sizing replacement spreaders

[Paul B]

Originally Posted by Ad Hoc

So drawing the triangle of forces, to maintain the directional flow of force and equilibrium, the only direction the force can be, is to the right, ie into the bar, which means..compression!

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?

[Paul B]

Originally Posted by PAR

The best part John is the actual part, which isn't made by Kenyon (exclusively), is commonly called, at least by it's parts catalog number a "spreader compression bar". It floats in a slot through the mast, but hey what do we know.

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

Originally Posted by PAR

Of course it's in compression and a cantilever would suggest some sort of purchase with an overhanging something or other.

Now you don't underrstand what a cantilever is?

[water addict]

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.

[Ad Hoc]

Originally Posted by Paul B

It does not address the topic we are discussing.

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

Originally Posted by davisr

I must replace the OEM spreaders on my Ericson 25.

Originally Posted by Paul B

The sketch you present seems to show you don't know what a spreader bar is.

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.

[Paul B]

Originally Posted by Ad Hoc

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

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

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.

[Boat Design Net Moderator]

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.

[CRM]

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