Model Boat Mayhem
The Shipyard ( Dry Dock ): Builds & Questions => Pleasure boats, Sports, Race, Power and Leisure Boats: => Topic started by: sheerline on March 14, 2007, 12:20:06 am
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My son just bought a 40 inch shovelnose hull and associated bits off e-bay, it is an unbuilt kit with no plans or instructions and it looks like its been around for some time. It's of lightweight glass construction and came with an ally prop stamped with the number '22 27'. It also has the skeg for the propshaft and a straight parallel sided rudder with water pickup, along with fuel tank and a tuned pipe. We would like to try to put this thing together for a bit of fun but can't find any information re maximum engine size, location within the hull or C of G. Basically we are in the dark with the general layout of this type of boat and wonder if anyone can help or knows of a website where all this kind of info can be found. We reckoned a 61 size engine would be about the maximum and would really get it moving but wer'e just guessing .
Never been stumped over a model before but this type is all new to me...............HELP!!
Regards.......... Chris
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Maybe some photo's so that the hull may be identifiable would help. There are sites you can try that are American where you may find what you are looking for. Try here:
http://www.rcuniverse.com/forum/forumid_229/tt.htm
Look foward to seeing some photo's.
Glenn
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Thanks for that Glen, when it comes back inthe workshop I will attempt to post some pics. Having surfed the net, there is surprisingly scant information regarding this type of boat so it's become something of a challenge to get it together. There seems to more interest across the 'Pond' than here in the UK. I will come back with some pics very soon.
Regards. Chris
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Hi sheerline,
This site may also be of some interest.
http://www.rcunlimiteds.org/
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A 10cc "sport" engine should make it go ok. A similar 15cc engine would be ..... interesting!
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Go to Roger Newtons web site http://www.newtonmarine.com/plans.htm (http://www.newtonmarine.com/plans.htm) for 1/8th scale hydroplane plans. His plans cover most of the boats since 1967. See http://www.newtonmarine.com/pop_ups/101a_pop.html (http://www.newtonmarine.com/pop_ups/101a_pop.html) as a typical boat.
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Great, I knew I could rely on the chaps who breath nitro and methanol fumes to come up with something. We've ordered a 91 marine unit for it and have other bits to get like the drive shaft and possibly a couple of new 'waterproof' servos. I believe the rudder servo has to be a bit of a beast to take the pounding, probably needs loads of torque and metal gears. I hope this all works out ok as I am really looking forward to giving this thing a damned good thrash. This is certainly a deviation from the subs but who knows, if we get it all wrong, we may yet end up with another sub!!
I will get back with some pics soon.
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Hello all, finally got some pics of the hydro, its actually 48 inches long by 21 inches at its widest point. We found some pics of a boat on a site which showed the layout of the rudder and skeg at the aft end so we fixed them in place but once done, found another pic on another site which showed the rudder on the opposite side... I think it depends on which circuit you run eg clockwise or anti clock... not sure though. We even found a pic with the rudder right in the centre, mounted on the skeg assembly but the skeg for that boat was specifically designed for that application.. unlike ours.
I would guess that one has to fit a piece of thin ply on the inside, along the bottom of the hull so blocks can be bonded in place to accept fittings like the motor mounts etc.. The hull is wafer thin so it needs something in here. I believe these types of boat use something like expanding polyeurethane foam to fill the nose and sponson cavities for floatation and siffening of the cavernous glass areas which are rather delicate.
With aboat of this length and based on a little data from a smaller model, we calculated the c of g to be around two to two and a half inches behind the sponsons but not entirely sure yet.
Regards........ Chris
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hi if you want to water proof servos get this stuff!! also try these servos ,great price and powerfull.i paid 11.90 for shipping but only 15 pence for the servos!!
]] (http://)http://cgi.ebay.co.uk/ACF50-ACF-50-Motorcycle-Anti-Corrosion-Formula_W0QQitemZ190092691514QQcategoryZ10464QQssPageNameZWDVWQQrdZ1QQcmdZViewItem
http://http://cgi.ebay.co.uk/2-X-MG995-Metal-Gear-High-Speed-Torque-Digital-Servo-A_W0QQitemZ290094053994QQcategoryZ19164QQrdZ1QQcmdZViewItem
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DONT use expanding foam or your boat will split apart!! the foam is strong ,easier to by pipe insulators from B&Q and stuff those in the hull where you can not just up front or if you flip your boat will float nose up !! if you have floatation the full length of the boat she will float level and some things might stay dry.also in the hull you may try to install engine rails inside, you epoxy them in and then use glass cloth strips either side and epoxy to fix them in.use slow setting epoxy usually 3 hr is the best.hers a pic of engine rails.notice the pipe insulators,these are cheap 42 p per mtre and will not soak any water up and yup they float.
