Bolts in spar

skutzabik

skutzabik

Sails the Bidet
Just picked up SF #2, a nice 76. The lower spar has four stainless 3/8 bolts through it. Two ahead of the gooseneck and two behind. Anyone know what they might be for? More importantly, can I take them out since the nylock nuts are abrading the sail edge, or will the spar be weakened having four the holes in them and I am better off leaving the bolts in. Perhaps I could change them to a bolt with a flush head if the open hole would be weaker than the hole filled with the bolt.


Thanks.........
 
Not sure what those would be for. Where are they exactly, pictures may help.

I would remove them. The spar does not get any weaker or stronger with or without them IMO.

Those are rather large holes though, which may cause a break in the future.
 
I'll give my 2 cents from an engineering perspective and not try to get too technical:
the hole(s) weakens the net section of the spar. when the spar is loaded and bends a little bit under the wind load, one side of the tube section is in compression, and the other side is in tension. you could probably argue that leaving the bolt in place might help a little bit on the compression side, but it does no good on the tension side, which would be more critical for stresses. the visual below is probably far more than you wanted to know (I found it via Google, but it shows the bending stress diagram):

max_bending.jpg


so (IMHO) the bolt being there doesn't really help, and I think you could take them out, and certainly be no worse off than leaving them in (at least in regards to pipe stresses). that being said, there could be other issues that I'm sure others will weigh in on.

cheers, my2fish
 
I got a set of spars once that had 2 hose clamps on it to keep a bent up gooseneck from slipping. Maybe your bolts were a former owner's attempt to do the same thing?
 
OO structural analysis.

Perhaps rotating the spar 90deg on its axis would help. This would bring the distance from the neutral fiber (y) down to zero in that plane.


I believe more more bending moment is developed on the top (C) and bottom (T) than the sides of the spars. Vanging down contributes a lot to this. Try to picture the forces the sail causes on the spar.

So theoretically, holes on the sides of the spars should be stronger than holes on top and bottom.
 
But....this is sunfish sailing not America's Cup.

Take of the bolts and use the spars. If they ever break you can worry about it then.

Also, corrosion compounds the problem, so keeping the spars clean and dry will help persevere them.
 
skutzabik said:
Just picked up SF #2, a nice 76. The lower spar has four stainless 3/8 bolts through it. Two ahead of the gooseneck and two behind. Anyone know what they might be for?
Click to expand...
I wonder if under the gooseneck is a split. The boom got worn by a loose gooseneck then broke. The pieces or a piece of a matching size tube have been spliced together over an insert.

The holes have already weakened the tube, but lateral isn't nearly as critical as circumferential would be.

Interestingly, this repair can be performed using a piece of close fitting inner tubing epoxied about 12" into each end of the break and the resulting repair will be incredibly strong.

.
 
I'm with Wayne. I bet that there is a clean break in the boom and the previous inserted a wood dowel or a metal tube insert and held the repaired area in place with the two bolts
(a bit of overkill if you ask me.) Let us know when you find out.

Alan Glos
Cazenovia, NY
 
You guys are good. What I thought was white tape marking the location on the spar for the gooseneck is really a pvc spacer that is slid over the pipe that has been used to splice the spar back together. The pvc diameter is so perfect it is nearly seamless. The repair seems very strong when the spar is worked by hand. I am going to cut the ends off the bolts are run this puppy for as long as she lasts, which may be a very long time given its resistance to my manipulations. I will post a photo as soon as I get the techno-wife on the job.

Thanks, Skutz
 
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