General Slipage questions.

[tmh]

I was using one of the prop slipage calculators someone had recommended and had a few general questions that one of you experienced folks might shed some light on.

1. Is "slipage" another name for efficiency or "loss" from no-resistance performance?

2. When going from a higher pitch to lower pitch, does slipage generally increase, decrease or stay very constant? Is the answer to this different at different speeds/RPM?

3. What would be a "good" range for slipage on my 19' deep V BR - just a range as I know it varies by hull design,etc.?

Thanks, prop gods.

 

[Silvertip]

Re: General Slipage questions.

Slippage can best be described as the % difference between what speed the prop would deliver "theoretically" vs "actual". A prop operates in a liquid so theoretically a prop with 20 inches of pitch would move 20 inches with each revolution provided there was no slip. There is always some slip so the boat hull design, prop design, engine height, etc are all factors that can affect actual speed. Slip will not be the same from one prop to another. Perhaps 12% slip would be in the ballpark on your boat. As an example, if a given prop would deliver 40 MPH theoretically at a given rpm, but it actually delivers only 36 MPH at that speed -- that equates to 10% slip.

 

[Texasmark]

Re: General Slipage questions.

As I said earlier in another forum my slip calculates to be 35 just on plane down to less than 10 at WOT. I am running a HP SS prop which is designed to enhance the WOT operation.

At slow speeds there is a lot of boat in the water and that has to be pushed, causing prop loading, hence slippage. At WOT very little boat is in the water so there is minimal prop load hence minimal slippage.

I have run a different prop, without all the whooplah (had some however), with 1" less pitch and it ran the boat faster at the lower speeds. This tells me that that prop didn't slip as much at the lower speeds.......but it fell on it's arse at WOT. So you prop for what's important to you.

Mark