What Is Underpinning On A Pontoon Boat?

What Is Underpinning On A Pontoon Boat? | Life of Sailing

Last Updated by

Jacob Collier

December 20, 2022

Key Takeaways

  • Underpinning is a typical installation of a sheet of aluminum under the deck.
  • Underpinning can improve performance, use less fuel and protect against deterioration.
  • Many marine dealers offer underpinning services, costing a few hundred dollars.

If you are considering the purchase of a pontoon boat, you might have run across an underpinning option on a website. What is underpinning on a pontoon boat?

Underpinning is the installation of a layer of sheet metal on the bottom side of a pontoon boat. This aluminum layer creates a smooth surface for water flow, helping the boat's performance. It makes the ride smoother, boosts speed, saves fuel, and protects the undercarriage of the decking.

There is no question that sales of pontoon boats are skyrocketing. More and more families are turning to these versatile boats for recreational activities. Whether cruising around the lake to a favorite swimming hole, tubing over the waves or just relaxing and picking up some sunshine, a pontoon boat can do it all. The only drawback is that these boats don’t break any speed records. If only there were a way to boost the performance of a pontoon without having to pay for a bigger engine. Many families opt to add underpinning (under skinning) to their boats to address this concern.


Table of contents

What is a Pontoon Boat?

A pontoon boat is a flat-decked boat that is kept afloat using two or three aluminum tubes (pontoons) on either side of the deck. Due to their configuration, they are built for cruising instead of speed like many V-shaped hulls. They are less maneuverable and nimble than a traditional boats, moving at slower speeds, and not built for the open sea. These crafts work best in lakes, rivers, and freshwater environments.

What are the Benefits of Underpinning?

Underpinning (also known as under skinning) is a plate of thin aluminum attached to a pontoon deck's underside. This layer of metal covers any existing metal studs or other protrusions that might create drag and keep the boat from moving as quickly through the water.

There are several benefits of underpinning, which is why many manufacturers are offering it as an additional option that owners can have installed on a pontoon boat.

Reduces Drag

Everyone has seen a car placed in a wind tunnel as the airflow is measured as it travels around and under the vehicle. The same principle applies to boats. Only air isn’t moving around the craft; it’s water.

Scientists have discovered that one thing that hinders a boat’s ability to glide through the water isn’t just how heavy a boat might be. Metal studs, rivets, and bars are used as integral components of pontoon decking and can also create drag. A thin sheet layer of aluminum eliminates these protrusions and creates a smooth surface for the water to move around, reducing a boat's drag.

Boosts Performance

The easier time a boat has to move through the water means, the less effort an engine has to make to perform the task. This benefit translates into longer engine life and less fuel to push the craft.

Smoother Ride

The layer of sheet metal means a smoother ride because the water moves more uniformly across the bottom of the boat. Instead of the water bouncing off metal rivets, the smooth surface helps the boat glide over the tops of waves and skim across the water's surface.

Less Fuel and Longer Engine Life

If the engine works less to move the boat forward, it uses less fuel to accomplish the task. While underpinning won’t make a huge difference in fuel costs each time you take the boat out, the savings can add up over time.

If an engine has to work less to perform the tasks required of it, then chances are it will last longer. Improved longevity for your motor and fewer maintenance costs are examples of how under skinning can save money for owners over the long haul.

Reduces WaterSpray

If you have ever been in a boat on a lake, you have encountered water spray. As the boat moves, the force of its hull sends water flying. Some water condenses into a mist and sprays upward and outward. A metal plate keeps the water down toward the lake's surface where it doesn’t soak your passengers and contribute to the amount of moisture your decking absorbs.

Protects the Decking

Since the underside of the deck is one of the portions of the boat that is most exposed to the moisture of the water, it tends to deteriorate at a faster rate than the top of the deck. A thin layer of sheet metal can provide another line of defense, and since aluminum doesn’t rust as steel does, it can be an effective deterrent to decay.

How Much Does Underpinning Cost to Install?

DIY underpinning kits are sold at marine dealers across the country, and you can do the project yourself. (It can be a hassle to handle a large aluminum sheet and attach it to the bottom of the decking). There are various grades of aluminum, so you want to choose the correct grade. Most boat owners use 5052 and find its strength and durability work as underpinning.

If you hire a professional to do the work, you should expect to pay a few hundred dollars for the service. The easiest way to secure under skinning is to order it as an additional option directly from the manufacturer. Be sure to have an installer spray coat the aluminum sheet metal with an anti-corrosive coating to help add another layer of protection.

Why is Aluminum Used as Underpinning?

Aluminum is ideal for marine environments due to its corrosion resistance. Most metals tend to deteriorate when exposed to moisture (they rust and oxidize), but aluminum alloys are highly effective against rust or metal fatigue. The strength of the metal can take a boat’s constant use, increasing the longevity of the watercraft.

Aluminum has more strength than fiberglass, a component from which many standard boat hulls are made. The metal underpinning will be less prone to punctures or cracking. Even though the aluminum can break if it impacts an obstacle hard enough, the consequences of a break in an aluminum sheet are less than in a fiberglass hull. (In other words, where a break in the fiberglass might be catastrophic to a regular boat, a crack in the underpinning of a pontoon won’t likely cause the boat to sink).

How Much Speed Will I Get Through Underpinning?

If you are looking for a massive upgrade in speed by underpinning your pontoon, you will likely be disappointed. Most boat owners acknowledge that the speed increase is about one to two miles per hour, all things being equal.

If you need to increase your speed significantly, buy a boat with a bigger engine or invest extra money in a tri-toon, which displaces more water than a pontoon. Many manufacturers are developing tri-toon boats that can travel more than 45 - 50 mph.

While most pontoon boats are not built to handle the punishment of those kinds of speeds, caution should be taken if adding underpinning or a larger motor. Consult with the boat’s manufacturer to ensure there are no warranty issues when installing an underpinning.

What Is Underpinning On A Pontoon Boat?
Jacob Collier

Jacob Collier

Born into a family of sailing enthusiasts, words like “ballast” and “jibing” were often a part of dinner conversations. These days Jacob sails a Hallberg-Rassy 44, having covered almost 6000 NM. While he’s made several voyages, his favorite one is the trip from California to Hawaii as it was his first fully independent voyage.

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