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Thread: Yamaha Prop Quandry

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    Member tlingitwarrior's Avatar
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    Default Yamaha Prop Quandry

    New-to-me boat (24 Sea Sport XL) came with 13 3/4 x 17 props on the twin Yamaha 150's. Worked great for me, I run them at 4000-4200, getting 27-30mph depending on seas and load, and 12.5-14.5 gph, also depending on load and seas. WOT I was able to get them up to max of 5400-5600 rpm. Talking with Buzz at Deweys and he said I needed a small prop to get RPM's up. Ok, I bit, and his shop sold me 14 1/2 x 15 Reliance props, which were crazy spendy. Two trips out now and I couldn't be more disappointed. Max RPM's didn't change, in fact on starboard engine they actually dropped. Engines are less fuel efficient now, I'm burning about 1.5-2 gph more than before. I do get a quicker hole shot, but that was never the issue or goal. So less max RPM and worse fuel economy ~ for $1,200 price tag! What am I missing here?? Their shop is closed today but will be bringing them back tomorrow for a chat. Also, I thought I was buying stainless props, after two quick trips here is what they look like. I can't believe this is "normal".

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    Member KantishnaCabin's Avatar
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    The question you should really be asking is what are you trying to accomplish? What you did do was prop your outboard down a pitch. If your goal was being able to get on step with a higher load, mission accomplished! The last numbers on the prop description are the pitch. 15 pitch is 15" of forward movement per one revolution of the prop. 17 pitch being 17" of forward movement etc. It's like a bicycle gear, the lower the number the faster you peddle and the slower you go. If you are trying to pitch up and you want more speed and fuel economy then you would go with a 19 or 21 pitch prop, known as speed props. 11,13 pitch props in that size range are known as work props. The first set of numbers are all about the outside diameter of the prop, and that is usually dictated by the size of the outboard. Bigger outboard can swing a bigger prop even though the pitch may be the same.
    Dewey's will usually let you exchange your props until you find the pitch you are happy with. Just ask.

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    Member tlingitwarrior's Avatar
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    I told them fuel economy was only goal, speed being last. I will bring them back tomorrow. Cant believe a prop would show rust that quickly.
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    Member spoiled one's Avatar
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    I thought you looked a bit "slow" as I passed you Saturday.

    Were your original props aluminum or stainless? Your original RPM numbers are with in the factory recommended parameters, but talking to many techs over the years they like to see those yammies spin up to 5500-6K. You can save about 50% purchasing online. No exchanges, but it might be worth it for you. I have purchased props through these guys: http://www.firstchoicemarine.com

    Spending my kids' inheritance with them, one adventure at a time.

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    Member KantishnaCabin's Avatar
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    Well, if economy is the goal and you are not typically hauling huge loads then you need to maintain hull speed and reduce engine rpm's. So you need to pitch up. Probably 19 or maybe 21. If you jump more than 2 pitch's you are really going to notice the reduced hole shot and load capability. However twin 150's on a 24ft boat is a lot of excess power. You have the right combination and should be able to play with it to find the sweet spot.

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    Member tlingitwarrior's Avatar
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    Yeah Pete the kids like a slow, easy ride. Your fishing recommendation was spot on, thanks! Stainless on the originals. They are back on the boat now. My normal load is three guys and gear for a weekend. By gear that usually means three cases of beer each- my guests are a thirsty bunch.......
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    Member spoiled one's Avatar
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    Quote Originally Posted by KantishnaCabin View Post
    Well, if economy is the goal and you are not typically hauling huge loads then you need to maintain hull speed and reduce engine rpm's. So you need to pitch up. Probably 19 or maybe 21. If you jump more than 2 pitch's you are really going to notice the reduced hole shot and load capability. However twin 150's on a 24ft boat is a lot of excess power. You have the right combination and should be able to play with it to find the sweet spot.
    If he jumps up in pitch, his RPMs will drop and he will be lugging the motors. Remember this rule of thumb: For every 2" of propeller pitch, rpm's will change approximately 400 rpm's. As you drop in pitch, rpm's increase, and as you go up in pitch, rpm's decrease.
    Spending my kids' inheritance with them, one adventure at a time.

