The West River Race and Lessons Learned

Swing Keel Trunk Repair and Improvement

Catalina 25/250 & Capri 25 International Association
C25 Association Technical Editor Seth Martin

Special thanks to Jeremy Duck for submitting this article. –Seth Martin

Cracked keel trunks are a common point of failure for Catalina 25s with the swing keel configuration.  Issues typically stem from keel lifting hardware failing when the keel is raised, which allows the keel to swing quickly down and crash into the aft end of the keel trunk.  Issues also arise from running aground on an obstruction at hull speed, which causes the keel to swing back and up, and then quickly back down after the obstruction is cleared.  Either scenario can result in structural damage to the aft portion of the keel trunk where the keel contacts the trunk in it’s lowered position.


Do not be wary of fiberglass projects.  No mythical art for a good job exists.  Anyone can obtain good results with time and patience.  Good surface preparation work is helpful.  When starting with a clean and dry surface, fiberglass work is easier.  A good sander can fair ugly layers while learning how to lay up fiberglass.

The total cost of this project, including building the keel trunk much thicker and stronger than it came from the factory so that future damage is less likely, costs less than $500.  

Damage may not be visible in the outer layer of fiberglass in the keel trunk, but water leaking from the keel trunk indicates damage somewhere in it’s layers.  Partially raising the keel can stop leaks at the damaged section, while lowering the keel fully can induce them.  Since fiberglass work is ahead in this project if done correctly, start cutting or chipping away at the existing fiberglass until the damage is exposed.   (Obviously, this should be done with the boat on the hard.)  A saw and a sharp wood chisel work well to cut away the fiberglass until the damaged portion of the keel trunk is exposed.

Accessing Damage

The keel trunk structure is more difficult to access on the dinette model than on the traditional layout with the two settees.  On the dinette, the keel trunk is below the forward dinette seat, abaft the mast.  On the swing keel, the keel trunk is hidden beneath a wooden box on the interior floor, abaft the mast.

The interior floor may or may not need to be cut away to access and repair damage.  Do not cut away the interior floor around the keel trunk until assessing damage higher in the trunk, which is more likely.

On the dinette model, four different materials may need to be cut away during this project:  gelcoat, fiberglass, plywood, and a gray epoxy.  Catalina apparently injected epoxy filler to span voids between the hull and the liner during construction of the dinette models.  This epoxy is hard to sand and clean, but can be chipped away with a wood chisel.  On the traditional layout model, after the wooden box is removed, only fiberglass needs to be cut away as no gelcoat, epoxy, or plywood were used in the keel trunk.


Do not use the red polyester resin found in most home improvement stores, which is intended for new fiberglass work.  Instead use epoxy resin, which is better for repair work.  Use a resin thickener when laying up vertical surfaces.  Otherwise the resin may drain downward, leaving cloth that is not completely saturated. Only lay up one to two pieces of cloth in each layer to prevent the cloth from sagging before it cures.  

Use heavy and medium weight fiberglass cloth.  Use heavy cloth for structural fiberglass.  Heavy cloth is more difficult to work and does not bend well, but provides for excellent structural layups.  Use medium cloth for the final layup (dinette models only).  Medium cloth does not provide structural integrity as does heavy cloth, but bends more easily and looks good when finished.

On the dinette model, gelcoat needs to be applied over the final layup of medium cloth to achieve an appearance uniform with the rest of the interior.  Traditional layout models are easier because the fiberglass does not require finishing.  They came from the factory with unfinished fiberglass keel trunks, finished by covering the trunk with the wooden box for aesthetics.

Using Foam To Fill Voids On the Dinette Model

On the dinette model, a significant void exists between the keel trunk and the interior liner that comprises the forward dinette seat, even after repairing the keel trunk with heavy cloth.  If the floor has been cut away to access the lower portion of the keel trunk near the hull, a void will exist there as well.

Two-part low-density pourable foam can be used to fill these voids.  Foam is much less expensive than filling these voids with additional layers of fiberglass cloth and epoxy resin.  This foam hardens within thirty seconds, and so must be applied in small batches, such as eight ounces per batch.  Cardboard lined with plastic wrap, held to the keel trunk and hull with duct tape, works well for making a form into which to pour the foam.  Lining the cardboard with plastic wrap is helpful because the foam does not stick to it like it does to cardboard.

After the foam hardens, it is easily sanded and formed with a chisel and butter knife.  Then medium cloth fiberglass can be applied, followed by gelcoat.  

Improving the Keel Trunk During Repair

From the factory, the keel trunk is generally 3/8" thick with some areas only slightly thicker.  In order to prevent similar damage from recurring in the future, consider building the aft side of the keel trunk to at least 1", the sides of the trunk to 5/8", and where the trunk ties into the hull to 7/8" thick with heavy cloth. Then build the final layup another 3/16" thick with medium cloth (dinette model only).  

If the aft end of the keel trunk is built up while the sides are not, then failure is more likely at the edges of the build up.  In order to prevent such failure, the layups should be feathered at various lengths into the sides of the trunk and down into the hull.  

Additional Reinforcement

Wood blocking, such as 1" thick oak, can be added to the aft side of the keel trunk and along the hull to further strengthen this high load area.  The idea is to to distribute some of the force of a quickly lowering keel from the keel trunk to the hull.  The hull, where the blocking is to be installed, should be built up with additional layers of heavy cloth to provide additional structural integrity.  The blocking should be coated in epoxy for waterproofing, and then epoxied to the aft end of the keel trunk and the hull to form a single structure to transfer forces.  Heavy cloth layups can be applied across the wood along the aft end of the keel trunk and the hull, to provide for additional structural integrity.  Jeremy Duck, Jeremy sails “The Lucky Duck”, Catalina 25 #1850, a dinette model with swing keel, on Tampa Bay in Florida


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