January 14th
Rey Theroux of Calgary in Canada has expressed an interest in the construction details of my radial jib fitting for the Js. What follows is just one way of making such a fitting and constructors may well make improvements. Some constructors have managed to make these fittings with just hacksaw, files and hand drill, but access to a metal turning lathe certainly makes things a lot easier.
The main parameters to be followed are: -
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Its overall size is commensurate with the general Canterbury J dimensions.
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An adjustment is included to tilt the swivelled pivoting assembly so that the swivel axis points to the hounds (point on mast where Jib halyard is attached).
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The point of boom swivel is approximately 5/8" (17mm) aft of the forestay swivel. This has the effect when the boom swings to the running position, of shortening the foot of the sail by that amount and gives a nice balloon "spinnaker" look to the jib which also becomes more stable when running down wind.
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A screwed adjustment on the jib boom to limit the amount of lift it can have and so function as the leech lift halyard. (only needs to limit the 'lift' , no matter if the boom drops down and tightens the jib leech in light airs)
Photo
shows the fitting as attached to a rather battle-scarred J50. (As
with all thumbnails at this site click or double click should
download the larger original)
The forestay halyard is hooked to a standard fishing swivel, and a sliding ring secures the jib's heel at the end of the boom. The deck securing alloy channel is 3/8" sq. x 2 1/4" long with 1/8" holes 3/8" apart. Generally the fitting needs little adjustment when changing from "A" to "B" rigs. The shorter foot on a "C" rig boom however would necessitate moving the fitting a couple of holes aft. Also visible in the photo aft of the fitting, is the sheeting turn-a-round to the winch below decks amidships.
The tilting block is an easy fit in the
channel but involves 
some
intricate drilling and shaping. The tilting adjustment screw needs
to have a sloppy fit in the block so that different angles can be
accommodated. The pivot rod (3/16") has a screwed base to fit
the block and this too needs accurate drilling and tapping. This
photo is dimensioned (in inches for Rey's benefit) but accept these
values only as a guide as variations within reason would probably
work just as well.
January 15th
January 21st
Finished the components of the radial
fitting today and assembled. Made a blue on the drill press by not
trueing the boom up with its slot vertical - consequently the
adjustment rod anchor on the boom is a few degrees off vertical. Will
work O.K., but to me the builder, looks horrible! Not so horrible
however is the colourful boom - try your local archery shop for old
aluminium arrow shafts (or new). They come in a variety of sizes
around 1/4" - 3/8" and tend to be much harder than the
usual alloy tube from your aluminium suplier.
Quite a number of us have cottoned on to the "ball and socket" kits that some of the radio controlled model car manufacturers (Tamiya ~ TL-01 Turnbuckle Tie-Rod set) put out for tuning up their cars. These balls have a 3mm screwed pin and form the base of a very easily built gooseneck. Again a metal turning lathe makes the drilling and tapping of holes a cinch but it can be done with hand tools alone.
More details tomorrow: -
Well I got delayed in building a "not so cheap gooseneck" fitting for a club colleague and with his (Bob Wing) permission I will describe it first before describing the "cheaper" version. Actually neither are expensive but Bob's little commission took a lot more time in the workshop and it is certainly a great little gooseneck!
January 21st
Bob's gooseneck involves a fair amount of machining and so I shall make the presumption that any one who wants to set to and make one will have all the facilities and know how to achieve it. So a building description will be rather brief and speak mainly to the four photos.
On J86, which incidently is Bob's partner Jill's yacht, the
gooseneck draws admiring looks.
Its special feature is that instead of a kicking strap or vang the
adjustment of leech tension on the mainsail is controlled by a
knurled screw nut on a 1/8" W screw. It works in compression
limiting the boom's lift and is capable of very fine adjustment. The
wire harness constrains the mainsail's tack adjustment. The adjuster
part is turned at its extremity to accommodate an ex arrow shaft
aluminium boom.
The construction drawing was drawn from dimensioning the photo of
Jill's yacht and was made slightly larger as I understand Bob
intends to use this one on a 10 Rater. The construction drawings are
not definitive and in the end I made a few minor changes, principally
with the addition of four external bushes on part B to give
reasonable depth for the 1/16" SS lifting pivot and the tack
harness wire and one on Part A to house the threaded end of the
swivel rod. I will be interested to see how these bushes survive as
they are made as a push fit and instant glued (cyno) in place.
Part A is best machined from a short length of 1/2" x 1 1/4" bar in the four jaw chuck to machine the mast radius seating. The swivel pin was made from 3/16" stainless steel rod turned and threaded 3mm at the end to engage a threaded bush and locknut.
Part B (from the same 1/2" x 1 1/4" bar) is quite
straight forward and the 3/8" slot was machined by endmilling
the piece as it was held on a vertical slide in the lathe. I drilled
through 1/4" and inserted a brass bearing reamed 3/16" for
the pivot pin.
Part C looks to be the most
complicated piece so I started with this first and discovered that by
using the four jaw chuck it was very easy to machine. The piece is
made from 3/8" x 3/4" bar. The rod to take the boom shaft
is in fact a seperate piece turned down to an easy push fit and
cynoed into a hole drilled down Part C as it was held in the four
jaw. After drilling the 3mm (or 1/8") hole for the adjuster
screw, reverse the work in the chuck and drill down at the correct
centre for the boom joiner. The pivot bearing was drilled out
1/8" and a pre-drilled (1/16") length of brass pushed in as
a bearing.
THIS CONSTRUCTION SERIES WILL PAUSE NOW (1st Feb 02) FOR A FEW WEEKS AS ALTERNATE SITE HOSTING IS INVESTIGATED.
I would be most glad to respond to any queries that builders of the Canterbury J might care to direct to me - left click the button below.
