How To Measure The Beam Of A Boat & Why It’s Important

In this article I outline how to measure the beam of a boat. I use a Jon boat as an example but the information below can be applied to any water vessel.

How To Measure the Beam Of A Boat

Measuring your Jon boat’s beam width is easy. The beam width of your boat is the widest part of its hull which is usually the stern of a Jon boat.

The quickest way to measure the beam of a Jon boat is to measure the back part of the boat at the boat’s widest point, taking the measurement from one side to the other.

Why I use a Jon boat as an example

A Jon boat is a good investment, especially if you are new to inland waterway recreational boating, or need a shallow water utility vessel.

They are affordable and easy to transport. Moreover, these boats are relatively easy to maintain.

But, there are very few things that you have to know to properly operate and maintain a Jon boat.

Among these are your boat’s measurements.

In this article I will focus specifically on the beam width but will also touch upon the importance of other key boat measurements you need to know.

If you want more detailed instructions on measuring the rest of your boat read the article that outlines how to measure a Jon boat.

Again I’d like to point out that, this article uses a Jon boat as an example but the information applies to all boat types.

Why it’s important to know the length of the beam of a boat

Having a clear idea of the length of the beam of a boat is important because it allows you to operate the vessel more effectively.

The beam width of a boat determines if the boat can pass through a passage or avoid obstacles.

The width of the beam also determines how fast a Jon boat can run and how steady it is in the face of waves and rough water (though Jon boats are not designed for rough water).

What is the beam of a boat?

The beam of a boat is the part of the boat that is the widest.

A wider beam means the boat can handle rough water better while a narrow beam means the boat will run faster.

To measure the beam of a boat you simply find the widest part of the boat, which is the back end of a Jon boat near the stern.

Measure from one side of the boat at that point to the other side. This measurement is the beam width of your Jon boat.

With that said, knowing your boat’s proper measurements is essential to maintaining its integrity.

Aside from the beam width, there are several other Jon boat measurements that you should take note of.

The added importance of measuring the rest of the boat

Now that you know your boat’s beam width, it is time to tackle all the other necessary boat measurements.

Although we have a full article showing you how to accurately measure your Jon boat we will quickly cover the basics again here.

It is important to take note of your boat’s length overall, waterline length, freeboard length, draft, and total height.

For the most part, you don’t need fancy tools in order to get the proper measurements of your vehicle.

All you need is a measuring tape and a couple of minutes to spare. It is also best to have your boat out of the water to get accurate numbers

Measuring the overall length of a boat (LOA – length over all)

Measuring the length overall, otherwise known as the LOA, is pretty straightforward. In fact, in some cases, you don’t have to bust out a measuring tape at all.

The number beside the name of most boats is actually it’s LOA measurement.

However, if you want to double-check, this measurement spans from the tip of your Jon boat’s bow to the center of it’s stern.

Word of the wise – do not measure until any extensions you might have upgraded your boat with.

The LOA only includes the center of the stern.

Measuring waterline length

Measuring the waterline length is important for several reasons. It shows how much water the boat displaces and where bow and stern waves will hit.

It also affects speed the amount of bottom-paint you will need when painting your Jon boat.

The waterline length measures the surface of the boat that touches the water.

In order to measure the waterline length of your Jon, take note of the part of the bow that touches the waterline.

Extend your measuring tape from that point to the area in the stern where the waterline ceases to touch your boat.

Expect your waterline length to be shorter than your boat’s length overall. It should also change based on whether or not your boat is loaded.

Measuring freeboard length

The freeboard on a boat is the vertical distance between the waterline and the freeboard deck.

Freeboard is a representation of the safety limit of the boat as far as load goes.

When you go below your freeboard length you are running the risk of sinking your boat.

If you are trying to measure every part of your boat, it is best to start with the waterline length before delving into the freeboard length.

This is because the freeboard length is derived from your boat’s waterline measurement.

The freeboard length is the distance between your Jon’s waterline length and your boat’s bow.

Like your waterline length, the freeboard length will change based on the boat’s total load weight.

Measuring draft

The measurement of your boat’s draft is essentially the opposite of its freeboard length.

The draft of a boat let’s you know how shallow it can go.

The shallower the draft, the smaller height of water the boats needs to navigate safety.

