Depowering off the wind

[Alan]

Someone told me that when you want to depower the sail on a beam reach or closer to the wind, you let out the main sheet. So far so good - I've read or heard that from any number of sources.

However, he said that the opposite is true - when you're sailing off the wind and you want to depower, you pull the mainsheet in. It kinda-sorta makes intuitive sense, but I can't remember reading or hearing that anywhere else.

The man who told me this is a lifelong sailor in keelboats. Is he correct?

[GreenLake]

Alan,

you write:

Someone told me that when you want to depower the sail on a beam reach or closer to the wind, you let out the main sheet. So far so good - I've read or heard that from any number of sources.

Expressing it that way makes it sound like you've never sailed before. This one's so in your face that I very much doubt you can sail for any time and not have ample personal observation of this.... No need to be coy, here. Anyway, yes, we can agree that this works as claimed.

However, he said that the opposite is true - when you're sailing off the wind and you want to depower, you pull the mainsheet in. The man who told me this is a lifelong sailor in keelboats. Is he correct?

Well, when you sail dead downwind, what counts is the projected area (see Scott's thread on "wind force calculation"). By putting a sail at 90 degrees to the wind, you maximize the projected area. (Full 90 degrees is not possible DDW on the DS, because of the back-swept shrouds, btw).

If you sheet in the main in those conditions, say to 45 degrees, you now have only about 70% of the projected area, and if you try this in moderate winds you'll find that you will sail more slowly than another DS with the main fully out.

When you have a flat surface at right angles to the wind, lift and drag are the same (the only power generated by the surface is through drag, and it's perpendicular to the surface). When you go to a different angle, two things happen. Flow will establish itself over the surface and resistance is no longer the only force. Drag will still point forward (with the wind from behind) but the sail will now generate lift as well. Lift is always taken at 90 degrees to the wind, so in this example, the lift would not push the boat forward, but cause it to heel.

Now, if you try this maneuver in high winds on a boat that can capsize, then creating large heeling forces (strong winds) might lead to capsize. In that way, a keelboat might indeed be different. The danger would be, that, with the main sheeted in, your boat would round up, and if it does, you'll find yourself with the wind again at 90 degrees from the sail, but now the whole force wants to heel you over, and in strong winds is likely to succeed. You might manage to lay over the keelboat, but the difference is, you wouldn't be in the water, swimming.

[Breakin Wind]

Now, if you try this maneuver in high winds on a boat that can capsize, then creating large heeling forces (strong winds) might lead to capsize. In that way, a keelboat might indeed be different. The danger would be, that, with the main sheeted in, your boat would round up, and if it does, you'll find yourself with the wind again at 90 degrees from the sail, but now the whole force wants to heel you over, and in strong winds is likely to succeed. You might manage to lay over the keelboat, but the difference is, you wouldn't be in the water, swimming.

Thanks GL - Your paragraph above, reminded me this what drove my comment about tacking being easier for me than gybing in my "10 things I learned from my first year sailing" piece. At the time I wrote it, I knew it to be true (for me) but wasn't recalling exactly why, until I read your posting here. While practicing gybing this summer on a windier day, I was pulling in the mainsheet (nearly completely in) preparing to gybe, and a big side gust caught me unprepared (again, learning here) and the boat heeled sharply. That may well have been the day I forgot to put the centerboard down too and if so, I took in about a foot of water before I kicked the mainsheet out of the camcleat and depowered. It scared the heck out of me, and now that I think about it, I was very uncomfortable gybing after that, deciding to tack 270 degrees around unless my spacing wouldn't allow it. Later in the fall I gybed a few more times and it all seemed to work great so I couldn't remember why I'd thought it was kinda scary until remembering it just now. Must've blocked it out.

[GreenLake]

Scott,

Having the CB up makes you less likely to capsize.

Why?

Instead of "tripping" over the CB and capsizing, the hull can slide sideways through the water in response to sideways force.

(as always, it's a matter of degree, and even w/o any CB, some conditions will make you capsize).

