Help with new mast and shroud arrangement.

[JimD]

My winter project will be to replace an aluminum mast with a wooden one. The boat is a 15 foot Glen-L Minuet sloop. It has a small cabin 300#s ballast, main sail 83 sq ft, jib 46, fractional rigged forestay onto which the jib is hanked, upper and lower shrouds, no backstay which is not possible to add due to the amount of roach in the main it would require a boomkin sticking out the back several feet. The chain plates are mounted on the cabin sides and should stay there. If they were moved to the sides of the boat I think they would prevent hauling the jib close enough.

I've never liked the position of the lower shrouds. They seem to angle too far aft to let the boom swing forward enough for downwind sailing but without a backstay I don't want to mess with them. So is it possible to build a tabernacle that would support the mast enough to eliminate the need for the aft angled shrouds? Hope I'm explaining this ok.

I will also consider an solid mast stepped through the cabin roof and onto the sole. I have a gaff sail kit very nearly the size and CE of the current bermuda main and if I converted to a gaff rig the mast could be a few feet shorter.

[Mike Field]

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Jim, I suspect the only reason the original mast was stayed was because it was aluminium. For a boat and gear that size you should be able to easily get away with an unstayed timber mast around 3" - 3½" dia.

If the idea makes you uncomfortable, take the jib halyard one side and the mainsail halyard the other, and make them fast out near the chainplates somewhere. Then you'll have some pseudoshrouds that should make you feel happier.

And if you keel-step the mast and build up some stoutish partners where it passes through the cabin-roof you should be able to go shroudless, swifterless, and backstayless in complete confidence. smile.gif
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[Ian McColgin]

These boats have been built with tabernackles and with deck stepped masts but keeping the same general configuration of the uppers athwartships of the mast and the lowers swept back about half the cabin trunk.

You absolutly need that sweep to oppose the jib stay.

Even if you let the sail lay against the spreaders a little, it won't hurt anything. Just don't let it off so far that the belly of the sail sags right around the spreader tip.

If you make a vang, you can get the boom out further as the sail will be flatter. There's not much room for a conventional vang. For off-wind sails of any length, you might have a pair of vangs, each from the lower chainplate (work in a shackle instead of the lower turnbuckle pin, bow part pointed aft free of the turnbuckle and shackle pin taking the place of the turnbuckle pin) to a point on the boom say above the aft end of the cabin. Just cast off on and trim the other with each gybe.

A bird's mouth spar could be made quite light and strong. You could make an unstayed version (keel stepped) if you change the jib to an unstayed jib with a clubbed foot with the club pivoting maybe 1/5 or less aft from the tack. Coupled with a high roach full batten sail, you'd be marrying styles in an interesting fashion. If you go in this way at all, go over it with a competant sailmaker.

G'luck

[JimD]

I think I like the the keel stepped unstayed solid spar idea the best. On this small a boat it shouldn't be too heavy to easily step singlehanded and no shrouds will also make it easier to move around on the deck. To make it I will probably dig through the lumber yard 2X4 stock for a few of the best ones and scarf and laminate as required. I'd go for a real tree trunk but I wouldn't know what to look for aside from it being straight.

[imported_Steven Bauer]

I've been very happy with birdsmouth spars. Easy to make with lumberyard spruce and plenty strong. Oh yeah, did I mention easy to make? :D

Steven

[Mike Field]

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Jim, i should have addedd that Aileen Louisa is rigged as in my second paragraph. She's 15' oa, and carries more sail than your Minuet. Her jib is mastheaded rather than fractional, but there's no standing forestay, the jib's set flying.

http://www.woodenboatfittings.com.au/public/aileen-louisa-s.jpg http://www.woodenboatfittings.com.au/public/on-the-creek-s.jpg

[Bruce Hooke]

Just remember that a boat that size will be rather sensitive to the weight of the mast. So, I would try hard to keep the mast light, or at least keep it from getting much heavier than the current mast. This will be more of a challange with a solid, unstayed stick than it would be with either a hollow mast (e.g., birds mouth) or a stayed mast (or better yet a hollow, stayed mast)...

[JimD]

The mast will be 3 feet shorter and the boat weighs about 600#s so I'm hoping it can handle a little extra weight

[JimD]

Originally posted by Steven Bauer:
I've been very happy with birdsmouth spars. Easy to make with lumberyard spruce and plenty strong. Oh yeah, did I mention easy to make? :D

Steven:D Yes, Steven, I do recall you mentioned they are easy to make. So you reckon that a birdsmouth, say 4 or 4 1/2" diameter would be strong enough to use unstayed? I really like the no shrouds idea. How about a hollow birdsmouth towards the bottom of the mast and a solid tapered section towards the top (I believe there are proper boat terms for the various sections of a mast but can't recall them at the moment)

Mike, nice boat, very different from a Minuet, though. I also took a look at Stevenson's Weekender boats which are nearer in size and gaff rigged. The Weekender masts look well stayed.

