Lowe 16/48 with Merc 40 setup question

[Cory_09]

I’m not exactly sure where to post this but here goes:
I picked up a project boat - Lowe 16/48 bare hull. Someone had previously removed the middle bench so it’s a bare bull, pretty light weight. I put a 1993 Mercury 40 hp short shaft tiller on it. I took it for test ride today and have some issues. The motor runs good alright, too good. I can only run about half throttle. Anything past that, the boat seems to lose contact and start to dart sideways and dig. Not motor cavitation but simply the boat gets out of control. I’ve had multiple 16/48 hulls in the past with 40hp tillers and none acted this way. I don’t think it’s necessarily a prop issue (running a 16p stainless). I also tried running at different trim levels with no noticeable difference. The motor is mounted correctly. I believe anyway. Cavitation plate is even with bottom of hull.

Any recommendations would be greatly appreciated. Maybe need less prop? Maybe more weight? Maybe motor is just too much for the boat?

Been lurking here for quite awhile. Nice resource.

 

[southkogs]

Max HP on that boat is listed as 35HP. Are you sure the center bench isn't structural? I'm pretty sure that boat has ribs, but often those benches are helping control the structure. Maybe the removal of the bench causes a hook in the hull or something like that?

Welcome aboard.

 

[Cory_09]

The boat does has ribs running across at varying distances (15" or so). I'm sure the old bench did provide some support. I hope to add additional support with a floor and front deck.

I'm thinking a hydrofoil might help. Its not really traditional porpoising though. The bow doesn't bounce up and down, but more of a sideways dig. Really weird. Does anyone have any experience with a hydrofoil helping similar situations?

 

[Silvertip]

That center bench is structural. It's removal allows the entire hull to twist. If you are not careful when installing a floor and deck you might just create a permanent "hook" in the hull. The boat needs to be properly supported, with the keel spot-on straight and absolutely no hull twist while doing this work. If the boat had been operated for some time without the seat it may already be beyond straightening. It would appear you need to make a fairly sophisticated jig so you can make very accurate measurements.

 

[Bondo]

Ayuh,..... I agree with Silvertip,..... Sounds like yer problem is the boat's bottom, aka: the runnin' surface,.....