Boat Specs Explained: First-Time Buyer’s Guide

Purchasing your first boat can feel like diving into a world with its own language. From abbreviations like LOA and GT to concepts like draft and beam, it's easy to feel overwhelmed. But understanding boat specifications is essential to choosing the right vessel for your needs — and for navigating conversations with brokers and sellers with clarity and confidence.

This guide breaks down the most important boat specifications and explains what they mean in real-world terms. Whether you're shopping for a family cruiser, a fishing boat, or a long-range yacht, knowing how to interpret these figures will help you make informed decisions.

Hull: The Foundation of Performance

The hull is the structural base of any boat — the part that floats, supports the vessel’s weight, and determines how it moves through water. Its shape, size, and configuration directly impact speed, fuel efficiency, stability, and handling.

Common Hull Types:

• Monohull A single hull that’s common in both power and sailboats. Monohulls offer excellent responsiveness and classic handling but tend to heel more under sail or in turns.

• Catamaran (Multihull) Features two parallel hulls, creating a stable platform with increased living space. Popular among charterers and cruisers for their comfort and shallow draft.

• Trimaran (Multihull) Incorporates a central hull flanked by two smaller hulls. Known for high speed and exceptional stability, often used in performance sailing and long-distance cruising.

Each hull type has unique strengths. For example, monohulls often cut through waves more cleanly, while catamarans offer minimal rolling at anchor and expansive deck areas.

Length: More Than Just a Number

Length is often the first specification buyers notice — but it’s not as simple as it looks. There are two primary ways to measure boat length:

• LOA (Length Overall) This is the full length of the boat, from the very tip of the bow to the end of the stern, including all protruding parts (like bow sprits, swim platforms, or anchor gear). It’s what matters most when determining marina berth sizes and registration.

• LWL (Length at Waterline) This measures only the length of the hull where it meets the water. It directly affects performance characteristics like hull speed, fuel efficiency, and handling, especially in displacement-mode vessels.

For example, a luxury yacht like the Lürssen-built WHISPER (formerly KISMET) may have a LWL of 75.5 meters and a LOA of 95.2 meters — a nearly 20-meter difference due to extended design features like a projecting bow or deck structures.

Model Name ≠ True Length

Boat model names can be misleading. A Sea Ray 420 Sundancer might sound like it measures 42 feet, but it’s actually closer to 45 feet LOA. Likewise, a Navetta 30 model from Custom Line is named for its approximate length in meters but measures 28.43 meters LOA in reality. Always verify specifications, especially when choosing a boat based on berth availability or towing limitations.

Beam: The Boat’s Width and Stability

The beam is the widest part of the boat, measured at the hull’s broadest point, perpendicular to the centerline. It plays a major role in both stability and interior volume.

• A wider beam enhances stability, especially at rest, and creates more room inside — great for socializing and liveaboard comfort.
• A narrower beam tends to increase speed and maneuverability, especially on performance boats, but may reduce interior space and feel more “tippy” at anchor.

Beam size also affects where you can go. Wider boats may face restrictions in narrow canals, locks, or trailer transport.

Draft: Depth Below the Waterline

The draft refers to how deep the boat sits in the water — specifically, the vertical distance from the waterline to the bottom of the hull (often the keel).

• A shallow draft allows access to shallow bays, beaches, and coastal areas. It’s ideal for inland waters, sandbars, and cruising grounds like the Bahamas or Florida Keys.
• A deep draft improves performance in open waters, providing better tracking and resistance to rolling or side-slipping in heavy seas.

When considering draft, think about:

• The depth of your home marina or boat lift
• Tide variations and sills in local harbors
• Whether you plan to anchor in shallow coves or explore remote islands

Buying a boat with the wrong draft for your cruising region can result in frustrating limitations, or even safety risks.

Air Draft: Clearance Matters

Air draft is the vertical distance from the waterline to the tallest fixed point on the boat — often a mast, radar arch, or hardtop.

This measurement is critical if you plan to cruise under bridges, power lines, or other overhead structures. Even in open waters, some areas have height restrictions that limit access for boats with a tall superstructure.

Example: A boat with an air draft of 6 meters might easily navigate most coastal routes but could face challenges in canals or river systems with fixed bridges.

Many manufacturers provide both maximum air draft and minimum air draft (with antennas and masts removed or retracted), especially on boats with folding components. Always confirm this number before finalizing your route or slip reservation.

