Friday, January 22, 2016

A Bird's Mouth Mast for the Spidsgatter Smil

By Kristin Stewart

If you are unfamiliar with the construction of a bird's mouth mast you may wonder how these pieces of spruce...

become this this.

Although I had seen a cross section of such a mast, I had never seen the construction from start to finish.  The completed mast for the Danish Spidsgatter Smil would be 40 feet tall with a taper from 5" at the base to  2"at the head of the mast.

James did the math to determine the taper of the staves from the top of the mast to the base. 

Measurement and calculations of stations and tapers to shape the staves

The stations on the strongback are covered in plastic so that the glued staves do not stick
This is the top end of the mast, the circumference will be planed down to a 2" radius.

This is the first dry fit using hose clamps assuring tight connections.

Shawn is putting protective plastic down on staves #5 and 8#. So that when #1-4 are glued together they only stick together forming one half of the whole mast.

The staves are glued together with a paste of epoxy and wood flour.
The stave on the top of the picture shows a scarf joint.
16-18' boards were joined to make them 40' in total

James walks to the end to turn glued stave #3 to abutt with #2.

Hose clamps are added to the smaller end first

As Shawn tightens the clamps down the line James watches for extra epoxy to squeeze between the staves.

the second half is glued up and curing

Andy planing an octagonal brace

The two halves lay side by side.  They are ready for wires, bracing and the addition of the mast step piece.

The octagonal brace is fit for structure at the position of the spreaders.

The octagonal piece is transformed into a crown brace on the bandsaw
A crown brace distributes the stress load.

Mast light wires are strung through the inside before the final glue up of the two sides.

The white tub protected the wires from being glued together.  After the glue was cured the wires were pulled out the side of the mast, through a hole, about a foot up from the bottom.

Piles of shavings from the initial rounding of the mast.  Next, concave pieces of  styrofoam and sand paper
were used to sand it even and round.

Purpleheart wood 'hounds'  where the mast bands set for rigging and sail track mounts

The mast gets its top coats of varnish.