Displacement, variable deadrise, strakes, planing, deep-V, deadrise, barge, punt, chine, multi-hull, it all gets a bit confusing, doesn’t it? Then there are essential elements such as speed, efficiency, stability and seaworthiness. That's all before we consider personal tastes, boating use and style, aesthetics, ergonomics and passenger requirements. Let’s see if we can make some sense to help you find your elusive perfect boat from all the separate and distinct hulls.

It seems that the earliest known boats were built in ancient Egypt for use on the Nile in the third millennium BC, but really, who knows? There may well have been ancient bark canoes and rafts from even earlier in humanity's evolution. However, boat hull types have developed and refined since the old flat-bottom hulls.

Significant developments in hull type, structure, design, and construction, as well as revolutionary new materials such as fibreglass and aluminium, have only occurred recently—well, since the industrial revolutions of WW2, anyway!

Yet, while hull designs have evolved, so have engine and drive technology, communications, and electronics to make boating more accessible to the masses, safer, and easy to predict and navigate.  

All boats have a common reason - to float! (Except for submarines and submersibles, I guess!) But we are also now seeing boats that lift onto foils, which I think is a new category altogether.

Converted commercial fishing boat with plenty of deck space and creature comforts

However, the three major definitions of hull design are:

Displacement Hulls

A displacement hull uses buoyancy to support its weight. It displaces the same water weight as the combined/aggregate hull weight at rest.  A displacement hull moves through the water by pushing water aside, not riding on top (planing). 

Displacement hulls are generally relatively slow moving and stable as they sit low in the water pushing aside a weight and volume of water, but slightly differing by actual shape. They are mostly deep hulls with pronounced keels that generally travel through the water at low speeds, mostly up to around 8 knots. They will not get up and plane on the surface no matter how much horsepower is applied; in fact, in most cases, adding too much horsepower is a disadvantage as it inefficiently forces the stern down and the bow up. Most flat-bottom work barges, tugs, commercial, and long-range cruisers are displacement hulls due to their stability, load capacity, and efficiency. Larger planing hulls often travel at “displacement speeds” to increase fuel efficiency on long treks.

Displacement hulls generally have added ballast and stabilisers combined with deep keels to stabilise the ride. Some good examples are larger ships, yachts and cruisers. The formula calculates the maximum speed; “Hull speed in knots equals 1.34 times the square root of the waterline length in feet (HS = 1.34 x √LWL).”

Cape 50 semi-displacement hull

Semi-displacement Hull

A semi-displacement hull is similar to a displacement hull at rest, generally allowing tremendous stability but adding limited planing features and horsepower to create lift at cruising speeds.

Unlike a displacement hull, their design generates lift at fairly low speeds from a combination of low draft, limited keel, low deadrise and extras such a wide, hard chines. Semi-displacement hulls provide a great combination of cruising speed, fuel efficiency and stability making them very popular amongst recreational and commercial motor cruisers and professional fishing boats.

It's hard to beat the ride of V shaped hulls

Planing Hulls

A planing hull supports its weight mainly by hydrodynamic lift created by its hull shape and speed combined with thrust from horsepower. For example, a surfboard is a planing hull, utilising the planing surface for lift, and the wave power for thrust.

Planing hulls are designed to ride on top of the water at higher speeds, mostly at varying speeds over 13 knots. Their hydrodynamics allow the hull to lift out of the water when power is applied, reducing drag and, hence, high-speed ability. Planing hulls come in various designs, including deep-V, multi-hull, cathedral, punts, pointy nose punts and even foils.

As with most hull designs, the flatter the hull shape, the more stable the ride; however, the shallower the deadrise and Vee, the harder it rides, as there is no shape to allow smooth entry or wave piercing effects.

Hull shapes

Punts

Depending on the size, shape, and horsepower, punts can be recreational or commercial, planing or displacement, and any size, up to large work platforms.

In our recreational sense, we see a range of punts from as small as 2.5 metres for applications such as duck shooting to approximately 5.5 metre “pointy nose punts” that are well suited to calm waters and sweetwater sports fishing. The majority are in the range of 3.5 to 4.5 metres and are generally constructed from pressed aluminium.

Punts are traditionally flat bottom hulls with a flat folded entry at the bow, providing tremendous stability but very little rough water performance. However, pointy nose punts and other entry shapes have developed much greater ability in choppy waters. Examples are the Savage Jabiru, Stessl Edgetrackers, Quintrex Hornet and Discovery.

