Intra/inter island ferry/cargo vessel for Timor Leste.
Concept Drawing notes

It is assumed the reader has some knowledge of sailing and boat design. Those who don’t should contact Rob Denney ( for further explanation of anything which is unclear

Overview of Requirements:
The capacity to sail up, down and across the wind, in restricted spaces, in light or strong winds and in shallow water. ie, it should only require an engine when there is no wind. The engine requirements for this are much lower than for a boat which is primarily powered, with sail assist.
Easily and safely handled by 2 crew for trips up to 2 days duration.
Shallow draft and tough structure for beaching to load/unload.
Built and repaired by local semi or unskilled labour with minimal equipment and easily obtained materials.  Minimum structure and maintenance.
Large tender for accessing places the mothership cannot reach.
Easily accessed stowage space for 10 tonnes of cargo.
Comfortable covered seating for 25 passengers.

The boat type that best fits this requirement is a harryproa, ( which is essentially a large, decked in outrigger canoe.  It has one long hull with the rig mounted on it and one small hull which provides stability under sail.  The benefits of this are:
Easier to sail.  A proa shunts (see instead of tacking and gybing. Shunting is a low stress operation that does not require boat speed or well coordinated crew work. The boat can be manoeuvred with less sail area and crew effort, in more confined spaces than conventional boats. Apart from shunting, sailing techniques are the same as conventional boats.
The loads on the structure do not alter appreciably regardless of whether the long hull is loaded or not.   The boat will sail faster when empty, but the loads on the beams and rig are unchanged, saving structural weight. Harryproas are typically ~65% the weight of similar catamarans.
Proas originated in the South Pacific and are still quite prolific in smaller sizes.

The requirements are addressed as follows:
All of these have been tried and tested on various harryproas.

The capacity to sail up, down and across the wind, in restricted spaces, in light or strong winds and in shallow water.
There are 3 essential efficiencies for upwind sailing: rig, leeway preventer and hull shape:
The rig is 2 mainsails on unstayed masts which rotate through 360 degrees.  This allows them to be completely or partially depowered by easing a single sheet.  It is not necessary to lower the sails to reduce the drive force in a squall or unexpected drama.  They can be made appreciably larger than conventional sails due to this.  The extra area enables lighter air sailing.  If reducing sail is necessary, it is an easily controlled process with the boat stopped and no flogging sails or ropes.
Sail shape is controlled by the flexible mast and a self vanging wishbone boom. The boom is well above head height for safety reasons and acts as a bag for the sail when it is reefed or lowered.
The rigs are each controlled by a single sheet.  The loads on these and the halyards are not high enough to require electric winches.
The leeway preventers are oversize rudders, mounted on the inside of the lee hull.  These give improved manoeuvrability and can be lifted to balance the steering loads,  for sailing in shallow water and for beaching.  They kick up in the event of a collision or grounding.
The hull shapes are flat bottomed with small radius chines and minimal rocker. These have been shown to be highly efficient both theoretically (Michelet) and practically.

Easily and safely handled by 2 crew.
Raising the anchor and the sails to get under way will require both crew, sailing only one.  The rig and rudders can be balanced so the boat self steers on most points of sail, leaving the on watch crew to navigate and keep a look out.

Shallow draft and tough structure for beaching to load/unload.
Empty weigh is ~10 tonnes with similar cargo capacity.  Draft is ~0.5m fully loaded, ~0.3m empty.  This enables it to be beached at half tide, unloaded/loaded at low tide and sailed off at half tide.  The hull bottom is heavily reinforced for landing on sand and 3 easily deployed skids (2 under the long hull, 1 under the short one) are used for coral or rocks.  The bottom of the hull is flat, so replacing or repairing the reinforced area is a simple matter of gluing on a replacement sheet between tides.

Built and repaired by local semi or unskilled labour with minimal equipment and easily obtained materials.  Minimum structure and maintenance.

