Multihull Structure Thoughts

A story about Mr Rob Gillet who built a tacking outrigger about 30 years ago. It was intended to be a fun machine for cruising around the local islands of Fiji which are often EG 20 miles apart so you can do it in a nice daysail. Then he got a little adventurous and shipped the boat to Tonga and sailed back to Fiji. A trip of 500 miles in open ocean with only a few stops in between. Fun with an outrigger that had less than 1 foot of freeboard when loaded for ocean travel.

The boat is “Nakono”, a tacking outrigger. Nakono is 23.8 x 14 foot with an unladen weight of 850 lbs and a normal displacement of 1100 lbs and a ocean loaded displacement of 1300 lbs. The 16 foot mast carries a gunter rig mainsail of 118 square foot with 13 foot spars on the leading edge and boom. The total rig height is 24 foot. The jib is 43 square foot. The length to beam of the main hull is 10 to 1. The float is 16 x 1.1 foot with a length to beam of 15 to 1. The rudder is stern mounted on the main hull. The draft is 1.2 foot. There is a small outboard but paddle power is also used.

Nakono is an open boat, but after initial trials, if the outrigger was going into rough weather canvas or plywood covers were put on the ends of the main hull to minimise wave water ingress. This meant the “off watch crew” only had to do a small amount of bailing of water when sailing.

Nakono was originally intended to be a timber boat but the owner could not find a builder interested so a fiberglass builder offered to build the boat. The construction is mainly solid fiberglass with timber beams. I will quote the owner “A wooden jig (temporary frame) was constructed to which sheets of 6mm Divinycell foam were stapled. Seams between the foam sheets were filled and faired. Over this surface (eventually to become the outside of the hull) three layers of fiberglass cloth (300g and 450g chopped strand matt, 330g woven cloth) were laid. The structure was then turned over and glassed on the inside (two layers of 300g chopped strand matt, and one layer of 16oz roving). Departure from the original plywood design included a completely sealed watertight stern section and floor area, re-inforcement of the hull in the area of outrigger support attachments, extension of the foredeck further aft, and the use of a fiberglassed solid foam outrigger float.”

“The cross beams were timber made of a local wood called "dakua" (Agathis vitiensis), the solid-stock pieces measured 2" x 6" x 14'. After snapping one in a moderate sea 5 miles offshore, modifications were necessary and the beams were replaced with ones made from 12 laminations of timber”.

The performance of Nakono in 15 knot tradewinds aft of the beam produces an easy 7 to 8 knots average. It has sailed 240 miles in open ocean in one leg which would indicate 36 hours of sailing for 2 crew in a boat that required the off-watch crew to cook, provide coffee, bail and try and get some rest in a near open boat. The crew would need to have a fairly easy boat to sail. Also, you would need to choose your weather window and course selection well as I would not expect great upwind performance.

An interesting concept which partially formed the basis of the FOA tacking outrigger Kir 2 design in timber which can be found on the web. The jpegs give the idea. Nakono has a canoe stern whereas the Kir 2 design has a transom stern but the rest is very similar.

 

@oldmulti those photos are making outrigger canoe sailing in the tropics look most appealing. No doubt all hands were too busy for photography during challenging periods, but vessel and crew obviously handled it well.

 

The Stiletto catamaran is a fun boat that provides high performance and was trailable.

About 500 Stiletto 27s were built during the 10-year production run from 1976 to 1986. However, like most older boats, custom buyer options and owner modifications over the years mean current Stilettos can vary widely in design details, deck hardware, sail options, rig sizes, etc.

Some of these boats broke which left spare hulls, rigs etc. The result is this Stiletto tacking proa. I know very little about this boat. The main hull appears to be a Stiletto 27 catamaran. The smaller hull might be a 16 or18 foot beach cat hull. The sliding mechanism was a component of the Stiletto 27 catamaran.

The basic Stiletto is 26.9 x 13.8 foot can be folded to 8.5 foot by sliding beams. The weight is 1100 lbs with 336 square foot fractional rig. The draft over the bridgedeck board was 4 foot, some were converted to daggerboards in the hulls. The cats were fast due to there low weight and many aggressive skippers.

The structure was inspired by the original part owner of the business who used to sell Ciba Giga products including Nomex and epoxy resins etc.

Back to the tacking proa, If you study the 3 jpegs, we have a trailable version but the in water version appear to have different cross arms. The build is excellent for recycling parts but I know nothing about its performance.

Sorry about the limited jpegs but I can find no further details.

