Holy "Welded on Chain Plate Covers" Batman!!!

[Cool Beans]

So, last spring I went to remove the port side chain plate cover for re-bedding (it was leaking) and after trying to pry it off to no avail. . .I just set a bead of sealant around all the edges and that stopped the leaking.

Fast forward to today, I pull it for inspection and had to take it off with the cover in place. . .

Why you ask?

It is fully welded to the chain plate

And the worse part is the weld is concave all around. . .reducing the cross section from 1/4" at the CP to less than 3/16" at the weld

I'm not sure what to say. . .Why would someone do this? The weak spot is past all 9 bolts holding it down, kinda defeating there purpose? I guess the two thru-bolts at the cover help hold it down? BTW, the pics below are looking at the underside. . .

I'm not even sure it is worth checking the welds for crack were there is some rust starting. I wouldn't mind making new ones, can I get away with regular covers and CP? Is there any reason to attach them like this?

Thanks!! And thanks to all who responded to my last post. . .The boat is back in the water and hasn't sunk yet

 

[Mike B1026]

From the factory?

 

[Rick Sylvester]

The two bolts just locate the top of the assembly.

I'm guessing here since I can't see the entirety of the chainplate in your pic.

I have a similar (though much larger) arrangement on Anthem. Instead of sealing at the deck on vertical and horizontal planes as with traditional plates and covers (what you were expecting) this design relegates sealing to the horizontal plate only. Theoretically easier for the sealant to manage.

It actually works fine. I'd have new ones made though, those welds do look pretty skanky.

 

[Cool Beans]

I would assume they are factory original. . .I guess there has to be something said that they have lasted 36 years in this setup. . .just doesn't leave me sleeping easy now that I know

Here is a full height pic. If the welding was just for sealing purposes and not structural, I'm going to have them duplicated with traditional covers then. . .many thanks!!

I guess I can look into enlarging the pin hole so I can upsize to 9/32" 316 rigging there as well

 

[Maine Sail]

There are many, many builders who used& still use welded plates. This is not a problem so long as what they are attached to is solid & remains solid. Ours were still 100% leak free at 31 years with welded plates & butyl tape as a sealant.

As they came out..


After polishing and inspection..

 

[Cool Beans]

Yes, definitely anything getting rebedded on my boat is going in with butyl

What would you suggest I do then? I hate spending money where it is not needed. . .I thought these were some funky jack-legged setups but. . .

Other than the being worried about the welded area, it looks like it should polish up fine. . .and that the weld is on the underside of the cover leaving the exposed seam to fill with grit and water. Can these be professionally checked? And would that be significantly cheaper than just making new ones?

Many thanks!!!

 

[Roger Long]

I guess I can look into enlarging the pin hole so I can upsize to 9/32" 316 rigging there as well.

I almost did that on my boat but decided against it after calculating probable rigging strains. I would be surprised if it was justified on your boat unless you are doing a circumnavigation. If it is like most production boats, you'll find a lot of weak links in the chain up aloft. Look up the threads on my standing rigging replacement and new tang design.

This is a good guide to conservative chainplate design that's followed me around since I worked for Philip L. Rhodes.

http://www.cruisingonstrider.us/images/Chainplates.pdf

 

[Roger Long]

After polishing and inspection..

Wow. Did you do that? I'll be in touch as soon as Phil roughs out my tangs. I need him to get onto my chainplates. The fishermen keep coming in with emergencies and it's going to start holding me up soon.

Did you see how my compression tube came out?

http://www.facebook.com/album.php?aid=57051&id=1846284215

 

[Cool Beans]

Currently signed up for Tom McNaughtons design school. . .don't have the extra cash or time right now but have been running numbers from Skene's book against my boat and unless I'm doing it wrong my boat seems to be very lightly designed. . .every chain plate looks to be undersized compared to his chart (basically the one you linked too) and even my own calcs and old rules of thumb I've read Same goes for the rigging, unless the boat has a RM of 17500 or less. . .which seems to be on the low end of his graph of righting moments @ 30*

The main reason I considered moving to 9/32" uppers was so I could go to 316SS rigging. The PO did that on the bow furler but had a custom toggle from Furlex allowing him to use a 3/8" pin which seems kinda jack legged. . .

The original is 1/4" 304SS uppers. I've ran numbers giving me loading from ~8000 lbs to as low as ~7100 lbs. . .which would let me use Rigging Only's 1/4" 316. . .

The boat is mostly sailed around the Chesapeake. . .I want to go to the Bahamas and the like, maybe farther south into the Caribbean one day. . .mostly just want to move aboard, lol. The upper ends look hella beefy, all 1/2" pins, marine eyes, and double tangs. . .

And I'm rambling, probably for another topic, lol. . . sorry. . .

 

[Roger Long]

It may be too late for you since your chainplates are out. However, for anyone else who is curious, here is how to determine the rigging loads on your boat “close enough”. You might want to postpone any wire size increase until after you’ve put things back together enough to do this.

You’ll need an inclinometer and two people.

Swing the mainboom out over a float and guy it forward swung out as far as possible and tighten the mainsheet. Tie a rope to the end of the boom with a bowline loop large enough to get your foot in hanging about two feet above the float. Measure the distance from the rope to the centerline of the boat.

