Hwsiii

[Les Young]

I purchased a 13&1/4 by 17 Stiletto stainless prop(same pitch & diameter ) as the original aluminium that came with engine. Dropped rpm from 5900 to 5500. Now boat is a lot slower coming out of the hole. Throttle isn't nearly as responsive as with aluminium , but stays on plane at less rpm. I noticed the angle of the engine was tilted toward the front of the boat way more(trimmed a lot higher than before) Speed gps was 38.8, the same as before. Do these props like to run shallow??? I have 2 holes I can go up. Cavitational plate is 1" above bottom & engine has a Atwood Hydrofoil. Boat is a 1993 Sprint 255. Engine is a 1992 70 Hp Johnson. 5500 rpm 38.8 mph by gps. Do I need to raise engine.

 

[hwsiii]

Re: Hwsiii

Les, if I remember orretly I asked you to fill my form out and take pitures of the props and you hose not to. I told you that I didn't understand why there was only a 100 RPM differene between the 17" and the 19" pith props. The only way I an help you is with the information that you supply to me, beause I am not there and now you see why.
But, putting all that aside let's see what you have now and what we an do about it. There are two things we an try at this stage, take the hydrafoil OFF and raise the motor 1 noth at this time. Then take the boat out and get me some numbers of speed and RPM starting at 3,000 RPM going to WOT in inrements of 500 RPM and lets see how the prop is doing raised one noth and without the hydrafoil.
In the meantime fill out my form and take me a piture of both old props side by side in the same pitures o I an ompare them and see what the differenes are. As soon as you get that information I will start working on it.


H

 

[Les Young]

Re: Hwsiii

One prop destroyed. I also told you I verified tach by a mechanics tach & was right on. Was told to get a 19pitch & even a 21 not by you, but by IBOATS & knew I couldn't turn a 21 stainless. Glad I didn't get a 19 . I appreciate your time & help that you have tried to give me. You ran your program once for me & I think it was 6% slippage for the 13&1/4 by 17pitch aluminium prop at 5900 rpm &38.8 mph. I don't have any way of taking or posting pictures. What else can I do. Thanks

 

[hwsiii]

Re: Hwsiii

Les, I found your gear ratio to be 2.42:1 and WOT RPM to be 6,000 RPM, please verify this. Using these numbers I find that your prop slip with the Aluminum prop is 1% and with the Stiletto it is -6%, these numbers are not real but they are what we have to work with. But they are relative to eah other and they show that the Stiletto prop definitely has less prop slip than the aluminum prop. Here are my numbers.

Prop Slip

Now what we need to do at this stage is take the hydrafoil OFF and raise the motor 1 noth at this time. Then take the boat out and get me some numbers of speed and RPM starting at 3,000 RPM going to WOT in inrements of 500 RPM and lets see how the prop is doing raised one noth and without the hydrafoil. While you are doing this trim the prop up and make some halfway aggressive turns to see how muh ventilation the prop is reating so we will have an idea if we an move the prop up another noth or not. We should get an inrease in RPM and speed by doing this and it will let us know what else we an do.


H

 

[kick bass]

Re: Hwsiii

Good luck! I can't help you with this one. His boat Max HP rating is 80 HP. He has a 70 which is 87.5% of the boat max HP. His engine has to be turning 6000, and with a 17 pitch prop his theoretical speed would be 39.91 MPH. his real speed is 38.8 which makes his efficiency 97% which is hard to accept, I guess it is possible. none of the numbers match anything. did not mean to jump in, but I like a challenge, and this is a good one. can't wait to see the out come. So, I'll just sit back and watch. where is the boat at? like to look at it.

 

[hwsiii]

Re: Hwsiii

Gary, you are not jumping in, we all an use help. I always say,
I NEVER make a mistake, UNLESS I am breathing. LOL

 

[Les Young]

Re: Hwsiii

Gary, your right max hp is 80 hp. These speeds are by gps & tach was verified by a mechanics tach. I did notice running the stainless the other night that it was throwing water from the back an awful lot. Thought maybe by having to trim so high it may have been causing the hadrofoil to drag causing this because of the resistance of it against the water. I.also noticed it used a lot more gas than usual. Figured engine needed to run shallower to accomidate the stainless prop as it definitley pulled it down. I removed hydrofoil & will raise engine . I'll give full report when I take her out next time. Thanks

 

[Les Young]

Re: Hwsiii

Hwsiii, here is the model # of my motor just incase it will help be sure about gear case & ratio. Model # VJ70TLEND. Thanks I'm trying to get someone to take pictures & post them to help you out if I can. I'm not to computer literate & have no camera so it's up to someone else lol. Will the boat VIN # help you any if so it's FIW14234E393. Again thanks. I'll let you know as soon as I can get her tested & also when I can get pictures & get them posted.

 

[hwsiii]

Re: Hwsiii

That sounds great Les.


H