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chainplates...

 
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Steve Abel



Joined: 16 Dec 2005
Posts: 37
Location: Mount Vernon, WA

PostPosted: Mon Sep 24, 2007 1:47 pm    Post subject: chainplates... Reply with quote

I may have opened pandora's box... or maybe what I didn't know wouldn't hurt me. We just finished the passage from Seattle to SF, and as part of our continuing outfitting of the boat for full-time cruising, my wife opened the chainplate inspection areas on our T-37. She found some rust around one of the bolts on the aft starboard chainplate. So, I asked her to remove the bolt, and the dang thing sheared off. Could this be the "crevise corrosion" that has been discussed here before. I removed the chainplate, and found moisture in the deck core.

I know that we'll have to replace all the bolts/studs that hold the chainplates, and I've downloaded all the info from the FTP site. Now the big question: Is is reasonable for us to try this without any specialized knowledge in fiberglassing or metal fabrication... or might we be better off having a local yard complete the job. If it's relatively simple, I'm game to attempt to tackle it. But I don't want to have the mast come down because I goofed on something relatively simple.

In obtaining quotes from boat yards, what is the average amount of time that may take to replace the studs on the plates? Also, the chainplates themselves look OK... would you recommend replacement, or just having them checked. The boat is a 1983 model, and has completed one circumnavigation.

Thanks for your input.

Steve
Sitting in Alameda, CA with one chainplate removed.
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Steve Abel
SV Victoria Rose
Tayana 37 #384
Sailing out of Anacortes, WA
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jgrant029



Joined: 17 Oct 2005
Posts: 76

PostPosted: Mon Sep 24, 2007 4:30 pm    Post subject: Reply with quote

Steve,

I just finished my chain plate beds and it wasn't too bad. It took to days per to complete. That's everything. Fein tool cutting, removing old material, rebuilding etc. It wasnt too bad really. I've got many photos. Now may Togers may think that I took the wrong path as I rebuilt the beds to original instead of anchoring to the outside of the hull. My thought was that the original lasted 20 plus years, my job is better than original, so it should be good for 20 plus that will make me 60 plus. Anyway, I would be happy to discuss. Call me on SKYPE my screen name is jgrant029 or email me at mail@svab.ca. Also there is a few photos on www.svab.ca

Jim Grant
1983 T-37
# 370
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Steve Abel



Joined: 16 Dec 2005
Posts: 37
Location: Mount Vernon, WA

PostPosted: Wed Sep 26, 2007 7:52 am    Post subject: Reply with quote

After reading all of the ftp info regarding the chainplate knee replacements, I'm leaning towards having a boatyard complete the repairs. Primarily because we're currently cruising, and don't have all the facilities and tools available that we would have had while living in a house. What I'm wondering about, is to have the old knee area drilled and injected with epoxy, and then have the new bolts (1/2") go through the hull. If the loading on the bolts is primarily in shear, and the knees act somewhat as a spacer, it would seem that this would be a relatively easy fix, especially since the cabinets would not need to be dissassembled. Any comments regarding this approach?

Steve

PS- for those who haven't checked their chainplates... I really recommend that you do it. In some cases, I really didn't want to know if they needed replaced, and they looked good from the deck up. Besides a stud that crumbled, the chainplate is developing a crack. I have yet to pull the others. I took that aft lower plate into the metal shop, and the foreman immediately said... hmmm, another Tayana chainplate. Guess they've done a few of them.
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Steve Abel
SV Victoria Rose
Tayana 37 #384
Sailing out of Anacortes, WA
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Kamaloha



Joined: 28 Oct 2005
Posts: 225
Location: Lebanon, NH

PostPosted: Wed Sep 26, 2007 7:48 pm    Post subject: Reply with quote

Either way. It took me about a week to do mine all around. I left the knees in place and injected epoxy from the outside, chopped all the studs flush, and replaced with 4 x 1/2" studs through to sister plates on the outside. I spent about $1000 to have seven new chainplates and sister plates manufactured in 314 stainless. I made them 50% thicker and about 3/4" wider than the old ones, for a gain of about double the cross sectional area. The only tools I really needed were a few half inch bits (broke a few) and a big drill with side handle, and an angle grinder to cut off the old ones. The fabricator made a drilling jig for me so all the holes went in parallel and straight. Details are on the FTP site.
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Charlie
s/v Kamaloha
1987 T37 #542
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hjkarten
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Joined: 21 Jul 2005
Posts: 642
Location: Del Mar, California, USA

PostPosted: Wed Sep 26, 2007 9:38 pm    Post subject: Reply with quote

Steve,
Glad to hear that you had a safe journey to San Francisco.

