What Is Draft on a Boat & Why Does it Matter? Complete Beginner’s Guide

Are you gearing up to buy your first boat? Congratulations! As a brand new boater, this is an exciting time in your life!

The process of buying or even looking for a boat is bound to be more than a little daunting as well, however — not least because, as a first-time boat shopper, you’ll inevitably be overwhelmed by the countless big and little things you have to consider. The fact that you will almost certainly run into new and unfamiliar terminology and boating jargon only makes it harder to buy a boat you will love.

Of course, you will have “big picture” things to think about as you go boat shopping. What type of boat do you want? How many people should the vessel be able to accommodate? What kind of budget can you allocate to your new boat, and should you buy a brand new or used boat? What about boat registration, insurance, and taxes?

All in all, buying a boat can be just about as stressful as buying a house — and it’s easy to forget important things, unless you break the boat-buying process down into more manageable chunks.

As you’re making yourself a handy checklist that will bring you one step closer to enjoying the boat of your dreams, always remember to keep a close eye on the draft of a boat.

Before you can shop for a new boat like a pro, of course, you’ll have to know what draft is on a boat, and why it matters. After reading this guide, you will understand exactly why the draft is so important — and what to think about as you hunt for the boat of your dreams.

The Basics: What Is Draft on a Boat?

A vessel’s draft measurement is a critical element to take into account when you are shopping for a new boat, as well as while you are operating a boat. That is because the draft measurement determines what you can do with your boat — unquestionably the thing you’ll care most about!

A draft is, in technical terms, a measurement that indicates the distance between the very bottom of the vessel’s keel (or the boat’s deepest point) and the waterline of the boat.

• The keel is the “backbone” that runs along the boat’s entire bottom.
• A boat’s waterline — the point at which the boat’s hull makes contact with the water — depends on the load the boat is carrying.

Since the a boat’s keel is not simply a straight line, and hull designs vary greatly, this concept can further be expanded to include the draft aft, draft forward, and mean draft:

• The draft aft can be measured at the stern’s perpendicular.
• The draft froward can, meanwhile, be measured at the bow of the boat.
• To find the mean draft, simply calculate the average of the two.

The draft on a boat isn’t simply an immutable number — you can’t ask a boat dealership what the draft on a boat is, receive an answer, and then walk away thinking that the draft will never change. The draft does shift depending on the weight the boat is carrying. The more heavily a vessel is loaded, after all, the more deeply the watercraft will lay in the water. This affects the waterline, and therewith also the draft on the boat.

The freeboard is, as a related detour, the a measurement that refers to the difference between the draft and the entire height of any given vessel — in other words, the portion of the boat’s height that is not covered by water. It is critical to have sufficient freeboard to operate a vessel safely.

If you have only just started to seriously consider buying a boat, you may want to consider the implications of a boat’s draft in altogether less technical terms. You can just think of the draft on a boat as the volume of water needed to be able to float your boat safely, or without reaching the bottom of the body of water you’re on. The greater the draft, the deeper the water has to be for your boat to be able to go on it.

That’s precisely why you need to be aware of the draft on a boat before finalizing a purchase. Whether you are keen on exploring shallow waters or intending to sail deeper waters, the draft matters. It is risky to take a boat with a deep draft into shallow waters, just like it is risky to take a boat with a shallow draft into deep waters.

To introduce you to another term you may hear, instead of draft, you may also hear that a particular boat “draws [followed by a measurement, such as, for instance, 14 feet]”. This refers to the same concept.

What Hull Types Do You Need to Be Aware of When Buying a Boat?

As you’re beginning your boat-buying journey, you will want to consider the three different main hull styles boats have, and how they impact the dimensions of the draft. Boats can broadly be divided into three categories — skiffs, bay boats, and offshore boats. (For the record, any watercraft that weighs 500 tons or more would be considered a ship, while smaller and more compact vessels would fall under the category of boats.)

What are the differences between each hull style?

Skiffs

The term “skiff” covers a very wide variety of boats that share important common characteristics — skiffs are small boats that feature open hulls and operate using fairly basic systems. Beyond that, though, skiffs are incredibly diverse. Skiffs are often leisure vessels intended for river or coastal use, one popular example being racing sailing boats. However, skiffs can also be used for fishing or as utility vessels. They’re either a one-person operation, or they may have a few seats to accommodate several passengers.

Skiffs are boats that have shallow drafts — often drawing no more than three to four inches — and these boats are exclusively suited to shallow and calmer waters.