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Thanks 'M', we will avoid the expanding foam and take your advice. Looking at your engine which appears to dwarf your boat made me think of an American saying when referring to race cars... "There's no substitute for cubic inches' I bet that thing of yours is going to be a real flyer. We did think of buying a petrol motor for this hydro but figured it would be a bit too bulky and would'nt churn out the rpm for the kind of response we might need. I know there are a lot of tuned petrol engines out there which would probably do the job but they can be very costly for the kind of use my lad seeks from this model. If he gets hooked (or I do), we can always look at that as an option with some other kind of boat.
Thanks for your help and advice.
Chris
Ps my workshop does'nt normally look this grotty but the pics suggest I ought to paint that ruddy wall one day!!
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Looking at the photos I would say that yes, the wall needs painting.
Might I suggest the calming and non - offensive tones of Magnolia as an option?
To the boat: The pipe you have looks to be a water cooled Prestwich pipe, I may be mistaken but am fairly sure it is. If it the size I am estimating it would indicate it is for a 10cc motor. About.
The drive on these boats I am not sure of, the hardware you have looks kind of like what you would use on surface drive, but the strut you have looks like it is placing the prop too high on the transom on your boat to achieve surface drive.
Can you adjust it up?
Engine mounts: You have basically two choices:
1; fit "rails" - 1/4" ply running fore and aft at 5" centres which the engine mounts are bolted in between.
2; bond fixings into the hull that the rubber mounts fix to.
Choice is yours, both systems have advantages and disadvantages.
Looks like you need the following to complete:
radio box, engine and mounts, prop shaft tube, prop shaft flexi, prop drive dog, water pick up (unless the rudder has one built in), a fuel tank.
Just noticed that you are planning a .90 in it. Might be a bit too much engine, will be interested to hear other members input.
I have never seen one of these running in the flesh, will be interesting to see this one get up and going.
Good luck. Have fun.
Glenn
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Have a look at this lnk for finding the balance point on your hull, sound advice that will apply to your boat even though it is Methanol burning.
http://p086.ezboard.com/Finding-Your-CG-of-your-Hull-when-building/fjimsrcboatdockfrm7.showMessage?topicID=697.topic
By the way, have asked some Americans for advice on finding out what your hull is, this may lead us to be able to track down some fit out instructions for it.
Glenn
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hi CHRIS the engine is only a 28 cc strimmer engine air cooled hence the open hatch and the air scoop to aid cooling it wont be too fast ,35 mph roughly but thats fast enough for me.the boat is 4 ft long 15 wide and heres a pic to show the engines not oversize lol.i have a build thread on here if you care to check it out.id say a zen 260 pum might fit in your hull ,you can pick them up for 134 quid from the usa shipped all depends what you have to spend.
http://http://www.oneillbrothers.com/rcboat/index.htm
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Just refering back to floatation, did you see the comments in the link .... ?
http://www.modelboatmayhem.co.uk/forum/index.php?topic=2149.msg21362#msg21362 (http://www.modelboatmayhem.co.uk/forum/index.php?topic=2149.msg21362#msg21362)
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thats why you need enough floatation so your boat wont sink even if its swamped!!
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thanks for the advice and links Chaps, we are slowly building up a picture now of how this lot's going to go together. We have most of the running hardware including aluminimum engine mounts with rubber shock absorbers. Looks like the only real missing piece is the drive shaft and its tube but it looks as though Prestwich can supply this. The aft skeg is adjustable up and down and I reckon that will need some setting up in the initial stages but I notice it does not have the facility for angular fore and aft setting so the prop angle in the water is preset. I look forward to any 'Stateside' info that may turn up re the C of G because I beleive these boats were very popular there at one time. I might put some feelers out on some of the other forums.
By the way, my missus has told me that green is a naturally calming colour as it's abundant in nature... given the choice, the wall will stay grotty!
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hi mate is it a surface drive? if so keep it level with the hull also the balance point on most boats should be about 25% to 35% .that boat is made for a zen im sure if not then a .60 nitro would do the job.
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Hi 'M', I guess by surface drive you mean a surface piercing prop and I believe thats what we have included with the bits that came with the boat. It's a rather beautifully sculpted ally prop with the numbers '22 27' stamped on the side.
We have ordered an SC 91 to put in this boat so as yet, don't know if that prop will be suitable for use with that size motor.