The presence of some moisture in the core of the deck is not too surprising. The critical issue is how far horizontally this extends. I cut back only a short distance before I got to solid dry deck core. I let it fully dry out, flushed liberally with Acetone, the gouged out still more, and then packed the cavity with lots of Kitty Hair (polyester mixed with chopped fiberglass).

Each person's experience on the chainplates may differ.
I found that there was severe crevice corrosion of our chainplates, and some of the cracks extended most of the way through the thickness of the chainplates. They must all be replaced. Sorry about that, but if you are planning a circumnavigation, it would foolish not to do this right.

As for the bolts, they are short bolt with a piece of steel welded across the head. The bolts are then pushed [sic] into some plywood and the short welded rod is intended to prevent them from rotating as you tighten down on the chainplates. But the design encapsulates the bolts in a completely invisible manner. You have no way of readily opening it up and checking the condition of the bolts.

Because of both the design and construction, water often leaks in, and the wood starts to rot and the steel bolts corrode. Over the years the plywood turns into mushy compost. Hoping that you can put in enough epoxy to solidify that mess is a fool's dream. It has to come out, and the whole cavity cleaned all the way back to the fiberglass hull. TaYang put in additiona filler of something akin to Bondo. Get it all out! And you have to then replace it with a solid piece of fresh epoxy saturated oak or teak. Then glass over the gusset/knee, run the bolts from the outside with an external backing plate. The bolts will hold the new chainplates in the same location as the old ones. But now you will be able to pull the bolts every few years to check on their condition.

There is also a small seam that extends from the hollow bulwarks into the deck at the exact point where they cut the hole for the chainplates. You have to open that small seam and pack it with "Kitty Hair" - a mixture of polyester and chopped fiberglass. This will hopefully prevent any new leakage into the wood backing.

The job on all four chainplates and gussets will take about three to four days. But cutting into the individual gussets requires a small grinder, and makes a hell of a mess of the interior, with lots of fiberglass dust. Since all your worldly possessions are now on the boat, you may want to put everything into large sealed plastic bags before starting this project.

The tools needed are fairly simple, and the methods are pretty simple, including use of a grinder, aligning all the holes in the new block, the hull, the exterior steel backing plate, the new fiberglass covering and the new chainplate. Hard to know if this is more than you are up to doing.
But do not ignore the problem. Depending upon the design and location of your cabinets, you may not have to actually remove any cabinetry. We were lucky in that regard.

Have you also changed all the standing rigging?

If you can postpone the job until you arrive in San Diego, I'll be glad to show you how we did it on Night Heron, and lend you all the necessary tools to do it yourself, including grinder, sanders, drill press, etc.

regards,
Harvey Karten
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Harvey J. Karten
Tayana 37
Hull #84
Del Mar, CA 92014
EMail: hjkarten@ucsd.edu
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Kamaloha



Joined: 28 Oct 2005
Posts: 225
Location: Lebanon, NH

PostPosted: Thu Sep 27, 2007 2:14 am    Post subject: Reply with quote

Harvey, your boat is much older than mine, and Steve's is somewhere in the middle. They changed the design between yours and mine; it will be interesting to see if Steve's is like yours or like mine. In my case the bolts were welded to an SS strap that is at least the width of the bolts, as I had to drill through that strap to put my four bolts in, which was a big PITA; I could only find non-cobalt bits in Sint Maarten and I had to sharpen the bit after every hole, and broke several bits as well. However, my blocks were solid teak or mahogany, not plywood, and none of them were wet or required removal and replacement; the knee was quite waterproof, and all of my damage was external to the knee, i,e, at the surface where the bolts exited the knee. Thus I didn't have to do any of the messy fiberglass work you described. The reason I had to inject epoxy is that there was a void between the steel plate and the inside of the hull of about 5mm, and when I tried to tighten the bolts it started to buckle the hull. After discovering this on the first one, I subsequently drilled only the top hole and only from the outside, filled the entire cavity with unthickened epoxy so it would drip in, and then drilled the rest of the holes using the drilling jig. It was still a non-trivial task, but I did no cutting and made little mess in the cabin once I figured out how to contain the hot metal grindy bits created by chopping the existing bolts off.

