Keep after it! You’re nearing the finish line.

Looks like we have good oil pressure now and after governor adjustment idle quality is pretty good too!


So we tried to get Fountain on plane but there come next issue, I broke left carbon drive shaft, they are way too flexible and get in critical speed. Tubes should have much much higher modulus of elasticity but usually theory and reality are too far apart.


There is third gear in and engine are just above idle, so much torque that only thing you can feel high load is black smoke. Shaft broke immediatly I give little throttle to get on plane.
I think shaft get above it's critical speed, this should not to be problem if modulus of elasticity and stiffness are that it should to be.








Shaft tube bend about 40mm banana and get hell of shake, then touch to G1/4" coolant drain plug and lathe itself broke. I think rpm is issue, not power.

Luckily it didn't broke anything else, bilge pump got hit but it only separate from fixing plate and are unbroken. In future I have to ask somebody strenght calculator guy to calculate critical speed, material, thickness and all physical properties to get driveshafts work. Carbon fiber is way better than other materials but it have to be done right and get properties that it should.






We take boat out of water, autumn have come in Finland. Last winter was too hectic to get Fountain on water but now I have more time to focus moe precisely all things to get this boat work.

Tomorrow start a new experience trip. In next week is my 40th birthday and I rent 47ft sailboat from Creece. Bright blue warm water and hopefully some nice wind for our boat.

that unfortunate,I'm sure those driveshafts weren't cheap.why didn't you go with chrome moly,us high torque diesel guys take out the aluminum shaft and go chrome moly for the strength.

One of the issues with the US Navy Carrier upgrades for every new hull design, is the risk of changing too many systems and what effects that has on other systems is often difficult to anticipate.

OP has done amazing work.

Glad there was minimal damage.

Propshaft rpm and TQ is what the driveshafts will see.

There's some serious TQ being applied.

Maybe the props would benefit from some ventilation?

Rather take steel tubes; they’re easier to size numerically.
Carbon is stiff but brittle, and even if it survives now, it will eventually fatigue. In the picture, it looks as if the fibers are oriented only radially, with no visible longitudinal fibers. For a torsion-resistant laminate, I’d expect the fibers to be oriented at 45 degrees in both directions, not simply wound in a single direction.

If it really is as it looks in the picture, the behavior of these shafts is similar to using a helical spring as a torsion shaft. Even small delaminations, visible as white cracks, show that the shafts are probably wound incorrectly. And good tempered epoxy, when stressed to much, shatters like cracked glass.
And I think this should have been made from prepreg in a high-pressure autoclave.

Any “tubular shape” that needs to be torsionally stiff has fibers oriented differently—whether it’s a fast motorboat, a composite aircraft wing, or a wind-turbine blade... All of those would fall apart if built like what can be seen here.

awesome project but switch to steel drive shafts and put the 380 tabs on or extend yours

Agreed. If he needs stern lift, burying the surface drives will only increase shaft tq vs getting them ventilated.

The large tabs have better adngle of attack for less dynamic drag.

OP has done amazing work. 2 factors. So much is new/custom design. All put together. Seperate testing would eliminate a lot of issues. Obviously not possible with real world single person budget.

2nd factor, being in the matrix makes it difficult to see potential issues. Anything this complex is going to have them. A writer has a harder time proofreading their own material for spelling mistakes.

NBD...this is part of the process. Please keep posting the updates.

he discussed driveshaft construction back around the teen pagees, the pictures i got from page 24
Kslame; Whatever it takes to get on plane, you have done a fantastic job with incredible attention to detail to perfect every part "you" made, modified or customized,
It's gonna work. Keep going

In this interesting topic there are so many new things that I missed this page.
Such a carbon shaft will not hold, and the epoxy used is too soft for the carbon to show its full potential. One should use prepreg, or a high-quality epoxy that is tempered at least at 80 °C. And without a high-pressure autoclave it also won’t work, because you end up with too high a percentage of epoxy in the laminate. Good karbon laminate will not crack, but just eksplode when overloaded.

The winding in the picture is just classic winding, and it is not at a 45-degree angle.
Even the best-made carbon shaft is probably not suitable for the dynamic loads that a propeller delivers. With carbon you have almost no reserve in elasticity. Once it reaches the limit of plastic tensions, it collapses—and that is not good for a shaft, unless it is appropriately oversized.

Take a CroMo steel tube, which can be determined in terms of strength quite easily and reliably, and you’ll see it won’t be significantly heavier. pipe with wery thin wall. If you insist on combining it with an aluminum flanges like you are now with carbon, I suggest using a high-quality methyl methacrylate adhesive, or conditionally also the epoxy Smoth-On Metalset A4.

But it’s better if everything is made from CrMo steel.

That sounds amazing, happy birthday!

Take a break and get back after it.

Thats what I do when I hit a wall w/a project.

Amazing what you see with fresh eyes and a fresh brain!