Prop diameter increase?

[DuckLn]

Quick question... My boat has an issue with cavitation/ventilation at the current height (I can plane but an average turn results with too much "blow out") and I am trying to prevent lowering the engine. This morning I noticed that I could run a larger diameter prop based on the 3/4 inch between the blade tip and the bottom of the cavitation plate (anti-ventilation plate) and my question is how close is too close regarding the distance between blade tip and the plate? Thanks.

[GHMiller]

You don't want to be any closer than about 1/2" to the cavitation plate. With that said the only way to cure blowout is to lower the motor incrementally until the blowout goes away. Why do you not want to lower the motor? What style of hull do you have? Answer these questions and maybe you can get closer to the right answer for your setup. Hope this helps.

[fs5]

sometimes a bit of cupping helps mate

[DuckLn]

The boat is a 6 degree V 340 lb aluminum 15 foot boat. Long story short the transom angle on this boat (angle measured where the hull meets transom) is less than industry average (more upright) and when my engine is set up 2 degrees positive trim (it really likes this setup) the leading front edge of the gearbox is 10 inches from the junction where the hull meets the transom. This is very little offset (compared to most everyone that has an aftermarket hydraulic tilt n trim) and prevents you from raising the cavitation plate any higher than the hull. I do not want a setback plate or tilt n trim or hydraulic lift as I like to keep this boat as gadget free as possible and also I dont want to add any more holes to the transom.

I have tried 4 props and yes all but one has come cup and the current prop just got back with "moderate cup" and it honestly didnt do much as far as reducing the cavitation issue. I have one inch between the blade tip and the bottom of the cavitation plate and would like to have width added to my prop. If I added 1 inch, this distance form balde tip to plate would be a half inch and I wanted someone to respond as to whether or not this would cause any problems. Thanks.

[DuckLn]

Note that I obviusly dont want to lower the motor as my cavitation plate is already buried (non -visible at WOT) and lowering it just slows my down.

[oledawg]

:)You can easily run the blade tip to within 1/4" of the cavitation plate.We have come even closer than that. This information comes from 30 years of manufacturing and testing propellers.
Note that I obviusly dont want to lower the motor as my cavitation plate is already buried (non -visible at WOT) and lowering it just slows my down.

[Fastjeff57]

Does your boat have a substantial keel? If so, turbulence from it in a turn can upset the 'bite' of the props.

Jeff

PS: Been there, done that!

[DuckLn]

Am i correct to assume larger prop diameter will help reduce blowin out?

[DuckLn]

Yes my boat has a substantial "center runner" to help it turn

[fs5]

you can cut it off mate,then power slide around the bends .you'l pick up some topend to.
may void the warranty on your hull though.
forgot to mention we used to run with a couple dogs in our boats over here and found everytime the dogs seen something a went to one side the boat wanted to follow and steer that way. cutting the keel of helped heaps with this.

[MWhite]

sometimes a bit of cupping helps mate

fs5 clear out your pm messages