Going on the C of G, your figures of 30 - 35% are roughly where we marked the hull. When we finally get all the bits together, we will locate them in the boat and position the engine to gain the desired position. I suppose when the boat is finally tested it will become apparent if the C of G is out in much the same way as it is with our model aircraft experience but as I said before, this thing is quite new to me and I bow to your superior wisdom and experience.
I am impressed with the level of feedback and help we have been receiving from everyone and really look forward to getting this on the water and wringing its neck... if I can prise the TX out of my sons hands! Gotta a lot of work to do yet and still waiting for the motor so must be patient.
Best regards..... Chris
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i think the .90 will be a bit too much motor for it to be honest but i could be wrong seeign as its a sports engine you might get away with it.i had a sc .61 in a deep v 32" long its a modded plane engine with a flywheel fitted and cooling coil for the head works good but ive given up on nitro to build this petrol boat.
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The 1/8th scale hydros they run in the States have 11cc engines in them (rcunlimiteds.com) of around 3bhp. Your SC.91 is around the same power so should be ok for a hull of 48". That pipe looks a bit small for a .91 though.
Great looking boat. We watch with interest.
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The 1/8th scale hydros they run in the States have 11cc engines in them (rcunlimiteds.com) of around 3bhp. Your SC.91 is around the same power so should be ok for a hull of 48". That pipe looks a bit small for a .91 though.
Great looking boat. We watch with interest.
SC91's are not the easiest engine to start. On cold engines they usually require a big Sullivan 24volt starter and two 12v batteries plus decompression by loosening the plug. Not sure about your power figure - I thought it was well below your 3hp figure
Found this for SC91 AERO engines from Hobbins Models site.
480360 - SC91A AERO RC ABC ENGINE (MKII)
C.C. - 14.93
Bore - 27.30
Stroke - 25.50
Power (kW) - 2.0/15,000
R.P.M. - 2000-11500
Weight - 825g
Piston - ABC
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i agree with that i have the .61 sc engine and it just about turns over well enough on a 12 v starter using a motor bike battery for power,but only if i loosen the plug first ;).still say stick a zen in it the americans say that boat was designed for one?.
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I had a read of a SC.91 instruction/specs. booklet and I seem to recall that it gave a power figure of around 3bhp. Anyway, 2kw is around 2.72bhp. What about a CMB or OPS 11cc?
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Hello all, the SC91 has arrived and having read the booklet, can confirm BJs figures on rpm but it does'nt give BHP delivery. It specifies a 25 50 prop (recommended). As we have a 22 27 we are going to try it with that first and I reckon it will probably work ok but we will, after initially having the pants scared off of us at the first attempts to run the boat, play around with prop sizes to gain optimum performace from this motor. I am not too worried if this prop is inclined to load the engine a bit too much as we will be running it rich for a while and if the prop keeps the rpm a little lower than normal, it should run the motor in quite nicely prior to blasting it to death. Just waiting for the drive shaft and coupling to arrive then we can get down to assembly.
I am in the process of knocking together an electric boat to act as a rescue craft. As a submarine builder, I am not used to having to rescue boats and have no intention of getting my feet wet.
I don't normally run or build boats but looking around the workshop, found an old racing hull which has been gathering dust here for years. I broke up an old electric drill which rendered up an FRS750 motor which originally ran with an 18volt pack. I found an old drive shaft and 40mm three bade brass prop and bunged it all in the hull and find I can barely keep hold of the thing in the test tank when run at 12 volts. I boosted it to 18 volts and the tractive effort of this combination is scary. The current at 12 volts was 12A (did'nt measure it at 18v) so given a power dissapation of 144W, am going to watercool the motor.
All this work is my lads fault for buying the shovelnose hull but I must admit, it's all a bit addictive and pretty interesting.
It will be good to get the smell of methanol and castor back up our noses again as we have'nt been flying for a few years.
Will keep you posted as things progress.
