sizing replacement spreaders

The sketch you present seems to show you don't know what a spreader bar is. I went to the trouble of including photos of 2 of them earlier in this thread.

Your sketch does show the forces we all know act on sailboat rigging. It does not address the topic we are discussing.


One other interesting thing. It seems to contradict the second part of the claim "designed to transmit loads through the mast, rather then to the mast." I wonder how you will resolve that?

 

Commonly called? That's a hoot! Kenyon, Fores, Sparcraft, Hall, etc., none of them add that adjective. There's a reason for that.

Now you don't underrstand what a cantilever is?

 

A brute force way to size the spreaders would be to do the free body diagram at the shroud intersection. Knowing the breaking strength of the shrouds, resolve the forces at the spreader tip and compute the compression transmitted to the spreader. Add a safety factor if you wish.

Then you know the shroud would fail before the spreader does, and you should be set.

 

Not sure who the “WE” are…since the orginal poster makes it clear:

Im not a fan of Wiki, but even they get this right what a spreader is:

http://en.wikipedia.org/wiki/Spreader_(sailboat)

Even tell you the nature of the forces:
http://en.wikipedia.org/wiki/Spar

Compression…hmmm. I wonder how much of the world confirms to your definitions?

As for the rest…not worth engaging with someone when they do not even recognise the normal nomenclature and accepted definitions of items/parts on a boat and simple structural analysis and its own definitions, yet venomously prostrates to the contrary.

 

A spreader is not a spreader bar.

If you had bothered to read the thread before posting you would know we are discussing spreader base designs. A spreader bar is a type of spreader base. The OP specifically asked about this and I even included two photographs of spreader bars.

I find it ironic when someone accuses me of not knowing acceptable definitions of parts when they are the ones who have a basic lack of knowledge of the subject.

 

Some insults directed toward other members have been removed. Please, let's stick to discussing the topic without the insults directed towards other members. Thank you all for your understanding. I believe the request with post 20 to cease further insults was reasonable.

 

Spreader bars, by any other name!

I always understood the spreader bars as an inexpensive but sound engineering method of steering shroud loading Thur the spreader on to the mast side wall. Dick Gates & Alain Holt 'Spar tech' Redmond, Wa. always employed this simple concept building there rigs. That must have run about 5000 mast, Star, San Juan 24,26, 7.7, 1/2 ton 30, etc, etc systems. I all ways thought the spreader base set up an expedience of mass production. Locate them bang, bang with the pop rivets job done. As opposed to a spreader bar hole to be crafted into the mast. I got lost in all the above stuff, Paul B, had it wright from the start!!??. The fellow with the E-25 only wanted an inexpensive, but sound way to fix a troubled spreader !!!! My C&C 34r uses this spreader bar arrangement, and am going to post a snap of a custom Spar craft tube that well go into a Davidson 29, that uses a hand crafted spreader base & bar set up. The bar only position the spreader to the proper geometry ; up dihedral and negative angle of attach. I never considered these bars as a compression member Thur the mast to the slack shrouds??

I used a very small but thick wall spreader off a San Juan 7.7 #4000lbs boat to a race ready Ranger 26 # 6000lbs all up & on the water with out trouble.
crm