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Go Back   SailNet Community > Skills and Seamanship > Seamanship & Navigation
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Seamanship & Navigation Forum devoted to seamanship and navigation topics, including paper and electronic charting tools.


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  #11  
Old 02-27-2012
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Quote:
Originally Posted by CalebD View Post
This usually results in a lee helm that always wants to fall off, so in order to make any way going upwind you always have to steer hard up wind, which further slows your forward progress.
I know I'm being a dog with a bone here and your science is of course good but I just noticed another anomaly.

Leg two that starts at the bottom of the page and goes about NE is amazingly fast. I checked the track details and from 3:51 which is about the start of the turn to 4:11 which puts "8A" abreast the log show speeds of 6,7 and 8 knots. I'm pretty sure I had only the jib up reefed to 100 percent so the only other explanation I can figure is that the current is wicked fast right there like maybe 4 knots, more than double what is predicted.
The other anomaly is that I remember not being able to head up any more than my 50 degrees.
That particular leg really bugs me.
Given the conditions I thought I had I would have predicted a course of about 10 degrees.
What I got was 50 degrees and super fast.
I expect my predictions to be off 5 10 degrees. I'm not good enough at ascertaining the actual conditions to be more accurate than that and in this case I know they changed too.
But to be off 40 degrees hurts. And 8 knots, I was moving but it did not seem that fast.
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  #12  
Old 02-27-2012
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Dave-o, I just saw this thread. Awesome.

This is what a sailing forum is supposed to be about. Thanks.

Ah, and being a FightClub alum where dipping a rail is all that...

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Originally Posted by davidpm View Post
Anyway after looking at my track again I think I see a leaning opportunity.
Awww hell yeah.
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  #13  
Old 02-28-2012
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OK then dog bone David, you said your GPS "log show speeds of 6,7 and 8 knots" on your way to "8A". That should be the first clue.
The theoretical hull speed of a Catalina 25' with only the jib up in winds around 20 kts. is what? About 4 - 5 knots? You were not flying a spinnaker and you might have surfed a few waves but 8 knots in a C25? Not likely without the influence of current. Perhaps a 2 - 3 knot current and maybe even more, all setting you to the ENE.
The theoretical hull speed for a Catalina 25' with both sails up should be somewhere around 6.5 knots, which is slightly faster then my 27 footer which has a slightly smaller LWL then the C25.
Did you notice your SOG on the GPS as you headed back in a westerly direction? I'd bet that the same ENE current pushed your speed down closer to 3 knots SOG on the way back.
TomMays posted this link before which gives a nice graphical display of the expected currents in our local waters (for any hour of any day): Stevens Maritime Center: Urban Ocean Observatory

If you had an accurate knot meter you would have seen a difference between your speed through water and your speed over ground (SOG) which would have indicated the speed of the current.

Still a good learning exorcise.
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Old 02-29-2012
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Quote:
Originally Posted by CalebD View Post
...
The theoretical hull speed of a Catalina 25' with only the jib up in winds around 20 kts. is what? About 4 - 5 knots?...
The theoretical hull speed for a Catalina 25' with both sails up should be somewhere around 6.5 knots, which is slightly faster then my 27 footer which has a slightly smaller LWL then the C25....
One point: theoretical hull speed is just the speed at which the wavelength of the wave (bow wave) produced by the hull is the same as the LWL of the hull. The attached pic is of a Catalina 25 is at, or just shy of, hull speed (note the bow wave). It doesn't matter if you have zero, one, two, or more sails up; hull speed is hull speed. Given enough wind a Catalina 25 could be pushed to or slightly beyond hull speed with just the jib up.

Could a Catalina 25 go much faster than hull speed? Maybe, in short spurts. (OK, that's two points.) They aren't very heavy boats, and the bottom is fairly flattish. But I think that you're right about the current. I can't see a Cat25 keeping up that sort of speed for any length of time.
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Seamanship fail (Or how things add up)-cat25.jpg  
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Last edited by SlowButSteady; 02-29-2012 at 12:49 AM.
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