Multihull Structure Thoughts

Thank you oldmulti, great covering on existing adoption of wishbones.

One of the first to my knowledge is designed by Hereshoff, that inspired Dave Clark to the rig of UFO. The People’s Foiler: A Design Brief on the UFO Foiling Catamaran - Professional BoatBuilder Magazine https://www.proboat.com/2017/03/design-brief-peoples-foiler/.

I have used it on a small dinghy, but with a round slinky stayed mast with diamond spreaders combined with a forward pointing trmmable third, see image.

Began thinking of using the same windsurfer boom together with a stayed carbon mast with 20cm chord on my small foiler build, but haven´t found anything about how to adopt it without hampering rotation.

Also my idea has been to use sails designed for conventional booms, not the modern ones specially designed for wishbone, used on F18, A-cat etc.

 

Thanks SolGato,

Seems like you have checked my thread about the small 19ft build.

Reminds me a little of the German or Dutch I found on Pinterest.

The one you found, with Bucc24 style waterstays looks like a really serious build, albeit the rig might be on the small side.

 

Revintage. For further information on the 27 foot tri, please look at epoxyworks magazine which had some of Jons projects including the tri. Jon Staudacher’s Approach to Projects - Epoxyworks https://www.epoxyworks.com/index.php/jon-staudachers-approach-to-projects/

 

Tahiti based Nicolas Gruet - NG Yacht Design has an interesting designer who does modern designs and does multihulls that combine the modern with older concepts. His latest design is a power charter proa. The “Blue Lagoon” is described as an aluminium outrigger canoe. The power proa is 39 x 16 foot with an unknown displacement. The power is a 300 HP outboard. The boat is intended to do short range day charter cruises through some lagoons of Raiatea or Tahaa. The proa has a bulb bow and thin float to try and limit pitching etc by driving through smaller waves not follow the surface patterns.

The bow and float shapes are developed from flat aluminium plates and is V for the majority of there length. On the main hull the bottom aft is flattened for better water flow to the outboard. The construction of the proa is aluminium.

The layout of the proa is mainly seating with tables, a small “galley” and toilet facility.

No performance information is available but I suspect this would be an economical vessel that could reach 20 knots if conditions and more importantly charter guests would allow.

The jpegs give the idea.

 

That looks like a great boat for the purpose. Need to ditch the 300 and use something more in keeping with the world we live in. Who's in such a hurry? Make it longer and lighter and make a better profit while being a more positive example.

 

Hello oldmulti @ all, you did a post about the bob oram 32r, wich is very interresting to me. But i cant find any further information nor contact to the designer. Could you help me? Thanks

 

Andrea, Bob Oram posted this recently on the "offshore power proa" thread (October 9 2021).

"Sorry All, nothing to do with this thread, but I'm just letting people know that there is some scammer that has started a website that has the address Boboramdesign.com.au. This is a scam and absolutely nothing to do with me, it has zero legitimacy.
Most will know I have retired.
Please advise others.
With regards to all.
Bob Oram"

Sorry but I suspect Bob has retired and not selling plans now. Hopefully this thread is read by the NZ builder of the Oram 32R and may be able to give some indication of how to contact Bob, but Bob may just want a quite life. The Oram 32R post was on page 46 Multihull Structure Thoughts.

 

Solgato, I found this while looking for something else. I do not know who the person is in the smaller jpeg.

I have been searching for any photo's of Joey Cabell's cat Hokule'a. No luck so far. It is a pod cat designed by legendary waterman Joe Quigg. It was built in 1975 and was heavy by today's standards, but is still very active. From Joey's story....I mean this guy is a legend among st waterman.

My memories of living there are vivid and intense. Surfing 20-foot tubes at Hanalei Bay. Sailing my 40-foot catamaran out of Hanalei and dropping in on 50-foot walls projecting down the line on the way to Nawiliwili. Swimming the Na Pali Coast in the summer and surfing it in the winter. Diving for lobster to make omelets for breakfast.
The passion is still strong today. Last summer my son, Trevor, my first mate, Ranney Warburton and I sailed the Joe Quigg-designed catamaran – that I built with Joe in 1975 – 1,200 miles to Fanning Island. We surfed open ocean swells at 15- to 20-knots plus, and spent the month of June down there surfing, diving and fishing.