Jon boats, like most other flat bottom boats, have very shallow drafts which means they can be used in very shallow water.

In order to get an accurate number, measure the distance between your Jon’s waterline and the bottom of your boat’s hull.

Jon boats have a naturally very shallow draft due to their flat bottom hull design unlike v-hull boats that have a deep draft.

This makes Jon boats one of the best shallow water vessels for private use especially in rivers and creeks.

For a more in-depth explanation of the differences between shallow draft and deep draft read this article.

Measuring total height of the boat

Word of the wise, take the total height measurement last. The total height measurement is simply the combination of the draft and the freeboard length.

The importance of accurate boat measurements cannot be overstated

Measuring your boat seems like an tedious activity. However it is actually an essential part of being a boat owner.

All seasoned boat owners agree that having the measurements of your boat is not only an essential safety step to take but also makes maintenance and upgrades easier to take on.

How accurate measurements affect transportation

In general, a Jon boat is easy to transport but you need to know both the length and the beam of the boat.

It is especially important to know the beam of your Jon boat to ensure you can haul it through certain tight passages – like a toll both for example or a passageway between two buildings or other obstacles (like boulders).

Aside from its affordability, its compactness is one of the main reasons why boating and fishing newbies prefer this type of water vehicle.

The portability of Jon boats allows them to explore various bodies of water across several towns.

Smaller Jon boats can be transported on top of an SUV.

If you own a Jon that is on the bigger side, you would need to purchase a trailer. Your boat’s measurements would come in handy when choosing the right trailer model.

How accurate measurements affect towing

You need to know the dimensions of your boat, including its beam width, to ensure you load it correctly, and on the correct, trailer.

Not all trailers are good for all boat sizes.

By knowing your Jon boat’s dimensions means you will not run the risk of damaging your boat due to unsuitable trailering.

There are also legal concerns.

For a boat enthusiast, there is nothing that can put a bigger damper on a fishing trip than incurring fines from hauling your boat.

If you think about it, violating township rules on boat hauling can stop the party before it even begins.

Towns and cities across the country have different regulations when it comes to hauling Jon boats or just boats in general.

More often than not, bigger Jon boats are only allowed to be hauled and transported at certain times of the day.

Knowing the size of your Jon would ensure that you don’t incur any violations no matter where you transport your boat to.

Accurate measurements leads to a more accurate boat evaluation

The price value of a Jon boat mostly depends on its size. In general, the bigger the boat and the wider its beam the more valuable it is.

Your boat’s measurements are important especially when you are about to upgrade to a better, bigger Jon boat model.

Having a clear idea of how much your property is would allow you to sell at a reasonable price.

Performance and Jon boat dimensions

The size and dimensions of your Jon boat affect its performance.

Knowing the exact measurements of your boat will allow you to set your expectations for your Jon boat’s performance.

You may find that when you review your intended uses for your Jon boat that you need a boat with a wider beam.

Speed is affected by boat beam and length

As you might have already guessed, the longer your Jon boat and the narrow its beam width is the faster it is on water. It simply covers more area.

However, more than the length, the boat’s overall measurements play a role in determining the resistance and hydrodynamics of your Jon.

These two factors play a role in its speed.

The less contact your boat has with water, the faster it is and therefore the narrow the beam of the boat the faster it will.

Moreover, a smaller length to beam ratio also results in a faster Jon.

Choice of motor is largely dependent of the beam width and boat length

The size of your boat affects the choice of motor that you have to purchase for it.

This is especially true of the width of the transom (which is located in the beam area).

While you can install a heavier motor on a small Jon boat, this practice is generally deemed as unsafe as it weighs down the stern.

If you want a faster boat, opt for a longer hull instead of relying heavily on a big motor.

You should consider measurement dimensions when selecting the right Jon boat

Choosing the size of your Jon boat is a personal decision.

Many Jon boat buyers will only look at the length of the boat but you should always remember to take into consideration the beam as well as the length.

The beam of a Jon boat has a huge effect on its performance and its weight capacity.

To determine the weight capacity of a Jon boat read this article and also be sure to read our Jon boat buyer’s guide before buying a new boat.

The best fit depends on your preference and the activities you plan to use your boat for. Nevertheless, various Jon boat sizes suit different needs.