Regards... Chris
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i wouldnt use the small prop theres a big difference between a 27 mm prop and a 50 you will probably blow the engine up by over revving it with that tiny prop ,id also suggest the 50 mm might also be too small , id say at least a 55 mm one .buy a larger one .your engine will be revving its *****off with the small prop and getting no where.the electric sounds promising keep us posted but my recomendation is buy a bigger prop for that .91.for a hydro prop prather recomended for 11 cc engines a 250 a 260 or a 270 prop for best performance and you will be looking at speeds up and over 50 mph easy!!also you cant just potter arround with a hydro to get her up and moving you need to give a few revs then launch it into the water a bit forward is best but watch for that prop!! these boats are made for out and out speed not cruising around!!.hope this helps you out ,maybe you should pay a visit to RCU and ask the guys on there as there are more guys there running hydros than on here,go to the nitro forum and do a search for hydros or post a new thread asking for advice .ive seen a video somewhere of a similar boat ill try to find it. ;)http://http://www.rcuniverse.com/forum/default.asp?fh=1&forum=229
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i just found this too check it out gives you all the prop sizes for hydros for prather and octura.basicly your looking for a 50 mm prop minimum preferably a 60 mm.the last two numbers on the prop charts are the props diam in mm.a 27 is far too small.
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Thanks M, good info and will check it out, the last thing we want to do is screw the motor in its early phase of break in. One thing has occurred to me even though we have'nt started yet, is how much rudder movement should we give this type of model. Any thoughts?
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When you set up an unknown boat, it's always best to err on the side of caution regarding steering. If you set the rudderr up with about 30 deg each way, it may be too much so you may well find that you won't be pushing the stick so far over to turn. This can then be modified by reducing the throw based on how much the boat turned relative to stick movement. If, on the other hand, you set up too little throw, at best it will take huge circles and at worst will be up the bank :-
The 2227 prop you have (as it's ally) may well be a submerged drive prop! The 22 refers to the diameter which is 2.2" and the 27 is the pitch. If there is a thread in the boss (usually 5mm), it is for a solid propshaft and will not be suitable for surface drive which normally have a 5/16" straight hole with two notches at the front which engage into a 'dog drive'. Another way to tell is, if the back of the blades are straight, it is surface piercing, if they are convex, it is submerged. I suspect that it's a "Propshop" or "Mocom" which has just been "chucked in" with the sale.
To confuse you even further :-\ Octura props are available in plastic, beryllium copper or stainless steel. The diameter is the SECOND pair of numbers and the pitch the first pair ie. 1447 where the 47 is the diam in millimetres and the 14 is the ratio of the diam to the pitch ??? ???
Prather don't make plastic (i think) so they are only BeCu or Stainless. The sizing code is beyond me even though I actually use them :-[ They are numbered 220, 225, 230, 235, 240 etc.
To cut to the chase so to speak, your SC91 is a 'sports' engine which will probably not be tuned?? If so I would suggest one of the following, Prather 260 (2.52" x 3.9" pich) Octura X465 (2.56" x 3.58" pitch) or better still start with a couple of Octura plastic (GRP but not the hard GRP) which you can experiment with (cut down) until you get somewhere near.
As a point of interest, your tuned pipe is an early PMC pipe, with the water cooling jacket covering the front expansion cone. It looks, from the pic, about a 40 size. If you can let me know the diameter at the widest part of the cone, I'll tell you what it's for. Irrespective, if it will go over your header (manifold) you could still use it although it may be too small. Using a smaller than optimum pipe will still give some improvement to RPM as long as it is set up to the right length. Looking at the long pipe at the front, I suspect that this is how it's been used (and with the cost of a new pipe nearly £100, who can blame them). Your most difficult task, I think, will be to get the manifold from the side of the engine, round to behind it, then through the tunnel at the rear. You may end up having to make your own - but it's not that difficult, if you can silver solder.
Hope that helps and sorry for being so long winded ;D
Danny
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Hello danny, thanks for taking time to explain that lot and yes, props can be a bit of a minefield as we have found out with one or two other projects. I have stuck some pics of the prop on here so you can see exactly what we,ve got and it is a surface runner made of ally and as you can see, it has a pair of notches at the rear to engage the drive dog on the shaft.
I have included some pics of the rescue boat which is a bit rough at the moment as all I have done so far is chuck a motor and shaft in it. It's about 34" long by 10 inch beam and although I only intended it to rescue the hydro, it looks as though it will be a bit brisk across the water with just a 12volt battery driving its FRS750 motor. This boat is made up of all the odd bits I have lying arund the place and I think it will be a bit of fun on its own even before the hydro is ready.
Regards......Chris
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Well Chris
That prop should do for starters, at least it will give you a guide.
