Cummins 6bta 375 hp

I bought a used one, it is overfueling but that should be an easy fix
For my 8m deep vee design
trubble is I need a box zf 220a or similar and the cost moonbeams need 1.2 to one as it is trailer launch so need prop 4 blade with smaller dia fitted aqua drive coupling in the past but now 5k for this boat, so that is out

 

It’s best practice to design a hull before specifying the power.
An 8 meter power vessel may not be best suited for a relatively slow turning high torque producing diesel motor.
Choosing a small diameter propeller to effectively propel the boat with the chosen power may prove difficult.
Can you Show the bottom configuration?
The pics provided leave many questions!

 

The ZF 220 is barely adequate. Do not overprop at all. I'd go with the 1:1 ratio on the 220, or a ZF 280 at 1.12:1. I'm assuming a 9-10k pound craft and 28 knots.

 

I Designed it years ago, I forgot to say that I will derate it to 250 this will give 37 knots max
I drw many bottoms inc. with a tunnel
others i built I used Volvo with a jackshaft to the leg, this enabled the engine to be further fwds and stand up game fishing was easier as one could walk around aft end of the engine box tell me what you want deadrise aft flattens, ny boats have to wave jump because they operate off of NZ and Au coast, coming off of plane is not an option one gets smashed prop will be 4 blade 18x26.4 inch

 

disp is 5500 lbs, rerating to 250 gives 37 knot top, ratio 1.3 to one 18 x 26.4 4blade, may i ask why you treat folk as knowing bugger all, I built a lot of this type

 

Derating to 250 is good. My concern was that you were going to go offshore with a barely adequate tranny and get someone in trouble. It would be a lake and river craft only at 370hp with the ZF220. Your original post didn't give us a lot to go on. There was no reason for us to think you had ever built a boat before. Why are you building new boats with used powertrains? That's not something that would lead anybody to think you were experienced in boat building.

 

I put a Cummins 6BTA 280 (continuous duty version of your engine) in a New Zealand built Marlborough 26. Looks similar to your design but heavier layup. With a 1:1 transmission, Konrad outdrive at 1.43:1 reduction, and an 18x19 3 bladed prop I reached 27 knots at 2700 rpm at sea trial and cruise at around 22 knots at 2200 rpm. You should do better with a lighter hull. Marlborough hull is 23* dead rise with a delta plate and 8 lifting strakes, not all full length. Performance in a sea is awesome, with all that iron down low in the bilge and the torque and big propellor, nothing slows it down. There is a strong case to be made for an inboard diesel pilothouse offshore fishing machine.

 

i know nothing of zf, only what i read, yesw I done thousand of offshore miles served also on Tugs. I will listen to your recommendations thank you

 

Derating only incurs additional costs to the project.
Simply holding the throttle back accomplishes the same thing.

 

pf course or smaller prop

 

Naah, smaller prop at the same speed gives lower efficiency, better stick to kapnD's advice.

 

I have no room for bigger screw, it is trailer launched

 

I bought twin disc mg 507 x 2 for 8k Au 1,5 to 1

 

After buying the 6bta and zf, 2:1 prop arrived at 22 or 23 x 32 , then being a trailer lauch, I had to bury pa rt of prop in a tunnel Chat GP was a huge help in tunnel and prop

 

I guess you've done all your calcs, but that is a lot of iron in a relatively small hull. Now you are going to lose more volume/ buoyancy with that tunnel.