Trailerboating: Choosing a vee hull

When US naval architect Raymond Hunt developed the original deep vee planing hull back in the 1950s, he was likely unaware of the lasting effect he would have on the power boating industry. The introduction and development of the deep vee hull allowed relatively small boats to run quickly and comfortably through choppy waters while remaining reasonably economical to run.

Before the vee hull, hard chine planing hulls tended to have a rounded, vee shaped bow, but from amidships aft, the hulls were basically flat-bottomed. As you can imagine, this resulted in a very harsh and uncomfortable ride in anything but dead calm seas – the vee bow shape could part the waves, but once the boat rose up onto the plane it rode on the rear, flatter hull sections and would subsequently pound and slap in even mildly choppy seas.

Raymond Hunt adapted the knife-edged shape used at the bow of both planing and displacement hulls and applied it to the underside of the hull. The result was a shape that, when viewed from the bow or stern, looks much like the letter "V".

Compared with the traditional flat bottom hull, Hunt's deep vee hull required more effort and therefore more power to push through the water. Smaller deep vee hulls were also found to lack stability, meaning that the boat would be very "tippy", leaning over at rest and underway.

Building a series of "planing strakes" or planks along the hull on a fore and aft axis fixed this problem. These strakes give the deep vee hull more support, or lift, by providing a flatter running surface without too much of a compromise in ride comfort. This extra lift improves the stability and balance of a deep vee hull and allows smaller, more economical engines to power the craft.

These days, most trailerboat planing hulls are based on Raymond Hunt's original vee hull shape. This does not mean, however, that all hull shapes are basically the same. On the contrary; modern manufacturers are constantly developing and experimenting with different angles of vee or "deadrise", as well as changing the angle, position, and number of planing strakes in an effort to produce a hull that is not only soft riding, but also stable, dry and easily powered.

Powerboats are classified as displacement, semi displacement, or planing hulls. A displacement hull is designed to travel through the water rather than over or across the top of it. It has a rounded, rather than hard chine, and a long, thin, streamlined shape to allow it to slip easily through the water.

Racing yachts generally have the most sophisticated displacement designs, and some are capable of speeds up to 25 knots or more. Small displacement cruisers generally have a top speed of around 12 knots, although the actual attainable top speed is governed by the hull's waterline length.

A semi displacement hull is a compromise between the displacement and planing hulls. This hull type has a flatter stern hull shape in combination with the streamlined bow shape of the displacement hull. With a big enough engine, the semi displacement hull can push to a slightly higher speed than a regular displacement hull.

As we have noted, a planing hull is one that travels across or over the top of the water surface rather than through it. At least 90 per cent of recreational trailerboats in Australia have planing hulls, so this hull type is all you really need to be concerned with.

Selecting an appropriate planing monohull (single hull) shape for your preferred style of boating and fishing is very important. Should you have a shallow, moderate, or a deep vee hull?

A shallow vee hull, commonly fitted to lightweight aluminium boats, is best for inshore boating. The shallow vee hull offers great stability. Because the hull bottom is flatter and will plane or skate across the top of the water with less resistance than a sharper vee bottom shape meaning it can use smaller, more economical outboards.

The good performance from a smaller outboard makes a shallow vee hull the cheapest to buy and to run. You'll save hundreds, possibly thousands of dollars on buying it, and on refueling costs. However, a shallow vee hull will not be as comfortable riding as a moderate or deep vee hull. For this reason it is less than ideal for offshore fishing and boating, where you can expect to run for long distances at sea.

For coastal and offshore applications, a moderate or deep vee hull form is a better choice. Generally speaking, the deep vee hull shape is limited to larger, usually fibreglass monohulls or 6.0m-plus heavy duty plate alloy boats.

Smaller fibreglass boats less than about 5.0m in length, and aluminium boats less than 5.5 m tend to have moderate (15-18 degree) vee hulls. Were these smaller craft fitted with a deep vee (19-23 degrees) hull, they would be very unstable and potentially very dangerous.

By contrast, trailerboats longer than about 5.5m are commonly built with a deep vee hull because they have the size and weight to carry the deeper vee angle, yet still retain acceptable stability at rest.

Most deep vee hulls also need substantially more power than a shallow vee hull to achieve similar performance. The deeper the vee, the more power generally needed to achieve a similar speed.

There are exceptions. Australia’s own vee hull pioneer, the late John Haines, addressed this problem by designing his Haines Signature hulls with a variable deadrise, concave hull shape. At the keel, these hulls have a very deep vee, but as the hull rises out to the chines, the vee shallows progressively. This shape, in combination with the strategic position of planing strakes, allows the boats to perform well with smaller engines, whilst still achieving a comfortable ride and excellent stability at rest.

Quintrex, too, has adopted the variable deadrise, concave hull shape with its innovative Apex hull, introduced in 2017 –itself a development of the 1999 Quintrex Millennium hull bottom.

Another way of retaining good stability with a deep vee hull is to incorporate a hollow keel section – a tube or keel compartment that fills with water when the boat is at rest. Filled with water, it takes away some of the buoyancy created by the deep vee, allowing the hull to settle deeper into the water. The weight of the water also acts as ballast to reduce side-to-side rocking, and stiffens up the hull so that it does not lean over as much when weight moves over to one side of the boat.

These “flooded keels” are not common, but several manufacturers (mostly alloy brands) use them, including, Formosa (Sea Rod models), Bar Crusher, Surtees, and Sea Devil.

Not surprisingly, a number of other factors influence the ride and handling of a planing powerboat. The shape of the hull at the bow, the width of the shoulders, the amount of flare, and the angle and position of the chine and planing strakes will influence the ride, handling, stability, and dryness of a boat.

Some fibreglass manufacturers even have a “stepped” shape to the hulls so that these steps, or cut-outs, break up and aerate the water surface along the hull to help provide a smoother ride in chopper water. You may have seen this feature on big offshore racing boats – but you can also find it on several US-built recreational cruisers and high-performance boats.

The matrix of hull shapes, flares, designs, chine positions and so on is what makes one boat perform quite differently to another.

For example, a study of the forefoot shape, or entry, of a planing hull can reveal quite a lot about its on-water performance. A hull with a sharply vee'd, protruding or extended forefoot or entry in combination with a narrow, more vertical stem shape will tend to be very soft riding into a headsea, but may not handle as well as some other craft in a following sea.

By contrast, a similar-sized boat with a more finely angled stem, fuller entry, broader shoulders and planing strakes will tend to handle very well in a following sea, but may not be quite as soft riding when running upwind.

Vee monohull hull design is complicated for sure, but once you understand the fundamentals you will be able to look at a particular hull and determine its likely ride, handling and performance characteristics with a fair degree of accuracy – and this will help you choose the right vee hull boat for your favourite boating or fishing activity.