28ft Outrigger Canoe - attempt 2 - now 32ft

Key features

• Length overall set at 32ft
• Sail are 224 sqr feet, 112 sqr feet plus 112 sqr feet
• Estimated light weight 550kg
• Optimised for long distance travel by one person in remote areas
• Optimised for low capital cost
• Intended to be highly seaworthy
  
  
• Idea is simple to build, and employ local lower cost labour, say in Solomon Islands to lower overall cost and reduce build time
• Boom connected to mast via gaff jaws
• Use of three crossbeams rather than two spreads out torsional forces and lowers point loading
• Crossbeams are kept high, and curved to give high clearance in seaway
• The long overhang bow acts as a wave piercer, yet has low enough buoyancy not to induce high pitching forces
• Masts at 33kg each are light enough to be taken down at sea by one person
  
  
• Each mast is solid wood round section, inexpensive and easy to make, 7.1m long, 80mm diameter at top tapering to 100mm diameter at base
• Sails are laced to mast, an inexpensive method
• A spare mast would be carried, lashed to the three crossbeams just outboard of cockpit
• A large paddle would be carried as an emergency steering oar
• A spare daggerboard would be carried, I tend to break mine
• Tumblehome forward is intended to shed green water when travelling at reasonable speed in larger waves
  
  
• Sail center of effort is placed just forward of center of hull lateral resistance
• The horizontal base distance for the stays is kept as wide as possible to reduce loads on stays and in turn to reduce mast compression loads
• The use of unstayed masts on mulithulls is in IMHO silly, it throws away one of the multihulls innate positives via its high beam
• All stays are 6mm synthetic rope
• No stainless steel or galavanised wire, no turnbuckles, no crimping
• All stays are secured to natural strong points like boat ends and crossbeams, thus no chainplates are required
  
  
• Hull construction approx 12mm strip planking made from locally sourced timbers
• The hull is divided into four watertight compartment, divided by bulkheads. Each of the three bulkheads is directly below each of the three crossbeams
• The foward hull is for stores, access is via hatch on deck, not ideal but the board and case make access from cabin too difficult
• Occupants of the cockpit are protected from the elements on all four sides by bulwarks of at least 12 inches high
• Netting is placed forward to protect from falling overboard, sails can be worked while not having to be close to edge of netting
  
  
• Cabin size is kept deliberately low to minimise weight, cost and windage
• The starboard cockpit coaming is extended forward to the front crossbeam to distrubite torsional loads, tapering as it moves fowards of the center crossbeam
• Use simple solid stainless steel single and double pulleys as blocks instead of higher cost, lighter, dedicated nautical blocks
• Estimated ama weight approx 70kg and an additional 40kg in spare water and stores. Ama volume approx 500 litres,
• Ama maximum upwards force calculated as 390kg, 500kg - 110kg, when on the tack where the ama is used as a float.
• The externally mounted rudder pivots aft on grounding, thus reducing chance of rudder breakage
  
  

Here are some updated sketches of the 28ft canoe I drew up a few months ago. Idea is a canoe for one person, optimised for longer distance voyaging in more remote places. Note for typical western style use which involves boat ramps, trailering, moorings etc, a shorter, more roomy vessel would be preferable Hullshape is optimised for ocean swells with accommodation well aft, away from spray. The bow sections use a lot of tumblehome allowing for green water to drain away easily.

Hull depth
In regards to hull depth, here I am referring to the vertical distance between the foredeck and the keel. The higher this distance the greater the freeboard, and the dryer the boat will be. The higher deck also allows for more volume forward for more stores, and provides for more buoyancy. The negative of a higher hull depth of is of course is more windage and more hull weight. Thus a compromise between these factors needs to be determined. One way of doing this is to compare craft of a similar class and weight. In this case comparable craft are trimarans in the 22ft to 24ft range. Looking at these we have the following. We can see that the canoe is a fraction lower than multihull vessels of the same weight, however the overall concept of keeping crew well aft at almost all times would permit the concept of a foredeck that is a couple inches lower and thus wetter than others

• Seaclipper 24 116cm
• Piver Nuggest 24 114cm
• Farrier F22 - 103
• Nicky Cruz 6.9 - 103cm
• Klis III 24 - 139cm
• 28ft Canoe - 104cm

Crossbeam clearance
Low bridgedeck or crossbeam clearance can cause pounding or unnecessary drag in higher sea states. The general rule of thumb is that crossbeam clearance should be a minimum of six percent of waterline length. This being a small boat and optimised for blue water, crossbeams are higher at 9.7 percent. At higher weights this decreases a little, however the forward beam, the most likely to strike waves is curved upwards in the center. Thus we can conclude that beam clearance is very good

