Fixed Vs. folding 3 blade propeller for Cal 39 MK2

[DougR]

As noted by fstbttms, it is certainly possible that your prop is mis- pitched.

But, as you have stated in this thread and in your other thread, the engine is currently able to reach its recommended 2900-3000 RPM at WOT with a clean bottom. And it doesn't achieve the speed that the available power should be able of reaching.......

This indicates to me that the prop is pitched to match the engine power curve, but it's still not the optimum prop. Making drastic pitch changes one way or the other will either overload or under load the engine, neither of which are good.

However, if you're interesting in some experimentation, do this:
Get with a qualified diver who can change the pitch under water, and have him clean the bottom and especially the running gear. Then do a series of test runs from 1000 RPM to max RPM recording speed and RPM every 250 RPM. Do upwind/down wind (or up current/down current) runs to get an average.
Then change the pitch (in inches) going up two inches and repeat the test runs...again at 250 RPM intervals. Then change the pitch two inches from the original, but this time going down in pitch. Repeat the test runs. If one direction ( up pitch or down)seems to be particularly favorable, keep going in that direction. Believe me, this is what is done in an OEM sea trial, and I've done dozens of them.

Now you will have some data that can be examined that will tell you what you need to know....is the pitch wrong?, is the pitch as good as it can get?, is the prop too small?, would a different gear ratio be more suitable?, etc.

Is this time consuming and maybe a bit expensive? Yes, but not as expensive as blowing $3500 on a prop that isn't needed.....or running around with a prop that can't get out of its own road.

DougR

[Dean Paul]

Just want to share my experience.

A few years ago I replaced a 2 blade fixed prop with a geared 2 blade folding Flexofold propeller.

Installed on a 72 Islander 30 MKII with a Palmer P 60 inboard.

One of the best decisions I have made. Speed has increased considerably, power forward and reverse is better than the fixed prop. No vibration ever.

Prop walk is less too.