 

This is an update on Little Boat a John Patterson design that is much admired (page 83 Multihull Structure Thoughts). The ”Little Boat” is 21 x 16 foot and can be folded to 8 foot wide for trailing. John made a statement that the tri weighs about 500 lbs, a number I doubt, the displacement is approximately 1600 lbs based on the main hull plan in the jpeg. The reason I doubt the weight figure is a Corsair Pulse 600 racing tri weighs 990 lbs with a displacement of about 1600 lbs. The wing mast of the “Little Boat” is 27.5 foot high with approximately 160 square foot main and wing and 95 square foot foretriangle. A kick up spade rudder, daggerboard, and wing mast made for performance up wind or down. The tri is fully trailable.

The main hull length to beam is 9.5 to 1. John designed his larger tri’s with 200% buoyancy in the floats. I am assuming a similar floats ratio based on the jpegs. “Little Boat” had a porta-potty under a single berth forward, small galley, centre cockpit, and an optimistic “double” berth aft. The maximum head room is 4.25 foot. John lived aboard for over four months at one time as he cruised around the Caribbean. According to John, Little Boat is capable of offshore sailing if required and he feels safe in strong winds with just the wing mast and a drogue in difficult conditions. According to John Patterson can handle 40 knot plus wind conditions (not sailing just towing an anchor drogue).

As you can see from the jpegs Little Boat is constructed from strip plank cedar with e-glass epoxy inside and out with plywood internals and deck . There are 4 plywood bulkheads. The crossarm structure is a combination of strip plank cedar e-glass epoxy, solid timber lower support straps and metal hinge straps. The setup was complicated and hard to build. It was a variation of Farriers but at the time it was designed Farriers patents were still in force. The cross arm structure could now be simplified as farriers patents are no longer in force.

The hull line jpeg is the actual hull lines of the main hull of the 21 foot tri. The lines give you enough to develop your own version if you have the desire.. If anyone has a set of plans please advise as John Patterson has said they can be published but no build support will be provided.

The jpegs are of 1 of the only 3 known Patterson 21’s in existence. From the limited reports this is a very good tri that is a fast cruiser for 1 or 2 that has limited offshore capability. The only issue would be payload. This is a very attractive and practical boat.

The following is a quote from John about Little Boat. “Some of my most enjoyable sailing was on my smallest tris. I no longer want to sell plans as I am usually on the move cruising on my 44-tri in the West Indies or visiting family in Mexico and I don’t feel I could give good follow up for builders. The boat in question was 21-ft by 16-ft and folded to 8ft for trailering. I sailed it over 2,000 Great Lakes miles, 6,000 ocean miles and 15,000 road miles. It had a porta-potty under a single berth forward, small galley, center cockpit, and double berth aft. I lived aboard for over four months one time. A kick up spade rudder, daggerboard, and wing mast made for great performance up wind or down.

Three were built that I know of — one by me — but there could have been more as I think the plans got passed around (I hope). There is only one photo of it at my old website, PattersonYachts.com, as at the time I was trying to do larger boats before I retired.”

A quote from the next owner. “I bought “Little Boat” from John Patterson. That is me sailing in the pic’s. This was an amazing little boat. Ceder strip built beautifully. Aft cabin really a single but comfortable. I know john sailed her in the keys for 6 months. Had a head and tiny galley. Wing mast was great and rudder system worked very well. As I sail mainly in light air I wish the stick would have been 34′ instead of 29′. Very stable boat to sail and easy to trail.”

 

Part 2 of John Patterson Little Boat the 21 foot trimaran.

 

Thanks Oldmulti!

I think that photo is of the owner Cabell and his statements about Hanalei and surfing his Catamaran makes total sense when you look at the construction and features of the boat. Only a guy like that who knows how to “read” the waves and swell would charge down 50’ faces in a 40’ Cat for fun.

I do it on occasion when our winter swell starts, but on a much smaller scale with a HobieCat on waves 1/3 the size, still it’s thrilling and a lot of fun, and if I misjudge it’s only a HobieCat not a 40’ Cat!

 

Today we will discuss a man who wanted to develop a boat to suit his needs. He started a development path that will be discussed over several items as each iteration of the design concept is different and teaches us something about rigs and boats. The first tri was M3 being designed and built in 1998.

