Needing Spare Prop

[wallychaser]

I just purchesed a 2012 Yamaha 150, it came with a 19M 3 blade prop. I'm the kind of guy that believes that you should always carry a spare, just in case. I'm glad I did once before, saved a fishing trip. The current 19M gets me out of the hole extremely fast and I dont have to trim down far at all with a top end at about 44mph, this was with 4 people and equipment in the boat. Should I be looking at something higher as the main prop and put the 19 as the spare. I was thinking trying a 21. I dont want to go to stainless at this time. Any suggestions.

Thanks
Nick

 

[jestor68]

Re: Needing Spare Prop

I assume that you know what rpm your motor is turning at WOT. Check the owner manual for the WOT rpm range. Most four strokes should be turning about 6000 rpm at WOT.

Make your adjustment(s) based on the fact that one inch of pitch equals 150-200 rpm change.

 

[wallychaser]

Coming back to this... The "19 M" that was on it is a 14" diameter, if I stay with a 19 pitch but move to a 14.5" diameter, will I see any top end difference? I suspect I will loose some hole shot, but with the current 19 M it jumps out like a jack rabbit., so I'm not too worried about that. It currently runs in the spec'd WOT range.

 

[wallychaser]

Coming back to this... The "19 M" that was on it is a 14" diameter, if I stay with a 19 pitch but move to a 14.5" diameter, will I see any top end difference? I suspect I will loose some hole shot, but with the current 19 M it jumps out like a jack rabbit., so I'm not too worried about that. It currently runs in the spec'd WOT range.

 

[walleyehed]

In the range??? Top or bottom???? If max is 6000 then you should be no lower than 5500-ever. If you "always have" this type of load then you need to be at the top 200RPM of your range. When choosing a spare it's usually best to go with the same pitch- or 1 step lower if you are in the bottom of the range.

 

[walleyehed]

The larger diameter will usually give you better hole shot but on your style of boat it "may" cost a tad on top-end, all depends on blade type, model, etc...

 

[wallychaser]

Thanks, my full operating range is 5000 - 6000 (manual spec), which I can creep up to 6000 when trimming up, not out... I certainly don't need more hole shot, I feel short changed on my top end. As I trim, my RPM's go up but no additional speed, it's like I loose grip (ventilation - ?) A local dealer suggested staying with a 3 blade 19 pitch but try a 14.5 diameter. I'm running my 150 on a 19' alum Harbor Craft, I get about 43mph out of it, maybe that's all I should expect? I'm not interested in a stainless, I spend a lot of time on Northern Canadian lakes, too many rocks. Appreciate your wisdom.

 

[walleyehed]

If you do much trolling, stay with 19. If trolling is not part of your normal day on the water then a 21 would be "OK" but not my first choice because your 19P is producing Max rpm with a normal load-Best case. If the 21P was not in the same model so geometry is the same, you "may" see a bigger change than you want to.
It could drop to 5500-5600 which may be in the range but best economy, performance and engine longevity will be at 5800-6000. That's why a few years back they upped the rpm recommended on about all 4-strokes.

 

[wallychaser]

I tested a 21 Pitch x 14.3" diameter, dropped RMP as expected to 5000 with GPS speed of 47, I could trim to get more RPM but no extra speed. I Tried a 19 Pitch x 14.5", RPM of 5600 at GPS speed of 45, again I can trim up to get more RPM with no extra speed. (Hole shot is awesome), I understand that an aluminum wont grab as well as a stainless will when trimming up. A question would be "IF" I decided to go to a stainless steel prop, how much more performance can I expect? Is it worth the spend? Patience, I'm trying to learn...