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Outboard Chainplates: Why?

8K views 34 replies 16 participants last post by  MikeOReilly 
#1 ·
I've seen several boats where the chainplates appear to have been moved outside. That is, they have been bolted through the topsides rather than sunk into the deck and bolted to a rib. I think this is normal on some of the old Garden Formosas. But I've seen a CT 54, a Peterson 46, and recently a Southern Cross 39 where this has been done, and I'm pretty sure that these boats did not come from the factory like this. I cannot fathom why someone would do it as an aftermarket modification. Anyone know why someone would do this?
 
#2 ·
I suspect they had serious chainplate leakage issues on the through-deck-to-bulkead connections and decided to eliminate that possibility. I don't think it's all that uncommon.
 
#13 ·
I was and remain suspicious that something like this was behind the modification, some kind of tipping point where it was no longer possible to repair or refit to the original design spec due to accumulated structural damage. I have (somewhat instinctively, since I lack hard facts) shied away from these boats, but my curiously was piqued.
 
#3 ·
A lot of people believe (mistakenly) that external chainplates are less subject to corrosion because there isn't a dead space where it passes through the hull. In reality there is more area in externals that is subject to corrosion, since the entire side of the chainplate against the hull is not a danger zone.

There are some structural advantages since it allows a wider spreader base, and reduced tension on the rig, but for most boats it isn't a meaningful difference.
 
#9 ·
No they aren't. You still have to get to the bolts on the inside, and you still have to completely remove them to inspect them. I have replaced a lot of external chainplates that looked fine from the outside, but the entire back was destroyed from poltice corrosion.
 
#6 · (Edited)
On some older yachts (like Suhaili.. and mine...) outboard chainplates are simply required by design - there is nothing located further inboard strong enough to carry the loads.

One often overlooked disadvantage of outboard chainplates is that the side-stays, mounted further out, prevent a nice tight headsail sheeting angle meaning you can't sail as close to the wind as you might if they were further inboard.
 
#11 ·
Pros: easy to inspect (I can remove the bolts one-by-one to inspect without taking down the rig); no holes on deck to leak; easy to replace (when the time comes).
Cons: you lose some sheeting angle; they can damage other boats tied alongside (fenders!); they might look ungainly on a more modern design.
 
#12 ·
Makes it slightly easier to transit the side decks, with shrouds attached to the topsides. At the least, you lean inboard to get around the shroud, as opposed to outboard on so many that pass through the side deck.

However, I would never modify an original chainplate design.
 
#17 · (Edited)
..although be warned that the forces exerted by the chainplates can be so enormous that if the job is not done properly with the addition of adequate bracing and force distribution under the guidance of a qualified shipwright, the structural damage that can result (even if you don't lose the rig in the process) can be so extensive it's often cheaper to get another boat!

Personally, if I saw evidence that the chainplates had been relocated on ANY boat I was looking to buy, I wouldn't care how good anything else is... I'd run a mile.:eek
 
#18 ·
Sorry but that is just alarmist and not helpful to the OP. Many boats have had this done and nothing bad came of it. Half the fleet of CSYs had it done. Chainplates fail and that is a fact. Having them in a place where they can be inspected and replaced easily if needed is just good seamanship.


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#19 ·
Sorry but that is just alarmist and not helpful to the OP. Many boats have had this done and nothing bad came of it. Half the fleet of CSYs had it done. Chainplates fail and that is a fact. Having them in a place where they can be inspected and replaced easily if needed is just good seamanship.

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This is just not true. The only way to inspect external chainplates is to access the bolts on the inside and remove the plate from the exterior of the boat. it takes just as much disassembly to get to those bolts as to get to the old plates in almost all cases.
 
#21 ·
On a CSY no I can't say I remember doing so. But I sold titanium replacement chainplates for two years. I have disassembled a lot of boats to get at them, and never really noticed accessing external chainplates being any easier to get too.

The real answer is just to get rid of the stainless and buy titanium btw. For a couple hundred bucks a boat you never have to access them again.
 
#22 ·
I don't think I've seen many hard-core blue-water boat without chainplates on the outside (though just about every boat here takes on serious miles every year in open ocean). I think there are two or three boats on my dock here that are either in the process of or have just completed doing this. It allows them to expand the length of the chainplate (by a lot). Doing this on deck would take up too much real estate. But going down the hull with more bolts increases the spread of the load. Also, all bolts are pulled from the same plane, so if one does fail, the others can still hold fast and the direction of forces never changes, meaning the rig maintains its shape, although possibly weaker.

Jeanne Socrates' boat Nereida (that she completed her solo on and has been hanging out here in Mexico for the last year) drew my attention because the SS chainplate for the headstay goes straight down the bow and to the waterline. It's gotta be 3 to 4 feet long. Now, I haven't asked her (but I will and will update) but I assume that that length creates some strength that the holes so close to the water line are worth having for some structural reason.

You won't see this modification on many smaller boats that are sailing lakes and coastal trips, but I'll bet it's quite common around the world, as that is what I am seeing here in Mexico. It helps that getting custom SS work done here in Mexico is inexpensive and the best guys do a good job. Maybe it's just a fad...maybe not.
 
#24 ·
TQ... do you know if any of the loads are transferred to the hull proper below the joint on the inside??
 
