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Old 26-11-2005, 13:24   #16
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Awe Yes, the chain plates.

Without seeing the boat, it's hard to say how to do the chain plates. The main thing is that they are bigger and better then the originals.

Manufactures save as much as they can by reducing on materials. So, they only put in what is adequate.

One point though, is they should be as accurate as possible!! The less slop, the less movement. And the holes in the hull should be tight on the shoulder of the bolts, not the threaded area. Take longer bolts and cut off the excess thread. Use nyloc nuts and flat washers. SS lock washers have a reputation for splitting apart.


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Old 26-11-2005, 13:33   #17
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Peter:
Chainplates must be engineered to accommodate the loading patterns - You have to transfer the rigging load to a solid structure.
Inboard chainplates pemetrate the Deck, then must be tied to the hull, a bulkhead, or other sound structure. The "engineering", I was referring to, lies in designing the path the load energy must take from deck eye-pad to structure.
Outboard chainplates are generally pretty straightforward.
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Old 26-11-2005, 19:48   #18
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More about chainplates

Golly, I hope I don't wear you two out. I just started using polyester and am glad I did. It is so easy to use and much less expensive. But, like you said, it has specific uses as does epoxy. I started using West System years ago and just kept using it. I was curious about the method you used to plug the holes because I just did a similar job on my deck where the stantions were bolted. The previous owners kept tightenig when they leaked and crushed the deck. I was concerned about the difference in materials, creating a stress problem, and if there was going to be a price to pay later on down the road.

About chainplates. The way the Yorktown is constructed you can't see how they are attached. They are hidden under fiberglass and I'm not sure exactly how to approach getting to them. I was thinking of just adding chainplates to the outside of the toerail and attach them to the hull. This is the reason for all my questions. And then there is the inboard chainplate, what do I do with that one?? It would be nice to hear from another Yorktown owner to find out how they handled the problem.

I've attached a photo of a Yorktown that shows the outboard chainplates and how the were replaced.

Thanks again for your ideas.
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Old 27-11-2005, 11:25   #19
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Question pjfsail

If you have inboard chain plates, I'd recommend repairing/replacing those over adding outboard, for several reasons.

To access the inboards you'll probably have to go threw the headliner. Just below them, there should be a bulkhead or substantial strut that runs down the inside of the hull where the chain plates attach. This keeps the hull from being pulled inboard under stress.

If you attach an outboard chain plate, it'll have to be right next to that strut and possibly even attached to the strut with an angle plate of some sort, depending on your hull construction. It would be best to consult a marine engineer.

Whereas, by repairing/replacing the inboards it would be much less work as well as cost. Not including the engineering and labor involved in the modification. And, how would your sail plan work with outboard stays???

BTW What's wrong with your old chain plates????

Another problem I see with outboard chain plates it that it'll squeeze the hull more with the same amount of effort. That's one reason modern boats have gone to inboard chain plates. Lighter hulls can be built and still handle the stress.
On some of the old wooden boats there use to be beams that ran between the chain plates called Mast Beams with a secondary going down to and attached to the Apron (keel) and Deck Hook. This kept the deck from rising (bulging up) when the vessel heeled over.
So, by adding out board cp it'll be putting more stress on this "Mast Beam" area without the added support.

This is why you see some stays go slack while heeled over. The mast beam area is weak or not adjusted properly. A keel mounted mast has a downhaul rod that is suppose to take up this rising effect. I sure know I need to beef up mine.

Over & standing by......................................_/)
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Old 27-11-2005, 21:36   #20
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wow when I asked this question I did not relize I would get so many answers. I figured by removing the exsisting u-bolt type pates I had,( which probly took up less than 2 square inches of area to displace the force being pulled on it), to Plates that are using 30 squre inches and have a substacialy bigger bolts attaching them. Would streghthen an already proven rig. Why change what is proven? Bigger is better. As far as the hull being squished: I figure as long as somthing is not pulling my mast strait up, the force of the wind will always push in one direction.
Just my thoughts. But as far as how my chain plates work. Well I changed the out yesterday (well... 6 of the 14) I went sailing today. I felt no difference in the performance of the boat. But I did feel like my rig was stronger.
Cheers.
D
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Old 01-12-2005, 10:43   #21
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Here is a web site that has good info on pickling or polishing stainless.

http://www.vecom.co.uk/pickling.htm
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Old 01-12-2005, 16:02   #22
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Nylocks - NEVER

Delmarrey-
Nylock nuts should be considered 'single useage' and shouldnt be used where UV or water immersion is a possibility. Better to use a standard nut and simply drill through the nut and bolt and use RED Locktite on the threads ... and then insert a cotter pin.

