Multihull Structure Thoughts

I have never mentioned Ontong Java in my post. You must be confused. And i do have another thread about (strip)planking a Tehini. And yes i would like to build a Vaka Moana/Motu. But i would need drawings for the hulls etc. Because i found your older post about this design, i thought i ask if you would know anybody or anywhere i can get in contact with.
Thanks for your reply
islander63

 

Islander 63... Sigh. ... 2 posts back jamez shared a link to the builders of the vessels . Salt house boats

 

Islander63. The basis of the Vaka designs came from Captain Cook drawings and dimensions in the 1770’s. To quote Salthouse below this what they used as a guide to design the modern version. These would be the guys to talk to about the design or plans but there are other versions.

“When the idea emerged of building seven traditional Vaka for crossing the Pacific within a year, we had no idea of how to start. Fortunately we found Greg Salthouse and Nick Peal to take up the challenge. They helped us to take the best of the ancient design and knowledge and mix it with today's experience and materials to create the best outcome. All of the seven Vaka have been built with one mould. Their fiberglass-hulls are a tribute to the environment; they are robust without having cut a single tree. We appreciate Nick Peal's contribution to the newly designed centerboard as well as to the shape of the sails; they were adapted with modern knowledge of sailing, and interestingly they are meeting very ancient shapes again. One year after this huge project started all seven Vaka were indeed completed. Now they are ready to cross the entire Ocean in beauty and dignity. They can now make a stand for the heath and integrity of the ocean and reconnect all the Pacific people to it. Without the expertise of the Salthouse team we wouldn't have been able to reach this goal.”

A strip plank version is very possible and would be a better proposition than a plywood version. But the hull structure is secondary to the crossbeams on catamarans. You can build a good set of hulls then have the cat in real trouble because the crossbeams rot or were poorly designed. Tehini’s were not known for structural longevity. They needed to be well built and use a lot of epoxy saturation for a long life and even then, there crossbeams needed to be very well maintained. Strip planked by its nature is structurally stronger and has epoxy saturation as a feature. PS. there are many versions of Vaka’s around with similar shapes etc. EG 2 things below to read.

When James Cook first came to the Tuamotus and other Polynesian islands around 1770, he was inspired by the canoes and made drawings of them. Fortunately, these drawings facilitated the lore of the ancient Polynesian knowledge and traditional design and enabled the construction of the first Vaka Moana in recent times. On the basis of James Cook’s old measurements and lines and through the initiative of Sir Thomas Davis, the first Vaka Moana “Te Au O Tonga“ was built in 1994 in Rarotonga/Cook Islands.

Marumaru Atua Vaka rebuild https://lloydstevensonyachts.co.nz/news/marumaru-atua-vaka-rebuild

TRADITIONAL TREASURES PART II ~ Boating NZ https://boatingnz.co.nz/traditional-treasures-part-ii/

Finally, if you have the trees one version was built from 80 foot trees with 5 foot diameter trunks that were cut down and hollowed out to form 2 canoe hulls.

 

Hi, we will start with a proa from Alessandro Comuzzi Yacht Design. The “Rebel Otto” proa was built as a specialist project between 2019 and launched 2021. This proa can be an Atlantic or pacific proa. The proa is 26.25 x 8.2 foot with a displacement of 3,300 lbs. The sail area is 333 square foot on 2 freestanding carbon fibre masts. The draft is between 2 foot and 6.5 foot with a fin keel daggerboard that has a 550 lbs torpedo keel at the bottom. This keel is intended to make the proa “uncapsizable”, that may be the aim but any multihull below 60 foot can capsize given big waves and inexperienced crew. The rudders are “daggerblade” but there is little detail. The hull length to beam is different between the 2 hulls with the mast hull being fatter. The engine is a 10 HP outboard.

The proa is a minimum cruiser with a maximum of 4 single berths (in tents on deck if preferred), a porta potti and minimum galley. There is sitting headroom at best. The cockpit is quite large and has useful seating and storage areas. The proa is only 8.2 foot wide and can be easily trailed. Sail handing and shunting appears to be well thought out.

The build is from plywood encapsulated in epoxy with some fiberglass reinforcement, some aluminium and a little lead. Carbon fibre masts.

An interesting idea but there appears to be no plans available.

