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Old 14-02-2011, 16:29   #16
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Where I sail 3+ knots of current is commonplace. I have never known it change helm pressure.
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Old 14-02-2011, 17:10   #17
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I'm not sure I understand what is meant by "helm pressure". In many, if not most, of the passages where current is a factor neither the vector or the speed of the current are constant and, dependant on draft and weight of the craft can move a boat around considerably. It feels like helm pressure to me. Clearly not weather helm but a pressure non-the-less. Is it the wrong term to use?
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Old 14-02-2011, 17:24   #18
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Quote:
Originally Posted by daddle View Post
Current will not affect weather helm, heeling, sail trim, nothing. It only affects your destination, your speed over the ground.

Sighting up the mast on both tacks was a good suggestion. As is headsail sheeting angle and main traveller position. Or how stuff is stored below. Inches can make a difference.

It really doesn't matter too much. Simply trim for best effect.
I used to think this before I spent time in strongly tidal areas with strong currents.

In fact the reason why this is not true is because you move in relation to the WIND. So when sailing in a strong tidal current, you can seem to be superboat -- pointing at 20 degrees -- then on the other tack you can't get within 50 degrees -- that's because your real heading is different from where your bow is pointed -- because of the current.
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Old 14-02-2011, 17:35   #19
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Weather helm is felt as helm pressure. You could add more balance to a rudder, decrease helm pressure and still have the same amount of weather helm. Once again, I have sailed in Puget Sound for 50 years and we have very strong tidal currents. Most of my sailing has been racing and in that environement we are acc uely aware of the feel of the boat. I have never known helm pressure to be effected by current.
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Old 14-02-2011, 17:50   #20
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Originally Posted by Dockhead View Post
I used to think this before I spent time in strongly tidal areas with strong currents.

In fact the reason why this is not true is because you move in relation to the WIND. So when sailing in a strong tidal current, you can seem to be superboat -- pointing at 20 degrees -- then on the other tack you can't get within 50 degrees -- that's because your real heading is different from where your bow is pointed -- because of the current.
You guys are whacky You are referencing to stuff ashore, or the true wind (which might be zero). Boats and skippers only feel the apparent wind. Only affected by the apparent wind ... until land or a buoy appears ...

A few months ago I sailed across the Celebes Sea. The adverse current varied from .5 to 2.5 knots. Without GPS (or the occasional island that passed us) I wouldn't have known I was often traveling backwards.

It's Sailing 101 knowledge that only the apparent wind is felt by (affects) a boat, which is the vector sum of current, boatspeed, heading, leeway and true wind.

You could be sailing in a 100kt east setting current with a true easterly of 90 knots and think it's a pleasant sail. On any heading. Without some external navigation you'd be none the wiser. Not the boat wake, not chop, not birds, not helm pressure, not nothin'.
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Old 14-02-2011, 17:51   #21
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Originally Posted by Dockhead View Post
I used to think this before I spent time in strongly tidal areas with strong currents.

In fact the reason why this is not true is because you move in relation to the WIND. So when sailing in a strong tidal current, you can seem to be superboat -- pointing at 20 degrees -- then on the other tack you can't get within 50 degrees -- that's because your real heading is different from where your bow is pointed -- because of the current.
Even though this is correct, the current has only helped you point higher (or perhaps lower) but has not increased or decreased weather helm.
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Old 14-02-2011, 17:53   #22
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Daddle:
You said that so much better than I did.
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Old 16-02-2011, 11:15   #23
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Well,I'm glad we got past that...relative wind,sailing 101,etc.My point being,that a boat with a little weather helm in a 10knot breeze will have more in 12.5 knots.My boat has weather helm.Close-hauled I lash the tiller to one bias,it's only good until the apparent wind increases...and the boat rounds up.
This could be due to hull shape,mast placement etc as a constant....It could (and often does change as Dockhead was saying),tack to tack.It can even change shore to shore on the same tack,in the middle and near the shores.Downwind as well if you are gliding along with wind+tide then,hit a rip and you will suddenly find the helm is very difficult...
If you have a tiller (a 25' sailboat is likely to have a tiller)this will be really obvious.
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Old 16-02-2011, 11:24   #24
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Originally Posted by daddle View Post
You guys are whacky You are referencing to stuff ashore, or the true wind (which might be zero). Boats and skippers only feel the apparent wind. Only affected by the apparent wind ... until land or a buoy appears ...

A few months ago I sailed across the Celebes Sea. The adverse current varied from .5 to 2.5 knots. Without GPS (or the occasional island that passed us) I wouldn't have known I was often traveling backwards.

It's Sailing 101 knowledge that only the apparent wind is felt by (affects) a boat, which is the vector sum of current, boatspeed, heading, leeway and true wind.

You could be sailing in a 100kt east setting current with a true easterly of 90 knots and think it's a pleasant sail. On any heading. Without some external navigation you'd be none the wiser. Not the boat wake, not chop, not birds, not helm pressure, not nothin'.
Tide rips are really obvious in a breeze.Perhaps you are sailing in one for days and can't tell but inshore ,when the chop and wind build up or down with no apparent reason(nearby shore,stale seabreeze etc.),current is a good candidate.No shore reference is required,but it is a proof.
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Old 16-02-2011, 11:25   #25
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I have a 26' boat, frac rig with a big outboard spade rudder. My boat is perfectly balanced all the time, given that I pay attention to sail trim and no my boat is not my design. Off the wind I have to steer all the time. My boas zero directional stability off the wind. I think that's a function of size more than anything else. I have a tiller activated auto pilot. I love it.