BTW, I think this would likely have all been avoided if Tayana had used shoulder bolts sized such that the shoulders extended into the chainplates. This is the required technique used in aircraft for attachments of this nature. It is because the bolt was threaded where it left the knee that we exacerbate the crevice corrosion problem. I tried to do that with my new bolts, but wasn't able to either since now that the bolts go through to a curved hull they each end up a different length on the inside, so only the bottom bolt has its shoulder the proper length.
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Charlie
s/v Kamaloha
1987 T37 #542
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hjkarten
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Joined: 21 Jul 2005
Posts: 642
Location: Del Mar, California, USA

PostPosted: Thu Sep 27, 2007 5:58 am    Post subject: Reply with quote

Hi Charlie,
The construction of the gussets on your chainplate base is a much better design, except for their use of that buried steel plate and bolts. The buried plywood was not treated or sealed with epoxy, was completely delaminated and soggy. I initially experimented with drilling small holes and injecting Smith's CPES. When a bolt snapped and I realized that I had to open the gusset/knee, I realized that there was no way I could have solidified that soggy mess of compost. If yours was filled with a solid block of dry teak and then you filled the gaps with epoxy, you were much luckier than I.

Having the bolts on the outside of the hull now will allow me (or whoever follows as owner after I leave this mortal coil) to simply pull the bolts to check on their condition.
regards,
Harvey
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Harvey J. Karten
Tayana 37
Hull #84
Del Mar, CA 92014
EMail: hjkarten@ucsd.edu
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Rich Hampel



Joined: 15 Aug 2005
Posts: 391
Location: Chalfont Pennsylvania

PostPosted: Thu Sep 27, 2007 7:06 am    Post subject: Reply with quote

Guys
Ive stated several times in my rants in the past that the whole original design of these bases has some deep elemental flaws that develop over time that really should be considered when 'restoring'.

Structurally the OEM design was quite suitable although somewhat complicated and vulnerable ....... but nevertheless still good when you omit the 'wood' rotting away. That wood (between the internal plate/strap and the fiberglass base) performed an "important structural function" ... not just a geometric 'filler'.

1. those chainplates have a bend in them .... structurally MUCH weaker than if the plates were straight. The relatively sharp bends (stress risers) being the principal site of fatigue fracture. I still recommend that the plates be mirror polished, have NO sharp edges or 'irregularities', and be made 'much thicker' (in cross section), and that 'bend' be a longer radiused bend ... not a 'kink'.

2. Through-bolting to the outside is going to put the bases (and especially the bolts) in whats known as 'cantilever stress' .... requiring the overall structure to be 4 TIMES stronger than if in simple (pure and stronger) compression/tension. ANY time you make the stress 'turn corners' you wind up with an inherently WEAK structure.

3. When the wood in the 'contraption' rots/fails, the system transfers/uses the fasteners/bolts to support the loads ... never a 'good' idea to use bolts to support 'loads'. Fasteners should be primarily forcing the adjacent structures together in compression .... and the extreme friction between the mating 'faces' due to the compression should be what transmits the loads ... NOT the bolts.

4. If you remove that internal 'contraption' that holds the original bolts in place, you will have to somehow otherwise need to 'imitate' the FUNCTION of the contraption. My cursory analysis is that Perry, et al did have the FUNCTION correct in that the "E shaped contraption" does REACT to the forces of the bolt tightening ..... and both the chainplate AND the contraption being 'forced together' ***STIFFENS*** the web of fiberglass being held between them. If you dont have these reaction forces acting on the fiberglass web of the base it now becomes much weaker!!!!!!! Sister plates behind and in contact to the web to react to the chainplate being forced into the fiberglass will return you 'close' to the original design.

Simple speak... the chainplate and that 'internal contraption' make the
bases STRONGER. Through bolting to the outside of the hull removes these compressional forces ... weaker. It is NOT a good idea to 'hang side-loads' on 'bolts''.

