Well, I finally found my shaper knives for cutting the birdsmouth so I'm tooled up. I was thinking through the assembly and I'm wondering if I should put blocking inside the mast at rigging attachment points, the gooseneck hardware,etc,etc. I know this would strengthen the mast but it would also prevent the mast from natuarally expanding and contracting with changes in temp and humidity. Part of the mast, being hollow, would be unrestricted to shrink and swell, and the part with blocking would be restrained. This would seem to create a lot of stress within the mast and promote cracking. Is this the case? Is anyone having this experience? Why do my feet stink? Help! Andy
Andrew if you are going to use eyebolts through the mast for your rigging then use the blocks. They will dispurse the point load stresses on the thin mast walls. If using band clamp type attachments no reinforcement is necessary. Happy building. Not sure about your feet.
A few problems arise when you attach things to masts with through fasteners. Of course, the localized weakening of the mast in the penetration area, but a block with no taper will also create the same thing when the mast takes a bending load.
To solve these types of issues there are a number of methods you can use. The traditional method is "swallowtails" installed inside the mast at all hard points, which typically are the heel, head, gooseneck, spreaders, hoisted gaff landing, stay and shroud locations. A swallowtail is a tapered (in both the up and down direction) block, inserted inside the stick. In a birdsmouth or any "built-up" style of mast, each stave will need be fitted with this sort of blocking to increase the stiffness and spread any "stress risers" that may occur in these areas. This tapering blocking gradually increases stave wall thickness then gently decreases it so as to not generate a sudden increase in stiffness, such as a plug would do. The swallowtail (or any type of blocking) would have a centerline hole drilled, if for no other reason then to permit moisture to drain to the bottom of the stick.
Another method is to drill an over size hole, fill with thickened epoxy, then drill for a dowel, which gets buttered with thickened goo and inserted in the through bolt location. The dowel is then drilled for the fastener. The dowel serves as a "compression post" in this location, so the mast can't collapse under the strain of a well tightened through fastener. This is typical of aluminum mast construction for the same reason. It also permits the use of internal halyards, which can pass the dowel easily.
If you are using stock plan dimensions for your mast and don't plan on frequent trips in 30 knot winds, then non-tapered blocking will work just fine (remember to drill a hole in the center for drainage, also a good place for masthead wiring). The stock mast dimensions are at least 20% over size for the sail area and rig loading expected in moderate weather.
When you build, using epoxy encapsulation methods, you eliminate the moisture gain/lose issue in lumber, basically freezing the moisture content to the level it was when coated. If using epoxy as a glue only, then you will have some expansion and contraction within the stave lumber, but the glue line should hold with the stave dimensions used in these masts.
A birdsmouth mast for a Weekender (16', full length taper) will weigh about 20 pounds if made of Douglas fur with a 20% wall thickness, Sitka or white spruce will weigh about 15 pounds. A solid Douglas fur mast would be around 30 pounds and Sitka or white spruce about 25 pounds. The Weekender only needs a 2 3/4" tapering to 2 1/4" (12.5 pounds Douglas fur and under 10 pounds if Sitka or white spruce) mast for the loading and sail area she carries. This doesn't seem like much at first glance, but look at it this way, the 10 pounds you save from a stock, solid mast equals about 100 pounds of additional righting stability, which you'll feel the first time you sail her.
Ahoy Paul,
Twp Years before the Mastâ well, I hope it won't be quite that long before we start our own mast. I'm sure others are reading all these good comments as well. Swallow tails are intriguing. Who would have ever thought?
They are called swallowtails, because of the way they look (much like the "V" tail on a swallow) when being installed in a built up mast. It's the way professionals build masts. If designed properly, they can permit thinner wall thickness (read a lighter, more flexible and adjustable rig) because the high strain areas are sufficiently accounted for. In the typically over engineered gaff rig, they are less important then accessing the compression loads placed at the hard points, like through fasteners, gaff landing and gooseneck areas, then placing something there to keep the mast from collapsing.
A gooseneck or gaff jaw can easy crush a hollow mast in a wild, unexpected jibe or big gust, that buries the rail, before the crew can release a sheet or two. I like the dowel method, because I also like internal halyards (which save considerable windage aloft) and they can be installed after the mast is glued closed or as a retro fit. Most gaff rig owners, like their halyards and lifts hanging in the breeze, even if it costs a point or two in pointing ability. They sure are salty looking, tied to a shroud mounted pin rail, but they also are a great source of chafe and windage, easily stripping many carefully applied coats of varnish or paint off a mast, gaff jaw or whatever they rub against in use.
In spite of what may seem counter productive when owning and using a wooden boat, most sailors are a pretty lazy lot. Most preferring to sail their craft, rather then perfect it's repair or the owners abilities at performing maintenance. In general these loafing sorts don't get the joy when applying coats of varnish, that they would from squeezing the last ounce of breath in a dieing sea breeze. The result is paint and varnish that usually is well past needing a touch up and requires putty, sanding and filling to forgive the willfulness of the owner.
