How to Plug a Leak on Your Sailboat

How to Plug a Leak on Your Sailboat | Life of Sailing

Last Updated by

Daniel Wade

June 15, 2022

Whether it's a loose rivet, perished O-rings, or a gap that allows water to filter in, boats are known to develop minor leaks. Unfortunately, these leaks are the bane of a sailor's life and must be fixed immediately. Here's how to plug a leak on your sailboat.

As a boat owner, you certainly want your boat to be leak-proof. Although this is achievable, there comes a time when your boat may develop a leak and this spells doom. Well, boat leaks are not only inconveniencing and aggravating but can also cause serious damage to your gear and the boat itself. The fact that the source of the leaks is typically hard to find or even harder to stop can only compound your misery. While the best thing to do if your boat has a big leak is to immediately make your way to a hoist, there are simple procedures that can help you plug a minor leak.

Some of the best ways to plug a leak on your sailboat include using a 3M 5200 or a moldable polymer known as Stay Afloat. Using Stay Afloat is probably the best as it can be molded exactly into the shape of the hole or gap that causes the leak. You can also use imaginative but temporary solutions such as a towel, potato, a carrot, or whatever is in hand to stop the leak! More importantly, proper and regular maintenance will ensure that your boat doesn't suffer from leaks in the first place.

In this brief guide, we'll take a look at various forms of leaks and how to properly plug them.


Table of contents

How to Check Boats for Leaks

Checking your boat for leaks should be so overwhelming. All you have to do is open things up and start looking. Besides the very obvious indications such as water on your boat's deck, numerous stains on various parts of the boat should be a sure indicator that your boat leaks. Heavy amounts of mildew and water trails on the interior of the hull sides, as well as water stains on headliners, can be an indicator that your boat is leaking. Do not ignore discolored cabin soles, water puddles under berths, and damaged paneling.

Different Types of Leaks and How to Plug them 

Leaky Hull-to-deck Joints

This is, without a shade of doubt, the grandmaster of all boat leaks and arguably the most difficult to repair. A hull-to-deck joint can be so leaky that it severely damages the boat or even makes it uninhabitable. Such a leak can end up damaging the boat's internal plywood structures, leaving you with rotting mattresses and structures that can make the repair extremely expensive.

Depending on how the deck is joined by the hull and the extent of the damage, you may have no choice but to have the deck removed and reinstalled anew. Needless to say, this can cost you water and fire. Keep in mind that buying a new deck or damaged parts may be more economical than trying to repair the damaged parts.

If you're planning to buy a used boat, it's, therefore, very important to ensure that the boat is thoroughly checked and inspected for leaking hull-to-deck joints as it's a problem that you shouldn't inherit for the previous owner. Remember, many modern boats are not as rigid as they should be, and repairing a severely leaking hull-to-deck joint may be futile.

Leaky Chainplates

A chainplate is essentially a strong metal plate used to fasten a stay or shroud to the hull of a boat. One end of the chainplate is usually fastened to the tumbuckle and connected to the stay or shroud while the other part of the chainplate consists of several holes that are bolted to the hull. The main aim of the chainplate(s) is to help in distributing the load across the hull so that a normally lighter hull can effectively support the weight of the shrouds and stays.

The part of the chainplate that fastens the shroud by passing through the deck can be a common source of leakage on a boat. The fact that there are numerous regular loading and unloading that occur at these points makes it utterly impossible to keep them properly sealed. In fact, keeping them sealed is a constant battle in some boats, especially if the boats are poorly designed. Things can become worse if the shroud and stay chainplates are attached to plywood bulkheads. If this is the case on your boat, it would be wise to stop the leaks immediately and protect the wooden parts of your boat.

Many boat owners are guilty of using the wrong material to caulk the leaky chainplate points. Using materials such as silicone-based caulks or polysulphides will be a recipe for a disaster waiting to happen as they won't do the job properly because they have poor adhesive qualities. With that in mind, you can use Stay Afloat or the dreaded 3M 5200 as they can offer a strong and long-lasting solution to leaks around the chainplates.

The downsides of using materials such as Stay Afloat and 3M 5200 revolve around the fact that they're messy. Once applied, it will be almost impossible to detach or remove parts bedded with it. On the contrary, that's exactly why they're the best solution when it comes to sealing leaky parts of your boat. If anything, these materials work so well with metals, wood, and all other materials except some types of vinyl and polypropylenes.

