Heavy wind maneuver

Moderator: GreenLake

Heavy wind maneuver

Postby Shagbark » Tue Dec 22, 2020 6:59 pm

I was recently watching a youtube video posted by Tom Cunliffe "Jolie Brise - the boat that changed Tom Cunliffe's life". Around the 22 minute mark of the video he discusses how when the wind comes up he turns AWAY from the wind instead of rounding up. Albiet he is on a very heavy displacement gaff-rigged boat, but I've never given this maneuver much thought in dinghy sailing. Has anyone tried this method, any success? I don't know if I could even bring myself to trying it.
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Re: Heavy wind maneuver

Postby tomodda » Tue Dec 22, 2020 7:59 pm

Jolie Brise is beautiful, thank you for pointing out the video. As for bearing away in a gust, remember that they have a big old ballasted keel. 10.5 feet of draft, 16 tons displacement according to Wikipedia, and completely different underbody lines compared to a "modern" boat like ours. Without overanalyzing the hydrodynamics, let's just say that it's like comparing a Sherman Tank vs a motorcycle. A maneuver that makes sense for one will capsize the other..... Anyway, we shouldn't luff up in a gust either - ease, hike, trim. Just like any other dinghy.
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Re: Heavy wind maneuver

Postby GreenLake » Tue Dec 22, 2020 8:14 pm

If you have too much wind power, you depower your sails by changing the angle of attack. (Or by reefing, if it's ongoing).

To change the angle you can leave the trim where it's at and turn into the wind which flattens the angle of attack (angle between leading part of the sail and wind). Or you can let out the main, which also reduces that angle.

If you fall off in response to a gust, leaving the sail trim as it is, you increase the angle of attack, and if you fall off far enough, you get your sail square to the wind, turning it into a drag device. At that point, capsize is inevitable (if your sails are still sheeted in). If you let out the sail while turning down, you end up with competing actions. However, the vector of your sail force moves forward, which, in theory, should reduce the heeling force.

You also end up not adding boat speed to wind speed as directly and once you are pointing downwind, you even subtract the former from the latter.

I'm not sure how suitable this is as a gust response, but it's clear that you can sail downwind in pretty strong winds and the winds will feel less. Let's say, you go from 5 knots upwind boat speed to 5 knots downwind. If your apparent wind was 25 going upwind, it will now be a balmy 15 knots. And sail force goes with the square of the wind speed, so that difference will be like 625 compared to 225, or, in other words, down to a third.

In dealing with a temporary increase in wind speed, gust, when sailing upwind, the goal is to keep the boat manageable while not giving up any gains made to windward. Hence feathering (luffing up a bit) or (better) letting out the main (ease).

If sailing downwind, the old saying is "down in the gusts". Going deep downwind is slow (because of the subtraction of boat speed), so you do that during a gust, while in the lulls, you come up again, which changes the angle between boat speed and wind speed, leading to an apparent wind that's a bit higher, and perhaps even a course where you can use the sails as foils instead of drag devices. With luck, averaging these two directions points at where you are going, so you get the best of both. If not, you'll have to gybe at some point, but still will be sailing faster downwind than pointing straight at your objective.

From your mention (I have not tried to find the video) it's not clear in which context these reported remarks fit.
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Re: Heavy wind maneuver

Postby Fly4rfun » Thu Dec 24, 2020 12:01 am

I came across it a few weeks ago, very enjoyable.
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Re: Heavy wind maneuver

Postby GreenLake » Thu Dec 24, 2020 2:14 am

A PS: just remembered someone noting that if you get the DS on a plane in strong winds, it feels more stable. That was supposedly that guys way of dealing with stronger winds. Repeating that for what it's worth
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Re: Heavy wind maneuver

Postby tomodda » Thu Dec 24, 2020 12:32 pm

GL:

The video in question is here:

https://m.youtube.com/watch?v=ZzyGJeQg7bc

And the discussion about bearing away is at minute 22. As you wrote, the context of the discussion is key to understanding this bear away maneuver. They were discussing how to handle the sails on the Jolie, as she has no mechanical advantages. No winches, no windlasses, apparently just pulleys and "heave-ho." So, they bear away to reduce the forces involved. They talk about reducing apparent wind speed, but I don't think that is as much a factor as the gaff main simply being overtrimmed when they bear off. Notice they don't slack the main for the new downwind heading, nor trim when they head back up.

More interesting, notice the guy in background quickly trimming the running backstay. I'm curious about how they use that backstay in normal sailing, it's an old square-rigger trick, never seen it on a gaff cutter. I'm referring to the single backstay that they swap from side to side as they tack or jibe, not the modern running backstay. It's well inboard of the tip of the boom, so you can imagine the "fun." A bit of Googling showed me that they hit the backstay once in an uncontrolled jibe (I think in the Fastnet Race, 1920s?), tearing off their topmast - 40 feet worth! Must have been some "salty" words uttered after that....
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Re: Heavy wind maneuver

Postby Fly4rfun » Thu Dec 24, 2020 1:12 pm

Went back and watched what Tom had mentioned at 22:00 mark, at 25:40 ( or close) the bells went off again, confirmed what I had been suspecting but not yet jelled in my brain. he mentions that when heaving to, that the boat was loosing way because the sail were not SUCKING the boat along, thus the wind dose not push the boat with the sails but pulls the boat. again a laminar flow wing. :roll:
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Re: Heavy wind maneuver

Postby tomodda » Thu Dec 24, 2020 2:13 pm

Yes exactly. Upwind sucks and downwind blows, kind of like my first marriage! <rimshot> In all seriousness, read Avril Gentry's articles on aerodynamics in sailing. PM me if you don't have them and I'll email them to you.
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Re: Heavy wind maneuver

Postby Fly4rfun » Thu Dec 24, 2020 7:46 pm

Thanks Tom Have them
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Re: Heavy wind maneuver

Postby lemsteraak » Thu Dec 31, 2020 4:07 pm

You really feel this stability dynamic in a big catamaran (class B cat). If I felt the cat was unstable, like the windward hull was too high, I would steer "down" and keep the sails the same. If you steered up, you can even dump wind and the hull would still rise until it would lose power and dump back in the water. That is a very scary uncontrolled feeling. Steering down is very controlled. You almost feel like you steered back under the mast. This is a useful maneuver when racing as you gain speed.

On the other hand, you need to look at the boat and rig that Tom sails. Pilot cutters have a long keel so they don't turn, you need to ease the main to turn. Gaff rigs are set up for power so they create a lot of drag and heeling force so you can really feel it if you make a slight turn downwind, the boat powers up and gets more stable at the same time.

If you are racing in gusty conditions and feel you are overpowered you can use the steer downwind trick but ... it may mean you have encountered a lift. Sometimes you can make a radical turn upwind, like 20 degrees and go upwind like a banshee. I believe it is a combination of lift and since the boat is heeled over it is like the mast is really raked. Hike out and hold on.
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Re: Heavy wind maneuver

Postby Shagbark » Thu Dec 31, 2020 6:22 pm

Easing the main in a gaff rig to turn downwind; is that to allow the headsails to force the bow over?
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Re: Heavy wind maneuver

Postby tomodda » Fri Jan 01, 2021 12:48 am

Shagbark:

Yes, easing the main will throw the Center of Effort forward and give you a lee helm. However, this has nothing to do with a gaff sail. They do it on a gaff cutter because of the amount of the entire setup. Multiple headsail, lots of canvas forward of the mast. And it's usually a heavy boat with a long keel, not exactly the mist maneuverable boat on the water! So every bit of help turning is good. As I wrote before on this thread, every boat is different, every boat has its own "best" way of doing things.
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