STV prop slip% change

[inspectorlance]

Does prop slip % go down with more speed ? I was figuring 10% at 96 mph. will I likley see a lower % at 110 or 115 mph with the same prop ??

Lance

[ChrisXS2003]

The faster you go, the "harder" the water appears to the prop. Prop efficiency should increase. All things being equal, slip should decrease.

Also, as speed increases the drive point on the blade moves out toward the tip where pitch is typically greater on progressive pitch props. This could also make your slip appear to decrease.

Chris

[inspectorlance]

Thanks Chris. Great points. Anyone have slip # changes on an STV differences between 95 mph, and 115 mph ? I quess some of the gain will be like chris said from the incresed pitch at the tip of the blade.

[RBT]

oddly my fastest STV's had huge slip. I kinda always looked at it like if the acceleration and MPH was there I didn't care about the slip number. I was like 20%....... but also in the high 120's

[Trikki1010]

oddly my fastest STV's had huge slip. I kinda always looked at it like if the acceleration and MPH was there I didn't care about the slip number. I was like 20%....... but also in the high 120's

That's just 'cause you're a slippery charachter:eek: ;) :p

I run MUCH slower so I get about 12% at 115;)

[RBT]

Thanks Trikki, how you been you ADHD old fart?

RT

[AnthonySS]

Yes slip should decrease / efficiency increase on a long run but can be typically high on a short run.

I have seen slip as high as 13% on a short run and as low as about 6% on long runs...the way to figure is take a long run (say 5 miles) and watch the speed increase as the RPM stays the same...all becasue the efficiency is improving/ slip decreasing.

My test was done with a 14 1/2" x 30" Merc Cleaver. The Cleavers are generally higher in slip because of the low rake that slices more then it lifts compared to a high rake RE