Multihull Structure Thoughts

om: Thanks for the elaboration.

 

Richard Woods SHADOW is the plywood version of the fibre glass STRIDER CLUB cruising design. It offers a good compromise between speed, accommodation and low cost. The Shadow is 24 x 14.1 foot with a weight of 1,550 lbs and a displacement of 2,250 lbs. The 27 foot aluminium mast can be fixed or rotating and carries a from 200 to 275 square foot depending on the rig options you choose. A large beach cat rig could be used like a Hobie 21 etc but the cat will have to be kept light as the stability is on the limits of beach cat rigs here. The low aspect ratio keels draw 1.7 foot. The rudders are transom hung and kickup. The Shadow/Strider Club are trailable, but because of the keels and large cockpit tray it is not as easy as the standard Strider. The trailer system includes a specific road trailer and launching trollies.

Shadow has a solid cockpit floor with a deep mast beam. All sail controls are simple (no winches) and the cockpit area is kept clear of ropes. The side opening hatches allow safe access when under way. This is the boat that Richard Woods and friends sailed in a convoy of 3 boats singlehanded to the Soviet Union in 1989. We lived on board for the 3 months of the trip and sailed over 3000 miles from Plymouth UK to Tallinn. You can see more about this trip on our video "A Day Sail to Russia". The accommodation has up to 4 single berths in the hulls a small practical galley and portapotti. The headroom is 4.5 foot. There can be a small covered cockpit area (solid or tent) with a double berth on the bridge deck.

The performance is very good with testing comments like "She is certainly close winded and tacked round without fuss" Practical Boat Owner. "The longer she is sailed the more she grows on you. She makes a seaworthy coastal cruising boat which offers great satisfaction and enjoyment under sail" Yachting Monthly. The hull shape is basically a Strider 24 foot racer and that is a very fast cat.

The construction materials for the hulls are cold moulded or strip plank with ply decks. The material list is of the plywood version but an excellent web site of a strip plank version is at: https://saideira.net/

This is a good web site about strip plank building of any cat. We can learn a lot from his experience.

PLYWOOD
Hull skins keel - stringer 2 3 mm ply 11 sheets, Topsides 5 or 6 mm ply 6 sheets, Bulkheads 6 mm ply 3 sheets
Beamboxes 6 mm ply 1 sheet, 12 mm ply 1/2 sheet
Decking 5 or 6 mm ply 8 sheets
Keels 9 mm ply 1 sheet
Rudders 18 mm ply 1/2 sheet
Platform/cockpit 9 mm ply 3 sheets
Beams 6 mm ply 3 sheets
Use best quality gaboon throughout. Note if 5mm ply is un-obtainable then 6 mm ply can be used.

TIMBER: Use Douglas fir, Sitka spruce, yellow cedar. Note sizes are nominal and should be "planed all round"(PAR) ie final size of 1 " x 1 " = 20 x 20mm

1 " x 1 " 70m (meters), 1 1 / 2 " x 3/4 " 120m, 2 " x 1 " 160m, 1 1/2 " x 1 1/2 " 22m, 3 " x 1 1 / 2 " 2m, 3" x 3/4 " 10m
2" x 2" 3m, 3" x 1" 4m, 1 1/2" x 3/4" 15m (hardwood for outer gunwale)
2 " x 1 1 / 2 " 4 off 4100mm plus 15m (beams), 1" x 1 1 /2" 8 off 4100mm plus 10m (beams), 4" x 1" 2.5m
4" x 2" 2m (cedar, outer stem - can be laminated from smaller pieces)
6" x 1" 12m (keel planks - can be laminated ), 4" x 1" 15m, 3" x 1" 5m (hardwood - sacrificial keel)
3" x 2" 1.5m

 

The F-22 is a modernized version of the Farrier Trailertri 680/720 which was featured on page 165, which pioneered the folding trimaran concept. The F 22 is 23 x 18 foot (folded 8.2 foot) with a weight between 1320 and 1500 lbs depending on build technique and materials used. The 31 foot rotating mast can carry a 294 square foot or 328 square foot of sail depending on the performance wanted. The draft is between 1 and 5 foot over the daggerboard or centre board.

