Mast, spreader, shroud design, help - SailNet Community
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post #1 of 2 Old 11-22-2008 Thread Starter
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Mast, spreader, shroud design, help

Hello community, I have searched for information on this topic throughout sailnet. Read many great rigging articles.

Firsts my boat. August 2007 I bought a 1979 SJ built Morgan 45 masthead sloop rig. The standing rigging is not original to the boat. It was installed in 2003. I have unstepped the mast to inspect it and take some measurements. The "I" dimesion is 50'6". single spreader system.

Second, the situation. Looking up the shroud from the chainplate, the spreaders are pitched forward of the mast centerline thus making the shroud pitch forward to the spreader and then back to center at the masthead. I asked the surveyor about that and he had no answer as to why, or if it was engineered right or wrong. Swapping the spreaders side to side will not change the forward pitch unless I flip them over but the spreaders are asymetrical teardrop shaped extruded aluminum. If this rig is from another boat I can understand if the re-install wasn't thought out completely. The masthead and the chainplate are in the centerline of the mast. It just seems odd that the shoud has 2 conflicting angles to it. The mast currently had zero degrees of rake. The spreader is 45 inches long with 2 degrees of forward pitch. the steel rod shows the line from the mast center to the shroud center.

Third my question. Should spreaders ever pitch forward? Since the masthead and chainplate are in the mast centerline, should the spreader be at that same centerline giving the shroud a flat plane?

Forth, my plan. My plan is to cut the spreader mounting plate out of the spreader teardrop extrusion and correct the angle to zero pitch, then, set the correct bisecting shroud angle and reweld it. Results in the spreader and shroud in the centerline plane of the mast.

Any information or books on rigging desing do's and don'ts ?
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post #2 of 2 Old 11-23-2008
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You'll probably want to consult with a professional rigger or marine architect, but having the spreader tips out of a straight line between the chainplate and the mast tangs strikes me as being a bad idea. The tension on the spreader isn't just in compression then, it is also torsional, and most spreaders aren't going to tolerate that well. The shroud, ideally, should be a straight line when viewed from the outboard side looking in.

Is the mast original to the boat? If not, you might want to find out what the original mast and spreaders setup for your boat, as originally designed, looked like.

A good book on rigging is Brion Toss's The Complete Riggers Apprentice.


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You know what the first rule of sailing is? ...Love. You can learn all the math in the 'verse, but you take
a boat to the sea you don't love, she'll shake you off just as sure as the turning of the worlds. Love keeps
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