Prop question

[fishhrd]

I have a 209 grady that we repowed with a 225 honda. The prop I have now is a 141/2 by 19 pitch and we can only turn 5100 rpms. Someone told me I need to get a 151/2 in diameter because I always want the largest diameter possible and then work from pitch then. The rpm range is 5000 to 6000.

Is this correct?
And does anyone else running the same setup that can help?
Thanks,
Matt

 

[catch22]

I'm certainly no expert, but imo, increasing the diameter, (same pitch) will not increase your rpm's, if anything they'll drop. Larger diameter props are for heavier loads, (more bite). Bigger boat, bigger prop. 14 1/2" diameter is typical for that set up.
If your boat performs fine with your current prop, (except for the rpm's), I think reducing the pitch to 17 or 18 would do the trick. It should also help with getting up on plane a little. Typically, I think you get around 200/300 rpm's per inch of pitch.
I would talk to a prop reconditioning shop and see what they recomend. I think they can adjust the pitch, (even with an ss prop) +/- 1 inch. If not, some shops/dealers will do an exchange for your existing prop, providing it's in good condition.

 

[fishhrd]

catt22 thanks,
If someone with basically the same setup could let me know what they are running maybe I can figure out how to get close to 6000 rpms. Right now I think it is hard on my motor running the way it is.

 

[gradyfish22]

More then likely, changing your pitch will give you better results then bigger diameter. Your best bet is talk to your Honda dealer and ask them what they recommend. You are under propped right now, especially if those numbers are not at full load. You should run the boat with full gear and fuel to test your props. You are at the low end of your recommended rating, you need more bite which pitch can help. A bigger prop can also, but often going too big is bad and will be harder for the engine to turn and will not allow you to reach higher rpm's as well. The largest diameter prop is not always the best. It really depends on your boat type and weight.

 

[catch22]

catt22 thanks,
If someone with basically the same setup could let me know what they are running maybe I can figure out how to get close to 6000 rpms. Right now I think it is hard on my motor running the way it is.

Try asking your Honda dealer if they have a 14 1/2 x 17 prop you could try out, (with the intention of buying). Ask them about credit for your existing prop too. I think that would put you right on the money.

 

[jimmy's marine service]

I'm certainly no expert, but imo, increasing the diameter, (same pitch) will not increase your rpm's, if anything they'll drop. Larger diameter props are for heavier loads, (more bite). Bigger boat, bigger prop. 14 1/2" diameter is typical for that set up.
If your boat performs fine with your current prop, (except for the rpm's), I think reducing the pitch to 17 or 18 would do the trick. It should also help with getting up on plane a little. Typically, I think you get around 200/300 rpm's per inch of pitch.
I would talk to a prop reconditioning shop and see what they recomend. I think they can adjust the pitch, (even with an ss prop) +/- 1 inch. If not, some shops/dealers will do an exchange for your existing prop, providing it's in good condition.

not good advice,but not bad either...pitch,every inch will give 150rpm change,use that as a guide...increasing diameter will decrease rpm...

 

[catch22]

I'm certainly no expert, but imo, increasing the diameter, (same pitch) will not increase your rpm's, if anything they'll drop. Larger diameter props are for heavier loads, (more bite). Bigger boat, bigger prop. 14 1/2" diameter is typical for that set up.
If your boat performs fine with your current prop, (except for the rpm's), I think reducing the pitch to 17 or 18 would do the trick. It should also help with getting up on plane a little. Typically, I think you get around 200/300 rpm's per inch of pitch.
I would talk to a prop reconditioning shop and see what they recomend. I think they can adjust the pitch, (even with an ss prop) +/- 1 inch. If not, some shops/dealers will do an exchange for your existing prop, providing it's in good condition.

not good advice,but not bad either...pitch,every inch will give 150rpm change,use that as a guide...increasing diameter will decrease rpm...

Like I said, I'm no expert, but explain something to me. If you have a larger diameter, and the same pitch, wouldn't it slow the prop down, because of more surface area and friction?

 

[catch22]

Worth reading;

http://www.solarnavigator.net/propellers.htm

"Bigger diameter is like adding bigger tires to your car: more traction or more appropriately, less slip. Larger diameters put more load on your motor because they move more water though so don't over do it. A blade moving through water does experience drag . The less blade there is (less diameter), the less the drag will be. Provided your motor and prop produce enough thrust, when you DECREASE your prop diameter your speed will increase a bit because there is less drag".

