Well, quite a few people have put big effort into building diesel-powered performance boats. As you know, there are a couple of examples of very expensive experiments here at OSO that haven't quite cracked the nut.

Locally, a gentleman working for the marine division of a world-leading manufacturer of large diesel engines put diesels into a Nor-Tech. This guy had access to resources that a lone guy in his shop or a guy who builds tractor pulling engines could only dream about.

Still, the boat wasn't very fast. And at what was high rpms for diesels, the engines were not very fuel efficient either. When moving on to the next project two years ago, I think he sold the hull without engines.

All in all, you are at the frontier of progress. As they say in the software industry: "You can tell the pioneers from the arrows on their backs".

Please keep at it, and please keep us posted!

Markus, sorry for delayed answer, but you are right, fast diesel boat is not easy build. We need good power to weight ratio and that kind of engine does not exist on market. Big diesels are heavy and at last they are not so rigid, tons of cast iron to attain reliable 1 million mile 500hp engine that have poor rpm range. Light duty engines are too small displacement to make serious power at long periods.
If I hadn't build Transmash, Audi V10 or V12 TDI was another option. V12 is light 6 liter and V10 5 liter high rev diesel that are designed to LeMans 24h race. Four 500hp+ engines coupled to two surface drives could be worth a try. They doesn't need multi speed transmissions, so overall weight is easy to keep down.

https://cimg9.ibsrv.net/gimg/www.off...eebbb58594.jpghttps://cimg4.ibsrv.net/gimg/www.off...01c2eb0094.jpg
https://cimg0.ibsrv.net/gimg/www.off...1e86f07110.jpg
https://cimg1.ibsrv.net/gimg/www.off...5b61c6b217.jpg
https://cimg2.ibsrv.net/gimg/www.off...74c8ba4f9b.jpg
https://cimg3.ibsrv.net/gimg/www.off...e53e210e91.jpg

Splitbox start taking shape. I have not enough money to mill billet case and special gears so I go this route. Case are 20mm thick 6082 aluminium, center piece will be weld together from three layer of 20mm sheet so it make room to 50mm wide module 5 induction hardened (except input gear that have to heat thread) C45 steel spur gears. They are not strongest but should be hard enough. Benefit are big diameter input gear that reduce teeth force a lot. Power split to two drives stress two teeth instead one, its also good thing.
Case bolts in picture are weld time only. Box is going to CNC mill to make all measures precise so they can mill hollow to hex socket or torx bolts. Bolts are M12
Fitting input gear to ZF output shaft have been challenge but I have one idea to solve problem. ZF output shaft and planetaries are heavy duty stuff, six satellite gears get teeth and bearing stress down. On the other hand, at fourth speed none of satellite gears are spinning, transmission run straight shaft mode, 1:1 ratio. Splitbox ratio are 0.555:1 overdrive.
ZF housing back cover got big modification so splitbox can be attached to it. I turn good centering guide to it. Its an absolute requirement that everything runs in same center, otherwise gears worn out quickly. All bearings will be tapered roller bearing so clearances can be adjust to zero and they can carry huge loads.
If splitbox gears start wear out, then I have to make new ones from better steel.
Lubrication is splash lubrication at first, dry sump maybe later.

https://cimg5.ibsrv.net/gimg/www.off...fca016bedc.jpg
split box is awesome, looks great. Don't worry about 1 piece billet housing and the hardest gear sets.
I doubt it since you pay good attention to the small details, but maybe there will be a design change during construction/assembly or sea trials.

2 questions i have about the split box, i'm sure gear diameter/ tooth count gives you the same final ratio on both left and right,
1. would there be a torque or load difference between the 2 sides since there is more and smaller gears on 1 side?
2. Output for driveshafts are on 1 side of split box or both ? I ask because you will have to pick the props rotation to spin in our out.
my vote is to spin out.
your making great progress keep moving forward.

the law of physics are simple when we look gears and ratios. If ratio double rpm, torque goes half. Intermediate gears doesn't affect total ratio, only input and output gear teeth count matters. There is tiny loss in right side three intermediate gears, they spin faster and have two more bearings than left side, but that friction loss is so small that it doesn't matter.
Module dimensioned gears are ingenious, for example module 5 means that if you have 20 teeth gear, working diameter of gear is 5x20=100mm so two 20 teeth gear centers are 100mm apart.
I draw two 30T to left and three 20T to right so overall dimensions are the same, split box is symmetrical. 2x5x30T=300mm and 3x5x20T=300mm, its so simple.
Input gear is 45T and output gears are 25T so ratios are symmetrical 0.5555:1 for both sides.

I can't change prop rotation after milling the housing. After long thinking that was written in earlier posts I decide to spin props in. If boat doesn't work spinning in I have to make new housing, gear centers won't be accurate if I flip end plates over and change rotation direction.

I like it.. And after playing with and destroying similar gear cases over the years, forget the dry sump ideas.

IMO the slight gain in power doesn't outweigh the costs of new bearings and gears if it springs a leak. Straight cut gears whine when they are setup correctly, an are just slightly louder when out of oil. So by the time ya realize they're actually really pissed, it's done to late. Stick an idiot light temp sensor in that case and call it done.

ok, and i agree with kid turbo and not going dry sump for the reasons he cited, also why incur more cost, perfect the prototype first.

then if it becomes popular like you want let the market decide on billet housings and dry sumps.

Why not use a chain?

If he used a chain he could not get the drives to spin in opposite directions

Actually you can change rotation direction when using chain drive, in theory. If chain pull sprocket on the back side of chain, rotation change. But there is not any chain on this planet that can handle 8000Nm and 29meters/second chain speed. For example I build few Bmw M3 rally engines that rev 9200rpm, average piston speed was 26m/s. 3 litrer natural aspirated made 392hp power:cool-smiley-011:
Gear drive is always better than chain, gears doesn't stretch and they does not care about rpm.

This engines I made years ago, enjoy the sound!