Re-mounting a snapped mast?

[lagspiller]

Snapped the wooden mast on my boat (22 Sq.meter) between cabin top and mast step in keel. Wooden masts are not easy to replace in my area - and I would like to try re-mounting the mast on the cabin top.

I am thinking of installing a support from the original mast-step on the keelson to the cabin top. A flush-mounted fitting resting on the support would be fastened to the cabin top. The support through the cabin can be reinforced at deck-level by attaching it to the original cross-beam which runs the width of the hull.

Can anyone see any problems with this?

Pictures and drawing of my boat here if you are interested...
http://home.online.no/~tjohnson/squares.htm

tom

[Paul Denison]

Since the forces acting on the mast step would be huge, I believe you need some engineering calculations. I wouldn't think your beam would be sized to carry such loads.

[John E Hardiman]

lagspiller;

My advice would be to swallow hard and replace the original mast. I took a look at your site and saw the photos and drawings of the rig. A true, low-margin, high bend, fractional racing rig; baby stay and all...with a huge (by modern standards) rake.

There are few ways to blow out a mast below the partners. Damage, hidden flaw, and rig tension being the choices. I bet the mast blew out fore & aft?

If you tried to restep the mast on the cabintop, the forward thrust of the heel would have to be supported in some fashion. Additionally, the balance of the fore, back, and baby stays would be critical. Stepping the mast more veritcal would require a complete new rig to try to get the CE back in the right place for the underwater profile. Besides all the shrouds needing to be moved and a new mast step to land the compression post in line with the mast.

I'd go asking around at the in country boat-building schools and see if any would like an advanced student project. On the other hand, it is only a mast; and the material is most likely to be the major cost. With modern glues the pieces need not even be that large with proper scarfs ;) .

[JimD]

I have plans for a boat with options for a keel stepped or cabin stepped. Significantly different approaches to the standing rigging. Cabin stepped version has a both a back stay and heavier shrouds.

[cbob]

lagspiller,
Assuming the remaining upper portion of the mast is still sound, the first thing I would do before comissioning thr building of a new stick would be to search out and find some old timer spar maker, capable of performing or supervising either building a new stick or just replacing the lower portion. If the mast is a box section, scarphing in four new side pieces, with adequate spacing betwen scarphs might be an economical, practical, and like original solution. Unless there are unusual bending forces involved, the stresses at the deck level are basically compression. Also there are a lot of umtried/tested things to be done to reinforce at deck level and move chain plated etc. which seem more extensive, then simply scarphing four sides spanning the break down to the step, or for that matter building a new stick.
I'm no spar maker, but have seen a similar repair on a solid stick on a aout a 45' gaff cutter by an experienced wood worker (runners had been anchored to the deck with padeyes rather than chainplates) If I recall this was referred to as a "fishmouth" type repair and was successfull.
Good luck on whatever you choose, cbob

[Nicholas Carey]

Also...don't forget that a deck-stepped spar must be stiffer (larger diameter) than a keel stepped spar of the same deck-to-mast-step height.

[lagspiller]

Ok guys. Thanks for the input. Looks like this was not a good idea.

The mast was old (I mean really old - the guy I got it from after the original mast disaster said his grandfather called this one "the old mast" back in 1920). Didn't actually break in two, but did get a definite angle and cracked square across its entire bredth about a meter above the mast foot. I was out in a good blow - and developed some gray hairs by the time I got back to port, believe me.

I don't believe any scarfing on this part of the mast will be of use. The experienced old-timers here say that masts that have broken around cabin-height cannot be repaired. Higher up is no problem. Lower repairs virtually always break again - and the repair is almost as expencive as the replacement. We are talking about a scarf of about 20:1

So I guess I am in the market for a new pole. Just wish I knew where to look... Wooden masts are not at all easy to find here. I have been offered "mast on root" by friends, but that looks like a lot of whittling to me.

tom

[lagspiller]

One more thing...

It didn't blow out fore/aft as suggested, but to starbord. I was on the starbord tack (or whatever you call it over there when you are sailing with right of way). It was quite a sight through the open cabin door.

tom

[Meerkat]

Originally posted by Nicholas Carey:
Also...don't forget that a deck-stepped spar must be stiffer (larger diameter) than a keel stepped spar of the same deck-to-mast-step height.Why is that? If it's all compression loading at the heel, why would there be any difference?