I have not forgotten the request for stressform wing mast instructions. Thanks for those who posted some items on the thread in the past month.

 

Welcome back Oldmulti. Things were pretty quiet around here without you.

 

Kiricraft is a boat builder located in Kiribati in the Pacific. Australian, Michael Savins, established KiriCraft after leaving Australia. Based in Tarawa, Kiricraft targets the Australian and New Zealand markets. He has produced several cats but the current model is a power cat of 37.7 x 14.85 foot. The displacement is unknown but a guess is about 13,000 lbs. The hull length to beam is 16.8 to 1 with a Tennant type canoe stern. The draft is 2.7 foot. The power is optional with either outboard power or installed diesel engines.

The accommodation is 2 double berth cabins forward with a toilet area in each hull. The main saloon has a galley, navigation/entertainment area, dinette and internal steering seating position. The cockpit is available through a large opening door from the saloon. There is also a flybridge with duplicate controls and steering.

These cats are intended for longer term cruising but do have a limited range. They can be powered to run over 20 knots or have lower HP to give a longer cruising range at 15 knots maximum. These boats are sei custom to suit the owner’s needs.

The boats are a foam and epoxy composite structures with the underwater sections being solid fibre glass. This construction achieves strength and durability at minimal weight.
The cat is painted, not gel coated to allow the owner to choose any colour or colour combinations they want. The cats were selling for about $400,000 prior to Covid. I do not know a current price.

An interesting side business that Micheal has, he raises giant clams that he exports to Germany for use in aquariums. Also in the final jpeg is his very interesting home over the water. Supposedly this reduces the mosquito attacks. Interesting guy and design.

 

We made two 60' Stressform masts at Rudy Choy's workshop in Honolulu 1980's.

 

oldmulti, do you take suggestions? I have tried and failed to find any further information, beyond one article in Multihulls Magazine, on Gaia, a bow-steered, pyramid-rigged catamaran designed by Joseph Norwood. It seems like a boat that people would remember.

 

Robert. An analysis of the Gaia design and logic to it was featured in:

High Speed Sailing: Design Factors, a Study of High-performance Multihull Yacht Design ; Author, Joseph Norwood ; Edition, illustrated ; Publisher, Dodd,

A copy for $6 Canadian is available from

High speed sailing: Design factors : a... book by Joseph Norwood https://www.thriftbooks.com/w/high-speed-sailing-design-factors--a-study-of-high-performance-multihull-yacht-design_joseph-norwood/1856636/#edition=4796157

Also Norwood wrote a later book: 21st century multihulls Norwood Joseph available on Amazon which may have an update on the design and its outcome.
The jpeg is just the cover of the book.

 

This is a silly design. It has the negatives of the proa configuration without and of the positives. Example you may wish to make one hull large to carry people and goods, and the other small and narrow for stability. Free standing masts have higher stress that stayed masts, so going to more expensive than a simple wood mast with some ropes on each side. Having the complexity to boards that have to swivel up is challenging. If they are deeper than the keel you need some mechanism for the board to go higher, otherwise it breaks. On a tacking boat with one rudder, the rudder can just swivel backwards and not break. Also 2 hulls of same size provides no benefit in reducing crossbeam loads vs hulls of different sizes. It would be much better as a catamaran

 

I read that book back in the 80s. I don't remember Norwood's rationale for bow steering, I do remember his enthusiasm for the pyramid rig and a proa configuration similar to what Rob Denney developed later. However, I was hoping for empirical information, rather than theory, especially regarding the pyramid rig. The first report I saw on that is in the AYRS Airs booklet #8 from 1974, and was quite positive. So was Norwood's report on Gaia's sea trials. Nevertheless, it has not spread in 50 years. The most informative account of why not that I have seen is a single paragraph in your post #1560 in this thread. I had hoped to find a bit more detail.

 

Robert. I will do an item on pyramid rigs if that is what you are after. The following is from memory, but I seem to remember that Gaia was converted to a sloop rig at one point but I will have to research this further. There have been 2 comparison articles between the same type of boats 1 with a pyramid rig the other with a sloop rig which shows the strengths and weaknesses of both

 

Several months ago, I asked if anyone knew about the Laser trimaran that appeared in a Jpeg. I still only have one Jpeg but we have learnt some more detail about the Laser tri. The standard Laser dingy is 13.75 x 4.75 foot and weighs 130 lbs. The 18.6 foot mast carries a standard sail area is a 76 square foot mainsail. The daggerboard draft is 2.6 foot. The length to beam on a Laser hull is 3.8 to 1.

