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Charlie · 08-10-2010, 09:01

Quote:

Originally Posted by rebel heart

From what I know of aluminum once you bend it the strength is gone. It's a strong-brittle-soft metal that doesn't do well getting bent around (steel can handle that fairly well).

I am not an expert in metalurgy(sp?)by any stretch of the imagination but I do know that race boats use mastbend to control the shapes of their sails. I have bent the mast of many boats by making adjustments to running backstays, Check stays, etc. Perhaps there is a different type of Aluminum that retains its strength when being bent?

Eleven · 08-10-2010, 10:16

Wouldn't worry me if I was a safe distance away.

rebel heart · 08-10-2010, 13:30

Quote:

Originally Posted by Charlie

I am not an expert in metalurgy(sp?)by any stretch of the imagination but I do know that race boats use mastbend to control the shapes of their sails. I have bent the mast of many boats by making adjustments to running backstays, Check stays, etc. Perhaps there is a different type of Aluminum that retains its strength when being bent?

I think there's a difference between bending and "bent". Bent to the point where there's a dent or dis-figuration in the metal. I'm just imagining a piece of aluminum bar. If you bent it, it will either snap, or snap when you try to put it back to where it was.

Flexing without bending I think is kosher. I'm not a metallurgy guy either and a lot of what I know is from bike racing (steel, aluminum, and titanium are the big materials).

**Jim Cate** · 08-10-2010, 15:29

Hmmm,

If it is a triple spreader rig, it is most probably discontinuous rigging. That is, there are diagonal shrouds between the root of one spreader to the tip of the next lower spreader and a turnbuckle on each one to adjust the tension in that individual shroud. From deck level one can't determine if the diagonal shrouds have been slacked evenly, or at all for that matter. If they were slacked unevenly, an apparent bend would result.

So, to evaluate the situation, you or a rigger MUST go up and check all those tensions before saying whether or not there has been deformation rather than simple bending.

I too would suggest the rigger -- tuning a triple spreader is not a simple thing! By the way, are the spreaders swept back or in-line? This too makes a big difference in the way it must be tuned.

Cheers,

Jim and Ann s/v Insatiable II lying Trinity Inlet, Cairns, Qld, Oz

Ocean Roads · 08-10-2010, 15:44

From an earlier question- Keel stepped.

I believe the spreaders are inline.

The boat was first designed for PHRF racing, but did not do to well. So was changed over the years as a cruiser.

I know the mast was shortened one year to help clear some local bridges.

Had running backstays, but they have been discounted.

From my vantage point on the ground I don't think there are any indentations in the mast.

Gonna talk with my buddy and work up a deal. The boat has been sitting for a while. The deal is I get the boat for $1, but have to bring here back to shape and pay for all the upgrades. Then when cruising my buddy gets to tag along when time permits.

In the next month or so hopefully I can post some pics from up the mast, and of the boat, Oh boy she needs some work, but the price is right!

Ocean Roads · 08-10-2010, 15:50

Here is an old pic of the boat, at least 10-15 years ago. Think this is with the bigger rig.

Blue Crab · 08-10-2010, 15:51

Sometimes even free is too much. Mast trouble AND you have to sit down to shower? Ha! Not in my world.

Blue Stocking · 08-10-2010, 16:09

Judging from that photo, and the rig design, I'd bet you that that mast is like a wet noodle when the shrouds are out of tune. The flexibility of the extrusion is designed into the shape. Walk down the dock at a racing fleet of J-boats, and simliar, and look at some of the induced bend. I often work with a well known rigger, and I would let him winch me up that mast. But then again, I have also worked at the head of 144ft ladder trucks in my Fire Dept days. FWIW

sabray · 08-10-2010, 17:53

Thats what I was thinking wet noodle. I don't think Ive read anything here with some speculation on a triple spreader rig that would send me running. It sounds like the rig is loosened not tuned and you pull on a stay it comes back in line. So its not bent kinked etc just not tuned and adding tension brings it back in column. We probably dont have enough information and if you needed to ask you probably need to get a rigger involved.
Nice looking boat

Stillraining · 08-10-2010, 18:31

Ill give you 1000% Profit for it....let me know where to mail the 10 bucks...

You both can tag along..

**GordMay** · 09-10-2010, 06:22

Quote:

Originally Posted by sabray

... So its not bent kinked etc just not tuned and adding tension brings it back in column. We probably dont have enough information and if you needed to ask you probably need to get a rigger involved.
Nice looking boat

Indeed, the extrusion may be "bent" (plastic deflrection or deformation); without having "buckled" or kinked.

zopi · 09-10-2010, 06:32

You bend any metal, it interupts the crystalline structure of whatever it is...sometimes in unpredictable ways...late at night...during a gale...nahh..figure on a new mast..

Blue Stocking · 09-10-2010, 08:28

Quote:

Originally Posted by zopi

You bend any metal, it interupts the crystalline structure of whatever it is...sometimes in unpredictable ways...late at night...during a gale...nahh..figure on a new mast..

--- unless the structure is designed to bend. There are lots of examples:
cats with rotating masts deliberately bend the mast to position draft
I never broke a mast in 15yrs of sailing Tornados.
Bridge struts
Aircraft wings. A B-52 pilot freind told me his wings tips deflected 17ft vertically from at rest to airborn.

**Adelie** · 09-10-2010, 09:13

All metal bends, nothing is perfectly rigid.

As Gordmay noted there is a difference between elastic and inelastic/plastic bending.

Elastic bending is what race boats do with their masts. When the rig loading is released the mast returns to its previous shape.

Plastic bending is permanent deformation. The mast will spring back some but not all the way towards its original shape. There are three forms of plastic bending damage to a mast that I think should be considered:
Bending, permanent deformation over a longer length of the mast characterized by a large radius.
Kinking, permanent deformation in a localized region of the mast ie. small radius.
Dimpling, very localized deformation, looks just like it sounds.

Dimpling is probably the end of the mast. Bending could be straightened carefully with the mast out of the boat, or the bend could be removed with differential rig tension. There would be slight reduction in rig strength but depending on your risk tolerance, acceptable.

Kinking is a lot harder to evaluate, straightening in the yard would involve a fair bit of work hardening and not strength loss but loss of toughness. This would definitely require a professional rigger to evaluate.

In reality the bending and kinking are part of a spectrum and there is a lot of gray area in the middle.

I have been involved in straightening 2 masts, one came out great, the other was OK. These were 21 & 26' boats which is a whole order of magnitude smallerin terms of difficulty.

Personally I would not be comfortable with a triple spreader rig offshore, and certainly not going RTW.
There are two reasons for this
A) the very light section implied by the need for 3 spreaders and running backstays
B) the difficulty in tuning a rig like that.

If the mast is going to be replaced anyway, you might consider using a heavier section requiring only 2 spreaders. You would still want to have running backs so you could rig a removable forestay and staysail.