Model Boat Mayhem
The Shipyard ( Dry Dock ): Builds & Questions => BMPRS - British Model Powerboat Racing Society => Topic started by: Ultraslowflier on February 25, 2014, 11:09:51 pm
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Hi all, I'm new to Mayhem but been a modeler for more than 50 years... Lego, Meccano, Boats, cars, planes etc.. over the years. Currently and active model flier and boater. I have scale boats, BMPRS class AA and A offshore racers and also RG65 and 1M yachts. I am a member of Kingsbury MBC in the midlands.
Graham
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Sadly found Mayhem forum due to the death of Rod Gabriel...
I hope normally there will be happier things discussed.
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Hi Graham,
Welcome to the Mayhem!
You don't have to be mad to post on here...... well you do every first Monday of the month! ok2
Are you building anything at the moment Graham?
Martin
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Currently building one of Bernard's Cavaliers for the AA class BMPRS offshore season. Need to sort out the thread size of my Pico 21 engine so I can order a flex coupling, plus BB shaft.
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Just can't beat Lego :-)) :-)) :-))
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hello Graham,great to see you on here mate.all the best :-))
kurt and sha
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Hi Graham
Welcome to this forum!
Welcome to the BMPRS!
You won't go far wrong with one of Bernard's boats. I will look forward to seeing you and your boat(s) in action soon.
:-))
Craig
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Graham
You mentioned a new build in progress.......
Just to add, if you are able and willing to upload some photos of your boat and build, please do. I love such photos as they will give so much vibrance to these threads.
:-))
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Hi Craig, Kurt and Sha..
Thanks for the comments.
You have seen me racing before... I'm the one that wears a silly hat more often than not. It keeps the sun (or rain) of my ever increasing bald patch. I have been a BMPRS member since it was founded.
I have raced a little red bat boat in the AA class, another little red boat in that class that has so far refused to be tamed (and about to be redundant as I move to the Cavalier, and a XXX in the A class. The latter ate a tiny washer in 2012, and I have been waiting for the repair completion ever since.
You are right about Bernard's boats, they just work.
There is a chance the Cavalier will be running for Leicester, as I might have all the parts next week.
Cheers
Graham
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The Little Red Boat (LRB) that will be redundant when the Cavalier is set up may get an electricery conversion. With the Pico 21 in it the thing was more out of the water than in it. A bit less power would be better for it. A flex drive with stinger etc. might have been OK, but I seem to get through flex shafts rather too frequently, hence a "simple" Cavalier. The LRB also had in flight adjustable trim tabs, which helped some, but failed to make it safe enough to race. It's embarrassing to have to get it back out of the hedge, a couple of feet above the waterline.
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hi graham,we know who you are mate,sha says you dont look right when you leave your hat at home lol O0 {-) the one thing i will say is to watch out for the cavalier they have a tendency to hook over if its over powered we found this out with a go 28 but other than that sha loves hers mate and im sure you will enjoy yours .they do what it says on the tin :} i take it you ,mark and judith will be doing leicester ?we may also be doing it so might see you there,
take care mate see you all soon
regards kurt and sha
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hi graham
glad you finally managed to join chat soon m8
mark
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Hi Mark,
Making slow progress on the engine recovery front.
Hi Kurt and Sha
What exactly happens when Sha's Cavalier "hooks over"?
Leicester should be good for Mark, Judith, Rod and myself. We are introducing the boats to the water again, some of them have got scared and needed a bit of coaxing.
Cheers
Graham
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Hi Graham,
Welcome aboard. Crank thread for the Picco 21 should be 1/4 UNF.
Ian S
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hi graham.
it digs in and veres to the left which can sometimes be abit worrying %% it hasnt happened now that we are running a smaller engine in it :-)) is the picco 21 a marine engine or buggy converted engine ?
regards kurt and sha
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Hi Craig, Kurt and Sha..
Thanks for the comments.
You have seen me racing before... I'm the one that wears a silly hat more often than not. It keeps the sun (or rain) of my ever increasing bald patch. I have been a BMPRS member since it was founded.
