23' Sceptre I/O - severe wandering at low speeds. Advice needed.

[Handful in NC]

All you wise Seacraft gurus, from whom I have leaned so much, please further enlighten me …

I just refurbished a 77’ 23’ Sceptre I/O. At slower displacement speeds, it wanders the worst of any deep V I/O boat I’ve ever owned. I mean, the Sceptre is all over the place, and so bad that you can’t just leave the wheel alone and let the heading “average out”. The sucker is gonna wear me out trying to keep it pointed anywhere close to the right direction, and something has to be done.

I always thought the tendency for the heading to drift at slow speeds in a deep V was due to weight in the stern (an I/O in this case) and the sharp and deep forward entry of the deep V hull. In simple terms, the back end wants to get in front -kind of like pushing a wheelbarrow, or maybe the way a tail wheel airplane (where the CG is aft of the main wheels) wants to ground loop.

Here’s what I don’t understand. My ’74 23’ Tsunami – an identical boat in every way that has been converted to a 250 Etec on a Hermco bracket and had a pilot house added, wanders just a very little bit- hardly noticeable. The pilot house with its hard top and glass windows has surely moved the CG forward, despite the outboard/bracket. Also, the outboard has less "structure" in the water than the I/O. So shouldn't the tendency for the heading to wander be worse?

I haven't gotten photos of both boats in the water, but the waterline at the stern seems to be about the same.

I’ve heard that lowered tabs will stabilize the Sceptre, but the boat doesn’t have them and doesn’t really need them for my usage.

Any thoughts or comments would be greatly appeciated.


Interesting numbers:
23' Sceptre soft top with 260 hp I/O - tops out at 42 mpg.
23' Tsunami pilothouse with 250 hp Etec on Hermco bracket - tops out at 49 mph.