I’m currently building a boat. 30’ by 9’6". It’s flat bottom except for the 3rd closest to the bow. When I first started building I was thinking twin outboards as I can pro is my get a set for reasonable price used. I started thinking of getting a diesel stern drive bc of the fuel and the extra power for the size of engine. I was looking at volvo pentas and the new ones mercury has out. I was also wondering how hard it would be to make a regular 4bt or 6bt cummins into a marine engine that I could adapt to fit a stern drive. Those are great engines and can find remans all over CL for cheap. Any help, pros and cons some of you experienced diesel guys can offer would be great
There are SAE 3 bellhousing adapter plates available for mounting on a Bravo transom assembly. Cummins currently offers a QSB5.9 230 HP at 3000 rpm. Older 4 and 6B mechanical engines have the same bell housing. One thing you have to be conscious of is that the Bravo drives do not like the torque of a Cummins diesel. That is why the only current rating that can be sold is 230 HP at 3000 rpm with the latest and greatest Bravo X or XR drive . That calibration is specific to sterndrive bacause the speed was increased to 3000 rpm instead of the normal 2600 rom for the 230 rating. If you want more HP or have a lower governed speed which is typical for the mechanical engines you will have upper gear set issues with the drive. Another issue can be the torsional vibration from a diesel. This can destroy the drive as well if the coupling is not spec’d correctly.
Not that this can be done. There are many that have, but you can take a lot of risk with creating a package that is not engineered with the above in mind.
Iain Pelto
Sea Hunt Triton 160 w/ 90 ETEC “JB3”
Native Manta Ray 14
As long as it won’t be to difficult to get the stuff to make all the connections I think it can be done. Anything that is used in marine applications has to be taken care of and not ran to hard. I just put 6200 hours on a Yamaha 115 in 5 years and just need to change the adapter plate and will prolly get 3 or 4 more thousand out of it so its hard for me to imagine going with something other than an outboard. From what I understand you double and in some cases triple a boats range with the right diesel set up so I’m making sure that I explore all my options for power for sure
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Just interested, why do you want a stern drive instead of straight shaft?
i made this up but i think it’s true
I commercial fish for a living. I was raised up doing it. My dad owns the His and Hers in Shem Creek. I crab for a living mostly but sometimes pull a small trawl for shrimp and I also started long lining sharks a few summers ago. I am building this boat to shrimp and shark fish with in the summer which a straight shaft would be ideal for, but I also want to crab it in the winter when it’s a little rougher and colder. The engine box being in the middle of the deck will take up a lot of work space. If it is in the stern it won’t be in the work area and I can build my rigging for shrimping around it and still have plenty of room in the middle of the boat for a big ice box/picking table. Also the stern drives are a lot easier to drive IMO.