Multihull Structure Thoughts

The next step in the design build of a series of small designs to develop a unique tri with a unique rig. this is step 3 of 4, tomorrow will be the final design version I know off. Now we are getting closer to the final design build but we have to do a combination of the twin sail rig with variation and a trimaran hull form. The tri uses a Hobie Rev 13 (13 foot long) hull and small custom fiberglass/foam amas, salvaged from earlier boat experiments, that clip on and off the hull with just two pins. The sails are upgraded from the square sails on the monohull kayak to a couple of small Ezzy learner kids windsurf rigs of about about 1.5 sq meter with a little amount of sail removed from the bottom, so total sail area is just under 3 sq meters (about 35 sq ft). The fore and aft masts are mounted on two pins on a turnbar that has a latch and rotates 180 degrees to tack or jibe. (Since the booms are longer than the distance between the masts they don’t clear each other to rotate around).

The twinsail rig was really fun to sail. Unlike the Hobie sail kit, it provided enough power to allow the boat to exceed its natural hull speed and run 6-6.5 kts on a reach, yet felt stable in higher winds of 15 kt +. It also provided options for adjusting both sail angle as well as the turnbar angle, which sets the position of the twin masts, so it was a more interesting mental game to maximize performance, particularly upwind. Even with the small sail area, the boat would easily do 4-4.5 kts to windward. The force on the sail control rods (the metal rod joining the rear of the booms together) was small, the seating was comfy, the visibility was good, and the boat was enjoyable in a lot of different conditions.

Even with a limited rig this version could sail well for its sail area and limited main hull shape. The designer builder had better control over the craft in a trimaran configuration, but it is very much a sheltered water boat. A fun experiment which provided a lot of information for the next development of the rig and tri design.

There are limited jpegs to give the idea. Final version tomorrow.

 

That twinsail rig looks a lot like Alex Querenmont's duplex rig. There are links to photos in the 26th October 2020 post in this thread Howard Fund - Amateur Yacht Research Society https://www.ayrs.org/phpbb/viewtopic.php?f=10&t=2195 A first season report is in AYRS Catalyst #59 Publications – Amateur Yacht Research Society https://www.ayrs.org/topics/publications/ Alex' boat being the title picture, that would be a quicker way to see it.

 

Bob designed the 32R for me initially. Building has not commenced due to covid and other of lifes idiocies. I can't PM you as you don't have enough posts (5 I think, its in the rules somewhere) but if you (can) PM me or post an email addy, i'll be in touch.

 

The final version of the trimaran rig developments of Steve Curtis designer builder of the 3 previous versions. After the twin sail and M3 trimaran etc the next one is called “Renegade”. The designer wanted the following, a trimaran hull layout for best stability with least wetted area with the main hull approximately 12 foot long and should be fully planning (flat or slightly concave), hopefully beginning in 6-7 kts and staying steady in 10kt+ of wind. Total sail area should be a little more than the M3, about 74 square foot. Center of effort for the sail area should be lower than the M3, so the double sail concept should be used, but this time with the masts side by side (biplane rig). The sails, masts, and booms should be kids’ windsurfer type for low cost and high efficiency, hopefully with transparent sail material, fiberglass masts, and curved luff socks.

The total design is 12 x 7.5 foot with 2 windsurfer sails of 37 square foot on 12 foot masts. Weight of the tri is unknown.

A used Mistral 12 ft longboard is the centre hull, with sufficient volume and a good planning shape on the bottom, a skeg slot to use to help in mounting a rudder, and light weight overall. For the two outboard hulls, a couple of Hobie amas were obtained from their Adventure Island trimaran. There is a main aluminium crossbeam joining the hulls together and also act as the mast steps for the windsurfer biplane rigs.