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#27 ·
Pretty. Shiny. But those bolt heads exposed to saltwater spray are worrisome. Hopefully it is easy to remove, clean and inspect the bolts. Better if such things are inside the hull. This type of plate is more commonly made up with studs welded into it making one solid piece. Nuts on the inside. No spray in the cracks between the head and plate that way.

Those fancy plastic guards look like they are hiding some corrosion of the fittings underneath. There is rust peeking out and stains under the rub rail. Worrysome.
 
#30 · (Edited)
With one inch thick fiberglass I wouldn't be so concerned with webbing to spread the load. Also the comments about salt water getting under the bolt heads is a bit alarmist. There are many deck fittings with bolt heads so why do we need to hide chainplate bolt heads below decks? A proper bedding (I suggest MaineSails butyl bedding procedure) makes these a no brainier.

Thousands of boats have moved their chainplates outboard. It works. Of course you have to remove them to properly inspect them so the argument about "inspecting the bolts too" is just a little over the top. You remove the chainplate, inspect it and the bolts and reinstall. So much easier on some boats. On boats with easy access there is no need to move them. On an Islander 32 they are right there in the main saloon and you can stare at them while you finish dinner and sip your third rum of the evening. Never a need to move those. On a CSY and many other boats they are in impossible places. Some so f@#%d up that you need to build special tools and spend two weeks watching your knuckles heal.


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#31 · (Edited)
Bleemus, if I understand you right, you're suggesting that a 1" thick hull is sufficient to carry chainplates without any other means of support? And that because "thousands of boats have moved their chainplates outboard" it's okay to just do it in your backyard without checking with a shipwright first?? :eek

Sure, some yachts have chainplates in strange places and are extremely hard to get at, but I would suggest they are there for a reason and to shift them without checking with an expert that it's okay to do so first is folly in the extreme.

I'm no structural engineer, but the way it's been explained to me is: rigging loads on the chainplates of medium-sized yachts you refer to are big (in the 1000's of kgs). Shifting chainplates outboard without altering the rig to suit means those 10000's of kgs are no longer acting vertically, but pulling inward also, squeezing the deck together like you might squeeze an orange, and causing it to buckle upward in the middle. Also, having no reinforcement for the bolts outboard means the hull fabric must take the loads as best as it can instead of these forces being distributed down to the keel like they should be. Assuming the new chainplates don't simply tear out in the first storm, this can, over time, cause stress cracking (and leaks) in all kinds of harder-to-get-at places (including the hull-deck joint) than where the chainplates used to be.

Either way, the result isn't good for future sale of the boat, nor the damage necessarily obvious to the average person. Anyways, don't say you weren't warned. :)
 
#32 ·
Maybe a no-brainer for you. Bedding with Butyl tape does not solve the crevice crack corrosion issue with the bolt heads. Those 8 relatively small bolts in the picture are more critical than other exposed bolts on most boats. From experience we know that those toerail bolts, and all their cousins, often break during removal. And they are not especially critical to the rig staying up. Staring at them while cooking is not apt to reveal cracking. The telltail rust stains in that picture hint that there is already trouble. It's too bad that the problem wasn't solved with more functional elegance.

As said by others above it would certainly be a good idea that a naval architect signs off on the plans. I know my current boat's topsides would not support the rig as they are there only to keep the wind, water and thieves on the outside...the shroud forces penetrate the deck with a simple weatherproof weldment and then continue via rods to the floors. No exposed bolts. The designer may have exchanged the problems of the original chainplates with a new set of problems.

No a trivial no-brainer project at all.
 
#33 ·
Everyone has their opinions and I respect yours but have no idea what your background is and since you don't know mine you have a fair right to disagree. I have built enough boats, rebuilt enough boats and repaired enough boats to feel confident that I would make a safe transition to out board chainplates. In fact the boat I am looking at on Monday, if I buy it, will get that treatment.

I have sat in design meetings with some notable people. Ted Hood, Bill Lee, Jim Taylor and Chuck Paine come to mind off the top of my head. It has always amazed me how much of what they do was by feel and experience and less so based on computer models and finite element analysis (FEA).

We all make our decisions and live with them. That is what sailing is all about. I wish you good decisions. Cheers.


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#34 ·
Everyone has their opinions and I respect yours but have no idea what your background is and since you don't know mine you have a fair right to disagree. I have built enough boats, rebuilt enough boats and repaired enough boats to feel confident that I would make a safe transition to out board chainplates. In fact the boat I am looking at on Monday, if I buy it, will get that treatment.

I have sat in design meetings with some notable people. Ted Hood, Bill Lee, Jim Taylor and Chuck Paine come to mind off the top of my head. It has always amazed me how much of what they do was by feel and experience and less so based on computer models and finite element analysis (FEA).

We all make our decisions and live with them. That is what sailing is all about. I wish you good decisions. Cheers.

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I wouldn't assume the average forum guy to have the judgment and expertise necessary to factor a redesign like this. I think that is what everyone is trying to advise on. Surely the debate will continue.
 
#35 ·
My Rafiki has undergone the externalized chainplate surgery. I don't know if it is better than the original design. I do know the external plates are completely accessible, inside and out, and are 2 to 3 times larger. This boat has circumnavigated. I'm not a structural engineer but plates, bolts and hull structure appear fine.

The advantages of our external plates are many, as has been mentioned. I (naturally) appreciate Bleemus' perspective. All I can do at this point is affirm that so far, the shift to external chainplates has been a benefit.


Why go fast, when you can go slow
 
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