I paraphrase Frank Timmons: the Ty37 chainplate system and bases are a WTF?? design.


In all reality and starting from scratch, I would turn the damn plates 90 degrees in the horizontal (suffer 1" less deck space clearance) , have NO bends in the plates, have the longitudinal/long axis of the plate STRAIGHT-in-line between the base and the spreader connection, have the plates in the form of a clevice or 2 plates per connection, and that which connects to a single (and accessable from both sides) thick WEB of fiberglass (at 90 degrees of the present design). All pure tension/compression and in a **straight direct line** (no stresses 'turning corners'). Think of conceptually building an entirely new base system out of RUBBER BANDS not metal ... and you will come close to 'very good' design.
Benneteau elegantly does this with 'rods' ... but needs to be much stronger/beefier in a 'blue water' boat.

That internal 'contraption' served an important stress function ... other than 'just holding bolt heads in place'. If you remove or omit it. You will have to substitute 'something else' to do that job !!!!!!
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Ty37 #423 "Aquila"
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hjkarten
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Joined: 21 Jul 2005
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Location: Del Mar, California, USA

PostPosted: Thu Sep 27, 2007 7:22 am    Post subject: Reply with quote

Rich,
Can you translate that analysis into the actual loading required for safe construction of mast supports/standing rigging. How would the two alternate configurations meet that requriement. If the safe loading is X foot-pounds, what is the capacity of the original design? How much safe loading margin would your less favored solution carry? (through bolts with backing plate and a solid filler vs. a totally internalized bolt system bedded in plywood then covered with fiberglass, resulting in the compression sandwich now adding the hull). I think that some of us have trouble seeing the severity of the compromise.
regards,
Harvey
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Harvey J. Karten
Tayana 37
Hull #84
Del Mar, CA 92014
EMail: hjkarten@ucsd.edu
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Rich Hampel



Joined: 15 Aug 2005
Posts: 391
Location: Chalfont Pennsylvania

PostPosted: Thu Sep 27, 2007 9:13 am    Post subject: Reply with quote

Apparently how all the 'good' boat designers arrive at the strength requirements is to conceptually attach line/rope at the mast head, pull the line until the boat reaches 45 degrees of heel and then either calculate/measure the loading in the capshroud wire. This is an assumption of maximum Target/functional applied stress on the rigging due to the magic of trigonometry. If you go beyond 45 degrees of heel, the induced load becomes less, 45 degrees over develops maximum stress in the cap shroud.

Perry has 'suggested' in internet conversation/posting that he then uses a saftey factor of ~4 (to handle the 'unexpected' or 'unforseen' or loads that can occur).
Myself being a one-time designer of mega lift and 'crane' type design would use a factor of 5-6 (intentional belt and suspenders and glue approach).

So, all you really have to do (and with a knowledge of trigonometry) is pull your boat over until it reaches 45 degrees ... and then simply MEASURE the tension in a cap shroud by a tension gage .... and then trigonometrically calculate all the vertical and horizontal loads as would REACT to these values IN the bases. Looking at his design I see additional 'back-up' and therefore make the claim that the actual FS value of Ty37 at the chainplate base probably approximates to FS 5 ... even FS 6.

If you assume that Perry used a FS of 4, then selected all the components/structure based on this 'four times stronger than needed' value.... youll have a 'starting point' with which to 'back-calculate' his design intent. Simply look up the ultimate tensile values of the rigging or weakest component in the cap-shroud rigging assembly - as selected on your boat. ... and that should give you a fairly close value of design stress - including the FS=4 value.

From my viewpoint, I dont think its necessary to do the miniscule calcs. I assume that everything needs to be 4 times typical loading to be consistant with Perrys design ... and go on from there.

