finding the right prop

[shine]

thanks for that !

[junior11]

Huh... I am temped to throw the 19 pitch 15.5 saltwater series I have on there just for kicks... I guess my slippage was pretty high, I am not sure what the answer is, and it doesn't sound like anyone is. The good news is that I fixed the cavitation issue, the bad news it didn't help performance though.

[76Red18]

Originally Posted by shine

copied from my post over at propgods.com......


27.7mph @ 3800
42mph @ 5600
30mph @ 4100
25.5mph @ 3600

20 mph beam wind, same rpm/speed running both ways up and down the river.

Load was 55 gallons fuel, 2 guys, full live well (about 360 pounds), with empty baitwell the speeds/rpm were the same but the hole shot was even worse. A little trim tab solved this.

5600 was as much as I could get without trimming the motor up too much. Prop really grabbed well, no problem keeping on plane at low speed, felt great. 3800 to 4000 seemed to be a really nice cruise. Hole shot was terrible but I expected as much.


AND

F225 manual says under a full load, the RPMs need to be in the upper half of the full throttle range. Full throttle range is 5000 to 6000. I was not at a full load and barely getting into the upper half of full range (5600).

I just wish they made an 18 pitch !

Hole shot should be great with the right prop. Just my opinion but I say its way too much prop. You need to gain 400 rpm minimum from where your at now. A 17 pitch in that lower diameter 4 blade or a 15 x 17 3 blade will get you there.

[junior11]

What was the diameter on that 19 pitch 4 blade you had? Is the 17 the same diameter? I think just the pitch change alone should get you the extra RPMs. At the same time I think that may be the prop I need.

[GodsReel]

I am thinking about gettting a new 300 to help with the hole shot. I'm working on putting together a team for the armored truck heist. LOL

[FishStretcher]

Originally Posted by shine

copied from my post over at propgods.com......
SNIP


AND

F225 manual says under a full load, the RPMs need to be in the upper half of the full throttle range. Full throttle range is 5000 to 6000. I was not at a full load and barely getting into the upper half of full range (5600).

I just wish they made an 18 pitch !

IIRC Yamaha makes an 18 pitch 4 blade, a guy was selling one up here on the NH or Boston CL for $275. 1 think 13-3/4 x 18, but there might be other sizes (for $500+ new!)

Yamaha lists it on their website-

13 3⁄4 18 4 Performance 4-Blade pressed in MAR-GYT4B-V6-18*

[eggsuckindog]

2" pitch in the same dia. will yield almost exactly 400 RPM - a 23 should have a decent Dia prop as well - I am not familiar with 4 blades other than pitched correctly top end loss has been only about 1mph that I have seen. Mirage+ had been pretty popular here, large Dia, good cup and progressive pitch - means pretty aggressive. The Stilletto and Tempest are also progressive but I would not recommend a Tempest for this application BTW my shop Piper Marine in Tampa had a used 17 Mirage+ for around 225 at one time.

That being said none of you are raising the motors - I mentioned earlier I was - ran it this weekend. First I removed an old thru hull transducer - then measured the engine - it was pretty high at least 1 -1 1/2" above the hull already so we only did 1 hole which is about 3/4, so 2"+ now.
Picked up 1.5 mph at cruise from 28@3400 to 29.5/30@3400/3500 - top end picked up 100/150 RPM to 5600 and 3 mph to 52. Prop still would never break loose regardless of how high I trimmed it or turned it. Odd thing, motor changed pitch at 3000/3200 ? used to have a marked change in pitch before, sounded almost like laboring - gone now? Motor sounds much happier

Props on 23's should be vented, pretty big boat to run correct top end and they should be vented for hole shot help IMHO

Stilletto 19" Merc 200XRI - when changing props, this prop did pick up the whole boat and made at it least twice as dry with amazing trim responce - I only bump it if needed. You could not get it from me without a gun - just say'in

Check the engine height before doing much more with props, if thats not right it will never run as good as it could - brackets are different because of the set back - you guys are on your own there I don't have one

[shine]

my motor is 2.5" higher than bottom of transom, no issue there.

Have decided to go with a larger diameter 3 blade 15.25" by 17 pitch. the 4 blade I tested was 14.5, so I am hoping to get a little less slip.

To this point I have just been trying to find a prop that will match the boat/motor well enough to operate. Assuming I have done that now the big 3 blade 17 pitch, I want to now dial in the fuel efficiency......Ordered a fuel flow meter, it does not make much sense to spend a lot of $ on props and and gas when you dont even know the efficiency of the changes your making

[eggsuckindog]

for what its worth I re-ran my slip numbers after raising the motor - before was 14% at cruise a 11% above 4K

Now its 11% at cruise and single digits 7% at WOT - I am using 1.87 gear ratio which I think is correct, been awhile since I did it.

[GodsReel]

will you fellows explain slip? Thanks