Pitch on prop?

[Nasty]

If a 90 hp has a 14 x 18 pitch and pushes a boat 40mph, will adding 115hp with the same pitched prop add more top end speed? Or, should a new prop with 14 x 20 be added to get the full benefit from the bigger motor? I know a little about props... just quite not enough. Any help is appreciated! I won't be wet testing because it will be a new boat and I know someone with the same boat with that 90 and that 14 x 18 pitch. Thanks fellas.

[Reel Bender]

No.

Theoretically both motors will have the same top end speed if both motors top out at the same RPM. Your speed is based on the RPMs and Pitch of the prop. The 115 gives you more Horsepower, which may help you to achieve top speed quicker.

[Reel Bender]

The 115 may allow you to run a prop with more pitch that will allow you to obtain a higher top speed.

[Nasty]

So, your understanding is that the additional hp won't make a big difference. I would need to go with a bigger pitch too get the benefit from bigger motor?

[Gerald]

There are web sites that have information .....Charts to calulate.....what prop "should" be best.

But I don't know what web site to go to. Can someone help him.

[Reel Bender]

Here is a little info that may be helpful:


http://www.boatinglife.com/article/W...ropeller-Pitch


http://www.rbbi.com/folders/prop/propcalc.htm

[fishinpox]

call power tech tell them the outboard size the hull design/brand length ect and what u wanna do with the boat and they will set u up with the best prop for the application u choose

[flounder_smacker]

lets see how i can explain this and make sense. say that 90hp revs out at 5500 and the 115 revs out at 5500 also. if you turn the same prop on diff motors at the same rpm you will get the same speed. but if your running that same prop from the 90 on the 115 the 115 has more power and will turn the prop past 5500 and hit the rev limiter. when going to a larger motor it allows you to turn a larger pitch prop. more pitch = more speed. pitch on a prop means every rotation you move that much. say if you have a pitch of 18 then every revolution you will move 18inches. if you get 18 inches out of a 18inch prop that is perfect. but most people dont. props slip in the water due to numerous things. they have a prop slip calculator that lets you put the best pitch and diameter for your boat. putting the best prop on your boat can take some time but most boat manufactures figure all that out for you and a simple call will get you in the right direction.

[flounder_smacker]

also find out the recommend top rpm for your motor and you usually want to get a pitch on it that lets your run at that rpm but not over it. also putting to much pitch can bog your motor down and not let it run smooth causing wear and bad fuel consumption.

[Nasty]

I figure the best way to make sure your pitched right is to run it at wot reaching its max rpm. Also, I figure to do it with a light, normal, or heavy load? My guess is a light load. Is that right?

[Dink]

check this out..........good read and vids!!!
http://www.boattest.com/Products/Pro...ubID=1230&ID=8

[Nasty]

Thanks for the website! It was very informing! Here is a new question... There is a boat that will reach 50 mph at wot being pushed by a 115 2-stroke yamaha with a 13.25 x 22 prop. Will the same identical boat reach 50 mph at wot pushed by a 115 Suzuki or Yamaha 4-stroke with a 14 x 22 prop? Or a speed/performance very close?

[jahosaphet]

Originally Posted by Big Nasty

Thanks for the website! It was very informing! Here is a new question... There is a boat that will reach 50 mph at wot being pushed by a 115 2-stroke yamaha with a 13.25 x 22 prop. Will the same identical boat reach 50 mph at wot pushed by a 115 Suzuki or Yamaha 4-stroke with a 14 x 22 prop? Or a speed/performance very close?

that 115 4 stroke will not turn the bigger diamiter prop, but let me give you the best advice you can take... every boat is different... ever motor is different, even though they may be the same model. you will need to water test each particular setup and read your tach at wot, but generally the 4 stroke will not turn that big prop as eficeint as the 2 stroke

[boben1968]

Run the 115 with the 18 pitch prop with boat loaded. Check RPMS you want to at the at the top of RPM range. ie 5800. You can gain approx 200 RPMS for every inch of pitch change. Good luck...