I want to figure out my prop slip%

[b.gagnon]

I want to figure out my prop slip%<br />I have tried a few of the calculators and the seem to give real low numbers.<br />Here is what I have...<br />1979 Chrysler 70hp<br />17p prop<br />5050 rpm (wot) Tiny Tach<br />34mph GPS<br />I read somewhere that the gear ratio is 2-1<br />The boat is a 1978 Sea nymph F/S 165

 

[Silvertip]

Re: I want to figure out my prop slip%

Here's a prop calculator. Using your numbers which seems to show 21% slip. I used 18 pitch since I assume your prop is cupped. Most calculators indicate to add 1-inch for cupped props. It's 16% if you use 17 pitch.<br /><br /> http://www.rbbi.com/folders/prop/propcalc.htm

 

[stevens]

Re: I want to figure out my prop slip%

Here's another one:<br /><br /> http://www.go-fast.com/Prop_Slip_Calculator.htm <br /><br />or this one:<br /><br /> http://continuouswave.com/cgi-bin/propcalc.pl <br /><br />According to your numbers, your prop slip is 17%.

 

[b.gagnon]

Re: I want to figure out my prop slip%

I do not think the prop is cupped. 17% seems kind of high why would that be. The prop is in pretty good shape.

 

[stevens]

Re: I want to figure out my prop slip%

17% is not necessarily all that high. I don't know the kind of boat you have, but please see this link for what some experts would consider optimum slip percentages: link If your boat is old & heavy, underpowered or with a deep V bottom, 17% slip might even be pretty good.<br /><br />Not much you can do about this, other than making sure the engine height is correct, the bottom is clean, the boat weighs as little as possible, and that the propeller is as good as it can be.<br /><br />If you try some prop known to be very efficient, like a Turbo or a Stiletto, this might lower your slip to say 12-15%. If so, that would mean a speed gain of 1-2 mph. It's up to you to decide if it's worth the hassle and expense.