Cavitation towing tube after deck rebuild - Force 50, Bayliner Capri 14

[chieftaing]

Project boat; took it out after replacing deck with plywood but before fiberglassing the replacement decking - all was good.

After a layer of 4 oz CSM fiberglass and resin, plus two layers of gelcoat, took it out and got wicked cavitation especially while towing a tube with 1 adult and on the turns. Nothing else changed - same prop, pretty sure the (manual) trim setting was the same.

Is this new cavitation and poor performance when in the water due to the weight gain from the fiberglass, or something else?

I did not try adjusting trim setting because the second tubing run experienced the motor dropping in RPMs due to either overheating (no buzzer, though) or I'm pretty sure due to the bolt that grounds the terminal strip coming loose, causing a major ground fault that took out the stator - repair in progress.

Will (manual) trim settings solve my cavitation problem? When do I need to look at a prop change? I'm sorry, but I really have no idea what's on there now - just know it was doing fine first time I took it out.

Thanks for any thoughts or suggestions!

 

[Maclin]

Is it Cavitation? Or Porpoising? Or Blowout? Cavitation is actual damage to the prop metal from high speed boiling water bubbles on the surface of the prop. Porpoising is bow oscillation, usually a trim issue, any weight distribution changes from the work done can affect that. Blowout is when the prop "loses" water bitr and gets airborne, can be trim and prop height issue or issue when turning hard and not trimmed correctly.

 

[steelespike]

What you have is likely ventilation,where the prop gets fouled with air.You don't feel cavitation.
If you replaced the deck how were the stringers underneath?
Also the transom may be suspect. If not properly stored/supported while glassing may change the shape of the bottom.
Put a straight edge along next to the keel should be no bulges or hollows.
Does the boat respond to up trim?

 

[chieftaing]

Great info, thanks! So know i know to call it ventilation. I replaced all bulkheads, stringers from mid boat to bow too. Stringers in rear were ok. Transom got some surface repair, inside, but its solid & seems in good shape. Plus it didn't act this way until I glassed the deck. Its only 14 feet, so the deck & bulkheads were not very big.

I'll check the keel & report back. Manual trim, which i did not adjust, so maybe thats the best thing to try when next on the water. I'll try adjusting the metal bar onto which the outboard latches so that the prop is a little further away from the transom.

 

[Scott Danforth]

if your old stringers, bulkheads, deck and foam were water soaked, you may have removed 400# of water weight which would have made the boat sit deeper in the water than it is after you repaired your boat.