The Complete Guide to Marine-Grade Fasteners

There's nothing quite like the feeling of being on the water. Whether you're a regular fisher, enjoy parasailing on the weekends or use your boat for transporting products, having reliable and durable pieces on your vessel can extend its lifetime and ensure you can enjoy your time on the water much longer.

You can use metal in many environments, including those with high water exposure. Marine-grade metals are best for underwater and wet environments to avoid corrosion and failure. These metals can fight off water's effects and prolong the life span of your equipment and tools. Discover the materials for fasteners, the impact of water on these pieces and the various uses for different fastener types.

 

Marine Fasteners vs. Regular Fasteners

Corrosion resistance is the most significant difference between marine fasteners and their traditional counterparts. Because your vessel encounters water frequently, the fasteners must be able to withstand the force and abrasion of the water. These pieces can build rust without suitable materials and inhibit your boat's ability to perform. Some materials offer more corrosion resistance than others, and your specific applications determine the most suitable material.

Effect of Fresh Water and Salt Water on Marine Fasteners

Fasteners below the waterline face much more wear and tear than those above the waterline. Below waterline pieces are critical for your boat's function, so finding quality materials is essential. Non-metallic materials typically underperform compared to metal alternatives, so you should always be aware of the corrosion-resistant properties of the fasteners you're considering. Additionally, you may need to consider different materials if you place your boat in fresh water or salt water, as the salt can accelerate corrosion and deterioration.

Fresh Water

Fresh water is less corrosive than salt water because it has lower conductivity and less penetrating power of chloride through metals. Fresh water typically presents fewer problems for boats, meaning you can have more time between maintenance sessions and don't need to be as careful about the materials you use. You can also opt for more budget-friendly coatings to protect your fasteners from corrosion, as the water conditions won't be as extreme or damaging compared to salt water.

If you take your boat from fresh water to salt water or vice versa, you need to prepare your boat for salt water use. Equipping your boat with materials suitable for salt water makes it easier for you to transition your vessel without needing to swap out parts and pieces consistently.

Salt Water

Salt water can damage many parts of your boat. From metal fixtures to rubber fittings to small screws keeping everything in place, salt can speed up the wear and tear your vessel experiences. It can cause rust and corrosion to build up on crucial parts of your boat, like the motor, leading to significant problems down the road. Rusting prematurely is one of the most important issues fasteners face in salty water. The grade and materials of your fasteners are essential for prolonged use and reducing the chances you face detrimental problems with crucial parts of your boat.

Grade 316 stainless steel, silicon bronze and aluminum are the best materials for fasteners exposed to salt water. These materials are highly resistant to corrosion. However, mixing aluminum and 316 stainless steel increases the chances of galvanic corrosion occurring and can shorten your fastener's life.

You could also consider a zinc coating to better protect your pieces in some environments. Water temperature, air temperature and whether you submerge the material can affect how the zinc performs, but it can be a budget-friendly solution if you're looking for a quick fix.

Materials Used for Marine Fasteners

Marine-grade fasteners consist of various metals. Depending on your use, such as whether you boat in salt water or fresh water, some materials are more suitable than others. Common materials for marine fasteners include the following:

• Stainless steel: All grades of stainless steel have corrosion resistance, but some are more suitable for marine environments. For example, grade 316 stainless steel can better resist pitting and saltwater corrosion. Another popular choice is grade 304, which is less ideal for high chlorine environments but can withstand high temperatures.
• Alloy steel: Marine-grade alloy steel metals have the strength of regular alloy steels and enough corrosion resistance to aid in shipbuilding. Some alloy steels, like MD, ME, MF and MG grades, are appropriate for offshore structural applications, giving you a wide range of opportunities to work with them.
• Galvanized steel: You can use this metal under certain circumstances. Cool freshwater environments are best because galvanized steel has a zinc coating. This material fares worse in warm saltwater environments because the chlorides can corrode the zinc, and the temperatures can quicken corrosion.
• Aluminum: Aluminum has a lower weight and higher durability and strength compared to steel. This material is excellent for boats and structural applications. With the addition of manganese and chromium, these metals aid in corrosion resistance.
• Brass: Naval brass is often used in military applications. It's frequently blended with zinc and tin to improve maneuverability and corrosion resistance. Brass can withstand extremely high temperatures, making it an excellent material for condensers and piping.
• Bronze: Silicon bronzes and aluminum bronzes are excellent for military uses and suitable for water environments. This material can fend off mussels, algae and similar disruptive organisms. It's popular in propeller shafts and propellers because it produces little friction.
• Carbon steel: These materials are typically unsuitable for wet environments because iron is vulnerable to oxidation and rusts easily. However, some marine-grade carbon steel metals are available, such as AH36, EH36 and DH36. These metals have more manganese and chromium than other types, which gives them more corrosion resistance and higher strength.
• Copper: Only some copper alloys are suitable for marine environments. Those with manganese and nickel can offer corrosion resistance and durability. Additionally, copper has high biofouling resistance, helping reduce damage from algae and barnacles.

