in the US, I doubt think it was ever attempted. In Australia, they did great. The problem with USA made kevlacats is 2 or 3 different people made them. Only one knew his stuff on how to make an excellent boat the others had QC problems. The motor they put in can be powered up to either 250 or 270 hp. If they can do it in a 24, it would surprise me if I can’t use the same blocks in a 30

I haven’t hit 10 post yet so I can’t post links. Look up diesel Kevlacat. First thing that shows up of google is a positive review

the nanni 270 is only 250lbs heavier than a Suzuki 300. Including out drive. I figured a lower COG would actually help sea keeping. I think a few the 20 degree inboard boat makers including Albemarle went up on deadrise when they went to outboards. I figured that was compensating to a different distribution of weight.

I shoehorned a Cummins 6BTA, velvet drive trans, and Konrad 520 into my 26 foot pilothouse, 23degree deadrise solid glass fishing and dive boat. Clearance is about 4 inches all around, with more at the back, but the entire upper half of the engine is exposed with the engine box off. In retrospect I should have gone 6 inch clearance or more, but that would have been a major rework and starts to cut into fishing deck space. Think about changing filters and how much room you need to swing a filter wrench and the diameter of the filter for removal before going too tight on side clearances. My boat was set up for diesel sterndrive when I bought it, and switching to outboards would have been a major PITA and likely not given me the performance I required without high fuel burn. Diesel is $2 a gallon cheaper here so it's a major saving, I can fish a 10 hour tournament for under $200 in fuel.

looking at the kevlacat that has the steyrs, the hull curves upwards a bit. I could set up a remote filter manifold. Or it might actually clear better than I thought. Anything on the sides will probably suck. How often does a ecm go out?

I think your idea of doing 50 knots in a 8 foot wide 24 foot tall sided cat is a little unrealistic as they don’t handle well at high speeds unless in calm conditions.

They are a 35 to 45 mph cat tops.

You stated that the Styer diesel was only 250 pounds more than a 300 horse outboard but most 24s have nothing larger than a 200 hp outboard and most have 150s as the additional horsepower and weight does not yield that much more in speed .

As far as towing I towed my last diesel parasail boat daily 10 miles round trip with a 1/2 ton Chevy conversion van.
It was 31 foot and 11 foot wide but 40 overall with my inflatable on the back deck. Weighed in at 12 thousand and drew 3 1/2 feet to float it off the trailer.

Big difference in 24 feet going to a 30 footer for sea keeping and ride. I would look for a used Hydro cat and hang some new outboards off it. With a 10 beam there is a lot of room between the motors to fish

The 2400 eastward is the 9.25 foot 3000 with 6 foot lopped off the back. The 3000s with 300s top end is 52-54mph light. Top speed is a good way to compare performance between engine packages. I’ve had calm enough for 40 mph on the ocean twice in 3 years. Most of the time I’m doing 30-35mph until I bottom out the 280, then it goes to 20. Just bites the best fishing boats are becoming classic models I’ll have to buy used, then redo them.

You’re not going to hang twin 300s off the back of that 24 foot cat much less add an additional 500 pounds in diesels . These skinny hulled Cats have very little buoyancy aft compared to a monohull.

As good as the cats ride a 24 foot cat isn’t going to ride better than a 30 foot v bottom in anything over 3 foot . Cats do eat up the light chop but I’d take my old parasail boat against a lot of boats in a 3-5 slugging through them at 16-20 mph.

My boat was an Ocean Pro 31 but it was a copy of the old Rybo Runner with the step taken out of it . Find a Rybo Runner and put a big diesel in the back with a v-drive and a Arneson with a giant swim platform on the back of it to cover the drive if your sold on diesel.

check this out. https://www.yachtworld.com/yacht/1989-rybo-runner-center-console-8342831/