 

[ocnslr]

More then likely, changing your pitch will give you better results then bigger diameter. Your best bet is talk to your Honda dealer and ask them what they recommend. You are under propped right now, especially if those numbers are not at full load. You should run the boat with full gear and fuel to test your props. You are at the low end of your recommended rating, you need more bite which pitch can help. A bigger prop can also, but often going too big is bad and will be harder for the engine to turn and will not allow you to reach higher rpm's as well. The largest diameter prop is not always the best. It really depends on your boat type and weight.

All good advice. Except you are over-propped when you can't get up to the correct RPM.

Are you seeing that 5100 RPM when trimmed up, or when trimmed all the way down?

With a lightly-loaded boat, you should be close to the top of the RPM range when trimmed up, but not so far that the prop is cavitating. Usually done by trimming up until you hear/sense that the prop is losing bite, then trimming back down until the prop is running properly.

Running "over-propped" means that the load on the engine is too great all all speeds. This is not good for the long-term health of the engine.

But your 5100 seems really low, even with a 19" pitch. Going to 17" would still be too low in the band, and you should be able to swing that pitch.

Is the bottom clean?

Are you sure the boat hasn't "gained a lot of weight" (i.e. water)?

Are you sure the throttle is all the way open? Has a mechanic checked the linkage adjustment?

Brian

 

[JUST-IN-TIME]

prop that boat to 6150 rpm at 80% loaded

 

[gradyfish22]

Oncslr, your right about the over and under propped, I wrote and did not proof read.

 

[Grog]

The 17p may be close but try to "sample" a friend's or dealer's prop. The cup of the prop also plays an important part of the load but your RPM's are 1000 low. If you go out in rough conditions try to get a 15 1/2" prop. What was your old engine combo?

 

[jimmy's marine service]

Worth reading;

http://www.solarnavigator.net/propellers.htm

"Bigger diameter is like adding bigger tires to your car: more traction or more appropriately, less slip. Larger diameters put more load on your motor because they move more water though so don't over do it. A blade moving through water does experience drag . The less blade there is (less diameter), the less the drag will be. Provided your motor and prop produce enough thrust, when you DECREASE your prop diameter your speed will increase a bit because there is less drag".

clearly you're missing what i wrote...increasing diameter will increase rpm,read what i wrote again... you're wrong with your rpm guess with changing pitch....

please forgive me...that genius "catch22",the knower of all things,pointed out that i made a mistake...clearly,i made a mistake...what i meant to state was "increase diameter and rpm will decrease"...please forgive me...i realize that i'm a complete moron,or was it idiot ??? i don't know...mabey,just mabey,i'll be lucky enough for that genius mr catch 22 to correct me...after all,he certainly knows much more than i would...i mean,he has his own shop too,right ??? :roll: :roll:

 

[jimmy's marine service]

I'm certainly no expert, but imo, increasing the diameter, (same pitch) will not increase your rpm's, if anything they'll drop. Larger diameter props are for heavier loads, (more bite). Bigger boat, bigger prop. 14 1/2" diameter is typical for that set up.
If your boat performs fine with your current prop, (except for the rpm's), I think reducing the pitch to 17 or 18 would do the trick. It should also help with getting up on plane a little. Typically, I think you get around 200/300 rpm's per inch of pitch.
I would talk to a prop reconditioning shop and see what they recomend. I think they can adjust the pitch, (even with an ss prop) +/- 1 inch. If not, some shops/dealers will do an exchange for your existing prop, providing it's in good condition.

not good advice,but not bad either...pitch,every inch will give 150rpm change,use that as a guide...increasing diameter will decrease rpm...

Like I said, I'm no expert, but explain something to me. If you have a larger diameter, and the same pitch, wouldn't it slow the prop down, because of more surface area and friction?

that's true,exactly what i stated,increase diameter and rpm decreases...if the pitch is the same,and you increases diameter,the rpm will drop...

do a search of my posts,i've explained exaclty how to prop a boat,follow exactly what i posted and you'll learn alot...

 

[catch22]

Are you on drugs?....

