Wooden mast building

One inch wide strips of innertube , or bicycle innertubes , free from any bike shop, make great gluing clamps. Don't put too much on, or it will definitely crush the wood .

 

Originally posted by PAR:

Perm Stress, I'm sorry your yacht club doesn't know how to care for it's wooden masts, but they all don't rot out from the inside eventually. I currently own a 50 year old hollow mast that's just fine. Of course it's been cared for, obviously better then your sailing club cares for theirs.
Originally posted by PAR:

Perm Stress, I'm sorry your yacht club doesn't know how to care for it's wooden masts, but they all don't rot out from the inside eventually. I currently own a 50 year old hollow mast that's just fine. Of course it's been cared for, obviously better then your sailing club cares for theirs.

Properly encapsulated birdsmouth or box section masts, of good design and reasonable care, will last many generations. For all practical purposes, these encapsulated surfaces are waterproof, not water resistant as you've suggested. This is born out with repeated testing and long term (decades) in service trials.

Nothing personal, PAR, but please inform about the conditions a boat you mention is wintered in. (And how hard it was really sailed all those 50years). What it mean "just fine"?

If there are no below zero (Celsius) temperatures, I could believe in Your statement. If vessel sailed rarely, carefully, in good weather and for short time, I could believe in Your statement.

However, in Eastern Baltic conditions, I am yet to see or hear about wooden mast, hollow or not, to hold for 50years.

About importance of waterproofing insides of hollow mast, when outside temperature is regularly at freezing point and below.
In my area (south east Baltic) it is an average of about 50 freeze-thaw cycles each year.
What happen than to the air, trapped inside a wooden mast?
There are two main possibilities to design a hollow mast:
1) Hollow is "sealed"
2) Hollow is ventilated.

In may little knowledge, "sealed" hollow is worst of all. And this is why: when air inside is cooled, it first -contracts, and suck in outside (humid) air trough any microscopic pinhole, second -humidity inside a hollow condenses and seep in the wood trough any paint, glue or epoxy -none of therm is waterproof. Please remember, that this is repeated about 50 times each winter. We do not yet mention daily warm-cool cycle. Consequences are easy to guess: wood is getting damp, with rot eventually catching on, unless the wood is 100% immune to rotting. Even then, mast is getting heavier and weaker over time, as wood accumulate moisture. We did not yet mentioned any effects of condensate freezing inside tiny spaces.

Ventilated hollows, when properly made, will make this process slower, but not more. Even in the best ventilated hollow of mast, some condensate will be in liquid state on the inside walls; sometimes it will freeze on the inside walls, and eventually open myriads of tiny pinholes in epoxy (or whatever), with same consequences.

Of course, if mast is kept in heated and air -conditioned space for the winter, this kind of problems do not have a chance to develop. But not every mast is kept in air conditioned and heated space over the winter.

I could add two examples from firsthand experience.

1) a hollow wooden mast of 30ft cat just collapsed while boat was standing on the hard for winter: exactly at the lower point of one of the "sealed" hollows.
2) Just now I am busy designing a replacement masts (steel) for Dutch built ~26m gaff schooner (built 1976). Until 2005 it was kept in Holland, where, by the standards of SE Baltic, real winter simply do not exist. Original wooden ones are just falling apart. They only have a hollows for electrical cables, protected against direct ingress of water. And impression from the crew is "this ship was not really sailed for the last 10 or 15 years before us".

Just my little bit of experience and thought.

 

No, Perm Stress, I'm lying to you in hope you'll ruin all of your hollow masts . . .

You obviously aren't aware of the facts in regard to encapsulated wooden pieces. The misconceptions you have, again, fly in the face of long term testing and industry acceptance. The industry leader in epoxy formulation and implementation in boat construction tests in environments much like your Eastern Baltic winters (actually more severe). I guess they are lying to you too . . .

Of course if you seal up hollow areas inside anything wooden (well maybe), you'll eventually have problems and no one is suggesting this. Also if you don't use or care for a wooden what ever, it will degrade quickly. One must assume reasonable care and maintenance or it's not a level playing field on which to base judgment or make comparisons.