[Mike Field]

Originally posted by JimD:
Mike, nice boat, very different from a Minuet, though. Yep. Same length overall, but longer on the waterline, less beam, less ballast, less top-hamper, and more canvas.

If she can carry an unstayed mast, so can a Minuet. smile.gif
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[Ian McColgin]

Some engineering thoughts: Two boats of equal size can easily have very different loads on the spars, due to differing stiffness. The higher displacement boat JimD has will be harder on the spar. That said, an unstayed bird's mouth spar should work.

The strength of most spars is in the outer mass - making part of the spar solid is tricky and does nothing much to add to strength.

With the bird's mouth construction, total mast diameter and wall thickness are related. For that reason, your question as to whether a mast of whatever diameter is adequate is not the right question. Check the WB article and other literature to get those scantlines right for your boat.

[Mike Field]

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I agree with you, Ian, in that different boats have different spar loadings for the same sea conditions. Heavier displacement means more mass to get moving (or more momentum to overcome.) But I suspect that this, of itself, would actually put a little less load on the mast because I would expect there to be be less snatching at the end of the roll. On the other hand, shock loading in a squall would no doubt be somewhat higher.

I know that Aileen Louisa's mast thwart was damaged at some stage in her history (as evidenced in this photo) --

http://www.woodenboatfittings.com.au/public/bp-al.jpg

and in fact I believe it happened because the mast was unstayed -- not because it wasn't properly supported in the normal unstayed position though, but because the owner allowed the rig to pull the mast foot out of the step before the halyards were properly made fast, thus putting an enormous moment on the partners and splitting the thwart longitudinally over much of its length. (The split has been fished by bolting stiffeners top and bottom, both sides, as can be seen.)

This would certainly be something to be careful to avoid. But in fact it could quite easily be avoided by using some sort of peg or catch on the underside of the partners to stop the mast lifting out of the step.

Having a hollow mast would save weight, but at the same time it would reduce the period of the roll. I'm not clear whether this would be considered A Good Thing in a Minuet or not. Certainly though, most of the loading is taken in the outer two-thirds annulus of the spar, which means that quite a bit of weight-saving is possible for little loss in strength by making the mast hollow. (But not NO loss in strength, as a certain Kiwi was once heard -- well, I'll say no more about it.... smile.gif )

A hollow mast would of course need solid plugs at the step, partners, boom and (all) gaff positions, and hounds if it was decided to use shrouds after all.
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[Ian McColgin]

Mike's remarks are well taken, especially about keeping the mast in the step. On many small boats, the hallyards belay to the thwart or, as I did on Leeward, through the thwart to a turning block on the CB case and back to a cleat also on the CB case, thus allowing one to raise or strike without getting too far forward in the boat. In any event, this keeps the mast located when the sail is up but you could have an awkward moment when the sail is down and the mast is up and the sea is a bit jumpy.

When I rebuilt Goblin's foremast I came to admire hollow construction. I had to rebuild due to rot at the partners - the interior compression block held moisture that wept in from the truck. When I rebuilt I put a drain in that block and in the heel. I discovered, to my surprise, that it did not have a compression block at the spreaders, where the lowers and forestay were also attached and where the gaff throat had once been.

The compression at the partners on that rig was considerable give how the wedges were designed but apparantly the builder did not want to change the bendy structure of the mast by hard spots elsewhere. I've since learned that, contrary to common sense and frequent practice, a compression block is not needed even at the partners if the strain is fairly even. If you've a bit of taper below the partners and a bit of leather padding at the partners such that the mast takes a snug fit - like a little work to pull it out so maybe you work a little foot activated lever into the step - the compression loading from your rig will make an interior compression bluck unnecessary. If you do put in a compression block, it need be no bigger than the depth of the partners.

There are many ways to make getting the rig one and off a snap. On a traditional sail, a loose foot allows for fast boom removal and you can brail the sail to the mast if you rig the lines. If you're wedded to an attached foot and especially if you go with battens (full or partial) to get some sail area in the roach, you might consider a removable bit of track below the normal gooseneck location. It can be held in place with hand pressure. With the sail furled on the boom, put the track on the guide pegs you put on the mast and drop the boom and sail slides onto the removable trask, which of course has a stopper at the bottom. Put a stopper on the top - the one you removed from the bottom of the fixed track will do - and take the whole kit and kaboodle off in one piece.

G'luck.

