I’m looking for a powercat design of around 6 or 7 metres that is ideal for towing. This means it would have to be less than 2.5 tonnes loaded. My ideal would be  for it to be powered by a couple of  150 to 200 hp two stroke outboards.

I’m only looking for a design as I wish to build the boat myself. I’m also interested to hear how these smaller powercats perform, as I’m well aware of the advantages of the bigger craft. That is – does there become a size whereby the advantages of cats tend to fade?

Anyone experienced either of the two designs depicted below? The one on the left is a Boden design.

Multihull Development, Inc, located in Pocasset, Massachusetts, lies in the heart of Buzzards Bay.  It is no accident some of the finest and most able power catamarans the world has to offer emerges from Buzzards Bay. This body of water ‘s boisterous conditions is a constant inspiration for our craftsmen and designers to build craft that can change a nasty chop into a fine afternoon cruise.

The Buzzarrds Bay 34 was designed by Chris White, a world-famous multihull expert. An accomplished worldcruiser, Chris brought an overriding concern for offshore seakeeping, performance and practicality, clearly seenin this design. The warm and inviting accommodations feature the interior space of a much larger boat, theconvenience of one continuous, level floor from helm station to transom, and useful design features throughout.

To read the review of this boat in the Multihulls Quarterly magazine, Click here

Visit the website at www.BuzzardsBayCats.com

Hill’s latest design, just after her launch from Alloy Cats in Tauranga.

BIRD of PREYØrnen’s Australian owners cannot wait to cruise their new boat up and downthe New South Wales Coast. John Eichelsheim took a sneak peek at RogerHill’s latest design, just after her launch from Alloy Cats in Tauranga.

Click on this link to view the report Review of Roger Hill 14m Powercat

The word catamaran is in common usage today but unlike many nautical words there is no obvious origins to its spelling and meaning. Time to go googling!

There are heaps of sites telling me what a catamaran is but I only found one plausible explanation to its origins. It is claimed to be from the Tamil word  kaṭṭumaram, with kaṭṭu meaning to tie  and  maram being a tree or wood. Hence it could be reasoned that a long time ago a couple of maram (many tree varieties exist in Asia and South America) logs were tied together to create a boat which we know know as a catamaran.

Does anyone know of other explanations as to its origins?

Also found out that, although polynesians have enjoyed catamarans (double canoes) for centuries, modern world sailing cats were designed in the 1800s, with the great American designer Nathanael Herreshoff being to the fore.

Browsing the internet the other day I came across a quite vociferous debate on a website forum between powercat and monohull adherents. Of concern was the harsh criticism of some brands of powercats, particularly in the 7 to 9 metre size range. Such was the venom of these attacks that one could only assume that the grounds for criticism were quite justified.

Mentioned was the habit of powercats ‘sneezing’, a term I concluded related to spray being tossed over the boat and its occupants. In my experience with all of our own powercats, the dryness of the ride was one of the most alluring features of these boats. The other comment of concern was the fuel economy, with claims being made that some of the powercats driven were hopelessly uneconomic – at most speeds. What?

As the forum was USA based, I have to ask what the hell are they building over there? I’m darn sure that the New Zealand and Aussie designed powercats, of all sizes, would leave their monohull counterparts for dead when it comes to the dryness of the ride. Powercats that ‘sneeze’ are dogs, not cats, and must bear some serious design issues.

Granted that maybe some of the earlier evolving designs of powercats may have had issues with slamming wingdecks, and bulldozing water and spray forward over the bow, but today we just do not expect that.

Like ourselves, I’m sure all powercat builders doing seatrials for potential customers would insist on moderate to rough sea conditions on the day to clearly illustrate that good cats don’t sneeze!

This article and graph has been circulated for a number of years now and was written by the well known powercat designer the late Malcolm Tennant. While its conclusions tend to favour the benefits of the displacement cat, I’m sure, with the benefit of hindsight and advanced design, planing cats are worthy of more credit. What do you think?

The catamaran may initially require more horsepower than the monohull because of its lesser planing surface but there is the same initial high drag hump which requires lots of horsepower to overcome. Once this hump is scaled there is a marked decrease in the hulls’ resistance to motion which only gradually begins to climb again as speed increases.

Although the displacement catamaran will have a wave resistance-determined hull speed just like the monohull, this hull speed will be very much higher. The speed of the displacement catamaran is largely a function of the fineness ratio of the hulls. At low speeds, see the curve, all the factors are similar and, in fact, it’s very difficult to get the displacement catamaran to go that slow (we found that at times we have to run on one engine to meet low speed limit requirements!)

Realistically, the upper speed range for a displacement catamaran hull is about 20-24 knots. This comes about because of the balance ultimately struck between the beam of the individual hulls, comfort considerations, the size of the engine that must be fitted in a relatively narrow hull and the desire for reasonable (or spectacular!) range required of a serious cruising boat. (In other words, further increases in the fineness ratio just don’t make sense for cruising!)

Displacement vs planing catamaran with the same displacement

At around 12 knots the planing vessel is using 4 times as much fuel. I.e. it’s hull resistance is 3 times as great and it needs 3 times as much horsepower to move at this speed. At 20 knots the planing boat is still using twice as much fuel but the curves are converging. At 24 knots, things even out. The planing vessel will continue to gain, though it too will eventually reach a point where ridiculous amounts of horsepower will be required for continual gains.

The reason for the ultimate limits rests on the fact that for a vessel to plane, the loading or weight on the planing surfaces of the bottom must not exceed so many kgs/sq.cm of surface area. If the loading is greater than this then the vessel will not plane and it will function as a rather inefficient displacement craft. This is the reason why the larger monohulled pleasure boats are displacement vessels. This principle is even more important with catamarans, which may have limited planing surfaces in the first place.

The trick, obviously, is to increase the fineness ratio (achieve the proportions) that move the resistance curve for the displacement boat further to the right, ie: it can be made to have a higher hull speed by making the hulls longer. It is advantageous in terms of fuel economy/horsepower requirements to keep your top speed, and particularly your cruising speed, as far down into the flat part of the resistance curve as is practically possible (in this case around 15-20 knots). (Going much slower than this does not reduce the fuel consumption by much.) Going longer increases the cost of the hull and power plants required.

Juggling the variables, inevitably, seems to mean coming out with a fuel efficient, semi-displacement catamaran hull which achieves cruising speeds in the 15-20 knot range while treating it’s passengers very gently.