Diesel 38' commander project

Hey all, clearly I'm new here but I have done research before posting this and I had found nothing close to the input I need so here goes.

I had found a popular mechanics article from the 1950's that had schematics to build a 26 ft "seacraft" cabin cruiser, my grandfather then took that design and built a 28 foot boat out of 1/4" plate steel and everything worked great til he sold it in the 90's. Now I would like to use those plans and extrapolate the dimensions an alter them to build a replica 1970 38 ft commander, I have experience working with fiberglass and know several people from the east coast that used to build their own fibreglass boats themselves. I digress, I don't want it to be an inboard unless its absolutely necessary, I much prefer stern drives, so my issue is what outdrive setup would be best suited to get that big cruiser to about 20 kn if possible using a 1993 international navistar IDI turbo diesel 7.3L engine. I'm hard pressed on using this engine because I know it inside and out like nobody's business and I have had it run on veggie fuel but that system is for another topic. I plan on fabricating marine manifolds for the engine along with buying heat exchangers for the fresh water cooling, now the engine has 190 horse and over 300 ft lbs of torque which is what we're interested since its diesel, now my plan is to mate it up with the transmission from the truck it came out of to gear up so it'll run at .72:1 from the crank since I don't plan on revving any higher than 1900 rpm to match torque peak close to horse peak. Now do I really need a dual engine setup or would one beefed up outdrive with an oversize prop be able to propel this behemoth down the lake?

I apologize for the length but I know I need to give you guys every bit of info I can

 

What you need is to buy a design for a 38 footer with sterndrives. Your other design will not scale up. Also, if you are thinking of marinizing the engines, make sure that everything fits, that torque and RPM match and also that you can get wet exhaust or can fabricate them, etc.

 

a 38' boat with a single i/o (sterndrive) of 190 hp to get 20 knots is a stretch. Twins.... maybe... on a good day

 

Alright so for the sake of argument lets say I throw two diesels in there with a crank speed of around 2200rpm with rediculous amounts of torque, shouldn't it be able to turn a large diameter steep pitch prop to get up to speed? My main question is if they could, what would be my drive and prop choices that would benefit me the best

 

Boatbuilding is a great hobby , IF that is your hobby for the next few years GREAT.

However with the price of used well built boats today it will be far far cheaper to simply purchase a used boat.

A friend just purchases a 40 ft Bertram from the 60's , very well constructed ,twin diesels, finished and running for $20K.

Price out the GRP and you cant build a hull for that money.

 

If you want a proper prop calc (power,speed, dia, pitch, #blades, DAR, etc) done I suggest you go to a prop mfr. and they can help you out.... if you have the correct input information.
Or, you can hire someone (naval archictect/designer) that knows what they are doing. The prop people need accurate & informed input and if you have a unique hull or boat, they may some help in assessing it for their calcs.

 

Thanks guys, think I found what I need, I may just find a junk boat with a good hull and strip it down and start from there and repower it, likely an inboard setup.