13 to 14 inch prop

[Tacklewasher]

My motor is finally running right so now I want to play with my prop.

Currently have a stainless 13X19 prop on. Can hit 36.5 MPH at about 5200 rpm.

I have (what I think) is a 13X15 alum prop. There are no numbers on it so I'm not sure. I get 32.5 mph at about 5800 rpm.

So, I'm thinking a 14X17 prop will get me into a better RPM range without the big loss of speed. And I'm thinking a 14 inch may help imrpove my speed.

Does this make sense?

 

[Dhadley]

Re: 13 to 14 inch prop

Rather than drop pitch to gain rpm, have you tried raising the motor? As long as the prop is a decent design and the blade tips are in good shape that should gain rpm and speed.

 

[Tacklewasher]

Re: 13 to 14 inch prop

Motor is as high (or higher) than it should be. The a/v plate is about 1 inch above the bottom of the boat. As it is, I have trouble turning the boat without slowing down first or the prop ventilates.

 

[Dhadley]

Re: 13 to 14 inch prop

OK, the motor may be too high for the design or condition of the existing prop. Let's look around and see if we can find something like a 17 or 19 Stiletto to test.

 

[Tacklewasher]

Re: 13 to 14 inch prop

BTW.

The prop is in real good condition. Are you suggesting I should be able to turn a 19 with a 1981 115hp and I might have a problem elsewhere? I've pretty much got the motor rnning as best it ever has (i.e. on 4 cylinders finally), which is why I started asking prop questions.

I'm gonna stop at the local boat place and see if he has something for me to try.

 

[Tacklewasher]

Re: 13 to 14 inch prop

Okay.

New local shop needed an excuse to bring in stock so he's got 4 different props for me to try before the weekend (including a Stiletto).

We'll see what that does for me.

 

[Tacklewasher]

Re: 13 to 14 inch prop

Here's a picture of my motor height. Almost exactly 1 inch from the framers square to the a/v plate.

 

[Tacklewasher]

Re: 13 to 14 inch prop

Dang. This previews better

 

[Dhadley]

Re: 13 to 14 inch prop

Good pic, great info. If I remember correctly the Holidays would tend to run a bit bow down so something like a Stiletto or a Raker may work pretty well at that height. If the ride attitude is more level or bow up, you may be able to go up some.

 

[Crownie2]

Re: 13 to 14 inch prop

You may not want to spend the $$ on it but I would think a manual jack plate would be beneficial - especially in light of the bow down comment. A 5.5" set back and the ability ro raise and lower the engine to fine tune height is wonderful.

Bob

 

[Tacklewasher]

Re: 13 to 14 inch prop

Remember, this is a custom (read me) built back end. The boat came with an i/o (Stringer) that I dumped money into, broke and got mad at (in that order). A set back would make me nervous.

As it is, it seems to run well with my stainless prop, just not quite into the rpm range I want. I wouldn't raise it as I do have troubles turning but I think I've gotten over trying to lower it.

It doesn't run bow down right now and seems to be running pretty level.

Anyway, we'll see how I do with different props.

 

[Dhadley]

Re: 13 to 14 inch prop

Look at the tips of the prop. Where the cup stops and how much is there will tell you a lot about it's ability to hold water in turns and coming on plane.

Yes, you may need to lower it for that prop but a higher technology prop may run higher. I wouldn't lower it and then test a Stiletto or Turbo or a Raker.

If you get a good close up shot of one of the blades maybe we can see what you're working with. You seem to have the picture taking thing down pretty good.

 

[Tacklewasher]

Re: 13 to 14 inch prop

Nah.

I'm the one holding the square.

My wife is the picture taking technician.

I'll grab a picture of the prop. It's one I picked up on ebay for cheap. Had to have the hub fixed so it didn't end up being as cheap as I wanted.

 

[Tacklewasher]

Re: 13 to 14 inch prop

Prop pictures. Have no idea if this tells you anything. Pretty much the shape it was in when I bought it except for a new hub.

 

[Crownie2]

Re: 13 to 14 inch prop

Remember, this is a custom (read me) built back end. The boat came with an i/o (Stringer) that I dumped money into, broke and got mad at (in that order). A set back would make me nervous.

It doesn't run bow down right now and seems to be running pretty level.

OK - I didn't know that...

Bob

 

[Dhadley]

Re: 13 to 14 inch prop

Looks like the aluminum prop. Actually it has more cup length that I thought it would. Doesn't seem to have a lot of rake but it's hard to tell. Anyway, I think you're headed in the right direction by looking for a 17 Stiletto to try. Once you get a prop with some decent lift you may pick up all kinds of efficiency. If we're still having a hard time lifting the nose up, a setback like Crownie mentioned would help. We'll test props for now and see what happens.

 

[Tacklewasher]

Re: 13 to 14 inch prop

It is way too heavy to be aluminum. At least three time the weight of my other prop. But I know it looks funny. Even the guy who replaced the hub said it looked weird.

Gonna have fun on the weekend playing though. Weather is looking nice.

 

[Tacklewasher]

Re: 13 to 14 inch prop

So, I've got three props to try out.

A 13X17 Hustler Aluminum
A 13X19 Stiletto
And a 12.5 X 19 4 blade Solas

All thanks to True Northwest in Kelowna. Nice range of options and I'll be writing up the results Saturday night.

 

[Tacklewasher]

Re: 13 to 14 inch prop

Well.

That was fun. Not one of these worked better than what I had and I think I'm back to thinking my prop is too high.

Took some pictures at cruising speed (~30mph).

The A/V plate is pretty much out of the water at cruising speed. At wot, all these props ventilated before I could trim out much. Top speed was the same or lower than with my old prop. Before ventilating, best speed was still 36 with the 4 blade being the worst at about 34mph. And I couldn't get any of them past about 4800 rpm.

So, what is involved in an extension? I really can't move the motor any lower but figure a short extension and then moving the motor up is my next move.

 

[Tacklewasher]

Re: 13 to 14 inch prop

Wish I could edit posts.

My old prop (in the picture above) is a 389510 which looks to be an OMC Stainless 13X19. That's what I'm leaving on for now.