Interior turnbuckle question

erikwfab

Member II
Inside my E36C there is a turnbuckle from the deck to the mast. What is the purpose of this and what is the proper tension? see photo
 

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markvone

Sustaining Member
Deck hold down conncetion

That turnbuckle resists the upward pull of deck hardware at the base of the mast such as halyard turning blocks for aft-led halyards. The upward load of the tensioned halyards pulls up on the blocks attached to the deck trying to pull the deck up locally around the mast. Since the mast is keel stepped and not attached to the deck, the deck is not that resistant to upward movement and the turnbuckle provides a connection to hold it down. It only has to be tight enough to act as a solid connection between the mast and deck, no slack with no loads on the hardware above. Too tight will pull down too much and distort the deck out of shape. Mark
 

Sven

Seglare
Inside my E36C there is a turnbuckle from the deck to the mast. What is the purpose of this and what is the proper tension? see photo

We have the same setup and were told that it is there to keep the deck from flexing up too much as the chain plates pulls the hull sides up and in.

We don't have any real tension on it under no load but I can imagine that when we are under heavy conditions it is under quite a lot of tension.



-Sven
 

AleksT

Member III
It is there to keep the deck from flexing upward as the shrouds pull up on the sides of the hull and the mast pushes down on the keel. it should be snug but not overly tight. One or two turns with a wrench past the point you can tighten it with your hand should be good.
 

Loren Beach

O34 - Portland, OR
Senior Moderator
Blogs Author
Up Force and Down Force

I remember when Bob Perry called this a "tie rod" when he had it go from cabin top to base of mast step on his V-40. Other boats have the collar that the turning blocks shackled to pinned right thru the spar.
Same purpose for all -- keeping the cabin top from being hauled upwards by the loads on halyards. (Main halyard load is not too bad, but you can get some major force on a spinnaker or jib halyard -- and on a heavy air reach all three are loaded.)

Keeping the boat sides apart is not really why it's there, even tho it would lend some strength to that idea.

Loren
 

Sven

Seglare
I remember when Bob Perry called this a "tie rod" when he had it go from cabin top to base of mast step on his V-40. Other boats have the collar that the turning blocks shackled to pinned right thru the spar.
Same purpose for all -- keeping the cabin top from being hauled upwards by the loads on halyards. (Main halyard load is not too bad, but you can get some major force on a spinnaker or jib halyard -- and on a heavy air reach all three are loaded.)

Keeping the boat sides apart is not really why it's there, even tho it would lend some strength to that idea.

Loren

Loren. In this case you are wrong. It had to happen sooner or later :egrin:

The turnbuckle is there even if there is no connection between the cabin top/deck and the halyards. If you draw a vector diagram of the forces you will see that as the shrouds pull up and in they will compress the deck between the shroud under tension and the mast, pushing the deck upwards. So by keeping the deck from flexing upward too much the deck also helps keep the hull from pulling too far inwards towards the mast, and is thereby stiffened.



-Sven
 

erikwfab

Member II
Interesting replys, thanks, especially since this vessel has no halyards that lead aft from the mast, and never did as I know.
 

Loren Beach

O34 - Portland, OR
Senior Moderator
Blogs Author
Loren. In this case you are wrong. It had to happen sooner or later :egrin:
The turnbuckle is there even if there is no connection between the cabin top/deck and the halyards. If you draw a vector diagram of the forces you will see that as the shrouds pull up and in they will compress the deck between the shroud under tension and the mast, pushing the deck upwards. So by keeping the deck from flexing upward too much the deck also helps keep the hull from pulling too far inwards towards the mast, and is thereby stiffened.
-Sven

I guess we'll just have to disagree; I'm siding with Bob on this one.
:nerd:

Loren
 

Sven

Seglare
I'm siding with Bob on this one.

If you mean Perry I should look him up and remind him that we paid him for a lifetime consulting contract 17-18 years ago so he owes me an answer.

More seriously, just draw the force vectors and you'll see it.



-Sven
 
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