Many of the yachts here are clearly above standard (except Jim Sanders boat, which surly needs considerably more effort to bring it up to a reasonable standard), but lets be honest, how many have 30 footers? Those of you that have been in the construction industry (or most blue collar type jobs) know what I mean. Is she a fine lady when viewed from beyond 30', but at 25' she starts to show her true colors? Many are 20 footers which is pretty good and a few ten footers are around, where the finish looks good even standing at the dock next to her.
This isn't an insult to the many fine boat builders here, not at all. Possibility a reality check about the nature of all boats in general. Are the rust stains from the chain plate bolts running down the sides of her (which would make her a 70 footer)? Surly no one here would have any flaking varnish (way past repairable) on their bright work. I'm working on a 50 year old 39' Atkins yacht. The owner has had me coat every inch, of the hundreds of feet of varnished trim with bright white, epoxy based paint. I buried many yards of beautiful mahogany under this goo, so he can get three years of uninterrupted use, rather then having to touch up the bright work twice (or more) a year. He has more money then anyone has a right to have, but he's no different then us lowly sailors of pocket yachts. I hope no one takes this the wrong way. It's intended as a part tongue in cheek, part realistic view of how many folks care for their vessels. Very few of us have the time, skill or willingness to keep a class A yacht (I sure don't), especially when a class B or C yacht sails as well, costs less to own and gets used much more often. And a long way around the circle for the arguement in favor of internal halyards and lifts.
Ahoy Paul,
As always, your comments are both helpful and insightful. Many of us are mere amatuers at what we are trying to do. Nothing wrong with that, of course. In my case, I had not even seen what I was trying to build until some 3 years into the build. A lot of folks are probably in the same boat, just trying to build upon a dream and hoping for the best.
I've seen several of these boats (some only from photos) with astonishing finishes. Yet, whether the finish was good, or only a notch above not-so-good, the folks who built them seemed to enjoy what they have done, and seemed to enjoy sailing their dream as well.
I may never finish my boat (though I believe that I will), but even so, I have enjoyed working on it. The experience has been a great adventure, allowing me to meet some rather good people along the way and to learn a whole new world. I rather think that is what is life is all about. It's the learning and doing that keeps us fresh, keeps us young. I personally cannot imagine any more boring life than watching TV, or waiting for the next new movie. Miss Pat and I are just not that kind. Our life is a little more fuller than that. Maybe that's why I appreciate anyone who sets out to build a boat with their own hands. As you build, just be patient and do the best you can. When you get stuck or something just doesn't turn out right, don't berate yourself or become disgusted. There are a lot of very talented people on this board. I would dare say that you could ask a question and somebody will have a good answer for you.
As to possible hurt feelings, Paulâ a man who plans to sail needs to be able to take a few bumps along the way. You can well expect the boom to hit you a few times, and do so right in the head. It'll get your attention alright. And if I may say so, there is good reason for a large boom to be affectionately called a widow-maker. If you plan to sail but never get hit, you will never leave the harbour.
I guess we all fret to some degree about what we are trying to do. I seem to be rather good at that. Yet all fretting aside, if you don't try to do something, you will never will do it. A boat does not have to be perfect (and believe me, it won't be), a boat does not have to be perfect for it to look good, to sail well, and to offer you the builder a sense of accomplishment. Most people will never see the mistakes you made. And those who admired your boat at the dock will be sincere with their comments. You can't go wrong in building something with your hands. Just get up and do it.
One approach to assembling the birdsmouth that has proven to be quite successful for me as well as a number of other builders is to glue it up in halves. Just seperate the two halves with a strip of poly between those staves and clamp it all up. Then seperate the two halves and install the plugs and finish the interior of the mast. If you want wiring for a mast top light, run the wires before assembly. Then join the halves and finish off the rest of the mast.
Thats a great Idea Barry, I think thats the way I am going to go. Thank You.
Brian.
I'm probably over-thinking this-I tend to do that when I'm building something. The wood has been in the high desert so it is very dry. My concern was that once built and brought to a humid enviroment, it would swell. Nothing wrong with that if it all swells evenly.Using epoxy coating would help, for a while anyway. Eventually, nature finds a way in. I'll just goo it up and hope for the best. Two halves, blocking, goo. BTW, I'm not really doing a birdsmouth. My knives are half-rounds so it will be a bead and flute joint. This will give me a bigger gluing surface and you can use the knives for any geometry hexagon, octagon, etc. Since the stave corners do not determine geometry, I'll be making a gluing jig for the octagonal mast I'm building. I'll post pix eventually. Thx for the replies.
PS Jim-I like your boat.