into WIGE. Have a look at
http://www.youtube.com/watch?v=nEHwRQilPRE (http://www.youtube.com/watch?v=nEHwRQilPRE)
There are 2 effects called "ground effect". The one displayed above, which really due to a sudden change in aero properties, and the effect known as WiG (Wing in Ground ) effect. See here for an over-view:
http://www.se-technology.com/wig/index.php
However, a *true* WiG craft is not a boat, it's a plane flying really close to the water in an optimal manner. The ideal, as far as a boat is concened, it to have a WiG aerofoil causing lift to the front of the boat, with the rear of the craft still touching the water. The concept above allows this to happen. The engine compartment is allowed to pivot upo and down. This means that the
The "middle bit" that touches the water is an engine compartment. This again is wave piercing. It is attached by a universal coupling to the main "wing". This means that, what ever the position of the boat, unless it is dramatically distant from the water, the prop will always be biting water and doing work.
In a racing situation, where collisions are highly likely, the aerofoil would have to be made of a durable material. Dave Marles and Ian Folkson both sell small 'wings' which also act as a lifting handle for use on multi boats. However their effectiveness is limited to the angle of the hull, which in multi racing ON FLAT WATER is usually a fairly constant 5 - 10 degrees (at a guess)
The aerofoil can be made immensely strong using standard plane building techniques. I would suggest that carbon over foam, or even glass fibre over foam, would be close to unbreakeable, especially if the aerofoil is a fairly think section, something like a Clark Y, and the foam used is a more dense version than used in aero work, such as the pink or orange stuff, rather than the more normal blue stuff.
The engine compartment not only holds the engine, but also the tank, exhaust and radio. It would therefore need to be much larger than your diagram (unless your sponsons are HUGE). I would hazard a guess that the prop will spend far LESS time in the water compared to a 'v' hull prop as it will be being constantly lifted from the water by the sponsons - UNLESS the water is DEAD FLAT!
Why? This is only an idea at the moment. there is nothing stopping the radio gear being in the sponsons. Yes, the engine is there, but again, it could be using a short pipe, rather than a long one, there are other ways of getting power out of an engine apart from the pipe. ( The pipe is a major factor, but not the ONLY factor ) The tank can be anywhere as well, as long as the engine is supplied with sufficuent fuel, it doesn't really matter. So you could have a smaller tank in each sponson, and a fuel pump.
As the engine compartment is free to move up and down vertically, and we assume for now that the engine comaprtment is boyant, but designed to plane ( again, it's still just a very rough concept ) then the prop WILL always be in the water.
turns can occur in two ways. The slower of the two mechanisms to to physically turn the engine compartment. This will force the boat to turn in the opposite direction. the universal joint will allow a turn to happen while still letting the compartment bouce abaout. This will not be especially fast, but it is essentially dragless
A faster turning option comes from turning the sponsons themselves. This would be done proportionally, with the outer sponson to the curve turning a greater angle than the inner one.
if these two mechanisms are used together, in some form of proportial system, it would lead to very fast, yet stable curves, with no slipping. End result is a faster turn without any slide and a reduction of drag.
The sponsons are also responsible for maintaining straight line stability. You will need to make a mechanism that can keep them dead parallel for the straights and then proportionally turn them on bends - without weighing a ton!
Not a problem. the pressure on them would not be anything that a modern digital servo with metal gears couldn't cope with. take for example a high speed glider throwing on it's crow brakes at 70mph. The force would be SIGNIFICANTLY more than the sponsons would be subjected to, and they are an off the shelf item with trivial weight. Proportional control is again simple, it either comes from mixers in a programmable Tx, or from solid state mixers in the boat itself. Again, these are both standard items in the aero world. and 2.4Ghz sets support both easily.
Prop would be a singled bladed, balanced prop. Wettable surfaces would be covered with PTFE to drop the reynolds number a few points for faster starts. There is also scope for adding aero section above the water to the sponsons to rapidly get the boat on the plane.
