Latest News: Forums Technical Compressive Loads Reply To: Compressive Loads

#7917
Anonymous
Inactive

@Swiebertje wrote:

@matoi wrote:

http://www.karver-systems.com/site/us_produits_hook.php
http://www.karver-systems.com/site/fr_produits_emmagasineurs.php

They say there is some benefit to reducing the compressive loads in the mast.

Bolocs!
The forces on mast and stay (or luff) are exactly the same regardless where the tensioning device is located. Tension on the stay (or luff) will compress the mast, that is simple (secondary school) mechanics. I for one, want my Genoa touching deck to close the “air leak”. That is far more important then the location of the tensioning device. (Mine is flat on the top of the CB case and the mast it still compressed 🙂 ).

Actually you are wrong.

Try thinking about the luff of the sail as a means of pulling down the mast.

If you anchor the top of the sail onto the mast, then pull (say) 400lbs down on the foot of the sail, then you are applying (approximately) 400lbs force acting downwards at the top of the mast.

If, instead, you route the halyard over a block at the top of the mast and bring it back down to deck level (as per a conventional halyard) then in effect the masthead sheave introduces a 2:1 purchase. Whatever force you apply on the tail of the halyard is approximately doubled in terms of the downward pull on the top of the mast.

The critical difference is that the system in the link locks once the sail is up, so there is no longer any load on the halyard and it works as per my first example – ie the compressive load is (approximately) whatever tension you apply to the luff, not double that amount.

It was fashionable at one point to use main halyard locks where you hoisted the main and it latched at the top of the mast so that the halyard was no longer under tension. This was exactly the same principle, and solely for the reason of reducing compressive load.