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

And as mentioned, call Brett, he definitely knows his stuff..

LE

I'm running Bravo drives and prop shafts are 7" deep from the part of the hull directly in front of them. The props are also spinning out. Setting the drive parallel to the hull about 1/8" of the blade is breaking the surface. At full trim one blade is out of the water. The bravos on the boat are a standard length.

I will get in touch with Bret see what he recommends.

All the info is very helpful and really appreciated.
Thanks, Reese

Power???

Something still doesn't add up. You cannot be spinning 30" props on a 311 at 5400 rpm unless you've got like 700 horses per side. Are you absolutely sure your props are 30 pitch?

22% slippage on a straight hull with 4blades is alot. He might not want to share what kind of power he has for what ever reasons, but it wouldnt be un heard off to have a couple blower motors in a 311..

I hope he gets it hooked up and posts some speeds. I'm curious how fast a 311 can go. I was thinking of putting some big power in mine when I had it, but I stubbled on to a 353 instead.

LE

The props are 30's and the rpm's are also correct.

No blowers here just a pair of good running 283's. LOL ;)

http://i742.photobucket.com/albums/x...h_DSC02535.jpg

It is funny you said that .... I thought you used to have one and I was going to ask if it was your old one ....

:grinser010:


Jeff

They must be them there "Hybrid" ones ....

:coolcowboy:

Jeff

I know a different animal but i STILL had 22% slip with these:eek:

It was a good boat, I sold it to a guy in PA and he loves it, keeps banging things up on the rocks out there though. I put so much money into it and was at a crossroads when I found it needed some stringer work. Decided to go a little newer, and faster. Happy with the 353 now.

After talking with Brett @ BBlades about my 353 with steps and higher X-dimensions, he said 13/17% on a step boat is a decent slippage. I fiqured 22% was way high for a straight hull. My 311 with the deep TRS's had great traction, but I'm sure that the deep drives also slowed me down.

Formula88: Engines look good.. Get those %'s in check and keep us informed on how she runs.

LE

I got the boat out for the winter, but I'll keep every one up to date.

Thanks again for all of the info. It sure is nice to have this kind of info. available.

Reese

Yea... one my mistakes in life... I should have bought it from you!! oh well....:angry-smiley-038: