Yes, it’s funny, but could be true.
The BB engine design (W-series) isn’t any newer than the T55 engine, yet Kalsmine significantly improved it. With the turbines, he practically created a modern engine. And it is bigger engine...

I remember consumption little too small, I calculatebit years ago.
3x525 boat should go 1mpg at cruse speed, it is 2.35l/km
Marine bbc is something like 0.45 and for example old scania 16liter v8 bsfc is 0.31.
My Fountain driveline efficiensy is better than three bravos running full of 140 weight oil and three drive leg drag.
So btfc is 29% better, all drag is maybe 15% less and boat are lighter.
2.35x0.85x0.71=1.42l/km not 1.2, but far less than tripple bbc boat

With tripple big blocks as the baseline, you will not be disappointed with fuel consumption.

But no, if the cruising speed is 60 knots.
https://boatingmag.com/story/boats/f...u7B3DxP8UGsWCk
And in practice, users usually never achieve results as good as those achieved by Fountain during testing.

If you reach 2 l/km @ 60 knots, you will be reall class winer if you ask me. Just forget consumption and enjoy, this will be the last problem.

Forgive me if this has been brought up already, or you have thought of it already, but there used to be a shop close to me that would build driveshatfs out of chromoly when aluminum wasn't going to be up to the task.

theres a lot of videos of carbon shafts letting go in drag cars i would go steel..... carbon chunks and turbos don,t end well its very violent when they let go!

Plavutka, 58knots is best economy cruising speed for that new 47 Fountain, 0.96mpg, it's 2.45l/km. Does anyone know how much M8 drives have. Those turbo gas engines have not good bsfc...

Tenth time, crmo drive shafts won't work because too low critical speed. No matter how thick wall tube used

And yes I'm not qorried about consumption, it would be just nice if this fat girl won't be thirsty.

If I understand your "M8" correctly like question:


In both cases, the gearbox comes first, followed by the drive. Both gearboxes, yours and the Mercruiser one, most likely have a very similar efficiency.

In your drive, you have five gear wheels on one side and four on the other. The approximate mechanical efficiency of your drive will be around 90–92%, plus the losses in the gearbox.

The M8 has two right-angle gear stages, with a likely efficiency of around 93–95%, plus the losses in the gearbox.

Overall, from the engine crankshaft to the propeller, the M8 drive probably has an efficiency of about 89–91%, while yours is roughly 2% worse. Both have probably a % or two more losses in reall world.

Hydrodynamics?

The question is how much trim you need and at what speed you are interested.

a) If you need a significant amount of trim, the M8 is better in any case.
b) If you don’t need much trim, your shaft will have less drag at higher speeds, and the propellers will bite better, because there is no torpedo-shaped housing planing ahead of them and disturbing the flow. At lower speeds it doesn’t really matter, since the drag of the torpedo neither adds nor removes much.ž

As I already mentioned, you can expect about 15% lower fuel consumption, no more. And that’s only if you really optimize the boat’s center of gravity and choose the right propellers. And diesel it is uncomparable more safe for explosions and fire.

You will be surprised how much work with finall adustements will be needed when you finally bring your motor and drives in order.

There was some loading or update error, should read ”Does anyone know how much power loss M8 drives have?”

losses are not that simple that you can say something have like 96% effisiency, it depends used rpm, loss increase when rpm increase. My splitbox upper gears turn slower than M8 and they are spur gears not conical, much lower losses. But these are just wondering, real data must be measured to be true and that is not necessary.

I have read somewhere that ssm6 takes 60hp when spinning 6000rpm, sounds too much to be correct but would be nice found some diagram loss vs rpm vs power used.
bravo have big hydraulic loss because drive is full of oil, drysump drive sre maybe better.