Stackpack sagging problem

[JimC]

In my experience, most problems of this type are caused by the attachment point on the mast being too low. I have a similar setup to you (I use blocks though) and on the advice of the manufacturer I fitted the mast blocks about 1.5m above my spreaders. Fitting them at the spreader root would give exaclty the issues you describe apparatently as theres too much of a forward component in the pull...

Would that help?

I'm sure you're right: the higher the attachment on the mast the greater the vertical component in the ropes' tension. Mine are attached about 3/4 of a metre above the spreaders and probably would be better higher up.

 

[Emjaytoo]

This is our system, seems to work well. Have to adjust the length depending on the boom height, but that is only prior to raising main and when putting it away.

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[Thistle]

I guess not, I just don't like the look of it. To my mind a stackpack, for all its convenience, is a rather unlovely thing and a droopy one is worse! Actually, in the course of following this thread I've become somewhat fascinated by the general problem of how to distribute the pull from a single rope equally between 3 subsidiary ropes. It's easy if there are an even number of ropes but seemingly impossible if there's an odd number.

Why are the attachment points evenly spaced along the boom?

 

[JimC]

Because that's how the stackpack is made I guess. The attachment points cannot easily be moved.

 

[Thistle]

Because that's how the stackpack is made I guess. The attachment points cannot easily be moved.

Yes, but would it be better if they were made differently? It shouldn't be too difficult (a big bulldog clip, perhaps) to create temporary attachment points for the middle string (of 3) to find out where it is best placed.

 

[wotayottie]

I've become somewhat fascinated by the general problem of how to distribute the pull from a single rope equally between 3 subsidiary ropes. .

That would not solve the problem since the pull needed at each attachment point is not the same. The angles are different as is the weight of the sail contained.

The best approach would be the "Dutchman" type where you hang the lazyjacks vertically downwards from the topping lift not the mast. That will give the equal pull at each point which you vary to allow for sail weight etc by moving the attachment points up and down the topping lift by a small amount. The Dutchman system actually had single lines running through cringles in the sail but I dont see why you could not make it work with lines either side

 

[Iain C]

I'm not sure I totally get the issue. Mine "self levels" assuming that there is some weight on the boom, and the topping lift is not on too much. I also have 3 attachment points, equally spaced...

Gooseneck end...a line goes up from the attachment point, round a block rivetted to the mast, and back down towards the middle of the boom. It stops at spreader height, where there is a block. The middle line goes from the attachment point, round the block mentioned before, and down to the outboard end of the boom. One the lengths are adjusted, that's it, the whole lot self levels with an equal pull on everything.

If I wanted to get super anal and wanted tight lines all the time, with a very open leach, I could splice some bungee into the inboard line to take up the slack, however you need a bit of give so as not to interfere with the draft of the sail...

 

[Emjaytoo]

I'm not sure I totally get the issue. Mine "self levels" assuming that there is some weight on the boom, and the topping lift is not on too much. I also have 3 attachment points, equally spaced...

Gooseneck end...a line goes up from the attachment point, round a block rivetted to the mast, and back down towards the middle of the boom. It stops at spreader height, where there is a block. The middle line goes from the attachment point, round the block mentioned before, and down to the outboard end of the boom. One the lengths are adjusted, that's it, the whole lot self levels with an equal pull on everything.

If I wanted to get super anal and wanted tight lines all the time, with a very open leach, I could splice some bungee into the inboard line to take up the slack, however you need a bit of give so as not to interfere with the draft of the sail...

Exactly the same as mine - see photo in earlier post.