Which propeller should I buy.....

[Capn Mike]

So I take my boat out for its annual maintenance and discover a small chip out of the prop. No mystery: probably some debris in one of the rivers. Time for a new prop.<br /><br />But for some time, I've been fussing with the ones I have. I run a Michigan 15 1/2 X 15 alum. prop on my 200 Johnson, on a 23' Seaswirl Striper WA. And I've never been happy with the performance: my maximum has never been much over 5000 RPM, about 32 mph @ WOT. <br /><br />Trouble is, when I've switched to the next size down (15X13), it easily over-revs to above 6000, and speed drops to 25 mph....don't even know what WOT would be, since I'm not interested in blowing up my motor to find out. In theory, I should only be increasing my rpms by 200/inch of pitch....so much for that myth. I've not been able to find a 14-pitch prop to experiment with.<br /><br />So I see on the I-Boats sale site, that I have a bunch of choices. For example, in 15-pitch props, Solas "Amita" has a 14 3/4" diameter 4-blade. And Express makes a 3-blade SS 14 1/4" diameter; Solas makes a 14 1/2" diameter SS 3-blade, and Ballistic has a 14 7/8" diameter prop.<br /><br />So my question is, does anyone have any real-life experience with the differences in prop diameter with heavy boats? (with full gas, gear and fat fishermen, mine probably weighs out @ close to 5000 lbs.) Yeah, more horspower would help, but that's not going to happen for a while.<br /><br />Non-SS props, I might try the Solas; the Express is the smallest SS. Any opinions?

 

[steelespike]

Re: Which propeller should I buy.....

Not sure but I think 5,000 rpm would be about the bottom of the recommended range for your motor.To stay healthy it probably needs to turn more.<br />Im no prop expert but I think it is pretty obvious there is more difference in your props<br />than 2 inches pitch.Is the 13" a known good prop of 13 inches.No chance of a bad hub or a repitch?<br /> If the 15 is cupped and the thirteen is not there would be a difference but over 1,000 rpm I doubt.If you are jumping over 1,000 rpm and losing speed with only 2 in. change something is up.<br />Maybe the thirteen is venting a little.A prop shop can repair your prop and maybe tweak the pitch a little.They should be able to tell you about your present props.Generally a 4 blade will grip better especially at take off,but will be a little slower top end.I would try to deal with a prop shop or marina for a new prop.As I understand it they will let you try a prop to see what is best.

 

[cuzner]

Re: Which propeller should I buy.....

Hey Mike.. depends on what you mean by performance. A larger pitch will improve top speed , and improve fuel economy. A smaller prop improve hole shot, lower top speed speed.I don't think you can get much better performance than going with recomended prop.If you don't mind spending some money, I would suggest instaling tabs. You will get better hole shot, and a smother ride.Investing a lot of money on props may give better performance in some area's, but you will pay in either top end speed or hole shot.<br /><br /><br /> Jim

 

[walleyehed]

Re: Which propeller should I buy.....

by Jim,

but you will pay in either top end speed or hole shot.<br />

This is not always the case unless you allow it to be. There are much more efficient props out there than the MW 15-1/2X15 in this case.<br />You don't state the year model, so I can't pin the RPM down, but 5750-5800 won't be far off and some 200's we want at 6000RPM.<br />First item would be to determine engine heigth above the transom or jackplate-where is the cav plate in reference to the bottom of boat.<br />Let's have a little more info on your set-up.

 

[Capn Mike]

Re: Which propeller should I buy.....

Walleye, the motor and boat are both year-2000. Motor was installed by the factory, and the cavitation plate is maybe only an inch or so below the bottom V (I think...now I'm going to have to go look at the boat.) Even though 2000 was the last year that OMC owned Seaswirl and Johnson, the factory personnel is still intact and for now, I'll presume the factory knew how to install the engine and that hieght is not a factor.<br />I'm interested in your suggestion that there are more efficient props available (what I'd really like to find is a 14-pitch prop). I know SS is more efficient....but would an "efficient" 15 x 15 SS prop slow my RPMs even more?

 

[walleyehed]

Re: Which propeller should I buy.....

Engine heigth is very much an issue. Not all boat/engine combos are created equal, and to obtain the best performance, some adjustments may be needed.<br />If the cav plate is truely below the V, we need to raise that engine a bit.<br />Does the boat have a built-in setback, or pod the engine sets on or is the transom flat all the way across?<br />I can't make a recommendation of a prop if we have mounting heigth issues that need attention first.<br />Find out where the cav plate is with the engine level to the bottom of the boat and let's go from there.

 

[steelespike]

Re: Which propeller should I buy.....

A change as little as an inch virtically could add or subtract close to 3 mph.<br /> Of course too high could result in ventilation problems.

 

[walleyehed]

Re: Which propeller should I buy.....

Correct...If we can go up one hole at a time and test, this is the best method.

 

[gutshot grouper]

Re: Which propeller should I buy.....

Simple suggestion, have a prop shop recondition your prop and take a half inch of pitch out, you need the diameter for the push, the pitch for the advance, Old Boater

 

[phatmanmike]

Re: Which propeller should I buy.....

walleyehead? could you email me pics of your home made outboard fixed height jack plate and what you used to make it?

 

[walleyehed]

Re: Which propeller should I buy.....

Mike, I'll find the pics and get them sent!<br /><br />

Simple suggestion, have a prop shop recondition your prop and take a half inch of pitch out, you need the diameter for the push, the pitch for the advance, Old Boater

Let's not get the cart ahead of the horse here....we want optimum engine set-up, and THEN work with different prop combos and fine-tune as we go.