Keel-stepped mast vibration - bangs cabintop

[Skipper]

My keel-stepped mast undulates when the wind picks up. When it does, it bangs into the cabintop inside the hole. It's probably been doing this 30 years, so I guess it doesn't hurt anything. It's just irritating, and raises the anxiety level in a blow. Also, if it's working the mast, rigging, and mast base, I don't see anything good here.

I stuffed a rag up in between the mast and hole, which eliminated the noise problem and much of the vibration. However, the remedy is hokey, and the rag eventually drops out from movement, requiring re-stuffing. I'd like a permanent fix. Has anyone ever addressed this? Fiberglass? an insert? etc?

 

[justsomeguy]

Google the term "mast partner", pard'ner.

 

[Jackdaw]

Sounds like your mast wedges are not doing their job. Rigerite can sort you out.

http://www.rigrite.com/Spars/SparParts/Mast_wedges.html

 

[Steve Dion]

There is also product called Spartite that you may want to look into. It sounds like the answer to your problem.

There is also a boot that can be made to prevent deterioration of the material that hold the mast in place called "Water Boot".

What prevents water from getting in there now?

 

[Ted]

Keel stepped mast vibration

Spartite is a great product to use to solve your problem. I installed it on my boat 11 years ago and have never had a drop of water enter the boat from that area since. Make sure you follow the directions otherwise you will have great difficulty removing the mast in the future. The Spartite stays on the mast permanently and does a great job of supporting the mast at the partners. This will definitely solve your mast banging problem. Spartite recommends that you apply a coat of paint to the cured product to protect it from UV breakdown.

 

[Barnacle Bill]

There are also rubber partner spaces available (or you can make them up custom too, if you can find some thick rubber). Usually oak wooden wedges do the trick. The Spar tite is a more expensive solution, but will last a long time and also keeps the rain and spray out.

 

[Skipper]

Sounds like your mast wedges are not doing their job. Rigerite can sort you out.

http://www.rigrite.com/Spars/SparParts/Mast_wedges.html

What mast wedges? I think they forgot those the last time they stepped the mast (PO). All of my previous boats have been deck-stepped, so this is fabulous knowledge. Thank you and to the other posters.

 

[capta]

Though I am not familiar with your boat at all, it sounds to me that your rig needs tuning.
Your mast should not move around noticeably at that point. If you are not familiar with tuning your rig, get a rigger aboard and he can teach you.
I would hesitate in trying to stop the movement by tightly wedging the mast in the cabin top as it really is not designed for those kinds of loads at that point.
If in fact, your mast has been moving around like that for 30 years, which is unlikely, I would want to inspect the step for excessive wear.

 

[Sandy Stone]

I'm pretty sure that with a keel-stepped mast the cabin top, AKA mast partner, is indeed designed for the loads of tightly wedging the mast. In fact, I'm pretty sure that is the intent. Mast tuning is another issue (which would probably be worth investigating).

 

[rgranger]

Yep. You are supposed to have mast wedges.

 

[NYSail]

Mast wedges are missing......

 

[capta]

I'm pretty sure that with a keel-stepped mast the cabin top, AKA mast partner, is indeed designed for the loads of tightly wedging the mast. In fact, I'm pretty sure that is the intent. Mast tuning is another issue (which would probably be worth investigating).

Unless there are some pretty large supports in the area of the mast, (a single bulkhead is not enough) the cabin top is not meant to support the mast, unless it is an unstayed rig on a fiberglass boat. The mast should be supported by the rig and if properly tuned there should be little or no movement at that point. The wedges seem totally superfluous these days and I've seen plenty of boats sail with some missing or none at all, without any problem.

 

[Merlin Clark]

There's not a lot of strain involved in keeping the keel stepped mast in position where it passes through the deck.

 

[justsomeguy]

There's not a lot of strain involved in keeping the keel stepped mast in position where it passes through the deck.

Correct. The partners are there to limit the OP's movement issue, which, if left unchecked, can lead to work-hardening/fatigue of the mast.

They don't need to be wedged all that tightly, but they need to be there.

 

[Sandy Stone]

Yes, we may just have to disagree on this one. I'm no naval architect, but I think what makes a keel-stepped mast superior in many people's eyes is that the base is supported in two places - the mast heel on the keel, and the partners - which helps make it more rigid. This is negated if the wedges are missing. Also, on many modern boats the mast is wedged forward at the partners to help induce prebend. (I doubt this applies to the OP's boat.)

 

[Geoff K]

What about the pumping?

Good advice re the partners, but no comments about the mast undulating/pumping? Is that expected? Mine does this also but without the knocking on the partners. Wedges present. There's still quite a bit of noise; enough to keep me awake. (and worried.) The pumping starts at about 10 kn of wind. Mast is keel stepped, fore and aft lower shrouds, furler on forestay.

Should I worry about the "pumping" or just put in some ear plugs?

Geoff

 

[justsomeguy]

Good advice re the partners, but no comments about the mast undulating/pumping? Is that expected? Mine does this also but without the knocking on the partners. Wedges present. There's still quite a bit of noise; enough to keep me awake. (and worried.) The pumping starts at about 10 kn of wind. Mast is keel stepped, fore and aft lower shrouds, furler on forestay.

Should I worry about the "pumping" or just put in some ear plugs?

Geoff

Well, you do want to limit the pumping to nada, but if your partners are reasonably tight, you might want to investigate shroud and stay tension, FWIW.

I think...

 

[Geoff K]

Well, you do want to limit the pumping to nada, but if your partners are reasonably tight, you might want to investigate shroud and stay tension, FWIW.

I think...

True, I need to evaluate the rig tensions. It's been a long time… like, I've never done it. Last time it was done was 6 years ago when the boat was launched after a prolonged refit. I guess I'd better learn how. <g>

If a good fit at the partners stops/subdues the pumping without changing the rig tensions does that mean it's OK? Or is it just covering up a problem? I'm guessing that pumping is a resonance that amplifies the force of the wind. Sort of like Galloping Gerde. If so, should the tension of the rig be reduced to set the resonance at a lower wind speed/lower force or raised to increase the resonance to a level not obtainable?

Hmmm. That sounds esoteric. Probably the right path is to get out there and try a few different tuning scenarios and see what works?

Geoff

 

[Chris Patterson]

It all sounds to me like a harmonic built up around the mast. I can't think of any practical approaches to solving, OR testing the idea, but it's the only thing that seems to make sense to me. I'm sure it's more pronounced at a particular point of sail, correct?

 

[Geoff K]

Don't know

Actually I've never noticed it while sailing; only when on the boat at anchor or marina. More likely at the dock, perhaps related to the restraint of the boat? Or perhaps related to that's where most of my non-sailing time is spent.

Geoff