4 blade props ???

We purchased our Islander new in 2002 with a single 250HP OX66. Great engine. Had the same prop as you have. I did a lot of experimenting, and the best overall improvement was a PowerTech OFS 4-blade, with the same diameter and pitch. That strong engine had no problem getting close to the recommended 5500RPM at WOT.

If you use this calculator for prop slip http://go-fast.com/Prop_Slip_Calculator.htm, with the 1.86:1 gear ratio of that engine and the speed and RPM you have indicated, then you have about 25% prop slip. Way too much. Best if under 10%, and any significant improvement would be well worthwhile on fuel savings if you use the boat much.

I recommend you contact a local prop shop to see if they will work with you on trying different props. They should do this at no cost, provided that you return any used for evaluation in completely undamaged condition AND agree to purchase the "right" pair from them once found.

Contact me if you need/want more info.

Brian

Captain Pete if you go to the Yamaha Motors website and look for performance bulletins you can find a 2000 Marlin with the OX66 250's and they recommend the props you now have. If I knew how I'd post the link for you. They are pretty good with the data they provide and you can expect similar results. 4 blade props will help you with holeshot but you will loose top end and efficiency. You will have to go down on pitch and maybe alsoin diameter, but if you generally run with a large load it wil lhelp getting on plane.

This link may help a little:
viewtopic.php?f=3&t=14837


Here is the link Cocoliso is referring to:
http://www.yamahaoutboards.com/sites/de ... -GRW-Z.pdf

Grady White also has performance reports that might help:
http://www.gradywhite.com/300/performance_data/1

I am very pleased with the four blade props.

All things being equal ( OK, they rarely are), your interest in improving performance depends on what parameters of performance you are interested in. In general, 4 bladers will improve low end torque but sacrifice hign end speed. 4 bladers may also add more drag. Of course, a good stainless 4 blader may outperform a soso aluminum prop across a wider range.
All that said, I am a bit doubtful that if propped with the Yami recommended pitch and diameter, that you would experience 25% slip. Some other factors may be involved. Did the boat ever perform better? Are you using GPS to measure speed and not the Yami speedometer?
Is you hull clean and smooth? Has the boat or the crew gained weight??
Have you inspected your current props for damage?

call ken at propgods.com if you want unbiased information based on real world tests and decades of experience. i have no affiliation with him but he worked wonders for me.

lgusto said:

call ken at propgods.com if you want unbiased information based on real world tests and decades of experience. i have no affiliation with him but he worked wonders for me.

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I agree that there is no substitute for a knowledgeable prop guru. I jsut suggest that you eliminate other potential factors whem possible.