Thread: Hollow Masts

I don't have much issue with epoxy in the tropical environment I'm in either. In fact, epoxies don't do much until you get to around 150 degrees, where it will begin to distort slightly and peel strength is rapidly reduced. Epoxy doesn't "melt" like other plastics, but will deform and lose it's grip on things above 150 degrees. It's pretty rare to have horizontal surfaces, even those painted black, get above 150 degrees in direct sun light. You'll have 60% less peel strength at 180 degrees, which is a substantial number, particularly on highly loaded items.

In mast work, I don't like the added weight, additional cost and thicker glue lines, which must be protected. You know I like epoxy Michael, I just find I'm using it less in recent years, in favor of more traditional adhesives, which are lighter, can have hair thin glue lines without starving a joint, etc.

Back to heat and epoxy. I do have a couple of clients, that live in the southwestern desert (USA). They both are having much difficulty keeping things stuck with epoxy. Highly sprung butt blocks and plank scarfs have let go or partially so, lots of creeping and movement induced cracks, checks, etc. Now they live in hell as far as I can see, with temperatures 110+ much of the warm months, during the day and 30 - 40's at night. These huge swings and cycling of temperatures (and humidity) can ruin anything, pretty quickly I suspect.

I've seen some creeping on decks with epoxied seams, but nothing like what I've heard from Craig and Jim out west. I've personally had no real issues with epoxy and heat, but I may be more anal about protecting things then others.

The twelve stave spar shown above has a 17% wall thickness, for what it's worth. I wouldn't consider much less on a cruiser.

Thanks for info guys,
I've got a stock of both Bote-Cote and Titebond III on hand, so I'm not fussed.
But I do have a question regarding internal halyards.....
If the internal hollow section of the mast is subject to abrasion from the ropes and moisture from the halyard openings, then shouldn't I coat the internal hollow section of the mast with something to protect it??
If I glue the mast in 2 sections as described by Par, then should I coat the internal timber before final gluing???


I had "one of those days" today. I took a sickie(note-Self employed so the boss already knows) to get the staves cut. I got everything cut and thicknessed...then got to the Birds-Mouth bit, and my Table-Saw packed it in. The On/Off switched died...it won't stay in the ON position ...its under warranty, but thats not the point.

I guess you could call it Karma...I should of gone to work instead.

Mickj,

As you will have seen from all those photos I sent you, I make my masts in one go, not as a two-piece arrangement. I believe that you should coat the internal surfaces of the mast regardles of halyards, and I do mine using a number of different methods. One system even involves partially filling the mast with low-viscosity epoxy, rolling it around, and pouring the residue back out of the mast. The procedure is repeated at least three times over a three or four hour period. This system only works if the tip plug is glued in afterwards.

Normally, I give the staves three coats of epoxy before assembly, but with the coating and assembly process all done inside the window for a chemical bond - i.e. wet-on-tacky to be absolutely certain - otherwise you could compromise the strength of the glue joints.

Ross Lillistone www.baysidewoodenboats.com.au

I usually have halyards and lifts inside a PVC pipe, rather then slapping around inside the mast, especially if wire.

Epoxy coating alone offers very little abrasion resistance, unless substantial reinforcement (fillers and/or fabric) are also used. Masts glued up in a traditional fashion will survive several generations with good care. Many years with poor care.

Internal sweating, condensation and rain will get into the masts or through sheave slots and other openings in the stick. Make sure to relieve this, permitting drainage is the key to a mast's survival. On most masts, where I'm given control over the construction, I'll use shellac on the inside. It's inexpensive and resists moisture vapor penetration better then oil or varnish (the traditional internal coating) and single part polyurethanes, plus it's light weight and not brittle. Most masts start out brightly finished, but quickly become painted once they get sore of the refinishing tasks each year or so.

Don't get me wrong, I've used epoxy on masts, but don't think it's necessary in most cases. I've got a 70 year old box section mast hanging in the barn that is just fine and quite serviceable. It's interior is coated with varnish and the glue is resorcinol.

Howdy PAR,

It is sometimes a bit annoying when I write a post and lose it.

Anyway - I was accepting all your other arguments about using epoxy less.