Almost any boat with a tendancy for weather helm will see it increase with heel angle. Weather helm issues are almost always due to keel/mast placement relationship. Other issues like sail shape and choice and mast rake can come into play but generally it mast/keel retionship that is at the heart of helm issues.
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Old 16-02-2011, 16:03   #26
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Gull:
I have a 26' boat, frac rig with a big outboard spade rudder. My boat is perfectly balanced all the time, given that I pay attention to sail trim and no my boat is not my design. Off the wind I have to steer all the time. My boas zero directional stability off the wind. I think that's a function of size more than anything else. I have a tiller activated auto pilot. I love it.

Almost any boat with a tendancy for weather helm will see it increase with heel angle. Weather helm issues are almost always due to keel/mast placement relationship. Other issues like sail shape and choice and mast rake can come into play but generally it mast/keel retionship that is at the heart of helm issues.
...exactly so-what I said.
....Given the model where current is responsible for a change in relative strength and/or direction,boat heel can change and therefore helm can change.I venture this because the Original poster HAS weather helm,even if less on one tack than the other.
...this without venturing into further hydrostatics where relative wind is not even required....the fresh/salt water shear experienced at river mouths(OP is in the Parana River) .....
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Old 17-02-2011, 10:20   #27
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Seagull:
You'd need a hell of a lot more than 2.5 knots of current (as the original post says) to change AWS enough to result in any signifigant heel angle change.
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Old 17-02-2011, 16:01   #28
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Seagull:
You'd need a hell of a lot more than 2.5 knots of current (as the original post says) to change AWS enough to result in any signifigant heel angle change.
Per my own post #15, 2.5 knots seems a significant change...all of this which you are no doubt familiar with and can correct where my simple logic errs while trying to answer a simple question.If so,How much more?

Given Velocity wind squared times the constant of air mass,and simply put,current is opposed to wind ....Real wind =10.
No current = 10 real"shore based" wind factor = 100.
2.5 current +10 =12.5 combined wind factor =156... a 50% increase.
I could redo a lot of ways:
5=25 and 7.5=56.25 (125% More)
15=225 17.5=306.25 (36%More)
20=400 22.5=506.25 (25% More)
.
This shows that a steady 2.5 current means "less" as Wind V increases.No suprise. But surely a 15 knot breeze will heel many 25' boats.Surely a 36% increase will heel it more....
Of course,A new relative wind aboard the boat becomes a new sum in speed and direction as the boat moves ahead...aerodynamics of sail etc...etc.etc.
Plus thispractically (but as an aside) if the chop builds up,a small boat especially may "unconciously" payoff to maintain boatspeed ,heeling more to foot and not backwind the harder-pressed sail despite not altering the "trim" as the OP said.

but this is beyond the simple answer to a simple question:"...Is it possible..."
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Old 17-02-2011, 16:40   #29
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I called a number of my cronies who I have raced with over the last 50 years. They are all better sailors than I am. They all agree with me.
I trust them. Current does not effect helm pressure.

You have it your way. Time to quit "venturing" and time to go sailing.
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Old 17-02-2011, 20:52   #30
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Yesterday I went sailing in my 25 footer and I noticed that when beating on port I `ve felt more weather helm that on starboard (same wind, same sail trim)........ Juan
Juan,

Assumuing every thing else is equal (mast in straight, foils not asymetric or misaligned, weight distributed evenly in the boat, waves the same on each tack etc, etc), this is your problem.

The sail trim shouldn't necessarily be the same on each tack just because the true wind remains constant. You must trim to apparent wind and this may vary from tack to tack if there is current present.

I hope I can explain how apparent wind may change - picture is probably best. Take the example of the port tacking boat in the picture below.

The True Wind Speed (TWS) is 10 kts. TWS is the wind speed the boat would feel if it was anchored. So it could be called 'Wind Speed over Ground", but it isn't.

The boat sails through the water at 6kts, but the water itself is moving because there is current (relative to the ground). So the current could be called "Current over the Ground", but it isn't.

The current effects how fast the boat moves relative to ground (and so relative to the wind as TWS is also referenced to the ground). This could be called "Speed over the Ground". Hey, it is - SOG!!

So, your Apparent Wind Speed (AWS) is the sum of the TWS plus the effect of the SOG and it's true angle to the wind (TWA). for SOG=5kts and TWA=45 degrees, this is 2.5kts.

So the AWS for the Port tacking boat is 10+2.5 = 12.5kts.

Now take a look at the starboard tacking boat in the second picture. Its SOG is not being slowed by the current, but increased. Therefore it's AWS has been increased.

So, if you have the perfect trim on one tack and then use the same trim on the other, you may indeed feel a difference in the helm as you will be either over, or under trimmed.


Which is all a very long winded way of saying - If there's too much weather helm, and the boat is set up OK, then it's the trim that's the problem.

Of course the trimmers will say it's the helm that is pointing too low ; )
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