Sealing Hull-Piercing Bolts: A Guide For Aluminum Boat Owners

Sealing bolts that go through an aluminium boat hull is a common task for boat owners. The process of sealing these bolts is important to prevent leaks, which can lead to water damage and reduced boat performance. The first step is to identify the source of the leak, which may be due to loose seams or rivets. Once the leak is found, the area should be cleaned and dried thoroughly. The next step is to choose the right sealant for the boat material. It is important to select a sealant that adheres well to metal, such as Life-Calk or Silicone Rubber Sealant. When applying the sealant, it is better to be generous to ensure a strong seal. After applying the sealant, follow the product's instructions for curing, which may involve leaving the boat undisturbed overnight. Finally, inspect the seal and test it to ensure it is waterproof.

Identify the source of the leak

Identifying the source of a leak in an aluminium boat can be a challenging task. Here are some methods and guidelines to help you in the process:

Initial Checks and Preparations:

• Start by checking the obvious and usual suspects: deck cleats, lifeline stanchions, port lights, and the base of the arch. Look for stress cracks, loose mounting hardware, missing bedding compound, or concentrated streaks of dirt or rust.
• If you have a rubber rub rail covering the deck-hull joint, consider the possibility of a hidden flaw. You may need to remove the rub rail for a more detailed inspection.
• If your boat has been in storage or out of the water for a while, fill it with water to check for leaks. Use caution and avoid filling it completely, as water is heavy and can damage the hull or trailer if overfilled.
• If you suspect a leak in a specific area, such as the bilge, dry it thoroughly and then relaunch the boat to see if you can identify the source of the leak.

Advanced Inspection Techniques:

• Use a flashlight, paper towels, and your fingertips to inspect the inside skin of the hull for wetness. Pay close attention to areas around thru-hull fittings, rudder ports, shaft logs, stuffing boxes, strut fasteners, trim tabs, and swim platform mountings.
• Differentiate between routine drips and more serious leaks. For example, a drip at the packing gland of a stuffing box or rudder port can often be controlled by adjusting the stuffing box nuts.
• If you have an inboard engine, check for a cooling system leak.
• Inspect the drain plug seal and livewell pumps, especially on the transom, as they can be hard to spot.
• Use food colouring or fluorescent dye in the water to make leaks more visible. This can be especially helpful when checking for leaks in dark areas or against an aluminium hull.
• If you have an outboard engine, check the mounting bolts for leaks.
• If your boat has through-hull fittings, such as seacocks, valves, hoses, instrument senders, or running gear, these are common sources of leaks and usually straightforward to fix.
• Consult a professional if you are unable to identify the source of the leak or if the repair is beyond your skill level.

Remember, boat leaks can range from minor inconveniences to causes for immediate intervention. Take the necessary precautions and stay safe during your inspections and repairs.

Clean the area with an aluminium boat cleaner

To seal bolts going through an aluminium boat hull, you must first clean the area with an aluminium boat cleaner. Here's a step-by-step guide to effectively clean the area:

• Choose the Right Cleaner: Select a cleaner specifically designed for aluminium boats. Look for products that can remove stains, scum, and grime from boat hulls. Some recommended options include STAR BRITE Instant Hull Cleaner, CRC Aluminum Pontoon & Hull Cleaner, and Boat Juice Extreme Boat Cleaner.
• Prepare the Boat: Before applying the cleaner, ensure the boat is out of the water and parked on a stable surface. Gather all the necessary tools and materials, including protective gear such as gloves and eye protection.
• Read the Instructions: Carefully read the instructions on the chosen cleaner's packaging. Different products may have specific directions for use, so it's important to follow the manufacturer's guidelines for the best results.
• Apply the Cleaner: Following the instructions, apply the cleaner to the affected areas of the hull. Pay close attention to the areas around the bolts, as these are the main focus of the cleaning process.
• Scrub and Rinse: Use a soft-bristled brush or sponge to gently scrub the cleaner onto the hull. Work it into the aluminium surface, focusing on any stubborn stains or discolouration. Once you've thoroughly scrubbed the area, rinse the hull with clean water to remove the cleaner and any loosened dirt or grime.
• Dry and Inspect: After rinsing, dry the hull with a clean cloth or towel. Inspect the cleaned areas to ensure that all dirt and stains have been removed. If necessary, repeat the cleaning process until you achieve the desired level of cleanliness.
• Protect the Surrounding Area: Before proceeding to the next step of sealing the bolts, cover or protect any surrounding areas that you do not want to get affected by the sealing compound. This will ensure that the sealing process is precise and contained.

