Author
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Topic: 13' Whaler speed w/15-25hp... ?
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CC25 |
posted 09-18-2005 05:51 PM ET (US)
Hi all, looking to downsize my outboard. Currently running a 40 hp 3cylinder 2 stroke merc on my 13. Its way too much motor for how we boat. Lookin for performance with a smaller motor, 15-25hp 4 stroke or 2 stroke, with 2 adults on board. Any info very much appreciated.
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BOB KEMMLER JR
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posted 09-18-2005 05:54 PM ET (US)
what year 13 do you have? |
jimh
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posted 09-18-2005 06:00 PM ET (US)
If you hold everything else constant and decrease the horsepower, the speed will decrease in proportion at an exponential rate of 0.5. |
CC25
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posted 09-18-2005 06:45 PM ET (US)
Its a 1974. Jim, I'm lucky I can spel.
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Binkie
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posted 09-19-2005 12:01 AM ET (US)
jimh. I don`t understand how to work your formula. If my 13 foot whaler goes 38mph with a 40hp, how fast will I go with a 15hp.? How about a 60hp? This could be usefull to me if I knew how it worked. Algebra class was a looong time ago. Rich |
jimh
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posted 09-19-2005 08:22 AM ET (US)
Q.: If a boat goes 38-MPH with 40-HP, how fast will it go with 60-HP?A.: Speed is proportional to horsepower raised to the 0.5 power. The increase in horsepower was 60/40 = 1.5 The speed increase will be 1.5^0.5 = 1.22 38 X 1.22 = 46.5 MPH |
fast13
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posted 09-20-2005 01:22 AM ET (US)
I got my 13 to go 46 mph. 87 40 Johnson mounted 2 inches up,a pair of carbs from a 50,and a 19" Pitch X 12" Ballistic prop. Hooks very hard. Boat leaps out of water from barly on plane, hitting it hard, the stern leaves the water for a few feet before settling down. To duplicate what I have done-you must know how to use trim, and be able to drive through chine walking. |
brisboats
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posted 09-20-2005 03:11 PM ET (US)
CC25, Last year I ran my 1966 13 with an 18hp 2 stroke 2002 tohatsu tiller with just me it would hit 20mph with just myself(250#'s) add a large friend boat would still plane off but speed dropped into the 15mph range, add one more person and the boat would not plane at all. I have also gotten the same boat to plane with my evinrude 9.9 2 stroke not sure of the top speed with that motor but seat of pants says low to maybe mid teens. My 1983 25hp 2 stroke mercury tiller pushed the same boat in the low 20's. I hope this info helps. Brian |
JL8Jeff
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posted 09-23-2005 09:51 AM ET (US)
One of my old 13' Whalers had a 1986 Suzuki 25hp on it and that boat moved pretty good. I had no way of measuring speed but it was faster than my cousin's 14' aluminum Starcraft with a 30hp Johnson on it. I have a Johnson 40hp on my 15' Hobie Powerskiff and it moves the boat perfectly fine. The only downside to going with a smaller engine is that you might end up running it at higher rpm's more often to keep the speed up where your 40 will cruise along nicely at a lower rpm. If I had kids that were going to be using the boat, I would max it out with a 25hp motor. |
c_mccann
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posted 09-26-2005 06:19 PM ET (US)
If speed is a concern and the motor is in good condition, why not just prop down? You would also get better fuel economy, not that it is a problem now. |
boatboy
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posted 10-05-2005 10:14 AM ET (US)
I have a 1969 13' with a 25 2 stroke and it runs about 22 or 23 with two 190 lbs guys but I am looking for a larger engine like a 40 or so. |