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Anke and I are building our next boat, and writing about it at ABargeInTheMaking.blogspot.com. Access to the net comes and goes, so I'll be writing in fits and spurts.

Please feel free to browse the archives, leave comments where you will and write, and I'll respond as I can.

Fair winds!

Dave and Anke
triloboats swirl gmail daughter com

Monday, March 12, 2012

Masts as if they Grew on Trees

Dried out for Mastwork... Lumberyard in Background.
 
Most of the boats who've ever sailed have had solid, grown masts.

Extruded aluminum, fiberglass, modern adhesives and even spiral welded metals have recently brought hollow masts to the fore. They've taken over to such an extent that it's sometimes overlooked that alternatives are possible!

And for some good reasons. Well made hollow masts are lighter, stiffer, in some cases stronger... and hollow. Haulyards and wiring to masthead electronics can be lead up the hollow, which can provide floatation in a beam-ends knockdown. That haulyards can jam and electronics fail causing mast high hassle somewhat detracts from the advantages, but still. Net plus, so far.

But solid, grown masts are generally free. They only take felling, cutting to length, barking and maybe a little shaping at the head and foot. A morning's work at an easy pace with bowsaw and draw-knife, leaving the afternoon for transferring hardware, erecting and rigging. Vamanos!

All this takes place in the woods or on the beach, requiring no shop, tablesaws, level sawhorses, clamps, scarphing, rounding, end-plugs or butterfly internal supports.

We live in a good area for spar stock. Sitka Spruce has been considered prime material since the age of sail. It's light weight and long fibers are bio-engineered for the high winds of the Pacific Northwest. Many other trees - fir, larch, pines and members of the cypress family, to name a few - work fine, and grow straight and true in almost any area that sports trees at all.

We find good candidates on alluvial fans and in dense, middle aged stands, where young spruce got a good start, but shaded out. Close to the water is always a plus!

One advantage of lug rigs is that, since the sails aren't fixed along the mast, they needn't be straight. There's a kind of funky beauty to masts with a wow... but I must admit I'm not yet taoist enough to take advantage. If you can, it's best to orient the wow fore and aft (in a plane with the centerline of the boat).

 I've read that more than 9 annular rings per inch gives no strength advantage, but figure the more the merrier. We generally avoid less, and regretted it the one time we made an exception. If flaws or rot pockets are found, then we've got a weeks worth of firewood.


Sizing is by formula - we use that from The Chinese Sailing Rig by Van Loan and Haggerty for our free-standing Junk Rig. This specifies mast diameter at the partners (hinge pin at the tabernacle, in our case). The mast may taper to half that at the masthead. CSR gives a method for trimming to an even taper, but life's too short! The tree's already perfectly engineered. We look for about the right proportions and go with that.

We like deck oils (UV resistant) to coat, and smear the upper endgrain thickly with anhydrous lanolin. Paints open when it inevitably checks. The lanolin seems to ride with 'em, and keeps water out. I doubt this is a real problem, though, if the head is shaped to shed water.

A Heron adorns the MastHead Fitting.
Something is required to anchor rigging up high. A simple wooden cross pin or two work perfectly well, siezed above and below with nylon marline to resist splitting. Spliced eyes in the upper rigging are slipped over the masthead and bear up on these.

To support a welder friend, we went with a metal weld-up from aluminum pipe with flanges at 0, 90 and 270deg off forward.  A fourth flange 45deg off aft on the side the sail hangs, and a bit longer carries the haulyard. The forward one anchors the lazy-jacks (which pass around the mast, down and aft). The other two are standby for if we ever want running backstays or somesuch.

If setting in a tabernacle (which I warmly recommend), the other piece of hardware is a hinge, affixed to the front or back of the mast at a level that lets the foot hang an inch or so proud of the deck. We use a heavy galvanized strap hinge used for fences. Lag screw it onto the mast and seize it with wire just under the hinge loop (to back up the lag screws).

Once the mast is in position and we've inserted the hinge pin (stainless rod). We tie a lanyard to the bolt, and start taking wraps... away from the bolt, round the mast, round the bolt on the other side and back, repeating until we're out of room, and then make fast. This further backs up the hinge mountings. Might be overkill, but we rest easy!

