Re: Prop selection 1989 Mariner 90
Not familiar with a wake board. Do you tow them like water skis and drive slow to make a big wake and the rider guides the board over and across the wakes like a big fat water ski? To me that is a big load with the board and pushing all the boat that's down in the water to make the big wake. You want a pretty shallow pitched prop. To get propped properly for that you will way overrev when running light so you will have to cut the throttle back to stay around the upper limit of rpms that your engine's rating.
21p for that engine and that estimated load is way too much. I am currently running a 21 ss on my 17' alum boat with 2 folks which I can also run a 24 on. It's light and fast and I don't linger making a big wake nor towing anything. The 24 is the right prop for rpms, the 21 runs 1000 over max when I check it so as I told you, I throttle back to hold the 5500 or so limit. I run the 21 when my girlfriend is aboard as she likes the noise and fast response.
Sooooo I don't even know where to start guessing. Best thing would be to find a dealer or prop shop that would let you borrow and test a prop before you bought it. Even if you paid $100 over what you may pay for one on here you could very well get the right prop to do the job for you.
Or, you could buy alum props for around $100 each and just swap till you get it. They sell them on here. Besides you would have spare props for whatever occasion. 3 of those would be cheaper than what ss props go for so you aren't all that bad off.
17p would be as good a starting point as any. On the 2.33 gearbox your (and my) engine have, a 17 will give you a lot of thrust and not load the engine. I have one that came with my little boat and it will snap your neck on hole shot......on my little, light boat.
Looking at the top of the page at props and clicking on that looking at Merc and pitch of 17P you get a long list of available props. The first listed is a Solas Amita P/N 1411-133-17 for $101. Apparently it has the rubber hub so no separate hub is listed. Besides you get free shipping! Can't beat a deal like that.
So, since you asked for help, help yourself. Get this prop and try it. See how it performs with your water toys and all and then get the WOT rpms. If you can go over 5500 go head and punch it up and get the number. Then come back on here with your results.
For what's it's worth I have pegged my tach hard on my current engine and the tach pegs at 7000. I was fooling around with it one day working on a problem and it took off on it's own. Besides I currently run 5700 on my 24p and my 21 will firewall at 6500.....but I cut it back to 5500-6000.
Waiting for your results.
Mark