First you say, "clearly you're missing what i wrote...increasing diameter will increase rpm,read what i wrote again... you're wrong with your rpm guess with changing pitch...." (increase diameter will increase rpm)

Then you say, "not good advice,but not bad either...pitch,every inch will give 150rpm change,use that as a guide...increasing diameter will decrease rpm..." (increase diameter will decrease)

You are the one who was wrong. Instead of simply admitting it, you come back with your typical, "read my posts" comment. As if to say, if you want to know anything, the heck with what anyone else has to say, just go back and read my posts, because I'm the greatest.... give me a break. Your the one who needs to do some reading, (you'll learn a lot). Maybe you'll actually learn something, instead of basing everything on what you think you know.

This, just like any other post, is about giving out genuine, reliable and friendly advice. Something you don't have a clue about.

 

[jimmy's marine service]

Are you on drugs?....

First you say, "clearly you're missing what i wrote...increasing diameter will increase rpm,read what i wrote again... you're wrong with your rpm guess with changing pitch...." (increase diameter will increase rpm)

Then you say, "not good advice,but not bad either...pitch,every inch will give 150rpm change,use that as a guide...increasing diameter will decrease rpm..." (increase diameter will decrease)

You are the one who was wrong. Instead of simply admitting it, you come back with your typical, "read my posts" comment. As if to say, if you want to know anything, the heck with what anyone else has to say, just go back and read my posts, because I'm the greatest.... give me a break. Your the one who needs to do some reading, (you'll learn a lot). Maybe you'll actually learn something, instead of basing everything on what you think you know.

This, just like any other post, is about giving out genuine, reliable and friendly advice. Something you don't have a clue about.

hey...reread what i posted...it clearly states what i said...truth is..i've got the flu right now and i'm pretty bored...i've never given bad advice,unlike you...i certainly don't believe i know everything..but if i'm wrong i state i'm wrong...
increasing diameter will decrease rpm...reread what i posted originally...reread anything i posted concerning props and propping a boat...clearly i know what i'm talking about...

and for the record...i've probably forgotten more than you will ever know... :wink: :wink:

 

[catch22]

YOUR THE ONE WHO NEEDS TO RE-READ IT!!!!!

Can you read?

I just quoted you!!!

First you said increases, then you said decreases. Going back and re-reading your post isn't going to change a thing, lol. Do you get it?.... do you understand?...earth to jimmy...earth to jimmy.... YOU ARE WRONG.

Well, which is it Mr. "I've forgotten more then you'll ever know"? Please come up with something better than, "read my post"....PLEASE.

For the record.... you truly are one thick headed idiot. And having the flu is no excuse.

Now, thanks to you, this thread has gone down the drain.

 

[jimmy's marine service]

YOUR THE ONE WHO NEEDS TO RE-READ IT!!!!!

Can you read?

I just quoted you!!!

First you said increases, then you said decreases. Going back and re-reading your post isn't going to change a thing, lol. Do you get it?.... do you understand?...earth to jimmy...earth to jimmy.... YOU ARE WRONG.

Well, which is it Mr. "I've forgotten more then you'll ever know"? Please come up with something better than, "read my post"....PLEASE.

For the record.... you truly are one thick headed idiot. And having the flu is no excuse.

Now, thanks to you, this thread has gone down the drain.

thread went down the drain...because i pointed out something ??? idiot?? what the hell is that supposed to mean ??? ever read something i wrote that was incorrect ??? i'll answer that,NO !!! the advice i give is quite evident in the amount of "pm's" i get from members of this board...so do me a favor save it....if you've got a problem,pick up the phone...609-214-7556...guys who wanna scream and yell,like you,really facinate me,you gotta problem,pick up the phone and tell me what's on your mind...here's the number again,ill type slow for you...609-214-7556...i'll be up for a while...can't sleep,coughing too much...you're more than welcomed to call me... :wink:

 

[catch22]

"ever read something i wrote that was incorrect ???"

I JUST DID... and you STILL don't get it, (too thick).

For the record... I get PM's too.... big deal.

 

[jimmy's marine service]

"ever read something i wrote that was incorrect ???"

I JUST DID... and you STILL don't get it, (too thick).

For the record... I get PM's too.... big deal.

i find it hard to believe anyone would ask you for advice... :wink: :wink:

i just went back and edited what i stated...for the record,you're wrong,as usual...every inch in pitch usually equates to 150 rpm,not the 200-300 you stated...be sure to correct that huh ???