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High Altitude Boating Question

Post By: AddictedAngler      Posted: 8/12/2017 4:23:43 PM     Points: 781    
Alright, need some opinions here. I plan on buying a 3 blade aluminum prop for the few trips I make a year Laker fishing at Spinney, Granby, Will fork and similar elevations.

My boat runs 300 RPM's lower than max output specs in the Denver Metro with a 21 pitch R rotating stainless 3 blade. I get 5200 and max spec is 5500.

I have a 200hp Yamaha Vmax 2-stroke.

Deciding between a 17 pitch or a 19 pitch. Thoughts?

I forgot critical information let me know. First prop I've ever bought.
 Reply by: catchem      Posted: Aug. 12, 6:25:16 PM     Points: 31    
Jim's Prop Shop in Denver can tell you the best options. 303-420-7815
 Reply by: shiverfix      Posted: Aug. 12, 10:30:36 PM     Points: 2913    
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.
 Reply by: AddictedAngler      Posted: Aug. 13, 2:08:06 AM     Points: 781    
Thnx for the replies. I will call Jim's Monday.

I think 19 is the way to go for mine Shiver.
 Reply by: malty falcon      Posted: Aug. 13, 4:49:12 PM     Points: 3617    
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: team FMFO      Posted: Aug. 13, 8:33:50 PM     Points: 3866    
I have been on this site for over 5 years and I would say if Ajax chimes in on this LISTEN to what he has to say , period ! Good luck .
 Reply by: Ajax5240      Posted: Aug. 14, 10:04:35 AM     Points: 21477    
^^^ Hey, thanks for the vote of confidence!!

When it came time to get a new prop for the boat I picked up this season, I even had to seek an expert opinion.

Most local shops have the props in stock, and will take return/exchange as long as you don't damage the prop. Basically they say "try a 19, and bring it back if it isn't right"

Science via trial and error!

There is a ratio of prop pitch to RPM that can get you very close.

If you're up north here, go to island lake marine.
 Reply by: shiverfix      Posted: Aug. 14, 10:49:44 AM     Points: 2913    
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.