round mast

[Bflat]

I've long been intrigued with the challenge of building a round mast via the "birdsmouth" method. I plan to get started building the Pocketship this coming spring. I will build the mast as designed but am wondering about the possibility of eventually trying a round mast at a later time. I imagine It may require a different tabernacle too. Any thoughts?
Thanks,
Bob

[Diving Duck]

The square mast is hollow, whereas I would think a round mast would have to be solid--unless you have an extremely long drill bit I think there would be a much higher strength-to-weight ratio with the square mast.

[Bflat]

The round mast would be hollow. I'd use the birdsmouth method.

[Diving Duck]

Wow! I read where you said birdsmouth method, but I guess I only thought I knew what it meant. Pardon me for assuming--I'm going to look it up now and learn something new. It's always great to learn something new, and this might turn out to be extremely useful.

[Diving Duck]

OK, I get it now. I had stupidly thought the birdsmouth referred to a cutting tool. I now see that the birdsmouth is cut longitudinally into vertical staves that form the outside of the mast. Looks like an elegant way to build a mast. Do you plan to round off the corners somehow or leave as a hexagon or octagon (or whatever -agon depending on the number of staves)?

I assume you would need a well-equipped shop and a lot of skill to do something like this.

[Bflat]

I plan to build the mast as designed, but am interested in replacing it with a round one (birdsmouth) at a later time. I do have a well equipped shop and a fair amount of woodworking experience and some boat building experience too. I'm up for the challenge. One of the attributes often mentioned with the birdsmouth method is that it's actually not as difficult as first appears. The concept is rather simple (execution may be another matter). I'm wondering about the practicality of doing so. I'd need to be advised on the dimensions such as diameter and thickness and taper.

[John C. Harris]

I'm a big fan of birdsmouth spars and have designed and built a number of them. For a moderately skilled woodworker they are a fun and rewarding bench project. A round, hollow replacement for PocketShip's mast could use the same taper profile shown in the plans for the box-section spar. Also the same 3/4" stave thickness, and the same sections blocked off solid. And you could use the same tabernacle without issue.

I think there are websites around that offer design tools for getting the staves right. I know Geoff Kerr is a big birdsmouth spar guy and has the formula memorized.

For the record there is no sailing performance advantage. They just look nice, and are fun to build---two perfectly good reasons to do it if you feel like it.

[Bflat]

Thanks John. That's just the advice I was seeking as well as hoping for. Like I said, I plan to build the mast as designed, but may attempt a round one as a replacement in the future.
Thanks,
Bob

P.S. I bought the plans a few years ago, but plan to order the kit in late winter.

[robroy]

To save someone the trip to Google - here are a couple of the Birdsmouth formula and calculator articles mentioned.

Lots of theory and a calculator http://www.duckworksmagazine.com/04/s/articles/birdsmouth/index.cfm
Another online calculator http://www.clintchaseboatbuilder.com/resources/birdsmouth_calc2.htm