Volvo D4 DPI on a 30 ft cat

I am considering inboard power for a fishing boat because I like the thought of a clean transom. Has anyone had to service a catamaran with diesels in the 28-30 ft size range? Did the engines fit below deck and were parts impossible to get to? I’ve looked on the Australian forums and no pictures of the Yanmar powered Kevlacats. Again my goal is a reliable, serviceable, fishing boat.

 

Cant speak to the d4 but did some work in April on a boat with some fpt based 4 cylinder with Volvo legs. It was 32 feet and had high enough deck that the hatch was only a minimal 4 inch step to clear. Was a little tight getting in around the engine, but this would vary boat to boat. Was impressed with the low end grunt compared to similar boats with outboards. Fuel consumption was also pretty good,l for the range of sea conditions we saw.

Downside is two fold, of the remaining guys running outdrives in the commercial fleet they all factor in an outdrive major or replacement 1500-1700 hrs. The ob guys factor in major work around 3k. The initial cost of the diesel package in my area is 30-40% more.

The owner of the boat bought it second hand with very low hrs, and at his rate of use 1500 hrs would be 8 to 10 years. So in his instance it was a good fit and he is very happy with the setup.

I'm sure Volvo has cad files of the specs you could look at to see how well it would fit in your application. Proper setup engine hatch can make maintenance feasible. For major repair it is hard to beat the convince of outboard repairs. To the reliability it's probably a draw, there are several well known very long lived big outboards. At the same time emission restrictions and the pursuit of ultimate power/weight has begun to negate some of diesels longevity. Dollar for dollar it's reliability is probably a draw.

 

Is it common to see outboard and diesels of the same horsepower side by side on similar hulls? I’m trying to guesstimate fuel economy and have the opportunity to either do a 250 gas or 250 diesel.

 

Not anymore, the outboards have pretty much taken over everything. This boat was from 20 years ago, at the time the builder was probably 80% inboards on that class boat by 2010 that had swung to probably 95% outboards.

In this instance I'd been familiar with one with suzukis, and was asked to help go through one that had diesels. It was 270 hp diesel, vs 300 suzuki in this instance. Memory isn't exact but the outboard one had maybe a 3 knot higher top end. Our sea state rarely allows the high end speed, so it's running around a bunch in the low to mid 20s. In that range the diesels had a healthy fuel savings, ballpark 20ish gph vs. Upper 20s for the big suzis.

We had a pretty big sport boat building boom from the late nineties to about the great financial crisis. The outboard built or converted ones definitely have a perceived premium. The inboards boats here always pose some sort of potential value for dollar proposition especially for the old millenials buying them. Debate is usually do they replace the diesels, or gas inboards or weld on a bracket and do outboards.

In my buddies case the diesels made sense, he does a big remote family trip and the several gallon per hr savings over the trip gave him a much better reserve. His kids are also young and he noticed they did better fishing of the stern of it than the ob boats. It reinforces my opinion that the intangibles make the decision better than the raw economics.

 

It might be worth playing on solidworks then and making absolutely sure I can make a proper engine bay with good access to fuel filters, aftercooler, heat exchanger, and oil filters. I got time and some design skills. Might as well put them to use!