Yamaha does use a larger gearcase with lower gear ratio and larger diamter prop on their High Thrust 9.9.
Mercury and Yamaha offer High Thrust (Merc calls it a Bigfoot) model with larger gearcase. Evinrude's 40/50/60 series come with the big gearcase standard.
As far as 0 to hull speed- it happens so fast you can't push the stopwatch switch to record the time. Mind numbingly fast!
Yes, and 150 and 15, 150 and 9.9 not so much. Would like to hear from Les, he hung the 15 on Daydream, as I recall he said either would work but we might like the 15 better for the extra torque, which if I read Matt right is pretty much non-existent.
Capital Sea":294lqj3r said:
All of that physics was nice and helpful and all but the real issue comes down to digits. 90 and 9.9 just go well together. 90 and 15, not so much.
In the case of Honda, since 2001/2002 the 9.9 and the 15 have been different engines. The 8 and 9.9 share a 222cc block, and the 15 and 20 share a 350cc block.
The reason I suggest a 15 on 25-foot boats most of the time is because the BF15 has more torque (read: does more work); it just flat pushes harder. It's not about speed at all (I never sell the BF20 as a kicker).
Back when Honda had the BF9.9/BF15 we almost never sold the BF15; the BF9.9 would do everything (as a kicker) the BF15 would do so why spend the extra money.
I just checked: Tohatsu 9.9's all use a 2.08:1 gear ratio. The only thing different is the prop. Hi thrust model uses a 4 blade 8.7"X5 and the regular engines use a 3 blade 8.5"X8.