The nylon insert is very subject to UV degradation and hydrolysis degradation when continually wetted ... never 'trust' a nylock nut to stay put.
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Old 01-12-2005, 18:43   #23
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Kingfish
Glad you replaced the plates.

Chainplates fail due to brittle or fatigue failure modes not ductile mode where the values that cause failure are predictable.
Fatigue failure mode is simply not something most boat designers consider (or know how to design) when designing their boats .... or the chainplates would probably never fail. Such brittle failure can be attributed to shape and surface finish as well as other special anomalies that are characteristic to such failure. "Beefing up" replacement plates is good .... most of the time - but not always.
Such structure exposed to 'cyclical stresses' typically involves microcracking from the very first load just due to the 'metalurgy' of components. Such microcracks are then vulnerable to crevice corrosion so once the failure starts it propagates within two failure modes: (micro) crevice corrosion and fatigue .... its just one of the little known properties of metals used in cyclically applied stress applications.

Although you just replaced many of the plates, here's some general 'rules' that will enhance the service life of such plates: No welding, no bending, no sharp edges or 'transition' points, passivation, mirror polished surfaces (then electropolish if you have the money), thicker and wider than the original, etc.

A posted digital picture of the 'shape' and configuration would have been helpful to offer corrections, etc.

Hope this helps.
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Old 01-12-2005, 19:37   #24
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Re: Nylocks - NEVER

Quote:
Richhh once whispered in the wind:
Delmarrey-
Nylock nuts should be considered 'single useage' and shouldnt be used where UV of water immersion is a possibility. Better to use a standard nut and simply drill through the nut and bolt and use RED Locktite on the threads ... and then insert a cotter pin.

The nylon insert is very subject to UV degradation and hydrolysis degradation when continually wetted ... never 'trust' a nylock nut to stay put.
I would agree, but I would assume that the nuts would be on the inside of the hull away from the elements. And not so EZ to drill for cotter keys.

I use them on trailer hitches all the time. No failures yet! There is also a crip lock nut, if that really bothers someone.

Over & standing by...................._/)
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Old 02-12-2005, 05:43   #25
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Chain Plates and Fastenings:

The commonest application for “locked nuts” is on any piece of equipment that “spins” (propeller shaft), or vibration prone equipment (engines), where the fastenings (or adjusting set-screws) are often “wire-seized”.

The mechanism most likely to cause loosening of chainplate nut/bolts is the “compression” of the hull under the “clamping” loading of the nut & bolt - a “Soft Joint”*. Under this scenario, the chain plate nuts must be re-tightened after “embedment” in the structure. This would seem to preclude the use of drilled wire/pin type locking devices, or “castellated” nuts, and favour chemical “threadlock” compounds such as “Lok-Tite”, or “Jam Nuts**”.

Curtailing the amount of structural compression (between the chainplate & backer) dictates the use of larger area chainplates & backers, which spread the clamping force over a larger area, thus reducing embedment and resultant loss of clamping force in a bolt which commonly occurs as a result of “relaxation”.

* “Soft” Joints are a joint in which the plates and material between the nut and bolt bearing surfaces have a low stiffness when subjected to compression by the bolt load. In such a joint, the bolt (or nut) typically has to be tightened by two or more complete turns, after it has been torqued to the snug condition, before the full tightening torque is achieved. Often the placement of a gasket in a joint results in a soft joint.

This also (partly) explains the recommendation to excavate the core, and backfill with epoxy, when fastening to sandwiched cored structures.

** Jam Nuts are a thin nuts, normally used under a full nut to develop locking action. Recommended practice is to torque the jam nut to seat only, then assemble a full nut on top of the jam nut and torque to full preload value while the jam nut is held stationary. The same effect can also be achieved with two full nuts if preload must be developed when the first nut is tightened into position.