Aft Tabernacle with cushion
Fore tabernacle showing lanyard wrap (doubles as cushion for this mast).

 One problem we've had is that the tabernacles tend to be a bit loose fit. We build them oversized, to take non-exact trees, but the slop lets the mast move, slightly, from tack to tack. Cedar wedges work for a bit, but compress and fall out. Our solution was to wrap narrow firehose (wide webbing would work, too) with just enough turns to make a tight cushion between tabernacle sides. It's a little more work getting it to set on raising, but stays nice and firm in all weathers.

Last bit is pinning the foot. Usually, this hardware goes with the tabernacle. We use a cross pin of the same stock as the mast hinge pin, passing so as to block the swing of the mast foot. We flatten the foot, parallel to this pin, and add a wedge from top. Typically, we'll set a screw through the wedge and into the mast, to ensure it stays in place. To prevent side to side motion at the foot, we stand planks to either side (they can't fall out, like the upper preventers did.

Forward tabernacle, pinned foot.
 *****

When we were finishing up with SLACKTIDE, we put the masts up and bent the sails - time for a party to bid farewell to our Sitka friends. One of them immediately dubbed it our erection party.

A good time was had by all!

11 comments:

  1. Hi Dave, I remember the sick feeling as my rigging knife slid deep into a soft patch in the main topmast on a brigantine I worked on. Three weeks later in a scheduled layup we struck it, cut out the rotten section and scarfed in two precious meters of replacement wood, in 8 days the ship was whole again, all while at anchor in Vanuatu, with no outside assistance.

    That spar lasted many more seasons and a trip half way around the world before it was finally replaced.

    The Foremast was later rebuilt during a big refit by chainsawing the old rotten insect eaten sapwood off the outside and carefully laminating a new skin onto it with epoxy. It was probably stronger than when it was new. All the yards were stripped and any rot cut out and patched at the same time.

    Mostly the brigantines spars rotted where water got trapped around fittings, fastenings or under paint, It seemed as long as the checks in the wood could drain naturally they didn't cause too many problems. The rot in the topmast was where a shake was filled as it went into the doubling and then was painted, rain water flowed down the shake in the mast and then got trapped by the paint and filler.

    The head of her mainmast had a big cork stopping up a long hole drilled into the mast near the hounds. Every month or so it was topped up with diesel to stop a pocket of rot from spreading. As far as I know the same mast is still in her.

    My parents old gaffer has a topmast made from about 3 sections, and a main boom the same, after having broken them a few times. They were all reasonably easy to repair with simple tools and epoxy.

    The masts are wooden made from 4 square four by fours of Douglas fir, scarfed, glued up and then rounded. The core two inches was removed and some scrunched tinfoil put in the middle, it seems to work well as a radar reflector.

    There is a lot you can do with a wooden mast even without the perfect trees you have in the Pacific NW.

    I was involved in the repair of an alloy mast in the Falkland Islands, it was not easy, needing skilled metal workers to straighten the bent section and make carefully fitted reinforcing plates. Mind you a wooden mast possibly would have broken rather than bent in the knockdown that ripped the cap shroud turnbuckle out from the chain-plate. Another benefit of your unstayed masts...

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    1. Hi Ben,

      Lot's of cool info, here... thanks for posting!

      I especially like the hot diesel injection... 8)

      Do you have spar trees growing down under? I'm trying to recall what Wray did in SOUTHSEA VAGABONDS for his mast. Surely something creative.

      Dave

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  2. Ahh, good old Johnny Wray, my favorite book of all time. glad you have read it, it's hard to get hold of these days, I have my Dads copy on loan... Johny used an young Kauri tree (next to impossible to get hold of these days!), but it was to flexible so before taking off to the islands an old baltic pine yard from the wreck of the Rewa was cut down to suit.

