How to use epoxy to fix the rudder of a sailing yacht


West System International Technical guru David Johnson explains how to fix a rudder that’s taking in water.

If there’s a top ten list of questions from boat owners who want to carry out their own repairs, “how do I fix the rudder?” is almost certainly up there. Especially if the boat is 20 years old or more.

Before the Recreational Craft Directive first came into force in 1996, it’s fair to say that rudder construction wasn’t always that robust. It was the era of the (now extinct) high production boatbuilder, who was producing 400-500 boats a year.

Typically, the poor guy making the rudder would have been the lowest-paid apprentice and yet he was making arguably the most important part of the boat –  the one thing that will steer you to safety if you’re in trouble!

“Most GRP rudders are constructed by bonding two half mouldings together…The problems begin when there is a flaw in these mouldings.”

Most GRP rudders are constructed by bonding two half mouldings together. These house the bonded rudder stock or transom fittings and are typically filled with two-component polyurethane foam.

The problems begin when there is a flaw in these mouldings, which allows moisture to seep in; the foam basically absorbs it like a sponge. I have also seen machined rudder stock that has corroded because the rudder has wicked up water into the foam.

Aside from this affecting the boat’s sailing ability, it’s worth noting that this moisture content can be picked up by a surveyor, who in turn may advise an insurer not to issue cover on the boat. With most insurers requiring a survey every seven to nine years, it’s important to get this sorted out.

Two different ways to repair

To carry out a repair that’s anywhere near acceptable, you firstly need to dry the foam scrupulously. This may well be difficult unless you can drill drainage holes and store the rudder in a heated dry environment for a lengthy period.

However, if you can indeed get the foam dry enough, you might consider a repair detailed in our Fibreglass Boat Repair and Maintenance manual (free to download). Chapter five in particular has details on how to chain-drill the skin of a laminate and then inject mixed epoxy via a syringe.

To be honest, this is a bit of a “get out of jail cheaply” option. It’ll work but a more professional boatyard-style repair would involve splitting the two rudder halves, completely removing the old waterlogged foam and perhaps re-bonding the stock.

You would then need to reassemble the two halves with epoxy and pour fresh mixed epoxy/filler material in slowly into the void – either a very slow-setting resin/hardener/filler mix, or our PRO-SET® expanding epoxy foam.

“Most GRP rudders are constructed by bonding two half mouldings together…The problems begin when there is a flaw in these mouldings.”

Whichever option you go for, sheathing the repaired rudder adds robustness and is a fairly straightforward process. We would recommend WEST SYSTEM 105 Epoxy Resin® with WEST SYSTEM 205 Fast Hardener® and Episize™ 739 450g Biaxial Glass Fabric. For more detailed information on sheathing, have a look at our Wooden Boat Restoration & Repair manual (also free).

It’s also a good idea to document your repair with photographs or a repair plan. You can include this within the boat’s papers, so you’ve got something to show a surveyor or a future buyer.

But of course whatever work you carry out, remember to seek advice from a qualified marine surveyor or yacht repair technician first. Even if you’re really confident with this sort of work, the old adage still holds: do it nice, or do it twice!

David Johnson is Technical Operations Manager at West System International. Discover his other articles for epoxycraft.  

For more information about how to use our full range of WEST SYSTEM epoxy products, visit our support pages.


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