[Rhodes22-list] deck mounted chain plates

Sun Jan 11 15:12:44 EST 2015

Hi Richard:
The upper shrouds go to chainplates that are bolted to the hull but the
lower shrouds, at least in the case of my 1979 model, go to chain plates
that attach to the cabin top. 

The chainplates, which look more like tangs to me (i.e., thinner), go
through the outer fibreglass skin and simply bend under the plywood core.
The end is held in place with a 1/2 inch screw. The screw merely holds the
chainplate in place and does not take any of the load. I have attached a
picture of one of my lower shroud chainplates after removal. I also attached
a picture of the cabin top after the chainplate was removed and the area
ground out prior to being filled. The third photo shows the cabin top after
the repair and with a base coat of paint. It is good enough job that I now
have no idea where the chainplates should be placed. I was very clever to
measure the exact locations of the upper chainplates before removing them. I
was not so clever, however, to put my notes where I can find them now. If
anyone with access to their boat at this time of year could give me the
precise measurements for the location of the upper chainplates, I would be
most grateful.

Given that my old chainplates did not fail in 35 years, that makes me think
that the lower shrouds don't carry a large load and I am convinced by
Dennis's logic that the fittings I have in mind are at least as strong, in
fact, are much stronger than the original. The metal is thicker on the
proposed chainplates, there are two pieces rather than one and they are
attached with two 1/4"diameter bolts. That has to be stronger than the
original bent tang. That was my thinking as well but I wanted to check it
out with those on the list who seem better qualified to make such
judgements. Mike's reference to articles that "allow me" to, in theory,
calculate the stress and loads is great but a tad over my head. I should
have known that if I asked for advice on this I would get more than I could
handle.

The problem with the old upper chain plates was that they flex with the
result that the fibreglass cracks around the hole where they come through
the cabin top. Water can get in easily and it seems impossible to
permanently seal the opening and having water get into the cabin top core
seemed lake a potentially serious problem to me. Also, it is not possible to
inspect or remove the chainplates without cutting into the head liner or
doing major damage to the cabin top - as my second photo demonstrates.

Stainless steel does rust in an oxygen free environment and , indeed, some
of mine showed rust where the bend is hidden in the cabin top. So, since I
am doing a major rebuild and would have to paint the deck anyway, it seemed
like the right time to change the chainplates. 

Graham 

-----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-11-15 10:09 AM
To: The Rhodes 22 Email List
Subject: Re: [Rhodes22-list] deck mounted chain plates

Am I missing something here? Chainplates are designed to distribute loads to
the bulkheads and to the hull. The deck is flexible and in the case of the
R22, is pop-riveted to the hull and is not designed to take the loads of the
rig.

Those tangs on the R22 may look flimsy, but they are directing the load to
the right places.

Richard
S/V Waif

On Sun, Jan 11, 2015 at 9:32 AM, The Rhodes 22 Email List <
rhodes22-list at rhodes22.org> wrote:

> Graham,
>
> This article should give you the basics of calculating the load on the 
> chainplates under sail at reasonable winds:
>
> http://www.sponbergyachtdesign.com/articlesengineering.htm
>
> The following forum posts deal with changing some of the basic 
> dimensions of chainplate hardware and calculating the resulting 
> changes in strength:
>
> http://www.boatdesign.net/forums/archive/t-3645.html
>
> The following article deals mostly with the process of replacement in 
> an effort to avoid conditions that might lead to premature failure of 
> properly sized hardware:
>
> http://www.cruisingworld.com/how/chainplates-101-inspect-and-refit
>
> I hope that this helps a bit.
>
> Mike
> s/v Wind Lass ('91)
> Nissequogue River, NY
>
>
>
> -----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.
>
>
> -----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: Saturday, January 10, 2015 8:52 PM
> To: 'The Rhodes 22 Email List'
> Subject: Re: [Rhodes22-list] deck mounted chain plates
>
> Dennis:
>
> That is very helpful. Thanks. I would have believed you if you said 
> the tension was thousands of pounds. Am I correct that the tension 
> gauge would give the tension when the rig is at rest and that it might 
> increase substantially in actual use - particularly when healing?
>
> 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 8:42 PM
> To: 'The Rhodes 22 Email List'
> Subject: Re: [Rhodes22-list] deck mounted chain plates
>
> I know the use of Loos gauge data is against Rummy's religion, but...
>
> Take a look at 
> http://loosnaples.com/how-to-use-pt-series-tension-gauges
> and
> you'll see the suggested tension for a 1 x 19 stainless steel 1/8" in 
> diameter is 240 pounds. The Loos guide goes on to say "In some rigs it 
> may be advantageous to carry a bit more tension in the uppers than the
lowers".
> Sooo... figure 240 pounds in the lowers.
>
> Given that Loos suggests that a 1/8" forestay should carry 320 pounds 
> of tension, and that my forestay is secured with a 3/16" pin, I'd 
> guess is that your bracket should work for the lowers. Give some 
> consideration to the size of the backing plate you'll use though.
>
> Dennis
> Magic Moments
> The glaciers have advanced back down the Detroit River. Aarrrg!
>
>
>
> -----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: Saturday, January 10, 2015 7:04 PM
> To: 'The Rhodes 22 Email List'
> Subject: [Rhodes22-list] deck mounted chain plates
>
> During the rebuild of Agile I removed the chainplates for the lower 
> shrouds with the intention of placing external chain plates on the cabin
sides.
> Subsequently I changed the design doe the windows such that I now need 
> to install deck mounted chainplates on the cabin top. Finding the 
> right hardware has turned out to be a challenge. I found something 
> that looks close to what I need but am unsure about its suitability - see
attached.
> Given that the old chainplates were fairly thin tangs that were bent 
> around the cabin deck core it would seem that this hardware is more 
> than sufficient for the purpose but thought I would check the list to 
> see if anyone has an opinion on these or  an alternative suggestion. 
> Does anyone have a clue what load the lower stays place on the boat?
>
> Graham Stewart
>
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