Prop slip numbers

[89retta]

Took the boat out for the first time today and kept track of some numbers. First off I've got a 2004 Caravelle 187 4.3 GXI-E and a SX-M drive 1.79 ratio turning a 19" 4 blade Turning point prop. Was running at 3000 rpm speed 27mph on gps gives me a slip of about 10% brought her up to 4000rpm speed 37mph slip is 8%. Finally ran her wot 4900rpm 47mph slip of 4.5%. I've always thought slip would increase with rpm and speed. But its just the opposite.

 

[jimmbo]

As speed changes, the boat will ride differently in the water, that will affect slippage. Engine drive angle may also affect it

Where did you splash, Lac St. Anne? I was thinking of going out to Waby, but at $1.35/litre. doubt the boats gonna see water this year or in the future. Oil Robber Barons

 

[89retta]

Yep dropped her in over at Westcove . Was a little rough at times with the wind. Premium was a $ 1.50 and to top it off the nozzle I used was leaking at the joint. Which reminds I gotta fire off an email to Safeway and do some bitchin. Not only lost gas but leaked on my boat. The guy working there was aware of it and I had him sign a letter stating what happened.

 

[porscheguy]

The faster a prop turns, the more efficient it becomes. Think of using an oar to row a boat. What’s happens if you move the oar through the water very slow? Pretty much nothing, right? Yet when you move it as fast as your arms allow what happens? You move quite a bit.

 

[QBhoy]

Your numbers make sense. The faster the boat runs and with well applied trim...the less slip you should get with less hull in the water. My boat can achieve around 3% slip or just less according to the calculator.

 

[Texasmark]

Your numbers make sense. The faster the boat runs and with well applied trim...the less slip you should get with less hull in the water. My boat can achieve around 3% slip or just less according to the calculator.

It's all about drag and prop efficiency. Bass boats run on a "pad" to reduce drag and run props tuned for high efficiency near the surface, or slightly above with high rpms. 3% is getting a bit questionable. A screw in wood is 0% if not stripped. Water isn't wood. Wink.

 

[QBhoy]

It's all about drag and prop efficiency. Bass boats run on a "pad" to reduce drag and run props tuned for high efficiency near the surface, or slightly above with high rpms. 3% is getting a bit questionable. A screw in wood is 0% if not stripped. Water isn't wood. Wink.

Hi there. Under normal circumstances I’d be right with you. She is quite a specialised wee boat. Also has a running pad at rear. Only evidence I have is at cruising speed in pic. Think this is about 6% slip. Running hot and trimmed up and high on the pad is around the 3% slip mark, last i checked. Special wee machine. Figures are gps off the plotter as you can see and tachometer is fairly accurate when compared to smart craft true data.

 

[QBhoy]

Prop also runs surfacing trimmed out.

 

[QBhoy]

Up on the pad Texas. She goes well. Running about early to mid 60’s gps here.