Here's my setup:
So, everything's perfect, right? Well - maybe. The problem is, I don't think I'm loading the engine up, and I think I might be able to turn more prop. Maybe. I hope. For example tonight, coming in, with everything trimmed up, I'm making 27MPH on the GPS at full throttle, turning 5700 RPM. If I back the throttle of to 75% (there's a nifty little "power curve" diagram thingee on my tiller), I lose about 1MPH and 50 RPM. You can hear the difference, sort of, maybe. At 50% throttle you can definitely hear a change, but I'm still turning around 5500 RPM and running 25MPH. 25% power is around 4500RPM, and still on plane and stable somewhere in the high teens.
I'm actually pretty happy with the performance I'm getting, but I need a spare prop and if possible I'd like to wring a bit more speed out of her. I make a long run every now and then, and 5MPH would mean less pounding around and more dead fish. I do NOT want some ridiculously-oversized prop that won't get me on plane in a good chop or makes me burn twice as much gas for 1MPH or anything, but I think I can turn more prop.
I'm leaning towards a stainless prop, but that's yet another variable that I'm not sure how to control.
http://www.mercurymarine.com/propellers/prop-selector says I can turn a 15-pitch. I doubt that.
What say ye?
- 2008 2-stroke 25HP Yamaha with about 25 hours on it ("new-old" engine). Just fully broke in and had a couple tanks of 100:1 fuel through it. So far a great little engine.
- 15' Gregor "semi-v." Lots of small bangs and dents in the bottom, but overall a fairly straight, lightweight boat.
- Normal load is me (180), dog (90), 6g fuel (40), G27 battery (50?), anchor/rode (20?), junk (30?), poles (20?), etc. Say 500 pounds, more or less.
- Stock prop - 9 7/8 x 11 1/4 aluminum white Yamaha thing, just getting the paint worn off the tips.
- "Whale tail" which completely fixed a cavitation issue.
- TinyTach, when the damned thing works. Around 5700RPM wide-open trimmed up.
- Right around 25MPH on the GPS - a bit more when everything's perfect, a bit less if it's rough, etc.
- Gets on plane more or less instantly, depending on trim.
- Tossing another person/more beer/extra gas/dead fish in doesn't make a lot of difference. I've had it plane out and run around 20MPH with 5 adults and a big pile of crab gear.
- Haven't measured fuel consumption, but it's not burning much - certainly less than the worn-out Johnson on the same boat was.
So, everything's perfect, right? Well - maybe. The problem is, I don't think I'm loading the engine up, and I think I might be able to turn more prop. Maybe. I hope. For example tonight, coming in, with everything trimmed up, I'm making 27MPH on the GPS at full throttle, turning 5700 RPM. If I back the throttle of to 75% (there's a nifty little "power curve" diagram thingee on my tiller), I lose about 1MPH and 50 RPM. You can hear the difference, sort of, maybe. At 50% throttle you can definitely hear a change, but I'm still turning around 5500 RPM and running 25MPH. 25% power is around 4500RPM, and still on plane and stable somewhere in the high teens.
I'm actually pretty happy with the performance I'm getting, but I need a spare prop and if possible I'd like to wring a bit more speed out of her. I make a long run every now and then, and 5MPH would mean less pounding around and more dead fish. I do NOT want some ridiculously-oversized prop that won't get me on plane in a good chop or makes me burn twice as much gas for 1MPH or anything, but I think I can turn more prop.
I'm leaning towards a stainless prop, but that's yet another variable that I'm not sure how to control.
http://www.mercurymarine.com/propellers/prop-selector says I can turn a 15-pitch. I doubt that.
What say ye?