advice on pitch for Yammy F115

[bhuffstutter]

I have a 2007 Yamaha F115 on a 2007 Duckworth Advantage Classic 19.5'. My current prop is a 13x19, at WOT I'm hitting about 6300 rpm. My range is 5000-6000 rpm. On a whim I bought a stainless 13x21 but have not tried it yet. Was looking for opinions on how the 13x21 ss will perform on this boat. I know it should lower my rpm about 300-400 but I was getting feedback from the local boat shop that it may work the motor too hard. Any feedback or fact based opinions would be appreciated. thanks....

 

[bhuffstutter]

Re: advice on pitch for Yammy F115

Let me provide a little more info to see if anyone has any input on the question: The boat weighs approx 1500 lbs dry, the F115 is 402 lbs, the kicker 9.9 suzuki 107 lbs, I have an electric trolling motor with 2 marine batteries up front guessing about 120 lbs, 42 gal of fuel approx 340 lbs and my dog, me and gear about 250 lbs. Total approx 2700 lbs. As stated before WOT running 6300 rpm at 43 mph would like to lower rpm to about 5900 rpm. Want to go with ss prop, thought about keeping the same pitch but didn't think at the time that it would effect the rpm so I went with a 21 pitch. Don't want to test the 21 pitch because once its in the water I can't return it. So looking for input to see if it will do what I need before putting it in the water. Should I have stayed with a ss 19 Pitch, went with a ss 20 Pitch? I'm just a little hesitant to put the new prop in the water if I won't be happy with the result. Pimary use for boat is fishing local lakes and the puget sound and pulling my kids on a tube. Thanks in advance....

 

[countvlad]

Re: advice on pitch for Yammy F115

Let me provide a little more info to see if anyone has any input on the question: The boat weighs approx 1500 lbs dry, the F115 is 402 lbs, the kicker 9.9 suzuki 107 lbs, I have an electric trolling motor with 2 marine batteries up front guessing about 120 lbs, 42 gal of fuel approx 340 lbs and my dog, me and gear about 250 lbs. Total approx 2700 lbs. As stated before WOT running 6300 rpm at 43 mph would like to lower rpm to about 5900 rpm. Want to go with ss prop, thought about keeping the same pitch but didn't think at the time that it would effect the rpm so I went with a 21 pitch. Don't want to test the 21 pitch because once its in the water I can't return it. So looking for input to see if it will do what I need before putting it in the water. Should I have stayed with a ss 19 Pitch, went with a ss 20 Pitch? I'm just a little hesitant to put the new prop in the water if I won't be happy with the result. Pimary use for boat is fishing local lakes and the puget sound and pulling my kids on a tube. Thanks in advance....

no... stay with the 21 ... 6300 is way too high whatever the boat shop told you... i think you should find another shop... theres a reason why its the "Recomended manufacturers WOT range" ... just like you said 21 will bring you down to 5900 and thats where you want to be....

im actually surprised your rpms are so high with that motor,prop and the weight of the boat....

hwsiii help me out here

and btw everyone of us learn it the hard way, through trial and error good luck and keep us updated

 

[crb478]

Re: advice on pitch for Yammy F115

How high is your motor set up on your boat now? I would think that the 21 pitch would be about right for your boat, but you may well want to get Hwsiii to run a prop calculation for you as he has them dialed in much more that I do. Dhadley could also probably give you great advise with is vast experience. If you can still raise the motor you may well be able to get a full 6000 rpm with the stainless prop, but the only good way to verify that is to run it. If I were you I would see if the above mentioned pair could help me out before committing to the trial.

 

[countvlad]

Re: advice on pitch for Yammy F115

I have a 2007 Yamaha F115 on a 2007 Duckworth Advantage Classic 19.5'. My current prop is a 13x19, at WOT I'm hitting about 6300 rpm. My range is 5000-6000 rpm. On a whim I bought a stainless 13x21 but have not tried it yet. Was looking for opinions on how the 13x21 ss will perform on this boat. I know it should lower my rpm about 300-400 but I was getting feedback from the local boat shop that it may work the motor too hard. Any feedback or fact based opinions would be appreciated. thanks....

ohh.. fact based opinions? before the tach didnt work used to have a 19p aluminum... once the new tach was installed i was at 4800 WOT... switch to a 15p SS and rpms went up to 5600 ..... every pitch is 200rpms

recomeneded WOT for a 120HP 1989 Johnson is 5000-6000.... right now im trying to get the WOT rpm closer to 5800...

 

[hwsiii]

Re: advice on pitch for Yammy F115

B, can you tell us what problems you are trying to cure. Are you changing to a stainles from an aluminum prop, in most cases you should see a drop of 400 to 600 RPM from a 19 to a 21" pitch in the same make and model of prop. And Vlad is right, 6,300 RPM is too high for that motor. But even with that much drop in RPM you should still be at 5,700 to 5900 RPM and that is well within the top RPM paramaters for that motor. But changing from aluminum to SS it doesnt always work that way. RPM drop or rise between pitch changes dramatically as you get into the lower pitches like a change from a 12" pitch to a 10" pitch is about 600 RPM per inch not 2 inches. But if you have a little more height to raise the motor as CRB states you can probably gain back another 150 or more RPM.
Right now you have a power to weight ratio of about 25 pounds per HP and I show your gear ratio to be 2:1, please verify that, and if that is true you have a prop slip of 24% which is high in my opinion, you should be able to reduce that. I think you ought to be down around about 12 to 14% of prop slip or less.


Prop Change

Prop Slip

What were you expecting from the change to a SS prop and what make and model of prop did you buy.


