new chain plate design to stop leaks

[togve]

Chain plates on Catalina 34 and 36 from 1990 to 2003

Ah, the age old problem of leaky deck stuff.  Particularly the chain plate design of the Catalina 34 and 36 from 1990 to 2003.  (Discussions with our Catalina sailor friends suggest the problem may precede 1990.)

The problem:

The design of the chain plates which are mounted from the interior of the boat on both the Catalina 34 and the 36 are, in my opinion, problematic in their ability to hold back the water which accumulates on the deck.  The centre chain plate on the C36 is actually a long bar bolted to the bulkhead but the general design problem is the same. (See Image 1 - Original Chain Plate Design)[attach=#]

Three design flaws come to mind.

Firstly, the current design of chain plate attempts to seal the bottom plate from underside of the deck (i.e. the inside the boat).  Eventually the sealant fails allowing water to make its way down the shroud bar to sit on the bottom plate where it can penetrate into to wood core of the deck or leak directly into the cabin.  Penetration into the wood core occurs because the core was never sealed with epoxy after the slot was cut through the deck during installation.

Secondly, the holes for the two 3/8" bolts are only protected by 3/8" washers, resulting in a small foot print with which to attempt a proper seal from the deck side.  The deck core of the bolt holes was likewise never sealed which can lead to further water penetration into the core of the deck.

Thirdly, the tension on the threaded rod (not seen in the photo) is pulling the current bottom plate away from the underside of the deck. When sail pressure is removed or the shrouds are removed for storage, this   tension tends to pull the bottom plate away from the underside of the deck and depresses the 3/8 washers into the deck, due to their small area.  This will ruin the seals meant to prevent leaks.

Similarly, when there is counter tension from the shrouds as the mast is up, the nuts at the bottom end of the rod are tight and the deck is at a neutral position. When you remove the counter tension from the chain plate by taking off the shrouds, or sailing in strong winds, the leeward shroud will lose tension and the rod tension is pulling on the two bolts and the washers on the top deck . Therefore it is critical to have the correct tension, and more importantly spread this load over a wider area so as to not have vertical movement of the screws or plate.


The solution: The first step to widen the slot in the deck, bevel the slot at the top side and seal the wood core with a coating of epoxy. This needs to be done in order to protect the plywood core from getting wet and eventually rotting. This is not a function of a new design but rather the right thing to do to protect the plywood.

The same needs to be done with the 3/8" bolt holes. Drill two 5/8" holes, bevel the top side of the hole, and fill with a liquid epoxy. Allow this to set, and drill new 3/8" holes.

A redesigned chain plate would have the bottom plate become a deck plate welded to the vertical bar (Image 2 - Deck Plate).  This chain plate will be inserted from the top of the deck and can now be sealed over a larger area rather than the small 3/8" bolt washers  that contact the deck in the current design. [attach=#]

Attaching the threaded rod to the vertical bar of the redesigned chain plate, and tensioning it, will pull the deck plate to the deck and the sealant will be trapped under the deck plate. The pressure on the deck will be widely distributed therefore improving the seal. Proper tension must be applied to this plate, as the counter tension of the shroud will affect this setting. Water now has a longer path to penetrate through the underside of the plate to reach the slot and bolt holes. Using a butyl tape or butyl putty will help to keep this seal flexible.

Remember the area under the deck plate is under pressure from the tightening of the nut at the end of the threaded rod. This pressure will also help to keep the seal under this plate. Because there is constant pressure on this plate, I feel that a glue type sealant is not necessary. Butyl putty will stay flexible and sticky for a long time and it will allow easy removal if necessary.

The last trick is now to attach the threaded rod in a manner that will self align the rod to the chain plate.

I propose an articulating joint using a toggle (Image 3 - Toggle). This joint connects to the bottom of the new chain plate. [attach=#]

Presently I'm working on this design. The goal is to have these new chain plates installed on our 1997 Catalina 34 for 2011 season. I will report any failures or successes so stay tuned.

Tony Germin /  Rick Verbeek
1997 C34 #G697
Lakeshore Yacht Club
Toronto

[2ndwish]

Tony and Rick- An interesting idea, but I wonder whether you are trading one problem for another. The chainplate is primarily loaded up under tension. This would tend to open the seal rather than close it in your design. The tie rod to the hull would then need to transfer almost all of the tension, which it is not originally designed to do. The tie  rods are not fully tightened under zero load and their purpose is primarily to prevent deformation of the deck, which carries most of the load through the chainplate. In your scheme the deck bolts, which have no interior backing plate, can't effectively distribute load to the deck, so the tie rods need to be tight to take all of the load. My primary concern is that the tie rod ends are mounted through a type of bushing which can only distribute the load to about 1 sq inch. This is probably ok given the thickness of the structural member through which it is mounted, but I am not privy to the design details in that area of the hull. I would check with CY and get their $.02 before proceeding.
T

[togve]

 
"T" - Thank you for your interest and very insightful comments.   As this project has been progessing, we have addressed many of the legitimate issues you raise.  How I addressed them is described below. I am planning a posting shortly to show the further revisions I have made to chain plate design.

