[Rhodes22-list] deck mounted chain plates

[The Rhodes 22 Email List]

Hmmm. I guess the best I could suggest for an upper limit to shroud tension
is 2100 pounds, the breaking strength of 1/8" 1 x 19 stainless steel cable.
You could fire up a CAD program and doing a stress analysis of the
replacement chain plate to verify it can take that load, but that seems a
bit over the top.

I guess I'd go back to the fact that the Rhodes' forestay is loaded more
heavily than the lower shrouds, both at rest and dynamically. The pin for
Magic Moments' forestay is 3/16", which will shear considerably sooner than
the 1/4" pin used by the part you're considering at
http://www.rhodes22.org/pipermail/rhodes22-list/attachments/20150110/e0fd47a
f/attachment.jpg. In addition, the new part appears to be a doubled piece of
stainless, 0.1" thick - which is thicker than our more-heavily-loaded
forestay tang. That leads  me to believe the replacement part will take the
load from the lower shroud to its mounting bolts without a problem.

The new chain plate has 2 - 1/4" mounting holes, and a 1/4" coarse thread
bolt has 1,750 pounds of tensile strength (if you believe charts on the
Internet). So the bolts should be adequate to take the 2,100 pound load to
the backing plate. Sooo... my vote is that the replacement part seems OK.

The last consideration is the size of the backing plate and / or epoxy plug
securing those bolts. To my thinking, this is the weak link in the chain,
but I don't have anything to reference for a suggestion.

Good luck with it.

Dennis
Magic Moments
Getting my sailing fix from books till the water softens


-----Original Message-----
From: rhodes22-list-bounces at rhodes22.org
[mailto:rhodes22-list-bounces at rhodes22.org] On Behalf Of The Rhodes 22 Email
List
Sent: Sunday, January 11, 2015 8:56 AM
To: 'The Rhodes 22 Email List'
Subject: Re: [Rhodes22-list] deck mounted chain plates

Thanks Dennis. However, the question related to the maximum tension that the
chainplates would need to withstand in use rather than the matter of tuning
the rig. I just don't want to use deck mounted chainplates that are not
sufficiently strong. That said, your reference to tension gauges will be
helpful should my boat ever see water again.

Graham Stewart


-----Original Message-----
From: rhodes22-list-bounces at rhodes22.org
[mailto:rhodes22-list-bounces at rhodes22.org] On Behalf Of The Rhodes 22 Email
List
Sent: January-10-15 9:18 PM
To: 'The Rhodes 22 Email List'
Subject: Re: [Rhodes22-list] deck mounted chain plates

Graham,

The idea is to set the rig tension while the sails are down / furled. Take a
look midway down the page at http://loosnaples.com/how-tos/tension-gauges to
see Loos' suggested variation in shroud tension as the boat heels. I suspect
something similar happens in the forestay / backstays.

The picture shows that a rig that's too loose loses all support in the
leeward shrouds, and notes that "The lateral stiffness of the mast and the
fore and aft stiffness of the spreaders is reduced by a factor of 2 when the
leeward shrouds go slack".

Dennis
Magic Moments
Wondering if rig tension should be reduced in sub-zero temps.