UK-Cherub Class

Get Your Heart Racing

Bethwaite Wing Mast

This is measurements and the story of the last round of Wing Masts in the 1970's.

It was handy to measure in a bit more detail

Overall section was lost, but was rule limited two four inches, and had a hyperbolic front The structural pine is 30mm wide, 38mm lengthwise at the tip 38 * 48 halfway between hounds and tip 43.5 * 59 hounds 47.5 * 69 diamond spreaders ~47 plus 20mm local reinforcement * 69 at the gooseneck 46.5 * 61 at the foot

tip to hounds 2120 hounds to diamonds 1820 diamonds to gooseneck 1550 gooseneck to foot 430

Section details at the hounds are width at aft face 41.5mm max width 43.5 width at front face 34 max width is 23mm from rear face

And finally the following was posted by Frank Bethwaite on the Tasar Forum…

The origin of the Tasar mast was the NS14 then the Nova. This was an
18ft mast with the forestay at 12.25ft. I made hundreds of timber
masts, the later ones faired with balsa as Jim Champ describes, and
the fastest were those which, when supported at the base and over a
fulcrum at the hounds (12.25ft) yielded at the tip at a rate of 4.9 to
5lbs per inch fore and aft (F) with a circular arc bend except near
the base and 2.8 to 3 lbs per inch sideways (X) with no diamond stays.
Often owners would call for different forestay positions and/or rates
of spring. They never won, and often were brutes to handle (eg if the
forestay height was made even a few inches higher.)
When the Tasar was developed, it was necessary to move to alloy to
handle the expected volume. The softest I could get alloy machinery of
the right aerodynamic shape was 8 lbs per inch F and 3 lbs per inch X.
This made the boat feel a bit “wooden” compared with a top Nova but
was as fast and has served well for thirty years. If you are going to
the trouble of doing an FRP core from scratch, I would shoot for 5 lbs
per inch F and stay with 3 lbs per inch X.

A handy Tasar mast might be good to look at section shapes, but the actual proportions got severely shortened to make it bend…

history/bethwaite_wing_mast.txt · Last modified: 2020/12/09 19:21 (external edit)