How do you decide on a prop if professional's can not?

I am shopping for a 115HP Mercury or Yamaha four stroke for a large and heavy 28 foot tri-toon Suntracker Party-Hut. I have been to two boat shows and talked with different motor dealers and prop shops. Every one has told me a different recommendation for Diameter size, and pitch of new prop. Boy am I confused. Is there a formula, or does everyone just try it and see what works best? Boy have I seen some wide ranges of prices also. Any thoughts or experiences?

Re: How do you decide on a prop if professional's can not?

Sandman, I know what you are going through. <br /><br />I would do a search on "prop" and you will read some very good posts on prop selection here.<br /><br />The real bottom line is you will probably need to find a dealer that will let you "try before you buy", if you want the perfect prop.<br /><br />Really though, you need a baseline to start from. Do you have a prop on your motor now? If so, what is your maximum rpms at wide open throttle?<br /><br />If you have no prop, I would start out with your boat dealer's (not motor dealer, if purchased separately) recommendation as a starting point. <br /><br />The reason I say this is the boat dealer should already have some "on the water" experience to help you.

Re: How do you decide on a prop if professional's can not?

Thanks for the suggestion. I currently have a "shot", much smaller motor on my boat. Since the much smaller motor does't compare in HP with a new motor, would the prop be similar? Unfortunately, I do not have a manual with my boat, but I did get a manual for a boat like mine only 5 years newer as suntracker did not have 1990 model manuals. Maybe they will be similar.

Re: How do you decide on a prop if professional's can not?

I bought a brand new boat/motor, and only because of some folks here I installed a tach, checked RPM's at WOT and found I needed to go from a 15 pitch, to a 13 pitch. I still can't understand how it was sold to me this way? It's a duck boat, so one can be fairly certain of the eq that would be being carried...oh well, it's FIXED NOW!

Re: How do you decide on a prop if professional's can not?

Check with some of the prop dealers and most will allow you to test different props that will most fit your needs.

Re: How do you decide on a prop if professional's can not?

I would make the dealer figure it out. Do your own research, so you know the verbiage. If your dealer is selling you a new motor, it should come with a prop. If you need to deviate from the standard, I would ask the dealer to warrant the motors ability to meet your need. If you don't, they may void your warrantee, or in other words, shift blame for possible malfunctions down the road. I would also have the dealer install the motor if its electronic fuel injection. The stability of the electrical to the motor is critical. Any thing goes wrong and they'll be sending you thru every wire on your boat. That was my experience on both topics, for what its worth. If your buying a used motor, don't over intellectualize your prop, its not rocket science. Here is a cool link. By a spare prop, and for goodness sake, skip the stainless, unless you’ve got money to burn.<br /> http://www.miwheel.com/

Re: How do you decide on a prop if professional's can not?

I am wondering what WOT is. On my last motor, I was unable to "fully" throtle up as I was limited by RPM's. If I were to have fully throttled or Wide open throtle, I would have exceeded the rpm red line of the motor. On second thought, maybe I should have. Maybe if I had abused it, it would have not lost a cylinder. Ha.

Re: How do you decide on a prop if professional's can not?

Sandman, you may have missed out on some higher top speed. It's best to let the prop limit your RPM's at Wide Open Throttle (WOT) Sounds like you could have gone up in pitch on your old rig.

Re: How do you decide on a prop if professional's can not?

OK how does one do that? I am ready to go to school. Thanks for the help!

Re: How do you decide on a prop if professional's can not?

For every 1" of pitch you go up, you will go down 200 rpms and vise versa. This is the std rule of thumb.

Re: How do you decide on a prop if professional's can not?

The best way to prop out any boat is on the water with a good shop tach. Run the boat at wide open throttle and record your readings. Compare those to your motors recommended maximum rpm. The rule of thumb is going up in pitch reduces rpm, as going down in pitch will raise it. For example, if you are running a 17" pitch and are 600 rpm below your motors max rpm, drop to a 15" and you will be in the upper 1/4 of your power range, witch is suggested by every manufacturer. Hope this helps.

Re: How do you decide on a prop if professional's can not?

Thanks all. I appreciate the help, and great information. I "finally" understand with your good help what I should be seeing on my tach.<br />