    I suspect you live in one of the last places in the world were good mast making timber grows on trees that are reasonably easily acquired. Most wooden masts down here are Spruce or Douglas fir (Oregon pine) from your neck of the woods. A friend has built a nice mast from the lighter swamp gum variety of Tas oak, but it is still a heavy mast, even with the thin walls he used. I have also seen a few made from Celery Top pine but it is much heavier (and knottier) than good Douglas fir, and very expensive.

    Maybe Radiata pine would be the cheap way to do a mast, but it is not a great timber. Douglas fir is also locally grown, but it is a poor imitation of your fine slowly grown trees, with very wide growth rings and lots of knots. Although I have sailed a ways with a laminated mast made from carefully selected lengths of this timber.

    Cheers

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    1. Hi Ben,

      Thanks for filling me in... we LOVED that book!

      At least at highway speeds, and some walking around, I see a lot of trees in the US and Europe that look like they'd do for masts. One can always beef up to make up for poor rings. Not ideal, but then the world's not what it used to be.

      Our masts have lasted about a decade before little soft spots have appeared at the edges of the checks. Not exactly the long haul, but since they grow on trees...

      Dave

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  3. Ha, that's what I love about your site, you make me reassess a lot of what I have been programmed to think.

    I am programmed to think that masts need to be optimized for strength to weight so you can go to windward efficiently. I look at a tree and think it would be more efficient if it was cut up into lots of small bits and then painstakingly re-glued into some fancy hollow mast

    But if we measure things differently your grown masts are much more efficient overall in terms of energy, cost and time, and still do a great job as a mast.

    I will look at all those trees on the roadside in a different light. Thanks

    Oh and some good pics of Ngataki here http://forum.woodenboat.com/showthread.php?112955-South-Sea-Vagabonds-Ngataki-Photos

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    1. Hi Ben,

      Thanks for those pics.. the copy o SOUTH SEA VAGABONDS we read didn't have any photos. What a great DIY epic!

      Dave

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  4. Hi Dave,

    Now that all sounds promising. Can you elaborate on how you select a tree to try? What you consider disqualifying flaws? And branches to be trimmed, or a qualifying tree has no branches, even little ones, in the trunk section destined to be a mast? Dead tree or living? In the other post about masts you talked about curing time, but it made me wonder how you handled that in the project you described on the beach... or would handle it now, if that's the one that broke!

    I love the part about that curved is really okay. I built a canoe sailing rig once, traveled to Maine with two friends, canoe and rig on truck for the first sail, and discovered that I did not have the mast. After initial disappointment, went scrounging in the woods. Sure was surprised when a goofy, seriously curved and somewhat jagged stick worked just fine. Of course, I'd go for not jagged, given a little more time! But the experience taught me something important (besides about departure checklists!)

    Could you say more about the strap hinge for the tabernacle? Width? Width of hinge relative to tabernacle? Like, is the hinge chosen to just fit between the tabernacle sides, or are there spacers on the steel rod? Or does it float a bit, side to side motion and twist completely controlled by the tabernacle holding the mast, and the rod and partial span of hinge?

    I did some looking at strap hinges on the Internet -- so many choices/styles, including many variations of the short side of the hinge. Which made me wonder if you just ditch that side of the hinge, keeping the long strap side and running the steel rod through that -- or do something with the short side, folded back against the long side to add strength, or something else?

    Hopefully so many questions are not annoying -- inquiring minds and all that :-)

    THANK YOU!

    -- Shemaya

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  5. Hi Shemaya,

    Questions are encouraged... helps me find my blind spots.

    RE targeting trees - First criterion is diameter, second straight-to-taste and smooth... tight branches are fine (fishermen liked 'em for trolling polls as their spikes and wave growth around them reenforce mast integrity and resist checking and wracking), third, 9(+) rings to the inch, and finally, taper to about half the diameter (in practice, some taper .

    We prefer standing dead, as they're light to carry, raise and help reduce weight aloft. If they're green, they're usually substantially dry after the first year, and completely dry after two. George Beuhler has good info on grown masts in BEUHLER'S BACKYARD BOATBUILDING.

    That beach project was installing the one that later broke (soft spots in the old one, hasty selection of the new... undersized AND wide rings... bad combo).

