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Old 26-11-2015, 06:17   #1
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Mast Moving Up & Down

When sailing I have a very loud "creaking" noise in the saloon of my catamaran which I finally tracked down to be coming from the base of my mast.

My mast sits on a metal foot that fits inside the base of the mast, and under sail one of the aft corners of the mast is moving up and down by a very small amount, less than 0.1 mm. And because the foot is a tight fit in the base of the mast, each time there is sufficient force to cause it to move, it "jumps" and makes a noise like someone hitting the mast with a small hammer.

So my question is...should the bast of a mast (or one corner of it) move up and down (by < 0.1mm) relative to its foot?
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Old 26-11-2015, 06:27   #2
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Re: Mast Moving Up & Down

I believe it's mast bending, not much to do about it. Use some lubricant to get rid of the noise..
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Old 26-11-2015, 06:30   #3
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Re: Mast Moving Up & Down

Sounds like the mast need tuning. If its a cat and the mast is bending, I'd guess that the diamond stays need adjusting
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Old 26-11-2015, 20:46   #4
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Re: Mast Moving Up & Down

Thanks for your comments on mast bending, I hadn't thought of that.

My boat is a catamaran and like most cats has only 3 attachments from the mast to the deck...forestay and 2 x side stays.

I tightened down the side stay on the side where the mast is moving up and down and found that it made little of no difference...if anything, it made it worse. I didn't understand this at the time, but if the mast movement is being caused by mast bending then what I did will tend to put more bend in the mast and probably make it worse.

Barrie
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Old 26-11-2015, 21:10   #5
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Re: Mast Moving Up & Down

A rigger would be ur best bet.


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Old 26-11-2015, 21:15   #6
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Re: Mast Moving Up & Down

Definitely check with a rigger. It is possible that tightening on the same side as you are observing could make it worse.

I AM NOT SURE THIS MAKES SENSE, but I will give it a go. Try this: put something straight end up on the table and press down to let it bend. All I can think of off the top of my head is a pool noodle, but you would need help. As it bends, one side curls up while the opposite stretches. This means that as the top part of that side comes down, the bottom side comes up.
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Old 27-11-2015, 08:23   #7
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Re: Mast Moving Up & Down

Quote:
Originally Posted by Cruisin Cat View Post
Thanks for your comments on mast bending, I hadn't thought of that.

My boat is a catamaran and like most cats has only 3 attachments from the mast to the deck...forestay and 2 x side stays.

I tightened down the side stay on the side where the mast is moving up and down and found that it made little of no difference...if anything, it made it worse. I didn't understand this at the time, but if the mast movement is being caused by mast bending then what I did will tend to put more bend in the mast and probably make it worse.

Barrie

Barrie,

If your Rig is like most cats, you also have diamond stays that keep the mast in column. these are the ones that You should be adjusting. The forestay and shrouds just keep the mast from falling over. the diamond stays control the shape of the mast.

The other question is why is the foot of the mast moving independently of the mast itself. they should be securely fastened together. the foot may have an arrangement that allows some articulation on the mast base. unlike monohulls.
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Old 27-11-2015, 10:40   #8
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Re: Mast Moving Up & Down

I would be looking at how the mast compression is absorbed under your mast. Is there a dolphin striker strut under your crossbeam to stop the crossbeam bending under the rig compression loads? If so are the wires out to each hull from the strut correctly tensioned?
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Old 27-11-2015, 10:45   #9
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Re: Mast Moving Up & Down

Quote:
Originally Posted by Cruisin Cat View Post
When sailing I have a very loud "creaking" noise in the saloon of my catamaran which I finally tracked down to be coming from the base of my mast.

My mast sits on a metal foot that fits inside the base of the mast, and under sail one of the aft corners of the mast is moving up and down by a very small amount, less than 0.1 mm. And because the foot is a tight fit in the base of the mast, each time there is sufficient force to cause it to move, it "jumps" and makes a noise like someone hitting the mast with a small hammer.

So my question is...should the bast of a mast (or one corner of it) move up and down (by < 0.1mm) relative to its foot?
My swag, if it is one corner? Check the shrouds for tension imbalance or one that is way under?
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Old 27-11-2015, 17:04   #10
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Re: Mast Moving Up & Down

Quote:
Originally Posted by GrahamHO View Post
I would be looking at how the mast compression is absorbed under your mast. Is there a dolphin striker strut under your crossbeam to stop the crossbeam bending under the rig compression loads? If so are the wires out to each hull from the strut correctly tensioned?
It's a medium sized cruising cat so no dolphin striker under the bridgedeck. Mast compression load is carried by a fibreglass A frame inside the front of the bridgedeck.
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Old 27-11-2015, 17:18   #11
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Re: Mast Moving Up & Down

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Originally Posted by pcmm View Post
Barrie,

If your Rig is like most cats, you also have diamond stays that keep the mast in column. these are the ones that You should be adjusting. The forestay and shrouds just keep the mast from falling over. the diamond stays control the shape of the mast.

The other question is why is the foot of the mast moving independently of the mast itself. they should be securely fastened together. the foot may have an arrangement that allows some articulation on the mast base. unlike monohulls.
I adjusted the side stay because I initially thought the movement at the foot may be caused by the top of the mast column moving forward under load...at that time I hadn't thought of mast bending as the possible cause. It does seem much more likely that mast bending is the cause.

My mast has triangular spreaders with with shrouds running up and down from them....I assume these are the diamond stays that you mentioned?

I'll check the tension in all of these to see if there is any significant difference between them. Unfortunately I don't have any way of checking tension other than by pulling with my hand so a very crude check!
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Old 27-11-2015, 17:25   #12
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Re: Mast Moving Up & Down

Quote:
Originally Posted by Cadence View Post
My swag, if it is one corner? Check the shrouds for tension imbalance or one that is way under?
Yes, it does sound like it may be caused my improperly tensioned shrouds...I hadn't thought of that until I read replies from you and others suggesting mast bending may be the cause.
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Old 27-11-2015, 18:41   #13
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Re: Mast Moving Up & Down

Quote:
Originally Posted by Cruisin Cat View Post
When sailing I have a very loud "creaking" noise in the saloon of my catamaran which I finally tracked down to be coming from the base of my mast.



My mast sits on a metal foot that fits inside the base of the mast, and under sail one of the aft corners of the mast is moving up and down by a very small amount, less than 0.1 mm. And because the foot is a tight fit in the base of the mast, each time there is sufficient force to cause it to move, it "jumps" and makes a noise like someone hitting the mast with a small hammer.



So my question is...should the bast of a mast (or one corner of it) move up and down (by < 0.1mm) relative to its foot?

Loud creaking noises like you describe are often creaking bulkheads. My boat talks a bit when the weather pipes up. A bulkhead acts like a drum when the hull flexes.


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