Cost benefit analysis

Kind of gets to the question of the cost of heavy duty marine diesels, vs conversions of truck diesels. In the 300hp range, does the lifetime cost of carrying a huge heavy continuous marine engine balance the fuel savings, and increased usable space of a massively cheaper marine conversion, given that the conversion will have a much shorter life. If the "proper" engine lasts 10 years but the conversion only lasts 2, how do the numbers compare. Or maintenance or replacement for that matter. I wouldn't think twice about pulling the conversion with some simple rig. Pulling the big beast would not be a task for a cheerful amateur.

 

A used diesel would be great for you, if you can find a small enough one that is considered and has enough hours. (Not too many, that is)

If not ob, diesel has a big upside. It gets better economy and it is safer.

When repowers are done, oftentimes, only one engine is really bad, or it is a size change.

It is less about cost/benefit and more about opportunity.

If you can find the right one; as long as it hasn't been rusting for 5-15 years; it could be good. I think the Detroits have less than a stellar record of not leaking an oily mess.

 

I don’t think you’ll get a real answer on a general question that broad.
Perhaps you should pursue a particular motor.
I would choose the Cummins B or C motor, due to the sheer numbers available.
Some conversion diesels have very poor track records.
There are enough used marine diesel motors on the market to make that a much more viable candidate than a used truck motor + conversion costs.

 

Cummins has a rebuilt marine engine program. Recon Engines. Might be worth looking at prices.
It might be worth checking with some of the Volvo engine dealers as there may be opportunities where a customer has done an upgrade and the dealer has taken the older ones in trade. Though I am not a fan of the D6's in the sterndrive duoprop configurations.