Skoota 20 Notes

Introduction

Power catamarans offer many significant advantages over monohull power boats.

They are safer, due to their twin engines, high stability and self draining cockpit.
They offer low wake and much improved fuel economy.
They are comfortable under way with no slamming or broaching in waves and have excellent handling in a seaway while being very maneuverable in harbour.
They do not roll when fishing or at anchor and are easy and safe to beach.
They have more deck and interior space for a given length, not just because of their wide beam, but also because they have an essentially rectangular living space.
Thus they do not have to be as big as a monohull to give the same interior room, performance and safety.

Interior

Skoota is a trailerable coastal cruiser and is as small as practicable to keep costs and trailing weight down. (There is no point in having a trailable boat to save mooring fees if you need to buy a bigger car to tow it).

It has a small central cuddy which has sitting headroom (standing headroom uder the raised main hatch) and room for a double bunk/dinnette, small stove and worktop.

The cockpit tent and bimini are not shown on the drawings, but are an integral and essential part of the design. Not only does the tent give another "room" with full headroom, but also provides a dry, private space at night for the toilet (portapotti). (During the day it is used in the cabin)

The hulls are only used for bulky storage (like an inflatable dinghy), fuel tanks and possibly bait/fish wells.

Performance

Most power catamarans are planing boats, with all the disadvantages that the type implies. Furthermore they tend to have a narrow, 8ft beam for trailing, so that many of the advantages of the catamaran form are wasted. Skoota, on the other hand, uses semi displacement, non-planing, asymmetric hulls.

The hulls are finer than those used on a sailing boat, because power boats always have power available to get over the hump speed, so low speed, wetted surface friction drag is less of an issue. Tank testing has shown that there is significant extra drag caused by wave interactions between the hulls (up to 20% at certain speeds) if the hulls are close together.

Thus, Skoota has widely spaced hulls, yet will still fit in a standard 14ft wide slip. The hull asymmetry helps fool the water into thinking the spacing is wider than it really is. The computer predicts a 12 knot cruising speed at 12mpg using 2 x 9.9hp outboards and 18 knots with twin 20hp outboards.

Trailing

The boat folds for trailing in the same revolutionary way that has been used very successfully for over 15 years on similar sized sailing catamarans (eg Wizard, Sango). In simple terms, the trailer is backed down the slip and as the hulls hit the water their buoyancy pushes them up, thus the boat unfolds automatically as it is launched. During retrieval the boat folds, again automatically, with this time gravity doing the work.

Of course four stroke outboards have problems when they are rotated, so there are two basic power options. First, to have a single central mounted outboard (ie similar to a pontoon boat) and the second to use rotating outboard brackets, as commonly used on tenders on trawler yachts.

A third alternative is to use 2 stroke outboard engines which don't have the sump oil problem.

The trailer itself is a simple flat bed with T-section supports to match the cuddy bottom. Flexible mudguards are used to help reduce overall height. A 4 wheel trailer is recommended. Final trailer details will depend on the country of use.

Construction

Not everyone can build complex shapes, but everyone can build in flat panels. So for mass appeal Skoota is built using conventional plywood-stringer-frame construction with all surfaces glass/epoxy sheathed. Fortunately this building method is still the cheapest and quickest.

Because the boat is modular, it can be built in an ordinary garage (lengthened as necessary to build the hulls). Building in sections also has a psychological advantage, especially important for amateur builders, which is that it is quick to build each section, thus progress appears to be fast. Furthermore there is little fairing to do, just smoothing the glass joints.

Conclusion

The Skoota offers: stability, low wake, the ability to maintain high speeds in rough conditions, superb directional stability, a self-draining cockpit, fully buoyant hulls for safety, fuel-efficiency, lots of interior space, low speed maneuverability and the security of twin engines. A clear winner by anyone's standards.

A 24ft version with a central cockpit and aft cabin (with a double berth) is planned for later in 2010