---Anybody here have experience in late 90's Donzi's and Fountains???

I guess they were also pretty early with stepped hulls.

---So compared to Formula Fastechs, do they have sturdy, foolproof hulls for a 50-mile offshore cruise???

Still talking about the 33-38ft class below 70k $.

Anybody?

I don't think you need to reinforce the transom. Mine Has HP500's and that wasn't the highest HP version. I would think that the bigger problem would be finding an outdrive that would fit a diesel, be able to handle the HP AND be geared for the lower RPM.

My head has the Vac U Flush with the integrated holding tank. I think there were non Vac U Flush heads that may have had separate holding tanks. If that is the case you may be able to install a bigger holding tank

Given the premium we now pay for diesel I suspect that diesels will not make a dent in under 40' boats until the automotive industry makes them in sufficient numbers to drive the cost down. There is no doubt though that diesels in trucks and boats command a premium that generally covers most of the initial cost.