Spreader Location

[pencema]

How important is the vertical location of the spreader brackets on the mast?

I ask because my very early C-30 has replacement aluminum spreaders mounted to the original welded-on brackets, which don't match the spreaders. Over the years the spreaders have become quite loose and are drooping dangerously.

My thought is to leave the old brackets where they are and install new bolt-on brackets just above them for new aluminum spreaders. The lower shrouds would keep their original mounting position, just below the old spreader brackets.

Does a few inches make any significant difference over the length of a 40 foot mast?

 

[Old Skool Neil]

Being unqualified to answer your question of changing the spreader location, I'll dodge it BUT if you decide to do it be sure to include a compression tube inside the mast at the new bracket location. Without it you risk crushing the mast section.

edit: just read an interesting bit online that addresses your question:
http://www.answers.com/topic/spreaders

particularly the following:
Single spreaders should be located between 50 and 52 percent of the mast height, measured upward from the deck.

By my rough calculation, that gives you a 10" window.

 

[pencema]

Wow! Just read your bio - and you don't consider yourself qualified?

I'm wondering about the need for the compression tube - and how to install one. Assuming the spreader angles are correct, as shown in your referenced article, the compression loads from shroud tension should be pretty small. They're a function of the cosine of the shroud/spreader angles, which should be nearly, but not quite 90 degrees. The cosine would be quite small.

The through-bolts mounting the brackets would have a much greater effect on the mast, but there are ways around having high tension on those. Also, I doubt that Catalina installed compression tubes if the brackets were welded on.

I welcome any further comment.

 

[Old Skool Neil]

Well, I admit to kicking around in boats for a Helluva long time but I didn't want to pretend my experience qualified me to advise on altering rig geometry. That's best left to the pro's.

I've worked on quite a few masts, completely refit one (my current C-30) and built one from a raw extrusion (the Westsail, followed the plan to the letter). Every single one of them had compression posts at the spreaders. And I can attest first hand that my 1977 C-30 is included.

The wall thickness of the C-30 mast ain't much.

 

[pencema]

Well, the main point of my first question was that the mast on my 75 is different from the later C-30's - welded brackets, riveted mainsail track, etc. I respect your experience, but I still can't visualize how to even install compression tubes, even if they are necessary.

 

[Old Skool Neil]

. . . . but I still can't visualize how to even install compression tubes, even if they are necessary.

On my Westsail I welded the tube in place with doublers on the outside but that's an extreme approach. Commonly the tube is placed where the lower shroud tang bolt goes through the mast. Holes the same as the O.D. of the tube are drilled on either side of the mast and the length of the compression tube is cut to match the mast width including any washers if present. The use of a fish wire through the holes prevents the tube from falling inside the mast during installation.

edit:
Just re-read your original post about spreader looseness and drooping. My rigger placed stainless cable clamps on the upper shrouds to hold the spreader tips at the proper angle. Maybe this will address your concerns.