What prop do I need?

[Captain_W_Alan]

Hello, I am attempting to replace my old tired SeaRay 17 footer with a used Pro-Line 17. Our cottage is on an island in Northern Michigan with no bridges or roads. We use our boat as a taxi in addition to being our fishing friend. We load it down with 5 average sized people, 3 average sized dogs plus all of our luggage and food. The hull that I have located is a 1985 Pro-Line central console. The motor came from a different source but it is also a 1985 ... a Mercury 4 cylinder, 2 stroke. It's prop looks bad and needs to be replaced. Here is my question. What diameter and pitch prop should I buy in order get my loaded boat to plane. I don't care how fast I go, I would be happy with any speed up on top of the water. Oh, by the way, I just purchased a used set of 12"x9" Bennett trim tabs that I will be putting on soon. I don't have the boat in the water just yet. Any advice would be greatly appreciated. Sincerely, Wayne

[231CALIFORNIA]

not the answer      but some direction
a lot of info left out --HP,max rec wot rpm, but loading and weight dist will be issues as well.
get any old clean  prop off an old motor that is in the same range as the one you have now for baseline test, they are often on craigslist and ebay for under $40. move  up or more likely down in pitch until you get to rec wot max loaded.
make sure cavitation plate is level with bottom of boat not too high
also start out with trim tucked in not out

[Captain_W_Alan]

Thank you 231California. Yes I guess that the horsepower rating of the outboard motor would be very essential here. I can't believe that I left that out. It is a 75 HP motor. Apparently Wide Open Throttle for this motor is in the 5000-5500 RPM range. I have seen several weights listed for this boat between 1500 and 1700 lbs. The motor weighs 265 lbs. The load might be 1200-1300 lbs, which is a lot. Based on what you are telling me, the correct prop can't be figured out on paper and the only way to do it is to put the boat in the water, load it down and then play around with various props until I find something that works. If that is the case, where do you think that I should start. I mean, what pitch would be your beginning point? Thank you, Wayne

[Country Water]

All props have some kind of marking on it.  Can you make out any of the numbers on the current prop?  Given the load you are going to put on this boat and the size of the motor you are probably looking at a 15 or 17 pitch prop.  A 4 blade may even be helpful in this case.  5 people + gear is a lot for a 17ft with only a 75hp motor.  What is the max HP of that hull?  231Cal has the right idea, there are lots of cheap (~$50) props you can pick up on ebay to test out.  Also many reputable prop shops will loan you a prop to try out.  I'm not sure if that is an option for you.  It depends on where you live.  Also call around to local marine mechanics, they typically have shelves of left over used props.  My guy has a few hundred sitting in his shop.

[231CALIFORNIA]

If you can i.d. old prop by stamped numbers., they should be there somewhere, try next lower pitch , 4blades will cost more but will likely work better with your load, if you arent always that loaded down that engine likely ok, but with your load its a strain, especially if the engine only rated 75 when new. it might only put out45- 50 if you cant reach wot revs.
however with your modest speed minimum plane hopes you should be able to do it in decent weather. if you lug it you may have a heat problems so make sure impeller and thermostat are up to task, plugs are clean and fuel fresh.

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