Can you describe this single bladed prop? I've not heard of one available commercially. The PTFE would be unable to be sharpened which a prop's leading edge HAS to be, otherwise it would never 'bite'. The same effect of surface tension reduction can be gained by 'matting' a highly polished prop rather like the 'dimples' on a dolphins skin.
Sorry, some confusion here. Two seperate subjects:
Prop: The "perfect" prop has a single blade. However, if you leave it like this, there is too much vibration. So a "blob", for want a a technical term, of lead is applied to the opposite face of the the body of the prop, and then finely balanced. This used to be done a lot. My dad had a number of boats for free running that were made in the 50's that had single bladed, balanced prop's.
The advantage is that, becuase of the single blade, it is always biting "clean" water, and is far more efficient. Single blades are also used in high speed applications in aeroplanes, such as the high speed pylon racers and control line flyers. They are a swine to make, but have significant benefits. I'm sure Octura used to sell them, as I have an old MMI that discusses them.
PTFE: this is about the smoothest substance known, and handily is incredibly cheap and available in large quantites (B+Qq sell it ). by covering the hull ( not the prop ) with it, the "pipe drag" of the hull would fall. Not a lot, but a little bit.
Something to mention here, as it applies to OneBladeMissing's post.
A single bladed prop will help a little bit. a PTFE covered hull will help a little bit. aero work will help a little bit. There is, I suspect, very little *revelution" left is boat design, although this is up for debate. So it's all about "Evolution". Using a single one of these idea's will not lead to a race winning boat. Equally, in race car driving, cutting the top 1/4" of a nut does not save a lot of weight. However, if you cut the top 1/4" off ALL the nuts, and you work on the aero, and you work on the power train, and you work on the clutch change speed etc etc etc it combines to make a faster race car.
The same with a racing boat. it's small changes, applied globally accross the vessel, that make for a higher sustained speed. There is no magic bullet. There are, however, hundreds of small things that can be fiddled with to make an over-all better boat
So, I guess my questions are:
1) Does it look like a boat?
A bit like a canard 'rigger' which is NOT based on a full size counterpart.
Fair enough. I can find images of something that looks very similar to this design, just running the other way around. Would that count?
2) Would it, or a derivation of it, be allowed in to the OMRA?
If a working prototype can be made, I would suggest it would be more suitable for MPBA Circuit racing where there are classes for 'outriggers' already. They also tend to race on lakes without large waves (some of their boats are increadibly fast but VERY fragile)
Ah, this is the bit I was looking for. If I go ahead, and it will need all sorting out in a CFD package first, which will take time, I might give it a crack. However, I'll leave discussions from this forum from now on.
3) Would it work?
As an interesting challenge, probably. As a racing model, probably not.
4) Does it seem like a silly idea?
Any idea that makes you think is never a waste and every advance in science (or anything really) started off with a silly idea!
Good luck (and keep up the 'Sketchup' practice) ;) :)
Danny
Firstly, thank you and others for taking the time to reply.
Secondly, let me re-iterate that I am not trying to trigger a war of words. These are idea's. I think they will work. If I get around to spending a weekend or two stuffing the idea's into a CFD package, I'll be able to find out, but I have to build my PCF, and re-decotate my entire house, so right now there are more pressing priorities.
However, let me leave you with a thought: Do the boats that are raced actually live on the bleeding edge of design and everyone is convinced that this is the case, or are they raced because everyone else races them?
An example: the Dave Marles lifting wing/handle thingy. Danny stated that these only work on the straight and level. How hard would it be to rig up a servo to move it up and down, and then use a heading lock gyro from the heli world to have it dynamically up and down depending on the angle of the boat? Honestly, it's an weekends work or less. Equally, how much work has been put into choosing the aerofoil of the handle thingy?
I'm not saying I'm right about ANY of the idea's above, not a single one. They are idea's, and they could all be completely wrong. Personally, i think there is merit in some of them, but its up for debate. However, I understood that the OMRA rules were designed to push design to the cutting edge, by leaving it as loose as possible. And from what I've read accross the net, I don't see that happening as much as it COULD be. There is ALWAYS room for improvement, there is ALWAYS room for innovation.
