propeller pitchs

[circle hook]

I just bought a 90 HP Mercury and it came with (2) props one is a 13 pitch and the other is a 19 pitch, witch of the two will give low end torque and witch one is for top end speed thanks Bob

 

[saumon]

Re: propeller pitchs

13p give better hole shot
19p give top speed

BUT, by the way, there's a lot more when selecting the right prop than choosing between hole shot and speed, the single most important point being revving the engine at the right rpm range when at WOT with your average load.

And there's too much difference, as i think, between a 13p and a 19p to be used efficiently on the same boat/engine combo. If the 13p is ok, the 19p will severely lug your engine, wich is a sure way to destroy it and if, on the other way, the 19p is right, the 13p will make the engine rev past 6000 rpm, wich isn't good either.

If your engine is a 2-stroke, WOT rpm range is 5000-5500, so open it at WOT with an average load and choose the prop that put you at 5200-5300, that will give you some ?play? to stay within the recommended range if you happened to have a person more or less aboard.

 

[j_martin]

Re: propeller pitchs

13p give better hole shot
19p give top speed

BUT, by the way, there's a lot more when selecting the right prop than choosing between hole shot and speed, the single most important point being revving the engine at the right rpm range when at WOT with your average load.

And there's too much difference, as i think, between a 13p and a 19p to be used efficietly on the same boat/engine combo. If your engine is a 2-stroke, WOT rpm range is 5000-5500, so open it at WOT with an average load and choose the prop that put you at 5200-5300, that will give you some ?play? to stay within the recommended range if you happened to have a person more or less aboard.

I have a very fat fishing partner and a fast 150 hp bass boat. I go down 4 inches in prop pitch when I haul this guy.

6 is a little much unless you have a fairly heavy boat and widely varying loads. The trick is the engine should run in the specified WOT range. The way the motor loads, that one reading will match the motor to the load throughout the range on most boats.

BTW, the way to think about prop pitch: -> The pitch is the number of inches the prop will theoretically screw through the water with each revolution.

hope it helps
john

 

[circle hook]

Re: propeller pitchs

what I was planning to use the boat for was towing so speed is not a factor I guess low end power to pull with would fit the task better so you thing the 13 pitch would do the better job thanks Bob

 

[saumon]

Re: propeller pitchs

what I was planning to use the boat for was towing so speed is not a factor I guess low end power to pull with would fit the task better so you thing the 13 pitch would do the better job thanks Bob

Re-read the answers! We never say that the 13p would do a better job. We say that you should try it and check your tach to see if it put your boat/engine combo in the recommended rpm range at WOT. Maybe it will do, maybe you'll need a 15p, a 17p, i dunno.

There's also a prop section with zillions of very informative threads upper in the main board page...

 

[circle hook]

Re: propeller pitchs

thanks will try running wot and see what the tack reads again thanks Bob