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Birdsmouth Mast


Tim

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I'm planning on starting the boat building with the spars and I'm planning on using the birdsmouth method.

Looking at wood choices the number one choice Sitka Spruce would have to be ordered at high price. The second choice would be clear Douglas Fir which is available locally but I was wondering why no one ever mentions western red cedar as an option. Its very light and springy. It might be that is not be strong enough but I think in the birdsmouth fashion with epoxy glue and covered with epoxy it might be strong enough. Any opinions?

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I don't know why cedar isn't mentioned as a wood for spars, but it isn't. I know its very light weight, but it also isn't nearly as strong as spruce or douglas fir. You would have to go with much thicker pieces to get the same strength. The Glen-L site at http://www.glen-l.com has some information on boatbuilding woods, and lists the relative strengths of the various woods ... when you get to their site, scroll down on the left until you see the link for boat building woods. They don't tell you how to translate that info into scantlings, though, so it isn't much help in determining how thick to make the staves.

You could always try an experiment with stock 6' long in both woods, and then do a "destructive quality test."

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I used clear Doug Fir for a mast that I built with the birdsmouth method and it turned out great. I read some of the older messages regarding mast construction for the Core Sounds and it seemed like the stiffer masts gave better performance. I think I will use Doug Fir again for the boat i'm building now since it will make a stiff spar, is cheaper than Sitka Spruce, and is easily obtained here in the Northwest.

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A router bit is now available for cutting the bird's mouth for the masts. I believe it is available from Lee Valley/Veritas. It gives greater control than cutting them on the table saw. It also allows you to move the bird's mouth off center so that the length of the outside leg of the V matches the thickness of the wood being used. This dramatically reduces the amount of planing required.

They sell bits with different angles for making hollow cylinders with a variety of different numbers of pieces. We've been using the one for an 8-sided mast.

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Is there a web site or other reference where I could learn abit more about birdsmouth mast construction. I am interested in the general technique, but dont know anything really about it.

Me either!! :) I do have an Exel spread sheet that will calculate teh widths and thicknesses. It was sent to me some time ago and it seems to function correctly. If anybody wants it, send me an e-mail and I will forward it. BTW, when you open it you MUST allow the macros or it won't funtion properly.. i have scanned it several times and found no viruses. :)

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I built birdsmouth masts for my CS20 (#17) out of clear lumberyard fir. They were 3 1/4" diameter at the base and up to halfway then tapered to 1 1/2" at the top. The staves had a 3/4" wall thickness and they went together really well. I varnished them and they looked great, I was really proud of them. I decided to use a mast track after meeting with Graham in North Carolina, I found a nice aluminum sheave, notched it in on top and ran my sails up with a halyard. At twenty feet plus they turned out to be really bendy. In a good blow one day I got scared they would break and then they did. The mizzen mast broke just above the thwart, it got crushed over time and gave out. When I stopped crying I got some .083 tubing and made the masts the way Graham spells out in the plans. They are lighter than the doug fir and and maybe three times stiffer (faster). Maybe I did something wrong but I think now that you can't beat aluminum for the CS20 masts. They need to be light, stiff, and strong.

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Guest Anonymous

Pat,

After reading your post i'm having doubts about about building my masts out of Doug Fir. I called the man that was featured in the Wooden Boat article about the birdsmouth masts and asked him about the scantlings for a 21 foot mast and if it would be strong enough. He assured me that a mast 3 1/4 to 3 1/2 at the base and tapered to 1 1/2 at the top with a wall thickness of 1/2 inch built from Doug Fir would be plenty strong. Are you sure the wood you used was Douglas Fir and not Hemlock? Here in the Northwest they sell both. I would like to build the masts from Doug Fir but I want them to last...

You can click on the www to see my current project and there is a link to the first boat I built.

Paul

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I remember reading on the net about a guy who built a birdsmouth mast for his Bolger Chebacco. His mast also collapsed, at the partners if I recall correctly. He felt that the problem could have been averted if he had installed an internal plug in the area that bore against the mast support. I think he said this plug should be tapered so there wouldn't be a hard spot on the inside of the mast. But I don't have first hand knowledge of any of this. There is a website, www.chebacco.com, that may have his post archived or I might have read it on the Yahoo! Bolger egroup.

Mike

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Paul

At this point I have not built a mast. That site is from another builder. I would like to be far enough along to have to worry about a mast.At this point my boat is ssetting upside down ready to be fiberglassed but I am waiting for the weather to warm up enough to do it.

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Pat,

Tell us about the method used to attach your sails to a nested aluminum mast. I am interested in attaching the luff with either a bolt rope (preferred) or slides, and have been looking at aluminum extrusions or the Schaeffer sail track for that purpose. I have concern about making smooth transitions across the diameter changes from the nested mast assembly.

---Brent

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My masts were, in fact, from Doug Fir, I got them out of some clear 2x8's I found at the lumberyard, resawed them and scarfed them so that the grain ran radially to the mast diameter. Maybe the lumber was of poor quality but I don't believe so. I also thought (after the fact) about running a plug up the center to the height of the partner then tapering it and I believe this probably would have prevented the mast failure. Still, I think the sticks were too bendy to keep a good sail shape.

After I built my new alum masts, I transferred the 5/8" SS sail track from the old masts to the new. I transitioned the differing diameters with fiberglass and epoxy in a conical shape about six inches long. The track bends well and the sail runs up and down without a problem. I scuffed up the aluminum and painted the whole thing with Petit Easypoxy which has held up pretty well, considering.

I like the sail track method though I still just furl the sails around the mast rather than drop them down. I do, however, have the ability to reef with reef points sewn into the sails and I can lower the mizzen if need be to lower the center of effort in a breeze.

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Pat's boat is fast.

Fast fast fast.

In a light breeze he just sailed right past my CS 17. I'm usually a bit faster than the other boats we sail with.

My masts have heavier than called for lower sections because that was what was available. The top halves are tapered fiberglass antennas that are very light and bend just right.

I got the fiberglass sections at a surplus store and can't find any more.

If I were to build another boat I think I'd go with the stiff lower section of aluminum and consider bird's-mouth for the top 8 - 10 feet.

I used to break down my masts and fold up my sails. The sails got dirty and I think it's easier on the sails to stow them rolled on the mast.

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Pat,

Thanks for the post about your masts. I think I will go with aluminum for the masts on the boat I'm now building. The boat I'm building is about 17ft and has a hull weight of about 275lbs. (You can click on my www at the bottom of this message and see my project.) Since I'm in the Seattle area, have access to material, and have a good friend that does aluminum fabrication, the aluminum masts sound like the way to go. The main mast is 21ft with a sail area of 72sqft, the mizzen is 19ft with a sail area of 45sqft. Pretty close I think to the Core Sound 17. I was thinking of using 8ft of 3" dia, 8ft of 2.5" dia, and the remainder 2" dia. For the wall thickness I was thinking .065". Does this sound ok? Does the aluminum need to be reinforced where the mast goes through the thwart?

Thanks for you input!

Paul Piercey

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