Most of the small diesel engines found in sailboats are derived from industrial based engines, such as garden tractors, wood chippers, and things like that. These engines are produced by the thousands or maybe millions. Compare those numbers (1000s) to the number of inboard powered sailboats built in the US last year (probably less than 400) and its easy to see why no one in their right mind would try to develop an engine strictly for sailboats. (Volvo Penta
quit in 1993)
Mid sized engines like the Volvo D3 and the Yanmar
BY series come from the automotive world....either Volvo cars for the D3, or BMW for the BY series.
Some of the Volvo Penta engines, The D4 and D6, are designed strictly for the marine
world, though that is rather rare.
Larger marine engines between say 400 hp and 1200 hp, typically come from the truck industry. Cummins, Cat, Volvo, MTU/Detroit Diesel, all of them.....there just isnt enough volume in the marine world to justify the expense of developing an engine this size.
As an example, the Volvo Penta D13 marine engine, ( 13 liter displacement
and up to 900hp), is also found in Volvo trucks, Mack trucks, Renault trucks, Volvo buses, Volvo Construction equipment
, it's used by gen set builders all over the world (Kohler, Generac, SDMO, etc.). And that's the way it is with all engine manufacturers.
Volvo Penta has been using the D3 engine for about 12 years now and it has been a successful product for them. Realistically, there have been many more of the sterndrive packages built than the inboard sailboat packages, but that's a function of the target market. There are many many more 24 ft. diesel RIBs, patrol boats, and small cruisers built than there are 60+ foot sailboats. That's just the way it is...