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Pull up slightly on the swing keel?

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indecentseas
1st Mate

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Canada
67 Posts

Initially Posted - 06/20/2014 : 10:58:18

Recently someone (whose judgement I trust) suggested that I not leave my swing keel at the lowest possible position but that I cinch up slightly on the cable. He said you need a bit of tension on the keel so it stays solidly in place.

Does this advice seem sound?

I gave it a try. I pulled my keel up about half a rotation. It sounded and felt like my boat was playing the double bass. When I reintroduced some slack the hum went away

I'm guessing I got bad advice. Any thoughts from the forum?

One note, I just cleaned my bottom and keel for the first time since getting the boat 2 years ago. Maybe that's just the sound of a clean cable.

Edited by - on

DavidBuoy
Admiral

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USA
707 Posts

Response Posted - 06/20/2014 : 11:27:47

I forget where I heard you were supposed to tension it 1/2 to 3/4 of a turn after lowering but I do it everytime. David usually starts humming once I hit a decent speed so I use it as a knot meter. He hums when hes happy!

Thinking in my head for a reason why this is good practice all I can really come up with is to keep tension on the cable and fasteners. If the cable is whipping around a bit while it's loose down there maybe it could loosen something? Maybe unspool the cable a bit on the winch? not sure..

Maybe just a bit of tension is enough to keep it from crashing through the keel box in the event of - lets say hitting a large wave.

Edited by - DavidBuoy on 06/20/2014 11:29:14

Deltarat
1st Mate

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USA
69 Posts

Response Posted - 06/20/2014 : 12:07:29

My reason for keeping tension on the cable is to keep the keel from slamming into the hull and sinking the boat if I run across something shallow and the keel is pushed up the drops back down in a hurry when the bottom falls away.

Edited by - on

pastmember
Master Marine Consultant

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2402 Posts

Response Posted - 06/20/2014 : 12:36:51

quote:
Originally posted by Deltarat

My reason for keeping tension on the cable is to keep the keel from slamming into the hull and sinking the boat if I run across something shallow and the keel is pushed up the drops back down in a hurry when the bottom falls away.

Good rational, it would have to something hard and substantial to move 1500 pounds but those things are out there.
Keel hum is a recurrent thread topic that has not been brought up for a while. It is annoying to some and fun to others.

Edited by - on

Davy J
Master Marine Consultant

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USA
1511 Posts

Response Posted - 06/20/2014 : 15:02:30

quote:
He said you need a bit of tension on the keel so it stays solidly in place.

Your 1500 pound keel will stay solidly in place without tension on the cable. If it doesn't, you have some other sort of problem.

I'm in the "that hum annoys the crap out of me" camp, so I leave slack in the cable and enjoy silent sailing....

Edited by - Davy J on 06/20/2014 15:03:20

GaryB
Master Marine Consultant

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USA
4275 Posts

Response Posted - 06/20/2014 : 17:56:42

My Hobie 16 used to sing when I was going fast. I liked it and used it as a speed gauge.

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Stinkpotter
Master Marine Consultant

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Djibouti
9013 Posts

Response Posted - 06/20/2014 : 20:38:38

quote:
Originally posted by GaryB

My Hobie 16 used to sing when I was going fast. I liked it and used it as a speed gauge.

That's a whole different song--sorta like ripping a bedsheet... I've heard it and love it!

Edited by - on

Lee Panza
Captain

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USA
465 Posts

Response Posted - 06/20/2014 : 20:46:16

I dunno, but I wish someone with metallurgical expertise could chime-in on this question; it does arise periodically.

My thinking is that a taut cable that hums is oscillating rapidly - vibrating - and vibration is often cited as the cause of metal failure. The vibration is concentrated in the cable and the pin connecting the cable to the keel, and I wouldn't want to stress either one unnecessarily.

On the other hand, when I back-off a turn or so, I would expect the cable to describe a slight arc as it drags through the water, not a loose bight flopping around. If it oscillates at all it would be very low frequency, very little energy involved.

To me it seems intuitive that a slightly loose cable would be less stress-inducing than a taut, humming cable. But, like I said, I'd feel better hearing from someone who likely knows more about this than I do.

Edited by - on

Dave5041
Former Mainsheet Editor

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USA
3754 Posts

Response Posted - 06/20/2014 : 22:03:17

Turbulent water behind the keel means that the cable will vibrate whether it is tight or loose. Loose will have larger amplitude oscillation at a lower frequency and begin at lower speed. Increasing tension means higher frequency, lower amplitude oscillations that come into the audible range. To a point, increasing tension raises the frequency and the speed at which the oscillation or vibration is induced. A loose cable snapping around seems less desirable to me. The hum also seems to pique the curiosity of dolphins when I'm sailing in the gulf.

Edited by - on

Jweikel625
1st Mate

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USA
59 Posts

Response Posted - 06/24/2014 : 07:59:46

I take the slack out of mine. I prefer to not take a chance of the keel head hitting my new fiberglass repair in the trunk. The previous owner told me to do it, so I did. But after repairing the aft end of the trunk from previous damage, I realized the thickness of the trunk is not thick at all. Repetitive hitting will crack it. I also like the hum to indicate speed. I also have to sail occasionally with the keel partially down (18 cranks vs. 28 cranks) because of shallow water. Light winds of course.