    We made one set of strap hinges out of bent-over 2" x 1/4" bar. ST's are bought, about the same thickness but only an inch or so wide (maybe up to 1 1/2"?).

    They float on the bar, but MAST is prevented from movement, so the hinge stays fixed with the mast. It just has to be strong enough to carry the weight of the mast, plus a little, if free standing, as no downward forces are generated by the sails (side thrust on a stayed mast generates a LARGE downward vector, like that in an A-frame crane). Chain-plates get the upward end of this, and forces are large enough to wrack a lightly built hull!

    There is considerable force, when off the wind, PULLING AWAY from the hinge when it's mounted on the aft side. That's what all the wiring and rope is for. There's also very little twist as the sheets take most of that force (no track).

    On ZOON (19.5ft LONG MICRO, 31' mast (lighter aloft), sprit-boomed leg-o-mutton), we used a plywood hook, which was looking good until maintenance issues took it out a few years after we sold her. Just a lanyard to hold the mast down, and keep it from jumping up and off the hook. That was actually, I think, a handier arrangement (though I'd go metal, these days).

    Not sure I understand your last question, right... the gate hinges locally availabe were kind of like a gudgeon and pintle. We gave away the pintle and kept the gudgeon (strap bend over in a U, with the bight formed around a rod-sized hole). That's where we used the SS rod or, in ST's case, a shouldered bolt (you can see the threaded end in the pic with the ship's bell... it's passing through hinge plates fixed to the tabernacle posts, and through the strap on the hidden side of the mast.

    These are really pretty simple affairs. They need more engineering the masts are stayed, but for free-standing, the stresses are relatively low at the hinge. The tabs and foot pin take more strain. Most of the stress we see is when pitching (as in bucking into steep chop). The mast momentum('whip') gives the hinge it's hardest work-out, and that's when we like the wire and other seizing to back up those lag screws fixing hinge strap to mast.

    Hope that's all clear! Let me know, if not.

    Dave

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  6. I've had a few words to say on the Trilobuild page:

    Even as the good advice found on the Triloboat site, "Masts As If They Grew On Trees" is welcome, here are a few remarks that are less of the... ahem... somewhat Disney version found there (with apologies to Dave Z).

    We've just completed work on four spars: Two full-size, 31-foot spars (one of which will be cut down to the needed 20-foot length) and two smaller spars intended for much smaller boats. (The same process will be applied to make our yuloh loom). One of the four spars we began failed its stress test after preliminary surfacing.

    There are things a person living in a Cool Temperate Rainforest must know when contemplating a natural, grown mast made after the 'Keep It Simple, Do It Yourself, Embrace the Sub-optimal, Local-resource' philosophy...

    1) You aren't likely to find a standing dead tree without any rot at all. Not in a Cool Temperate rainforest, you won't. Even in the upper Chilkat Valley, where we obtained the larger of our two spars--hauling it 50 miles from the farthest extreme of the upper valley just inside the border between Alaska and Canada--and where annual precipitation is significantly less than the minimum 60 inches per year that makes a Cool Temperate Rainforest, we found rot playing its role in two ways: a) There is a scurf of rot sometimes as much as an inch thick on the surface of standing dead trees of sufficient time-in-place to allow the peeling of bark and the dropping-off of limbs. Even limbed, barky standing dead trees included rot like this. The scurf of rot needs to be taken off with a drawknife or hand power plane to get down to sound, dry wood. This needs to be taken into account when choosing a tree and planning to haul it out. (With the scurf of rot in place, a spar-to-be weighs significantly more than it would when ready for the boat. Once MIGHT choose to try to pre-process a tree on-site, peeling off the rot-scurf to save weight, but aspect and surrounding vegetation may make such a choice impractical.) b) With all but the rarest of rare exceptions, there WILL be rot pockets. Your job as a naturally-grown spar-maker in Southeast Alaska is to choose a standing dead tree with rot pockets that are superficial, and don't go deep into the wood, and which will be "lozenged out" when the tree is processed into a spar.

