What is this for?

[chuck53]

Sorry I don't have a picture to ad to this, but...
Inside my cabin, there is a turnbuckle with one end attached to the mast and the other end attached to the cabin top.
What is its purpose?

[Gary]

Hi Chuck,

That turnbuckle is there to reduce flex and stress in the deck caused by the upward and accumulated lift created by jib,spinnaker and main sheet and halyard blocks at the mast collar.

Gary

[chuck53]

Makes sense to me.  Thanks for the quick reply.

[Ron Hill]

Chuck : What Gary is saying is that there is lateral compression from the chain plates that will cause the deck to raise.  That inside turn buckle is attached to a metal piece molded into the decking to hold the deck steady as that compression takes place.
 
The tension on that inside turnbuckle should be tight, not slack.   

[Gary]

Ron,

Interesting thought, and I agree that there is lateral compression from the chain plates, and I had not thought of that.  But, I am thinking there is considerable lift effect on the deck from the accumulated blocks, all at the mast collar. Of course all blocks lead aft to rope clutches (lateral force) but the first direct change of force at the deck is upward. It must be considerable since our furling systems stay pretty tight all season and while underway the main sheet has a lot of pressure which first forces lift at the deck before changing direction in a lateral way to the clutch.

Interesting ideas for conversation.

Gary