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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

Saturday, February 11, 2012

Free Standing Masts and the Tabernacles Who Love Them

Not much riggin' up there!

Free standing masts have been around a long time.

Bullet points in favor:
  • Simple - Easy to rig and maintain.
  • Inexpensive - No shrouds, stays, chainplates, spreaders, turnbuckles or swages... reduced shackles and tangs.
  • Works well in a very broad range of conditions - Not just a light weather rig.
  • Low windage - Rigging adds drag.
  • Quiet in a blow - No shrieking rigging.
  • May be raised and lowered with relative ease - Lots less weight and stuff to deal with.
  • Spill gusts and ease their impact - Willow vs. oak.
  • Impervious to jibes - You don't clobber the shrouds with the boom, possibly bringing the whole shebang down.
  • Have few parts to fail - Reduces the odds of failure.
  • Don't generate high stresses - Doesn't generate the crane effect, which torques the hull.
  • May be temporarily stayed with standing or running stays and shrouds - Can't temporarily unstay a stayed rig.

Disadvantages don't warrant bullet points. Not as fast to windward. Period.

The usual response I hear is, "Well yes, but carbon fiber masts are expensive!"  Carbon WHAT? Come on... the Chinese have been sailing unstayed rigs for millennia made from that exotic material, wood. You know... that stuff that grows on trees.

All in all, for a KISS boat, free standing rigs deserve a good, close look.

SLACKTIDE's forward tabernacle before installation...
Hinge pin goes thwartships,  high and aft.

Note tripod formed by box and struts.
Adequate, but struts could've landed yet further forward for greater support.

And, as long as you've a free standing mast, you may as well mount it in a tabernacle.

If you look it up, wade down the list of meanings until you hit the nautical one. From my Kindle OED:

A partly open socket or double post on a sailing boat's deck into which a mast is fixed, with a pivot near the top so that the mast can be lowered to pass under bridges.

Or, I might add, to perform maintenance, add masthead toys, sit out a really big blow or 'borrow' the mast for some other purpose (sea anchor, skids, lever, etc.).

Basically, the tabernacle forms a box, open on one side. A pin, near the top, passes through a hinge, strongly mounted to the mast. One of many stop mechanisms fixes the foot of the mast in place. When the stop is released, you can lower the mast.

A free standing mast needs a certain amount of bury, that is, a percentage of the distance from hinge (or partners) to footstop, divided by overall mast length. The range is a minimum of 10% to an ample 15%. More doesn't hurt, and gives better leverage for raising/lowering. With enough leverage and a  counter-weight butt, this can be a one handed job.

Of course, the tabernacle needs to be adequately supported... I still haven't found a rule-of-thumb for this, but, if we're gonna go hell for stout, this is the place! The more support we can bring to bear, the merrier.

The tabernacle must deliver adequate re-enforcement at the hinge, as well as below. I like to bolt to bulkheads, and the more the merrier. Solid, triangulated struts can be used, if not enough bulkhead is available, splayed to the sides and either fore or aft to form a tripod (or double up struts to forma a quintapod?). The less free standing tabernacle, the happier I am.

Timber tabernacle posts are inexpensive, simple and can also be more freestanding, in their own right, than simple plate. Their bury (I think) can be calculated as if it were a solid mast - from masthead to foot of tabernacle, with the uppermost structural support as the 'hinge'. They can be minimally secured at foot and 'partners' (where they pass through a deck), but I'm always happiest when they're bolted to along a bulkhead.

I like the total cross section of tabernacle timbers to be greater than that of the mast by a goodly margin. I also like to tie them together with a back plate to help equalize mast stress-loads between the timbers. On the s'brd tack, say, the port post would bear all the stress, if not bound to the s'brd post. In that case, both would share the load on either tack. A removable front-plate, fixed once the mast is erect, further strengthens the whole shebang.

Welded metal tabernacles have some advantages. They're not as bulky, clearing the view. Struts are very strong, reducing the need for post bury along a bulkhead. A deck plate at the bottom gives landing to the struts and a broad footprint for leverage and spreading out psi from stress loading. They're very handy where little or no bulkhead exists, and you don't want the mast or posts intruding below-decks. Still, don't get crazy. If you can't arrange a solid tabernacle, reconsider whether it should be stayed, after all.

Anke and I, with no special gear, usually dry out for raising. We use one mast as a crane for the other, and raise as high as we can. One of us (the short one) will be out on the beach with a line to the masthead, while the other, taller and dumber, strains and puffs it the last of the way up. As Tall and Dumb ages, I may add counter-weights or mechanical advantage. Lowering is just the reverse.

*****

Bonus free standing mast story:

One fine autumn day, we were sculling LUNA across Salisbury Sound in a flat calm. The sound is open to the Gulf of Alaska at its northwest end, and tapers down to narrows in the south. Low mountains flank it on three sides, high mountains to the north.

