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Old 10-10-2013, 05:42   #16
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Re: Depowering sails

The best way to learn is to understand why!
OK, as an engineer, I like to understand what is happening - sorry, but we get our kicks different ways, so.....
EACH sail has an effect that ultimately results in a force - this affects the boat by way of how it is attached. The Centre of Effort is a mathematical thing that results in an effect based on where the forces are attached. As such, reef your headsail and its force reduces, but that force still affects the boat somewhere between the forestay and the place the genoa sheet is attached to the deck.
What I am saying is that we can move the car forward and the application of force then moves forward. I have seen folks reef in strong winds, but the genoa car is well aft and thus they still get weather helm. Move the car fwd and that effect changes dramatically.

So do you want to reduce the power, or change its effect? Flatten the sail and you de-power it, reef and reduce the power, but change where it is sheeted and you change the effect of the power.
It is a complex thing, always changing but it is controllable in many ways. Some will suit you and others will not. Think of the effect and experiment - have fun and if the head hurts, blame the mathematicians, not the engineers!
Roger
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Old 10-10-2013, 06:31   #17
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Re: Depowering sails

I'm not sure if someone already mentioned it but before reefing you can also tighten the Cunningham on the mainsail. If you don't have one rigged they are simple and easy to install. By tightening the Cunningham it moves the pocket (or belly) of the mainsail forward depowering the main.

It will make the boat easier to control in high winds but the downside is it tends to take away some of your pointing ability. It can definitely be worth the trade off depending on your destination and how high you "have" to point to get where you are heading
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Old 10-10-2013, 07:43   #18
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Re: Depowering sails

Greetings and welcome aboard the CF, Roger.

It's about time you finally posted.
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Old 10-10-2013, 07:55   #19
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Re: Depowering sails

I would start with reefing the main and seeing how this changes things. Next I would furl the jib in somewhat to balance the smaller now main. Next I would take another reef in the main. And so on.

We only de-power in gusts - and in our boat this is simply easing the main sheet.

b.
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Old 10-10-2013, 08:03   #20
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Moving the car forward spills wind out of the top of the sail, creating a less efficient foil. While I do not deny that the CE is moved forward, I think you are more likely to notice that not only is the "effort" is greatly reduced, the CE is lowered, as the top of the headsail is not contributing much power. This helps reduce heel.

The same effect can be achieved by "twisting off" the main if you have a traveller. Raise the traveller, dump the vang, ease sheet, and spill the wind out the top.
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Old 10-10-2013, 16:44   #21
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Re: Depowering sails

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Originally Posted by I.Grind View Post
Moving the car forward spills wind out of the top of the sail, creating a less efficient foil. While I do not deny that the CE is moved forward, I think you are more likely to notice that not only is the "effort" is greatly reduced, the CE is lowered, as the top of the headsail is not contributing much power. This helps reduce heel.

The same effect can be achieved by "twisting off" the main if you have a traveller. Raise the traveller, dump the vang, ease sheet, and spill the wind out the top.
Moving the genoa car forward does exactly the opposite to the top of the sail.
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Old 10-10-2013, 18:25   #22
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Re: Depowering sails

Someone said raise the traveler and someone said lower it.

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Old 10-10-2013, 18:58   #23
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Re: Depowering sails

For most boats, a reef in the mainsail is the first sail area to be shortened. It has the most effect on reducing healing and weather helm. Most borts will sail faster with weather helm reduced though not always the case. Saw 7.2 knots sailing in flat water on my 25' water line boat with the rudder hard over against the stops to keep it on course. Heeling is also a function of boat's design. The newer flat bottomed boats experience big performance hits when the heel angle goes much beyond 20 degrees. The flatter they are sailed, the better. The older boats with slack bilges revel in putting the rail in the water and can make good time with heel angles up to 30 degrees.Sailing in SF Bay, you will get plenty of opportunities to practice your reefing skills. Seems Like we typically reefed and shook it out on the main at least 2 times almost everytime we went out. Usually furled the 135% genoa to about a 100% between the Bay Bridge and Angel Island as well as reefing the main in the summer.

As I said most boats will reef the main before furling the jib. If you got a boat with a small main, IOR type, may need to start with the jib. Experiment with your boat and see how she sails best.

Always best to tie in a reef early. Way easier to reef in 15k winds than 25k. You'll soon become familiar with where the wind will gust up in the Bay so you can plan ahead.