Everything seemed to function. In 5-7 knot average wind, the boat moved around the lake at 4-4.8 knots on GPS and occasionally hit max speed of 5.5 knots on a reach. That’s encouraging, since hull speed for an 11.5 ft waterline is around 4.6 knots. To quote Steve “Due to the side by side mast arrangement, it really likes going upwind, where the angle of the wind doesn’t shadow either sail, but is quite happy sailing on a reach, broad reach, or directly downwind. The sail power is substantial and clearly has both airfoils pulling, but at this point without a wind tunnel and some software I can’t say exactly what angles are the best and what the various factors are. It has a very stable and forgiving feel to it, but I can tell I have a lot of details to learn about sail angles in particular. Renegade jibes inside like a sailboat, and the process is quick and controllable. I sheet in as the stern goes toward the wind, shift my weight on the seat, and let the sails across with the rudder action. The rudder control is really easy and fast, and is especially relaxing on a reach, where I can sit comfy out on the seat with one arm draped over the wheel. The boat has a little weather helm, but stays pretty centered on the rudder while sailing. If allowed to turn into the wind, it won’t stay in irons, but begins to head one way or the other. If I want to change these things, I can always move the centerboard mount forward or back to adjust the balance if I want to.”

Also “Speed so far in ramping up is about 80% of average wind on a beam reach, even in low winds. And it will go 70% of average wind on a tight close reach (upwind), which I think is unusually quick. I’m not much good at driving it downwind yet, but I think there is good potential there.”

What is being explained here is biplane rigs can work well. They may not work as well as a full wing masted fractional rig but will produce more than enough power across the wind range and angles to drive a reasonable well designed multihull. The hull shapes Steve uses are not the best across a range of speeds being aimed at planning. Planning is good if you sail in strong enough winds but the majority of the world sails in winds below 15 knots and require efficient round bilge “displacement” hull shapes.

The jpegs give the idea.

 

Andrea. If you are seriously interested in Bob Oram 32R there may, repeat may, be a way to contact Bob. Just give an indication here and I will direct mail you as to a contact point that may get a conversation going.

 

It is with sadness that the last “manufacturer” of Farrier F 22 trimarans will no longer manufacture the tri or parts for the F 22 tri. This is a major problem for those who purchased home build plans for a F 22 as there is no crossbeam plans as you are required to purchase the crossbeams and support structure from an approved manufacture of those beams. As the company will not do any manufacture of F 22 parts there will be some of the home built F 22’s that cannot be launched.

The F 22 was a personal project for Ian before his death in 2017. The project had built 20 plus F 22 before the moulds etc were sold after Ian’s untimely death.

The F 22 was 22.9 x 18.1 foot (can fold to 8.2 foot) with a weight of 1,300 to 1,500 lbs depending on the materials. The 31 to 35 foot mast (depending on sail area and mast materials) carries between 328 square foot to 389 square foot of sail area in main and jib depending on mast chosen. The draft ranges from 1 to 4.9 foot over the daggerboard.

The main advantage of the F 22 was it had more room than a F 24, was lighter, had more beam and larger floats. In short, a more powerful tri than the F 24 that was optimised for sailing and trailering. The problem was it ended up being expensive for a “22 foot” boat. This was mainly due to the structural and build costs. The foam core sandwich construction throughout had double bias or bi-axial glass fabrics. Carbon fiber is used selectively in highly stressed areas, while main hull keel is reinforced with Kevlar, both sides of core. This helps stiffen the hull for rig loads, plus is an excellent barrier against hull penetration should boat go on rocks. Beams are a carbon/glass composite, with multiple layers of carbon fiber unidirectional, top and bottom. Fully resin infused with a vinylester/epoxy resin to optimize structural properties.

For more information you can visit: F-22 – Farrier International https://f-boat.com/f-22/ and Specifications – Farrier International https://f-boat.com/f-22/specifications/

So what options are available for people who want something of similar size that can be home built. The following Scarab 650 has been successfully built around the world and is specifically designed for home construction in plywood or foam glass composite. The Scarab 650 is 21.3 x 18.3 foot (can be folded to 8.2 foot) with a weight of 1000 lbs if built in foam glass. The displacement is 1800 lbs at DWL. The 29 foot rotating mast carries 280 square foot of sail area in the main and jib. The draft is 1 foot to 4 foot when the centreboard is down. The build as mentioned can be fiberglass covered plywood or foam glass construction. The crossbeam structures are fiberglass built at home mainly with e-glass, unidirectionals and some metal components.

