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post #11 of 37 Old 08-06-2017
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Re: Knot meter vs GPS speed.

My 3gm30 yanmar 600 hours runs about .5 gal/hour running 3100 rpm to push my Alberg35 about 6 knots. If any of that is helpful. Speed measured via GPS, but I sail on the Patapsco River/Chesapeake mostly, not much in the way of current.

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post #12 of 37 Old 08-06-2017
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Re: Knot meter vs GPS speed.

your gps SOG is accurate for speed over ground... current and all.

You speed log is likely off... fouled or needs calibration.

SOG is basically useless except to tell the wife when you will arrive somewhere.

Your fuel consumption has little to do with your SOG... more to do with boat speed... and consumption will be less efficient at you get to hull speed... 1.34 x sq rt of LWL.

Calibrate your boat speed on multiple reciprocal runs over a measured distance... better at slack tide.

I have a 3 cyl 36 HP Volvo and a 29'6" LWL and get about .6 gal / hr at 2,000 rpm WITH A CLEAN HULL and no towing of dinghy.
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post #13 of 37 Old 08-06-2017
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Re: Knot meter vs GPS speed.

When you paid the big buck for the boat and the fee for the slip and the wine and the beer and the barbi steaks, you worry about the fuel thru an engine that you didn't even change the oil in. ???
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post #14 of 37 Old 08-07-2017 Thread Starter
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Re: Knot meter vs GPS speed.

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When you paid the big buck for the boat and the fee for the slip and the wine and the beer and the barbi steaks, you worry about the fuel thru an engine that you didn't even change the oil in. ???
More just interested in the sweet spot for the engine as far as RPM.

As someone here said there is a dramatic loss in fuel efficiency as you approach hull speed.

If it was a rental car if l would push it's capabilities but if it floats or flys, I like to baby the engine. I'll put 300+ nautical miles on this engine in two weeks. I want to make sure it gets me there and back.

That being said I now disbelieve the bill of goods sold me by the guy who checked me out in the boat. Today I bumped the throttle to 1800 RPMs gave me 8+ knots on the speedo, which showed about 7 on the GPS. I did see 9.7 knots on the GPS ridding the tail end of the flood tide through Dodd's Narrows this evening with some wild swirling currents on the tail end. It reminded me of my early days as a whitewater kayaker staying in the calm part trying to avoid the swirling eddys on the sides.

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post #15 of 37 Old 08-07-2017
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Re: Knot meter vs GPS speed.

experiment with your boat and don't expect others to answer your questions. Stop being lazy. Remember... people solved boat problems on their own before internet sailing forums.
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post #16 of 37 Old 08-07-2017
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Re: Knot meter vs GPS speed.

Hey the Dodd Narrows is some big fun. Requires an IPA or after you get. A bit of the fun here:

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post #17 of 37 Old 08-07-2017
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Re: Knot meter vs GPS speed.

The sweet spot is hit by feel and sound, not GPS or knot meter.

The hysterical laughter you hear as you drive a way in your"new" boat ..... is the seller.
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Re: Knot meter vs GPS speed.

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The sweet spot is hit by feel and sound, not GPS or knot meter.
said the actress to the bishop.
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post #19 of 37 Old 08-07-2017
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Re: Knot meter vs GPS speed.

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said the actress to the bishop.
More likely the priest to the alter boy from what I read

The hysterical laughter you hear as you drive a way in your"new" boat ..... is the seller.
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post #20 of 37 Old 08-08-2017
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Re: Knot meter vs GPS speed.

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Originally Posted by SanderO View Post
experiment with your boat and don't expect others to answer your questions. Stop being lazy. Remember... people solved boat problems on their own before internet sailing forums.
People generally ask questions on here because they have real questions. Ridiculing them doesn't make sense.

If you don't have the patience to answer his / her questions without the snarky quips, just say nothing.

Comments like that aren't necessary.
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