We were making for Neva Strait, the strong-current passage near the south end. We were hustling to catch a fair current... miss it and we'd have to wait for fair wind or the next tide.

Anke was below, making lunch. I had all sail set to catch the occaisional zephyr. We'd made good time, and now, approaching Neva's entrance, we had plenty to spare.

I heard a rumble behind me. I glanced over my shoulder, expecting maybe one of the big ferries? What I saw was water being blown to spray by a wind bearing down on us. YIKES! Willawaw!!

I threw the helm over, shouting "Hang ON" to Anke. The boat had barely begun to turn (not much steerageway at a knot and a half), when a furious burst of wind jumped us.

We were still in line with the assault as both sails caught and filled. I felt LUNA's stern rise, the whole aft end levering from the water. With a splintery CRA-ACK, the foremast gave, breaking in two, just above the hinge!

"HOLY MOTHER OF FREAKING PEARL!! We've been dismasted!", I bleated, the wheels of my brain burning rubber. Rounding quickly under the full main, I steered off, a bit, to let the foremast fall alongside us (don't want em' falling on deck or self!), dragging from its haulyard and sheets.

After that first gust (how many knots of wind was that? No sea state to judge it by!), the wind settled down to a bit shy of 20 knots. We dropped the main and tightened the mizzen, holding the bow into the wind and slowing drift.

[LUNA is a cat-schooner with what we referred to as fores'l, main and mizzen. The latter is a little 'dandy', a.k.a. 'spanker' mounted on the stern, but those terms just don't fly in Alaska, nor with Anke, for that matter.]

A fisher friend had been approaching (Neva's a busy place) when the mast went down, and asked if he could help. We asked him to stand by until we got an anchor down. Backing the main, we were able to crab our way to the side, where - fortunately - the bottom is sandy. We dropped the hook, checked for holding, then waved him on, gulped our lunch and came up with a plan.

First, we hauled the broken butt aboard. Released the haulyard of the still set fores'l and clawed the battens uphill and onto the deck, panel by panel, untying their parrels as they came aboard .Once the lug was aboard and detached, we bundled the sail on deck and brought the upper end of the mast aboard.

[Batten parrels are short, standing lines that tie to the forward end of a batten, pass aft around the mast and retie to the same batten; they keep the sail in close to the mast and can be climbed like ratlines.]

Next, we removed the broken stub from the tabernacle, and detached its hinge hardware. This is just a large metal strap, bent over double, then drilled and counter-sunk for heavy screws. The whole shebang is served with nylon line to back up the screws and pad the mast in its tabernacle. We transferred it to the mast remnant, the correct distance up to provide bury, screwing and serving in place.

We set it across the tabernacle and reinserted the hinge pin, then raised it. This was a little tricky and fail-dangerous. We're bouncing around at anchor instead of our usual dry-out. Anke can't help at all, except to counter-weight the base, and pin the foot once it's up. I'm straining myself purple, alone, to raise the (mercifully) shortened mast without letting it slew off to one side (a 24 foot lever prying at our tabernacle!). Lucky I din't bust sumpin'.

But we got it up. Next trick-in-a-row was to re-rig the sail bundle (re-attach haulyard, lead through lazyjacks and fix them in position, re-tie batten parrels. Reattach the sheets and done!

Finally, we look up and around... HEY! Tides still fair... this whole mess only took an hour and a half! What're we waiting for? Up anchor and sails, wing 'n' wong in a fair breeze, one panel reefed on the shortened foremast.

Try that with your fancy, high-tech, marconi, witch-to-weather rig!

Free standing freedom


There's a little preamble to this story. We had recently replaced the old, trolling pole foremast, which had become pocked with exterior soft spots.

A friend had offered that we take a tree off his property (rather than the standing dead we usually harvest from the Tongass). It was a rushed search among young, living trees... we prefer trees that have gotten a late start in shaded understory. They grow slowly and densely ringed.

We found a nice, straight one, but the grain turned out to be wide. I've heard 9+ annular rings to the inch is optimal... this was about 5. A hidden flaw pushed us a couple of yards up the butt, leaving it on the thin side. Finally, it had only seasoned for a couple of months. Green (wet) wood is much weaker than dry wood, and spruce seems to have a wider difference than most. It takes about a year 'on the hoof' to get a standing mast dry.

So. Three strikes against the foremast. The full value main - to windward, having less bury and partially blanketing the fores'l - stood firm.

Conclusion? We're still perfectly happy with free standing masts, but are holding ourselves to their rules-of-thumb!




