Mast in tabernacle

dlovelock

dlovelock

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I've been wanting to ask this for about 40 years .... What is the correct way to set up a mast in a tabernacle? Should all the weight and compressive load of the mast rest on the pivot pin (must create some severe stresses) or its base (more difficult to lower mast due to friction)? Or should I be knocking in wedges under the mast foot? Seems like an engineering no-win situation to me!
David.
 
Wood or aluminium? With wood I suggest a wedge would be better, also a sleeve epoxied in for the pivot bolt is another improvement.
 
I think traditional boats on the Broads, which of course do a lot of mast lowering and raising, have a bevelled heel to the mast which engages with a matching bevel at the foot of the tabernacle. So it only contacts right at the last moment of raising, and introduces a suitable wedging effect as the forestay is tightened.
 
Older Wayfarers had a metal baseplate on the tabernacle foot with two raised lips drilled and a matching plate with narrower lips on mast foot drilled to match.
Weight transmitted through 4 quite thick lips to base plate, pin then just a pivot. Wedges for mast rake between tab front and foredeck

Redfox tabernacle had a full length back stopplate and mast reached to tab. base, and a lower hole into which pivot pin transferred after raising to help take the weight/ hold secure and allow mastrake.

Both systems worked ok
 
[ QUOTE ]
Older Wayfarers had a metal baseplate on the tabernacle foot with two raised lips drilled and a matching plate with narrower lips on mast foot drilled to match.
Weight transmitted through 4 quite thick lips to base plate, pin then just a pivot. Wedges for mast rake between tab front and foredeck....
/forums/images/graemlins/blush.gifForgot, ... and an adjustable stop bolt thru holes drilled in 4x lips to stop kickback of mastfoot and aid mastrake.

Redfox tabernacle had a full length back stopplate and mast reached to tab. base, and a lower hole into which pivot pin transferred after raising to help take the weight/ hold secure and allow mastrake.

Both systems worked ok

[/ QUOTE ]
 
My Catalac has a wedge shape foot on the mast. It requires a hardwood wedge to take the weight off the pivot pin. If you allow the mast to rest on the pivot pin, the compression loads will bulge the mast wall either side of the pin. This can also happen if the foot of the mast slips forward if you get the tension on forestay/backstay wrong. I have a bolt which goes fore to aft in the base of the mast and secured through the back of the tabernacle in order to avoid the foot moving.
 
I would suggest that in both wood and Al masts the weight when the mast is vertical should be on the base of the mast not on the pivot bolt.
This can be achieved by having a fair bit of free play in the bolt holes.
A chamfer (cut away) at the back of the mast base will mean that as the mast tilts back the base has less pressure to allow it to slide forward.

olewill
 
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