Ok, I have a Catalina 30 TRBS which I just put back in the water after a new bottom. In 15 knots of steady wind, I was sailing on a broad reach at 7-7.5 knots STEADY and peaks of over 8. Average speed after 3 hours (motoring and sailining in & out of marina combined) was 6.9 knots. I know the max theoretical hull speed is 6.7 knots. Can a new bottom really make that much difference? As a comparison, I was able to motor comfortably (engine at 2400) at 6 knots even. As far as I can tell, the knot log is reading accurate. Also, Many of you here have mentioned a "flutter" in the wheel when using a 3 blade prop above 4.3knots. I experienced the same problem, but with the new bottom, the "flutter" is TOTALLY gone. Any gurus wanna comment on this one por the speed increase? Thanks
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Joe Barrett
GPS
My knot meter often reads higher than my GPS. Now I sail in ocean waters where there is some current where I believe you are sailing on a lake? A new bottom though is definately faster, you probaby did feel that. You may also want to have your Knot log calibrated using a 1 mile course.
My knot meter often reads higher than my GPS. Now I sail in ocean waters where there is some current where I believe you are sailing on a lake? A new bottom though is definately faster, you probaby did feel that. You may also want to have your Knot log calibrated using a 1 mile course.
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David
Galveston Bay
I'm working on the GPS angle, but it's not in th budget at this time. The sailing was done on Galveston bay with no currents.
I'm working on the GPS angle, but it's not in th budget at this time. The sailing was done on Galveston bay with no currents.
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Joe
the effects of heeling...
...might be responsible for part of the speed increase. Besides creating more lift, when the boat heels, the water line is inceased a bit. That would change the theoretical hull speed model.
...might be responsible for part of the speed increase. Besides creating more lift, when the boat heels, the water line is inceased a bit. That would change the theoretical hull speed model.
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david
Heeling, maybe
Joe, I suppose the "heeling" theory might be able to raise the hull speed, but it seems unlikely that it would account for nearly an extra "knot" of boat speed. Who knows.
Joe, I suppose the "heeling" theory might be able to raise the hull speed, but it seems unlikely that it would account for nearly an extra "knot" of boat speed. Who knows.
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Lauraine
We regularly sail at 7+ knots on our C30.
Her bottom is cleaned and painted every year with VC-17 and we sail on Lake Ontario. Theoretical hull speed is just that -a theory.
Her bottom is cleaned and painted every year with VC-17 and we sail on Lake Ontario. Theoretical hull speed is just that -a theory.
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Dave
GPS vs. Meter
Just a quick note.....GPS is measuring speed over ground and meter is measuring speed through the water.....If the GPS speed is less than the thru water speed you are fighting a tide speed of the difference between the two..On the contrary if the GPS speed is higher than the thru water speed the difference is how much tide you have pushing you along....If speeds are the same....no tide or current push....
Just a quick note.....GPS is measuring speed over ground and meter is measuring speed through the water.....If the GPS speed is less than the thru water speed you are fighting a tide speed of the difference between the two..On the contrary if the GPS speed is higher than the thru water speed the difference is how much tide you have pushing you along....If speeds are the same....no tide or current push....
R
RonD
Calibration
Your speed sensor unit typically has a paddlewheel device that sits in the water under the hull. The paddlewheel device has a magnet in one spoke that generates a pulse each time it passes the sensor in the fixed shell. That sensor essentially sends a stream of pulses to an computer that smooths them into an average voltage level to be displayed on your speed display. This voltage level, corresponding to paddle wheel RPM, which corresponds to speed through the water, does require some calibration. Generally, the speed sensor owner's manual will describe how you can adjust the instrument (if at all). At the very least, you can make up a conversion table of indicated vs actual. I would find a measured-mile somewhere to do some calibration runs. Use your engine power at a fixed engine RPM to obtain a steady speed. Pick a day with little or no wind, and a time when the current is slack. It's general practice to do these runs in both directions and average the results. If you can, repeat at different engine RPM settings. While doing the speed calibration runs, record the GPS speed-over-ground (SOG) readings every couple of minutes and average them, too. Comparing SOG with indicated speed (corrected to the measured-mile) will give you an indication of any currents at work during the trials.
Your speed sensor unit typically has a paddlewheel device that sits in the water under the hull. The paddlewheel device has a magnet in one spoke that generates a pulse each time it passes the sensor in the fixed shell. That sensor essentially sends a stream of pulses to an computer that smooths them into an average voltage level to be displayed on your speed display. This voltage level, corresponding to paddle wheel RPM, which corresponds to speed through the water, does require some calibration. Generally, the speed sensor owner's manual will describe how you can adjust the instrument (if at all). At the very least, you can make up a conversion table of indicated vs actual. I would find a measured-mile somewhere to do some calibration runs. Use your engine power at a fixed engine RPM to obtain a steady speed. Pick a day with little or no wind, and a time when the current is slack. It's general practice to do these runs in both directions and average the results. If you can, repeat at different engine RPM settings. While doing the speed calibration runs, record the GPS speed-over-ground (SOG) readings every couple of minutes and average them, too. Comparing SOG with indicated speed (corrected to the measured-mile) will give you an indication of any currents at work during the trials.
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Joe
Dave, Not really that simple but sounds good.
... and what about waves, chop. cross currents, headwinds and all that other stuff.
... and what about waves, chop. cross currents, headwinds and all that other stuff.
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Dave
Joe
Joe: True not as simple as I made out....I agree with all your variables as factors....Where I live we deal with a 25 ft. tidal range, so we are always cognizant of the tidal flow....(and try to use it to our advantage)... I used a simple example that holds true more when there is pretty much a steady but relativly calm state....When you get backing seas, waves, crosscurrents, etc. usually you are just happy to know what you speed over ground is...
Joe: True not as simple as I made out....I agree with all your variables as factors....Where I live we deal with a 25 ft. tidal range, so we are always cognizant of the tidal flow....(and try to use it to our advantage)... I used a simple example that holds true more when there is pretty much a steady but relativly calm state....When you get backing seas, waves, crosscurrents, etc. usually you are just happy to know what you speed over ground is...
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