[JimD]

Please keep the comments coming, gentlemen. As for the effect of the mast's interia on roll I'm really not concerned. This is a dayboat for the lake. Not a whole lot of rolling going on. The overriding interest is to get an unstayed mast as light as possible but strong enough to handle wind gusts for a 600# displacement hull. The wind does seriously gust around here. Last week we had 100kph. Needless to say I would not have gone sailing that day. I was interested in a taper at the top mainly for aesthetic purposes. I think it looks proper on a gaffer. But the mast will need to be only tall enough for the placement of the hound for the jib. I have no control over this because I must work with the jib I already have. The hound to the waterline (which is where the sole is and keel step will be)is 18 feet, so that will be the total lenght of the mast. The cabin top will be about 3 feet so there will be 15 feet of mast from the partner (if that's the correct term in this case) on the cabin top.

[Mike Field]

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I think Ian's said it all, Jim. But it's interesting that he's found a plug unnecessary at the partners; and even more so that there was none at Goblin's hounds -- that's one place I know I'd want to have one, diminished bendiness notwithstanding....

Drainage holes are obviously worthwhile. I guess you'd make the top face of each block concave, and drill a vertical hole strraight through it. (Maybe slather a bit of CPES round inside there, too.) You'd want to make sure all the swarf was carefully removed before you glued everything up. (Or else run a limber chain through all the holes and out at the top and bottom. smile.gif )

What about posting some progress photos for us as you go?
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[Ian McColgin]

One of these days I'll find someone who's done empiracle studies on hollow wooden mast construction and can answer the questions.

I've come to believe that the only thing blocking inside the mast might do is keep the wall parts from shifting under the side loading of the partners or any stay or gaff or spreader push and pull. But even at the partners, this lateral stress does not seem so large that it needs to be bridged across the void to the other side.

You don't see compression blocks inside aluminum or (I think) carbon fiber masts and those cylindrical structures do not seem to me any stronger than well built wood.

[Jay Greer]

If I may add a bit to this fine discussion, here are a few comments on spars based on many years of personal experience building and repairing masts.

No one has mentioned glue yet. I have seen a lot of masts come apart at the seams due to glue failure. This includes epoxy, resorcinal and two part airolite. I have always used Weldwood Glue. That is the brown powdered stuff you mix with water. In all my years building spars, I have never seen Weldwood Glue fail!

It has been mentioned that blocking is often not necessary and this is quite true if one is interested in a mast that will bend without having hard spots. Halyards can also be run down the interior keeping loads down the center of the mast. If spreaders are used for support, a hollow compression tube in conjunction with a band around the mast over it and drilled for the spreader support bolt will transfer the load of the weather spreader to the band from both sides , thereby acting in dynamic compression, This is kind of like trying to crush and egg by applying pressure to all sides at once. Spreader attachment should be done in such a manner as to allow the spreaders to swing and take a natural alighnment when under load. Many mast failures come at the point of spreader attachment when a rigid mounting system has been used. As time passes, a rigid spreader tang usually needs larger and larger screws installed to compensate for the loosening of the rigid mount from shock loads. This eventually weakens the mast and eventually can contrubute to failure.
A hollow mast is more resitant to bending than a solid one. A solid mast, while more flexible than a hollow mast, is more prone to failure if not correctly supported as the core of the mast acts as a cantalever when the weather side stretches and the lee side comes into compression causing the weather side to tear the grain and break if enough load is applied.

A bird's mouth spar is an excellent choice for mast construction. The interior surfaces of the staves should be coated with thin shellac. This will allow the wood to breath while not obsorbing moisture.
The heel should have a drain hole since condensation will form on the interior with changes in temperature and humidity. in areas where heavy hardware such as cleats and winches will be mounted it is advisable to add thickness in the form of bolsters to the interior of the spars.
I hope all this rambling on about wooden masts has not been too boring!
Best Regards,
Jay Greer

[Mike Field]

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Thanks Jay, good stuff. A compression tube is obviously a good solution for transferring local spreader loads (as is an internal plug, of course.)

I can't speak for carbon fibre Ian, having had nothing to do with it, but I've seen an aluminium mast fail at the spreaders -- sort of just fold over, the way you'd bend a straw -- where I'm sure an internal block would have saved it.

The fact of the matter is that the lighter the wall thickness the more care is required with construction, and the more important is the staying. But my thesis in this thread is that Jim's Minuet is not the right vehicle for high-tech rigging, and that with her he would be better off going in the opposite direction -- giving her a solid mast, firstly to make construction as simple as possible, and secondly in order to do away with the requirement to have any staying whatever.
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[Ian McColgin]

I agree with going simple. I think a bird's mouth may be simpler than solid as it's so much easier to get out good stock. And the lightness of bird's mouth will make setting and striking the rig a snap.

But, different boats, different longsplices.

[JimD]

I've decided to go with a hollow mast, pivot stepped on the cabin top with the shrouds justs as they are. Only question now is whether to build a round mast and with oak hoops or box construction with track and slides for the sail. I have a suitable piece of oak for the hoops and a small steam box that I have experimented with and feel confident there'll be no big trouble making the hoops. On the other hand going high tech with track and slides sounds lower maintenance which has it's appeal as well. Any more thoughts or ideas?