Displacement: Weight That Shapes Performance

Displacement refers to the amount of water a boat displaces when floating — which equals the boat’s weight. It’s a foundational specification, because a boat’s displacement influences its:

• Handling in rough weather
• Fuel efficiency
• Speed potential
• Onboard comfort

Displacement is usually categorized into three classes:

Light Displacement

• Characteristics: Lightweight construction, smaller overall mass
• Performance: Faster, more responsive, easier to launch or trailer
• Ideal For: Day cruisers, trailer boats, performance sailing yachts

However, light-displacement vessels can be more sensitive to wind and waves, offering a choppier ride in open seas.

Moderate Displacement

• Characteristics: Balanced weight and volume
• Performance: Good mix of speed and comfort in various conditions
• Ideal For: Coastal cruisers, family boats, hybrid designs

Moderate-displacement boats are versatile, handling both inshore and offshore conditions with ease.

Heavy Displacement

• Characteristics: High weight, thicker hulls, larger fuel and water tanks
• Performance: Greater stability, smoother ride in heavy seas, less speed
• Ideal For: Long-range cruisers, expedition yachts, liveaboard vessels

These boats often have a deep keel and a low center of gravity, making them feel stable and secure — at the cost of speed and agility.

Tonnage: It’s About Volume, Not Weight

When you see terms like Gross Tonnage (GT) and Net Tonnage (NT), it’s important to understand that these refer to volume, not mass.

• Gross Tonnage (GT) Represents the total internal volume of the vessel, including machinery spaces, storage, crew quarters, and living areas. GT is used in official classifications, insurance, registration, and port fees.

• Net Tonnage (NT) Refers to the usable internal space — the areas available to passengers, guests, or cargo. It excludes crew areas, engine rooms, and other non-revenue spaces.

For first-time buyers, tonnage affects more than just paperwork. A higher GT generally translates to more living space, larger cabins, and a more comfortable onboard experience. But keep in mind: tonnage can impact marina fees and licensing requirements, especially for vessels over 24 meters LOA.

Engine Type: Inboard vs. Outboard

Your choice of propulsion affects not only how the boat performs, but also how you maintain, store, and enjoy it. Two primary types are commonly used in leisure boats:

Outboard Engines

These are mounted externally on the boat’s transom. Popular for smaller vessels, they’re compact, powerful, and easily replaced.

Advantages:

• Easy Maintenance: Simple to access, service, or replace
• Interior Space: Keeps hull space free for storage or accommodation
• Versatility: Can be tilted or removed, ideal for shallow-water navigation

Ideal For: Fishing boats, center consoles, day boats, trailerable cruisers

Inboard Engines

Installed inside the hull, usually midship or near the stern, inboard motors are integrated into the vessel’s structure and drive the propeller via a shaft.

Advantages:

• Quieter Ride: Engine noise is muffled by the hull
• Smooth Handling: Offers better weight distribution and balance
• Sleek Appearance: No visible engine on the back

Ideal For: Yachts, long-range cruisers, boats prioritizing luxury or interior space

Some modern builders offer models in both configurations. For instance, Fjord Yachts produces the Fjord 41XP with outboards and the Fjord 41XL with inboards — allowing buyers to choose the setup that matches their cruising style.

Final Thoughts: Navigating Your First Boat Purchase with Confidence

Understanding key specifications like LOA, draft, beam, displacement, and engine type is more than just technical jargon — it’s the foundation for making a smart and satisfying purchase. These numbers directly influence where you can go, how your boat handles, and how much enjoyment you get from time on the water.

Here’s a quick recap for first-time buyers:

• Want to explore shallow coves or island-hop? Look for shallow draft and outboard power.
• Planning offshore trips or open-sea cruising? Choose heavier displacement and a deeper keel.
• Have bridge height limitations or marina restrictions?Know your air draft in advance.
• Looking for easier maintenance and space-saving? Consider outboard engines.
• Prioritize quiet rides and balance? Inboard motors may be a better fit.

We’re Here to Help You Navigate

At every stage of the boat buying process — from selecting the right hull design to choosing the propulsion system — expert advice can make all the difference. Our resource hub offers detailed explanations of different propulsion types, hull shapes, and technical standards, so you can approach your purchase with clarity and confidence.

We’re here to support you from the first conversation to your first voyage and beyond. Let us help you turn your boat ownership dream into a well-informed reality.