Edited by - on

Merrick
Navigator

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USA
192 Posts

Response Posted - 06/24/2014 : 14:38:54

According to CD the cable is weakened by the back and forth movement when the cable is slack. I've wondered if there is any proof of that or it's someone's theory. Vibration is movement too. There seems to be many boats doing it both ways and I've not read any mention on this forum of premature cable breakage. I guess a good question would be has anyone had a cable break that was on a boat less than three years? 5years? and if so was it sailed slack or tightened?
Salt or freshwater?

Edited by - on

Deltarat
1st Mate

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USA
69 Posts

Response Posted - 06/24/2014 : 15:30:36

I just finished replacing my entire keel lifting system with the exception of the winch. New Pivot pin assembly, cable roller ball, Cable, keel bracket and an extra long keel bolt (2 1/2") I'm sure that mine had not been replaced in over 15 years and has been sitting in semi fresh water (the California Delta) and the only thing close to failure was the keel bolt, it seems pretty much the only thing holding it place was rust.

Edited by - on

DavidBuoy
Admiral

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USA
707 Posts

Response Posted - 06/24/2014 : 18:43:17

quote:
Originally posted by Merrick
...and I've not read any mention on this forum of premature cable breakage...

Have you not??

Edited by - on

dmpilc
Master Marine Consultant

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USA
4593 Posts

Response Posted - 06/25/2014 : 05:48:44

We were in a club race a few years ago and sailed too close to the first turning buoy. The keel caught the buoy cable, lifted up a little bit and came back down. We felt s bump when it came down. I had the keel cable slack. End result was a hairline crack in the keel trunk that leaked about a gallon per day. Cost me over $800 to have the keel trunk leak fixed and the trunk reinforced. After that, I always kept a little tension on the cable and do so in our C22 as well. As stated above, the cable also becomes an audible knot meter with the pitch going higher as you go faster.

Edited by - on

Steve Milby
Past Commodore

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USA
5851 Posts

Response Posted - 06/25/2014 : 06:38:25

I have never seen or heard any reason to believe that keeping it slack or taut matters significantly with regard to the durability of the cable. On my C22, I took up enough slack so that it didn't sway freely, but not so taut that it would vibrate and hum noticeably. If the cable isn't bar tight, the vibration doesn't get translated into the hull, and amplified by the hull.

Edited by - on

Merrick
Navigator

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USA
192 Posts

Response Posted - 06/26/2014 : 19:33:15

Davidbuoy I don't remember reading about a cable breaking under normal use that was less than 3 or 4 yrs old. Have seen some keel attachments breaking or pulling out.Butthen havent researched it either.

Edited by - Merrick on 06/26/2014 19:58:28

MrKawfey
Navigator

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USA
124 Posts

Response Posted - 07/01/2014 : 09:34:38

Vibration in the cable is definitely bad in the long term. The place where it's most likely to cause a problem is where the swaged fitting at the bottom is. The rest of the cable, being stranded, is like stranded electrical wire. Even with tension on it, the strands should be fairly resistant to work hardening from vibration because of the slippage between the strands. The swaged fitting, however, prevents the cable from moving freely and requires the metal to flex (and ultimately fatigue) at that point.

Removing the tension should help as the fitting itself could then flop around. However...I am surprised that no one else has mentioned hum in a slack cable. I find that the only way to minimize hum in my cable is to get just the right amount of tension on it. On our boat, even a totally slack cable will hum at certain speeds (short of letting out 2 feet of extra cable).

Generally, when we first put the keel down I have to play with the tension quite a bit while we are motoring at different speeds to get it just right. Even then there might be some fine tuning after we are under sail. Once it is set right we can basically forget it until we have to move the keel again.

Edited by - on

sweetcraft
Admiral

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USA
816 Posts

Response Posted - 07/01/2014 : 21:17:37

Interesting discussion as I put slack in the cable to stop the high pitch hum. Early years until the slack was put in the dishes and silverware would vibrate too. I changed the cable and ball with pin with a new hose up to the winch. The ball had a great flat spot and I believe would not turn when keel is lowered or raised. I do change the ball too with the new cable so I do suggest to check your balls too.

Edited by - on

DavidBuoy
Admiral

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USA
707 Posts

Response Posted - 07/02/2014 : 05:03:43

quote:
Originally posted by sweetcraft

...so I do suggest to check your balls too.

That's also what my doctor says

Edited by - on

Mark Maxwell
Captain

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USA
329 Posts

Response Posted - 07/11/2014 : 16:27:21

I had a 22 with a swing and would let the cable loose enough to just stop the hum. It would still hum at hull speed but not during anything less. My thought is the higher energetic hum from a tensioned cable imparts more wear on the swag and pin than by leaving it loose. Also if you are tensioning the cable in hopes of "catching" the keel on ground strike, I think you are dreaming. 1500lbs swinging to a stop can inpart much more weight than a static hold. (Take a 5 lbs weight and drop it on your foot from 2 inches....) Similar to the old discussions on trailering with the cable tight or keel up at the slip... or on the 22's the little lock down bolt in the keel trunk for preventing the keel from slamming back down in the event of a knock down.....ain't going to happen.. Too much weight.
Anyway, I digress, I believe I read in an old owners manual that the cable is to be kept without a load. The amount of slack is not defined, but as stated before, just enough to not be tensioned.

Edited by - Mark Maxwell on 07/12/2014 06:55:33

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