    2) You are likely going to be doing your spar work in the rain. It's difficult to make a dry working space in lengths greater than 30 feet, even if you have large sheets of 6 or 8 mil plastic. Certainly doing the work under a canopy of standing live Spruce and Western Hemlock will help, but again, topography and vegetation in the area will determine how practical this course can be. Rain falling on dry wood is the enemy of all but the most tolerant of wood preservatives. In our case, being in the Haines area, and working on our spars in an unseasonably dry summer, we were able to finish one of our spars with water-based Kilz primer (compatible with an oil topcoat) and a good quality oil topcoat. The other spar was finished over the course of a 30-day period, dodging raindrops throughout, with an oil primer and an oil topcoat. For this spar, the larger of the two, we also undercoated it with an oil-based copper preservative (a locally notorious "green gunk"). Because we were busy dodging raindrops throughout this production, we didn't find room in the rain-schedule to finish-sand the larger spar after planing it, so it's a bit rougher in appearance than we'd like. It's said that paint isn't the ideal choice for a natural spar finish. We're not sure this is necessarily so. The point of painting, for us--and we did strive to carefully preserve and paint in the cracks made by longitudinal checks without filling them--is the have water shed off the spar, and not hang where it could foster rot.

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  7. 2 of 2-- I've have a few things to say...

    3) Unless you are able to bring all your work inside--a course, however desirable, which takes a different direction than the Keep It Simple, Do It Yourself path--you will have to be willing to embrace imperfection. If you are building a yacht, you might do better choosing a different kind of spar material, or arranging for heavy equipment to bring you a large tree so you can completely process all surface imperfections away, and remove any hint of natural bends. Failing that, you will likely have a slight bend in one direction or another in your natural-grown spar. Your job will be to make sure that bend goes in a direction that works best for your boat--usually parallel to the boat's fore-and-aft center axis, either with the bend facing forward or aft. In our instance, we choose to EMBRACE the imperfect. Done right--which we are striving to do--the boat will sail fine, and when done, though clearly built after the manner of a work boat, rather than a "yatch-ette," will be seaworthy and comfortable.

    4) Surface preparation of a raw log is work. A sharp drawknife and a small pull-stroke folding saw are the best tools for removing limbs (the saw), bark and surface scurf (the drawknife). Have a stone for sharpening the drawknife handy, and use it. Often, a lot of material has to come off, before it's time to plane and sand. (The latter can be done fairly quickly with a power hand plane, a belt sander and an orbital sander.) Whatever the tools applied, spar preparation will be hard and dirty work. If you are unfamiliar with drawknife work (fortunately, having built cabins, we're not), prepare for some sore muscles. Even going back and forth again and again with a plane will force you to move in unfamiliar ways. We suggest you make sawhorses specially for this phase of the building process, so you can have them standing higher than ordinary sawhorses, saving back strain. (We chose decent-quality pre-made sawhorse brackets that allow for disassembly.) Having a ready-to-paint (or preserve) spar sitting higher than would be on typical sawhorses makes for easier brushwork, also.

    5) If you know some years in advance that you will be needing a replacement spar, it makes sense to mark and girdle a specific tree that will, in future, meet your needs. That would help with a fair amount of the problem with existing rot in a standing dead tree. With the several compromises we've had to make in our spars, we have done just this with some trees on family land. Future spars are now waiting for falling and pre-processing in 2 or 3 years.

    [Had to split up the post here, on account of a 4K character limitation per post...]

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    1. Hi Peter,

      Maybe more PRINCESS BRIDE than Disney? I'm thinking of the 'resuscitation' scene, where 'degrees of dead' are discussed.

      Recently dead trees (tight bark, maybe even a few needles, brown and clinging, 'ringing' to a blow from the back of an ax) are often in very good shape. We reject any with ANY rot in the stretch we want to use. Generally, a few sub-surface borers will have left shallow tracks, and we shave most of that away, along with the bark, but no more.

      No paint nor finish, and - as you say - embraced imperfection, and we avoid many complications.

      We dumb things down more than many (most) are comfortable with. Jury's still out on the long term benefits, if any. Certainly, there are many fine ways to reach one's goals, and those you present are commendable options.

      Thanks for sharing!

      Dave Z

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