Marinetalk is supported by its audience. When you purchase through links on our site, we may earn an affiliate commission. Learn more

What Size Boat Fenders Do I Need for My Boat? Find Out Now!

Fact checked by William Hart

what size boat fenders do i need for my boat

Every boat owner knows the importance of keeping the hull damage-free. It is for the boat’s aesthetic, lifespan, and money value if you intend to sell it in the future. Plus, many boats come with a hull protective coating, it’s best to keep the surface scratch-free to prevent algae and mold.

Boat fenders are excellent for protecting the hull. These cushion the vessel in the event of bumping against the dock or other boats during peak hours. However, the wrong size of boat fenders won’t be as effective. For maximal protection, you must consider the boat fender sizes, as well as the number and position of fenders that work best for your vessel.

So what size boat fenders do I need for my boat? Briefly, for every four to five feet of boat length, you will want a one-inch (in diameter) cylindrical fender or a two-inch round fender. That means a 15-foot tracker boat needs three to four-inch cylindrical fenders. But how many fenders should I get? And where to hang them?

Dive in for detailed answers to all questions above!

Table of Contents

How Do Boat Fenders Work

Generally speaking, fenders act as cushioning between the hull and hard surfaces like the mooring, rocks, and other boats. During peak hours or holidays, there is usually a lot of traffic, and colliding and scratching other vessels are unavoidable. Moreover, at large marinas, docking space is very limited. When boats dock closely to each other, you can really use the help of fenders, especially on days when the water is rough.

Types of Boat Fenders


Marine companies have developed many types of boat fenders with different materials and shapes to go with all kinds of vessels. In terms of materials, there are three basic types:

  • Rubber: Rubber is the most widely-used material when it comes to boat fenders. It is because they are cost-effective, durable, and able to absorb relatively large shocks. Huge fenders you see at marinas are made from rubber too. They help keep the dock from being damaged if a vessel bumps into it.
  • Foam: Most foam fenders are not made entirely from foam. They are usually made of two layers. The outer layer is polyurethane elastomer, a popular coating material known for its extreme resilience. Then, the fenders are filled with polyethylene foam. It is why you often hear foam-filled fenders, not foam fenders.
  • These have high absorption and little to no reaction force. In other words, they don’t cause vessels to rebound when colliding, giving more precise handling. This is the major reason why boat owners choose foam fenders.
  • Composite: Composite fenders are known as heavy-duty ones and are mostly used for massive vessels. They can withstand harsh weather conditions and provide protection against ice flow in the open sea.

In terms of shape, there are three basic types:

  • Cylindrical double-eye: This fender type can be hung vertically or horizontally and are used for lighter, shorter boats.
  • Cylindrical center-hole: These can also be hung vertically or horizontally. But with more cushioning, they are often used for larger, heavier boats.
  • Round: Among fender shapes, round fenders provide the highest protection. However, it comes with the cost that round shapes take up a lot of space. At large marinas where mooring is limited, they can be troublesome.

Boat Fender Size Guide


To get the most accurate size of fenders, there are three factors you must consider.

  • Boat length: This is the most critical Many boat fender size charts account for boat length only. The general rule is for every four to five feet of boat length, you will want a one-inch (in diameter) cylindrical fender or a two-inch round fender. For example, let’s say your boat is 10 feet long. Then, you will need cylindrical fenders that have a diameter around three inches. Take a look at this Polyform G series fender size chart.
  • You can see that for a boat up to 10 feet in length, you should use 3.5-inch cylindrical double-eye fenders.
  • Boat weight: The weight of a boat is the combination of the boat dry weight, people and appliances on board, fuel, and engines. To get the maximum weight your boat can be, look for the capacity plate near the captain seat. The plate will tell the vessel’s weight capacity. Then, add this number to the boat dry weight. Depending on materials and structure, some boats are heavier than others.
  • The heavier the boat, the larger fenders you should use. For instance, you are buying fenders for a 20-foot fiberglass bass boat, the recommended fender size is four to five inches. However, your vessel often carries at its maximum capacity and you catch a lot of fish daily. Then, to size the fender up, we recommend 6 to 6.5-inch cylindrical fenders.
  • Mooring conditions: The harsher the mooring conditions, the larger fenders you need to protect the boat. If your vessel is docked at a small, quiet lake, large fenders are not necessary. But if your boat is docked at bustle, narrow marinas where waves get rough from time to time, you should size them up.

Small boat fenders cannot provide much protection for large vessels. In addition, when lacking in number or placed improperly, fenders won’t show their maximum potential. Besides appropriate sizing, you must think about the number of fenders and their placement.

How Many Fenders Do I Need

Frankly, a vessel can never have too many fenders. However, you will need to consider the boat’s aesthetic. No one wants their vessel to look like a massive floating chunk.

We recommend installing three fenders on each side of a 10-foot boat. From there, with every ten more feet, install one more fender. That means a 20-foot vessel should have at least four fenders on each side.

Boat Fenders Placement

To place fenders properly, hang them so that their bottoms touch the water’s surface, then raise them an inch or two. Use these tips to ensure fenders function at their best:

  • Tie them to a solid point that is not made to handle any stress, like a station or a cleat.
  • Tie them as low as possible to limit swing from sea wind. This will help fenders to stay in position and last longer.
  • Use boat fender rope, also known as Jute rope, for strong and durable fenders.

Learn more about fender placement by watching this video on How to tie boat fenders or boat bumpers – and why we need them!


In conclusion, appropriate sizing is crucial when it comes to boat fenders. Learn about the size carefully to maximize their potential. Don’t forget other factors like boat fender rope, position, and number. They are just as important.

We hope you’ve gathered enough information to the question “what size boat fenders do i need for my boat?”. Hope you will make the smartest choice when purchasing boat fenders. Feel free to leave us a comment should you have further questions. See you next time!

5/5 - (3 votes)