Sail Slug Attributes

[cowlum]

Hi

I'm starting on a project to build a sailpack for my e27.

My main sail is currently a bolt robe that's slid into the boom track.
To facilitate a sailpack I'd like to sew a number of slugs to the foot so that there is space for the sailpacks slugs.
The slugs sewn into the main foot would likely be about 20cm apart.

Of the two slugs I have available at the local chandlery only the fully plastic one fits through the goose neck guide.
So my option's are,

1) Use the 10mm fully plastic slug.
2) Shave a portion of the gooseneck guide to allow the 10mm stainless slug into the track. The portion shaved is non structural and i'm sure I can do a tidy job.

I generally don't like cutting, drilling or making changes that are not reversible .

Does anyone here know if there is much of a strength difference between the two?
Any real advantage to the stainless slug?
Any advantage of one slug over the other?

Additional note:
I'd really like to go loose foot main but I don't think this is an option with the mainsheet gripping the boom at the centre. The boom would likely bend.

[JPA Cate]

Fwiw, I think you can go to a loose footed main. There's nothing about having the main food attached to the boom that affects your mid-boom sheeting. The boom, itself, if it's had hard usage, may be developing cracks on the inside. It'll let you know with a big bang if that's the case (don't ask). [Broken booms can be sistered and continue in use, stronger than before.]

In your picture, the slug is s/s reinforced: there are slugs that are all stainless, and I'd recommend two of them for right near the head of the sail, and the reinforced ones for the rest, down to the foot, to slide easily in the mast track. The all plastic ones just don't hold up very well, ime.

Ann

[cowlum]

Originally Posted by JPA Cate

Fwiw, I think you can go to a loose footed main. There's nothing about having the main food attached to the boom that affects your mid-boom sheeting. The boom, itself, if it's had hard usage, may be developing cracks on the inside. It'll let you know with a big bang if that's the case (don't ask). [Broken booms can be sistered and continue in use, stronger than before.]

In your picture, the slug is s/s reinforced: there are slugs that are all stainless, and I'd recommend two of them for right near the head of the sail, and the reinforced ones for the rest, down to the foot, to slide easily in the mast track. The all plastic ones just don't hold up very well, ime.

Ann

Thanks for the reply. Maybe i'm understanding it wrong but I would think the clew attachment at the end of the mainsail would create pressures other than just compression.

[JPA Cate]

Yes, I could tell you had concerns. All I can say, is that when we shifted to loose footed mainsails, about 30 yrs. ago, and there have been two different boats in that time, and a great many mainsails, none of the sailmakers ever expressed that kind of concern. I understand that that is 3rd hand, and if you find out solid information to the contrary, I would most appreciate learning if I am wrong.

Ann

[cowlum]

Thanks Ann.

Between yourself and the people on the ericson forum I've decided to go loose footed with two or three plastic slugs at the clew. Keep it simple. By sailing cautiously and keeping an eye things I'll soon workout if things will hold up.

[Lake-Effect]

Most mainsails don't exert that much pull at the center of the foot, so going loose-footed shouldn't cause problems even if the boom is sheeted from its center.

[Jim Cate]

Cowlum, while there isn't much load on slugs in the middle of a main's foot, there are big loads at the clew. All the leech loading travels through that connection, so you need a strong joint. For many years I've used a strop around the boom going hrough a hefty D-ring. The outhaul is shackled to the outboard end of the D ring and the clew of the sail to the other end. The strop can slide back and forth on the boom for adjusting the foot tension.

I've used both Spectra and plain nylon webbing for the strop. For your boat I'n sure that nylon would be plenty strong enough.

Jim

[RaymondR]

A loose footed main would put more bending load on the boom if it's sheeted mid point.

[Jim Cate]

Originally Posted by RaymondR

A loose footed main would put more bending load on the boom if it's sheeted mid point.

I don't think this is true to any significant degree, Ray. When we had conventional mains there was never much load on the middle slugs. They were more there to help define the sail shape than to deliver load to the boom. The big loads come down the leech to the clew.

Jim

[RaymondR]

Hi Jim.

In the instance of a loose footed sail with the sheet attached at some point not the end of the boom, the boom effectively becomes a cantilevered beam with the points of fixity being the gooseneck and the sheet attachment point.

The situation in the instance of slugs is slightly different as the section between the goosneck becomes and end fixed beam with evenly distributed loads and the outer section a cantilevered beam.

However, I suspect that were one to do all the calculations one would find not much difference in the loadings. I generally keep the outhaul fairly tight and I have noticed that most of the slugs stay loose in the track.

[Jim Cate]

and I have noticed that most of the slugs stay loose in the track.

Yep, that's it exactly. The foot of the mainsail does not load the boom much between the clew and the tack... in most mains, very little indeed, as shown by the loose slugs. Thus there is little functional difference in boom bending moment by changing to a loose foot.

I've made the change on several boats with no observable differences in the shape of the boom, and IMO the performance has always improved (highly subjective, of course!).

Jim