Prop Slip Calculator QUESTION regarding my results

[Strake]

I'm struggling to believe my results could be this good....... assuming I'm understanding the calculator online tool from BAM. Although the slip calculator tool doesn't ask, the tritoon had 3 full length toons, lifting strakes.

Known information: Yamaha F200 motor has a 1.86 final gear ratio. I have a 14.5" dia X 15" pitch Reliance SS prop. I can get a max of 5800 rpm trimmed up to about 75% and I am getting a GPS speed of 39.8 mph.

Using the online calculator, that is showing my theoretical top speed of 44.293 mph. If I take the theo speed, minus the Actual Speed and divide by the Theo Speed then my slip is 0.101. This seems crazy low. As the tool itself says most boats have a 5% to 25% ( for heavy work boat) slip.

To determine my Theo Speed ( using the online web tool) I am taking the 15 pitch X RPM (5800)...... this equals 87,000 and dividing 87,000 by the gear ratio ( 1.86) X 1056, which equals 1,964.16. When you do the math it shows my THEO speed of 44.293 mph .

Is anyone else seeing such a LOW SLIP percentage number ??? 0.101. Am I misunderstanding the result? Is it nearly zero percent, or do I have a decimal place error, and it's really 10.1% ???

[Bamaman]

I'm getting the same speed out of a F150 with a 2.00:1 gear ratio. I think that works out to be 6%.

My prop ventilates slightly starting from dead stop when trimmed up, and no ventilation is experienced when I drop the engine level--just like I like it.

As far as I can tell, my boat's setup to the optimal level.

I would think your boat's also doing just about as well as can be expected since you're getting 5800 rpm's trimmed out--within range. I'm sure you've got more mid range power than my smaller motor produces.

[Jake_Daddy]

You got it right at the end. Percent slip is just that when you divide the delta between actual and theoretical you will get a number smaller than one, multiply that number by 100 to get your percentage.

You cant get a number larger than one unless you mess the equation up and if you get a number less than zero, or negative, you have bad numbers for your data.

[rancherlee]

decimal error, should be 10.1% which is pretty good for a straked tritoon, I see anywhere from 7-13% slip with various props on mine.

[BobL]

.101 is 10.1 %

Theoretical top speed = 44.293 mph
GPS Speed = 39.8 mph

(44.293 - 39. / 44.293 = 0.101

.101 expressed as a percentage is 10.1%

EDIT - rancherlee beat me to it. Must have been hitting submit at the same time.

[Strake]

Thank you all !!!! I figured it was a decimal point conversion to percent thing.......

Overall I'm pretty happy with it. The first year I did manage to get 42 mph GPS out of it, but perhaps all the stars were aligned just right...... little fuel, little or no wind, no other passengers, temperature, etc....

Richard

[rancherlee]

[quote="Strake"]Thank you all !!!! I figured it was a decimal point conversion to percent thing.......

Overall I'm pretty happy with it. The first year I did manage to get 42 mph GPS out of it, but perhaps all the stars were aligned just right...... little fuel, little or no wind, no other passengers, temperature, etc....

Richard[/quote]

"Magical" top speed runs seem common on pontoons, mine will run 36mph constantly any given day with the top up, 38 on a RARE occasion. Waiting for the second Full moon of the month to remove the Bimini and go out early in the morning with a stiff tail wind and try for 40.0mph! Mine seems to like a little chop for max speed, all my 38mph runs were with some chop.