Design Requirement
A craft that is seaworthy enough to cruise the SE coast of Australia, can sleep one person aboard in shelter if desired, and be able to land through moderate surf onto a beach and be taken up above the high tide mark by one person. This boat is my solution to that design challenge

My solution to the design requirement is an improved version on my present 18ft tacking outrigger. These sketches shown here are preliminary, however it appears at face value to be greatly improved over my present boat.

When compared to my existing boat some key points are

• A steeper stem to cut through waves better
• A vee bottom to reduce pounding
• Larger storage compartments
• Foam buoyancy in all of foremost compartment and in a section of the aft storage compartment
• Rig at this stage is sprit and jib, combined sail area of 80 square feet as opposed to 45 sqr feet at moment
  
  
• A more vertical stern that allows for conventional rudder fittings
• The ability to quickly disassemble the boat into 2 parts.
• Water ballast compartment in outrigger
• A narrower hull with less flare
• Provision to store items between the 2 hulls on meshing - useful if sleeping in boat
  
  
• A double bottom that adds to structural integrity and is just above the waterline
• Provision of gratings in cockpit sole to raise sleeping mat and sleeping bag above any water in the cockpit.
• Provision to cover the cockpit with a rain and spray proof tarpaulin
• Crossbeams are matched to bulkhead position for structural reasons and to provide an unobstructed cockpit
• Outrigger has a flat top to assist in people stepping on it, volume approx 260L, length=16ft

Notes:
The above sketches represent a better boat. It is the same length as my present boat but ought be much improved. Time frame to building is still a fair way out, when I save up enough money I guess. The hull shape is heavily influenced by the Norman Cross 18ft trimaran, which in my opinion has superb lines. Note that the transom is of modest width that creates less drag at lower speeds.

Disassembly method
The boat is designed to be broken into 2 parts, so that each part can be dragged up a beach single handed. The crossbeams and outrigger are one part, the main hull is the other part. The crossbeams have strong bolts securely glued into them. These then slot into pre-existing holes in the main hull. Then 2 nuts per bolt are added. This is a superior method to my boat where the 2 holes have to be aligned and then the bolt threaded through. The outrigger is permanently attached to the crossbeams.

Outrigger
The outrigger is a deep V in cross-section type. This is the simplest type there is. It is just an extended version of my present outrigger. Approximate volume is 260L maximum width=40cm and maximum depth=40cm. Unlike my present outrigger this projected boat has a flat top to simplify the building process and to provide a flat surface when stepped on. The outrigger has sufficient volume to withstand people stepping on it without it sinking. The outrigger has a water ballast compartment that can be filled with a bucket and drained via gravity. Alternatively a small hand operated pump and tubing could allow the compartment to be filled from the main hull. The compartment can drain via gravity by releasing a pinch operated valve. The outrigger is divided into many compartments for greater strength and to provide watertight integrity

Is 18ft the ideal size
If the craft is too small it will not go trough waves too well. If it is too long weight and cost to build becomes too high. The length seems an appropriate figure and is derived by having 6.5ft for a cockpit, then adding another 40cm for the daggerboard section. Additionally sufficient storage is needed for camping equipment, food, tools, sail accessories, emergency equipment.

Appropriate freeboard and windage
Freeboard is 38cm at midsection at 250kg displacement. The stem is 51cm above the waterline. The freeboard is comparable to my present boat. The bow is a bit lower at 50cm as opposed to 60cm, but this is to reduce windage. Having a slightly higher freeboard than other craft means that more volume is available for storage

Sail Rig
Not shown but rig is planned to be a spritsail mainsail and a jib with a combined area of 80 square feet. A sprit sail (balanced lug or standing lug would work too), without a jib would also work, My thoughts are that the long length of the hull, combined with improved upwind performance, indicate that a main and jib would be better suited than main alone. Much of this is I have to admit an educated guess. I found that my 45 square foot lugsail had insufficient sail area in light winds.

Boat weight
These weights are estimates. I think that the main hull would weigh more than my present boat, and the outrigger would weigh less than my present outrigger. My estimate for main hull weight is 85kg. My estimate for outrigger is 25kg, when crossbeams and rig is added my estimate for total weight comes to 140kg unladen. The idea is that because the crossbeams can be easily separated from the main hull, the 85kg hull is light enough to dragged up a beach by one person. As background, I can drag my 70kg dory from the water and up onto the wharf single handed with ease, but with the combined outrigger craft (sailing mode) I can only manage a few feet

Hull Construction
Boat is built on a strongback with frames and stringers. Then 4mm marine plywood sides and 6mm marine plywood bottom is added. All components are covered with epoxy. Reinforcement with screws where appropriate (screws embedded with epoxy to prevent rust). Hull construction is heavily based on the Norman Cross 18ft trimaran

Rudder
I have shown a conventional fixed rudder. The idea is that this is at a depth where it is protected from damage by the depth of the main hull. Prior to going onto a beach the rudder can be removed and the boat steered by steering oar for the last 70 yards or so. A kick-up rudder would be a reasonable alternative. Rudder is controlled via a yoke and a long tiller.