"Concentrate on your destiny, young propwalker" - I feel a disturbance in the force - you are in danger of being seduced by the Dark Side (fast electrics) ;D
Danny
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chris buy the right prop from the start,you need a surface prop either stainless steel or ali, if you can find a plastic prop to fit your shaft which i doubt then give it a go but you need a 60 mm prop maybe even a 65 .the smallest i would even try is a 55 mm one but it needs to be a surface prop.surface props have a straight trailing edge to the blade.hers a pic of mine.mines a prather 280.under no circumstances would i try that 27 mm prop with any engine over a .16 my mate has a .16 engine and has a 35 mm prop just to give you an idea of how small that one is.a .91 is a beast of a motor and needs a big blade to spin or its going to over rev and blow up!!.heres a good place to get prather and octura props they deliver pretty fast and ive orderd lots from them and theyre cheap too.this prop ive linked should be ideal for your engine.it will need sharpening and balancing ,i used a file and wet and dry paper and some metal poilsh.i balanced it over a pint glass on a steel shaft .they come with instructions on how to do it.half what you would pay in the uk too.
http://http://cgi.ebay.co.uk/100-NEW-PRATHER-PROPELLER-S-260-PROP-STAINLESS-STEEL_W0QQitemZ5992658181QQcategoryZ34058QQtcZphotoQQcmdZViewItem
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It will be good to get the smell of methanol and castor back up our noses again as we have'nt been flying for a few years.
Will keep you posted as things progress.
Regards... Chris
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I'm sitting here chuckling thinking that you may well be flying again before too long if the balance ain't right on that hull or the engine overpowers it!
Only kidding, you should have great fun with it.
Enjoy.
Glenn
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Just a quick note re props, my lad has just informed me he has ordered a prop from Prestwich to fit the 91 ,along with the driveshaft so I reckon as they are specialists, they will probably source the correct prop. We'll see what turns up this week and hopefully, can finally make a start. Thanks to everyone for all the in depth and valuable information you have rendered up so far.
Regards. Chris
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yep dave will sort you out hope you got a big wallet though,i payed 15 quid for mine deliverd from hong kong about 10 quid cheaper id say, than if id got one from uk.i was trying to save you some dosh but oh well ::).dont forget to sharpen and balance and polish the prop before you run it either.have fun!!
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Hi 'M, I didn't realise he had ordered the prop so it was too late to do anything about it but I have had a look at the Prather site and if we need to try different props, then we'll give that a try. Nice looking props but as you say, I've no doubt Dave will come up with the best type suited for the job.
Waiting...impatiently!!
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just remember the prop will need balancing sharpening and polishing!!.do you know how?.if not i can go through it with you from some info i have on how its done .its very important to balance it and you sharpen it as you go but only on the one face of the blade,the convex side!!, the face looking at you from the drive dog side.dont take any off the concave side or you will alter the pitch.
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Ok 'M', stuff still not here yet, when it arrives, I'll send you a pic of the prop and see what you make of it. I thought aircraft props were dangerous enough but his one sounds like a regular screaming scalpel!! God help any fish that are'nt quick off the mark.... or us for that matter!
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Or, if your fast enough and he hasn't sent it yet, and you don't want the hassle for a one-off, ring Dave and get him to do it. Up to 60mm for £3.50. Given that it takes me a couple of hours (and mine aren't perfect) AND it's hardly the most exhilarating bit of boat building, what's your time worth ??? ;D
Danny
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it may come with info on how to sharpen and balance it all i did was put the prop on a small length of shaft suspended it over a pint glass see which blade falls thats the heavy one you sharpen the edge of it on the one face with a file and polish the face too either with a dremmel or wet and dry (hard work).do it enough so the blade is lighter than the other and is sharp.then work on the other one untill they balance!!.thats it its easy enough but hard work using wet and dry and a file, then get some ali polish from halfords and polish it till its gleaming .
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for £3.50 id get dave to do it but hes usually quick at posting and i usually get his stuff the next day or at the most 3 days later. ;)
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Martin
When I started doing my own props, I used a couple of old fashioned razor blades in a piece of wood to support the shaft. I thought I was doing a good job on them but after getting through three rear skeg bearings in a season and the prop waggling round like a dolphins tail, I bought a magnetic balancer. When I put my "balanced" props on it - they were MILES out, so I had to do them all again. Now the bearing lasts at least a season or two.
Danny
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Yea ive seen the razorblade trick too in fact ive seen balancers for sale using a similar setup.If your prop was waggling around a lot why did you run the boat? ,surely if its waggling around it isnt balanced or something isnt lined up right. ;D
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Martin
When I started doing my own props, I used a couple of old fashioned razor blades in a piece of wood to support the shaft. I thought I was doing a good job on them but after getting through three rear skeg bearings in a season and the prop waggling round like a dolphins tail, I bought a magnetic balancer. When I put my "balanced" props on it - they were MILES out, so I had to do them all again. Now the bearing lasts at least a season or two.