In commercial applications, punts have huge appeal due to their large internal work areas and massive stability. Oyster boats are a typical example. Other punts can be made from a variety of materials including plate aluminium, fibreglass and steel.

Lewis round back clinker ski boat from the 1960's - Image Bob Carter

Round Hull

“Round bottom” planing hulls are very much a remnant of the historic clinker water ski variations. They offer a fairly flat bottom, allowing tremendous lift and small wake, but the rounded chines and sides really gave more aesthetic appeal than performance. They don't lean much into turns due to the flatness of the undersides.  Some examples include: Ramsey Rebel, Lynx, Impala, Pilam and many more.

Deep V hulls are one of the most popular hull designs

V-Bottom Hulls

V-bottom hulls are the most popular recreational boat type, and there are literally thousands of variations in current or historic production. V-bottom hulls require more horsepower to lift to the plane than a flat-bottomed punt; however, their cutting-edge deadrise (the angle of the hull measured in degrees from the horizontal plane), usually combined with a properly formed bow and entry, allows a smooth ride in rough water. The shape is best described as a cutting point for slicing through waves.

In my opinion, punts vary from flat to around 12-degree deadrise, moderate-V hulls start around 13 degrees and progress to approximately 20 degrees at the transom, whereas deep-V's generally start around 21 degrees and go up to about 26, with some even deeper.

V-bottom boats generally handle superbly at speed and have terrific turning capabilities as they don’t “skate” into a corner such as a punt. Generally, the higher the deadrise, the less stable the craft at rest. However, many designs now utilize flooding ballast to increase stability at rest and provide a heavier, chop-absorbing ride in the rough.

Ski, surf and wake boats are generally low in deadrise to maximise lift but often use adjustable ballast, trim appliances, tabs, flaps and gates to perfect their wake.

The range of V-hull variations is endless with design options such as reverse, flat, hard and extended chines, running plank on the keel and various strakes. Then there's a range of entry and stem designs, including flared, convex, concave and variable offerings, both blunt and sharp to combine with standard pointy nose deep-V, pickle fork, cathedral and many other bow designs.  

For example, a bowriders or deckboats often combine a more bulbous and buoyant entry to allow for the added weight of passengers in the bow. In contrast, dedicated offshore machines will have a sharp entry to cut through the waves.

Signature Variable Deadrise Hull

Variable Deadrise

There are planing hulls with “Variable Deadrise”, which defines a varying angled hull, either convex or concave, particularly closer to the stern. They are aimed at keeping the ride of a deep-V hull with greater stability at rest from the hard chines.  

Harris multi-hull pontoon boat

Multi-Hull

The characteristics of multi-hull construction (often called tunnel hull) often raise a range of conjectures among boaties. In fact, multi-hull combinations have existed for almost as long as carved canoes, outriggers and the like. Nowadays, many people love multi-hull hulls, whether in sail or power craft.

Multi-hull construction offers exceptional stability, with most having sponsons on either side and a tunnel in the middle. Multi-hulls can even come in catamarans, trimarans, gull wing hulls, and many different tunnel boat designs. Most offer wonderful operating efficiency due to the lift of the hulls created by multiple planing surfaces and greater air flows.

Houseboats are often built on multi-hulls with multiple sponsons. We have also seen a rise in the popularity of pontoon boats, which have evolved from slow barbeque-style boats into high-speed luxury cruisers and sports boats.

Shark Cats, Noosa Cat, Sailfish and Markham Whaler are just some Australian favourites, with imports like Harris Crown, Regent and Platinum pontoon boats, plus luxury cruisers like Fontaine Pajot, Iliad and Lagoon.

The Shark Cat, and aussie favourite

The Perfect Hull

Just as the "Perfect Boat" has never been made, neither will the perfect hull. There is always a different set of hull features that may be optimal in some situations but don't suit others. An offshore cruising boat is a far cry from a dedicated sportfishing machine and indeed far different from a sweetwater punt and roof-topper.

Then, there are the physical elements from construction materials and the actual boating environment, including the passengers' boating preferences and creature comforts. In my opinion, the perfect boat is the one that keeps you afloat, enjoying your aquatic experience, and gets you home safely.

Maybe you need to be like me—one boat is never enough! Life is certainly better with a boat (or two)!

Wake surfing with a Malibu Boat

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