Now let’s look at the real differences between the TT 680/720 series and the F 22. The F 22 build is lighter, has a wider beam, taller mast with more sail area in the cruising and racing version. The main hull has a lower wetted surface area, while it has a slightly flatter bottom with less rocker so it will plane earlier. The floats are significantly larger (float displacement of 3050 lbs or over 140% of sailing displacement), with much more buoyancy lower down and further forward, for the maximum performance, and a lower heel angle. The extra buoyancy in the bows is very important for today’s taller rigs, as just adding a larger rig onto an older hull design can generate bad habits and control problems. All hull shapes are more rounded without any chines. Result is the F 22 is faster across the wind range than the TT 680/720.

The F 22 build is foam glass with either e-glass with vinylester or carbon fibre Kevlar epoxy options. To give an example of the build variations of an F 22 I will quote a few home builders about their float options. The float of an F 22 has a standard layup of 600 gsm biax e-glass outside 10 mm H 60 foam 400 gsm biax e-glass inside with vinylester or epoxy. Another builder did his F 22 float and deck with inside 295 gsm s glass biax, 10 mm H60 corecell, outside 2 (295 gsm s glass knitted biax) in epoxy. Another boat in Brazil outside 2(280 gsm biax) 10 mm foam and 280 gsm biax inside. A Finnish F 22 builder float has outside 240 gsm carbon kevlar 50/50 mix with 200 gsm carbon next to foam 10 mm corecell foam and on the interior 240 gsm carbon kevlar 50/50 mix in epoxy. One builder preferred 12 mm foam to strengthen his hull and laid additional glass in some spots. A least one builder went all carbon. Ian Farrier was asked to approve all these glass variations. If you are buying a second hand home build F 22 please ensure it was either built to plan or had Farrier approved variations.

Farrier recognized the difficulty of cross beam structures (the beams have carbon fiber flanges top and bottom and should be resin infused) and sold the beams and support infrastructure for the F 22. The Farrier Folding System has never had a failure of any lower folding strut, in over 30 years. Thus it was possible to begin eliminating beam bolts and shorten the beams compared to the TT 680/720 (and later designs such as the F-24 and F-31). The F-22 has a beam length set at the minimal optimum, with no interior intrusion into the main hull at all. The resulting short beams, braced by the lower folding struts, are the most efficient beams available for a trailerable trimaran.

The jpegs give the idea but there is 2 web sites (with many other web site links) to F 22 builders. A lot of these site give very good build information on materials and build techniques which you can learn a lot from. The sites are: Jay's F22: January 2007 http://seattle-f22.blogspot.com/2007/01/ My F22 Trimaran: 2009 http://matosf22.blogspot.com/2009/

 

You make mention of Farriers refined beam design above, and it is my understanding that one of the main motivations for reducing their length was to reduce their height on trailer when folded so that they created less windage.

I remember Ian commenting this on a Forum some time ago, that it was one of the things he disliked from the start, and something he was continually trying to refine up until his final designs with Farrier International.

To continue to refine something that has worked so well as you mention for so many decades is a testament to his love for a design challenge.

And as I have stated before, I have sailed my Tramp in some pretty crazy swell launching into and off waves and surfing down them, and in those conditions you really appreciate how over-built the earlier boats were with their oversized Oval beams and double bolt design. Multihulls didn’t have the best reputation early on, and I think it was wise that a number of builders understood this and chose to error on the side of caution.

I’m just glad he adapted the concept to the sailboat industry and not the flying contraption or gym equipment industry

 

This solar-powered catamaran was designed by Kreatif, a Slovenia-based designer studio, for a Rwandan (African) company. The cat design vessel is designed for Malawi, Victoria, Tanganyika, and Kivu lakes which required an affordable and reliable emission-free vessel that would meet the needs of the locals and overcome all weather conditions. The cat is 19.5 x 8 foot and a guess weight of 3000 lbs with a load capacity of 2200 lbs. The boat is powered by a 6-10 kW brushless DC motor combined with state-of-the-art technology integrated into the control system and whose power is generated by a roof mounted 10 Monocrystalline Solar panel array for 48 V 4000 Watts fed through a pack of LifePO4 Batteries (48 V 100 Ah/ 200 A). The Lithium batteries are similar to Tesla Powerwall units.

