[Rhodes22-list] deck mounted chain plates

[The Rhodes 22 Email List]

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
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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
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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
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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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