Out of control...

Moderator: GreenLake

Out of control...

Postby GreenLake » Wed May 30, 2018 11:26 pm

During a recent beer can race, we had a scary incident where we nearly sunk a boat three times our size. Well, we might have dented it.

We were both going upwind and they were on starboard tack (wind from the right) and we were on port tack and therefore had to keep clear. We weren't going to be able to cross in front of them, so the plan was to go behind. Nothing easier than that, just fall off a bit and duck their transom. Something we do dozens of times an evening on a crowded lake.

Well, things didn't work out as planned. A big gust hit, accelerating us towards the mid section of the bigger boat, no matter how hard we yanked at the tiller. Letting fly the sails did not help! :shock: In this instance, although I hate to admit it :oops:, it was the skipper of the other boat who saved the situation. We simply could not turn downwind.

After we recovered from the shock, we looked for a cause and soon, enough, found that the main sheet had twisted around itself in the part where it goes from the end of the boom to the block on the bridle.

1318

This is an older picture (I since have replaced both mainsheet and traveler) but it shows the location I mean. In the picture, the two parts are shown basically parallel, with just a small distance between the blocks. (In the old setup, the bottom block does not rotate, therefore forcing the quarter turn you see in the photo.)

What we saw that evening, was that the two parts had twisted fully around each other 4-6 times, and prevented the blocks from coming as close to each other as would be normal for upwind sailing.

Worse, though, the twists induced so much friction that the boom would not move out, even with the sheet fully released. Normally, the more force you have on the sail, the easier the main sheet releases, here it was precisely the extra tension during the gust that fully locked the twists, whereas earlier in the evening we had been able to let out the sheet as needed, say when going downwind.

The block at the bottom is free to spin, so normally any twist should pull out as tension is put on the sheet. Not this time. After we manually untwisted the sheet by rotating the block, the twist came back each time we tacked. At the dock we found that that end of the sheet had a huge amount of internal twist in the line; unusual, because it's a braided line that should normally not have it's own twist.

Anyway, this is the first time this ever happened to me and, of course, I'm curious to know whether anyone has a suggestion as to a possible cause. (We leave the mainsheet rigged, but take the boom off the mast when not sailing.)

One thing we realized later is that letting fly the jib, even though it helped depower the boat a bit, had the unintended consequence of making it even harder to steer down. But then we didn't realize that the main had been "stuck" until the incident was well past.
~ green ~ lake ~ ~
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Re: Out of control...

Postby GreenLake » Wed Jun 06, 2018 9:33 am

I completely untwisted the sheet and last time we went on the water there was no indication of the same problem re-occurring.
~ green ~ lake ~ ~
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Re: Out of control...

Postby hsumralljr » Wed Jun 06, 2018 9:47 am

Depending upon your rope coiling/uncoiling technique, you can introduce torsion into the rope. APS has a video on their site showing how to avoid this problem.

https://www.apsltd.com/aps-advisor/coil ... rt-advice/
Herb Sumrall, Jr.
Baton Rouge, LA

DS1 #3235
DS1 #2844
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Re: Out of control...

Postby GreenLake » Wed Jun 06, 2018 10:19 pm

Yes, I'm aware of that issue. And it's a good one to know about, so thanks for sharing the video.

In this case, I can confidently rule out coiling / uncoiling as a factor, because I don't ever coil the mainsheet. It stays rigged. All I do is take the boom off the mast and place it (with sail and sheet attached) on the seat. (I have a DS1 so I can fit the boom easily into the cockpit as there's no cuddy bulkhead/door to get in the way).

The mainsheet block on the CB trunk can swivel 360 degrees. It is possible that I may have inadvertently rotated it a full 360 degree during a tack (and somehow done that several times in a row in the same direction).

If that's the solution, why has it never happened before? - I've sailed about 100 times with that mainsheet. It doesn't show any signs of aging or wear; it's quite overdimensioned from a load perspective to allow for nicer handling, meaning that it's less likely to fatigue.