There’s some good reference notes at:
“ Design Systems and Select Components for Bolted Joints and Thread Fasteners”
http://www.co-design.co.uk/dpg/bol/bolhome.html
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Old 02-12-2005, 06:54   #26
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Actually what Gord describes is the 'best' method of attaching a chainplate to a base. The compressional force induced into the bolt 'drives' the chainplate into base' and creates sufficient force between the plate and the base so that essentially the plate/base is held together by friction of the the two surfaces alone .... and the bolting receives NO shear loads. To do this you must precisely torque the bolts/nuts. Its extrremely bad engineering practice to 'hang' a side load on a threaded bolt.

I'm simply amazed with how many boat designers use full threaded bolts in chainplate applications instead of (torqued) 'shoulder bolts'. Put shear across the threaded cross section of a bolt .... and expect that bolt to become several factors of safety LESS than intended properties of the bolt alone .... called stress risers. Many of the 'top-shelf' boat design houses now are employing structural mechanical engineers to improve/optimize their designs .... 15 years ago this was almost totally unheard of. There is NO reason for a chainplate or its base attachment to fatigue and fail ... all it takes is proper design.

That one encounters so many partial and full chainplate failures only gives testimony of the original BAD designs - designs based wrongly on ductile failure modes rather than designing for fatigue failure. Stainless is a 'nasty' material with respect to fatigue. In cyclical stress applications if not properly designed the material can begin to fatigue fail from the very first day that the new component is installed. Fatigue is a process that starts 'small' and 'grows' with each load cycle. Doubly bad is that when fatigue cracks begin they offer micro sites for crevice corrosion to begin .... two modes of failure all at the same time.

To my engineering mind, MOST of the chainplate designs I see are faulty especially the ones that use a single plate and a single attachement surface to the base which puts all the connections of the joint into a 'cantilevered' stress ..... and that reduces the safe working load of the 'connectors' by an approximate value of FOUR !!!!!
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Old 17-12-2005, 05:48   #27
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Thanks to Ken aboard s/v “Alaya”, who posted this sizing chart for chainplates (from Skeen's Elements of Yacht Design) at the SSCA forum:
Goto: http://cruisersforum.com/photopost//...php?photo=1325

See the SSCA “Chainplates” thread: http://www.ssca.org/sscabb/index.php...=10&topic=2140
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Old 22-12-2005, 20:16   #28
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kingfish,
I good navel architect can predict the shroud load to come up witht the design tension loads for the chain plate. As a structural engineer, I can tell you that size of the chain plate may not govern its strength but how it is connected to the hull (ie. how do you transfer the force from the shroud to the plate to the hull). With respect to richhh comments regarding clamping forces, I would never design this type of connection on that basis as you really don't know how much relaxation occurs after the bolts are torqued.

From my point of view, for a given design tensile load, the stresses in the plate need to be checked at the net section (i.e. at the cross section cut through the first bolt), the shear forces on the bolts need to checked and finally the bearing stresses as the bolt bears on the fiberglass. It's a matter of dissecting the load path - shrouds pull on the plates, the plates shear the bolts, the bolts bear on the fiberglass - and looking for the weakest link in the system. Hopefully if it is designed properly, the connection fails in as ductile a manner as possible - if you run the numbers and know the materials you are working with you can predict the failure mode.

In my mind, a well designed chainplate provides a smooth load transition from the shroud to the plate (ie the angle of the should should match the chainplate). If if doesn't, there are other forces that have to be addressed (i.e. out of plane bearing type stresses on the hull).

Cheers,
Kevin
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Old 22-12-2005, 20:46   #29
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Re: Nylocks - NEVER

[QUOTEDelmarrey-

The nylon insert is very subject to UV degradation and hydrolysis degradation when continually wetted ... never 'trust' a nylock nut to stay put.
[/QUOTE]

The custom outboard chainplates on my boat have the nylocs. Of course the nylocs are on the inside and no UV would be able to attack the key component. This is still solid after 10 years.
On another note, this cannot be a fly by night project. Profesionally done along with bonding the deck to the hull, sealant, and sterling LP was $30,000.00. Oh yea, flat wound standing rigging was also added. 1/3 of that was the chainplates and rigging.
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