Cutting Aluminum Boat Seats: A Step-By-Step Guide

If you're looking to cut out an aluminium boat seat, you're probably seeking more flexibility and space. Removing a bench seat from an aluminium boat is a relatively straightforward process, but it's important to be aware of the challenges and safety precautions. Firstly, ensure your workspace is organised and clear of any objects that could cause harm or get in the way. Identify the type of fasteners used for the bench seat – are they pop rivets or bolts? If it's the former, you'll need to use a screwdriver and hammer to pop off the rivet heads. For bolted seats, a cordless drill will do the trick. Be cautious of any loose or damaged rivets or bolts, and use locking pliers to remove them if necessary. It's also important to note that bench seats often serve a structural purpose, so removing them may affect the boat's stability. To counter this, you can add a stiff wood railing or a floor to reinforce the structure. Finally, don't forget to clean and prepare the boat after bench seat removal, checking for water damage and exposed sharp edges.

Identify the type of fasteners

When identifying the type of fasteners to use for an aluminium boat seat, it is important to consider the specific requirements and constraints of the application. Here are some factors to keep in mind:

Load Requirements:

The load that the fasteners will need to bear is a crucial factor in selecting the appropriate type. If the seat will bear significant weight or be subjected to tensile forces, stronger fasteners or additional support may be required.

Material Compatibility:

Using fasteners made from compatible materials is essential to prevent corrosion and ensure the longevity of your boat. Stainless steel is a common choice for marine applications due to its corrosion resistance, but not all grades are suitable for saltwater environments. Grade 316 stainless steel is ideal for saltwater use, while grade 304 is better for high-temperature environments but less ideal for saltwater. When using stainless steel with aluminium, consider using a galvanic insulator to prevent corrosion. Additionally, avoid mixing aluminium and 316 stainless steel, as this can increase the chances of galvanic corrosion.

Type of Fastener:

The type of fastener you choose will depend on the specific application and the materials involved. Here are some common types of fasteners:

• Bolts: Require nuts and access to both sides of the fastening hole.
• Machine Screws: Identical to bolts but thread into a tapped hole.
• Sheet Metal Screws: Self-tapping screws that cut threads into the surface of a drilled hole. They are suitable for fastening to solid or cored fiberglass and King Starboard.
• Wood Screws: Specifically designed for use with wood and should not be used with fiberglass.
• Rivets: Come with a factory head on one end and are deformed during installation to create a second "head." Blind rivets, commonly called pop rivets, are useful when you only have access to one side of the fastening hole.
• Nuts: Used in conjunction with bolts and machine screws to provide a secure connection. Common types include hex nuts, nylock nuts, barrel nuts, and wing nuts, each with specific advantages and use cases.
• Washers: Critical for through-bolting hardware to distribute the load and protect the surface from damage. Flat washers, fender washers, lock washers, and finish washers are commonly used in marine applications.

Accessibility:

Consider the accessibility of the fastening location. If you have limited access to secure nuts or washers, blind rivets may be a more suitable option.

Cost:

The cost of fasteners can add up quickly, especially when using stainless steel. Consider buying in bulk to get a better deal.

Maintenance:

Some fasteners may require regular maintenance or replacement, especially in saltwater environments. Consider the long-term maintenance requirements when selecting fasteners to ensure the ongoing performance and safety of your boat.

Removing pop rivets

Drilling

Drilling out the rivets is a common approach. Before drilling, it is recommended to measure the body diameter of the rivets to get the appropriately-sized drill bit. This will prevent the removal of excess material and the creation of a bigger hole. When drilling, apply light pressure and let the bit do the cutting. Using duct tape over each rivet can help hold it in place and prevent spinning. Drilling out the head of the rivet and using pliers to grip and loosen the blind end is another technique to consider.

Grinding

Grinding off the head of the rivet and then using a punch to drive out the core is another method. However, this approach may result in grinding parts of the boat, and it can be challenging to see the core hole to hit with a punch.

Snipping and Punching

Using heavy-duty snips to cut off the flat interior side of the rivet, followed by punching it out with a hammer and punch, is an alternative method.

Centre Punching

Centre punching the centre of the rivet can help keep the drill aligned and prevent the bit from walking. This technique can be used in conjunction with drilling to ensure accuracy and minimise the risk of enlarging the hole in the boat.

Chisel and Hammer

Using a chisel and hammer to pop off the rivet head is another option. After removing the head, the body of the rivet can be punched out.

Air Chisel

For areas that are not too fragile, an air chisel can be used to pop off the rivet head, followed by punching out the remaining body.