H

 

[bhuffstutter]

Re: advice on pitch for Yammy F115

I appreciate all the replys so far it sounds like I just need to try the 21p ss and see what happens.
Hwsiii,
The ss prop I got is a Michigan Wheel Apollo Prop #993146 Hub #103. The prop on the boat is OEM aluminum. My goal is to lower the rpm to normal operating range. As the motor sits when trimmed all the way down the cav plate sits about 1or 2 inches below the hull. It is on the lowest setting on the mounting plate so there is room to raise if needed. When I got the boat the rpm gauge was on the wrong setting from the dealer and I was instructed by them to set it on 5, I think its right because that?s the only position it works correctly in and my idle is about 800 rpm at operating temp unless the gauge is wrong?? My gear ratio should be what it is coming from the factory so I?m not sure, how do I verify that? I?m a little confused on the slip what causes it or how its calculated, can you explain it a little.

 

[countvlad]

Re: advice on pitch for Yammy F115

I appreciate all the replys so far it sounds like I just need to try the 21p ss and see what happens.
Hwsiii,
The ss prop I got is a Michigan Wheel Apollo Prop #993146 Hub #103. The prop on the boat is OEM aluminum. My goal is to lower the rpm to normal operating range. As the motor sits when trimmed all the way down the cav plate sits about 1or 2 inches below the hull. It is on the lowest setting on the mounting plate so there is room to raise if needed. When I got the boat the rpm gauge was on the wrong setting from the dealer and I was instructed by them to set it on 5, I think its right because that?s the only position it works correctly in and my idle is about 800 rpm at operating temp unless the gauge is wrong?? My gear ratio should be what it is coming from the factory so I?m not sure, how do I verify that? I?m a little confused on the slip what causes it or how its calculated, can you explain it a little.

the cavit plate should be at the same level with the bottom of the hull.... can you take some pictures?? show us how low does the plate sits in reference to the bottom?

im not 100% positive what kind of a tach you are using but acording to the faria's instructions you have 12 poles = position#6

make sure the tach is working correctly, very important... even though the motor is new doesnt mean either the tach or the power pack is not bad....

http://forums.iboats.com/showthread.php?t=190636

 

[hwsiii]

Re: advice on pitch for Yammy F115

B, you can go to Yamahas webite and check on gear ratio.
Prop Slip is the difference between the distance a prop moves through the water in one revolution and what it would move through the water if water was a soild, think of a screw into wood if it had a 19" pitch for every revolution of the screw it would move into the wood 19", but in water the water can let the prop slip. So it means your prop right now is only moving about 15" for every revolution it turns. Hope this makes it easier to understand.


H

 

[bhuffstutter]

Re: advice on pitch for Yammy F115

I will see if I can figure out how to post some pics of the cav plate to hull up on here, be patient I've got a lot on the plate right now so I will do my best. The gear ratio from yamaha web site is this:

F115 Gear Ratio: 13:28 (2.15)

F150 Gear Ratio: 28:14 (2.00)

Again mine is a F115, is that a 2-1 ratio??

Anyone know an easy way to post some pics on here???

 

[bhuffstutter]

Re: advice on pitch for Yammy F115

I will have to check on the tach setting, not really sure at this point....

 

[junior1113]

Re: advice on pitch for Yammy F115

the cavit plate should be at the same level with the bottom of the hull.... can you take some pictures?? show us how low does the plate sits in reference to the bottom?

im not 100% positive what kind of a tach you are using but acording to the faria's instructions you have 12 poles = position#6

make sure the tach is working correctly, very important... even though the motor is new doesnt mean either the tach or the power pack is not bad....

http://forums.iboats.com/showthread.php?t=190636

plate SHOULD be level wih bottom of boat. only on a flat hull boat. mines up about 4" to get best performance. most ss props like to ride closer to surface. on every v hull boat ive delt with plate is between 1"-5" above bottom of hull. if this boat has a pad it should be up at least a good two inches. run the 21 and come back with #'s. setup means so much.

 

[hwsiii]

Re: advice on pitch for Yammy F115

B, since you found out the gear ratio was 2.15:1 that changes your prop slip to 18%. I do not know what type of hull you have on your boat as I don't recognize the manufacturers name. I can tell you that I personally am running a Michigan Apollo on my boat right now and I love it. It is a progressive pitch and has a fair amount of rake as well as cup. I am running mine on a flats boat and I am able to raise the bow as much as I ever need, even with nauticus SX trim tabs. It should reduce the amount of prop slip you are showing very much. I am very happy with mine.
After you get us some numbers we will run them and see what we can do about getting the motor RPM up to the maximum.


H

 

[bhuffstutter]

Re: advice on pitch for Yammy F115

hwsii,
Cool as soon as I get back in town I will try the new prop and post some numbers. It may take a week or so but I will get it up as soon as I can. Thanks...

 

[hwsiii]

Re: advice on pitch for Yammy F115

You are very welcome B, and I would like to see the numbers.


H

 

[ivar]

Re: advice on pitch for Yammy F115

From my experience with the F115 and going from a stock alum prop to a more agressive SS, that you'll lose a couple 100 rpms more than the pitch diff indicates.
But with that low engine mounting, you may gain those rpms back - and get better performance too by raising the engine on the transom

 

[bhuffstutter]

Re: advice on pitch for Yammy F115

Ok guys, sorry for being late on the numbers but been really busy anyhow, I put the 21p ss prop on and went out to the lake and could barely get over 5000 rpm with it topping out at about 37 mph. I made a few runs playing with the trim and the best I got was about 5500 rpm but my speed was down to about 32-33 mph shooting a big blast of water off the back of the boat. So my conclusion is that the 21p ss is way too much pich for my boat. I went ahead and got a 19p ss and will try that as soon as I get it on the boat. It sure would be nice to have one of those hydro jack plates to dial this thing in.