1.) This is classic mechanical engineering, and the efficiency lies within the mentioned tolerances. It may be a few percent higher or lower. For mechanical efficiency, the load level does not play a major role. What matters is the surface finish of the gear wheels. In the case of the M8 they are relatively smooth; in gearboxes I know they are ground, while yours most likely are not.
Very lightly loaded gear reducers have a higher percentage of losses, because you still have to rotate the reducer itself; however, in marine use, as soon as you are planing you are already above that threshold and the reducer’s internal losses become minimal.
On dyno tests, measurements sometimes show differences similar to those caused by a lighter or heavier flywheel. But these are not real power differences that would affect power at the propeller — it’s just higher or lower acceleration that poor software interprets as a power difference.
Does the SSM6 consume 60 hp when spinning at 6000 rpm? Yes, why not. And at 5000 rpm it can have the same losses, but not unloaded — under full power. If the losses are 60 hp with more than 600 hp input power, that’s a good result regardless of rpm. But if that happens at 400 hp, then it’s trash.

2.) You have 5 gears on one side and 4 on the other. Even though they are only intended to change rotational speed, all available forces still act on them and on the bearings — they must transmit work, and in doing so you incur losses of about 2–3% per gear pair. There is absolutely no way around this.

3.) I know — surprising and at first glance illogical — but a bevel gear angular transmission has practically the same losses as a straight angular transmission. The differences are so small that it makes no sense to take them into account.

4.) Yes! Real losses must be measured in practice, because manufacturing always includes some tolerances, but the actual result will be within the predicted range. If everything is manufactured 100% correctly and you have a dry sump, efficiency will be about 92%. If it’s slightly less precise and the gears run in oil, efficiency will be around 89%. If there is a larger downward deviation, then there is a fault somewhere, and the reducer will not live long.



You know, in our hobby there’s a lot of marketing and smoke-and-magic. There’s also a lot of empirical knowledge, because the hull, drivetrain, and propeller of a planing boat operate in very unpredictable fluid-flow regimes that are almost impossible to define numerically.
When you combine that with marketing — where everyone claims to be the best — and with the average consumer’s limited technical knowledge, you end up in a situation where “magic solutions” start getting sold.

Any average mechanical engineer should be able to calculate the efficiency of your drivetrain, and from sketches available online it’s possible to estimate, for example, the efficiency of an M8 drive. Not precisely, but within a tolerance of a few percent — yes. And no amount of wizardry will save you from those losses.
The greatest potential for improvement lies in better hydrodynamics and reduced mass, which catamarans with relatively small 300–400 hp engines demonstrate very well. But even here there is no magic involved — just sensible technological progress.

If I were in your place, I wouldn’t worry too much about efficiency. What matters is that you manage to cool the gearbox and all the other components sufficiently, and above all that you succeed in carrying this interesting project through to completion.
If it flies, you’ll have the best-built and most efficient Fountain out there.

if you look back to ww2 engines theres many that had a long driveshaft from the engine to the prop p63 aircobra was one theres many others that put the engine in the wing or behind the pilot ita worth a look?

That aircobra looks interesting! Never seen before. Internet say that shaft is about 3" diameter, 3 meters long with one support bearing, engine rpm reduced to 2600-2700rpm so they were far away from critical speed. Basic aluminium tube can handle that, 1.5m long, 2700rpm power transfer. Looks scary, if drive shaft fails, pilot lose his balls.

What cruise speed? You mentioned 60knots before. 69mph is a very fast cruise for a 47 Fountain.

Cranking up the peak piston speeds of diesels at high rpm will start creating deep parasitic losses, that would dampen the diesel BSFC benefits. You have 7.32" stroke. 3000rpm is about a 5500fps peak piston speed. Getting up there.

It's going to take some steam to run the 47 at 69mph even with reduced propulsion drag.

Here is Fountain 47 test result with twin 1350's. Most economical cruising speed is 58knots. It may be caused by best economy for engines in that loading and rpm, but it may be best efficiency for hull.



My cruise rpm is about 1350 at most efficient spot, 67mph/58 knots if slip is 12%. Engine is very happy at that rpm, will live forever running low loading and rpm. 70GPH consumption in test boat gives about 800hp continous power for 67mph cruise speed. Transmash should burn 55gal/h in same load. 0.45BSFC vs 0.32 for Transmash, this is just guessing.

https://www.google.com/search?ie=UTF...critical+speed

Worth a shot or at least the math

Grid is complete now, it takes lot more time than I think as usual.

Next job is design and do some interior, Stringers are now lower so there is many options for nice overnight cabin.


Tabbing for transverse parts need lot of glass pieces, I first think to cut just one piece for each triangle times two layers but it was too big job so I just make smaller tabbing pieces. They should work fine.


Toilet floor goes 15cm down so there will be almost standing height. I wonder to get usable shower there someday. Toilet floor is part of grid system and make stiffening to quite large bottom area under the toilet, there can not be transverse parts if toilet have good free height.


Bonding and laminating under toilet wasn't funny.


I bought oak veneer, it's nice to handle because veneers is bonded to some cloth behind. 3mx1.2m piece,0.6mm thick. I use it in interior, need to be dye dark color first.



Alcohol based wood dye may be best way, need to make some test to find best color for my taste. Then I will use ultraviolet light curing varnish, that is future clear coat way. No odors, easy thick coat, no sanding between coats, etc. Clean armor have good products.


Every empty space have to get in use as storage if we go to long ocean trip some day, so some hatch to every locker need to be done.


Divinycell foam is very easy to work. Hatches and floor opening edges may get carbon fiber cloth on, floor will be oak veneer finish.
Interior may be dark oak, carbon fiber and beige or white leather, perhaps.


Engine need some upgrades too. Injection lines must be redone, now they are too soft tube and ends are made poorly, you should never have done anything on someone else, everything should be done on your own. These are too long also, looks ugly.
Electrics are not complete, rpm gauge signal didn't work.
Turbos have to remove and take turbine housings to insulating company that makes nice stainless steel/wool insulating. KKD Motorsport is right place for that.
Drive shaft CV joint infrared temperature sensors have to install.
Breather is too small, 50mm breather with centrifugal oildust separator is on list.
And of course drive shafts! I decided to make aluminium shafts for next summer, they are temponary but save me time to do boat othervice better. Transmash won't have that much power now to spin them in critical speed, it have no intercoolers, power should be somewhere 1500-1800hp now. will get 1000-1400 more intercooled.

In America, Fountain guys pee sitting. Like Democrats.

Man on a mission! Awesome work, keep it up brother!

Injector lines have inertia and can move/rub. Having wear points at contact locations is good failure prevention.

Good to hear on the alum drive shafts just to you on plane and functional.

As mentioned...is there an oppirtubity for a hydrid driveshaft? Carbon over metal? There is strength there, and bonding/shaping is pre-setup.

You have a few options with your tranny as well.

Dialing in your props...staying smaller diameter will help you in your post 100mph goals. Means you need to get your driveshaft rpm up. As you know. Looking forward to the alum driveshaft posts.