The best way to use the above-described materials is by thoroughly cleaning the fiberglass surfaces using a Dremel tool. You can use this to grind just a little bit to get a good bonding surface. In other words, it would be a waste of your time trying to use the materials on a dirty surface. Of course, you don't want to see all your efforts to seal your leaky boat fail. As such, make sure that there are no oily or waxy residues on the part that you want to seal. If you can't get a Dremel tool, you can use a very capable option: sand to grind all the surfaces to be sealed or bonded.

If the hole to be sealed is too large you can use suitably sized filler strips filled with Stay Afloat or 3M 5200 to reduce the holes. Once they've cured, you can apply the final bead of caulk to make sure that it's properly sealed. These types of caulks are very durable and should last for years as long as there is no excessive structural damage or movements to the sealed parts.

As we noted earlier, some boats have the chainplates attached to the plywood bulkhead. If this is the case on your boat, it would be a good idea to treat the damaged area and prevent further damage or deterioration. A perfect solution is to grind down the surface and then coat the bolt holes and the area with epoxy. This can help in shedding water and effectively reduce rot just in case sealing the leaks isn't a success.

Deck Drainage

You should never overlook deck drainage as they can cause serious hazards to your boat. So whether it involves installing a scupper or notching the rail, you must find a way of providing adequate drainage to your boat's deck.

Windows, Ports, and Hatches

Windows, ports, and hatches usually develop leaks if the structures to which they're attached are subject to movement or are not completely rigid. This generally leads to the breakage of bedding seals. The same thing happens on the sides of the cabin trunks, especially if you usually jump on the deck as the seals will break, leaving your boat with portholes. Again, using a Stay Afloat or the 3M 5200 will cure the problem. 

Thru-Hull Fittings

Today's boats are made of cored hulls and materials that can be easily damaged and let in water onto your boat. A possible solution to this problem is to ensure that a through-hull fitting is NEVER installed through a core structure. You should also ensure that the surface doesn't have a pronounced curve.

The best solution to ensuring that water never gets into the core is to never damage the core. This will ensure that there's no possibility of water leaking into the core because it's completely sealed off.

Leaky Packing Glands

Repeated packing glands leakage is normally caused by excessively flexible engine mounts, especially if your boat has a diesel engine. Diesel can cause vibrations that in turn lead to engine movements that can lead to shaft misalignment, which can then cause leakages in packing glands. This is because the shaft will spin oddly and cause wear on one side of the packing gland.

There's no good solution to this type of leakage as it revolves around the vibrations caused by your boat's diesel engine. Do not be advised to buy expensive dripless glands as it won't cure the problem. You can consider replacing the engine, especially if it's old.


Another common leakage problem that can be found on boats revolves around windlasses. The leakages usually cause extensive damage to the windlass motor drive and housing and can develop if the seals around the deck and bolts are broken because they're highly stressed, especially if extremely heavy loads are placed on the windlasses.

The best solution to curing these leaks is by pulling and rebinding the windlass, which can be very unpleasant. You should avoid using caulk because this will not help. Whatever the cause, it's important that you find the source of the problem and have it rectified.

Leaky Stanchion Bases

Stanchion bases are often subjected to lots of stress and even the best stanchion installations will begin to leak as the boat ages. Unfortunately, many boat builders do not provide access to the underside of the stanchions, which make repairing leaking stanchions nightmarish.

But if you can reach the undersides, repairing them becomes quite easy. All you have to do is remove the bases, check if the bolts and holes are of proper size. If the holes are bigger, you can refill them with epoxy or milled fibers. If the bolts are worn out, you can buy new ones. You can also bed the stanchion bases using Stay Afloat or 3M 5200.

To this end, it can be suicidal to think that repairing leaks on your boat is an easy undertaking that can be done at a low cost. Although repairing a leak can be easy, the fact that accessing the damaged part is almost impossible makes it a different task altogether. In most cases, it may involve tearing out a part of your boat's interior, especially if the leaks are on the decks. This is why you should always make sure that leaky parts are repaired by a professional boat builder.

How to Plug a Leak on Your Sailboat
Daniel Wade

Daniel Wade

I've personally had thousands of questions about sailing and sailboats over the years. As I learn and experience sailing, and the community, I share the answers that work and make sense to me, here on Life of Sailing.

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