Originally Posted by Carl
plus all that extra drag
In summary drag goes up as approx the square of your speed and the cube of the cross sectional area of what you're dragging through the water.
I'll bet the 90s have a substantially smaller gearbox than the 225. (Yam from memory uses (OK, used on the 2- strokes) the same gearbox on approx 50- 90Hp, so going to be about as small as a 90 gearbox will get), then add the fact the single gets a bit more speed so the drag goes up by the square of 6 knts - Ribcraft's numbers may not be too far out.
As for the servicing, you still need to keep the aux running, so you end up servicing two anyway. As you won't be able to buy a 2- stroke, I bet you end up with something in the 15-25Kg ballpark, so how much lighter is a big single really going to be?
My take on it - if those are tested figures, I'd go twin, But I do my own servicing....
On my previous posts, I have given examples where twins are actually lighter - Never generalise in these kind of discussions!