Alloy Cats

Is it easier to stand on one leg or two?

It is timely to examine the differences between the two hull forms and endeavour to find some justification for the often repeated sayings, “once you’ve had a cat, you’ll never go back to a monohull!” or “if its not a cat it’s a dog!”

Firstly, let it be said that all boats are compromises. What suits one person does not necessarily suit another – for a multitude of obvious reasons. However we can explore a number of the characteristics of each boat type that can be measured or quantified.

Stability

14m Roger Hill Powercat

14m Roger Hill Powercat

A powercat’s twin hulls focus the buoyancy around the outside of the boat, rather than in the middle, creating much greater stability. Very beamy monohulls do exist and they can be a pleasure to sail in. They do, however, produce a much greater wetted surface, which produces more drag and consequently affects fuel economy. The flatter deadrise of a beamy monohull also compromises its rough water attributes and dryness from bow spray.

A Smooth and Stable Ride

Underway, a well-designed powercat, whether of a planing, semi-displacement or displacement hull type, will produce a much smoother and stable ride than the average monohull. (Note: Some very heavy, and some narrow hulled displacement monohulls can give exceptionally smooth rides but other factors, like excessive rolling, nullify the benefit.)

More benefits

A powercat at speed gains lift and cushioning from spray and air being pressured through between the hulls. As well, there is the obvious advantage of two narrow hulls slicing smoothly through the waves. Think of the benefits when cooking, when travelling long distances, and when striving for a good night’s sleep!

Space

More beam means more useable space inside a powercat, and around the decks. Without the ‘pointed’ shape of the bow of a monohull, a powercat gains considerable deck space forward.

The wingdeck area does encroach into a powercats internal accommodation but designers have found very clever ways of getting around this, more often to the boat’s advantage.

Great use of underfloor areas

Two hulls also offer greater use of underfloor areas – all space can be used for berths, tankage, refrigeration and accessible stowage

Privacy Factors

Few boaties must enjoy sleeping in forward cabins of boats with others (apart from partners) a mere metre or so away. The noises and odours of nocturnal activities can often be unsavoury to say the least.

With a powercat there is at least the separation of the hulls to insulate against these unpleasantries!

Economy

Few boaties would argue against the desire to own a fuel efficient boat. Published trials have shown that between a planing powercat and a planing monohull there is very little difference. The cat takes a little more power to get up on the plane but then tends to run more efficiently.

Displacement Hulls

However the powercat with displacement hulls is a different beast altogether. Depending on the hull sizes it is not unusual for ultra efficient speeds well in excess of 20 knots to be achieved in the economical displacement mode. Hence the proliferation of large catamaran ferries in service all over the world.

Fuel economy is a major consideration when running any business!

Load Carrying

These same ferry owners recognise that powercats are able to carry much greater loads without significant loss of stability or performance. Overload a monohull and you may unleash an unstable monster, a fact demonstrated in some third world countries where overloaded monohulled ferries tragically overturn on a regular basis.

Manoeuvrability

Few other characteristics of a monohull turn people off boating more than the struggle to berth a single-engined monohull launch on a windy day. A powercat will out-perform even a twin engined monohull simply because the props are so far apart.

If you cannot spin a powercat 360 degrees within her own length, you should seriously consider giving up alcohol.

Dryness

Under way you cannot beat a powercat for dryness. The days of gallons of water sluicing across your windscreen when in a beam sea will be gone forever. The narrow hulls slice through the water throwing minimal amounts of water up for the wind to toss back at you, whereas many monos, at even moderate speeds, tends to throw large amounts of water much further out to the side, and up, for the wind to catch.

Haulouts, Marinas & Beaching

Powercats over about 12 metres do have problems with the odd travel lift operator either because they are two wide for the hoist, or the operator’s slings are too short.

That aside, the yards like them because they can be sat on blocks and require no lateral support. Smaller powercats with legs or outboards can even be beached.

Finding marina berths is generally not a problem. Unless excessively beamy, powercats merely fit more snugly into a berth and utilise the whole area.

Costs & Trials

Because of the need to build two hulls to create a powercat, the building costs will be greater than the monohull of similar length. However, the lengths of the two boat types do not equate in terms of space.

Costs

It is said that a 10 metre powercat equates in size more to a 12 metre monohull, a 12 metre to a 15 metre and so on. Hence, if your purchase is based on available deck and internal space, the powercat will actually be cheaper when lengths are compared.

Granted, a second engine does effect the costings, though these days twin installations in all power boats over 12 metres is almost commonplace.

Sea Trials

The ultimate test as to the merits of a powercat is a sea trial. When you are belting through a short 2 metre sea at 20 knots, there is no spray lashing against the windscreen, Mum’s leaning back reading a book, and the beer glass in your hand does not threaten to smash your front teeth each time you sip, then you will understand why powercats will soon rule the waves!

Here at Alloy Cats, we are prepared to show you these features – in real seas!

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