Cavitation/Ventilation issue

[healey8390]

I have an old 16ft Wellcraft Airslot 165. It has a pretty deep hull for a 16ft boat in my opinion. It has a 110HP Johnson and does about 37mph. That might be a tad on the slow side for a 16 footer?? I'm chalking it up possibly to the deep hull .I don't have a tach but judging by engine sound I'm guessing it's getting close to 5500 RPM at WOT as it screams pretty good.

My first issue is that the boat is very hard to put on plane, I have to hammer throttle close to WOT to make it jump and the bow goes very high before planing planing. I've experimented with a gradual increase in throttle but that didn't work.

The second issue is that at 3/4 throttle to WOT it cavitates/ventillates, whichever the correct term is, with any trim up. I have to keep it trimmed all the way in, any trim up will cause it to over-rev.

I have a feeling the prop may be a little small for the boat, the engine came off of smaller bass boat. Also, I think the prop is too narrow only measuring 12 inches in width and that the blades are too skinny. Pics attached of hull and prop. Opinions please.

 

[Sea Rider]

To start with need to get yourself an good quality induction tach. Doesn't matter if having a musician ear, no way that can possibly diagnose precisely what were the rpm achieved when the motor screamed. Do you know the min-max wot rpm range factory stated for said motor ? According to your description the combo has a badly transom/motor height match, bad deck weight distribution, improper trim running what seems a high prop pitch not suited for that size boat.

Happy Boating

 

[Faztbullet]

Thats a old SST prop.....

 

[ahicks]

My opinion, 37mph is a pretty decent speed for a boat like that one.

 

[Stinnett21]

Nice boat btw. However, it's very old. You could be waterlogged, i.e. carrying a lot of unwanted weight via soaked foam below decks. But, agree that 37 mph is pretty darn good. Make sure you're measuring speed via GPS and...ya gotta get a tach on it somehow. Buy one of those cheap mini tachs sold for small engines just to get a baseline. Then, as Sea Rider points out, compare against maximum stated rpm for motor and report back. Search Nauticus Smart Tabs. These are a great fix for porpoising issues on boats your size. I notice you're on the coast so you would want to buy the PR 500 plate retractor brackets so they can be defeated for following sea conditions. Worth every penny for $150.