First Choose a Design
Many people think that the power catamaran is a modern concept. In fact nothing could be further from the truth!
For history shows that possibly the second motor boat ever built was a powercat. It was launched in October 1788 in Scotland - the first ever motor boat was launched just a couple of years earlier in France. See more here
Next, and as a general introduction to power catamarans in general, here is a copy of a talk I gave a couple of years ago at the Port Townsend Wooden Boat Festival.
Side view Jazz 30 (above) with "English Channel" day cabin
It is now well proven that a power catamaran has a smoother ride than a deep V monohull. Furthermore a powercat runs flat at speed, the bow doesn't rise, thus reducing forward visibility, as on a planing monohull. Couple that level trim with no rolling in most conditions and it all results in a very comfortable ride.
Our own cruising boat is a Skoota 28 powercat which has asymmetric hulls designed for displacement, not planing speeds, and has a wide hull spacing to reduce wave interference which results in less slamming and eliminates "sneezing" (the phrase used when the underside of the bridgedeck fills with water and it is forced out forwards and then back over the deck.)
It has been comfortably cruised thousands of miles in the rugged PNW of British Columbia and Puget Sound.
It is fitted with twin 20hp outboards and will motor at 16 knots, or cruise at 12, when it then uses between 5-7mpg fuel. As it has been so successful I have used a similar hull shape on the Jazz 30.
In common with most larger powercats, the Jazz 30 is fitted with twin outboard engines. That keeps the noise and fumes away from the main part of the boat and frees up the interior. Of course no rudders are needed which simplifies construction and maintenance.
Obviously two engines are safer than one, while they also offer outstanding maneuverability, the boat can literally be turned on the spot - so in way less than a boatlength! There's no need for a bow thruster with two engines 12ft apart!
Yet it is also very directionally stable, can run straight through breaking surf, and won't get knocked off course when crossing a wake. And of course you can troll at slow speeds using just one engine, there's no need for a kicker.
There are five watertight compartments in each hull, making the Jazz unsinkable. With a draft of only 14in Jazz can be easily and safely beached, you can even get ashore dryshod, as shown in this photo of our Skoota 28.
The Jazz is lighter and longer than the Skoota 28 and, with less windage, will have relatively less resistance, so will clearly be a faster, more efficient boat.
The Jazz deck layout has been developed following advice from a number of experienced fishermen worldwide. It can easily be adapted to suit your own conditions or requirements, all based on a standard cockpit floor and beam arrangement.
In particular the steering and central cabin can have several options. First, the one as shown in the drawings, is suitable for a charter angling boat in temperate waters, like the English Channel or PNW. So it boasts a separate (composting) toilet and a small galley with an enclosed "wheelhouse" for a (professional) skipper. This version would also have an alternative steering position on the aft bulkhead of the cuddy.
Another option is to have an open backed steering position, and no cuddy, which is better suited for warmer weather and for fishing near shore.
And then there is a flybridge option with an additional helm as high as possible for sighting fish (although these days kites and drones probably do that job better)
A covered T top/bimini can be fitted on all layouts.
The deep forward cockpit beam incorporates lockers and its height prevents spray reaching the fishermen. The aft beam is full width and high enough to make the boat feel secure, even in bad conditions. Live bait storage lockers are built into the beam for easy use from both sides. The cross section sketch below shows the narrow wheelhouse/cuddy and the deep forward beam for protection. The Veed nacelle and sloping bridgedeck are discussed in the text below.
All catamarans have masses of flat useable deck space, and the Jazz has more than most because of its extra beam. However deck space alone is not always useful. You have to hang on to something when driving into a big sea, never mind needing to brace yourself when landing a big fish.
So an optional self draining "trench", approximately 8in below the cockpit sole, is fitted into each hull, with a back rest/hand rail for support and safety. Each trench is thus about 10ft long, 2ft6in below the gunwale and 2ft 4in wide. Under that are the 50gal fuel tanks, forward, and a fish hold aft. This is approx 5ft x 2ft x 2ft in each hull. Thus one can fish safely from each side and across the aft deck.
Jazz has wide foredecks that overhang the hull to reduce spray and to allow for a safe fishing position at each bow, well braced behind a pulpit.
A boarding door is fitted in each hull side to make access easier. The deck hatches shown are illustrative of storage areas. Rods can be kept under the foredeck (accessed from the trenches)
The Jazz has the two main crossbeams (front and back of the cockpit) either pinned together for a demountable boat, or rigidly fixed. In either version the hulls and beams can be built separately with final assembly by the water.
The pinned version will be a bit heavier and more time consuming to build, but does allow for legal road transport without an escort, essential if moving to distant fishing grounds.
So the boat is held together by these two big beams. That means the space between can be fitted out to ones own requirements. The cockpit floor is double bottomed for stiffness and self draining. The underside of the cockpit is slightly Veed, not flat. This is a feature that I have used for many years on my sailing catamaran designs and also on my Skoota powercats.
When the bridgedeck is flat underneath any wave that hits it has nowhere to go, so it slams badly. However even just a slight Vee allows the impact to be deflected sideways, thus reducing the blow. Wave hits are always glancing blows, not direct hits. Believe me, it makes a huge difference to comfort in bad weather.
To further reduce any slamming there is a narrow, deep nacelle running under the cockpit. It also helps stiffen the cockpit floor and allows for a lower cuddy and steering position.
The bridgedeck starts well back from the bows, as obviously that is where most slamming occurs. The forward part is flat and can be a trampoline or slatted deck. The cockpit is drawn at 22in above the water, a very high bridgedeck clearance compared to most 30ft powercats.
One problem with a narrow hull spacing, as used on most trailable powercats, is that the bow waves cross under the boat, so the boat is effectively slamming itself.
Making the hull wider means the waves cross behind the boat. Not only is comfort increased but drag due to wave interference reduces. Tank tests I have performed show that drag can increase by up to 20% if the hulls are too close together.
Jazz is built in plywood with single curvature panels throughout (except for the cuddy roof) so it's very economic, simple and quick to build. Estimated total building time is about 500 hours for each hull or 2000 hours complete for the cuddy version. Our Skoota 28 took 2300 hours with a more complicated interior and bigger cabin.
Finally, when not fishing it's even possible to fit a larger cuddy and convert it to a cruiser with comfortable accommodation for two. Very similar layout to the Skoota 28. See the sketch above, which shows the Jazz 30, top and Skoota 28, below. As you can see, the extra length and freeboard of the Jazz 30 makes the boat look sleeker. the cabin is also a bit shorter. Another option is to have a removable aft cabin. Normally the boat is an open fishing boat, but the aft cabin, similar to that used on the Skoota 24, allows for a double bunk when required
So as I say, you can have a number of different layouts based on the same hulls. Just keep the fore and aft beams in the same place
You can see a provisional studyplan as a PDF HERE
Building plans will cost GBP700 for the first three plans sold and will be available four weeks after ordering. Please email me for more details