How much prop slip is normal and how do you work to decrease the slip, i.e. increase the efficiency?

For my 26' Thoroughbred I have three props, all Hydromotive Q IV's - a stock 26", a blueprinted 26" repitched to 27", and a blueprinted 28" repitched to 27". With every one I turn 5200 with propeller slip of anywhere from 14% at cruise to 16% at WOT - always trimmed for top speed on my GPS speedo.

Looking at BAM's prop slip data and calculator I'd think I ought to be 10% or less.

Any thoughts, suggestions?

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...anybody?

I'm no expert with props, but have a lot of experience with them. One of the best ways to increase efficiency is with diameter, but there are trade-offs. Diameter also increases the amount of blade in the water and causes friction-losses. There are a lot of variables that you need consider: drive height, weight, hull design, etc.

I use 17.5 x 35 4 blades on my cat and get about 8% efficiency. (GPS-verified speed).

So far the only variable has been changine the pitch of the props. I would next try a different make of prop.