The difference between the F 22 and the Scarab 650 is the Farrier is really performance and space optimised and if built to plan with the larger rig will be a very fast mini cruiser. The Scarab 650 will be lighter and will perform well has slightly less space internally. The Scarab 650 will be slightly easier to build and probably be cheaper but the Farrier F 22 will have a better resale value. The Scarab 650 information is at: Plans for the Scarab 650 folding trimaran http://www.teamscarab.com.au/Scarab650Des.html Building a Scarab 650 folding trimaran http://www.yendys.com.au/Scarab%20650.html

The jpegs below will give you the idea of each tri with the Farrier F 22 first.

Tomorrow we will discuss the first of 2 simpler to build designs of a similar length but do not have the internal accommodation space.

 

The following tri is a fun boat that may not satisfy the Farrier purist but would be a good tri for those who want an easy build, cheap to rig tri that will be reasonably fast in the right conditions. M A Cooper designed the “Comet 21”, a 21’6” x 16’2” foot tri with a 4’9” main hull maximum beam, 1,000 lbs. empty weight and 1,550 lbs. displacement (includes crew and gear). The mast is 26.5 foot high with 220 square foot of sail. The boat uses a standard Hobie 16 or 18 rig: mast, mainsail, standard rigging. The jib is custom made and mounts on a roller furling unit. The length to beam is 9 to 1 on the mainhull. The 19 foot long floats are simple deep V’s with a maximum buoyancy of about 1200 lbs when fully depressed. The draft is 1 foot to 4 foot over the daggerboard and kickup rudder. The tri can be disassembled for trailing and home storage.

The main hull features a small cuddy cabin forward with space for a single berth and some storage and a small galley, a storage compartment aft, and a self-bailing centre cockpit. This tri is a minimalist camp cruiser for 2 and a good fun fast day sailor for 4. If the Comet is built to weight it would be a fast boat in light to medium airs. The design was done in an era when low buoyancy floats were in fashion, so in higher wind speeds the tri would require more careful handling. Also, the deep V float shape would have high wetted surface when being driven hard.

The main hull (vaka) is multi-chined with a narrow flat bottom, graceful stem profile, and vertical stern to carry the kick-up rudder. The boat is built of marine plywood over a light spruce frame. The topsides are ¼” (6mm) while the bottom and decks are 3/8” (9mm). The pontoons (amas) are a V-section type also made of ¼” plywood using the “stitch and glue” method. The cross beams (akas) are a hollow box section made of laminated spruce and fir. The cross arms and floats are bolted onto the hulls. This would be one of the easiest tri’s of this size to build and could be converted to a foam glass version fairly easily.

The jpegs give the idea. M.A. Cooper had a normal website that used to feature this design for a cheap price but that site appears to be closed. He now has a Facebook website but he does not feature this design on it. An inquiry at: M.A. Cooper Design https://www.facebook.com/macooperdesign/about may produce results.

Tomorrow we will feature another 22 foot ply tri that is ocean capable and easily trailable.

 

The final tri in this short series is the Thomas Firth Jones designed Night Heron. Night Heron was designed for day sailing or a weekend getaway as she can be trailered to just about any location and set up for sailing in short time. Thomas who has designed, built and sailed many under 28 foot multihulls around the Atlantic understands what it takes to design and build small cabin multihulls. Thomas thinks trimarans are faster than catamarans, especially in light winds. They are more responsive, and will tack quicker than the jib sheet can be brought over. But tris have less accommodation and more sea motion.

The Night Heron is 22.5 x 14 foot and can be folded to 8.2 foot for trailering. The weight is 1280 lbs and has a displacement of 2030 lbs. The 27 foot 105 x 84 mm wooden box mast carries 218 square foot of sail are in the main and jib. The length to beam on the main hull is 8.4 to 1. The floats are 20.7 foot length with a displacement of approximately 1800 lbs at full immersion. The draft varies from 1 foot to 4 foot over the daggerboard. The outboard can be a 5 HP.

