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| Crestliner 1850 FishHawk w/ 115 Yamaha 4-stroke.
19 Pitch prop- Turns 6200 rpm WOT at 42 mph.
Any suggestions to lower my rpm's and not lose top end?
21 pitch?
Thanks,
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| I'd say have your tach checked. Your speed is about right, but the RPMS are high for that prop. | |
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| Waterwolf,
Couple of things you can try.
First would be is to increase prop diameter, but not change pitch. Every 1/4 inch adds up to (I think) 100 rpm or so. But...without knowing your max rpm range, this could make for too large diameter. The next step would be is to consider adding cup to the prop, unless it already has it. If you have little or no cup, you will not have as good of handling, and the cupping will help to cure this.
Third, is to go up in pitch but keep the same diameter. Going up 1 inch is pitch is usually between 100 to 150 rpm loss. So..options are there.
Depending on where the motor is sitting on the hull, you may be able to go up a bit in pitch (3-4 inches) and raise the motor up to the third hole or so...uless you have done so already. In doing so, you will off-set things a bit, but you gain speed and efficiency.
If you could, drop a post on where your motor is on the transom,the gear ratio of the motor, the prop you are running(also if cupped, steel, etc) and the max rpm your motor is supposed to run at and I can run some numbers for you to see what might be a good set-up.
Steve | |
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| Water,
Went to the Yamaha website and pulled this info from their performance specs: Max RPM = 6000, ratio 2.15:1.
So...with your boat, you could go to a 21 pitch prop, or even better yet, go to a cupped 20 pitch. The increase in pitch of 2 inches will drop your RPMs about 200 or so...same with the cupped 20. the cupping tends to make the prop grab more, and give you the thrust of a 21. Yamaha has a link to a performance review and they pushed a rig like yours to 43 or so with a 12-5/8 x 21 and the motor was one hole up off the transom. They pulled 5900 rpm.
If your motor is on the transom, raise it to the third bolt hole. Try it there with moderate turning. If you are blowing out at all throttle levels on moderate turns, drop the motor down one hole and try again. If you are pitched correctly and you have a good prop, your boat will feel like it is riding on air (which it should...since there should be very little boat in the water at all). The boat will just loaf along in mid range rpm.
With the correct set-up, you could potentially get yourself another 4 - 5 mph. The biggest change you will see is in your prop selection. 5 props of different brands that have the same pitch and diameter will all run differently and you will be able to tell which runs the best for your rig. I would look at something with high rake (Michigan Rapture, stiletto, Trophy....) You have lots of options with your motor. If you find a dealer that has a selection of demo props for you to try, take a few to the lake and try them out. You will see a difference.
Steve
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| Waterwolf,
I have the same motor on a Crestliner CVX182. The boats are very similiar.
At the time of purchase, I tried out 4 different props. The standard Yamaha 17 & 19 pitch aluminum props revved over 6000 rpm.
I settled on a 19 pitch stainless Yamaha prop and run 46 mph on the GPS at 5800 rpm. The difference between the 19 pitch stainless and aluminum prop was about 250 rpm and 2 mph.
Landy Roepke | |
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| Thanks Guys,
When I had mine out, I didn't have any gear, just myself, with 1/2 tank of gas. I will try it again w/ boat loaded as normal. Talked to dealer, and he said he would do whatever is needed to see that I was satisfied.
Thanks again,
[:bigsmile:] | |
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Prop Help!