Prop slip???

Can anyone help, I have a 2006 29ft wellcraft coastal, twin 250 yam 4 strokes, I noticed my performance was lacking and the port side motor was reving so i had the prop serviced and put it back on. I used it on Sunday and had the same problem, ok, simple so far, If i put the port motor in gear and the starbord in neutral, and give the port throttle i can bring the rpm up to about 3200 and it pushes the boat, not well, but it doesnt slip, as soon as put the other motor in gear and raise the rpm up to 2700-2900 the port motor starts to rev. If i keep them at 2900rpm it will rev to 3300-3400 and back to 2900. If i throttle up on both motors the port starts screaming. Today i took the prop to another dealer and he says it looks good. No grass, no line, clean prop. Always a mystery...lol.

Re: Prop slip???

Cavitation? What happens if you turn to port or starboard? Does it get worse, better or no change?

Re: Prop slip???

To get the right advice post your WOT RPMs, top speed, pitch, and gearing and the xperts can help you out.

I'd almost guess the prop shop gave you back the wrong prop and it's a higher pitch than what was previously installed since your RPMs seem really low for your setup. As soon as your starboard engine starts to bite your port Yammie starts to seriously slip. Something definitely changed on ya and that would be my 1st guess to eliminate.

Re: Prop slip???

Thanks Cribber for your response, it is the same prop, iwas thinking that before i gave it to them so i marked the prop. The prop is very clean, SS.I wonder if something on the hull in front of the prop could create conditions to cavitate. I will try turning while throttle up and see what it does. I dont think there is anything in the lower drive gear that would create a slip...Thanks again........Al

Re: Prop slip???

Tig said:

Cavitation? What happens if you turn to port or starboard? Does it get worse, better or no change?

Click to expand...

Thanks Steve, I have not tried that but i will. If thats the case maybe i can just spread the motor angles appart more with the tie bar adjustment, what do you think?....thanks again...Al

Re: Prop slip???

My first thought was actually ventilation too (often incorrectly called cavitation). Has it run right with both before? I am guessing yes by your post, but thought I would double check.

Maybe the starboard prop is the problem . . . The way you describe it the air could be coming from the starboard setup.

Re: Prop slip???

Yes it was fine before, I did notice a loss of power. I usualy run 4200 @ 28-30mph @ 22gph i had to throttle up to 45-4700 @ 25-27gph to get 28-30mph. I thought maybe there was some growth on her bottom so i clean her hull while in the water. Not much was there. That is when i had the prop redone......Thank you....Al

Re: Prop slip???

Allan, welcome to Iboats prop forum and we will try to help you as much as we can but without more information no one can help you, and I will tell you I need more information than anyone else. But if you would like my help fill this form out and I will help you as much as I can, if you would prefer to not go to this much trouble there are other people who will gladly help you.

Iboats Boat and Motor Info

1. Year, make and model of boat
2. Length, width and base weight of boat, look for boat decal on back of boat
2a.What is the maximum recommended HP for your boat
3. Number of people and gallons of gas normally on boat
4. What do you use the boat for
5. Is it a Deep Vee and if so how many degrees of deadrise
6. Year, make. manufacturer and model of motor
7. HP and gear ratio of motor IMPORTANT
If you don?t know the ratio, you need to pull the plugs out and put a piece of tape across the prop and the lower unit and then cut it between the prop and the housing then do the same thing on the flywheel and turn the motor until the tape lines up with each other on the prop, it is easier if two people do this, so one can watch the prop while the other counts the revolutions of the motor
8. Manufacturer?s recommended Wide Open Throttle (WOT) range
9. Anti-ventilation Plate height above keel of boat if it is an outboard in inches, use a board under the keel and stiking out to the anti ventilation plate for a referene
10. Is it a bass boat or does it have a pad bottom
11. Does it have a hydrafoil, dolefin or trim tabs
12. Make, model, diameter, pitch, number of blades and whether SS or aluminum prop
13. WOT RPM and speed from your current prop and how much gas and how many people were in the boat for the test data and is the speed by GPS. Make sure you trim the prop up until it starts ventilating and then just trim in until it quits ventilating. If you do not have a tach you can buy a digital tachometer and hour meter here: http://cgi.ebay.com/ebaymotors/Tacho...Q5fAccessories $ 35
RPM _________ Speed ______ GPS ______ No. of people ______ Gal. Gas ________
14. Are you at sea level or a higher elevation, give us the elevation in feet
15. Has your motor been tuned up lately and have you checked that the carburetor butterfly is opening all the way by just pushing the throttle at the helm and not at the carburetor, checked compression, and looked at the plugs and checked spark as well as timing and advance, all of the foregoing could be the reason your prop is not attaining full RPM
16. How long has this prop been on the boat and why, at this time, do you think it is the wrong prop
17. Does the prop show any damage that you can see
18. What problems are you trying to cure or what are you looking for the boat to do that it is not doing the way you think it should or to your expectations
19. If you are trying to attain a better cruising speed and fuel savings or trying to attain a faster speed I will want you to take your boat and run it with 1 or 2 people and give me the RPM and speed readings starting at 3,000 RPM in 500 RPM increments all the way to WOT.

REMEMBER, The numbers I give you will be NO better than the information you give me

The only thing I ask of you is to come back and give me a report of WOT RPM and speed for my database.



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