Also, as far as I can tell without photographic evidence, the few times I had the boat out before that, this season, there wasn't any problem with the mainsheet and the boat sailed really well.

PS: gone over photos from earlier seasons and found most have the two parts of the mainsheet fully parallel, but a single 180 degree twist is on a couple of them (from the same week). Not that I make a point of taking photos of the end of the boom...
~ green ~ lake ~ ~
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Re: Out of control...

Postby badgley » Wed Jul 04, 2018 8:18 am

I've noticed this before on our DSII. For me, it's definitely a twist issue. If there is any twist in the sheet as you ease it, once that twist gets into the blocks it wants to wind one of them against the other and the whole 3:1 setup starts to twist. In this case, if I manually untwist one of the blocks they spring back, so they definitely don't want to unwind on their own, even though they are free to turn. I don't think it's from coiling, but just from handling the line during sailing. Sheet in the main, set down the extra line, next time you pick it up there's maybe an extra 1/4 to 1/2 twist of line in there because of a funny loop or someone stepped on it, etc. Then rinse and repeat this for a few hours. I think usually these cancel each other out as you go from one tack to another, but just by chance it can sometimes get randomly uneven and put a few full turns in the sheet one way or another. I've played with it, and if I sheet in the main, intentionally put some opposite twist into the line and then ease it out, it will work itself out and the blocks will return to parallel.

So maybe you had a bad luck rare situation where something about handling the sheet that day was putting many more little twists into your sheet in one direction more than the other? No idea how to prevent that though, if that's what happened. On ours, I do try to feel the line before easing the sheet (when there's time) and make sure it's slack and untwisted. Plus on the DSII the whole setup is right there in front of your face so it's easy to see when it starts happening.
Brian Badgley
1982 DS II #10911 EGRETTA
Blacksburg, VA, USA
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Re: Out of control...

Postby GreenLake » Wed Jul 04, 2018 12:52 pm

I think you have this figured out, Brian. Definitely how this works. Just my luck that I had to find out about this with a near collision. After years without issue I had like 4-5 full turns.
~ green ~ lake ~ ~
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Re: Out of control...

Postby badgley » Thu Jul 05, 2018 9:52 am

That was dumb luck for sure - I'm still surprised the goofy mechanism I described could have gotten you that far out of whack. So it might have been something else we're missing, but I'm not sure what it would have been. Either way, it never even occurred to me that ultimately twist like that could lock the main sheet inadvertently, so thanks for posting.
Brian Badgley
1982 DS II #10911 EGRETTA
Blacksburg, VA, USA
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Re: Out of control...

Postby GreenLake » Thu Jul 05, 2018 4:10 pm

Yeah, big surprise here, too. I may have somehow systematically moved the main from side to side during tacks so that the result was a clockwise turning of the mainsheet fitting one the CB trunk. On another boat I have that fitting cannot spin 360 degrees, which prevents this issue, but can leave you stuck if you pick up the sheet from the wrong end, because the fitting won't then spin to clear.
~ green ~ lake ~ ~
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Re: Out of control...

Postby K.C. Walker » Sun Mar 10, 2019 12:29 pm

You likely have this straightened out by now. However, I had a couple of close calls with the main sheet fouling with my motor. Yes different but the solution that I came up with would likely help you out, as well. I use a non-swiveling block on the boom and moved it forward. By having the sheet attachment on the boom and the block leading forward separated, there seems to be no tendency for twisting. It appears from the photo that your main sheet is double braid. I thought I had remembered that you had changed that out to single braid, but maybe not. Single braid is very low twist. I've been using New England Ropes Bzzz line and been satisfied with it.
KC Walker, DS 1 #7002
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Re: Out of control...

Postby GreenLake » Sun Mar 10, 2019 11:11 pm

I get some fouling of stern cleats and motor (less with the EP Carry) when gybing.

The twist issue has not reoccurred. At least not anywhere near as bad.

My line is similar to the Bzzz line, but not the same rope brand. (I have a whole thread on all the line I use on my boat).
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