ADVICE Please! pitch vs diameter

[Pas Bon]

19 ft baystealth 115 yamaha 4 stroke


13" 3 blade 19 pitch works perfect with a light load

BUT

When I REALLY load it down it is a DOG

could this be solved with a same diameter prop with a 17 pitch

or a smaller diameter prop and the same pitch?

 

[steelespike]

Re: ADVICE Please! pitch vs diameter

Would be good for us to know your present wot (wide open throttle)rpm and speed.
Don't worry about diameter as long as it seems in line with your 13"
ie: as pitch goes down diameter usually goes up. Yes same brand,same model 17 will add "about" 400 rpm and improve performance.

 

[Pas Bon]

Re: ADVICE Please! pitch vs diameter

WOT is close to 6K when trimmed up just right...but NOT with a heavy load..thats why I'm thinkin about a second prop for those heavy loads.

 

[1kruzer1]

Re: ADVICE Please! pitch vs diameter

It's very common to switch to a lower pitch prop for heavier loads, holeshot for waterskiing, etc. You need to know your engines max RPM rating and be aware while operating to throttle back when at full speed to keep the tach reading at or below redline.

 

[walleyehed]

Re: ADVICE Please! pitch vs diameter

Heavy loads require props built for such...usually the diameter is larger with more blade area..
From what you have described you need more blade to carry the load not more/less pitch. 13" diameter on a 4-stroke is SMALL for a 115. 13-1/2 to 14" dia. would be best.

 

[Pas Bon]

Re: ADVICE Please! pitch vs diameter

Heavy loads require props built for such...usually the diameter is larger with more blade area..
From what you have described you need more blade to carry the load not more/less pitch. 13" diameter on a 4-stroke is SMALL for a 115. 13-1/2 to 14" dia. would be best.

the problem is getting going..0 to plane speed is the killer...wouldn't
more prop just increase the problem? The motor just dogs along and can't get the rpm needed to get going. I need to get to plane quicker with a heavier load.

 

[Bondo]

Re: ADVICE Please! pitch vs diameter

the problem is getting going..0 to plane speed is the killer...wouldn't
more prop just increase the problem?

Ayuh,... You're still confusing Diameter, 'n Pitch...

Buy the Pitch you need,.... Diameter will work itself out along the way...

 

[lonesouth]

Re: ADVICE Please! pitch vs diameter

can someone explain why diameter doesn't matter? Best I can tell, my 115 was originally propped with a 14" 17* and now they recommend 13 3/4". The physics side of my brain tells me diameter should absolutely make a differnce, although likely not as much as pitch.

 

[Bondo]

Re: ADVICE Please! pitch vs diameter

can someone explain why diameter doesn't matter? Best I can tell, my 115 was originally propped with a 14" 17* and now they recommend 13 3/4". The physics side of my brain tells me diameter should absolutely make a differnce, although likely not as much as pitch.

Ayuh,.... Diameter is a function of blade Design....

The Engineer that designs,+ tests the prop determines the diameter necessary for the design objectives...

Diameter is also somewhat a function of lower unit diameters...
A certian class of hp motors uses a certian diameter class of props...