Loosen the dock lines enough so the boat can heel freely. Calm wind and no current or slight current off the dock is good. Both people sit in the cockpit as close to centerline as possible and read the inclinometer. If you are using a temporary one, you can tweak it to zero.

The heaviest person goes ashore. The other person tries not to move.

Think about whether your topping lift is up to the task.

The person on the float steps into the rope loop and puts their full weight on it slowly to keep the boat from rolling too much. If the rope loop hits the float, shorten the rope.

As soon as the boat settles down, the person on board reads the inclinometer and records the degrees of heel.

If you haven’t already done so, weigh the person who heeled the boat before too much beer has been consumed post experiment.

The weight of the person times the distance off centerline is the righting moment. Righting moment increases at a fairly constant rate up until the time the deckedge starts to go underwater. For typical sailboats with the freeboard common today, this won’t be too much under 30 degrees.

Divide 30 by the heel angle with the person standing in the rope loop. Multiply the righting moment by that amount. If the boat heeled 5 degrees, for example, you would multiply the righting moment by 6.

Print out this other data sheet from my Phil Rhodes days:

http://www.cruisingonstrider.us/images/Rigging.pdf

Use the formula at the top of the page to find the upward pull on the chainplates in total and the corresponding compression on the mast. Skip the stuff in the middle, except for recommended safety factors, and go down to the rigging sketches at the bottom of the page. Select the one that looks most like your rig and apply the percentages to the number you got above. I know they don’t all total to 100% but, like I said, close enough. For a typical single spreader rig with two lowers, the lowers take 65% of the load and there are two so each one takes 33%.

Remember that the load on your rigging is limited by the hull’s stability. The 1.5 factor in the formula at the top of the page is a reasonable approximation of the additional righting arm at the peak of the righting arm curve (See: http://www.cruisingonstrider.us/Stability.htm if you don’t know what a righting arm curve is.) If your boat is blown flat in the water by a 100 mile an hour wind, there will be no more strain on the rig than if she is blown flat by a 50 mile an hour wind. There are some reasons for making rigging stronger but imagining strong winds is not one of them.

 

[Cool Beans]

HA!!

The entire mast is down

Can an inclination experiment be performed without the mast stepped? There is one described in the back of Skene's that involves people on deck. . .I could try that this weekend with some help??

Or, is there an inexpensive 304 SS rigging supplier cheaper than West Marine? LoL

I think everything else is good, just need to determine the upper shroud loads. . .

 

[Roger Long]

Can an inclination experiment be performed without the mast stepped?

Yes, but you have to know the weight of the hull, the weight of the rig, and have a pretty good idea of the center of gravity location of each. I wouldn't be practical without a lot more data than you probably have.

 

[Cool Beans]

. . .this is almost to much trouble, LoL.

The rig was designed for 7/32" lowers(2) and 1/4" uppers. . .back in 1975, I'm assuming 304SS.

If I take the max load of the lowers, and work backwards I get 6462 lbs for mast compression and at a 2.5 safety factor I get 7270 lbs tension for the upper shroud. More than the std 6900 breaking strength of 316 but under the 7821 breaking that Rigging Only claims. . .which is also close to the 2.75 safety factor of ~7990. . .

Oi! My head hurts, can I just be over analyzing this?

 

[Roger Long]

Oi! My head hurts, can I just be over analyzing this?

Probably. It is very, very rare for cruising rigs to come down when all the components are up to spec. It is usually fatigue, loss of a cotter pin, a cracked swage, etc. If a boat of your age had a problem, you probably would have heard of it by now.

My rig had engineering issues and that just amaze me but I've never heard of one being dis-masted. I'm putting a big chunk of my re-rigging budget into mast tangs and proper compression tubes as well as bringing the upper chainplate to the proper thickness.

Few engineering situations are provided with as effective a load limiter and shock absorber as is provided by the hull of a monohull sailboat. The design stresses in cruising are usually only encountered no more than once in the ownership of the boat after which the wife refuses to ever get on it again and the owner takes up golf. At normal heel angles (deck dry) where the cyclical loads occur, the stresses are considerably lower.

You will probably get the most bang for your buck in terms of rig strength by looking closely at chainplates, tangs, and terminals.

 

[Cool Beans]

Thank you for the help and information

Now, I have had a chance to polish up the welds and around the toggle pin hole. . .well, the rust on the weld on the underside was hiding some small cracks radiating from the weld into the chain plate cover. . .the weld itself in that area has a smattering of small pits as well :neutral:

$55.00 for 2 - 24" lengths or 1/4" X 2" SS flat bar delivered to my door. . .I see no reason not to make 2 new ones

 

[THECUSCUS]

From a welder's standpoint, those plates should not have been continuously welded around the flat stock, especially at the edges. Welding at the edge cuts into the edge and can weaken the stock and give a place for a crack to start. If I was welding those plates on, I would run a bead of weld in the center of the flat stock, staying at least the thickness of the material away from the edge. Also, if you can see those welds from the inside, I would have them TIG welded, it would look nicer.