Bay Boats

Bay boats are also called flats boats or, among fishermen, simply “flats”. Bay boats are most famous for their use in fishing, whether commercial or recreational, as these larger but still extremely agile boats perform well when it comes to reaching tricky areas.

Contrary to what you might think when you hear the word “flats”, bay boats don’t always feature a flat hull. Some do (and in fact, some would consider skiffs to be a type of flats boat), but most bay boats have a V-shaped hull design. This design makes a bay boat uniquely maneuverable, but the precise design and angle also have a great impact on the boat’s draft measurement.

If you are investigating the possibility of buying a bay boat, you’ll have another term to pay attention to in addition to the draft on the boat — deadrise. The deadrise measures the angle of the hull’s V shape. The sharper the V, the deeper the boat’s draft will be. Unless there is a particular reason to do otherwise (which depends on the boat’s design), the deadrise of a bay boat is measured midship, at a cross-section of the hull.

Because there is such enormous variety of bay boats, both in terms of size and deadrise, some bay boats are primarily suited to extremely shallow waters, while others are designed for use in deeper waters. The draft on a bay boat may range from 10 to 14 inches, or the draft may be even deeper.

Offshore Boats

Welcome to the big leagues! Offshore boats are not compact fishing or leisure vessels built to be used on rivers, lakes, and close to the shore. Offshore boats are seaworthy vessels designed for the open waters. Not only are offshore boats much larger, they are also equipped with significantly more complex systems.

Examples of offshore boats include, but are most certainly not limited to, center consoles, sport fishing yachts, and walk-around boats. They represent the largest possible boats — and will, as such, have a deeper draft as well.

An offshore boat may draw anywhere from 14 feet, which enables them to be used with ease in deeper and more hostile waters. Keep in mind that salt water weighs more, per unit, than freshwater, and that this affects the boat’s draft measurement as well.

Why Is Knowing the Draft on a Boat So Crucial?

Being keenly aware of this important measurement is crucial for many reasons — not only as you begin to narrow down your options when you’re hoping to buy your first boat, but also after, when your boat is in active use. Here’s why the draft on a boat is so important.

You Need to Understand Draft When Deciding What Kind of Boat is Right for You

What are you intending to do with your boat? The answer to that question will, to a very large extent, consider how deep of a draft your boat should have.

If you are looking to maneuver your boat easily, across shallow waters, a shallow draft offers many advantages. You will be able to sail right by without any rocks and other obstacles getting in your way, you’ll enjoy increased stability on your boat (which equals improved safety), and you’ll have a great boat to enjoy during solo fishing trips or joyrides.

A boat with a shallow draft will not, on the other hand, allow you to safely move around in even slightly deeper waters, and a shallow draft also means your boat will easily get into trouble on livelier waters.

A boat with a deep draft is designed to be operated on rougher and deeper waters — where the boat will have the stability she needs, while still remaining maneuverable. These boats are also, on the whole, much larger. Basically, if you’re hoping to buy yourself a leisure vessel to enjoy yourself out on the shore with a bunch of friends and relatives (as a huge number of boating enthusiasts are), a nicely-sized bay boat, which will usually draw 10 to 14 inches, may be right for you.

To answer the deeper underlying question you probably have, no — you absolutely don’t need to know an exact number when you are buying a boat. When your boat dealership asks you about the draft you are after, it is recommended that you have a basic grasp of what they are talking about. You can, however, simply answer your boat dealership by describing the activities you are hoping to engage in with your new boat!

You Need to Know Your Boat’s Draft to Operate the Vessel Safely and Responsibly

Boat operators need to remain aware of the draft on the boat to be able to operate the vessel safely and responsibly at all times. This goes far beyond knowing what types of waters your boat can safely traverse, although that is certainly an important component.

Being able to read the boat’s draft also allows you to determine the maximum load a boat can bear without causing a safety risk to yourself, any passengers, and the wider environment. Knowing the draft measurement, in turn, allows you to assess how many passengers your boat can take, and how much other cargo can come on board.

Overloading the boat will increase the draft while decreasing the freeboard. If you push a boat beyond all reasonable limits, you risk flooding — even if you come up against a relatively tame wave. In extreme cases, large amounts of water can quickly collect on the deck, and you could find youself facing an emergency.

In cooler climates, the effect of ice accumulating on the deck of a boat with an insufficient freeboard also has to be considered. Water that builds up on deck will freeze over time, adding weight to your boat and posing a serious safety hazard in terms of slipping as well.

