Prop slip calculators

[buyfire]

i've always read that 10% prop slip is a very good goal to go after when prop testing. but on another forum i frequent members are trying to convince me that i can get better performance out of another prop (mercury enertia) often claiming slip ratios of as little as 5%. when i test my own setup i end up with 8.3% slip. some here have claimed that even this figure isn't possible. what's the real deal?

here are my #'s

4800 RPM
54 GPS
1.62 Ratio
21 Pitch

am i doing something wrong in my testing? i'm pretty sure my tach is correct, and my GPS reads dead on.

[JasonSmith]

How heavy is the boat? Stepped bottom? Tell us whatcha got.

[Hell Ya!]

http://www.mercuryracing.com/products/propellers/propcalc.php

Here is the one I use. Are you sure of your gear ratio? If you do your numbers with a 1.5 ratio it is 15% and that is a more normal number for a V bottom. What kind of hull is it? .


Jeff

[buyfire]

How heavy is the boat? Stepped bottom? Tell us whatcha got.

it's a 21' bowrider/3400# dry. the hull has an extended running surface (the drive is tucked about 16" into the transom). there's also an 8" wide pad along the keel. 20 deg deadrise. no steps.

Hell Ya,

the Mercury calculator gives me 8% slip. the ratio is stamped on the drive.

so, have you heard of a prop delivering on 5% slip?

[JasonSmith]

I have never heard of a v-bottom propeller giving 5% slip. If there is one, I want 2!

[Hell Ya!]

Only on triples and a few Cats. I don't have much experience with your kind of boat. But those numbers seem very good if correct.

[QWKRN U]

This is the one I use.
http://www.rbbi.com/folders/prop/propcalc.htm

Comes up with 8.3% using your numbers as well. That doesnt seem right for a V bottom but anything is possible.

[HiTechRedNeck]

is this a bravo 3?

[buyfire]

is this a bravo 3?

no, it's an alpha.

[bbladesprops]

Back in the "day", we used to consider under 15% as dialed in pretty good. If you were under 10%, it was a race set up scenario. Today, with the enhancements in propeller tech. and drive heights plus boat bottom configurations, the slip numbers have gone down. I still find very few boats on the whole running under 10%. Some times gauges and even people look to use the best numbers they have ever seen in the boat. Verifying speed with 2 reliable sources, using a shop tach to gauge the real rpm and having a true pitch reading will give the most accurate slip numbers.

Remember, in some situations, a few mile per hour can make a few percent of slip difference.

Also, slip numbers can be over rated. Seriously, slip can at times help to add speed by letting the engine or engines get into a better zone and the ultimate top end number can be the best the boat will see. Try not to focus too hard on the slip number unless it is a bad number.

Slip well!