I think my main motivation for not considering others much is that most of my writing is aimed at people who haven't built a boat before - so something that fills gaps is good.

If joinery is as good as yours (or mine on a GOOD day) then there is little argument - either is fine. However for people whose joinery aint so good (me on a BAD day) the epoxy will fill the gaps with no structural defect.

Also the low clamping pressures often allow brown polyethelene packaging tape to be enough for many clamping jobs - removing the necessity for lots of clamps.

So I think that is the main difference to our approaches.

I guess a minor point too is that the one product does everything (gluing, filleting, glassing, filling etc) rather than saying to use on in one place and use others somewhere else. So aimed at first time builders rather than a production situation.

One thing I did want to ask PAR, are there any other glues that have handling advantages over epoxy and are starting to be useful as structural gap-filling glues? That would be great to know as more of my plans are being built in far flung places it is not always possible to get the 'pox.

Cheers
Michael Storer

Originally Posted by RossL

If you want the photos just drop me an email to [email protected] and I'll send them to you.

Ross Lillistone www.baysidewoodenboats.com.au

Hi Ross,
Thanks for the pics very helpful.

At the risk of being accused of hijacking this thread may I ask you to explain some detail of your shop bench. I think all members will be interested in the bench shown in several pics on your web site. It appears to have some unique features that I assume would be especially useful for boatbuilding.

Cheers
Mike

Since the advent of epoxy in the marine industry, most every other adhesive has taken a back seat in comparison. It's a tough competitor, with peel strength, elongation to yield, compressive ability, moisture vapor resistance, ability as a coating, moldable plastic, room temperature cure, low clamping pressure requires, etc. It's fully cross linked molecular structure and 100% solids content are the keys, unlike most other polymers.

Michael, some aliphatic resins (TiteBond III for example) have slight gap filling properties, though tension strength drops off pretty dramatically over a 1/16". TiteBond III does pass the military spec type one water proof tests, but just barely and I wouldn't trust it below the water line on a moored or berthed craft. PL (Gorilla glue is an example) is also gap filling (and a better type one), but I just don't like the stuff and the foaming action can be troublesome, especially on brightly finished surfaces. Some of the polyurethanes have tremendous gap filling qualities, but lack the other qualities that epoxy excels at, such as compressive strength.

I will admit, on all my designs intended for home building, I'll spec epoxy more then anything else. The ease of use, coupled with the insurance of things staying stuck, under a variety of conditions and torments, makes it the official back yard builders goo of choice. This said, one of my 14' skiffs will have it's build costs doubled, if the boat is encapsulated and an exterior 6 ounce sheath applied. I honestly feel this particular boat would serve just as well with sacrificial bilge runners, that get replaced every few years and some good oil based paint, rather then embalming in goo and fabric. Would one be better then the other, maybe, but the paint and runners boat would be faster and cheaper to build, which is my idea of down and dirty, back yard building.

I work on a number of different construction types, design for the same diverse groups too. This has me looking for different adhesives in different applications. When it comes to glued seam (stitch and glue) or many of the other modern construction methods, epoxy is the choice, usually the only one suitable. Some of the "cross over" methods and certainly most of the traditional build types, require different things from an adhesive, which epoxy may not be as well suited.

Mike,

The bench you have asked about was made primarily for use in scarphing 8' x 4' sheets of ply. It uses 300mm-deep "Hy-Beams" as the main structural elements. The heart of the table is a 300mm deep, strong beam which runs crosswise midway along, fabricated from heavy marine ply and solid stiffeners. This beam carries a plywood plate on its upper surface - this plate being about 100mm wide, to support most scarph widths.

A pair of light hoop pine-framed plywood table tops sit on either side of the central web, attached to the "Hy-Beams" by removable hex-head screws. In normal use the whole thing sits like a conventional table, and ends up being about 2450mm x 1220mm. However, when scarphing is being done, the two table tops are move outwards and re-screwed at a total table length of about 4000mm. This allows a pair of 2440mm x 1220mm sheets of ply to sit on the table top without over-balancing.

