That seems a tad slow to me. Get a TLDI
. I've had mine at 50mph (after tinkling with the power trim) on Loch Fyne heading back to Strachur after diving the Minards. That was 3 up with 2 twinsets and a dug
. What pitch of prop are you using? What sort of revs show at WOT?
With regards to engine choice the following rules seem always to apply.
1. If you decide to go DI 2 stroke, you'll wish you went 4s.
2. If you decide 4s, you'll wish you went 2s DI.
3. If you buy 90hp, you'll moan about the poor performance and wish you'd gone for the 125hp.
4. If you go for the 125hp, you'll greet about the fuel consumption and wish you'd gone for the 90.
4. No matter what make you go for EVERY other brand would have been better/cheaper/more reliable.
You get the jist
There are a lot of mid 5m dive boats out there with 90hp engines. It's a good balance between power and economy. I went 115 because thats what was on the boat. It's nice to have a wee bit more oomph when the boat is a bit heavier. I reckon circa 100hp is ideal for a mid 5m boat.
Anyway you'll need to get at least a 115 to ensure I don't beat you over to Arran in the summer when we head out to dive the Tuscan.