Hmmm.... actually, ignore that completely. You chaps are the experts at this, I'm an outside observer, so I guess I'm missing stuff as I simply don't understand the mechanics of it.
Right, I'm off to build my PCF with it's minimally planing hull and plywood deck. sorry for crashing this area of the forum.
Steve
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It sounds to me that you are defining something like this boat.
Three Point Reversed Canard Miss Circus Circus (1980) as shown in picture
1/8th scale plan from Roger Newton http://www.newtonmarine.com/134_plans.html (http://www.newtonmarine.com/134_plans.html)
If i am wrong then my apologies.
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ripslider dont get us wrong you deffinately have some interesting ideas,no harm in trying new things what so ever but just remember the deep vee design has been arround for ever and its still used for a good reason,its forgiving ,stable and reasonably fast when set up right O0.omra is offshore racing id like to see a hydro or similar design run in those conditions but i wont hold my breath ;).good luck with your ideas and keep us informed.
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RipSlider, I wasn't having a dig at your concept, but if you're talking about going racing ... keep it conventional. Speed is handy but not everything. I've got two decent sized boxes upstairs full of trophies, and I usually didn't have the fastest boat when I won them. I'd sooner trade off a bit of speed for reliability any day. The races I took part in were usually 30+ minutes though, up to 2 hours.
I've personally never seen one-bladed props. I've watched control-line planes and pylon racers, and they've all had 2-blade props. Tethered hydros also run 2-blades. I can't imagine what advantage a one-bladed prop would give. You say that a one-bladed prop means that the blade is always cutting into 'clean' water, but a 2-bladed air-piercing prop does so as well, surely. With one blade you get one 'push' per revolution, with a 2-bladed you get 2 'pushes' per revolution, and what about torque-reaction (paddle-wheel effect) with a single blade?
If a bulbous bow is better than a pointy one on a monohull, I think Don Aronow, Don Shead, Renato Levi, etc. would have known about it first.
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A few points, and then I'll leave this topic and go back to cursing my dremel for not being able to cut through thick GRP hull layups.
first, it should be always remembered that what we're talking about is a hobby. So really none of this matters at all. When I'm not building boats, or planes, I play with toy soliders. It's just for fun. So I'll say again that I hope I'm not causing any one any annoyance.
Second, I'll say that I always shudder when people say "lets leave things how they are, because if there was something better, some one else would have though of it".
Is everything to do with boat design for racing SO GOOD that it is only miniscule changes that are left to work on? If so, that means that there will soon be an optimal formula that will never be bettered.
To me, looking in from the outside, it seems unlikely. While not an expert in any way, I know enough about hydro and aero dynamics to at least make the statement "There are other alternatives that are worthy of exploration". The concept I discussed about may, as I said, be completely and utterly wrong. But there are LOTS of completely different paradigms that seem to remain completely un-explored in the model racing world that are either being discussed or actively used in the full sized world. examples are dynamic ballasting, asyemtric hulls ( which there is a lot of work on at the moment in float tanks ), beaver tails, aero properties etc etc etc.
let me give one, small and trivial, example: In the standard configuration of a mid mounted engine exposed to the open air, or under a canopy, that is used in most ORMA boats, there is going to be a lamiear shear that acts on the surface of the top deck at speed. End result? The faster the boat goes, the less air is available to it, as most of it will be buffeted away by the hull. Obviously there is air present, but their could be more.
Could aero properties, or even just a simple cone linked to the inlet of the engine, be used in such a way as to provide a positive pressure on the inlet to the engine? Absolutely! It's a principle used in every racing car. And it would take very little work, depending on the design chosen, to add this to the boats. It DOES happen in the full sized boats.
By making this one adjustment, will a slow boat turn in to a winner? Nope. But it will be acting more effeciently. So what happens if you add dynamic ballsting AND air ramming AND a different hull design AND aero work AND enhanced surface properties to a single boat? Will you will then? it's not definate, as a lot of it is in driver skill, and reliability, and lots of other factors, but it certainly won't hurt....