I have raced a little red bat boat in the AA class, another little red boat in that class that has so far refused to be tamed (and about to be redundant as I move to the Cavalier, and a XXX in the A class. The latter ate a tiny washer in 2012, and I have been waiting for the repair completion ever since.
You are right about Bernard's boats, they just work.
There is a chance the Cavalier will be running for Leicester, as I might have all the parts next week.
Cheers
Graham
Hi Graham
Ah...now I too know who you are, Mr S? I pitted for you with the red AA-class boat a time or two last season. And that certainly was a lively hull ;) If you don't mind me saying, there was one striking aspect of the set up of your red AA-class boat that I thought was a little too extreme for the hull. And that was not the powerful engine inside. It was the prop shaft angle. It seemed very steep in my opinion and I often wondered whether the hull would be faster and more stable if the angle was reduced. Only my observation for what it is worth.
It is good that you have joined this forum mate :-))
Cheers
Craig
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Hi Craig
You did indeed pit for me. Very well too I recall.
Yes, I agree the prop angle is somewhat steep, but that was done exactly as prescribed by the manufacturer. Other folk have also commented on that angle. Sadly I can't easily correct that aspect as it is well and truly buried beneath loads of carbon and the servo tray, which is also well fixed in. Plus the manufacturer popped his clogs last week, so no longer available to discuss his ideas with him. I might well eventually dig the shaft out, and re do the shaft at the shallowest possible angle for the small prop needed by the engine.
In the meantime the Cavalier will be ran, it's a bit more tried and tested. I am just a little concerned that it can become a bit of a handful if over powered. The Pico is rated at 2.7hp when properly set up. That power was one of the factors in the LRB, as well as shaft angle, prop depth, rudder position and size, centre of gravity, trim tab settings etc... On it's last outing it had long "live" trim tabs, which I suspect made the effective hull length greater, as well as being adjustable while running. They helped some, but it still leaped out of the water unexpectedly from time to time. I still have loads to learn in this game, both in driving skills and boat building and set up. I suppose if it were easy we would soon get bored.
Cheers
Graham
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Hi Graham
That little Picco marine engine of yours has more than twice the power output of my A-Class SC46 so your potential is massive! :-))
When it comes to boat driving skills and set ups, I am with you on that. I too have loads to learn.
That is perhaps what makes this hobby/sport so addictive and fascinating :-))
Cheers
Craig :-))
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Hi Craig
The (potential) power of these little engines is amazing. I grew up learning we get up to 1hp per 10cc on a good glow engine. That is now still largely true of "standard" petrol engines, but tuned high reving engines, glow or petrol blow that limit away. But if we get near the new potential outputs then durability becomes a real challenge, as everything become so stressed at the high RPM needed to pull the power. From drive shafts to big ends, the chance of it giving up is much higher. Your A class SC should outlive the screamers.
Cheers
Graham
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Sorry to hear about Rod, Graham. I only met him once - at Kingsbury last year, but had a good chat.
If I remember rightly, the Piccos all have SG cranks, and I think your flywheel and coupling came from Rod. If the flywheel was made so that it only sits on the inner, plain section of shaft, and the thread is beyond the flywheel, you should be able to use a standard type of coupling; the vast majority of .21s and .45s use 1/4 UNF thread. If it was made so that a spigot on the coupling screws into a recess in the flywheel, it gets a bit more tricky. I can say, from personal experience, that the old crank induction CMB 21RS (and some of the other crank induction CMBs), had SG cranks, and CMB made a direct drive version. The flywheel for one of those will allow you to use a standard coupling with a SG crank engine. I know some spares are available, so that may be one option - if the flywheel is the issue.
Ian
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Topic renamed :-)
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Hi Ian
Thanks for your comments.
Yes, 'tis sad about Rod.
The crank is 1/4UNF. Rod had lightened the flywheel some, partly because he believed the flywheel was too heavy, causing problems with it's intertia damage should the prop hit something and partly because when mated to his pin coupling that added to the rotating mass. The flywheel sits on a taper collet, with the thread inside a rebate on the flywheel. There is enough diameter inside the recess to fit a hex bar tapped out to 1/4UNF. The other end of the bar will go onto a rubber coupling, which in turn will go to the solid drive shaft.
