Chain Plate Leak Refit on Your Catalina 34 and 36 (MkI and MkII up to 2003)
By: Tony Germin, Gato Via, 1997 C34 Tall Rig #1331
Rick Verbeek, Southpaws, 1999 C36 #1763
Most Mk I and Mark II (up to 2003) C34 and C36 owners have encountered problems with leaking chain plates. The websites of both owners’ associations are replete with discussions on how to address this problem. While many solutions have been proposed, most describe how to re-bed the original chain plates and acknowledge that the need to re-bed every few years is inevitable. In this article, we outline why the chain plate design on this vintage of Catalina is so prone to leaking and the problems this causes. In our next article we will describe what you can do to effectively deal with this problem including a new chain plate design.
Why Chain Plates leak
The chain plates are mounted from the interior. The “bottom plate” is through-bolted to the ceiling by 3/8” bolts which are backed only by small washers on the surface of the deck. The center chain plate of the C36 is a long bar bolted to the bulkhead and therefore does not have a “bottom plate” however the general design problem regarding leaking in the same. The vertical part of the chain plate (which we call the “shroud bar”) passes up through the deck via a rectangular slot hole which just accommodates the shroud bar. On the deck is a small cosmetic cover plate that fits over the shroud bar to hide the rough edges of the slot hole. The cover plate does not provide any meaningful surface area to seal the slot hole.
Leaks occur when the sealant between the shroud bar and the slot hole fails. The sealant is prone to failure for several reasons: 1) Sealant doesn’t adhere well to polished stainless steel. 2) The slot hole is not chamfered resulting in next to no space for sealant between the shroud bar and the slot hole. (This also applies to the bolt holes). 3) The sealant is not under compression between the shroud bar and the slot hole. Sealants work far better when compressed between two surfaces. 4) The sealant is subject to a small but constant vertical and horizontal shearing force when the chain plate is tensioned by the shrouds and the tie rods (which anchor the chain plate to the interior structure) resulting in flexion of the deck. 5) The sealant is further subject to frequent minute tensioning and detensioning shear forces under sailing conditions when the chain plate moves ever so slightly in relation to the deck. Add weather and aging to this and you have created the perfect conditions for leaky chain plates. For similar reasons, leaks also commonly occur via the deck bolts.
Why leaking Chain Plates are a problem
This is more than just an annoying cosmetic problem where water leaks into the cabin. The slot hole and the bolt holes pass through the inner core of the deck. The slot holes and bolt holes were never coated with epoxy during manufacture. Therefore leaks result in the inner core being directly exposed to water and subject to water penetration.
To compound this, the “bottom plates” on many boats have a layer of sealant where it contacts the ceiling of the salon. Although this may prevent water from entering the cabin, it also traps water that has gained access to the slot hole. This further increases the exposure of the inner core to water. The result is high moisture content in the deck surrounding the chain plates of any C34 or C36 that has experienced chain plate leaks. This can lead to mold growing between the deck plate and the ceiling of the salon.
In a worst case scenario this can lead to deterioration of the inner core of the deck which can require complex (i.e. expensive$$$) repairs.
What can you do to prevent leaking chain plates?
Many blogs and forums have proposed various ways to prevent chain leaks. In our next article we will review the limitations the various “solutions” that have been suggested and will outline what we consider to be more definitive solutions. Our goal has been to essentially eliminate the possibility of chain plate leaks. In the rare circumstance that a leak occurs our solution prevents water penetration into the core of the deck so water damage cannot occur.