When removing pop rivets, it is important to consider the structure and integrity of the boat. Removing seats from an aluminium boat can affect its stability and strength, so reinforcing the structure may be necessary. Additionally, ensuring that any replacement rivets or screws are made of suitable material, such as aluminium or stainless steel, is essential for longevity and ease of future removal if needed.

Taking on closed-end rivets

Understanding Closed-End Rivets:

Start by understanding why closed-end rivets are a popular choice for aluminium boats. They offer a secure, watertight connection that is corrosion-resistant and aesthetically pleasing. The closed-end design prevents moisture and corrosive substances from entering the joint, reducing the risk of water leakage and extending the life of the joint.

Selecting the Right Rivets:

Choose the appropriate closed-end rivets based on the raw material and head type. Common types include aluminium-steel, all-aluminium, aluminium-stainless steel, all-steel, and stainless steel 304/420. Consider the specific requirements of your boat, such as corrosion resistance, strength, and aesthetics.

Determining Rivet Size:

To determine the correct size of closed-end rivets, measure the diameter of the existing holes in your boat. Common sizes include 1/4 inch or 3/16 inch in diameter. You can also use a drill bit to measure the hole size accurately.

Grip Range and Thickness:

When selecting closed-end rivets, consider the grip range, which is the thickness of the material you need to fasten. For solid rivets, the length should be the thickness of the material plus 1.5 times the diameter of the rivet. For closed-end rivets, choose a grip range that suits your application, such as 1/2 inch.

Installation Tools:

Closed-end rivets can be installed using standard handheld rivet guns or tools like the 3M5200. Ensure you have the appropriate tools before starting the installation process.

Installation Process:

Follow the manufacturer's instructions for installing the closed-end rivets. Ensure proper installation techniques are used to create a secure joint. Remember that closed-end rivets form a closed head after installation, providing a smooth and sealed finish.

Maintenance and Inspection:

Regularly inspect and maintain your closed-end rivets to prevent loosening or failure. Follow the manufacturer's recommendations for maintenance and inspect for fatigue cracks, especially if the boat is subjected to vibration and stress.

By following these steps, you can successfully take on closed-end rivets for your aluminium boat, ensuring a strong, reliable, and corrosion-resistant connection.

Dealing with bolted seats

If you plan to remove bolted seats, it is crucial to put in a replacement structure, such as a floor or deck, that ties the sides of the boat together and restores rigidity to the frame. This new structure should be securely fastened to the hull, with cross members, to ensure it effectively reinforces the boat.

Additionally, consider the flotation of the boat. Seats in aluminium boats often contain foam, which provides buoyancy in the event of swamping. If you remove these seats, you will need to compensate for the loss of flotation by adding alternative flotation devices or materials.

When installing new seats, it is recommended to use stainless steel bolts and nuts. Go through the entire mounting surface if possible, and use stainless-steel reinforcing plates on both the top and bottom for added security. If stainless steel plates are unavailable, good hardwood can be used instead.

For added stability, you can bolt wood across the length of the bench and then attach the seats to that. This will reduce flex and decrease the chance of ripping the bolts out of the aluminium. Do not use treated lumber, as the copper in it will corrode the aluminium. Instead, opt for untreated lumber treated with a sealant or coated with fibreglass resin.

Finally, always exercise caution when modifying your boat, and consult with professionals or experts in boat design and aluminium boat building if you have any doubts or concerns.

Check for loose rivets

When cutting an aluminium boat seat, it is important to check for loose rivets. Aluminium boats are sheets of metal held together by rivets and welds. Over time, the aluminium flexes and springs back to accommodate loads and impact, causing rivets to loosen or break. To identify loose rivets, you can either beach your boat and gradually slide it into the water, marking the leaking rivets as you go, or raise the boat off the ground, fill it with water to the waterline, and mark the leaking rivets.

Once identified, loose rivets can be retightened or replaced. To retighten a rivet, you will need an assistant. One person holds a buck (a hunk of steel) against the flat side of the rivet, while the other hammers the crimped end. A ball-peen hammer can be used to retighten the rivet head. It is important to avoid excessive hammering, as old aluminium rivets can split or break under heavy force.

If you need to replace a rivet, you will need a source of solid aluminium rivets from a marine supply store or sheet metal vendor. To remove the old rivet, file or grind off one head, or drill it out, being careful not to enlarge the hole. When installing the new rivet, ensure that the unpeened (headless) end protrudes by about 2/3 of its diameter. Drill a hole just larger than the rivet's diameter in a hardwood dowel or steel bar. Place the rivet in the hole and the buck against the rivet head. Slip the dowel over the unpeened end and hammer it to secure the rivet in place.

As a temporary solution until you can install a new rivet, you can use a small stainless steel machine screw with an acorn nut. Applying flexible marine epoxy or sealant to the hole before tightening will help this repair last longer.

Frequently asked questions