[Rhodes22-list] deck mounted chain plates

Sun Jan 11 14:52:11 EST 2015

Keep in mind that we're talking about the inner stays here... Their load 
is going to be considerably lighter than on the outer stays. In fact, I 
read somewhere in the past that their primary function is backup for the 
outer stays, so you don't lose the whole rig in the event of failure of 
one of the main stays.  Consequently, deck distortion may only be a 
factor if you lose an outer stay and you're in an emergency situation.  
'Course then you certainly want to be sure attachemnt point is strong 
enough!

--
Cheers!
John Lock
~~~~~~~~~~~~~~~~~~
s/v Pandion - '79 Rhodes 22
Lake Sinclair, GA
~~~~~~~~~~~~~~~~~~

On 2015-01-11 14:40, The Rhodes 22 Email List wrote:
> I believe the question should be not how strong my shroud is or how much
> weight before my pin sheers.....it should be what is the load before my
> deck distorts. Having worked on large yachts for many years one would never
> dream of attaching a shroud directly to the deck. It is essential the load
> is dissipated into the hull either via a direct hull attachment or via a
> strong-point bulkhead attachment.
>
> You may get away with it on the R22 as the loads are fairly light, but I
> suspect you'll never get the shrouds truly tight as the deck will distort
> as you tighten them up.
>
> My 2c worth
>
> Richard
> S/V Waif R22
> (and S/V Tembaya Tayana V42)
>
>
>
>
>
> On Sun, Jan 11, 2015 at 11:03 AM, The Rhodes 22 Email List <
> rhodes22-list at rhodes22.org> wrote:
>
>> 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.
>>
>>
>>
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