Are you sure it was a gust from a novel direction, or did you perhaps "round up" without noticing, putting the wind from the side.

[Breakin Wind]

Thanks GL,

May well have been rounding up. There were a good number of bad experiences last year and they do tend to run together, and I suppose they mostly occured when I was paying attention to something else. Fortunately there were many more good experiences to offset that bad ones, plus the bad ones add to the learning curve too, so I guess as long as one survives them, they can be said to be good as well.

Thanks,

[Alan]

GreenLake,

My 20-hour sailing career includes only one instance of letting out the mainsheet to depower, but, yeah, it worked as advertised.

I suspected the downwind question had to be more complicated than just "pull in the mainsheet to depower," but I couldn't quite puzzle it out. Now I have one less way of getting in trouble once I actually get back to the water. Thanks.

[GreenLake]

My 20-hour sailing career includes only one instance of letting out the mainsheet to depower, but, yeah, it worked as advertised.

Alan,
first, I'm glad that things worked as advertised for you.

Even if you've not sailed as much yet (you were probably hoping for more, last season, weren't we all) the basic mechanics can be observed almost every minute. Mostly you might have observed the reverse, that is, the acceleration of the boat when you sheet in.

Btw, I did not intend to put you on the spot in any way - sailing is a sport where you can pick up the basics in a weekend and then spend your life trying to get good at it. I like discussions like this one, because that's how I learn - by puzzling out things, and by getting explanations for things that I can observe but for which I don't yet have a full understanding of the ramifications, factors and underlying causes involved. When I think I do have an explanation, trying to write it down will quickly let me know whether I really possess a coherent understanding or whether I'm just fooling myself into believing I do. Trying to put things into words is what I do here, so I don't lay claim to having the "best" answer on any subject - and more often than not, after another season or two, my own understanding of things tends to evolve as I pick up new tricks or have more first hand experience in whatever it is. That goes for sailing as well as fixing boats.

Now, back to depowering off the wind: sheeting in the main briefly in anticipation of a gybe is standard practice, but once you make the turn, you want to let the main out smoothly but quickly and in moderate winds I've never come to grief with that. As Scott points out, there's always the alternative of rounding up and tacking, instead of doing a gybe, in higher winds.

[Alan]

No worries, GreenLake. I know you weren't trying to put me on the spot. You've given me a lot of really good advice over the last few years.

My only sailing experience this year was to help a friend move his Pearson 323 from South San Francisco to Redwood City, with a side trip into SF Bay. It was fun, and I learned quite a bit about the interaction of commercial ship traffic and sailboats, but not a heck of a lot that translates to a DaySailer.

The consolation prize for my lack of sailing experience over the four years (!) I've had the boat is that I'm able to read advice from you and others, which will probably keep me from making rookie mistakes when I finally do get to the water (I'm retiring early next year, so, hopefully...).

I shudder to think of all the things I did wrong the time I took the boat out on Lake Tahoe, before I found this board. Let's see here - left the shrouds slack because they came that way, pulled the outhaul as tight as possible in little to no wind, flew just the mainsail in the same conditions because someone had told me I should get a few weeks' experience before I flew the jib, did an unintended jibe (with no damage, thanks to the light air), and didn't secure the jib halyard very well so it fell down, dragged alongside and wrapped around the propeller shaft just as I was discovering that if you lower the mainsail without a topping lift, the sail and boom pretty well fill the cockpit. The dented fender from grazing the boat ramp wall was just gravy.

You're right about observing the reverse. I've also observed that when the helm doesn't follow the captain's instructions to let the mainsheet out, the jib sheet crew on the lee side ends up sitting in a puddle of water that came in over the rail. (The jib sheet crew was me, of course.)

Especially since the Tahoe trip, I've spent my enforced landsmanship dreaming up things that could go wrong (or reading about them here) and coming up with solutions. So, I expect most of my sailing adventures to be the good kind.

A few years ago a 75-year-old friend mentioned that he'd been sailing for 60 years, and he still learned something new every time he went out. By the time I've been sailing for 60 years I'll be 120, but dagnabbit, I intend to still be learning.