311 Prop slip
 

I was wondering what % prop slip are you getting on a 311 sr1. I have 30P Bravo1 4 blades and at 2800 rpm I'm going 40mph. That came out to be 25%. Is this too much or does that sound right for a heavy classic boat? My WOT rpm is 5400 and I have 22% slip then, but also the drives need to be fully trimmed to get the boat to run flat.

Reese

It is normal to see your slip numbers increase some a slower speeds. Normally you will see slip decrease with increase in speed. You are doing good if you can get between 10-15% at full throttle. Ideally the props carry the hull nicely when running close to neutral (not trimmed really high).

Here are slip numbers on my 292 which is a twin stepped deep V that weighs 7500-8000 lbs running 28P Bravo1 4 blades.

Thanks for the info 4mula. I was not sure if some thing was way off or what. The WOT slip should improve if I get some bow lifting props that are the same pitch, that way I can keep the drives straight out. If I run WOT with them straight the bow is way down in the water and feels like the tabs are down.

Any more info will be greatly appreciated.

Reese

You're running 30" four blades on a 311?!?!?!?:eek:

What the heck is in that thing for power? That's a ton of prop for a 311 with standard power.

what is the speed calculation formula again to get the theorical max speed?

max rpm x drive ratio x pitch?

Theoretical MPH = (RPM/Gear Ratio) X (Pitch/1,056)

Dividing by the 1,056 gets the inches/minute to miles/hour.

I am running 24" four blades w/330s and I am getting 40 mph on gps @ 3000rpm ....

Something doesn't make sence ??? ....

Jeff

What drive gear ratio do you have? I think I have 1.5, I have not confirmed it yet.

My next question is, could I have to much prop and I'm just cavitating? I boat does need to be brought up on a plane gently or it will blow out the props.

I have 1.5 .....

I used to have major cavitation when I used my 23" labbed Mirages (3 blade).

Call Brett @ BBlades he will give you the best solution or answers you need .... he helped me out a lot .....

Jeff

If your spinning 30p Bravos @ 5400rpm on a 311, that calculates to 102mph with out any slip, and 79mph with 22% slip. If thats right I would have to guess you have some pretty big power, and too high of an X dimension.

I had 550/575hp in a 88 311 with deep TRS's, it ran 77/78mph on GPS with labbed 25p Mirages @ 5400/5500rpm with 10/11% slippage.

If all your data is accurate, you need to get your slippage in check. What drives are you running? Bravos? If so you can buy drive spacers to get the drives a little deeper without buying new props. The only other choice would be 5 blades, which shouldnt be necessary on a 311.

The 311 was designed for a 3 blade prop and a deep drive. Get the X dimension right and keep your 4blades and you should get some pretty good performance from that hull.

LE