The vessel allows a cruise at a speed of six to twelve knots, with a range of about 25 miles (40 kilometers). The entire control system for the cat is done by a 10” display and a dedicated app called AMAZIAPP, which comes with navigation features, range calculation, optimal speed calibration etc. The main tasks of the system are to manage solar energy input, battery storage, engine performance and power consumption along with navigation. The accommodation is seating in an open cockpit for up to 12 people.

The cat is meant to be a durable and solid, and is constructed mostly from polyethylene (HDPE) which is supposed to allow the boat to “absorb a large number of shocks before being damaged” according to the design team. The concept is to “mass” produce a group of these vessels for various locations and functions.

The jpegs give the idea.

 

Many years ago the TT enthusiasts had a CD with the 680 and 720 plans on them available for owners to help with maintenance. No one seemed interested in the 18 anymore. I managed to find a set of 18 plans and they were handed on and added to the set. Back then you had to pay a nominal fee for the supply of a CD, and postage. Now they are as you say available for download. IF endorsed their distribution.

You would be mad to build one now. They are massively overengineered and the cost in time and money is silly. RK's scarab etc are much better propositions in timber. Occasionally a set of Farrier plans come up second hand. Last I looked the people who now own the NZ business seem uninterested in building boats now. Terribly sad. There are a couple of licenced builders who can (last I looked) still supply a new boat if required.

 

A simple one today. Tanton Yacht design produced a simple relatively fast build power cat design for coastal and inshore use. The Coastal Power Cat is 15.5 x 6.95 foot with a weight of 450 lbs. The draft is 0.9 foot. The design is more of a tunnel hull with the tunnel bottom at water level when at rest. Once the cat is powering along a venturi effect lifts the tunnel clear of the water allowing higher speeds. The cat can be powered with a 15 HP to 100 HP outboard. This cat is trailable with a smaller cat.

The cat has a maximum capacity for 8 people in the cockpit and has a small cuddy forward for some shelter but mainly stowage, a center console with a seat half way to the stern, and plenty of room for guests.

But the real value of this design is its “flat pack” egg crate type build. The cat is mainly constructed of 9 mm plywood for the hulls and 6 mm plywood for the decks. There is 500 foot of 25 x 25 mm timber used for cleats on the bulkheads, transom and decks supports. 2 longitudinals of 9 mm plywood, 1.4 foot, provide the fore and aft structure over the length of the boat. Six bulkheads tied into these give great rigidity. The space below the sole is filled with polyurethane foam. The bottom is 9 mm plywood; the topsides, the sole, and the deck are 6 mm plywood. The transom is a 9 mm plywood panel, heavily reinforced by cleats. Also, a 25 x 150 mm piece of solid wood is bolted and glued over the entire width of the transom to support the engine, to absorb vibration, and for strength. This is a relatively simple build that can have a West epoxy saturation technique through out an cover with a light glass cloth in epoxy for added strength.

A fun design for a quick fishing trip. Sorry about the limited jpegs. The plans cost $300 US.

 

The following series of jpegs came from a hole drilled in a Farrier 31 (I suspect a production build) built in 2012 to fit a transducer. The core material is Balsa no problems if the hull glassing is well done and sealed well. The jpegs tell a different story. The cut out is antifouling, gelcoat/kevlar/glass/very hard balsa/kevlar/glass painted grey inside. Kevlar is yellowish. From jpeg f31 cut 4 onwards is at least one layer of dry unidirectional (assumed to be) kevlar between the inside skin and the balsa core. Translation minimal strength in this area which also happens to be beside the daggerboard case. Farrier was wise in overengineering his designs but even he would have been shocked at this lack of quality in building. As John Shuttleworth once commented resins do not work well with Kevlar unless they are specially formulated for Kevlar.