What does SG stand for re crank?
Thanks
Graham
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Graham....in materials...SG usually signifies spheroidal graphite [iron]....but not necessarily to be confused with bog standard 'flakey' cast iron
Some of the higher grades of SG iron...eg., the German DIN GGG63 is an excellent material with low elongation & high impact resistance
SG iron is usually centrifugally cast, as opposed to poured & sand cast............
Having said that...I have never heard of SG iron being used for crankshaft manufacture........Derek
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Hi Graham and Derek, I'm not sure what SG stands for in this context, but it's the term used for a type of crankshaft originally used for RC cars. Compared to a marine crank, the inner plain section - protruding from the small bearing, is relatively short. The thread is shorter than a marine crank too. It's not really an issue for geared drive - where you don't have to take drive directly from the crank, and a long sleeved nut is normally used through the driver gear, to acces the available thread, but they're a bit more tricky for direct drive. Less crank for the taper collet to sit on, less depth for the flywheel, and less thread for the coupling to grip. The SG crank has another plain section beyond the thread, which is internally tapped for a small screw, but this section is often cut off for marine use. Manufacturers who make car and marine versions of the same engine, often fit SG cranks to both. Uncut, they look like this https://www.modelmarinesupplies.co.uk/proddetail.php?prod=P7-R21
Whereas this OPS has a standard crank: https://www.mantuamodel.co.uk/Engines/OPS_Model_Marine_engines/_OP88761__OPS_Marine__21_Engine_1134.html
EDIT: SG is apparently after the engine manufacturer of the same name.
Cheers:
Ian
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Thanks Gents..
I remember SG as Spheriodal Graphite too, but couldn't see why it would be particularly good for a crank. I'm an electrical engineer, not a mechanical specialist, though my dad was, and he had a big influence on my engineering knowledge. He designed a centrifugal casting machine for making piston rings when I was, ermm, about 50 years younger. Not sure what grade of cast iron went into that. He was a designer for BRICO then. I thought the strongest cranks were forged from special singe crystal castings. Far too expensive for model bits?
But to summarise, in this instance we are taking SG to mean "car" cranks cut down for marine use. That tallies with the failure of the coupling thread. The thread is short, and the engine is very tight to turn over when starting. So the high starter belt load on the short (aluminium) thread caused the original failure. I can't say I am a great fan of the pin type coupling, as the fore and aft movement of the engine can be as much as the length of the pins with my high impact driving skills. A more standard bobbin couple would be more robust for me, and has the advantage of a steel thread onto the engine crank.
Could an air cooled car engine be used in an offshore boat? I would imagine they would get as much air around the fins as on a car, plus a few splashes too. How often do air cooled engines get fitted in racing boats?
Cheers
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Hi Graham, air cooled car engines are fairly common in riggers - where the fins can get direct, cold air, and also speeds (or expected speeds) are significantly higher.
I don't think you'd be able to get enough cold air across the fins - in the types of boat we run, but I don't know of anyone who's actually tried it.
Marine conversions of car engines are often pretty straightforward. For engines which have a marine equivalent, it's usually as simple as taking off the car type finned heat sink head (which more often than not sits on the head button itself, and replacing it with the marine water chamber / cooling ring. These often transfer from one engine to another, because many engines have the same head bolt patterns - especially those with four head bolts. It's also within the capabilities of a well equipped home workshop (large enough lathe, or a mill plus workpiece rotating fixture), to make one.
Be careful with your choice of bobbin type couplings. A lot of them have ali end pieces....
Ian
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hi graham i run air cooled buggy engine in my small rigger but have also converted a few to run water cooled heads,got a mate who does the conversions and has done at least 6 for me so far which all work well :-)) wouldnt like to find out if one could be run in the boat with the standard fins on %%
all the best
kurt and sha
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Thanks Gents
Looks like the safest thing is to stay with water cooled for my Cavalier.
Cheers
Graham