9 comments:

  1. Love it! That's the sort of independence I'm looking for.

    ReplyDelete
  2. You mentioned using one mast to help raise the second mast. How do you raise the first mast? How is the aft mast supported when lowered? It must hang out over the stern quite a bit. Are the two masts off-set, or is the foremast tabernacle slightly twisted
    for the foremast to be able to clear the aft mast when lowered?
    John

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    Replies
    1. Hi John,

      I see that I missed saying how we raise the first mast.

      We dry out, or cock the boat so that it forms a long angle with a dock. Anke takes a line lead to the masthead and gets out far enough from the base to make a long angle.

      I'll lift the mast to my shoulder. Then, while Anke pulls (with constant, steady pressure; not jerky), I work my way toward the tabernacle. My constant shoulder height raises the masthead, and as Anke's lead improves, more and more weight is relieved from me. Once 'over the hump', it easily pulls upright and into the tabernacle.

      While Anke maintains pressure, I set the foot bolt and we heave a sigh of relief.

      The critical point is about 45deg... Anke's lead is still rather low, and the forces on me are about maximum. Still, it has been relatively low stress.

      CAUTION: The person lifting is in the crotch of a nut-cruncher, where already considerable forces are multiplied. IT IS ESSENTIAL that the person tailing the masthead not release or bounce the mast in any way! Good communication is essential and all transitions must be slow and steady.

      If in doubt at all, stop, ease down and consider reconfiguring for a mast lift with full mechanical advantage and safety lines (use any standard method).

      Hope this helps!

      Dave Z


      PS... The after mast lowers forward. It is offset from the main mast, so there's no conflict. Alternatively, the hinge bolt (rather than the tabernacle) can be installed at a slight angle to clear the masts, one from the other.

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  3. Not to forget shrouding: Tom Colvin eventually seemed to favor tabernacle steel pole masts, taking advantage of a steel house fore or aft plane for bracing, and two shrouds per side. I remember a story of his son sailing to Colvins house dock in his 42 foot lug rigged boat and father and son lowering the mast for maintenance.... but as I recall it took about a half day. And not to forget just sinking the mast to the keel and thru a partners tube.... I did this with a steel pole and ran two shrouds off each side and it worked fine. But going up the mast was NEVER fun and required a complicated ascending rig with my wife tending a backup safety rig from the deck. Finally, not to forget Phil Bolgers wonderfully counterbalanced free standers that went up and down with mere hand pressure: LOVELY!!!!! (pain in the ass to engineer the butt to stow below deck though) Ultimate simplicity with your rig although I'd still add a few shrouds. Never had a problem with my big 430 sqr. foot lug sail whacking the shrouds but over time I'm sure it would have eventually. Colvin would consider such a whack unseamanlike and sloppy but then sailing with him probably would have been a bit like sailing with Nietzche. Not my ideal sailing fren but any correspondence he ever graced me with I saved like a little piece of treasure.... he was a gifted master naval architect-builder-sailor.

    ReplyDelete
    Replies
    1. Tom Colvin... one of the Giants!

      His GAZELLE is one of the designs of which I've always been fond.

      Steel's great stuff, but it takes a lot of know-how to work, keep fit and handle. A whole 'nuther learning curve!

      -DZ

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  4. And then there's this question: not having any shrouds, when the willawaw struck would it have been an option to have released the sheets, and let the sails go completely forward to dump the wind? Not that there was perhaps enough time, but as a concept? One of the things that I love about freestanding masts is that ability to slack the sails even on a run...
    -- Shemaya

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    Replies
    1. Hi Shemaya,

      That would have been preferable, in retrospect. It went very fast... the first line of defense is to round up. In fact, if the mast had been well sized and with better grain, this shouldn't have been a problem.

      We've certainly been in bigger gusts with no problems. Usually, though, we're partially reefed in willawaw weather, anyway, and seldom straight down the wind (we tend to broad reach, rather than run, most times).

      - DZ

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  5. You mention raising and lowering the masts by hand while dried out. Does this happen often? Also, I take it that when you say you use one mast to crane the other in raising and lowering, you are referring to maintenance (see previous question), rather than initial installation. (When you first put up your masts, how did you do it?

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    Replies
    1. We don't do this often... once a year for inspection.

      The first time up, we raise the one with the deepest bury (portion below the hinge) for best leverage. In each case so far, a couple of friends have helped by hanging on the bury end while I puff and grunt at the base of the upper section... once to about 45deg, Anke hauls and up they go.

      As Gomez mentions, above, Bolger often counterweights his for very easy raising/lowering.

      In my present youthful vigor, our masts have been only JUST at the point where we can raise and lower them without extra mechanical advangate, even without help from friends or the second mast. But it's not what I'd call fail-safe. It's like being in the business zone of a giant nut-cracker!

      As we age, I have vague plans for a block and tackle to the base, or possibly a gin pole.

      - DZ

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