[Rhodes22-list] Mast Bend With A Masthead Rig & Double Lower Shrouds

[Steve]

Excellent Roger.  I was wondering when this was going
to come up.  Those double lowers make mast bend much
easier & more stable.
Steve

--- Roger Pihlaja <cen09402@centurytel.net> wrote:
> Richard,
> 
> It is precisely because the Rhodes 22 masthead rig
> has double lower sidestays that it can exploit mast
> bend.  Please reread my rig tuning procedure.  Note
> that, with a standard rig, I specified about 200 lbs
> differential tension between the fore & aft lower
> sidestays.  With the forward lower sidestays about
> 200 lbs tighter than the aft lower sidestays, the
> mast is constrained from rotating around the mast
> tabernacle at the lower sidestay attachment points
> just below the spreaders.  Now, when backstay
> tension is applied, the mast must bend, primarily
> from the spreaders upwards to the masthead. 
> Actually, the curvature extends below the spreaders
> as well because it is physically impossible for
> there to be such an abrupt discontinuity in the
> strain curve of the continuous mast extrusion.  So,
> the bend curve tends to spread itself out along the
> entire length of the spar with the centerline of the
> mast actually moving slightly forward to relax out
> some of the differential tension in the lower
> forward sidestays in the region around the
> spreaders.  This curvature is easy to see by holding
> a halyard up against the aft edge of the mast while
> varying the backstay tension.  Rather than argue
> with me, I challenge you to go out on your boat, set
> up the rig as per my procedure, & see for yourself.
> 
> Roger Pihlaja
> S/V Dynamic Equilibrium
> 


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