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
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.phpHowever, 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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Topic: Quick question about OMRA boat design (Read 10947 times)