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Go Back   SailNet Community > Skills and Seamanship > Seamanship & Navigation > Seamanship fail (Or how things add up)
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Thread: Seamanship fail (Or how things add up) Reply to Thread
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Topic Review (Newest First)
02-29-2012 01:47 AM
SlowButSteady
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.
02-29-2012 12:05 AM
CalebD 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.
02-28-2012 12:03 AM
smackdaddy 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...

Quote:
Originally Posted by davidpm View Post
Anyway after looking at my track again I think I see a leaning opportunity.
Awww hell yeah.
02-27-2012 11:07 PM
davidpm
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.
02-26-2012 11:07 PM
CalebD Also, by using only your jib you move the CE (center of effort) of the sailboat forward while the CLR (center of lateral resistance) stays the same. 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.
If you balance the forces of the sails (CE) by using both the main and jib then the CE is usually slightly behind the CLR which results in either a neutral or weather helm. Even using a heavily reefed main with a jib will move the CE aft and behind the CLR which gives you weather helm. Of course it is best to have them as close to balanced as possible so you use less rudder which acts more like a brake to boat speed.
Most of us instinctively know this (and I know that David certainly does) but here is a link that breaks it down a bit more scientifically then I can: Helm Balance – Center of Effort, Lateral Resistance, Centerboard, Mast Rake - Waves « Jordan Yacht Brokerage
Good discussion btw.
02-26-2012 08:49 PM
SlowButSteady
Quote:
Originally Posted by davidpm View Post
Thanks for that. I had 15 to 23 knots and wasn't paying attention at all until leg 3 and the main is very tired.
Next time I'll try to get better numbers.
A blown-out main, by itself, will kill your windward performance.
02-26-2012 08:47 PM
davidpm
Quote:
Originally Posted by SlowButSteady View Post
I almost never sail with only a jib. If I sail with only one sail it's the main. However, I would expect to lose at least 10˚ - 15˚ of pointing ability with only a jib; particularly as the wind pipes up.



A light, little boat like that is going to have a tough time of it to windward in a stiff breeze. Current and waves are going to make it that much tougher. However, with a tightly sheeted working jib and a helmsman who is really paying attention, you should be able to make some progress in anything shy of 25 or 30 kts, or so. The key is to not be too over-canvased (reef early, reef often), and "work" the waves and the puffs as much as possible, scratching out every bit of windward performance you can.
Thanks for that. I had 15 to 23 knots and wasn't paying attention at all until leg 3 and the main is very tired.
Next time I'll try to get better numbers.
02-26-2012 08:32 PM
SlowButSteady
Quote:
Originally Posted by davidpm View Post
Is it your experience that you loose 10 degrees plus of upwind performance when using the jib only?
I almost never sail with only a jib. If I sail with only one sail it's the main. However, I would expect to lose at least 10˚ - 15˚ of pointing ability with only a jib; particularly as the wind pipes up.

Quote:
Originally Posted by davidpm View Post
If everything is against you, wind, waves, current and you have to reef is a 160 degree tack angle not surprising, IE almost no upwind progress?

Every boat is different of course, this was a Catalina 25
A light, little boat like that is going to have a tough time of it to windward in a stiff breeze. Current and waves are going to make it that much tougher. However, with a tightly sheeted working jib and a helmsman who is really paying attention, you should be able to make some progress in anything shy of 25 or 30 kts, or so. The key is to not be too over-canvased (reef early, reef often), and "work" the waves and the puffs as much as possible, scratching out every bit of windward performance you can.
02-26-2012 07:46 PM
davidpm Anyway after looking at my track again I think I see a leaning opportunity.

I did the vectors on my chart based on wind of 280 and current at 2 knots from the west.
Based on that leg 2 should have been closer to North rather than the 50 degrees I got.

I didn't keep a log, it was just a fun night sail, mybad, but I knew I had only the genny up for leg 1 and furled to 100 percent. Leg two I don't remember. I'm pretty sure I didn't put the main up until leg 3 when I started to try to get back in earnest.

Anyway leg 2 at 50 instead of 0 is a bit of a puzzle.
Maybe the wind was closer to 320
Can I expect to loose a bunch of degrees with only the jib up.
The waves were pushing the bow off I'm sure loosing some more degrees.
Notice the shoal going from 100 feet to 7 feet. I wonder if the current is a little faster on the edge of the shoal?

All in all I was trying to go west and it looks like everything, wind, waves, current, shoal and my own misjudgment was pushing me east.

Like I said I was expecting to be off by a bit but I really wanted to stay on leg 2 for a while as I was making 8 knots over ground for part of it and it was fun.
The surprise was how I lost a whole two miles plus east in only half an hour.

So in summary:
Is it your experience that you loose 10 degrees plus of upwind performance when using the jib only?

If everything is against you, wind, waves, current and you have to reef is a 160 degree tack angle not surprising, IE almost no upwind progress?

Every boat is different of course, this was a Catalina 25
02-25-2012 07:05 PM
SlowButSteady
Quote:
Originally Posted by davidpm View Post
me too that's what I usually do. In this case I was having too much fun going fast and knew I was going to have to pay.
Was just surprised how much though.
Fair enough....don't get me wrong, I didn't want to sound preachy. I've been caught in similar situations, particularly when enjoying a weak or moderate Santa Ana wind (our version of offshore wind).
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