Plate Thickness, Deadrise & Hull Performance: What Actually Matters

When it comes to designing and building a plate boat, every decision counts—especially if you’re the one cutting, welding, and running it. Getting the core elements right makes all the difference to how your boat performs, handles, and holds up over time.

Let’s break down what really matters: plate thickness, deadrise, hull stability, weight distribution, and engine setup. This is the stuff that separates a decent boat from a great one.

Plate Thickness: Where Strength Meets Practicality

A common question when choosing or customising a kit: “Should I upgrade the plate thickness?”

The answer? Only if there’s a good reason.

For example, going from 4mm to 5mm sides might sound like a smart move for added strength—but you’re also adding weight up high, which increases your centre of gravity. That extra weight also affects the balance, performance, and towing requirements of your boat. If you’re not hitting rocks every weekend or building a commercial workhorse, it’s likely unnecessary.

Our kits are designed with real-world use in mind. 4mm side plates strike the ideal balance between strength and ease of fabrication. They’re also less likely to warp during welding—an important factor for DIY builders. If you’re coming from 3mm, moving to 4mm is a worthwhile upgrade. But going to 6mm? You’ll need deeper pockets, and further consideration of your centre of gravity.

Deadrise: Ride Quality vs. Stability

Deadrise is one of those boat design terms that gets thrown around a lot, but it’s rarely understood properly.

We use variable deadrise hulls—meaning the angle changes along the length of the hull. Up front, the steeper angle helps slice through chop. At the transom, it flattens out to improve stability and fuel efficiency.

So what’s a “good” deadrise? It depends on how and where you plan to use the boat:

• 0–8°: Ideal for stable work platforms

• 12–15°: Great for rivers, estuaries, and light offshore work

• 17–19°: Built for offshore performance and smoother rides in rougher conditions

Our different model ranges reflect this thinking:

• EX Series: 8° deadrise for stability and simplicity

• BARRA Series: 15° for inshore versatility

• Offshore Range: Steeper angles for performance out wide

Performance: How the Hull Feels on the Water

Hull performance isn’t just about thickness or deadrise—it’s about how the boat behaves in real conditions. That includes how it feels under load, how it corners, and how it sits at rest.

Most time on the water is spent stationary, so stability matters. That’s why we focus on things like:

• Centre of buoyancy

• Fuel tank position

• Weight distribution

• Trim consistency throughout a trip

For example, our fuel tanks are mounted on the centreline and kept low in the hull to maintain balance whether the tank is full or nearly empty. Baffles inside the tank help reduce sloshing and keep movement under control.

All of these design considerations come together to create a boat that feels stable, smooth, and confident on the water.

Myth Busting: Thicker Plate Doesn’t Always Mean Better

There’s a common misconception that more plate thickness equals a better boat.

Truth is, every CNC Marine kit is already designed to commercial specifications. These aren’t just flat-pack kits—we’re building boats that are meant to be used hard and hold up to real-world conditions.

It’s not about overbuilding. It’s about designing smart from the start, with balance, weight, weldability, and cost all taken into account.

Advice for First-Time Builders

If you’re comparing kits or suppliers for the first time, make sure you’re looking beyond surface-level specs. Here are a few tips:

• Check the real hull length—some brands count bowsprits or outboards in the number

• Look at beam and height—these affect comfort, storage, and capacity

• Compare actual aluminium weights—more weight often means more structure

• Know what’s included—CNC Marine includes everything that is shown in the General Arrangement, some brands kits don’t include critical parts like structure, decks, or fittings

• Ask about builder support—are you getting a full plan and guidance, or just a flatpack?

The right design will give you a smoother build, a better ride, and far fewer headaches down the track.

Final Thoughts

Building a boat isn’t about following trends—it’s about making smart, informed choices that match how you’ll actually use the vessel.

The difference between a good boat and a great one often comes down to the small decisions made at the design stage. Know what matters, ask the right questions, and build something you’ll be proud to run for years.