Sailboat masts

      A discussion of species and techniques for seasoning wood used for sailboat masts. March 2, 2000

Question
I am building a sailboat and have found a couple of books recommending using trees or saplings to make the mast. One talks of seasoning the wood in water. It says to peel the log and place it in water enough to float in. No time frame is given. Then the book says to "pluck the tree from the water" and begin to cut it down. Apparently the water helps keep the wood from checking.

Is anybody familiar with this type of seasoning? Any ideas on how long the wood should stay in the water? The author says the mast will get stiffer over the first year, as it dries on the boat.

Forum Responses
Your book only gives part of the story. The seasoning of some woods, mainly oak, in SALT water, is an old drying method. However, it needs to be cold salt water or the shipworms, etc. will invade the wood. Usually, it was submerged for a year or two. It would not be done for masts -- they used white pine and the risk of checking is very small. Also, any wood in contact with ferrous metal could not be dried this way.
Gene Wengert, forum moderator



Just to clarify, the book I have is called "Boatbuilding; A Complete Handbook..." by Howard I. Chapelle.

I agree that the author is not giving me all the information, but there does seem to be a bit of confusion. The beginning of the section on masts states, "Sitka spruce, white or Norway pine and Douglas fir" are best. The next paragraph states, "Spar timber, theoretically, should be well seasoned; this is best done by first removing all the bark and then placing the sticks afloat in water deep enough to permit floating at all times." Nothing about salt water or the time frame. I am wondering if there is anywhere I can go to find more info.

Also, I understand that the salt water would have reduced or eliminated dry rot, but how does wood season in water? Should it then be air dried or kiln dried?



The wood absorbs the salt and this allows more rapid drying (after treatment) than without the salt and also almost totally eliminates the checking problem.

(In "Drying Eastern Hardwood Timber" [U.S. Dept. of Agriculture Handbook No. 528] a salt paste is described for seasoning large disks. Again, there is a problem with corrosion of metal in contact with the wood, plus the bleeding of the wood at high humidities. The process is called chemical seasoning. Morton's Salt has a patent on it and it was called Morton's Cure [I think]. It was used for gunstocks in WW II, and there were corrosion problems in the Pacific theater. Several lawsuits followed but I do not know the outcome.)

Regarding "Sitka spruce, white or Norway pine and Douglas fir," this is an interesting list as Sitka spruce is very strong for its weight and was used for aircraft building (Howard Hughes' "Spruce Goose"). However, for a given size, it is quite weak -- not nearly as strong as white pine, which, in turn, is not as strong as Douglas fir.

Spruce is basically a West Coast species, so would not have been used in early times (prior to 1860). But Douglas fir was not a popular wood prior to 1900 either, since it grows mainly in Washington and Oregon, and neither the early settlers nor the British Navy had access to it. So Douglas fir must be a recent addition to the list. I suspect that ship building on the West Coast used Douglas fir and spruce, as they were readily available.

The inclusion of Norway pine is also interesting, as it generally is not a large tree and is not very widespread. But the high resin content in virgin growth would provide resistance to decay. People are allergic to this tree (contact skin dermatitis). It shrinks twice as much as white pine, so it is not a good choice! (Spruce also shrinks twice as much as white pine.)
Gene



The comments below were added after this Forum discussion was archived as a Knowledge Base article (add your comment).

Go with Gene's answer. White pine is by far your best choice, unless you have access or live in PacNW. Growing up on the Chesapeake and seeing and helping to restore different sloops, schooners, etc., I know white pine predominates.

If you are dead set in having a completely wooden boat and are not going to consider glass/composite for the mast (easier to step, stronger and lighter) especially above 40' (no varnish either), then fall your tree. Remember to add 5' - 10' in height and 3" - 6" in girth when sizing up tree to fall. Lower carefully with pullys/ropes if possible. Trim and seal all branches, top and bottom. Serrate bark in 3" strips, running vertically, around entire circumfrence prior to storage in barn or shed. Leave bark on for a few months until it falls off or is easy to peel. Store 3' - 4' high on X braces, one brace per every 5 to 6'. X braces stop possibility of childern accidently knocking or rolling it off, plus they allow you with help to turn it 1/4 turn every 6 months x (4) turns. Do not cover but protect from rain/leaks. A tarp or lean-to with a few feet clearance above is fine if barn/shed leak. Remember a nice air flow allows more efficient and even/natural drying. Once seasoned it is time to size it vertically. Since you left it 5-10' longer than needed, checks and cracks at ends will be cut off anyway. Correct sizing is imparative. From the bottom of mast box on sole to tip of mast top. Bark will have fallen off by now. With a draw knife, start to work off membrane and layers to desired shape and conture. When complete, fill any cracks with exterior grade glue or epoxy. Sand and then use a high quality marine varnish. Time for rigging. Happy sailing!



Comment from contributor B:
In choosing wood for spars, a greater amount of consideration is given to the weight of the wood, assuming that it is strong enough for the anticipated loads. The reason for this is the effect upon the stability of the vessel of topside weights located above the theoretical center of gravity - the more weight and the higher up it is placed in relation to the center of gravity for the entire hull, the more adverse is the effect on transverse stability. Sitka spruce is particularly desirable for spars due to its relative light weight as well as its considerable strength. Though many species are much stronger, a properly crafted mast of quality spruce timber, and supported with adequate stays and shrouds, is amply strong enough for the job, yet lighter than many other species that are equally strong enough. Before the days of carbon fiber and composites, hollow masts were being fashioned of laminated strips of Sitka spruce. This technique added strength while reducing topside weights at the same time and was probably considered a high-tech method in its time.

Whatever your choice in mast construction, it should meet three requirements: strong, light, and durable. Perhaps more thought should be given to rigging, for even small changes in rigging plans can dramatically increase or decrease the ability of the mast to handle dynamic loads.



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