need prop help ( Up-Date)

[svilla]

1) I can't get to my Max rated RPMS

2) Stiletto 3 blade, Stainless.

3) 14.25, 15 pitch

4) Best I got was 5000 RPM I want to say 36MPH but that is a guess, at 4000RPM I was cruzing at 30 MPH on the i-phone GPS.

5) Yamaha Saltwater II 1997 150hp, I am running her on a Jackplate, trimmed out to the max. The weird thing is I think I heard the prop surfacing (Humming) it was differnt to say the least. And not it was not cavatation.

6) Sunbird Odessey 21 ft, I just re-built her so I am gonna say 3500 lbs. Neat boat, it is a Multi-hull deck boat. And it is a planing hull

 

[hwsiii]

Re: need prop help

Re: need prop help

Svilla, I ran some numbers on your 30MPH and it shows a 2% prop slip and I have a hard time believing that. If you can lower the motor please lower it 2 holes if possible. If you will take the boat out after that and give me some numbers for RPM and speed starting at 3,000 RPM at 500 RPM intervals with a GPS even the Iphone I will try and see what is happening.


Prop Slip

H

 

[svilla]

Re: need prop help

Re: need prop help

Yeah I will get better data. I will have a helper on friday. So I should lower the motor 2 holes, so that would be 3 inches on the jackplate or 2 inches? Thanks for running those numbers for me.

 

[hwsiii]

Re: need prop help

Re: need prop help

Try 2 inches then 3 inches. You will know when it is right.

H

 

[Dhadley]

Re: need prop help

Re: need prop help

If you can use 100% of the trim range at wide open and it is not venting, that indicates the motor is too low. What kind of a jackplate do you have?

 

[svilla]

Re: need prop help

Re: need prop help

It is a CMC manual Jackplate has 5-1/2 inches of set back. Yeah I had her all the way trimed out, steady stream on the ol' pee indicator. Realy weird harmonics coming from the prop. I belive the prop was surfacing. Still only able to pull 5000 RPM. The prop does cavitate a little when jumping onto plane. So I have it adjusted 2 inches down and will re-test tomarow.

 

[svilla]

Re: need prop help

Re: need prop help

Got the boat out today here is the data all numbers are MPH and I used a garmin hand held;

Lowered jackplate 2 inches;

RPM Speed/MPH
900 4.5

1000 5.1

2000 8.3

3000 20.4

4000 29

5000 37.2

Cruz is 3500 RPM at 25.3 MPH. Still cannot get the boat above 5000 RPM trimed as high as she will go. I wounder if my Tach is set wrong? I get 600RPM at idle so that is right on the money.

 

[junior1113]

Re: need prop help ( Up-Date)

so you can only get 5000 no matter where the motor height is? rpm should go up as motor goes up. you should be able to go up till you get blow out then go down from there untill best grip is achieved. wondering about that tach. can u post a pic of cavitation plate level with bottom of hull so we can see what where talking about thanks, paul

 

[svilla]

Re: need prop help ( Up-Date)

Ok here is what I am working with.

http://i17.photobucket.com/albums/b62/ghostrider-SBC/DSC02040.jpg

http://i17.photobucket.com/albums/b62/ghostrider-SBC/DSC02041.jpg

The cav plate is about 2in below the bottom of the center hull. I had the cav plate even with the bottom the first time I tested the boat.

Sorry about the links the files were to big to attach to the post

 

[junior1113]

Re: need prop help ( Up-Date)

cool you have a jack. that is way to low. i would say keep going up untill you get blow out then go down till you get grip. the best way to tell if your too low is to trim it up. if you can trim it all the way up with out losing grip its too low. have someone hold the wheel while on plane and with motor level and look at plate is it plowing the water. i should be barely skiming the water

 

[svilla]

Re: need prop help ( Up-Date)

The most I can go up on the jack is 2 more inches. The max RPM for this motor is 4500 - 5500. So I guess 5000 RPM is good. I think the stiletto is a high rake prop, I ran the numbers using 16 pitch and it comes out to 8% slip which is great, only I want a 4 blade prop.

I wonder what the prop selection chart would say the perfect prop for my boat would be? I would like to run an 17P 4 blade.

 

[hwsiii]

Re: need prop help ( Up-Date)

Svilla, if you buy a 17" aluminum 4 blade prop you will lose at least 250 RPM probably closer to 350 RPM and that would move your RPM down to 4,650 RPM and that will be worse for the motor. You want to run it as close to max RPM as you can not at lowest that it recommends. If you do anything buy a 15" pitch 4 blade prop, but I will tell you your prop slip is excellent right now and I can't imagine it getting any better.
Here are my numbers for your boat.


Prop Picker

H