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Pontoon Boat Underpinning [ Why and What it Is ]

Just like your car, pontoon boats can be modified to your liking. No other boat comes close to the level of modding freedom a pontoon boat gives.

I’m sure you have heard people talk about underpinning. And you probably want to know what is underpinning on a pontoon boat, and how to do it.

Underpinning is the process of adding a protective layer on the underside of a pontoon boat. The place between the two tubes is a little fragile, and you need to reinforce that area by underpinning it with suitable sheet metal.

Underpinning also reduces drag created by water splash and makes the ride smoother. The layer of sheet metal also helps protect the pontoon boat against corrosion.

Any competent boat owner would invest some time to get their boat underpinned. In this article, I’ll explain everything you need to know about the underpinning process, so stay tuned.

What Is Underpinning?

Underpinning is a fairly common reinforcement technique for boosting a pontoon boat’s performance and durability. The underside of a pontoon boat needs additional protective layers to deal with the strong splashes when the boat reaches high speed.

The sheet metal makes the underside sturdier and makes the surface more suitable for resisting water spray. I’m sure you have felt the incessant water spray colliding under your feet.

The spray can reach a frightening level once the boat reaches speeds above sixteen to eighteen miles per hour.

Underpinning a layer of sheet metal will protect your vessel against that onslaught. The smoother surface area also increases the overall performance.

However, you need to use lighter metal for the job because heavier sheets will affect the pontoon negatively.

What is an underpinning kit for a pontoon boat? I’ve heard this question from many people. It was an underpinning material set introduced by Sun Trackers.

Later some other manufacturers also made their versions. These kits are just some sheet metal suitable for underpinning and some tools to make the job easier.

You could just buy some aluminum sheets from a regular store and get the same performance.

How To Underpin A Pontoon Boat?

So far, I have explained what underpinning is and why it matters. Now, let’s talk about how to reinforce a pontoon boat from scratch.

The whole process is straightforward, so it should not take too long even if you are inexperienced. 

Step 1: Select Materials

Selecting the sheet metal is crucial for underpinning. Different materials offer different levels of protection. People generally use aluminum sheets, but there are two variants you can choose from.

Aim for thin sheets because heavy underpinning will slow the boat down.

5052 aluminum is the most stable choice. It offers the most corrosion resistance and a decent amount of stiffness. 3003 is a lot more common, and you can get them from almost any relevant hardware store. But 3003 is weaker and does not have a high level of corrosion resistance.

6061 aluminum is tougher because of its magnesium and silicon elements. It is a lot stronger than 5052 and has higher stress resistance. Heat resistance is an irrelevant perk, but 6062 is primarily known for this quality.

Overall, I suggest sticking to 5052 because 6061 is a bit more expensive and harder to get while the performance is not that different.

You now need to get your hands on enough fasteners to secure the sheets to your boat’s crossbeams. Corrosion resistance is a must for fasteners because they will stay exposed to the water all the time.

Carbon-steel fasteners are a good choice because they don’t corrode easily. Also, get some self-tapping screws and water-resistant rubber washers.

Step 2:  Sheet Sizing

First off start by measuring the panel size of the boat’s underside. Depending on how large your boat is, you can either cut the sheets to fit from top to bottom or have them separated into segments.

You can do the slicing and dicing at home, provided you have the required tools for the job. Otherwise, it’s better to visit a metalworker to get it sorted.

You do need to leave some space around the pontoon tubes to ensure proper performance. About an inch or half an inch should be enough, do not leave more space than necessary.

You can cover the whole underside with a single sheet if your boat is small enough. But you would have no choice but to use segments for a larger boat.

Step 3: Attachment Style

Attaching the sheets to the pontoon boat is the most crucial part of the underpinning process. Now, there are a couple of ways you can go about it.

The first option is using segments. Cut the sheets into smaller pieces and start fastening them from the back.

Starting from the back lets you have seamless joints facing the water. That is essential because you need that streamlined surface to deal with water drag.

The installation process in this way is simple. You place one segment at the back, then place another by overlapping an inch over the previous one.

Pay attention to crossbeams if you are using a single sheet to cover the whole thing. The sheet metal will bend in odd places if you neglect to align crossbeams at the sides.

You might need to call over some friends when dealing with a large sheet. Otherwise, you will need to invest in some lifting gears to hold everything up while you work.

Segmented sheets require you to use more sheets, so you end up taking in extra weight. On the other hand, a single-sheet installation offers less weight and more security.

The segment joints can cause future complications if you leave any holes in the joints. Overall, segmented is the poorer option, sadly it’s the only option for large boats.

Step 4: Applying Coatings

Underpinning is a protective reinforcement, so it doesn’t hurt to add some extra protection.

Even the marine-grade underpinning material is not entirely safe from corrosion. They will also receive some water damage after some time.

You can increase the corrosion resistance of your underpin with some anti-corrosion spray. These are the simplest form of corrosion-resistant coating you can get on the market.

A properly applied anti-corrosion can increase the overall life of your underpin by a lot.

Benefits of Underpinning a Pontoon Boat

So, what’s the difference between an underpinned pontoon boat and a regular one?

There are many benefits such as durability and safety, but most people get their boats underpinned for the following reasons:

Less Vibration

Every time a pontoon boat goes over 15 miles per hour, the water impact at the bottom gets ridiculously high. You would feel the whole deck vibrating from the incessant impact of the water splash.

An underpinned boat would have significantly less vibration compared to one that was not modified. I guarantee that your ride will be a whole lot smoother on an underpinned boat.

Faster Speed

A smoother underbelly means less drag from the water. The underpinned boats have a smoother surface, and they resist the water drag better than a regular boat.

Owners generally get their boats underpinned because of the speed boost. Most people care a lot about the max speed, and the difference between a modified and unmodified boat is huge.


I hope you now understand what is underpinning on a pontoon boat. Underpinned boats straight up have better performance, stability, and durability. The coating protects the boat from corrosion and gives it increased mobility.

Thanks for reading. And I hope this article helped you to learn how to better use your pontoon boat.