Testing for these bad building practices in a second hand boat is difficult but a good surveyor may be able to locate someone else’s problem before they become your problem. To fix this would cost a serious amount of money.

PS Another F31 owner made this comment on F31 builds. "Most of the F31 is foam cored. This may vary from boat to boat but some areas like the companionway bulkhead, on ours, are balsa. All of the boats have a balsa core strip running down the centerline of the hull bottom."

 

The following is a Scott Jutson Powercat designed for cruising is a smaller version of the 42 foot aluminium cruising cat featured previously in this thread. The 38 x 14 foot cat weighs 25,000 lbs. The length to beam of the hulls is about 12 to 1. The propellors are in a semi tunnel at the stern. Jutson selected tunnel housing for the propellers as an added layer of propeller protection in light of the vessel’s expected heavy duty operations. “The tunnel also is designed to keep the vessel at neutral trim through the speed range so no additional trim control is required.” The draft over the propellors is 2.7 foot. the underwing clearance is 3.3 foot. The engines are 2 x John Deere 4045 @ 180 hp. About 18 knot sprint and 12 knot cruise at about 4 litres per mile

The accommodation has 6.5 foot headroom throughout but the number of berths are limited to one spacious double queen berth cabin forward with a full toilet in the other hull. The main saloon has a galley, dinette and navigation/steering area forward. An interesting comment from the owner (Pelican_38) “I wouldn't call her a comfy "liveaboard" - but I've been aboard and lived...I guess that's the same thing.” The cat has full walk around side decks and a large aft cockpit with large deck hatches over the hulls to allow access to and removable of engines if required.

The construction of the shell is aluminium supported by T stringers and many frames. The cross section and longitudinal section jpegs give the idea of the hull shape and structure of a 45 footer used in Glacier Bay in Canada. The hull structure of the 38 footer is probably lighter than the iceberg avoiding 45 foot cat. The final 2 jpegs are samples of Jutson stock plans.

The jpegs give the idea of an interesting serious cruising cat.

 

We looked at the Excess 15 cruising cat designed by VPLP and built by Groupe Beneteau on page 63 of this thread but some new information has been found. The cat is the Excess 15 which is 48.5 x 26.33 foot and weighs 40,600 lbs and is capable of carrying a 18,000 lbs payload. Its standard rig has a 75 foot mast with a 1124 square foot Square top mainsail, 592 square foot self tacking jib and a 1259 square foot Code 0. The “Pulse” rig has an 81 foot mast with sail area of 1850 square foot. The hull length to beam is about 8:1 at the waterline. The draft is 4.6 foot. The engines are 2 x 57 HP diesels or 2 x 80 HP as an option.

Now we come to the interesting bit. There was a comparison between the Lagoon 50 and the Excess 15 in one magazine. It was a valid comparison because the Excess 15 uses the same moulds for the inner hulls, underwing, bulkheads and a lot of the deck as the Lagoon 50. Only the mouldings for the outer hull halves have been changed above the waterlines to allow more internal room in the bows for berths etc. When VPLP were asked to do the design work they were also asked for a lighter structure and Groupe Beneteau reduced the build weight by 2,400 lbs over the Lagoon 50. Put a bigger rig on the Excess 15’s and you have a “sportier” catamaran to suit the younger market.

The construction of the Excess line is vacuum-infusion with balsa coring in the deck and hulls above the waterline. Built in three sections, the Excess 15 has the same bridge deck and inner hulls under the waterline as the Lagoon 50, but different outer hull halves. Design firm VPLP took about a ton of weight out of the Lagoon version by lightening up interior fixtures and doing away with the flybridge.

The Excess 15 comes with four cabins/four heads or three cabins/three heads with the owner’s version having the entire starboard hull to a master suite. The main saloon and cockpit are an integrated space for the galley, table and seating with a navigation area. Comfort is ensured with all the entertainment and lounging spaces required.