The performance of standard Lasers is as follows: “In general, I've found that the sustained boat speed is usually around 1/2 the wind speed, up to about 10-12 knots. In 15 knots of wind, the Laser will do 7-8 knots, and in 20 knots, it will do 10 knots.” The fastest peak speed recorded is as follows: “Laser sailboat fastest recorded speed is 18.6 knots.” The jpegs of the 18 knot run required a very brave very fit person who was heading to some broken equipment.

Now back to the Laser tri jpeg> this version of the Laser tri (by Tom) weighs 310 lbs, has a 21 foot mast with a square top mainsail of 100 square foot and a 40 square foot jib. There is also a 86 square foot screecher from a Weta tri. Tom weighs 190 lbs so when sailing the all up displacement is 500 lbs. The floats have 330 lbs of buoyancy, which makes them submersible floats.

The standard Laser main hull has two 52 x 65 mm laminated spruce cross arms with additional biaxial glass in epoxy on the beams. The floats a 4 mm stitch and glue plywood with glass skins, keel, chines and gunnels. It appears to be a well built boat.

The Laser tri is fully powered up in 12 knots of wind which is just right for Chesapeake summers according to Tom.

The first tri jpeg is Toms, the second jpeg Laser tri is a British build by a different guy featured previously with CLC floats. Fun boats but I suspect a Weta tri may be lighter, faster and easier to get second hand.

 

I would appreciate that. Thanks.

 

This is about ambition versus reality. The Race to Alaska is a 750 mile coastal race open to any vessel non engine powered vessel. From stand up paddle boards, canoes, multihulls and monohulls. The course has strong currents, little to strong winds and a lot of floating logs to avoid. All boats can be rowed or powered by a peddle to propeller arrangement for light winds. Tactical anchoring is also done. The main requirement in this race is you look after yourself and you arrive with all the gear you started with except consumables like food and water. Stopping onshore is acceptable. Good so far.

The course is broken into 2 components. A proving course of 40 miles to Victoria which all boats have 48 hours to complete. If they complete the proving course they can do the rest of the race. In 2022 there was a strong wind warning on the first day so the organisers extended the time to 72 hours to allow the smaller boats to safely complete the 40 mile course.

Now reality sets in. As I said anything can enter so Team B entered a 14 x 11 foot Weta trimaran that weighs 260 lbs and carries 135 square foot of sail in the main and jib with a 86 square foot genoa on an 18 foot mast. Team B decided to start the race immediately into a rising wind. Team B only got a few miles into the 40 miles race course before it capsized. The owner was sailing into a 25 knot wind against a 5 knot current with waves. He was picked up by a rescue helicopter shivering violently wearing jeans, shoes. a jacket and a life vest. Hypothermia was setting in.

Several comments. Weta have never claimed their tri is a long distance ocean racer, it is a day sailor. Sailing a Weta in 25 knots of wind in a seaway requires real skill and a bit of luck. Also, you carry any gear for the race on the boat which means the Weta may have been overloaded (cannot verify). Finally, if you are going out in difficult weather over a 40 mile stretch of open ocean that is cold, you should be wearing some sensible warm gear like a dry suit.

This about using an appropriate boat for a function. The Weta tri is very good for daysailing and is enjoyed by over 1500 owners globally. It is a strong well built boat in its 2 versions (originally solid glass then foam glass). In day sailing mode it can sail along at 10 to 12 knots without much problem. The highest speed recorded is 21.4 knots (24.63 MPH) by Tom Kirkman, USA.

Understand your skills, preparation and weather forecasts. If the race organisers give you another 24 hours to complete a course in reasonable conditions in a boat that can sail in 5 hours, sit and wait for reasonable weather. Being first to capsize is not an award to go after. Please consider the risk reward ratio.

The jpegs are of the capsized Weta and the basic Weta tri. There is also a hypothermia chart and a mono view of capsize. PS i still will do the mast instructions and pyramid rig.