Birds Mouth Mast Material

[Maria CS20 104]

I am almost convinced to build the mast but am struggling with material selection. Fir, Cyprus, cedar, considering spruce ($), yellow pine. other pine species? I think I have the math down and it does not look impossible and I figure 60 to 70 board feet or so to complete both main and mizzen mast with 20% or more waste. Staves about 1.2" wide, 5/8 thick. Plan on cutting the birds mouth on a router table.

INPUT BEGGED for from those that have gone before...........

Approximate weight of fir mast at 21 feet?????????? guesses welcome

Jim

[hokeyhydro]

No input on Doug Fir, but the BM mast I built for my daughter's catamaran is about 21', give or take a few inches, 70mm round at base, slightly tapered top section, staves 14mm x 28mm, made out of cypress and weighs around 20 pounds with hardware. Doug Fir is heavier than cypress but stiffer, and I seem to recall one can reduce the scantlings of the staves quite a bit and come out about even. Think I ran across that info on DuckWorks website mag.

Additional info: Cat mast is shrouded, 4mm Dyneema line, not free standing, so it is skinnier (70mm) than a free standing rig.

[PAR]

Douglas fir and cypress are a bit heavy for small craft. Many use these, but I wouldn't. Cypress tends to check and move a lot too. Try to find white spruce. Most of the yellow pine will also be quite heavy. Most of the commonly available cedars don't hold fasteners well enough to consider and these too "move" a lot.

[Hirilonde]

Sitka Spruce is always my first choice for spars. It has a superb weight to strength ratio, glues well and holds fasteners well. All of the related white spruces are very similar. I guess I agree with Paul.

[Charlie Jones]

Kinda hard to disagree with the two preceding posts, but I am anyway Sitkqa spruce can be difficult to locate in some areas, fir is usually pretty available.

I've done 8 or 10 spars using the Birds mouth technique, all from Doug fir. One pair was for a CS 20. All have done very well. In fact, the upper halves of the masts I built for a Princess 22 weigh less than the aluminum lower halves.

But I think that cutting on a router table is slower than on a table saw. I cut all the staves, and cut the mouths, in about an hour and a half on the TS. Tapering took about as long.

There used to be a formula somewhere on this site for stave sizing.. I can't find it anymore and the copy is on ther hard drive of my desktop, which has a crashed power supply. Maybe some else can find it?

A picture of me "stress testing" a 23 foot mast for a gaff rigger. If I recall correctly it was 4 or 5 inches at the base and weighed around 40 pounds

[Howard]

The experimental birds mouth mast I built for the Spindrift 10 is just over 17' and weighs 14 pounds with gooseneck fitting for the boom and a solid core section pine closet rod in the base to a about 4 feet. I made mine of 3/8" staves, but there are 12 of them. This one is 2 1/4 inches diameter at the base, and tapers to 1.5" at the top, which may have overdone it. It has a bit of flex at the top. It is made of doug fir.

I used a special birds mouth router bit and a router table. Took forever to get setup to suit me, but once I did, I simply ran them through and they were done. I glued it up with epoxy, which turned out to be the easiest part of the whole thing.

I was unable to find sitka spruce in Missouri, but did bit the bullet and ordered a clear piece for the boom. Should have been priced by the ounce and gold would have been cheaper! After it arrived, I didn't have the nerve to hack it up and it's still here just as it was when it arrived. I used hem fir for the boom instead.

[ecgossett]

In my job laminanted Sitka spruce is used for missile nose cones and very strong and thin. http://www.turbosquid.com/3d-models/3ds-max-trident-c4-missile/459556

The grey area is all laminated Sitka, on top it has very carefully built lug teeth so the top piece can be rotated and locked on.

- Edward

[makenmend]

http://www.duckworksmagazine.com/04/s/articles/birdsmouth/index.cfm#online-calc Her is the Duckworks link. Made several paddle shafts and masts for my small trimaran from inexpensive pine and western red cedar, so far without failure, even in good (20+) winds,actually pretty fun when you get into it. MM

[makenmend]

Here's an example

[Twetmore]

I built my core sound 20 masts out of douglas fir 2x material. I will warn that I have not used them yet so I am not sure how well they will work but they seemed to turn out nice and really look nice. Here is what I posed and my thread so you can look at all the question I asked previously:

http://messing-about.com/forums/topic/6629-core-sound-20-130/page__st__60

I used wood the entire way and actually I built the mast this last weekend. I used some really nice 2x material that I found at the lumber yard and let it dry inside for almost 8 months. I ripped the 2x down to 3/4" strips which gave me a 1-3/4"x3/4" strip which is pretty close to what the plans call for. Then I used an 8 sided birdsmouth router bit to birds mouth one side of each rip. Finally, I setup a jib for my table saw to rip the taper of 3/4" at the top down to 1-3/4" at the bottom 6' per the plans on the non-birdsmouth side. The jig was just a 2x6 set tight against the fence and blade and nailing the rips onto a pre-marked angle so that all were uniform. Finally, I put glue on all birdsmouths, fit 4-5 pieces together, inserted the blocking, and slipped the last couple of pieces together. Then I used some nylon webbing straps as tourniquets to pull the mast tight together and taped it with re-enforced parking tape. Pulling the mast together really takes 3-4 guys to do it right as well as many of the other tasks since the wood is so long. I chose to use gorilla glue as a dark resin glue was recommended on several different websites that I looked at. I am comfortable with gorilla glue, it is waterproof, and it has greater strength then the wood, as does epoxy. I could not believe how easy this whole process turned out to be in the end and would definitely recommend it to others. Then again, I still have to sand the mast smooth and we will have to see how they hold up.