For Bay sailing, the best thing I did with my boat was run double line reefing lines back to the cockpit. Way way easier to tie in a reef sheltered by the dodger in the cockpit than standing at the mast.
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Old 10-10-2013, 19:06   #24
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Re: Depowering sails

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Originally Posted by Rick01541 View Post
Adjusting backstay tension applies to masthead rigs as well as fractional rigs if it is setup with backstay adjustment. Tensioning the backstay on a masthead rig bends the mast and flattens the mainsail. This along with flattening the foot of the sail with the outhaul depowers the mainsail. The next step in depowering the mainsail is to reef.

That's right. Just in case this doesn't quite make sense to our newer sailor, when you flatten the sail -- take out its belly -- it just can't catch as much wind. Also it no longer has an aerodynamic shape. It is a way of depowering, or having the boat catch less energy from the wind.

I think the first time you reef you will be astounded at how well the boat sails, and how much a frustrating sail turns into a delightful one. My favorite way of sailing my old boat, a tender tippy cup of a thing, was reefed.
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Old 10-10-2013, 19:08   #25
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Re: Depowering sails

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Originally Posted by barnakiel View Post
I would start with reefing the main and seeing how this changes things. Next I would furl the jib in somewhat to balance the smaller now main. Next I would take another reef in the main. And so on.

We only de-power in gusts - and in our boat this is simply easing the main sheet.

b.

That's right. Spilling the sails is for a momentary gust. If the winds are building, it's time to reef.
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Old 11-10-2013, 03:57   #26
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Moving the genoa car back twists the genoa and spills wind off the top. Loosening the mainsheet twists the main and spills wind off the top. I view these as temporary depowering moves in a gust.

The sequence of events should be to flatten the sails as the wind increases and then reef as the wind continues to increase. Do just the opposite as the wind decreases.
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Old 11-10-2013, 04:48   #27
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Moving the genoa car forward does exactly the opposite to the top of the sail.
Oops, you are correct, right idea, wrong action.
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Old 11-10-2013, 04:52   #28
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Re: Depowering sails

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Originally Posted by I.Grind View Post
Oops, you are correct, right idea, wrong action.

P-TOUCH labels are extremely durable, even outside on a sailboat. I have a friend who is a fanatic about sail trim. he has his tracks labeled according to point of sail, which usually gets the twist right. Whether it works 100% I can't say, but it must be pretty dependable, because he put the labels on four years ago when he was racing so there would be no doubt.

He also used to label all the running rigging. I've done the same, for instance with my clutches. People who are on the boat for the first time really like it.
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Old 11-10-2013, 07:06   #29
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Re: Depowering sails

Quote:
Originally Posted by Djarraluda View Post
The best way to learn is to understand why!
OK, as an engineer, I like to understand what is happening - sorry, but we get our kicks different ways, so.....
EACH sail has an effect that ultimately results in a force - this affects the boat by way of how it is attached. The Centre of Effort is a mathematical thing that results in an effect based on where the forces are attached. As such, reef your headsail and its force reduces, but that force still affects the boat somewhere between the forestay and the place the genoa sheet is attached to the deck.
What I am saying is that we can move the car forward and the application of force then moves forward. I have seen folks reef in strong winds, but the genoa car is well aft and thus they still get weather helm. Move the car fwd and that effect changes dramatically.

So do you want to reduce the power, or change its effect? Flatten the sail and you de-power it, reef and reduce the power, but change where it is sheeted and you change the effect of the power.
It is a complex thing, always changing but it is controllable in many ways. Some will suit you and others will not. Think of the effect and experiment - have fun and if the head hurts, blame the mathematicians, not the engineers!
Roger
I don't agree. Moving the car aft moves the CE down, because you are flattening the chord, depowering the sail overall, and twisting the top, further depowering it. In my experience the benefit of this is going to be more efficient to the overall performance of the boat than keeping the car forward. If you have weather helm that is inducing drag and making the heel foil inefficient with the car aft, it's time to reduce sail.

Every boat is different in how it responds to sail trim. The key is to understand the principles of sail trim and experiment with them to determine what works best on your boat in various conditions.
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Old 11-10-2013, 08:12   #30
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Re: Depowering sails

All good advice, but I find it helpful to also understand what was going wrong.

I don't think that in this case reefing the main (although it is the right thing to do) would have reduced the weather helm.

I am a beginner but this is what I see:

He was well healed on a beam/broad reach with the main luffing and tremendous weather helm (the wheel was all the way leeward).

I think he was probably a little past a beam reach and the boat was so healed over (due to the genoa being all out, and maybe over trimmed) that the shape of the wetted hull had him heading up. And the fact that the rudder was almost horizontal made in difficult to correct. Sort of like rounding up and broaching with the spinnaker out.

Of course he should have been reefed and had much less genoa out, I just think it might be helpful for the OP to also understand the dynamics at play.

Like I said, I am a beginner, does this make sense?
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