To be able to avoid any undue risk, having the boat’s draft solidly on your radar is always a good idea, and that is true not only for large seafaring ships, but even for boats. It is exactly for this reason that minimum and maximum drafts have been established. As a responsible boater, you want to adhere to international safety standards.

How to Calculate the Draft on a Boat

Are you getting ready to buy your first boat? Whether you are looking to buy a used boat, or are working with a boat dealership and are planning on purchasing a brand new boat, the boat will almost always come with published draft specifications.

These draft specifications offer a very handy point of reference, but are ultimately just approximations. Draft specifications, as published when you buy a boat, are made “dry” — meaning, they refer to the boat’s draft without any fuel, with empty water tanks, without any cargo or gear, and without any passengers. The draft specifications and the draft you’ll see in action will be worlds apart.

Where a new boat is on the market with various engine options, each of which have different weights, you will be able to get an accurate approximation of draft specifications in most cases. However, the hull design of a boat also factors in when it comes to changes in the depth of the draft as heavier loads are carried.

If you want to be able to calculate the draft of a boat manually, meanwhile (perhaps because you’ve come across a boat design and are curious), you can do that, too. Here’s how — but a word of warning, this process isn’t for the math-shy and it also takes a lot of work.

1. The first step you need to take lies in measuring the distance between the hull of the boat and the waterline accurately. If you have the boat in your possession, you can do this by removing the boat from the water and measuring it manually, with a measuring tape.
2. Next, measure the length and the width of the deck.
3. Now, you can calculate the area of the deck by multiplying these two numbers.
4. The unit weight of the water you will be sailing on also has to be taken into account to calculate the draft on a boat manually. For reference, freshwater weighs 62.4 lbs per unit per cubic foot, while salt water weights 64 lbs per unit per cubic foot.
5. Add the weight of all passengers and cargo together.
6. Add all the figures you discovered in steps one through five together. You will then know precisely how much water is displaced by the boat.
7. Next, divide the total volume of water displaced by the boat by the area of the boat’s deck.
8. Add the distance between the hull of the boat and the waterline to the figure you came up with in the preceding step, and you’ll have the exact draft on the boat!

Reading the Draft on a Boat

Did just reading that give you a headache? You’re not alone. The good news is that there’s a much easier way to find out the draft on a boat — one that doesn’t require you to be math-savvy, and doesn’t force you to take your boat out of the water, either.

Simply look at the draft measures on your boat.

Draft markings can usually be found on the sides of the boat, near the stern, and they look exactly like a very large ruler. On cargo ships and other large vessels (including, often, offshore boats), you will find draft measures in multiple places, but on bay boats and other small watercraft, draft markings will be close to the stern.

Are you interested in buying an offshore boat? In that case, you need to know that draft markings are not only present in multiple locations to make determining the draft on the boat easier for the crew. Another purpose for multiple draft measures lies in the fact that the load of a boat affects its inclination. Uneven and asymmetrical loads can lead to an inherent heel or an inherent trim, factors that can render the vessel unstable and dangerous.

Where Is the Draft on a Boat Measured?

The right method to calculate the draft on a boat further depends on the type of boat in question, as the deepest point of the boat will vary.

For instance, for boats with direct-drive inboard propulsion or an inboard pod drive, the draft would be calculated by starting the measurement at the lowest point of the gear sitting below the boat. This would be the propeller or rudder. Boats that are outboard or sterndrive powered will have to be measured twice to calculate the draft — once with the drive down, and again with the drive up. This has a practical purpose, as such boats can safely be operated with the drive up in especially shallow waters, while that would not be possible with the drive down.

What Are Draft Surveys?

Draft surveys are a scientific method of calculating a vessel’s draft with great precision. This allows operators and crews to know precisely how much cargo can be loaded onto a vessel, and where the load should be placed. Draft surveys rely on the vessel’s technical information, in combination with the Archimedes Principle. They are used, however, for large cargo ships and not for leisure or fishing boats.

The Draft on a Boat: A Final Word

In conclusion, you now know that:

• The draft on a boat is the distance between the boat’s lowest point and the waterline.
• A boat’s draft is an important factor in determining what kinds of waters a boat can safely enter.
• Shallow drafts are suitable for shallow and still waters, where they render a boat safe and agile.
• Deep drafts are seen in larger boats (bay boats and offshore boats), where they add stability and ensure that the boat can venture into deeper and livelier waters.
• Boats are sold with draft specifications, but a boat’s draft is continuously influence by the conditions, including the load a boat carries.