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    Member KantishnaCabin's Avatar
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    Lugging the motors is not a big of a deal as it was in the old 2stroke days. Those big fourstroke 150's have no trouble running 4k RPM for years. They are fuel injected and computer controlled. Gone are the days of carbs and 2stroke oil fouling plugs. 4strokes produce way more torque in the lower rpm range and run their best around that 4k range. Yes they can run 5500-6000 all day too, but you are just burning fuel for no real gain. If your mechanic tells you to run your Yammie at 6,000 rpm for the best performance then he is probably hoping for work and you should find a new mechanic.

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    this should be interesting ??

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    Member spoiled one's Avatar
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    Quote Originally Posted by KantishnaCabin View Post
    Well, if economy is the goal and you are not typically hauling huge loads then you need to maintain hull speed and reduce engine rpm's. So you need to pitch up. Probably 19 or maybe 21. If you jump more than 2 pitch's you are really going to notice the reduced hole shot and load capability. However twin 150's on a 24ft boat is a lot of excess power. You have the right combination and should be able to play with it to find the sweet spot.
    I believeyou misinterpreted what I wrote. I was not saying to run at 6K. I was just saying that you should be able to hit the upper half of the recommended operating range, so optimally he should be able to hit 5500 to 6K IMO. Like you said, he can run those motors all day long at 4K as long as he can hit those upper RPMs.
    Spending my kids' inheritance with them, one adventure at a time.

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    Quote Originally Posted by tlingitwarrior View Post
    Also, I thought I was buying stainless props, after two quick trips here is what they look like. I can't believe this is "normal".

    It depend on what you call normal.

    Stainless steel propellers can discolor and form areas of light rust. Brushed finish stainless props are more susceptible than brightly finished stainless steel props. Rust stains can occur from polluted water, galvanic corrosion from the boat or marina, or from oxygen depletion. The propeller can be easily cleaned with rubbing compound or Scotchbrite. Do not use steel wool. After cleaning, use chrome polish to protect the finish. Stainless steel props can also turn white from calcium or lime in the water. In this case, clean the prop with household mineral bath and tile cleaner. Again, do not use steel wool. Follow-up with chrome polish to protect the finish.

    Personal I would not try to clean it up with out more information.

    Good luck

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    Member tlingitwarrior's Avatar
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    So here is the quandry, i dropped in pitch and lost rpm at WOT. Also, since putting those props on my throttle controls are a bit funky, the starboard throttle needs to be pushed down a few more inches than the port in order for both engines to get same rpm. Wasnt that way before Deweys put the new ones on.
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    The F150 has VVT and a Rev limitation. The ECM will adjust engine performance and try to prevent damage if your running too close to redline. The throttle cable issue shouldn't have anything to do with the props, the starboard cable probably just needs adjustment. Kinda hard to mess up the throttle cables when changing a prop but they could have had the cowlings off when looking at something else. Spoiled is right, for the best all around performace you should want your max RPM's around 5,500-6,000 on the highest pitch prop you can. However, if you are looking to maximize fuel economy and you don't haul heavy loads don't be afraid to pitch up. If you are running a 23 pitch and max RPM is 5K and your cruise is 3800 rpm and you are still on step go for it. You will find that you won't like a real tall prop in heavy seas though. Big waves will knock you off step and you will have trouble powering through. Its a balance with boats power-speed-economy, which is most important to you.