There doesn't seem to be any ruling against it. So why isn't it done? I expect there are a lot of reasons, but I'll hedge my bets, and say that one of the main reasons that would be given, conciously or sub-conciously is "That's the way we've always done it". And thats where traps lie.
A second example: I go fishing a lot. Often for carp. carp fishing is the most expensive type of fishing in UK fresh waters. The amount of gadgets, kit, equipment etc etc that the magazines suggest is enormous. Ultimately, carp fishers only use three rigs, but there are at least 1,000 different published variations, tiny variations on those three. Use Hook X rather than type Y. Use a square weight rather than a round one etc. Most of the entire sport is utterly locked onto making tiny changes to those three rigs.
Turns out that often, by using a float, or by fly fishing, rather than a weight, you often catch more fish. But very few carp fishermen do. Why? becuase there's no float in any of the three basic rigs. And they've had the concept of those three basic rigs hammered in to them, sub-conciously, for years. SO they MUST be right. Right? Nope, it's just that everyone has convinced everyone else that three, often sub-optimal designs, are the only way of fishing.
Is there a lesson here? maybe. I could, however, be talking utter rubbish. And I wouldn't know, like I said, I'm not an expert. But I do read the design forums for the full sized boats, and the stuff on there which is considered "fast" or "cutting edge", bares no relation to the Deep V, Tuned Pipe and Struuder set up that the model boats use.
Lastly, one bladed props:
Pro's: they are better. On boats a lot better than on planes.
Con's: They are a swine to set up and have to be re-set up on a regular basis.
Why aren't they used? I don't know. I *do* know they are a more optimal design. My Pa said they were, and a few guys at my old boat club also discussed them. becuase I'm a cynical so and so, I never believe anyone about anything without lots of proof, so I went away and researched it. And my research made me comfortable with the concept. But I assure you that when I first started to think about it, it seemed completely and utterly stupid.
In my personal opinion, and in lots of peoples opinion who studied this sort of thing at school, they are a useful tool to the "how to make a boat go fast" arsenal. But I could be wrong. So could the clever blokes. A hell of a lot of clever boat builders argued against building ships out of steel. A lot of material scientists thought that the idea of glass fibre was silly. A lot of clever economists though communism was a good plan.
Anyway, once again thanks for the inputs on the concepts I was thinking about.
Steve
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I'm not into racing but I have found the recent posts on both sides of the discussion very interesting. This is exactly what Marin means by using the Forum for constructive discussions. Whatever the "truth" may be we can all learn something from the points being made. Ultimately, I suspect, it will be a "suck it and see" situation.
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Steve,
You certainly write a good article ! ! ! !.
JayDee, ;) ;) ;)
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Hi Steve
You have raised some very good, obviously well researched points and I would consider looking to test some of the concepts you have aired. It is not easy because, as I have previously said, most of the stuff we use is 'off the shelf'.
If you get to a firm design, or even some modification which is possible to make to an existing design, I'm sure that we would be able to incorporate some prototyping or testing into our busy racing schedules ;)
One small point - "Air rams". I normally cut a hole in the sloping front of the 'cabin' to allow the entry of combustion/cooling air. I have also fitted a crude deflector inside the 'cabin' to deflect any spray away from the engine top. This works well until the boat submerges when the sheer volume of water coming in is too much for the auto-bailer, sloshes along the bottom of the hull and is then sucked into the carb stopping the engine. Can you think of a design which would allow air to be drawn in, yet prevent large amounts of water entering? I have tried a 'snorkel' on the carb without much success (maybe it was the wrong material/design).
Oh - and don't worry about upsetting any "experienced" racers, most already try 'little tweeks' which is why ALL model boat speeds have increased steadily over the years. Your never too old to learn!
Danny
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Off the top of my head, I guess that the easiest way to have a crack at it would be to produce what is, essentially, a trumpet. wide gape at the front, narrow section at the end that goes into the engine.
if the tube looped through 180 degree's or even better 360 degrees in the middle, then this would act as a water trap. If you had a wee little downwards pipe with a tap on the end, you could drain it at the end of every race.