Danny
It is not hard work to balance a prop BUT a good balancer makes a lot of difference. Mine is a Top Flight Magnetic
Balancer. It is impressive to see a prop rotating rock steady with only one end of the balance shaft touching an end magnet but do not make that gap too large - just a few "thous". I broke a skeg due to an improperly balanced prop once and that was once too often!
If you search on "Octura Prop Charts" you will find many sites offering the information (Remember that PRATHER ceased trading at the end of January).
You can also get Octura props from Tony Ellis at http://www.modelmarinesupplies.co.uk/shop/ (http://www.modelmarinesupplies.co.uk/shop/) either balanced or unbalanced. His turnround from order is fast.
I do not know where you can ABC props form in this country - did find http://www.niagaramarinehobbies.com/ABC%20Props_1.htm (http://www.niagaramarinehobbies.com/ABC%20Props_1.htm)
Here is a "complete" props chart - follow the link - http://martysrcboats.com/props.htm (http://martysrcboats.com/props.htm)
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Ok 'M', stuff still not here yet, when it arrives, I'll send you a pic of the prop and see what you make of it. I thought aircraft props were dangerous enough but his one sounds like a regular screaming scalpel!! God help any fish that are'nt quick off the mark.... or us for that matter!
whats happened with the boat? is it running? did it work ok or was it a disaster? let us know but the silence maybe says it all?.hope alls worked out ok for yaa!! ;)
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Hello all, I have not finished the hydro yet but in between work have gradually fiddled with it and have now carried out the following: hull assy now joined and sanded, driveshaft assy in place (with free running driveshaft), rudder servo installed and rudder capable of around 30 -40 degrees of swing. Now I know you will all say "lazy sod, it should have been run and crashed by now" but I have not been able to dedicate a lot of time to it.
I have run the sc91 in on an 18 x 6 aero prop and a gentle drip feed of cooling water to allow around 60deg C head temp. The engine was run at around 3000 to 5000 rpm at a guess as I didn't want to cane it from new, the large prop gave it a nice load and that big flywheel action meant she ran as steady as a rock for around two hours. It has freed up beautifully and starts with one good swing.
I have spent a fair amount of time making a silencer system in an effort to keep the whole thing quiet and although it's not a tuned system by any stretch of the imagination, I think we are going to have our hands full with the setup as this is a large and powerful motor which, in a boat is untrodden ground for us.
The idea is to arrange an exhaust manifold in the removable top deck/ engine cowling and have twelve working exhaust stubs sticking out (6 each side). I hope to arrange it so the manifold will engage with the silencer (which is fixed in the lower hull) so that when the top deck is placed on the boat, we should have exhaust emanating from all twelve stubs.
I have also arranged a small venturi in the main exhaust outlet so engine cooling water will be expelled with the exhaust gasses instead of squirting out of the side of the boat. It is hoped the water injection into the exhaust will not only keep it cool but will also contribute to quietening the exhaust note. It should also create quite a mist of vapour when the engine is opened up.
As you can see, we are hoping to make this boat look quite good rather than going for all out racing performance. If we want to make it perform better, we can always fit a tuned pipe at a later date.
I have'nt got any pics to put on here for you as yet but I will post some soon, so you can all have a good laugh at my feeble attempts. I think the motor is going to be a real cow to start when installed in the boat as the flywheel has no mass and is really quite small for such a large motor. I reckon the rpm will go through the roof even if I shut the carb barrel right down so I think a bit more running in at some elevated throttle settings will have to be done before I finally bolt it into the boat.
By the way can anyone tell me if these engines should be mounted on flexible rubber mounts when installed in boats? We had such a mount in the kit of parts which came with the hull and I have fitted it but obviously could'nt use it with the aircraft prop setup. Should I fit it to the boat?
Best regards everyone........ Chris
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good luck with it mate and yes fit the rubber mounts ;) also use nyloc nuts on everything,a tip for starting using the flywheel loosen the plug when engines primed ready to start then attach glow plug starter and start it as normal .loosening the plug lessens the compression allowing it to spin easier.once shes running tighten the plug back up and toss her in!! what prop are you running in the boat did you get a good sized prop? dont use that small one the engine will over rev and blow up!! :o.
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hi
nice to here it is still going on
as mart says use rubbrr mounts some boats without them make more noise through solid mounts than there exhaust
also the water exit will be hard to see if it exits to the rear. that is why most exit to the side just to make sure water is flowing
good luck steve
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Hi Sheerline.