Deliberate low volume bow concept
The bow is wave piercing yet the prow also has low volume, permitting the bow to disperse water in form of waves, yet the low volume reduces sudden pitch up as can be found in a vertical stem with higher end buoyancy found in western designs. The fine stern permits entry back into the sea after beaching by going stern first. It also provides protection against a following sea in rough weather. Stays are kept simple and wide as possible to reduce mast compression loads

Some degree of self steering should be possible by connecting forward mainsheet to tiller lines Each mast is kept light to permit taking down of mast at sea by one person, say for repairs or for anticipated extreme weather Think the general layout is good, All depends on life circumstances, when can get away from life in Australia, when can just leave commitments, job etc and go I moved the cabin to port, made no sense to have cabin on centreline on a vessel that by definition is not symmetrical port and starboard

Vessel shape into software. Freeboard draft etc, see diagram above
As can be seen above by the fairly rough hullshape put into software, that the draft was a little more than expected. In order to keep draft from getting too deep I widened the maximum beam to 0.9 meters. Hull depth, feel to foredeck I set at 1.04 meters. For displacement I set as my first attempt a value of 900kg. Now at 900kg I found that draft was 46cm and freeboard was 54cm. Waterline length at 900kg was 7.2 meters and waterline beam at 900kg was 0.69 meters, giving a wl hull fineness ratio of 10.5. Now for longer distance touring weights may well be higher. Ideally empty vessel weight would be 500kg, however I dont see this as realistic, 600kg seems more likley, this leaves 300kg for crew, supplies and stores. If we say 80kg for crew, then 200kg for food, water, tools, accessories may not be sufficient. Thus say we have 600kg for vessel, 100kg for crew and clothing, and 300kg for food, water, tools, spares, safety equipement. This gives a total weight at 1000kg. Note that at 1000kg draft = 47cm, freeboard = 53cm, wl beam = 71.6cm, wl length = 7.36m, wl fineness ratio = 10.4. Note that at 1200kg draft = 51cm and freeboard = 49cm, i think that this would be close to maximum weight, more weight might be possible not sure if desirable

Vessel concept and ideology
Idea to keep cabin small and spartan. Concept is more canoe than conventional vessel. Cabin could be lengthened a bit, since the masts are offset and do not need to move. Cabin could go forward and be extended if required, probably push the centre cross beam forward if the dagger board as opposed to aft as it is now. Note that the 38ft wharram Tama Moana has zero cabin, so this is something in between of that and more conventional multihulls which tend to be shorter and carry more structure above gunnel. So adjusting cabin length does not affect mast placement

Speed SA/D ratio
The vessel is not designed to be fast, it is designed to be conservative. Each mast carries 112 sqr feet of sail for a total of 224 sqr feet. Now on a loaded displacement of 900kg, that gives an SA/D ratio of 21.5 or a bruce number of 1.18. This is a fraction higher than the Richard Woods Surfsong catamaran, but much lower than other vessles

When doing sketches years ago I might be happy with the hull, however the complexity and costs of modern western rigging put me off. Then looking back at older lower technologies that work gave me ideas. These methods might not be quite as fast, nor quite as light, however they are cheaper, simpler and still work. Examples are simple round section wood masts (even I have made a couple) which not as light or as aerodynamic as extruded aluminium are far cheaper, easir to make, simpler and repariable. Simple synthetic ropes instead of SS wire for stays that eliminated the need crimping, turnbuckle s etc. Gaff jaws instead of expensive goosenecks. Camping stove instead of galley. Bucket of water in cockpit vs sink with tap to do the dishes. Tie stays to overhangs and crosspbeams and forget about chain plates. Use three crossbeams to spread torsion forces all along the hull and avoid point loading.

Different concepts, different thinking, I am sure conventional shorter vessels that fold for trailering make sense in western settings, however for use in remote locations then perhaps different concepts work better. This same design could be scaled up or down a couple feet, the larger being optimised for longer voyages, the smaller being optimised for ease of getting ashore with help of rollers, make rope and pulley or maybe with aid of one or 2 people.

Thoughts on overhangs
Western designers seem to despise overhangs, it is almost as though you are asking them to design a multihull out of concrete. Lets discuss a little, overhangs add cost in western settings through higher storage fees, marina fees, more difficult trailering, complexity in storing a longer boat in a backyard etc. Now historically overhangs were used as the norm on canoes in the Pacific though. In this context the extra reserve buoyancy when caught out in really bad weather speaks in favour of the overhang. Such a scenario is less likley for the western boater due to modern weather forecasting providing a heads up to bad weather. Also to consider is that overhangs assist in getting boat on and off a surf beach, a scenario common in the Pacific, but rare in western settings. Thus we might conclude that overhangs make little less sense when used in western nations but more sense when travelling between remote islands in a big ocean

Maintaining consistent w/l ratio through hullshape
In this hull shape, defined by eliipitical sections when viewed end on, and when combined wtih overhangs fore and aft, we notice some things. As weights are increased due to higher loading, the waterline beam increases due to the flare of the hull, however the waterline length of the hull also increases at higher loads. These two factors work together to maintain a fairly consistent wl l/w ratio of 10.5 to 1. This allows for a nice smooth hullshape whether lightly or heavily loaded.