 

Guessing by the name (Haole Kai) of that Franken Proa and the background scenery of the photos that it may be a Hawaiian boat.

Here’s another interesting Hawaiian build I came across the other day.

It’s an Electric/Kite powered Trimaran that looks to be nearing completion.

Lots of videos documenting the build thus far.

Here’s the latest:

 

@oldmulti great discussion, I was wondering if you've any coverage of Walter Greene's trimarans A Capella, Happy, Friends and Lovers or the original Friends, I didn't see anything listed in the index

 

This is what happens when you have left over material from a house build which used some wood and ply for concrete form work. You build yourself a boat. Kejak started as a doubled ended design from an article in Mother Earth News, but was simplified to suit the materials available.

So we have a 21 foot main hull that is 4.5 foot wide with a 4 foot wide bottom and 2 foot high sides. Notice, cut your ply in half and you have 2 sides, use 3 sheets join them together you have slightly longer than 21 foot. The 2 masts were 50 x100 mm pine roughly cut to a shape. He also made his own sails. The oars were made from 50 x 50 timber with ply blades on the ends. The gunnels were some 50 x 150 mm for some strength and good looks. The centerboard/rudder size were finally determined by the amount of spare wood laying around not any calculations. The 21 foot “dingy” was initially trialled in this configuration. It did not sail well, was unstable and then had steel plate used as a keel. A slight improvement but not significant but the boat could carry a load. The more weight, the more stable.

Next step was to try and get more stability. The owner builder then said how about and outrigger. He ripped a 1/4" ply two foot wide, nailed it on the keel and bow/stern (This thing could go either way), jammed in some bulkheads. Attached two 50 x 100 mm timbers for the crossbeams between the main hull at a float bulkhead, and this formed the new outrigger. He now had a Pacific/Atlantic Proa. The steel centreboard/keel was removed and a semi shaped, much lighter wooden centreboard, was inserted.

Result a more stable boat that was a lot more controllable and fun to sail. The boat was lighter and easier to move onshore. The owner did not care if it was faster but now could go where he wanted not where the boat limitations would let him to go.

A nice way to reuse some old scrap timber and have fun as well. The limited jpegs give the idea.

 

A Sea Pearl 21 was built by Marine Concepts (USA) and designed by L. Francis Herreshoff, and was first built in 1982 by Marine Concepts. The first Sea Pearl 21’s were narrow beamed monohulls with cat ketch rigs and either a lee boards or minimum keels. They were tender but sailed well and could have water ballast. Later in the production run there was a request for more stability so another version was created The Sea Pearl 21 Tri. Of the 415 Sea Pearls built, the majority were the 21 foot monohull version and a few 21 foot tri’s. We will focus on the Sea Pearl 21 trimaran.

The Sea Pearl 21 trimaran is 21 x 14 foot with amas that retract to 8.4 foot. The base weight is about 950 lbs depending on options. All versions of the rig are cat ketch but the masts vary from 21 foot to 23.3 foot and can be carbon fibre, 2 part aluminum or single part aluminum on tabernacles to allow folding. The sail area is for the tri is 166 square foot with the main and mizzen. The draft with twin leeboards is 2.8 foot and when raised the draft is 0.8 foot. The power options are 2 to 4 HP outboards.

The Sea Pearl 21 tri is an open boat but many owners had a canvas tent for night protection. There was 1 built with a cabin that had 4 foot headroom and a double berth inside.

Basically, a fun beach cruiser that can do camp cruising. The performance of the tri is good on all points of sail but do not expect very high speeds. Reports of a 5 to 10 knot type of boat. As the main hull of this tri is basically a monohull hull there are limitations as what it can achieve but have no doubts in racing it is competitive with old trailer sailor monohulls up to about 25 foot.

The great pleasure of the Sea pearl 21 tri is its easy set up for sailing from a trailer. The floats are on swing aluminum cross arms that swing the floats forward. The unstayed masts can be lifted into the mast bases or if you have folding masts just lifted up. According to many users it takes 15 minutes to launch or retrieve.

The construction is fiberglass, There is an outer hull that is fiberglass balsa core of about 15 mm thickness and an inner deck cockpit molding that provides an easy to maintain structure. The folding cross beams are aluminum with a solid aluminum bar with 2 pins at the fold joints. From my research only I of these joints have broken in an extreme sailing situation. I would regard Sea Pearls as well built.

The jpegs give more of the idea of a good practical day sailor for a family that performs well.

