louder than normal keel hum

Stu Jackson · Jun 16, 2015

Is the hum from the cable for the swing keel?

If so, just change the tension on it with the winch.

shanester · Jun 17, 2015

My keel only hums with tension on the cable. I always put slack in the cable. If you like the hum that you had before then try to slack the cable and then tighten it a little. Maybe your keel is not all the way down for some reason. Try to get some underwater photos or video of the cable to see if there is any debris on it.

centerline · Jun 17, 2015

artfull dodger said:
I have sailed my 22 for years and am very used to the hum around 4 tp5 knots. Something is wrong. It is starting to hum at 1 knot and just gets louder and louder. I am about ready to sink this thing I am so frustrated.

The boat was pulling to starboard as I think I picked something up. Now it is straight again but really loud hum.

Please help.

The guy I bought my first boat from, a mac 21, purchased it new, and didnt know that loosening the keel cable would stop the hum... he actually named the boat "Dynamo Hum"... giant bold black letters down the side of the boat, 8 feet of name on each side of the boat.
He did not lock his keel down, so the cable tension could not be loosened... which causes humming.

My sailing practices are much differnt than his, so i never had an issue.

But anyway, you could have some debris on the cable that could be causing the viberation at a lower speed than normal, but inserting the lock down pin and slacking the cable will cause the hum to go away completely, even if there is debris on the cable.

centerline · Jun 17, 2015

artfull dodger said:
ahhh, good tip!

I have never used the locking pin. do you have dimensions of the pin? can i use a stainless bolt?

The keel is all the way down and as i was writing my first post i realized that there must be some debris still caught on the cable. good to hear some positive enforcement on my speculation.

the boat was aggressively pulling to starboard the other week, i was prepared to lift the boat out of the water to inspect and repair. as i was motoring over to the lift a few days ago there was no pull. so i decided to go sailing lastnight! the wind was soo light that i made only 1 or 2 knots but the humm was not tolerable. So i decided to go over to the beach to dive on the keel. due to the rain the water is soo murky i cant see anything so i didn't even go over to the side.

I have always thought the hum was really annoying. will there be excess drag with it slacked off?

No excess drag, and arguably even less drag as the cable can then wash around and take the path of least resistance thru the water behind the keel..
The hold down pin usually is a 3/8 bolt... on that particular boat, i dont know for sure, but if you ask another question in the "ask all sailors" forum on this site, about the keel lockdown bolt for that particular boat, you will likely get all the information that has ever been written on the subject, plus some commentary... ;-)

shanester · Jun 18, 2015

On our boats you do not need the lock down bolt to slack the cable. If used it should be made of aluminum so it sheers off in case of an accidental grounding without causing damage to the centerboard trunk. I can't remember what diameter it is off hand.

centerline · Jun 18, 2015

shanester said:
On our boats you do not need the lock down bolt to slack the cable. If used it should be made of aluminum so it sheers off in case of an accidental grounding without causing damage to the centerboard trunk. I can't remember what diameter it is off hand.

this is quite possible, but not many boats were designed to have the weighted keel rest against the keel trunk, as this places the stress in the wrong spots, especially when you hit a bump or stump with the keel, it raises and then slams back down against the trunk.... designers dont usually leave these things to chance.

also, its very unlikely that an aluminum bolt is the proper thing to use, for these reasons....

aluminum corrodes too easily and quickly...
aluminum bends too easily unless a strong alloy is used, in which it will defeat the purpose that you propose...
when the aluminum bends, it will easily bend in a horseshoe shape making it very difficult to remove...
if in fact it did shear, and unless you carried spares, you would be without, leaving the boat vulnerable to severe damage in a knockdown...
or if it only sheared halfway thru, you could never remove it, until you grounded again and sheared it the rest of the way.
the designers knew all of this and could never know what remote location or severe weather the boat may be in when the owner grounded the keel, so for simplicity and dependability, I would bet they used a 3/8 stainless bolt in the original design... but some PO of the boat may have tried to second guess the engineers and installed something of their own that will be inferior to the stainless bolt.

shanester · Jun 19, 2015

I just looked in my owner's manual to see what is says about locking down the keel. It does not say what material the bolt is. I am going to assume SS because that is what mine is and the manual states that severe damage will occur if left in and the boat grounded.

this is quite possible, but not many boats were designed to have the weighted keel rest against the keel trunk, as this places the stress in the wrong spots, especially when you hit a bump or stump with the keel, it raises and then slams back down against the trunk.... designers dont usually leave these things to chance.

The manual also states that the bolt is not necessary except for rough weather.

aluminum corrodes too easily and quickly...

We have cast iron keels so I doubt this bolt would be an issue compared to our keel corrosion.

aluminum bends too easily unless a strong alloy is used, in which it will defeat the purpose that you propose...

This could be a real issue in the event of a knockdown. There would be a LOT of stress on the bolt from all that leverage. It would shear though as there is not much clearance between the keel sides and trunk. (small gap)

In fifteen years I have not locked my keel down. It may seem unsafe to some. We trailer sail a lot. We beach (or nearly) our boat a lot. We sail in areas of shallow water sometimes. We do not sail in nasty conditions. I have the pin if ever needed.

I like the Catalina 22 design better. Maybe this design can be retrofitted to our boats but made larger/beefier. It would allow you to loosen it if grounded. The old Catalina 25 did not have a keel lock down. 1500lb keel by the way.

srust58 · Jun 19, 2015

I would agree with shanester. We seldom use the locking bolt in 30 years of sailing our Sirius 22. Although we do sometimes sail in rough conditions on Lake Superior. Those are the only times I have used the looking bolt. I am pretty sure it's a cheap zinc plated 1/4 inch eyebolt....that's what we use..in freshwater it's not a problem. 3/8 is way to big and not necessary. We lower the keel until it rests against the stop and then put some tension on the cable so it takes the load. This so if we do hit something as the keel comes back down it does not slam with full force against the trunk. Another way of doing this is to let it rest against the keel locking bolt so that will act as a shock absorber if you hit something. This of course negates the locking aspect of it. I have done this and after hitting something it did bend the locking bolt as it slammed back down but I was still able to extract it. I have also hit a rock with the keel down and slack in the cable so the keel slammed back down against the trunk with no damage. It made a hell of a bang and scared the crap out of me. I don't recommend this but the Siruis 21/22 has a very robust hull construction better than most of boats it's size. I couldn't see a Catalina 22 or a Mac taking that kind of abuse. It may sound like we are careless and not paying attention but we are a bit adventurous and tend to go places others don't...we spend time in the blue part of the chart with no soundings. We hit something almost every trip and we are still in one piece.
The hum has never been that much a bother and in deep water I will slack off the cable to quiet it....putting tension back in when we get near the shallow rocky bits. It's never hummed at low speeds. We have the large diameter OEM cable which could be downsized a bit IMO. I wonder if a smaller diameter would hum more. Maybe something has wrapped around the cable and is just sliding up and down the cable as you raise or lower the keel.