By following these steps and using the appropriate aluminium boat cleaner, you will effectively clean the area and prepare it for the subsequent sealing process. Remember to wear protective gear and work in a well-ventilated area during the cleaning process.

Choose the right sealant for your boat

When it comes to choosing the right sealant for your boat, there are several factors to consider. The marine environment is harsh, and the right sealant can be the difference between a boat floating or flooding. Not only will the correct sealant safeguard against leaks, but it will also make repairs easier and more durable. Here are some tips to help you choose the right sealant for your boat:

• Types of Sealant: Marine sealants come in four main types: silicone, polyurethane, polysulfide, and polyether. Silicone sealants have the weakest adhesive properties but make great gaskets and seals. Polyurethane sealants have the strongest adhesion but don't seal as effectively. Polysulfide is a versatile, rubbery sealant that is easy to work with and can be used on wood and metal. Polyether combines good adhesive qualities with great resistance to water and chemicals and can be used on wood, metal, and some plastics.
• Adhesion: Consider the strength of adhesion required for your repair. For example, polyurethane sealants are ideal for repairs that require a very strong adhesive bond, such as deck and hull joints. However, a strong adhesive may not always be the best solution, as it can make future repairs or replacements more difficult. In such cases, a polyether sealant or a lower-strength polyurethane may be a better choice.
• Flexibility: A good marine sealant should remain flexible and elastic after curing to form a watertight or airtight seal. Polysulfide and polyether sealants are excellent choices for sealing teak decks or wooden boards that expand and contract with changing weather conditions. Silicone sealants are also a good choice for sealing through-hull fittings as they create effective seals.
• Curing Time: The curing time of a sealant varies among different types, ranging from a few hours to several days. Consider how long your boat will be inactive during the curing process. If you need to complete a repair quickly and use the boat soon after, choose a sealant with a curing time of less than five days.
• Compatibility: Different sealants are compatible with different materials. Always consult the manufacturer's instructions to determine a sealant's compatibility with the surface you'll be working on. For example, polyether sealants are compatible with some plastics but harmful to others.
• Ease of Application: Choose a sealant that is easy to apply and has the right viscosity to penetrate small seams while still being stiff enough to form an even bead.
• UV Resistance: If the sealant will be exposed to sunlight, ensure it is UV-resistant to prevent degradation and failure over time.
• Waterproof: A good marine sealant must be waterproof and able to withstand exposure to chemicals and fuels commonly found in boating materials.

Remember, using the wrong sealant can be dangerous and costly to repair, so it's important to select the right one for your specific needs.

Apply the sealant generously

When sealing bolts going through an aluminium boat hull, it is important to be generous with the application of the sealant. This is because it is better to over-seal than under-seal. You can always go back and scrape off any excess sealant, but if you under-seal, you may have to start all over again.

To apply the sealant generously, start by identifying the areas that need to be sealed. Look for any leaks, paying special attention to the seams and rivets, as these are common sources of leaks in aluminium boats. Once you have identified the areas that need to be sealed, use an aluminium boat cleaner to thoroughly clean the surface and ensure that it is dry before applying the sealant.

Choose a sealant that is specifically designed for use on metal surfaces, such as Life-Calk or Silicone Rubber Sealant. These sealants will adhere well to the aluminium hull and protect the metal from corrosion.

When applying the sealant, be sure to follow the directions on the product label. You will typically need to keep the boat stable and allow the sealant to cure overnight. After curing, inspect the seal and test it to ensure it is waterproof.

By following these steps and applying the sealant generously, you can effectively seal bolts going through an aluminium boat hull and maintain the integrity of your boat.

Cure the boat overnight

To cure your boat overnight, you will need to leave it untouched for at least 7-10 hours, or possibly up to 24 hours, depending on the product you are using. Some sealants will need to cure for 48 hours, so be sure to read the instructions on the product you are using.

If you are using a sealant such as 5200, you will need to use it all at once, as it will harden within 24 hours. If you are using a sealant like GOOP, you can keep the tube for future use, as it will not harden unless exposed to air.

For the best results, ensure your boat is stored in a dry place, at a temperature of around 60-90°F.

Frequently asked questions