 

In response to a request. A Capella is a sistership (yes folks, a sistership) of an iconic 45-year-old trimaran (Olympus Photo) that has a place in multihull history by just 98 seconds. Walter Greene was inspired by Newick style trimarans, so Dick and Walter designed then Walter built his version of a 38 foot racing trimaran. When skipper Mike Birch and the small trimaran stole victory on the finish line by 98 seconds from Michael Malinovski’s specialist designed 21m monohull Kriter V, after 23 days of racing in the 1978 Route du Rhum, it ensured that racing multihulls were the way of the future.

A Capella (Olympus Photo version) was also originally built in 1978 and is 38 x 25.6 foot with a displaced of 5,600 lbs. The original mast was 55 foot with about 640 square foot of sail area in a sloop rig. The draft is 7.25 foot.

Now things go a little astray. There were 6 A Cappella’s designs built with different names. The original A Capella was raced in the 1978 Around Britain Race by Walter and Joan Greene. That A Capella later in 1978 was raced by Mike Birch. The A Capella here was built in 1980 but has been abandoned and rebuilt 3 times, the last time in about 2014 by Charlie Chapple who commissioned Nigel Irens to upgrade the boat and improve it. The main hull was lengthened, had new floats added and a wider beam.

The latest version of A Capella has been extended to 40 x 27 foot and displaces 6,600 lbs carrying an upgraded rotating carbon fibre mast with additional sail area. Result, getting accurate specifications is hard, as you do not when the boat was measured and if the A Cappella is the original or a copy of the original. Finally, the racing A Capella also raced under several names including Olympus Photo etc

Back to the original A Capella. The A Capella trimarans were designed and built as if to prove their strength, speed and longevity. Capelle recalls: “Walter Greene taught me how to build boats using moulded wood and epoxy with floats made of composites. There was a classic aluminium rig. “What was interesting about these boats was that they were built with economy in mind in terms of the construction and fittings. They started to attract people. Mike won the 1978 Route du Rhum, proving that it was possible for a 38ft trimaran to cross the Atlantic and win races.”

Translation, the main hull has 3 layers of 3 mm timber molded onto a timber and plywood frame structure which had multiple stringers. The main cross beams are plywood and timber. All timber work was done in West epoxy. The floats are composite. The redesigned Irens floats were also composite but a better fuller shape especially aft. The rotating carbon fibre mast and improved foils helped all round performance. Walter Greene really understood what was required to build an effective ocean racing tri.

So how well does a 1980 A Capella trimaran go? Well, very well. It’s been in 7 Route De Rhums, the last one in 2022, it has finished as high as 9 th, done other Transatlantic races and local races. The racing schedule has been done around rebuilds of the boat due to a collision and a “sinking” where the boat had to be recovered from the Atlantic after it had drifted for 14 months. The boat also capsized in one race and needed to be recovered from 250 miles offshore.

Yes a spectacular trimaran that between the original Walter Greene/Mike Birch version and the A Capella sistership changed multihull sailing. The jpegs give the idea.

 

I am occasionally frustrated by home designed, home built cats especially in the larger sizes. This 40 foot fiberglass catamaran has taken time, effort and money to put together but unfortunately will only bring a fraction of the money second hand that it cost to build. Why? Because it does not have a “name” behind the design, the proportions are not quite right and its neither a floating palace or a outright sailing cat.

What do we know about it. Its 39.5 x 18.4 foot and has a cutter rig. It has low freeboard of 3.1 foot and round bilge hulls. It has low aspect ratio keels and a draft of about 4.5 foot. It has a very low underwing. It has two 15 HP outboards for power. My guess summary is it was designed for a lower weight and added the weight in the build process judging by the transom depth at rest, painted waterline and the low underwing.

It has 3 double berths, galley, saloon, toilet and shower with gas hot water system.

The build is listed as fiberglass, I would suggest that it is solid fiberglass in the hulls with foam glass in the decks and/or bridge deck. No further information is available. The performance is unknown but the cat has cruised up the east coast of Australia.

The problem of early designs was professional designers told the world that there cats were “light” and told the world the displacement was X. The real displacement was often twice X. The displacement figure was often a weight if built from light weight materials.

The reality of early boats, especially home built, was they were often built heavily by EG another layer of CSM, resin rich layups, additional equipment onboard like a second fridge then a freezer, additional water tanks, a larger motor, heavier anchors etc. The 9,000 lbs intended “displacement” becomes a 12,000 lbs weight with extra toys etc for an all up sailing weight of 17,000 lbs. Those boats have low freeboards and low underwings.