The accommodation is 2 single berths, storage, a small table and mini galley. The headroom is 4.7 foot. The accommodation is basically a weekender but as Thomas said this tri is ocean capable but is limited by its payload capacity.

The boat is basically plywood and timber. Hull bottoms and decks are 9 mm plywood. Hull and float topsides are 6 mm okume plywood. The floats have taped seams in the chines. There are frames every 3 foot with stringers about 400 mm centre lines. The cross beams are basically I beams that have an 18 mm plywood web with 32 mm square Douglas fir flanges on both sides of the web top and bottom. At the fold point for the cross beams there is a 6 mm stainless steel hinge plate on either side of the cross beam held on by stainless steel bolts. There is stainless steel water stays under the cross beams. The mast is a box section with 9 mm (very good quality) plywood on the sides and 65 x 16 mm Douglas fir front and rear. The sail track is screwed on the rear of the spar. There is 3 reinforcing timber blocks at various heights in the mast. The boom is an X timber section. Again, this tri could be converted to foam glass on the hulls and a large Hobie rig could supply the sail plan.

The righting moment of this tri is 12,400 foot lbs which is at the upper end of the strength capability a Hobie large rig. A Hogie 21 with 2 people on trapeze has a righting moment of about 8,000 foot lbs. Older Hobie builds had strong rigs but even so be a little cautious. Night Herons 12,400 foot lbs righting moment means the tri will reach its limits in 23 knots of wind with full sail up. Realistically you would be reefing at about 20 knots of wind. The performance of Night Heron in lighter airs is described as good which means a maximum of 15 knots of boat speed and about 80% of wind speed below 15 knots of wind speed.

So, in summary. A F 22 will be the fastest, most expensive, take the longest to build, have the best accommodation and best resale value. The Scarab 650 will be a good boat that will have similar speed, slightly less accommodation, be slightly easier to build and slightly cheaper. The Comet 21 is the cheapest, is designed to carry Hobie rigs, is a close to shore tri, easiest to build, has the least accommodation and will have good performance in light to medium airs but is only trailable by disassembly. The Night Heron has some accommodation, is truly trailable, is offshore capable, realtively easy to build, will be second cheapest and has good cruising performance. Take your choice.

The jpegs give the idea, plans are still available. I will not be posting for the next few days to allow for Xmas cheer. Have a good time see you in the new year.

 

I would suggest that the only reason the Night Heron is offshore capable where the others aren’t is with TFJ onboard.

 

Redreuben. I agree that Thomas and his wife were excellent sea people but the list of under 28 foot multihulls that have crossed oceans amazes me. I am excluding people doing stunts like beach cats across the Atlantic, I am talking about sane people cruising what they have on Transatlantic or Transpacific runs. The range from 16 foot catamarans to 25 foot Farrier and Piver tris. When I return in the new year we will do an item on these multihulls. PS all these boats had skippers who were well prepared for the risks they knew they would face, only one of them got the boat a week before he went sailing for the first time on the first leg of an ocean voyage. Have a good Xmas.

Finally, Jamez I hope you are recovering well and thank you for your input. It helps fill in the gaps.

 

Small boat voyages.
Great topic.

 

I didn’t see any mention of this one in the handy index OldMulti added to this great thread we all enjoy, so with my friends permission I thought I would do a little post on his Catamaran named Dragonfly.

The following info is from a submission to Yachting World Magazine by Richard Ackrill.

The boat was designed by Scott Jutson and built in Australia for competing in the Formula 40 circuit in Europe but didn’t make it there before the circuit ended.

Originally named Simply the Best, it was subsequently upgraded to Pro Formula with taller mast and sugar scoops added to the transoms, and it went on to win many races in Australia.

It was then sold and used as a prop in a cigarette commercial for which it was given a one-of-a-kind paint job in Thailand, and after it was sold again and made its way to the Pacific Northwest where it was renamed Dragonfly and was successfully raced setting records in the Seattle circuit.