Timeframe to building
To be realistic I will not be building this year. Actual building time would be modest as I have my experience building my present craft to assist me and speed up the process. It is a question of saving money and then finding a good place to build and store the craft

Crossbeams
I am fairly happy with the crossbeams on my present boat.  I made mine by splitting a 4x2 timber lengthwise to make two 4x1 (in reality about 110x19mm). I then made some 70mm long spacer blocks on the table-saw so that were all exactly the same size. I then made a box beam with width of about 110mm and height of 110mm. I covered the 2 opened sides with plywood which was both epoxied and tacked on. 

At right can be seen a crossbeam under construction from my present boat.  These proved to be overly strong, as we tested a 3m crossbeam with 300kg load at midway and ends supported on bricks (the beam passed easily). 

The spacer blocks are secured into the timbers using heavy gauge coach screws. Where through bolts are in the beam wood reinforcement is required to make a solid beam at this point to avoid it crushing. The beam for any future boat would ideally be scaled down a fraction to minimise weight and windage,  Future box beams should be build in a jig to ensure the timbers are straight and do not warp. A jig can be as simple as a ladder

Freeboard and Windage
If it was not for waves freeboard and windage could be less. My projected boat has more freeboard than the dory hull I have now. So perhaps I can take some ideas from the dory, and some more sheer, and reduce windage and freeboard a fraction amidships. The trouble is that a degree of height is required to provide protection from the elements when the crew sleeps aboard. Additionally some height it prudent to give some puchase for the unstayed mast.

Looking at the below comparison it can be seen that the projected boat has a much longer waterline length. This will improve speed that can be obtained. Additionally it should slice through waves as opposed to just going over them.

Main hull crossbeam linkage
The method proposed is to use embedded bolts that are tight fitting and glued into the crossbeams. These bolts slot into corresponding holes in the main hull. Obviously there a large stresses at this linkage position and attachment points and timbers need to be reasonably substantial

Because the bolts are fixed into the crossbeams it is easier to align the two structures. This is a better method than I use at the moment of having to align two holes, and then thread a bolt through. It may be that the first bolt than goes on is a simple butterfly nut that secures the beam temporarily then conventional hexagon nuts are added. Also note that where the bolts pass through the crossbeam, the beam is under great compression. Thus wood blocks are used here. Grain of this timber should lie horizontal, not vertical, so as to avoid splitting. Ideally these blocks would be of layers with grain at 90 degrees to each other

Sail Rig
Here is a preliminary attempt at working out a sail rig. Mast is shown at 11.5ft high, which is 2.5ft higher than my present boat. Sail area is a combined 75 square feet. This is a modest sail area, but the boat is meant for voyaging not racing.

The Sprit rig has the benefit of having a low center of effort, it has a good reputation, perhaps not the fastest, but certainly capable and robust. Another option might be a lugsail, either balanced or standing. I have a balanced lugsail on my present boat and fine it very easy to use. The sprit sail would be laced to the mast. At least one line of reefing points would be used.

My thinking at the moment is to add another foot of mast height to allow for more sail area, I am not sure. Mast is a simple un-stayed affair of solid wood, round section as per my present mast (I used the cheapest pine that I could find, planed then sanded it round,  then coated with epoxy). Very simple and very cheap. I find my present mast is quite light enough to be lifted into and out of the boat single handed with great ease. One feature of a short un-stayed mast, is that it allows the crew to remove the mast as sea and store it lengthwise on the crossbeams. I have done this on my present boat and find it very convenient. 

Another viable option is to do away with the jib and have a single sprit or lugsail. My guess is that upwind performance would be a bit less, but set-up and takedown time would be less. The trouble is that I do not know how well a lugsail or spritsail will go to windward without a jib. The small cat I used to sail did poorly to windward compared to the larger hobies with a small jib.

16ft Outrigger
Below can be found the lines for the 16ft outrigger. The length is derived from having the rear crossbeam being located at the back of the cockpit, and the front having to be located near the main hull bow, so as to provide resistance to pitch poling. Does the bow of the outrigger have to be at the same position as the bow of the main hull? Cant say for sure, but based on what other tacking outriggers do, and based on photos of traditional craft I have seen, the far forward position seems prudent

This hull has a volume of approx 270L. Beam is 41cm and maximum depth is 40cm. Based on some feedback the position of maximum width has been moved forward. The V section may not be the ideal shape for an outrigger, but it is very simple to make.

Outrigger weight. When working at a float the outrigger is ideally as light as possible, when acting as a counterweight, the outrigger is best if it has some weight. A solution to this is to use water ballast. Unladen weight is estimated at 25kg, added to that is another 30L of water ballast, combining to 55kg of ballast. Now more weight could be added, but I feel 55kg is a useful weight without going to the extreme.

Water ballast can be added via a small hand pump and tubing. Draining can be accomplished by having a small hose at the bottom of the tank, normally the outlet is high up and kept there via elastic. To empty the tank a line is pulls the outlet hose down, stretching the elastic. The water will then drain via gravity out a small hole in the outrigger. A one inch diameter hose should drain a 30L tank very quickly. When sailing in moderate conditions, it may be simplest that the tank is half filled and left unchanged with the extra 15kg of weight penalty being relatively modest

Another Method of draining the tank is to use a short length of pipe on a swivel. Pipe is kept high via elastic, and pulled down via a line to drain the tank through a small hole

A pyramidal style mast partner seems logical as it has low windage and is simple to make. Additionally it would provide some protection from water and spray coming into the cockpit from the bow