Designers today are more realistic but home builders do not always build light boats as they do not have the same facilities and equipment as a professional.

The jpegs give an idea of the boat. Don’t be to inspired. PS This cat has nothing to do with the Manta range of cats from the US.

 

@oldmulti there was one for sale recently with similar looking davits and similar no need for a boarding ladder type freeboard somewhere on the east coast.

 

This very one at Tuross Head. Std disclaimer, no affiliation, information purposes only. Custom: Sailing Catamaran for Sale | Fibreglass/grp Sail Boats | Boats Online | New South Wales (NSW) - South Coast Region Tuross Head NSW https://www.boatsonline.com.au/boats-for-sale/used/sailing-boats/custom/310535

 

"...3 double births..."

 

I conducted a Q&A with Andrew Fennell on his 40' Shuttleworth designed racing trimaran "Morpheus".

Trimaran Projects and Multihull News: Morpheus, Shuttleworth 40' racing trimaran Q&A https://trimaranproject.blogspot.com/p/morpheus-shuttleworth-40-racing.html

 

A short one about a man with a dream of a nice power trimaran and an experienced boat builder of 50 years Jon Coats. The owner specified what he wanted and Jon built a cardboard model of it, both agreed and John then started to build. There is a lot of experience and little computerisation involved in this vessel which was meant to be a “charter” vessel. There are some jpegs but minimal detail, Bajansailor, Fallguy, Tansal and a few others tried to help but not all suggestions were considered.

We know the power tri is 64 foot long and the shell weighted about 9000 lbs. The final displacement was to be about 20,000 lbs. The power is intended to be two Yamaha 115, 4 stroke outboards that were going to live in wells forward of the transom. At 75% of throttle the tri should do 12 to 15 knots. The calculated fuel economy was 2.3 MPG for each engine at 75% throttle or a range of 437 miles from the 190 gallons (830 litres) of fuel.

The stability of the tri was being discussed but the owner simply said “I will trust Jon”. If Coast Guard approval is required, questions like stability and stress calculations will be required to be answered fully before approval will be granted.

The build is Nida Core honeycomb panels, resin and cloth. Mostly vacuum bagged flat panels but some shaped bilge panels included. There is not much detail beyond that.

Unfortunately, the shell was just about complete prior to Covid then a hurricane blew the shell of its stands and the build was still going in 2022. I hope it was finished. I admire the idea but am unsure about the conception. If the performance meets expectation good.

The jpegs give the idea.

 

Borge Quorning of Quorning Boats designed and produced the Trident 27 trimaran. There were about 200 of these tris built but many of them were kit boats. The hulls and deck shells were delivered to customers who then completed the tris. The production of the tris started in 1974 and continued in various lengths until about 1979 when the first Dragonfly trimaran was produced.

The Trident 27 was 27 x 19.6 foot with a designed weight of 1900 lbs but the reality was they weighed between 2700 lbs and 3800 lbs depending on who completed the tri. The (often) fixed aluminum 33.5 foot mast carries a 260 square foot mainsail, a 215 square foot genoa, a 538 square foot gennaker and a 753 square foot spinnaker. The length to beam on the main hull is 8.5 to 1. The draft ranged from 1.3 foot to 4.6 foot over the centreboard. The outboard was a 5 to 6 HP outboard.

The accommodation is a forward portapotti with a single berth over. The main cabin has a single berth on each wing, a galley on one side of the main hull and a seat on the other side of the hull. There is a roomy aft cockpit. The tri is transportable by disassembling the cross arms.

Now we get to construction. This varies. The basic hull shells appear to be balsa, e-glass on either side and polyester resin but over time this evolved. The initial cross arms were an upper and lower about 60 mm diameter aluminum tubing crossbeams. Some ended up with single piece aluminum cross beam tubes. Home builder fitted out bulkheads etc with plywood, some had foam glass bulkheads etc. To quote one owner “The specimens vary somewhat in terms of material in cross beams and superstructure.”

Performance for the tri ranged from good to very good depending on the owners choice of rig and sails. A fairly standard version can achieve 8 to 10 knots in good conditions with peaks of 14 to 16 knots. The tri could go upwind well and had few vices. The intention of the design was a day sailor coastal cruiser but some have crossed oceans.

This is a very interesting boat that formed the basis of the Dragonfly trimaran company. It was a very good design for its time and some are available second hand today.

The jpegs give the idea.