Join Date: Nov 2007
Location: SF Bay area
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In ideal physics world, no, using spreaders doesn't make a difference because the loads on the two shrouds are identical and the angles of the two shrouds to the mast are identical and the mast is perfectly vertical. Also, in ideal physics world, there are no waves, no air drag, no shock loading, and all spars are perfectly rigid.
In the real world, however, a variety of conditions might cause the pull of the shrouds to be not perfectly identical. Masts bend, sometimes suddenly. And the set up may not have been perfect in the first place. On a beat, the tension in the leeward shrouds drops significantly. If the shrouds connected at the masthead at a very acute angle, the horizontal component of the force at the top of the mast would be much less and the top of the mast would be much more likely to fall off to leeward (either suddenly or gradually).
The downside to spreaders is that, while they increase the horizontal component of the force at the masthead, they do so at the cost of increased tension at the deck and throughout the shroud. If you had a stumpy little mast you could get away without spreaders; spreaders are for taller rigs common to modern sloops (which use modern materials and building techniques that can withstand the higher loads).
Anyway, regarding screwing your spreaders into the mast. A better set up might be to through-bolt the brackets to the mast and just have the spreaders sit in the brackets. This probably won't wear away at the material of the mast as quickly as sheet metal screws would, and you wouldn't have the issue of tightening the screws or enbiggenating the hole once in a while. I recently replaced the small cast aluminum spreader brackets on my boat with a new set of large stainless brackets welded onto a plate with a nonconductive coating underneath. The two plates are held to the mast with four bolts. One sheet metal screw on each side keeps a compression post aligned athwartships inside the mast. It looks quite robust and secure.
s/v Laelia - 1978 Pearson 365 ketch
s/v Essorant - 1972 Catalina 27