Composite boat building has undergone a revolution in the last decade. Vacuum infusion of laminates has removed most of the mess, wastage and labour resulting in lighter, cheaper and easier to build hulls.  If the hulls are specifically designed for infusion, the savings are even larger.  Infusion requires a vacuum pump, but apart from scissors to cut the fibreglass, few other tools.
Conventional boat building requires full size, expensive moulds.  The harryproa hulls, beams, booms and bridgedeck are all single curvature shapes built in low cost moulds made from mdf or similar materials, which can be cut and joined using hardware store tools.
The hulls are identical apart from the length of the flat centre section. They are also symmetric top and bottom, with parallel sides. Hence, a single quarter hull mould can be used for both hulls, which are built in sections, with male/female joins which are bonded together.  The joins, hatches, mast and beam reinforcing, ribs, stringers, furniture landings, doors, window spaces, shelves  etc are all included in the infusion.

The standard laminate is woven rovings/csm/woven rovings. The masts and rudders are built using similar techniques to the hulls etc but from fibreglass and carbon in it’s low cost ($20/kg) unidirectional form.  Fibreglass is ~$3/kg) and resin $8/kg.

Performance sailboats use pvc foam cores for panel stiffness at minimal weight.  This is expensive and is replaced with ring frames and stringers which are included in the infusion.

Most of the work in building the moulds, cutting and placing the fibreglass, infusing and assembling the components is unskilled. A supervisor is required, but the rest of the labour force could be local. By the end of the job, they would have a very marketable skillset.

Because the boat is simple and voyages short little fitting out is required.  Solar shower, icebox, 2 bunks and a cooker for the crew, composting toilets and bench seats for the passengers. Radio, lights, chartplotter and AIS run off a small battery and a solar panel.

There are no holes in the hulls below the waterline and no deck fittings apart from turning blocks to route the sheets to the control station and a pair of winches for the anchor, halyards and sheets. Steering is simple wheel/chain/line to a quadrant on the rudders.

The sails are of comparatively high tech material, chosen for low stretch and longevity.  The panels could be machine cut in Australia, then assembled and sewn on site.   There is very little rigging (2 x halyards, 2 x sheets, 2 x 6:1 blocks and tackles, anchor and mooring warps) which would need to be imported, although terminations (splices, etc) are easily learnt and could be done locally.

It would be possible to build the boat on the open, but qc would be easier in a covered space.

Repairing flat or single curvature panels is simple.  Remove the damaged material, cut a sheet a little bigger than the hole and glue/screw it in place.
The ropes and sails will have finite lives, but with a long period of obvious deterioration giving ample time to replace them.
The bottom of the hulls will need to be kept free of growth for best sailing performance, but this can be done between tides, perhaps once a fortnight to minimise the work.
The composite components will not need any maintenance apart from painting every 10 years or so with industrial paint. The unstayed mast will not require regular inspections or rigging adjustments to keep it straight.

Large tender for accessing places the mothership cannot reach.
The 11m long, 3m wide, 1m high catamaran tender has payload of 2 tonnes and excellent seakeeping.  It is powered by a 50 hp diesel outboard, set up to use coconut oil.  It will be used to access the few places the mothership cannot and in settled weather, to make short side trips to deliver/pick up passengers/freight allowing the mothership to continue sailing.
The tender bows are attached to the beam on the mothership with a hinge, allowing the tender stern to be lowered and the outboard used to power the mothership.  This would be the only source of external power for the mothership, which would be expected to sail anywhere as long as there was more than 6 knots of breeze.  In less than this, the tender would propel it at ~6 knots.

Easily accessed stowage space for 10 tonnes of cargo.
The long hull has the masts and the beams at 25% and 75% of it’s length.  The space between them (10m x 2.8m high x 1.3m wide) is for cargo. It is accessed through deck hatches using the masts, booms and halyards as cranes and/or manhandled through side hatches onto the tender, beach or dock.

Comfortable covered seating for 25 passengers
Bench seats around the cabin in the ww hull provide seating with plenty of space for moving around. This area is separate from the crew’s quarters in the ends of the hull and blocked off from the wheel, winch console and navigation station from where the boat is sailed. There is also safe seating/lounging space on the deck if the weather is suitable.  Access to the cabin is via a stairway on the windward side of the boat.

Preliminary Specifications:
Length/width/height leeward hull: 24m/1.5m/3m
Length/width/height windward hull, incl cabin: 17m/6m/2.5m
Beam overall: 11.4m
Empty displacement: 10,000 kgs
Loaded displacement: 23,000 kgs (25 people, 10 tonnes cargo)
Draft empty: 0.3m
Draft loaded:0.5m
Mast Height: 22m
Sail Area: 155 sq m