Individual examples of rotten masts or long term survival stories don't prove anything. Testing and long understood and well established care and maintenance routines, have repeatedly shown that wooden structures; masts, boats, flag poles, you name it can be designed and kept for generations. You don't have to believe this if you don't want to, but enough of us have seen it occur and sufficient testing has reinforced these understandings to mitigate anything you might have to say to the contrary.

 

I built a small sailboat last year (2009) and made a 2-piece hollow mast for it. I did not use the birdsmouth method, I simply cut 8 staves with the edges bevelled at 22.5 deg using simple handheld power tools. It was not difficult, details in post #10 here http://www.boatdesign.net/forums/sailboats/small-sailboat-design-advice-requested-26169-8.html

I haven't glassed or epoxied them, just varnished the outside. However they haven't had much use yet so I will see how long they last in due course ...both halves of the mast came out well although I think I made the lower half too light. If it breaks I'll just make another, it will give me a chance to try out the birdsmouth method! My main mast is 2.5", topmast is 1.75", your mast sounds too light at 1" dia, I tried that in a sailng canoe and it snapped in seconds.

One point about tiny boats; the parts are so small they can winter indoors so the questions of durability may not apply to us!

 

Really nice talking, thank you...

What I was pointing, at, however, was several points not directly addressed in quoted post:
1) any hollow will be less well protected by surface saturation or paint or whatever, as the outsides;
2) any hollow is totally inaccessible for any maintenance (except for pouring in some liquids), once the mast is built;
3) when air inside a hollow (sealed or not) cools down, a condensation do happen, and some of condensate will be in form of water droplets on the walls;
4) when air or surface or both are below freezing temperature, sometimes there will be enough moisture to form frost.

None of the above do add to longevity of hollow wooden mast.

And, for some obscure reason, from the time the metal spars became available for reasonable cost (that is from about the second half of XIX century), wooden ones are built in increasingly smaller numbers.

From the other side, wood is very far away from being a "standard material" with perfectly predictable properties. It is also highly dependent on skillful execution in many details, (often considered as not that important by anyone not really deeply involved, maybe temperature and humidity in the shop, when hollows in the mast are sealed, for example).

"Individual examples of rotten masts or long term survival stories don't prove anything." That is the possible point for agreement on the matter.

In case "Individual examples ...don't prove anything." is not the base for agreement, we should use either:
* statistics with really wide database, or in absence of them
* hard data of tests -how they were performed, etc., etc..

Nothing personal -we are talking about masts here.

 

I have know idea what this means. But encapsulated wood, doesn't care if it's inside or outside the mast. It will react the same to environmental changes.

This is obvious, though with considerable difficulty you can apply new coatings if the need arose.

Again this is obvious, but the moisture will not affect the mast if the wood has been epoxy encapsulated. The mast would have to be filled with water, before damage would occur, at which point you'd have bigger issues to deal with then condensation inside the spars.

A epoxy stabilized wooden piece isn't going to be effected by moisture content in the environment. If done properly, with the wood's moisture below 12%, it can freeze and thaw all it wants and the structure will be fine with no ill effects.

I can go on and on, but the basic issue is your understanding of what epoxy encapsulation does for wooden structures. This can be had through several web sites or books.

Like all innovations in yacht design aluminum spars took the industry by storm, though nothing like what happened when sailors realized they could use wire for shrouds and stays or turn buckles to replace deadeyes. These two things rolled through the industry so fast that within a couple of years 80% of fleets that previously had hemp and deadeyes would have wire and turnbuckles (called rigging screws back them). Aluminum's replacement of wooden spars isn't a surprise, nor was it when the first metal spars (steel) showed up in the late 1800's.

 

Except for free standing rigs , birds mouth construction is a gimmick, with no advantage over box section and major disadvantages.
Given the way salt was used in the old clipper ships to stop dry rot, I was wondering if a brine solution sloshed inside a hollow mast would be a good way to stop dry rot inside. It probably wouldn't stop formaldehyde glue from sticking, so may be a good wood preserver to slosh on and dry , before gluing. One could always try test pieces.