Types of Marine-Grade Fasteners and Their Uses

Understanding marine-grade fasteners and which are best for your applications can aid you in finding the quality pieces your boat needs. You can reduce confusion and ensure your boat stays running for much longer by knowing which parts you might need. Marine-grade nuts and bolts have many uses in boating applications, and other fasteners are also available. Refer to this guide to learn how you can use them in your applications:

Bolts

You can use marine bolts to secure parts together, install large pieces, stabilize moving items, mount the motor, secure hardware and similar applications. Check out these common marine-grade bolts:

• Hex head bolt: You can use these bolts to draw and secure two pieces together tightly.
• Allen head bolts: This bolt is designed to fit flush with the surface you're working on and works similarly to the hex head bolt.
• Carriage bolts: These bolts have a low profile that allows them to "lock" into place on the surface. You must use a nut to secure these bolts.
• U-bolts: Use these bolts to wrap around objects and secure them to other objects, such as bow eyes or trailer parts.
• Eye bolts: These bolts have a loop at the end and are great for running rope through.
• Hanger bolts: You can install these bolts in wood to provide a stud to secure hardware pieces with nuts and washers.

Nuts

Nuts can help you complete projects like installing mounting brackets, tightening bolts into place, mounting engine cover latches and finishing interior lighting. Consider these nut types for your application:

• Hex nuts: These are great for general use and have six sides. Applications that don't experience heavy vibrations are best for these nuts.
• Nylock nuts: Nylock nuts are thicker pieces with a ring to prevent the nut from coming loose.
• Barren nuts: These nuts have a low profile and unique threaded socket with a truss head.
• Castle nuts: This nut is a hex nut with a series of slots on one side to provide space for wire or cotter pins to lock the nut in place.
• Tee nuts: This nut is excellent when using a washer and nut isn't possible. You can also use them for flush applications.
• Wing nuts: You can hand-tighten these nuts with the two tabs at the top of the piece. These may not be sufficient for marine applications as they can become loose much easier than other pieces, but they can work well for interior applications.
• Cap nuts: These nuts are shaped like an acorn and can provide a finished look to your applications. They isolate the sharp end of bolts and screws, and using them often involves cutting excess threads to tighten the piece properly.

Screws

You can use marine-grade screws to complete things like securing table tops to their base, completing cabinetry or decking, finishing interior framework, securing doorknobs and similar projects. Screws you can find for these applications include:

• Wood screws: Marine-grade wood screws are excellent for fastening two wood pieces together.
• Deck screws: You can use deck screws to secure soft plastics, wood and fiberglass.
• Sheet metal screws: Sheet metal screws can secure thin, soft metals, wood, plastics, fiberglass and more without needing pre-drilling on most surfaces.
• Lag screws: You can use lag screws to anchor heavy metal pieces to wooden structures.
• Bugle head: Bugle head screws can give a flush finish in softer woods.

Washers

Washers help secure rod holders, stand-up blocks and canvas panels and keep nuts and bolts from moving in areas like those near the engine. Here are four standard marine washers:

• Flat washers: Use these general use washers where loads don't need to take up large spaces, such as bolting stanchions bases.
• Fender washers: These washers have double the surface area of flat washers and can spread loads over a larger space. You can use these to through-bolt hardware carrying heavy loads.
• Lock washers: You can use these washers to prevent bolts and nuts from coming loose through vibrations.
• Finish washers: These washers give a clean look to non-countersunk screws.

Rivets

Blind rivets are excellent for installing hardware and non-critical applications when you don't need the strength and durability of stainless steel. Many boat owners use rivets to install hardware and similar structures with limited access to secure nuts or washers. You need a specific tool that matches the rivet's mandrel diameter to install these pieces.

Nails

You can use marine-grade nails for upholstery, interior cabinetry, copper sheathing and canvas waterproofing. Ring shank nails, which have large heads and ribs, are excellent for these types of projects. They have outstanding holding power, making it difficult to remove them.

Pins

You can use escutcheon pins to complete interior trim or wooden accessory racks. This pin is relatively small and has a design allowing it to stay exposed after application. The look and color act as an accent that can complement your interior.

Anchors

Wedge anchors are excellent for heavy-duty applications. The design of these pieces reduces the chances of the anchor spinning, keeping it in place and your applications secure. You have to clean the hole to install them properly, and you can use them for many different projects, like installing machinery, storage racks, dock bumpers and handrails.

Frequently Asked Questions About Marine Fasteners

Understanding all the uses for different types of fasteners can help you determine which pieces will be most beneficial. With so many options on the market, finding the best option can be challenging. Here are some common questions about marine fasteners that can help you find what you need.

What Fastener Is Most Corrosion Resistant?

Stainless steel fasteners are best for corrosion resistance. For the best results, you should opt for pieces with high levels of chromium alloy.

What Is Different Between 304 and 316 Marine-Grade Stainless Steel?

Grade 304 stainless steel is an alloy combination of nickel and chromium, while grade 316 is an alloy combination of nickel, chromium and molybdenum. This additional material makes grade 316 more corrosion-resistant. Grade 304 stainless steel is not as well suited for highly corrosive environments such as salt water.

Will Stainless Steel Corrode in Salt Water?

Although stainless steel is the most corrosion-resistant option for marine use, it can corrode with continuous water use. Despite the alloys that help protect from corrosion, prolonged corrosive conditions will wear your fasteners. Ultimately, stainless steel is not immune to corrosion, but it can still provide the durability you need for water applications.

Is Marine-Grade Steel Strong?

Steel is a strong and durable metal. Its alloys make it even more durable for many applications, such as marine use. Steel can withstand high and low temperatures and weather changes. With resistance to corrosion, grade 316 stainless steel is an excellent choice for marine use. Investing in stainless steel fasteners can extend your boat's lifetime and allow you to enjoy the water for longer.