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    Your difference in rpm has Alot to do with going with a different brand of prop. Even though they are both stainless the amount of cup built into a prop can vary dramatically. I ran the Yamaha brand Saltwater stainless series props on my yami 150. That motor loved that prop. Jumped out of the hole compared to the cheap black painted stainless props. Held and boat on step great in heavy seas and wasn't prone to cavitation in big seas either like many are. They run an inch larger diameter than the cheaper stainless and aluminum also. Yamaha is proud of them judging by their price tag but would buy them again. Great props. I also agree that you want to be able to hit your max rpm with a NORMAL for you load in the boat. Nothing worse than getting in bad water and having sluggish throttle response. Adjust your cruise speed to your best burn rate and run that rpm. Usually around 3800 on my 150. Good luck. Every boat and motor combo is different and it takes trial and error to dial one in. Most dealer will let you exchange props til you get it right. That is as long as you don't ding one. I was lucky when I bought my 1t0 new. Dealer let me take home a arm full of props and I spend one evening of testing and tuning to get what I wanted. Found the best performing aluminum prop for a spare, and the Yamaha Saltwater series as a main. What a difference that prop made over anything else I tried. And then the right diameter and pitch.

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    Member Sobie2's Avatar
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    Dewey's was correct in pushing you towards the Reliance props based on what you told them (economy is king) because Yamaha designed them specifically for their F150 fourstroke with fuel economy in mind and the geometry of the blade is designed for efficiency of that motor's sweet spot by having a larger blade area than their other props. What they did wrong was not stepping down enough in pitch for you to hit your rpm range, because that prop has more blade area, AND a larger diameter than your old props (14 1/2 vs 13 3/4).

    Either way I hope you get your props dialed in. As long as the props aren't dinged they ought to exchange them for another set. I just read about the Reliance Series on Yamaha's website and the 14 1/2 x 15p is the smallest pitch Reliance model they make though.

    Sobie2

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    The reason you dropped RPM is because of the larger prop diameter. My Yamaha saltwater SDS prop has the same slight rusting issues that you saw - even after the first trip. The SDS sure shifts sweet though.....I was impressed.

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    Member tlingitwarrior's Avatar
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    Bringing them back to Dewyes tomorrow. So ince again if I am looking for max mpg then going to a 19 pitch is the step?
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    There has been some impressive mis-information on this thread. Thanks to Sobie for getting you some good useful info at the end.

    KantishnaCabin - A Yamaha F150 does not employ any variable cam timing or any other wonder cure for over propping. A large diameter, or too high pitch prop will over torque your bearings and crank and send a rod out the side of the motor, it's only a matter of time. Any fuel injected engine that can't achieve close to 6000rpm at WOT won't operate efficiently. The only mechanisms the motor has to compensate for too much prop will be advancing timing (leads to detonation and piston failure) or to add more fuel. If your prop won't allow the motor to turn it's desired RPM for a given throttle position, the motor will add fuel, but if the RPM doesn't increase this extra fuel is wasted. Excess fuel can get past the rings and dilute oil causing further deterioration of the bearings.

    Tlingitwarrior - talk to your mechanic, he has a vested interest in your satisfaction with the product he represents.
    Casey
    Yamaha Dealer
    Petersburg, AK

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    Quote Originally Posted by tlingitwarrior View Post
    Bringing them back to Dewyes tomorrow. So ince again if I am looking for max mpg then going to a 19 pitch is the step?
    If you want to up your RPMs, assuming you stick with the same series/model of prop (similar rake and cup) and same diameter, you want to lower your pitch. When you start changing too many things at once (in this case you changed the design of the prop, the diameter, and the pitch) you won't really know until you try. Also as a general rule a smaller diameter prop (with a smaller cup surface) will increase your RPMs.

    Try getting the same prop you had to start with in the same diameter, but a lower pitch by 2.
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    Another factor to look for is prop slip. Just google "prop slip calculator" on google and there are many out there. Prop Slip is the difference between the theoretical distance you travel per rpm vs what your actual distance per rpm. A good target is somewhere between 12%-15% slippage. Anything over that and your losing efficiency. Your move up in diameter would theoretically reduce slippage a bit... with the more surface pushing more water. That should give you better fuel economy in the mid range 3500 - 4500 rpm. As mentioned already on this thread, Yamaha motors need to have a WOT range of 5500 to 6000 ... anywhere in that range is acceptable.

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