[kmoose]

I have experience with Tsunami hull with both I/Os (502 + duoprop) and outboards mounted on the transom and my current set up of a single 300 on a Hermco double. All have their highs and lows.
The big block I/O was a beast that rode very well in the 25-28 knot range. Very stable and responsive with plenty of grunt. Deck space was the biggest issue with the engine box taking up the most used part of the boat. Due to the weight and distribution it rode the best but cruise speeds were typically lower than outboard models and it would cost you in fuel if you tried to run hard to make time. Maintenance and repair were misery and if you needed to change the starter the entire exhaust manifold had to come off.

Outboard on the transom was a great option and performed very well. I removed my motor well so I had more room than most but I also had a 10" offset bracket to make that happen and my transom was built for a 30" motor. All around handling was best with this set up with good low speed plane and trim control.

My recent build is well documented here and radical changes were made in layout, weight and configuration. It would be hard to compare my current ride with a Tsunami that wasn't modified as mine is. That said I have lost in some handling characteristics like turning radius and trim responsiveness but gained in cruise/top speed and overall fuel efficiency. The boat is effectively longer and bridges Gulf chop gap better which is a big deal for me and the usable room in the boat has almost doubled due to the full transom, storage and platform.

Most performance changes between the versions can be adjusted with different props, tabs and engine height so it really comes down to how much you want to spend and how important usable space is to you. With a modern 4 stroke outboard of any make, 75 gallons should easily give you 150 nautical mile range with plenty of reserve.

Feel free to PM me your contact if you want to chat about this in more detail.