small block at bottom of tabernacle

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Re: small block at bottom of tabernacle

Postby Pasi in Finland on Fri Aug 02, 2024 12:51 am

fairly soon I will be at the stage where I'll have to make a decision on this myself.

The engineer in me says the mast should not touch the block or tabernacle rear face. The book calls the halyard to be "guitar string tight" meaning the shrouds will also be tight, and they are designed to carry all of the aerodynamic loads. If the mast bottom touches anything, it will only add a bending load twisting the tabernacle forward without adding any strength. And any stretching or movement of the shrouds will only add to this bending force.

My vote is to use the shroud length to set the mast rake, and maybe only use the block to calibrate the angle.

Pasi
Pasi in Finland
 
Posts: 38
Joined: Mon Dec 07, 2020 7:37 am

Re: small block at bottom of tabernacle

Postby Tom G on Mon Aug 05, 2024 6:33 pm

I am not sure I believe that any amount of jib halyard tension or shroud length will keep the bottom of the mast from touching both the sides of the tabernacle and the forward edges. I suppose it is possible to achieve this balance in a static condition at the dock where the lower part of the mast below the pivot doesn't touch anything. I have had several sailboats and can't think of one where the bottom end of the mast is not touching something and /or restrained in some fashion to be in a stable condition.
I think you risk unnecessary loads on the rig to try and achieve this "no touching " situation. Maybe I am misunderstanding what you are describing. I know when sailing , no matter how snug I have made the Jib Halyard that the leeward shroud relaxes some and in fact looks a bit loose . This is pretty easy to see especially in windier conditions. I think a soon as this happens that the bottom of the mast will move to touch something. I think that this not unusual . I agree you don't want it loose . I always re-tension the halyard every morning on a cruise as it can loosen a bit during the day. I understand
Tom G
 
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Joined: Tue Dec 04, 2018 2:25 pm

Re: small block at bottom of tabernacle

Postby Pasi in Finland on Tue Aug 06, 2024 8:10 am

I may not be clear in what I meant, sorry about that.

You are right Tom that the mast will inevitably touch the sides of the tabernacle when under wind loading. My concern is that if you have the block and the mast is touching it, there will be a static bending load on the mast and tabernacle. This is already without the sails, just the halyard pulled tight. Of course if the shroud length is absolutely perfect the mast bottom will only ever so slightly touch the block and there is no bending, but then it also might as well not be there at all. When you then hoist the sails, there will be additional dynamic loads which will be on top of the static load. My point is that there is no added value in introducing the static bending load to the rig.

Happy sailing
Pasi
Pasi in Finland
 
Posts: 38
Joined: Mon Dec 07, 2020 7:37 am

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