The tri multihull design that involved locating the mast in the stern of the centre hull and connecting it directly to a seat/frame that supported the sailor. It was nominally a trimaran, (or perhaps a dinghy with amas) to get more stability with less wetted area. The tri is 11.5 x 7.5 foot. No weight specified. The windsurfer sail had a curved spar in the leading edge that was fastened with a pivot at the top to the rear mast and at the bottom to the deck with a windsurfer mast foot. It had a wishbone boom, and instead of using line for the main sheet, it had a foldout rod on each side of the boom that pivoted out to control the sail. The sailor drove with the boom rod in one hand and the tiller extension in the other—really simple and direct with no control lines. The mast forces go directly into the sailor’s seat support frame, the hull didn’t have to carry the heavy mast torque and could be cheaply molded for a consumer product. The slightly back-tilted sail had a lower center of effort than a regular rig and kept the drive vector pointed up out of the water when the boat heeled.

The solid rods instead of a mainsheet allowed much better control of the sail than a line, especially in gusty or uneven wind. The ratio of sail area to wetted area was high, and with the amas for stability, the M3 would begin to plane at 6-7 kts and run 1.2 times windspeed in 10kts of breeze on a broad reach. Not bad for an 11.5 ft fixed-mast boat. And it was easily handled and transported on my small pickup without the need for a trailer or ramp.

The underside of the center hull was double concave, like many windsurfer boards, so it would truly plane. The amas were less than half the length of the 11.5 ft center hull and placed toward the stern, so they provided stability from heeling, but would have a very difficult time pitchpoling the boat forward. (I understand that there are now some cutting edge Navy destroyer-size ships with a similar small-outboard-hulls-aft design which they say gives very low drag but high stability.)

I built and sailed two prototypes, the second one with a custom hull and amas in foam/fiberglass designed in Solidworks software. An aluminium tube frame, and a modified 65 square foot windsurfer sail. I called the boat M3.

There are limited jpegs but you get the idea. Tomorrow we will see the next version.

 

Looking forward to see the next evolvement.

 

I really like John Pattison's little tri. Thanks for posting all the info on it. Had a crush on Buddy too.

 

M3 was a sailing success and there was an attempt to commercialise the concept, but as many before have found the production moulds etc would have been more expensive than any likely profit. Also, a patent on some of the technology cost a lot. Result, no commercialisation. So still in an experimental mood the designer builder decided to improve sailboat rigs and got interested in seeing if a kayak could also be a good sailboat. He purchased a Hobie kayak and sailed it with their stock sail kit. This was fun in low winds, but the heeling forces from the sail very quickly got difficult to handle when the wind got up to 8-10 kts or so. The sailor couldn’t move his/her weight sideways, the hull was narrow, and the sail center of effort was relatively high overhead.

He decided to experiment working out a rig that used two identical sails close together and mounted fore and aft, which I call a twinsail rig. (two identical sails side by side is called a biplane rig). The first sails were rectangular, made from PVC pipe frames and hand-sewn Dacron, and they worked pretty well. Having a pair of sails automatically lowers the centre of effort to about 65% of the same total area in one single sail, so the tipping problem in 10 kts of wind saw immediate improvement. Two sails close together are also a very efficient airfoil system, like a jib and main, and generate a lot of drive force for their area.

The masts are mounted on a “turnbar”. A flat piece of metal mounted on a stub mast in the hull. At each end of the turnbar is mounted a welded mast base stub. The masts are inserted over the stubs. The sail area of each sail is about 20 square foot. The turnbar is a flat piece of aluminium plate and there is a .875″Dia. by 23″ long aluminium pin rigidly mounted at each end, pointed upward. The masts are made of PVC tubing and each one freely slides down over one of the pins, so the masts are held in the vertical position, but can rotate around.

The rig is very good upwind, reaching, and broad reaching, but if the turnbar is latched with masts in line fore and aft, the sail area is small going straight downwind because one sail blocks the other. A possible solution is to allow the turnbar to rotate so the masts are side by side, and then more sail area is presented. But mostly it was sailed like a catamaran, angling on a very broad reach downwind with more hull speed.

This version could sail at about 6 to 7 knots which was more a limitation of the hull shape and lack of stability than of the rig’s capability. This concept of a twinsail rig can work well in smaller boats but the forces on the mast base at the turnbar of the free standing masts can rise very rapidly with increased sail area. You can engineer almost anything but the structural strength and weight required at the intersect of the turnbar and mast stubs grows very rapidly with increased sail area which would result in a significant weight gain.

Sorry about the lack of jpegs again. Tomorrow the latest version which combines a new variation of the rig and a tri hull shape.