Your quote:  "The chain plate is primarily loaded up under tension."

Actually in this new design the load will be primarily set by the rods inside the boat. The shroud load will not be able to pull on the deck plate directly as the load is transferred to what I call the shroud bar part of the chain plate down to the rods and to the hull angle beam inside the boat.

Your quote: "The tie rods are not fully tightened under zero load and their purpose is primarily to prevent deformation of the deck, which carries most of the load through the chain plate."

In this new design the rods actually do take the full load of the shrouds. The deck becomes more stiff and it is the only thing that can move or distort under load. But the rods will actually take all the load as they were designed to do. This new design allows for more pressure to be exerted down on the deck so the chain plate will always be under load of the rods pulling down on the deck. This is necessary to maintain the seal under the deck plate portion of the chain plate where the load is transferred to the rods by direct connection to the shroud bar. In the original design you are quite right - the tension on the chain plate exerted by the rods is intentionally minimal because they exert all their downward pull on the deck through just the washers on the two bolts through the plate and deck. Under sailing conditions, this allows the deck to move more relative to the chain plate such that the caulking seal is broken much more easily.  Hence the leaky chain plates we commonly experience with our boats.

Your quote: "In your scheme the deck bolts, which have no interior backing plate, can't effectively distribute load to the deck, so the tie rods need to be tight to take all of the load."

I haven't described this yet but the final design of the new chain plate will have a backing plate to sandwich the top deck plate and the deck. This will further reduce lateral movement of the chain plate. A more detailed description will follow in the next posting with pictures.

Your quote:  "My primary concern is that the tie rod ends are mounted through a type of bushing which can only distribute the load to about 1 sq inch."

In the original  design the load from the properly tensioned shrouds which should be in the range of 1625 foot pounds for the center shroud and approximately 1000  for the forward and aft shrouds when the boat is at rest. When the boat is sailing the compression on the 1" bushing increases and the original design  obviously  is adequate. In the new chain plate design, the compressive load on this bushing does not change. Any increase in wind pressure will exert the same load on the shroud and the rods and subsequently the bushing in either design. The deck does not and should not take this load.

Thanks for your comments please stay tuned for the next post.

Tony Germin
1997 C34 #1331
Rick Verbeek
1999 C36 #1763
Lakeshore Yacht Club
Toronto

[Ted Pounds]

My thoughts:  You are both partly right and partly wrong.  The rods are what take the primary shroud load that's for sure.   The deck is not stiff enough to handle that load.  So the rods do keep the deck from deforming (and failing) by taking most all of the load.  The plate on the bottom is not the sealing plate.  The plate on the top that slips over the tang and is screwed to the deck is what seals the deck.  The plate on the bottom is there so that any, very slight, tang movement under load will also move the deck.  That ensures that the tang does not move relative to the deck and break the seal. 

[Ted Pounds]

BTW check out this thread:  http://c34.org/bbs/index.php/topic,6202.0.html   Seems like a better way to seal up chainplates.

[BillG]

I like the concept of your design but agree with Ted's comments.  Perhaps a slight modification by adding a removable bottom plate, same size as
the top plate that would create a sandwich of the deck.  This would not be a sealing plate as Ted has pointed out of the original design, but would act more as a backing plate and help guarantee that if there is a small amount of flex in the deck, the seal on the top plate would remain intact.

[togve]

Hi Bill

Thanks for your comment.

I will post the next installment tomorrow or Wednesday with pictures and I will show the actual design which will show the 3/16" polished and removable backing plate. I'm not sure if I was clear but the top plate is welded to the shroud bar or tang. That would be the point and that is  to make the top plate the sealing plate as you said Bill.

Cheers and Stay tuned.
Tony Germin
1997 C34 #1331
Lakeshore Yacht Club
Toronto

[Ken Juul]

I thought that Catalina Engineering might be interested in this topic.  This is Gerry Douglas's reply.

"Ken,
Thank you for refering me to the 34 thread.
1. Should a 34 or 36 owner wish to change out the chain plate tie rods I suggest the ball and socket type use on the later 34s and 36s and in all 42s. These can be purchased through the Catalina Parts Department.
2. I will not get into a technical debate on the website, but I would not recommend the design proposed by the 34 owner."

He is busy, don't think he has the time to devote to an engineering discussion such as this.  But he has been designing and building Catalinas for a long time, there must be some nuances we are missing so far in the discussion.

[lazybone]

Does anyone have a picture of the new type ball and socket that Gerry is refering to?

[togve]

Hi Ken

Thanks for getting CYs perspective.
In fairness to Gerry he does not have all the info as I have not posted it all yet and he is quite right one can purchase the ball and rod design which I had an opportunity to eyeball on a brand new 355. This is a much better design then the old one and should be given consideration however more extensive work would need to be done to the fiberglass and gel coat on the deck to accommodate the different foot print.

Our new design works on the same principle as CY's new design and it's an attempt to be a simple retrofit that most owners could install them selves.

Cheers:
Tony Germin
1997 C34 #1331
Lakeshore Yacht Club
Toronto