Notice in your last post you mention the engine running fast with the carb shut down. This is not uncommon on the SC engines, my .61 did it. I cured it on mine by fitting a bit of silicon fuel tubing over the fuel needle screw. It seems there was an air leak there.
It also helps to stop the screw undoing with all the vibration.
I have heard of people changing carbs., apparently the OS carb that just engines sell works well on the SC. I have no direct experience though.
As to starting, I do have direct experience!! I concur with Martin regarding loosening the glow plug, I found with mine that I had to buy a Sullivan high torque starter, the standard one I had previously just would not touch it. Maybe it was a bad one.
Good luck with it, look forward to seeing pictures as it goes on. The exhaust system sounds interesting, like retroboats, I personally like to have the cooling water flow discharging out the side as a "tell tale" so's I can tell the engine is being cooled when running.
Regards,
Glenn
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Hi again, and yes you have a point about the water outlet, we thought we would try it as an experiment first and were hoping the resultant and water vapour trail would be sufficient indication of water flow through the motor. If it does'nt work, it is all reversible so we'll just stick a pipe out the side. I won't be able to do anything to it next week but I think with the work I have done so far, the bits will be installed and it will go together quickly in the end. We want it to look the part so a decent spray job will have to be done.
One last thing, the prop Prestwich sent me will ballance in the horizontal plane but if the blades are rotated to the vertical, it will return to the horizontal on one side only. This indicates to me that the prop has had its hole bored off centre and I don't think there is much we can do about it. I have already sharpened it and polished it as I have gone along and tried to eliminate this bit of imbalance, but to no avail. It may have to go back to Prestwich as it would appear incorrectly made.
We have got a Gold series starter which we are going to try on 24Volts, as the aircraft starter we had is no match for the compression of the 91.keeping fingers crossed on that working. We will try your tip of loosening the plug if it won't play ball.
If this had been an aero engine, I would have been tempted to machine the cylinder head and fit a compression relief valve in there but there's no easy way to do it with a marine motor
I will come back with pics when I have the boat in some semblance of order.
Regards........ Chris
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id loosen the glow plug no matter what starter your using it will make life easier trust me.as for the prop sounds odd ive never heard of a prop having the hole drilled off centre!! ::)i dont understand what your meaning about balancing horizontal and vertical?i put my props horizontal on the balancer and the heavy blade falls to the bottom if neither does then its balanced?.
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Hi Mart, here's how I checked the prop.. Firstly I found a piece of 4mm ground stainless shaft and checked it was true and in balance itself. Next, I inserted it into the prop (good close fit, no slop) and placed it on the balancer. Found one side a bit heavy so filed and polished until prop blades sat level, didn't have to do much really as it was'nt far out. The blades sit level and thats fine so I turned the blades upright, one above the other and they fell back to the horizontal position. I thought that was odd so I turned the blades over so they were horizontal again but now rotated them through 180 deg and found they rolled completely back to the original side. If the prop were perfectly statically balanced, I should be able to place it in ANY position and it should remain there, not just horizontal.
So to sum up, the prop will only horizontally on one side only which would indicate the hole is offset in the casting. I can't take anything off the blades to improve it nor can I realistically take or add anything to the hub to correct it .... I think I have a naff prop!!
I find this sort of thing par for the course whever I buy anything.. you could have a hundred items on a shelf and sods law says I will always wind up with the 'friday afternoon' one!
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i still dont see how you know your getting it 100% vertical? surely its normal for the prop to roll over from vertical?youd have to get it exactly vertical for it not to.when you spin the prop on the shaft does it wobble? if not id say its fine!!also if one blade is slightly larger but same weight would that acount for it rolling over?.stick it on and start the motor up and let it spin or do as i have fasten the prop on the shaft and put the shaft in a drill and turn it on and see how it spins if its not balanced you will soon know. ;)
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Chris
Your prop is probably OK but just still out of balance.
Don't forget that a racing prop is heavily pitched and the blades go round the hub almost 360 degrees (poor explanation but will do).
If the BACK of both blades are horizontal, then the FRONT of the blade at the bottom is too heavy. You will have to remove weight from the part of the blade that's at the lowest point. Don't try to remove your edges, just go in a bit at the lowest point and start filing!
Also don't forget to remove any casting flashes that are still there (although being so far from the edge doesn't make a HUGE difference to the balance).
The fact that it's dropping straight to the same position quickly would indicate that there's a LOT of weight at that point.
I've never come across a prop where the hole has been "off centre", so if it is you are EXTREMELY unlucky. ;D
Think yourself lucky it's not a THREE blade which I also use :o ;D ;D
Danny
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What prop are you grinding on? If it's beryllium I hope you are taking the proper precautions, face mask, gloves, long sleeves etc. beryllium is not nice stuff. Do the work under running water..............