You will still pick up water, but much less. If the cone ( doesn't have to be a cone, just a wide shape ) is mounted as high as possible, this would also help. You could also retard the engine timing slightly. That might actually benefit you a little more. If you can squeeze a fraction more compression out of the engine, and use the fact that there is water vaupor in the air to reduce/eliminate pre-ignition, you would also be getting a little more work for you cc's.
Would work best if the pipe was constantly narrowing. If it widens, you'll be wasting energy in a pressure change/
Have just re-read your post. I'm guessing that the boat isn't actually sinking, but just getting a dunking as it goes nose down after a wave of some sort.
A few work arounds I guess. More bouyancy in the bow of the boat would mean it submarines for a shorter period, so less volume of water is thrown up. A second option would be to leave what ever mechanism you use to force air to the engine, for example the trumpet, as far back on the boat as possible. Right on the stern if possible. As long as the air collection mechanism point forwards, there is nothing wrong with routing the air forwards to the engine.
I guess you could also go more technical. Is there a reason that you couldn't have a hatch that opens or shuts in some manner. Shutters, butterfly flap etc. This gets actuated by a servo. using a piezo gyro, it's easy to work out when the boat pitches past the horizontal, and then the servo closes the hatch/shutter/valve what ever.
the engine compartment would have plenty of air from the engine compartment, and it would recycle when the boat goes horizontal or back on the plane again.
Lastly, what do Jetski's do? They can have the engine running full pelt for 5 seconds under water. Guessing they aren't using servo's.
Steve
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You're right, sorry should have been more specific.
The boat is happily leaping from wave to wave then catches the odd spacing - the nose (which is already full of buoyancy foam) dives into the next wave, slows dramatically (throwing any water forward to the engine) and then pops up.
I've just been thinking already that one of your 'workarounds' might be the simple answer - a lightly sprung flap, normally slightly open but sprung enough to hold against wind resistance. When nose goes down, water force pressure 'seals' flap long enough for boat to pop back up (engine using air inside hull), water runs off, flap opens - and off we go!!
Got a bit of measuring to do!
Thanks pal!
Danny
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Danny just get some wire gause and put that over the scoops thats what i use and i never get water going in the boat through mine and its big and on the deck.that is unless your piercing waves lol but then it wone matter wether you use a scoop or not you will get water in anyways ;D.
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Hello,
Not had any dealings with racing boats, but plenty with racing cars/engines.
Any flap ect which is sticking up into the airstream, hoping to " ram " induction air into the engine, will fail.
The air drag caused by the flap ect is far greater than any gains in engine power - - even at 100+ mph !!.
True, it looks good, looks "fast", but its not !.
Gran Prix cars have a air intake over and behind the drivers seat, maybe they can gain a small amount of extra power from ram air, but it will not be much - - - they are travelling at 200+mph.
Watching the race in Japan on Sunday, it may have enabled the engine to stay above the water !.
JayDee.
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Some/most people like to stay with the status quo because it works. Look at the racers who are winning world championships, they stick to what works. True, boat designs are developed over the years, but basically they're pointy at the front and blunt at the back.
On the subject of full-size offshore boats, Lorne Campbell has designed many three-pointers over the years and some of them have gone very well. I did see one of them flip before even making it to the start line at Great Yarmouth once though. What do they use in offshore racing these days? Cats and monos.
Jim Hall's Chapparal cars were full of innovation but they didn't win as many races and championships as Bruce McLaren's designs. Even Hall admired the McLarens' rugged simplicity.
Devices for keeping water out of a model boats' carb would be useful, but is there really a problem with the amount of air getting into the engines at full speed? F1 cars are operating at up to 220 mph and their airboxes have to be very carefully designed. Even the drivers' helmets are shaped to promote smooth airflow into the inlet, and F1 designers don't like tall drivers for the same reason!
As a potential speed record-breaker project, I think RipSlider's ideas are interesting.
Build it! ... but we want to see pictures!
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i think your last point is about right his idea could make for a very fast drag boat so long as the water is flat calm O0.
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To slightly misquote the line from the Kevin Costner film Field of Dreams ... If you build it, we will watch!
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Kevin who ? :o