Originally Posted by Pete7
Olly, I think Duncan had a Mariner 75 on his. Nearest I can come up with was my Osprey Sparrowhawk and a 3 cly 60hp Merc (designed by Yamaha). Probably similar overall weight (hull lighter, but had A frame + big built in tank) and used 5 gallons per hour with a top speed of 26 knots (30 mph) lightly loaded). 20 - 24 knots with 4 divers and kit used about the same fuel.
From memory you have a bigger slower turning prop compared to the Merc 60 which is good news as it won't ventilate as badly when bouncing through the waves. As Nos suggests start with the 15" prop but you must have a rev counter to confirm the WOT or risk overloading the engine with the 17". Strangely I have a suitable rev counter in the garage if you don't have one
Thanks pete, I'll let you know the score