Reply by: shiverfix Posted: Aug. 12, 10:30:36 PM Points: 3021
We can give suggestions, but it is pretty boat specific. I had a 17p 3 blade on my boat when I got it, and in the metro didn't come close to max RPM at WOT. I switched to a 19p 4 blade, mostly because we also use the boat for wakeboarding and I wanted the better hole shot. It actually gets me pretty close to max RMP at WOT. I have a 19p 3 blade I keep talking about putting on just to see what the difference would be. Should be higher RPM and higher top speed, but slower on to plane.
My boat is 19' with a stern drive with a 4 cylinder engine. So the pitch is going to be way different from yours, but it still gives an idea.
I had it up at Granby last year with the 19p, but I didn't check the RMP to WOT, so I can't tell you what the altitude did.
AA- If you are really concerned, get a 4" smaller-pitched prop. If it's only a few trips a year, I wouldn't sweat it too much, compared to being 300RPM low on your home waters. I think your engine has a range of 250 RPM for WOT--5250-5500 RPM is ideal for normal conditions, loaded normally. So you are close to perfect at home, at least.
I believe you lose about 200 RPM for every 1000 foot elevation gain.
Reply by: shiverfix Posted: Aug. 14, 10:49:44 AM Points: 3021
Looking at this again, I realize I had it backwards and misstated. My RPM was too high at WOT, and my top speed was too low. Going from a 17 to a 19 brought my RPM down and speed up. And actually, my speed didn't increase as much as it could because I went with the 4 blade for hole shot instead of the 3 blade for top speed.