Watertight integrity
The main hull is divided into four compartments by use of three bulkheads. The first and last compartment are empty and used solely for reserve buoyancy. The remaineder of the hull is divided in two at the natural location, just aft of the board. The second compartment is for stores and accessed by a hatch on deck. The small safety ama has 170 kg of buoyancy, which when combined with the overhanging cabin pod provides protection against tipping to port. Having the safety ama extend forward provides an edge to the safety netting on port side and assists in resisting yawing forces transmitted by the forward crossbeam

Righting a tipped canoe
In the absolute worse case of having to right an inverted canoe, it might be possible via use of a spar with heavy weight via a sack of water, lifting the ama up and above and then over. This would not be easy, in this scenario having the safety ama flooded would make the job much easier, thus thinking proactively and having two small bungs on the underside of the ama, and using these to fill the ama with water might be a good idea. Lets look at whether it is possible to lift the ama up and over and thus right the tipped canoe.

We can safely assume that the center of the main hull is the center of axis of out rotation fro this task. Note we really need to flood the saftey ama to begin process of righting the canoe, or alternatively temporarily removing the safety ama, which might be easy if it is secured by lashings. The weight of the ama is 70kg and is 2.5m from the main hull centerline. We also having weights of crossbeams that extend more on the ama side that the non ama side. If we forget about the crossbeam masses fairly cloise to left and right of the centerline as these cancel eachother out. Then we have say an additional 20kg of crossbeam at approx 1.5m fom the centerline, please note this is a very rough approximatiion. Thus to lift the ama we need to overcome the combined turning moments of 70kg x 2.5m plus 20kg x 1.5 = 205 kg.m. Now say out righting pole is a spare mast or a spare paddle, or even the spare mast cut in two and lashed togther as a double side to side pole, a reasonable estimate of where this pole might reach to is 1 meter from the centerline in the horizontal plane. Thus we would need at least 200kg of weight to tip. Thus a 80kg crew plus 120kg or extra weight via a waterbag. This is plausible, not going to be easy, but in warm water should be doable, but not to be recommended. Note that the buoyancy of the leepod works against us here, thus partially flooding the cabin even if done intentionally, and then having the water drain into pod on port side as the righting process starts should assist.

As difficult as the above process sounds, my understanding that it has been done on at least 2 occasions, once by the owner of a Klis III trimaran when sailing from Europe to NZ, and once by Meade Guogeon who righted an inverted small ama volume trimaran. Note that an outrigger canoe is going to be much much easier to right than a trimaran, because there is no huge very buoyant ama that needs to be sunk and then rotated under the inverted boat

Why such long overhangs?
The long overhangs are dictated by geometry. Firstly the rig chosen was two stayed triangular sails of equal size. In order to get a rear stay which is directed fully aft, a long overhang is required to give the stay clearance from the sail. Yes an aft spar, boomkin could have been used. For the bow, geometry states that for sail balance, the sail center of effort must approximately line up with center of lateral resistance. To achieve this geometry dictates that the foremast be quite far forward. Then in order to get a sufficient length of horizontal stay base a large bow overhang is required. Yes a bowsprit could have been used. A shorter bow overhang could have been considered, however this would give a shorter horizontal stay base distance (distance between the mast step and where the stay is secured, this would give higher stay tension and higher mast compression loads

Other notes
The reason for the ama on starboard is that for me it looks better, perhaps a deep psychological or personal thing. A few years ago circumstances would have permitted me to drop out, go sailing. Not at moment, in future yes . Overall feel concept is sound. I was impressed by the offset rudder blade described by Kevin Hutchinson in July 2022, I have illustrated the same method here

Cabin internal layout, probably a berth in section of cabin that overhangs. In the main hull section of cabin, probably a seat that faces forward do that the person can eat, read a book, play games on phone etc in comfort

As to the question is a proa better? For me a proa is an absolute no. I despise the extra complexity and hassle the proa comes with. The modern technology of the lightweight, hollow, watertight ama, one that can be weighed up and down with removable ballast, completely eliminates in my opinion the justification for the proa in this medium vessel size, for the solo sailor. For larger vessels then the lower structural loads and lower weights of the proa configuration have significant upside, however at the medium size the benefit is very small. In the lower size again, then the small crab claw sail that can be shunted easily by one person can have its benefits.

As to when it will be built, some day but not in the near future

Lines are easy to determine, take the existing lines from Anuta canoe, add some more depth (freeboard) scale it all up by ten percent. The lines tend to draw themselves