Making the birdsmouth mast and more

One of the fun things about boatbuilding is next:  spars!  For this boat, I'm making a solid-wood boom and gaff plus a hollow mast (to save on weight aloft).  I decided to go with the "bird's mouth" technique for the hollow mast.  All the spars are made with nice clear Douglas fir.  Why not Sitka Spruce, you ask?  Well, have you seen the price of Sitka Spruce lately?  Also, Doug fir looks very nice varnished--nicer than many types of spruce, in my opinion--and the weight difference won't be significant for this boat I don't think.  Gaffers like BELLE have relatively short masts, so that helps too.  If you want to know more about wood spars, here's a few links:

• There's a good discussion of how to dimension small-boat spars in William Garden's The Making of Tom Cat.  He uses the small catboat Tom Cat as an example, giving numbers for both Doug fir and spruce and hollow vs. solid spars.
• I used the Birds' Mouth Spar Size Calculator to figure out the dimensions of the staves...many thanks to Clint Chase for posting this!
• Skene's Elements of Yacht Design also has good information about wood spars.

First I ripped out eight identical strakes on the table saw with the trademark "birdsmouth" on one side.  Since the spar tapers at the top, and a bit towards the butt too, each piece needs to taper as well.   I marked one piece with a batten, rough cut it on a band saw, and planed down to the line.  I then used this master to mark a second piece and cut and planed that one down too.  I then used these two identical "master pieces" (so to speak!) to plane down the remaining six pieces to size.  In this photo, the master pieces are on the outside, separated by spacer blocks from three strakes that I'm planing down to size. As you can see, the plane (a #5) rides on the "masters" and cuts down the inner three strakes.  A couple of passes with a power plane got things started. ( There are various ways of cutting out these strakes...using routers etc...for a small spar like this I'd say this worked quite well.)

I'm going to use pipe clamps to glue up the spar, here's a test run.  I'll double the amount of clamps shown in this photo for the actual glue up.

Voila...the glued-up spar.  This is actually Phase One.  A strip of packing tape along two strakes allows me to split the spar open to add blocking...see next photo. To the left of the mast are the "blanks" for the boom--glued from two pieces--and gaff.  I'll eight-side, then 16-side, these the old-fashioned way.  The hollow mast starts out eight-sided, so it only needs to be 16-sided on it's way to becoming round in section.  Then a bit more planing and a bunch of sanding to produce the final tapered, round spars.

With the spar opened up, I'll now shape blocking at the butt, deckline, and top to add stiffness to these areas.  In theory you could do it all in one step...but it seemed easier to do it in two discrete steps.  Once the spar is glued back together, I'll then shape it to 16 sides with planes and then sand it round. 

Meanwhile, I made up this centerboard pin from 3/8" bronze rod.  The plywood discs have pieces of 3/8"-inside-diameter bronze tubing to act as guides.  These will be screwed/glued to the side of the centerboard case.  There are removable brass plates (not shown)  on the outside to hold the pin in place...and keep water from getting in the boat.  There will also be a piece of bonze tubing embedded in the centerboard for the pin to run through.

Here's the discs shown in the last photo being glued to the side of the centerboard case.. I also screwed/glued cleats on each side of the case, towards the top.  These cleats line up with the tops of the seats and will allow me -- if all goes well -- to have lift up floorboards.  To make a (relatively) large "sleeping platforn",  the forward floorboards will fill in the space between the side bench seats and the centerboard case, resting on these cleats.  Not clear?  Well I'll be working on that in a bit, more photos to come...

Finally, after much hand-wringing, I finally cut down the transom!   This changes the whole look of the aft end of theboat...and I have to say I'm happy I did it.  Yes, that's a 35-yr-old British Seagull Forty Plus hanging there...my father bought it new years ago...and it actually runs!  There's a temporary piece of plywood clamped to the transom to protect it from scratches.  I have a nice block of yellow pine that I'll use as the final outboard clamping block.  To be honest, I may buy a more, umm, modern outboard at some point.  But the ol' Seagull will be the Official Power on launch day, that's for sure.

Next time:  more work on the spars plus maybe get started on the floorboards and seats.  Until then, good night and have a pleasant tomorrow.

Finishing off the deck

This week I finished off the deck, so here's a few photos of how it all came together.

This shot shows the various blocking pieces cut and fit.  These are made of scrap 1/4" ply left over from planking/decking, and they add strength to various key parts of the boat.  For example, the foredeck will support a mooring cleat and, of course, there will be a hole through the deck for the mast, so there's a fair amount of blocking in that area.

With the blocking done, I finished rough-cutting the various 1/4" ply deck pieces.  Here are all the pieces drilled for screws (little #6x3/4") and ready for glue up.

This is called a "jump stick".  It lets you "jump" over something to mark on the other side. In this case, I'm marking the inside edge of the plywood deck where it meets the carlin.

The shrouds will be attached using these 1/8"-thick bronze tangs which stick up through the deck.  Two bronze machine screws go through the clamps and, for good measure, the tangs are bent around and under the clamps. This transmits the load coming from the shroud directly to the clamp which is securely glued/screwed to the hull and decking.

Here are the four tangs, ready for installation.  Why not two, you ask, since there's only one pair of shrouds?  Well, for fun I'm going to have two "settings" for the shrouds:  a "single handing" setting using tangs along the sheer about one foot aft of the mast and a "racing" setting where the tangs are about four feet behind the mast.  The shrouds, which will be made of wire with rope tails or possibly a modern low-stretch rope like Spectra, will terminate at a cleat on the coamings (not at a conventional turnbuckle) so I suppose these would technically be called running backstays.  When in the "racing" setting, the shrouds will provide extra support to the top of the mast but also require resetting for each tack.  The "single handing" setting should provide more-than-adequate support and, importantly, won't require resetting when tacking.  In either case, the windward shroud can be slacked off if necessary while running.  Note that this feature is NOT shown on the Sail Plan at my Sketches and Plans page...which I'll update after the boat is done.

OK I'm finally ready to glue in the deck pieces!  I started with the forward triangular piece.  I broke the deck here so that I could reach forward under the deck to clean up any glue mess.  The deck is screwed down about every 18" with addition small ring nails as needed...but, as usual with this type of construction, the glue is doing most of the work. 

Here's the rest of the deck getting glued in place.  I'll put some epoxy putty in the various screw holes and dings and sand it smooth for the Dynel later on.

Well that's it for now.  Next time I'll have some photos of the Dynel going on the deck...plus the start of the spars.   I figure it's about time to start on those since they will need multiple coats of varnish and I don't want that to hold up the launch spars.  Plus it's a fun thing to do, so I don't mind getting started...