prop help. bad slip %

[erider81]

hi guys,
I just tried out a new turning point Legacy prop (13.25x21) to try and lower the bad slip i was getting with a black max 12.75x21 and it appears the TP prop was a bit worse in top end, where i was hoping it would of fixed my top speed/high slip issues. heres' my specs. what do you guys think i should go with lower pitch TP or just go to a 4blade stiletto? something else?

2001 merc 90 hp 2stroke
2001 Bayliner 160 capri BR.
with the black max prop i would hit 39mph (gps) at 5400 rpm, lots of blow outs in turns and about 8 to 15 seconds to plane. stay on plane around 25mph.

with the new TP eventually would hit 38.5mph at 5200 rpm, no more blowouts and about 6 to 13 seconds to plane. could stay up on plane around 24mph.
These are both with about the same average load 2 people, 3/4 full gas tank, 2 batteries.
boats main use is crusing and occasional tubing.

those numbers tell me im getting a very high slip %. i thought going to the new prop would of brought that number down but it seems worse. Any thoughts or ideas are much appreciated.

Thanks,
Glen

 

[hwsiii]

Re: prop help. bad slip %

Glen, see where your motor height is before you go looking at changing any more props, you can potentially gain a couple more MPH and higher RPM as well.

You might try reading this for a better understanding of changing props for better performance, and for the major differences between aluminum props and stainless steel.

http://forums.iboats.com/showthread.php?t=369057



H

 

[erider81]

Re: prop help. bad slip %

yeah i have to measure that when i get home. what do you suggest 1 inch or two inch from plate to bottom hull? i have a feeling its not even an inch right now.

Glen

 

[hwsiii]

Re: prop help. bad slip %

That TP ought to be able to handle at least 2" above the bottom. Your prop slip with the TP is right at 14% and I recommend you need to change props at 15%.



H

 

[steelespike]

Re: prop help. bad slip %

H, You intend for him to raise the motor don't you?He may think with the previous
venting you may want him to lower.
I assume you feel the Turning point will allow more height.

 

[hwsiii]

Re: prop help. bad slip %

You are 100% right Spike as always, I went back and rewrote it.



H

 

[erider81]

Re: prop help. bad slip %

thanks for the info. I'll check this tonight.

 

[torbjorn]

Re: prop help. bad slip %

hi guys,
I just tried out a new turning point Legacy prop (13.25x21) to try and lower the bad slip i was getting with a black max 12.75x21 and it appears the TP prop was a bit worse in top end, where i was hoping it would of fixed my top speed/high slip issues. heres' my specs. what do you guys think i should go with lower pitch TP or just go to a 4blade stiletto? something else?

2001 merc 90 hp 2stroke
2001 Bayliner 160 capri BR.
with the black max prop i would hit 39mph (gps) at 5400 rpm, lots of blow outs in turns and about 8 to 15 seconds to plane. stay on plane around 25mph.

with the new TP eventually would hit 38.5mph at 5200 rpm, no more blowouts and about 6 to 13 seconds to plane. could stay up on plane around 24mph.
These are both with about the same average load 2 people, 3/4 full gas tank, 2 batteries.
boats main use is crusing and occasional tubing.

those numbers tell me im getting a very high slip %. i thought going to the new prop would of brought that number down but it seems worse. Any thoughts or ideas are much appreciated.

Thanks,
Glen

Is the prop properly cupped? It should be cupped out to maximum diameter. 2" above the bottom should be fine, but if the prop's well cupped and the problem continues you can try dropping the motor 1/4" at a time with shim sticks. Also matters whether the boat bottom's nice and straight or badly hooked.

 

[SingleShot]

Re: prop help. bad slip %

Your problem could also be you are trying to trim up higher to get your bow more out of the water. If this is the case you may need a higher raked prop. I have 21 that is no faster then my 19. Same company but the blade geometery is different, go figure. One other example is I have a 22 in/pch prop with higher rake and more cupping, it likes to run trimmed up. With this prop my slip is greater but I get higher mph due to less wetting surface. Always keep an eye on your wot. This is still key.

Hope this helps some

JK

 

[erider81]

Re: prop help. bad slip %

well looks like im 3/4s of an inch above the bottom of boat as far as height. But i only have 1 set of bolt holes left to raise it. I dont think i'd be able to even drill new holes since this sucker is pretty close to top of transom to begin with. (transom slopes down in area where motor is mounted). when I'm trimming to get top MPH/WOT the motor has to be pretty close to all the way in to get best results, I'd estimate its only about 2-3 inches out from all the way in. Would raising it just that one bolt hole even be worth the difference it would make? (I know this answer would be based on experienced assumptions). also if i trim out much further then that I tend to get some venting.
The TP prop definitely has more cupping the the BM that I had on there. I'm not sure how to tell its cupped out to max diameter like torbjorn stated.

Also in case someone suggests, trim tabs arent really an option on this boat, just not enough room on transom, things would have to be removed/relocated.

thanks again guys, all this input is really appreciated.
Glen

 

[hwsiii]

Re: prop help. bad slip %

Glen, i don't know exactly what changes will happen with the TP raised to the last hole, but you could possibly gain a couple hundred RPM and a couple of miles per hour.



H

 

[erider81]

Re: prop help. bad slip %

H
whats your thoughts on a jackplate on this small of a boat? Im thinking that if im going to move it up one notch maybe i should just install a cmc 65 so i'll have much more play in it.

 

[hwsiii]

Re: prop help. bad slip %

Glen. I don't really think that TP prop can handle more than one more notch up on the transom, and I just believe there are better ways you can spend your money.



H

 

[erider81]

Re: prop help. bad slip %

Ok thanks again. I'll try and get that motor bumped up this week and see what happens.

Glen