Posted 28 August 2012 - 02:29 PM
I have a dinghy, which I sometimes use for racing, and sometimes I get these ideas: Why is this or that done as it is done? And why not differently? So now I have this jib, which has halyard, which has a sheave on the mast. In my boat, this sheave is about 25 cm below the forestay/shrouds attachment point. Rig tension is applied via the jjib luff wire.
Why is the jib halyard sheave lower than the forestay? Why not at the same height? Why not lower?
Obviously the minimum height is such that I can still hoist & tension the jib ... as it is now, I have about 15 cm space between the head and the mast, so plenty of room for (at least theoretical) experimentation.
Now, please give me some thoughts & ideas!
Thanks. Have fun.
Posted 28 August 2012 - 04:21 PM
Posted 28 August 2012 - 04:58 PM
As for the displacement between the jib halyard and the shrouds, as JimC says it's about mast bend. And likely constrained by class rules.
Posted 28 August 2012 - 06:12 PM
Posted 29 August 2012 - 08:33 AM
But the question is: What is desirable? Putting the halyard sheave low, to get more bend? Or put it high to get less bend (e.g. only bend from the spreaders)?
I assume that one of these is good, so it should be either as low as possible (-> limited by the jib luff length) or as high as possible (limited by the forestay height). As it is now, it is right in the middle ....
Class rules don't restrict it in my case!
Posted 29 August 2012 - 09:14 AM
If I understand you correctly, you don't give a hoot what the class rules say, you just want to make the rigging work.
If that is the case, you have truly opened Pandora's Box and you might end up being an expert in the end haha!
The mast bend induced by the shrouds and spreader is affected not only by the offset of the halyard and shroud attachment, but also by spreader length, sweepback, and chainplate location, and rake. As you rake the mast, assuming you have provision to change shroud length (like a 505) then with non-swinging spreaders, the rake induces bend.
How much bend? It depends on what you are trying to do and why, and what other controls are at play.
Posted 29 August 2012 - 07:20 PM
Posted 07 September 2012 - 12:42 PM
so far, thanks for your replies. So what I have learned is what I have to take into account when moving the jib halyard heigt. Class rules do not mention anything about the jib halyard, which is why I started this thread. Moreover, new sails will soon be necessary anyway, which makes all kind of things possible.
So, let's move a step forward and have a look at the advantages and disadvantages of having the halyard high or low or somewhere in between.