 

I beg to differ. With modern epoxy construction, birdsmouth offers a larger gluing surface, and better saturation of the core due to the larger glued surface area. Epoxy saturation effectively renders the resultant material a composite, not just "wood" if done properly. The moisture barrier in wood epoxy saturation technique ("WEST") construction is far more effective than brine, salt, linseed oil or creosote. Box construction results in a mast with different bend and flex characteristics than birdsmouth - the rounder the construction and more uniform the cross section in all perspectives, the more consistent the bend.

All mast bend characteristics can be compensated for in standing rigging, but it certainly is beneficial to start with a spar that bends uniformly in all directions.

--
Bill

 

Box section spars have their place, but must be strung with wire and have their limitations, just like everything else. Birdsmouth can be free standing or placed in compression and also look a lot better then box section, which is a big deal to a lot of boat lovers that have selected a wooden spar. Box section is at an advantage in that it can be smaller in dimension then an equally strong birdsmouth, though looking at the types of yacht that would consider one over the other, likely a small consideration.

 

Whao fellas! There are some good ideas on here and some worthy contributions but masts are not worth getting in a tizz about.

A few points:

I believe in epoxy usage and not using it inside a hollow mast would be foolish given the ease of application, durability and cost.
If I have a mast which is strong, durable and which encases the lines so that the sail tags around the mast can move freely then I doubt that my time would be wasted.
I have other modifications in mind in order to make this a dinghy capable of sailing in rough conditions. I have a mad idea in mind but its fair to say a mast that is strong will be needed.
The mast will be removed from the dinghy when not used and stored in a dry garage after rinsing with fresh water.

Again, many thanks for your posts and contributions.

Gaffers

 

Bird's Mouth Mast method

Hello PAR

What are the problems with the method on Frank's site? Can you suggest any websites that have a better explanation?

I wonder if anyone has come up with an easy way to taper the staves both in thickness and in width. Not so much of a need in small masts, but it might be useful for larger hollow wood masts.

Thank you,
John

 

With wire on a marconi rig, fore and aft staying is nowhere near as strong as athwartships staying, which is why marconi masts are greater in their fore and aft dimension than athwartships. That is why birdsmouth is, as I stated ( go back and re-read my posting) is not as good asbox section on a stayed marconi rig, but only useful for unstayed masts . Several friends soaked their wood in west epoxy, in accordance with the directions, and all had rot, eventually. They began with blind faith but time cured the blindness

 

Brent, I seriously doubt your friends used accepted practices with their "soaked wood", which pretty much voids expectations. Encapsulation techniques are well understood and proven. For what it's worth, you don't need epoxy for mast construction to be long lived either.

You can also make oval section birdsmouth mast, by simply using wider staves on the sides on the spar, so your dislike for the birdsmouth method will require a different horse to flog, then the round, verses rectangle debate.

The drawing is one I posted previously that shows the two different stave notch arrangements and of course the oval. The red line indicates the finished dimensions and this particular section has a 20% wall.

 

Bambusa oldhamii is what my next mast will be. I have it growing in my back yard. It is very strong and when it degrades I will just cut a new one. Free for me. It lasts well if kept out of weather when not in use.

http://www.bambooweb.info/ShowPictures2.php?BooID=54&Desc=&Loc=&Match=54&Cat=*&Genus=*&s=4

 

Your oval birds nest mast is a good shape for a marconi rig, but one can accomplish the same starting with a box section with fillets in the inside corners then rounding the outside, with far less work.
I found formaldehyde glue to be excellent for mast construction, and far more heat resistant than epoxy. It is also far less working temperature critical.
The guys who had blind faith in epoxy were all perfectionists, who would follow any instructions to the T. Time and experience has cured their blindness.
Try see how far epoxy will penetrate, by saturating a long piece of wood, the thickness of a mast wall, then cutting it in half. It will be nowhere near a saturated all the way thru. What is not saturated is like veggies in a plastic bag.Very rot prone.