This is where my friend and current owner enters the picture as he use to race against Dragonfly in his F25C, so knowing it and its capabilities, he decided to purchase the boat when the opportunity came about.

Dragonfly was eventually shipped to the Hawaiian Island of Kauai and now sails out of Nawiliwili Harbor and Hanalei Bay and is not hard to miss still sporting her dragon themed custom paint job.

Some details about Dragonfly:

Length: 40’ + 7’ Bowsprit
Beam: 25’ + hiking nets
Displacement: 3500lbs
Composite Construction
Aluminum Beams
63’ Hall Spars Carbon Mast

I have attached the article mentioned above which has more details, and a link to the cigarette commercial she was used in, as well as a few photos provided by the current owner.

Happy Holidays, and much thanks to OldMulti for this great thread!

 

Thanks SolGato. Good to see the old girl is still sailing.
I steered it for a season when it was Simply The Best. 2 strong memories:
We were dropping the spinnaker, the sail flapped and one of the crew were flicked off the boat, landed 6m/20' away. Scary, but no lasting damage.
On a broad reach, do we luff or bear away in the puffs? Puff hit, nose went under, rudders came out, luff or bear away becomes academic. I'm pounding on the hydraulic sheet release as the boat goes over sideways. Fortunately close to shore, power boat rights it and we are sailing again the following weekend.

 

Hello Jamez, I think, I also can't send you a PM because of the less posts. I found the sketches of the 32R in this thread and I think, the have a few ideas, that I would like to go on with. It's fine to know, that you have the plans and I am interested in having a diskussion with you about them. On what I Think, I have seen, Bob in this design did not set the the center of the hulls symetrical to get a wider beam? That is one of my thoughts to build a catamaran, that is around 9 or 10 m lenght, with a maximum size of 5m width and having a full standing headroom bridge. I would like to design/build a catamaran, that is fine for a couple and part time guests. What I tink, was very interesting about this design, was to choose asymetrical hulls.

 

Andrea. If you are interested in the Oram 32R as a starting point then wish to modify the concept for narrower beam etc then can I suggest that you look further into options. There are many designers out there that can provide a base design about 9 to 10 metres and who are still doing design work nd can modify the design to suit. I have shown some samples for consideration.

The Grainger Raku 32 is a sample of a fast 32 footer, The Coastal Passage 30 foot cheap cat has full plans with it but be warned some people have commented it may not be the best design. The Spirited 320 is a new concept design done in 2022. Other designers to look at include Richard Woods who has many 9 and 10 metre cats. Mike Waller who has the Waller 880 and larger cat designs etc.

RAKU 32 https://www.sailracingyachts.com/raku32/

The $21K catamaran: Build a cat fast and cheap https://www.thecoastalpassage.com/cheapcat.html

For the Spirit 320 info@spiriteddesigns.com.au

A final entry for consideration: BoatCraft's 9.5 m catamaran has been designed to offer exhilarating racing performance combined with comfortable accomodation for 5 - 6 people for cruising weekends and holidays. It has all the features of much larger boats, cleverly designed into a compact economical craft. The vessel, from multihull designer Ashley Holliday, has narrow, low resistance hulls are very easily driven, and with their long waterline they provide exceptional stability and performance. At 4.23 m, the beam has been kept to a minimum which results in a compact, highly maneuverable, light weight craft, with lower construction costs, and which can utilise a standard marina berth - another cost saving feature. The hull weight should be around 1500 kg, with a design displacement to 2500 kg. Cruising speeds of 10 - 12 knots can be anticipated, with faster passages under racing conditions. LOA 9.46m LWL 9.28m Beam 4.23m Draft 0.347m Displacement 2530kg Sail area 45sqm Waterline beam: 4.07 m Midsection freeboard: 0.888 m Mass per unit immersion: 9983 kg/m Prismatic coefficient: 0.619

9.5m Boatcraft Performance Catamaran Plans : Boatcraft Pacific, the home of wooden boat building. https://boatcraft.com.au/Shop/index.php?main_page=product_info&cPath=32_35&products_id=71