Center support can not be used without making two piece drive shafts. Shaft move sideways and up/down when steer or trim drives. Surface drive flange is fixed straight to prop shaft, this is my own drive system idea to get socket housing smaller to get drives lower and make them more strong because no need for small size joint in socket housing. This system need long drive shafts to work, otherwise CV angles go too big when steering or trim is fully tilted.

But I get simple idea for autoclave and heating accurate temp easily in 8 bar pressure, I tell it you later. I'm very happy at your help plavutka, thanks! I think now I try prepreg and autoclave route, like you said it's simple thick wall tube with ends, very cheap to fabricate. Water (or some other liquid) heating through mold tube will make accurate and even heating and its easy to do inside pressure chamber.

There are datas for Prepreg "UNIPREG" from R&G web page:


Technical data of the fibre:
Tensile strength: 4137 MPa
Tensile modulus: 242 GPa
Elongation at break: 1.5 %
Density: 1.81 g/cm³
Filament diameter: 7.2 μm

Technical data of the non-crimp fabric:
Areal weight (dry): 150 g/m²
Curing temperature: 80 - 150 °C (176 - 302 °F)
Glass transition temperature (Tg): 70 - 140 °C (158 - 284 °F)
Prepreg weight: 234 g/m² (6.9 oz/yd²)
Resin type: Epoxy
Resin content: 36 %
Laminate thickness: 0.15 mm (+/- 2.5 %)

Width: 50 cm

Typical properties of Unipreg® laminate (curing at 80 - 150 °C (176 - 302 °F), see technical datasheet):
Tensile strength (EN ISO 527-4): 1800 MPa
Tensile modulus (EN ISO 527-4): 139 GPa
Flexural strength (EN ISO 14125): 1670 MPa
Flexural modulus (EN ISO 14125): 115 GPa
ILS strength (EN ISO 14130): 73 MPa
Density (EN ISO 1183): 1.57 g/cm3


Good, but expencive:
https://www.r-g.de/en/art/192230060-SUD

Thank you for posting your challenges and progress with this project. This is the best morning coffee reading material ever!!

Racing drag cars, I had heard the term critical speed and knew it was a bad thing, but never really leaned or asked what caused a failure. I always just ordered a shaft from a reputable racing driveshaft company for my application and figured I was good. According to the video below, it's centrifugal force that starts bending the shaft. Makes sense.

It’s not a centrifuge, but rather oscillations caused by the wavelength. Nothing is fully 100% balanced, and the higher the revolutions, the greater the centrifugal force — and consequently, the greater the imbalance forces that cause the long shaft to start vibrating. At certain rotational speeds, the shaft bends enough for the mass of the shaft plus the imbalance to reach resonance, and if the rotation continues to accelerate, oscillations become so strong that the material fails.
The stiffer and lighter the material is, and the better the ratio between the moment of inertia and the shaft length, the higher rotational speeds it can withstand. This is the reason Ksalmine wants carbon shafts.

33 pitch @4360 prop rpm @15% prop slip is 116mph.

I suspect you're not trying to go that fast?

As you know, 16.5 props are very small. My 30ft tein Arneson hull has 17" props.

80mph for you and 33 pitch props would be about 3000 prop & driveshaft rpm.

Dodge Ram 1ton extra cab dually trucks trucks have a factory aluminum 1 piece drive shaft are pretty much 90" they'll turn up close to 3300rpm and have a lot of tq through them. Hauling heavy going up hill etc.

Yes I try make it run 120mph some day. From that post I have raise engine rpm and prop shaft speed is now 4500rpm max, but I may turn it little more some day.
I have three set of props 18x28, 17x33 and 16.5x34. 18’s was in use this summer. 16.5 are too small, but I get them in some other deal.

90” aluminium drive shaft can not turned over 3500rpm, 3300 is ok then. Dodge may use special tube called MMC or something, inside tube are some honeycomb layer an another smaller tube to make more longitunal stiffness. That way tube frequency and critical speed go up.
I think this solution too, but didn’t get idea to manufacture it yet

It feels like the drive shafts will be the weak link in the overall system.

Quite the achievement.

Is there no way to re-engineer the transom plates of the drives to have a steady bearing system?

Surely a double U-Joint in front of the drive socket would be sufficient. Then you can shorten the driveshafts.

Have you considered... if you have an problem with a drive or a prop, are you able to uncouple the shaft/drive etc? If you do, will a single driveshaft be sufficient to get the hull on plane?

What about fixed shafts and steering with a separate ruder?
For trim, only a small oscillation is needed, which could be absorbed by an elastically mounted bearing in the middle of the shaft. Since it would be rigid left-to-right and would only oscillate up and down, a stiffer damper would solve the problem.

winter is coming in Finland, below zero celsius now. Garage is pretty much cleaned and in order, today I tow Fountain home from the yard of my company. Road have ice cover and my Massey Ferguson don't have studs in tires, pretty slippery tow 8 ton trailer.







I get materials for new drive shafts, they will be made of carbon fiber by vacuum infusion. Prepreg may be better but I talk local composite company and they have made big tank end caps, like 2 meters diameter, from carbon. more than 6mm thick laminate can be saturated perfectly by infusion when packing is done right. I should to archieve 60-40% fiber-resin ratio that is enough for my application. Cost is much lower too.

I bought 850g/m2 triaxial non crimp carbon fiber, it's 45-0-38 degree oriented so I can maximize longitudinal rigidy to archieve very high critical speed. I will make test pieces first, like 100mmx1000mmx6mm flat bar and make tests and measures before build drive shafts. Cloth is so heavy, thick and dense so it should be pretty easy to get tight package, I have few ideas for that.


Vacuum infusion construction needs a lot of different packing and resin flow stuff but they are pretty cheap.

I have planned to make new engine hatches from carbon composite, boat should lighten over 100kg from back. Bow thruster instal, swim platform extension, longer trim tabs, new rub rail and refresh window frame is on list in winter. These story will continue soon and updates should come more often. Stay tuned

My phone camera is so bad condition that I haven't take much pictures and no updates for a while.



I start disassembly interior for some modifications. Little girl need own bed that I figured on right side sofa, for left side I want two opposite each other chairs, table between them.

BUT some big adversity show up. Grid (stringers) have some rot here and there and racing history on big seas have beat some stringer tabbing off from bottom.








I desided to take all interior out and rebuild boat with composite grid cockpit front bulkhead to bedroom bulkhead, they seems to be fine.

Now I have good opportunity change interior layout way I want. Boat will lighten up maybe 150-200kg easily.


Window frame have to sandblast and paint, Salt water is not friend of aluminium. Windows are fine just clean and polish them. Does anyone know where I can find new trim rubber to window frame groove? New rubrail have to change also and fill all holes first to preven any water leaks inside boat.


I will do new engine hatches too, PET core carbon fiber maybe.
Lot work to do before next summer. Tomorrow me and my friend will saw grid out. boat is directly supported under chines so grid can be removed and boat won't twist or bend.