[John E Hardiman]

Originally posted by lagspiller:
One more thing...

It didn't blow out fore/aft as suggested, but to starbord. Was the design bury of the 2nd broken stick the same as the 1st and the boat?. For a build up mast ( I assume) to fail on the tension side straight across sounds like the blocking (i.e. interior stiffing to hold the mast section in shape) was wrong. Oh well :( . It is important in a built up mast that some blocking be located exactly at the partners, not above or below, to prevent a stress riser. As you found out, the mast takes an S curve with the change of curvature at the partners, the stick between the hounds and the partners sagging off to lee and the bury bowed to weather.

And to answer Meer's question, the section must be larger for a cabin steped mast because the moment caused by linear sail loading cannot be supported by the bury of the mast. A cabin steped mast will bend in a "(" curve with no moment supported at the step. A quick look at the different moment diagrams between the two will show the cabin stepped mast has the higher maximum moment. Add secondary euler buckling due to shroud loads (i.e. mast compression on an already deflected beams of pin-pin vice pin-support-pin) and the section modulus has to be considerably larger.

[Steve Clark]

I may be silly, but I don't see why you could not scarph on a new bottom section. Done properly it should be strong and reliable. The only wooden masts I have ever broken all failed on the compression side. Formed a nice neat compression check 90 degrees from the outside and kept going until the mast was going to fall down. ( I actually stopped in time. ) Oars and paddles usually have a hardwood backing on the compression side to deal with this. I suspect this mast was breaking for some time before it actually came down. Might have been the result of too much bend at the partners or simply years of wear and tear denting up the mast. Before going to the trouble though, inspect the rest of the glue joints and see if they look like they are going to be around for a while just to avoid the good after bad problem.
SHC

[htom]

Is this the second mast you've broken? If so, perhaps the mast and rigging design should be checked before you purchase or build a third.

[John B]

Scarf it. it's a simple process and I don't see any reason why it shouldn't be just as strong as the original timber.12:1 is bullet proof.
I've done it twice to a mast, both about 48 ft from memory, once at the gooseneck with resorcinol.... 5 years later we lost that stick to a fitting failure( aft lowers at the spreaders) but the scarf was good. the second time was when I replaced that mast with one out of another boat and it was 18in short. that scarf was well buried . It was epoxy.Never had an issue with it.
hell, everything of mine is scarfed. bowsprit, gaff , boom ,mast, jackyard, staysail boom...
Oregon or spruce is like hens teeth out here.

[Phil Young]

I used to own a tumlaren, similar sort of rig. Solid spruce mast Its mast was scarphed at the lower end, can't tell you the ratio, probably around 12:1 I'm guessing that before I had her the mast broke at or below deck level. I never had a problem with it.
Phil

[lagspiller]

The original mast snapped above the spreaders due to turnbuckle failure - nickel plated bronze. Looked perfect but must have had long term stress cracks under the plating.

Then, while I was mounting the mast after scarfing a repair I was extremely unlucky. A fishing boat steamed out of harbor at full speed after the repaired mast was in place but before I could get the rigging fastened. The rolling caused the mast to wip in over the warf, almost killing a couple standing there. I had only managed to get 1.5 turns on the fourth stay turnbuckle in the panic after the fishing boat was discovered. That wasn't enough. The mast then cracked right over the cabin top. I was pissed and reported the fishing boat to the authorities... but nothing much came of the police investigation.

The second mast was meant to be a inexpencive solution while I figured out what to do to get sailing again. I talked to a bunch of boatyards, but none were interested in doing the mast repair. And the second mast has done the job up to now.

About scarfing near the cabin top....
The common wisdom here is that a mast that has snapped in this area is more or less doomed. Higher up is ok... but a lower fix usually broke again. However, that may be old news. Perhaps newer glues can manage the pressure.

Tom
(still thinking...)

[Ian McColgin]

I have repaired several masts that broke near the partners. The common wisedom is part of what I ran into first time and is dead wrong.