After the scarphs are cut, the sheets are clamper together under a flat timber plate topped by a strong Oregon beam which has a parabolic concave curve cut into its lower edge. This is clamped at each end, on each side of the table. The concave face ensures that the clamping pressure is applied evenly across the width of the scarph. The deep, strong cross-wise beam supports the underside of the scarph.

This table is strong and light, and gets used for everything! Holes cut into the webs of the "Hy-Beams" facilitate clamping of many items requiring a long, straight edge (e.g. oar laminations, short spars etc).

The idea came from the combined mental depths of myself and my friend, Doug Laver (a very practical ex-Army Engineering Officer).

Photos attached, including a couple of views of a finished 'Bird's Mouth" mast.

Ross Lillistone

Woops! In my last posting I should have said "convex" not "concave". Sorry.

Ross Lillistone

G'day Ross,
Very cool, the bench isn't bad either, thanks for posting.

As they say necessity is the mother of invention. I was thinking maybe you used it as a sort of adjustable strong back for assembly, what a great idea.

Regards
Mike

Hi guys,

I have a 1978 Cheoy Lee Offshore 41 that, eventually, I plan to circumnavigate with. She needs a new mast and I want an unstayed mast. I admit to not knowing much about the physics of a spar and so I wonder, can I build a wooden mast, about 65-70 ft off the deck (it will be keel-stepped and I will have to strengthen the hull, deck, partners, etc.... that I do know). I thought I would get some aluminum tubing for a core then laminate strips to it (bead and cove) and wrap the whole thing in several layers of cloth. I will have an oversized sail, much like the s/v Barbara-Ann. In the end, I will have what appears to be a wooden mast. I know I could build it in pre-preg and epoxy, but the wood would be so much more aesthetically pleasing.

Thanks,

Kevin

You could produce an aluminum/wood/fabric laminate, but I'd be too worried about the aluminum/epoxy bonds to the wood every time I was caught in a blow or heard a strange noise from the stick.

Getting a good aluminum/epoxy bond can be challenging. The aluminum ideally should be etched then have epoxy applied directly after, as the aluminum will begin to oxidize immediately after the cleaning/etching process, which screws with the bond. On such a large pole, you'd have difficulty during the lay up in this regard without special precautions.

You could have your stick out of all wood, maybe with a light cloth sheathing to provide some abrasion resistance, but you'll need to secure mast plans and upgrade the hull structure to support an unstayed rig.

A buddy just an hour or so from me is Eric Sponberg (WWW.SponbergYachtDesign), has considerable experience designing carbon, free standing spars. Typical costs would be $750 to $1,200 for spar plans, with additional for yacht structure considerations. A carbon mast as you've described would be around $12,000 here in the USA with inexpensive labor. This places these out of reach for most of us, who struggle with stretched out sails for more seasons then we'd like, because of the cost of a new set.

The basic problem is carbon fabric cost, with 6 ounce, 3K plane weave being around $60 (USD) and the good stuff - 6K, 11 ounce, 5HS weave about $80 (both 50" bolts). In a mast application you could wind around a mandrel with tape, but again a 1" x 10 yard roll of plan weave is $60.

This leaves you with engineering a hollow wooden stick, which offers some interesting engineering issues, though none that couldn't be overcome.

I've built birdsmouth spars that were over 40' and felt I was getting to the limit of the method. From a technical angle, there isn't a limit, but from a practical view weight comes to bear and aluminum is a better option.

Par, I've seen a few good photos of a birdsmouth spar/mast,but what an ignoramus such as me would love to see are a few good pics of the various techniques and machinery ( router setups, datto blades, etc.) used to produce a birdsmouth joint, your drawings would be even better. Hope you can spare the time to educate one who hopes to construct such spars . Cheers mate

Hi Huon,

I've just started the sanding phase of my hollow mast, and while I really am enjoying the challenge, I have to admit that ITS A LOT OF WORK.
Next time, there will be one thing that I would do differently. I would find a local Joiner to cut my staves for me.

My neighbours really got with me for making so much noise, and at the end of the weekend, all I had to show for it, was 8 thin sticks.
All the cutting, thicknessing, and cutting can be done more efficiently by a pro, who has the space and right gear to get the job done quickly, without the neighbours complaining.

Everything else I would do the same.

Good Luck


Mickj