I have a 1977 Evinrude 15hp 2 cycle on my Valco 14' Dry weight of boat is 150 lbs, about as light as they come. The prop is a 9.5"10 three blade aluminum which I believe is the OEM stock prop size. I've rebuilt the carb and replaced the plugs. With myself (260 lbs) and my 9 and 6 year old kids it maxes out at 5150 rpm for 15 mph. Just me I hit 5250 rpm and 16 mph. Gas and battery are moved forward under the bow and I'm running the trim on the lowest hole to keep bow rise down. Also have a fin mounted on the plate to help get the stern up, I'm considering building a jack plate to lift the prop as the ventilation plate is about 1.5" below the transom. It's a 15" transom but the motor is more like 17". I tried a 2X2 under the motor mount to get the plate even with the bottom of the hull and it got me up to the above rpm's and speed, before I was only getting 13 mph with the kids in the boat so raising the motor got me 2 mph with a load. Boat is mostly used for trolling for kokanee with the kids, I'd really love to be able to hit 20 mph. I also intend to use it in shallow rivers for duck hunting, hence the jack plate intention to get the skeg up as high as possible.
Reading online I've seen several people claiming to get as high as 24 mph out of similar motor and boat with a 10" pitch prop. Motor is rated for 5500-6500 rpm and I am falling 300 rpm below that. Seems like my motor just can't spin that pitch prop. I am looking to replace the current prop which is lightly worn, wondering if it might be keeping me from hitting the power band. First I am considering getting a 4 blade 8" pitch aluminum. Figure with the boat empty I will hopefully hit the upper end of the rpm range and with a load still be in the power band. Also for running shallow in the river with a hunting load the lower pitch and 4 blade should help get me on plane at lower speeds.
I would also like to get a second prop, maybe a stainless 3 blade 10" pitch. For chasing kokanee around the reservoir (currently a 20-30 minute run with the kids in the boat) hole shot is not as important as top end speed and for the time being the kids are still a fairly light load.
My question is will a 4 blade 8" prop get me in to the upper range of the power band.
Is the 10" stainless worth the extra cost if my motor won't spin my current aluminum 10" over 5500 rpm?
Is there some other underlying issue I should look at if a 15hp Evinrude won't hit the power band with a 10" pitch prop?
Video of running it with the riser block: http://www.youtube.com/watch?v=beheazk_ElA&feature=youtu.be
Reading online I've seen several people claiming to get as high as 24 mph out of similar motor and boat with a 10" pitch prop. Motor is rated for 5500-6500 rpm and I am falling 300 rpm below that. Seems like my motor just can't spin that pitch prop. I am looking to replace the current prop which is lightly worn, wondering if it might be keeping me from hitting the power band. First I am considering getting a 4 blade 8" pitch aluminum. Figure with the boat empty I will hopefully hit the upper end of the rpm range and with a load still be in the power band. Also for running shallow in the river with a hunting load the lower pitch and 4 blade should help get me on plane at lower speeds.
I would also like to get a second prop, maybe a stainless 3 blade 10" pitch. For chasing kokanee around the reservoir (currently a 20-30 minute run with the kids in the boat) hole shot is not as important as top end speed and for the time being the kids are still a fairly light load.
My question is will a 4 blade 8" prop get me in to the upper range of the power band.
Is the 10" stainless worth the extra cost if my motor won't spin my current aluminum 10" over 5500 rpm?
Is there some other underlying issue I should look at if a 15hp Evinrude won't hit the power band with a 10" pitch prop?
Video of running it with the riser block: http://www.youtube.com/watch?v=beheazk_ElA&feature=youtu.be
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