As were dumball ideas like scarfing in a solid lower 4' onto a hollow spar.

You can easily do this repair, but duplicate the mast's construction - If solid fine. If round and hollow or oval and hollow or box - whatever it is do thou likewise.

If hollow, you'll need a compression block at the partners. Nothing huge, just as big as the partners.

Plan ahead and give it a shallow V on the top with a weep hole in the middle. Put a weep hole in the mast base where it goes solid.

G'luck

[James R]

What Ian said. I've repaired two masts that broke at the partners, one with a 12 to 1 taper and the other with a 20 to 1. The last time that I saw them they were still in perfect shape more than 10 years after being repaired.

[lagspiller]

OK folks. You have convinced me. (On the other hand, what have I got to lose?)

I have talked to the local woodworking shop and they will take on the mast repairs. It would be nice to be able to give them a picture or explanation of the proceedure. Can anyone give me a link to a 'how to do mast repairs' website? The guys I talked to looked kind of blank when I started explaning what I wanted. They are used to building houses.

tom

[David Tabor (sailordave)]

quote:
--------------------------------------------------------------------------------
Originally posted by Nicholas Carey:
Also...don't forget that a deck-stepped spar must be stiffer (larger diameter) than a keel stepped spar of the same deck-to-mast-step height.
--------------------------------------------------------------------------------

Why is that? If it's all compression loading at the heel, why would there be any difference?
Well a deck stepped mast is like a beam on a roller, while a keel stepped mast is like a fixed end cantilever beam. (think sticking a 6x6 post a couple of feet in a concrete wall and then standing on the end of it)

The simple fact that the end is resting on the keel and then it is supported several feet above that by the deck means that it needs less stiffness or less support by the shrouds or a combination thereof...

;)

[James R]

Tom, there's more than one way to repair the mast. One way is to cut the mast back to sound wood and then plane a 20 to 1 taper on each side of the mast. If you're going to be reusing the shorter bottom section do the same to it. Plane corresponding tapers on two rectangular pieces of wood at least half the thickness of the mast then glue everything together. Plane the outside of the new wood to match the mast after the glue dries.

The new wood should be the same species as the mast and if hollow simply cut the hollow before gluing the two halves to the mast. Take note of any filler pieces. Sometimes the mast is solid at the partners but is hollow below and/or above.

As to what glue to use, I like epoxy. It's tough and flexible but you have to be careful not to use too much pressure when clamping or you'll squeeze out too much resin. Epoxy also degrades when exposed to sunlight so you'll have to apply a few coats of a good UV resistant varnish. Some will advocate using resorcinol glue but you need to apply more pressure than normally possible with clamps. It's a little too finicky for my taste but there are newer resorcinol glues that apparently don't require as much clamping pressure.

[Ian McColgin]

You may want to do this job yourself. Guys used to general carpentry may not have the glue and hand tool practice to do this without a lot of wasted time and explanation which you'd have to learn and provide. Not really much more work to do it yourself.

Couple of basics.

The mast needs to come out at the same height. Before you do anything else, measure carefully.

If the heel is still sound, by all means use it. If not, go with new.

You can save wood if the general scarff type is what's called a 'cloths pin scarf.' In essence you get a 12:1 glue surface on a 6:1 total job.

Sorta like =====>====>===== .

What is the original construction?

[lagspiller]

Thanks for replies. They will be a big help.

The mast is solid - and laminated of very long scarfed pieces which look about like this:
=======>======<=======
... the middle section made of 2 halves. The scarfing is at least 20:1 and top and bottom section of the mast meet in the middle of the scarfed section. The highest break is slightly over the scarfing. The lower break is well below the scarf.

I will reuse the entire mast.

I have already tried a scarf repair on the mast once - but didn't ask the right people enough questions the first time. My scarf was much too short. It held pretty good, but not that is not good enough. You know.

I am going to go with the carpentry guys - because they have the workspace to do the job indoors and all the tools. I know these guys pretty well, and one has done quite a bit of work on boats previously. But probably not a mast. They are kind of careful, and it is a good sign when they ask for whatever details I can provide.