Southbay flex and porpoising

D

david finney

New member
With the mild temps and no wind, I had my SBDB in the water this afternoon for the first time since the work began on it in December. All in all, the sea trial went well. This was my first run with the new (to me) Merc 15hp. I definitely noticed some flex in the hull at higher RPMs and porpoising at top speed, even with the starter battery, tank, anchors, etc. stowed under the bow for weight. None was apparent, not surprisingly, when running the 4.5hp 2 stroke I purchased with the boat.

A couple of items for the group. Some of you have indicated that a hydrofoil will greatly improve the porpoising issue ... however, I don't see models that will fit inside the 10" cutout in the stern. Any recommendations? I suspect the hydrofoil will also help with flex, but I'll keep an eye on it to determine whether reinforcing the stringers and the transom might be needed. I left the structure as is because the original work seems dry and tight.

David
 
The flexing is normal and while it might appear disconcerting, as long as your ribs aren't cracked, you can't kill a South Bay (I've tried.) This boat will ride very differently when grassed with decoys. I can't see why mine with a 15hp Johnson would not porpoise and yours would. Play with the tilt pin and see what you see. Don't do anything drastic until you've experienced the boat grassed with gear.
Good luck, it's a great boat, you may just have to dial it in. Are you standing forward while running the boat with a tiller?
 
I was not far forward ... I don't have a tiller extension at this point. The trim pin was in, one spot up from fully neutral. I'll tinker with that. Appreciate the thoughts, Paul -- especially that the flex is normal. There are no issue with the hull or ribs.

David
 
Get yourself a tiller extension and stand midship while underway. The porpoising will stop. Once you have gear and grass, it'll get better too. Be sure to have a kill switch tether.
 
after i move forward on mine the porposing stops then i can move back again definatley need a tiller handle extension though ,
 
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