My gripe with though bolting through the hull sides and leaving the plates attached to the original base.... only stresses the important inner base (web) from one side only AND unduly depends more on the bolts rather than the 'structure' to do most of the 'work'. Move the plates to the outside ... no problem as the bolts can be run-up to the proper torque and will probably stay torqued. With bolting running trough from the outside to the inner face of the original base, unless you have or added some sort to compression member (sister plate, ferrule, tube, etc.) between the base face and the hull side to REACT to the compressional force that results when you torque down the bolts ... that WEB/face in the present base is going to want to move/creep towards the hull (also possible inducement to cause buckling failure of the web), the bolts will relax .... and you have nothing to support the load other than the cross section of the bolt (a BAD functional design in 'cantilever' stress) VERSUS the projected cross section of the holes that were cut into the face of the fiberglass.
-----------------------------------------------------------------------------
Simple calc. based on 'guestimate' strength values to arrive at web thickess of the web:
webthickness = "x" inches.
Assume breaking strength of 5/16 wire rope = 3000 pounds force
Assume 5 bolts @ 3/8" dia.
Assume compressional strength of 'fiberglass' at 25000 psi.
Factor of Safety = 4

Projected cross section load bearing area of fiberglass web.:
3/8" X 5 bolts X 'x' thickness of web = 1.87 times "x" square inches = square inches = 1.87x = square inches, where x = webthickness in inches.

Correction of FG material for Safety factor .... 25000 / 4 = 6250 psi (target max. design stress in FG web)
(1.87x) X 3000 lb. = 5600x lb. max load bearing of 5 holes @ FS=4

3000 lb. = 5600x lb
x = .53" Thick .... and we KNOW that that oem web is ~1/4" thick.

sooooooooo it appears we MUST depend on the force of the two opposing structures (plate & contraption) being forced together to prevent the web from compression/crush failure AT the bolt holes as the FORCE of the two against the web 'distributes' the reactance bolt-load across a MUCH larger area than 3/8 X 5 X .25 = .47 sq. inches of bolt bearing surface in that web
..... and we KNOW that its impossible to have all the bolts bearing simultaneously/equally in the bearing SURFACE of those holes.

I dont have any ref. texts available so all those 'values' are guestimates and Im not 'seeing too good' today ... so Id appreciate if someone can check the calcs.
The above calc. is based on the max breaking strength of the wire (and I dont KNOW what the FS of the selected wire is/was) and NOT the max. actual developed load with the boat forced to 45 degrees heel. If the wire is/was selected with the typical FS=3 or 4. then the above values/results would have to be corrected. Get your gauge out, heel the boat over and read the gage, then recalculate.

Wink
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Ty37 #423 "Aquila"
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Sonamara



Joined: 10 Feb 2007
Posts: 12
Location: Anacortes WA

PostPosted: Wed Oct 03, 2007 4:12 pm    Post subject: chainplates... Reply with quote

I appreciate what an important topic this is and donít want to minimize it in any way. But I would like to know if any Tanaya 37 ever had a mast come down due to chain plate failures. Has anyone actually ever heard of this happening?
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Rich Hampel



Joined: 15 Aug 2005
Posts: 391
Location: Chalfont Pennsylvania

PostPosted: Thu Oct 04, 2007 6:37 am    Post subject: Reply with quote

I guess I was the one who started all this 'chainplate' contoversy.

The short version is: I periodically 'proof load' my rigging to 60%+ stress levels to 'check' the rig integrity. In doing so I had a caststrophic failure that resulted in the bobstay breaking free from the bow connection, the bowsprit raised about 3 ft., both forward lower chainplate base ripped out due to the impact .... and the mast top 'went-back' about 4 ft. 60% stress values would normally be encountered when the boat is loaded to 45 degrees of heel.... can be encountered in severe weather conditions, etc. especially if the backstay is tensioned to a 30% value to affect 'normal' headstay tension/sag.

I found that most of the OEM toggle bolts were hideously designed (cheapened by an OEM home-made screw-together design instead of being forged), the chainplates (fore lowers) that separated opportunistically broke because of crevice corrosion in the bolts due to the wet bases, etc.

No, my mast didnt come ALL the way down .... just loose and hanging by a thread.

Investigating and analysing the OEM design (total rigging system) and yard execution I calculated an approximate 5:1+ factor of safety ... and the 'system' still functionally failed. I used to design 'high mobile steel' - cranes, heavy lift, etc.'

The OEM cranse collar is extremely poor mechanical design vs. fatigue.
The Grand Deer toggle bolts used are a 'deathtrap'
The upper rigging toggle straps are undersized.
The chainplate bolts are not removable and will usually be found with severe crevice corrosion and evidence of developed fatigue failure.
The chainplates are of inferior design and are probably undersized .. fatigue failure occuring at that 'kink' where the plate comes through the deck.

Your choice.
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