Try to reduce prop slip or let it rip ?

[Scottdownsouth]

Per my last post I have tested two props on my tritoon and both have high slip numbers, around 40%. Powered by a Honda 150.
Black max 3 blade 15.25x15 20mph@ 5000rpm
Solas amda 4 blade 14.75x15 22@ 5500rpm
Should I try a bigger diameter prop to reduce slip or just leave it as is ? Do you reduce pitch when trying to reduce slip ? It just seems 40 % slip is very inefficient and maybe getting it down would help the motor live longer not to mention gas mileage.
Thanks!

 

[alldodge]

Read thru your other post
http://forums.iboats.com/forum/gene...s-and-topics/10465242-tri-toon-poor-top-speed

Your issue is its a toon, and it will take a lot more power to get the boat up. Tri's are great but they also require more HP to more due to more drag

 

[Scottdownsouth]

I understand that part, but I'd like to know if a bigger prop will reduce slip , not go faster. It seems to be wasting a lot of energy at 40% slip. Would a 16x13 prop be better than what I have ?

 

[shaw520]

more pitch,...bigger prop,..just dont over prop,..over torque the motor,... check what max rpm at WOT is supposed to be,...you could come down from that maybe 2-3k,...any more than that you could over torque the drive.

 

[ahicks]

On paper, I would think that all else being equal, as blade area increased, prop slip would decrease. Larger diameter props, and 4 blade props, would both offer more blade area than smaller diameter or 3 blade props.

Still on paper, the downside to more blade area will be reduced performance at higher rpms and higher speeds due to prop friction/drag on the water. With this boat, I don't think higher speeds are going to affect what's going on.

Bottom line, from a practical perspective, I'd be looking to compare props that allow the engine to turn up max rpm. I honestly don't know how you would predict 3 blade vs. 4 blade performance. I think it would be really interesting to have one of each, that would both allow max rpm, to compare them.

Regarding a 13" pitch, our 2 tube Honda 90 boat is running a 13" Honda OEM 3 blade, turning it at 6K, and making 24-25mph when lightly loaded. Point being, if your engine is rated for 6k as ours is, you could still be picking up a couple mph, while likely having much more lively performance while getting there - while running a 13" pitch.

 

[alldodge]

Agree with others, need max rpm. The lower the pitch the less slip.

Short example (long story): My 11K cruiser,
Using 22 pitch 4 blade slip is 14 cruise and 12 at WOT, with max speed of 48 mph and will over tach
Using 26 pitch 3 blade slip is 23 cruise and 21 at WOT, with max speed of 50 mph

 

[Scottdownsouth]

Power is a honda 150 and max rpm is 6000.

 

[ahicks]

So with a target rpm of 6k and this experience under your belt, it's not hard to endorse the 13" prop plan.

Black max 3 blade 15.25x15 20mph@ 5000rpm
Solas amda 4 blade 14.75x15 22@ 5500rpm

The more difficult call will be 3 blade vs. 4!

 

[Scottdownsouth]

Update with a 16 x 13 3 blade black max prop.
23 mph @ 5500 rpm. This was in choppy water wwith a stiff wind. Mph did not drop heading into the wind and did not speed up going with it .it felt faster and it did not lose speed in a turn like the other props. I took my son tubing and it pulled him just fine.while perplexed with the outcome I am going to wait for a better day to test it again.