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Hi chaps, firstly, I think the prop is simply brass, I work a lot with brass and this item appears to exhibit all the qualities of the stuff. I think, given the amount of imbalance I would have to remove a considerable amount of material from the hub area of the blades to get this prop to statically balance but that would really screw up the hydrodynamic balance which may cause more problems than I already have. I am not nitpicking over this balance thing and am prepared to accept that nothing in this world is perfect but knowing how much importance you fellas place on balance given your own personal experiences, I would like to know I have got it as right as can be. I will try spinning it on the shaft as you described but I know it aint right.
Martn, just to elaborate on the balance theme, I liken the prop to a flywheel, it should be able to come to rest in any position throughout 360 degrees...that would be truly statically balanced. If each of the blades were perfectly symetrical and imparted exactly the same amount of thrust at a given rpm.. they would be exhibiting perfect hydrodynamic balance.
In the real world, I will never achieve either of these perfect goals and certainly have no means of checking the latter.
I will look at it again and see if it can be improved a little more. I suppose I have to take into consideration that this boat will not be receiving the hard graft and continual use your boats get so we will probably fit it regardless and use it for trials. We can always get a better quality prop (Prather) at a later date I suppose.
Thank fellas........... Chris
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chris the prop will not balance at any position through 360 degrees if its balanced it will allways come to rest in a balancer with both blades horizontal to each other its not like a flywheel.also can i ask what prop your using who makes it? is it octura? if so it will almost ceratainly be stainless steel or berrylium .
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Martin, the prop came from Prestwich, there was nothing with it describing it or its material type, all I know is it appears to be brass. It looks, files and polishes like brass and thats about all I can say. How would I be able to tell if it was beryllium ?
I have now fitted it to the shaft, also, the motor along with its rubber mounting and silencer assy are now ready to bolt down into the hull as I have fitted blocks to accomodate them.
I reckon I will get back to it after next week and finally fit the top deck out with its manifold.
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ask dave but what prop did you buy it as? what size and pitch etc?.he sells mocom props (submerged) and octura and thats it i believe.it should say what they are made of on his site.
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yup octura are berylium copper(bronze) hazardous to breath in.
http://www.prestwich.ndirect.co.uk/octurapropellers.htm (http://www.prestwich.ndirect.co.uk/octurapropellers.htm)
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Ok Mart, Berylium it is, but I don't think I have done that much work to the prop to render me any more knackered than I already am... hopefully. I will have another look at it when I get time. Thanks for that.
Regards... Chris
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http://www.zippkits.com/rivslow.wmv
Sheerline, all seems to have gone quiet, hope the build is progressing. See the link above for some video of a shovel nose hydro running, this one is pinched from another forum but I thought you might like to see what the boat performance looks like, I believe the boat in the video has a 26cc petrol engine, so similar or maybe a little less performance than the .90 methanol burner you have.
Shuld be fun.
Glenn
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Glen, sorry I haven't been on this thread for ages and although I have trolled through and contributed towards other threads, I obviously didn't look in here. The shovelnose is virtually complete although work ground to a halt a while back, I will post some pics when I get a moment and you can all have a good larf at my attempts and tell me where I've gone wrong. The last hang up was over an engine starter, my lad reckoned he would have one man enough for the job languishing in his loft somewhere but as he had moved and stuff was still in boxes, I have grown even older waiting for it to appear. :(
I have run the motor in on an aircraft prop for about three hours at third throttle and set rich. It starts with one flick and runs faultlessly so I have high hopes for it providing I am able to turn it over and start it in the boat. I have taken note of the advice given, regarding slackening the plug to lose a bit of compression when set up for boat use. Needless to say but with the aircraft prop fitted it was a delight to start and no plug fiddling of course. Shame it has been fitted to a boat really as I would love to stick it in the nose of an aircraft!
I will come back with some pics soon.... promise!
Regards to all ........ Chris
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Nive to hear that the model is near completion Chris. Look forward to seeing pictures and some updates as it goes on.
If the motor is run in, which it sounds like it is, it may well strat easy enough on a more standard starter. Here's hoping. My SC61 now has around 8 hours on teh cylinder and piston, but not the con rod - long story! It starts really well now. Although I did replace the carb with a replacemetn form Just Engines. Well worth 20 quid. Easy starts and great low speed performance. Idles at 3k!!
All the best.
Glenn
Happy Christmas.