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| Have a 2010 proguide w/ 115F yamaha, started out with the top hole on the motor. Prop was a stock yamaha 13 1/4 x 17 i had to watch redline 6000 to limit when trimmed out. Went the wrong way to a 15 pitch couldn't even trim up and had to watch the tach. Finally got a stock 13 x 19 yamaha prop turning a sweet 5800 rpms at wot trimmed up. but the boat felt bow low. Another guy said he had the same bow low effect in a 1825 and a 90 yamaha. Problem solved he said by going to a mercery stainless. So i find a custom prop shop and try out a 18 pitch vengence and a 21 pitch solas 4 blade. turning way to low rpms with both 5200 - 5400 with the vengence and 4400- 4600 with the solas . I finally make the decision to order a 13x19 solas 4 blade because of the way the prop got the boat up out of the water so much better. Prop comes in, the guy works it over, a thing of beauty. put it on the boat and i'm only turning 4600-4900 trimmed up. So i have the motor raised to the 3rd hole from the top. Today i tested it and the boat is running like it has angel wings but the problem is I only gained 200 rpms by raising the motor. Now I run a very solid 4900 and can trim it out to almost 5200 before it starts to blow out. If by everything a read a one inch drop or gain is ruffly 200 rpms. I know that the aluminum stock prop is flexing and also spinning but how do i lose 800 to 900 going to a stainless and raising the motor 1 1/2 inches by my caculations I should be running this prop in a 15 pitch to get back up towards the upper half of redline at wot. is this correct? I know im probably leaving info out so let me know. But any sort of info would be a help. Thanks |
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Member
Posts: 3899
| Because there is virtually no flex in a SS prop like there in with Aluminum, the SS has a lot less slip. Usually, I found that the same pitch when going from AL to SS lowered the RPM's quite a bit. My guess is that you need to be in a 17" prop in SS. |
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Member
Posts: 127
| try seeing if your prop guy will let you test a 13 1/2 x 16 s.s. prop. you should get around 5600 to 5800 r.p.m.'s at wot. |
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| Birdwatcher,
Try some calculations and compare them to your current speed and RPM. Your gear ratio is 2.15. It looks like your RPM is too low you should be up around 5900. Now that you have raised the motor, you could probably go down a pitch or two. The Mercury performance test on your boat with a 115 Merc shows 39 mph using a 13 3/8" dia x 14p Vengeance. They do allow higher (6300) rpm on their motor and have a 2.07 gear ratio. You may have already done so but play around with the calculations below as it may help to establish a starting point. One would think the 15 to 17p should do the job. The Merc props do have more cup and make a difference over the Yamaha props.
RPM / Gear ratio = Prop RPM
Prop RPM x pitch = inches per min
inches per min/ 12 = ft per min
ft per min x 60 = ft per hr
ft per hr/ 5280 = miles per hr. |
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| thanks for the info, I had talked to my prop guy and he said its just holding to much and that i dont have the horsepower. He said he may have put to much cup in it and can adjust the pitch down but can't take it up past 19. I took it back to him and will have it back in a couple of days. Ill let everyone know what has happened. |
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Member
Posts: 344
Location: Manitowoc WI | I would highly highly recommend you try some HI-5 props. In my humble opinion, this would be an application that they excel in. |
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