A test sail on the Excess 15 produced “Again, test-sail conditions were ideal, with 12-18 knots of wind and a light, 3ft chop. With three of us aboard, the XCS 15 is a large platform, the boat is by no means difficult to manage. If you think two boats within sight of one another equals a race, then you probably know what I mean when I say three A-types on one boat will yield similar results. In the end we maxed out at 10.5 knots with the Code 0 on a broad reach. Under jib and main alone, we made around 8 knots sailing within 60 degrees of the true wind. Good times!” My simple performance calculator indicated at full displacement the Excess 15 has a Bruce Number (BN) of 1.06 and a 240 mile/day capability (calculated from boat stats).

The Excess 12 and the Lagoon 39 also share a lot of the same mouldings. So, if you have the option of a second hand Lagoon 50 or 39 at a reduced price compared to a new Excess 15 or 12, you may be buying a very similar cat for a discount. The jpegs give the idea of the Excess 15.

 

This is a short but an interesting one. Tanton Yacht design produced a simple sailing foiler design based on a concept from a 1984 US Patent number 4635577. The sailing foiler was original called Palmquist 1 (sailing jpeg). Tanton designed his own version for a New Zealand client in 1992 who did not build the boat. The Tanton version is 24.5 x 24 foot with a displacement of 1,075 lbs. The 33 foot wing mast carries about 300 square foot. The main hull beam is 4 foot at the gunnel. The length to beam on the main hull is 11.2 to 1. The draft is 230 mm.

The real interest is the large forward angled foil which also acts as an attachment point for the cap shrouds on the outer end of the foil. The foil is also thick and has a long enough chord to provide some buoyancy in light air. The structure of this foil is unknown but probably a wood structure as the main hull is plywood. Do not underestimate the forces acting on the foil/beam, as not only is it resisting the overturning moment on one side it is resisting an equal load from the cap shrouds on the other side. It is doing this whilst trying to maintain the correct angle of attack on foils leading edge. The torque forces would be interesting.

There is no indication of performance beside the one sailing jpeg but it could be interesting. Foiling sailing craft have come a long way since this design but it may be a way of producing a cheap fun boat for experimentation. The first jpeg are of the original Palmquist. The next jpegs are of Tanton Yacht design. The final PDF is the original US patent.

 

Michael Pope designed and built the following monomaran “Away”. Why a monomaran, because it is basically a monohull but has a tunnel aft that leads to twin sterns. There have been several versions of this type of boat with a 52 footer in New Zealand and a 55 footer built in Australia. In each case they were after differing things but came to the same conclusion. The twin sterns were designed to reduce rolling down wind of the 52 footer, in the 55 footer to reduce the waterline beam and wetted surface for sailing and in the case of the Michael Pope design to allow a dingy to be docked easily in the stern then raised on a winch. The result is the same in all boats if the rear tunnel is correctly designed, reduced rolling and slightly increased speed at the cost of reduced accommodation aft. Modern monohulls have wide beams going all the way to the stern which achieves similar results and it often increases the available accommodation space. The designer builder of the Brisbane 55 footer told me that the tunnel design is critical, as an incorrect tunnel design slows the boat down creating drag according to his tank and model testing.

The Michael Pope design “Away” is 44 x 10.2 foot with a light displacement of 15,000 lbs. The rig is a schooner with 2 free standing 45 foot masts with fat head fully battened mainsails. The draft is 4.3 foot over the keel and 9.5 foot over the dagger/centreboard when it is down. The dagger/centreboard can kick forward if it hits bottom and is capable of being trimmed fore and aft to help boat balance. The twin outboard rudders will provide control under all conditions. The sail plans advantages are unstayed masts eliminate expensive rigging and the divided rig gives lighter sails and smaller individual sail area. Sail inventory is reduced to 3 sails of 2 mainsails and a storm staysail. The number of control lines, winches and deck gear are minimized. Flexible masts and the wishbone choker allow control of sail camber and twist.

The accommodation is simple with a double berth cabin aft of a large storage cabin forward. The main saloon contains a galley, seating and table, navigation and inside steering and a single berth aft. This is a serious cruising boat for a couple that will perform well with a minimum of crew effort. The size of the propeller indicates that “Away” will be able to motor well in most conditions.

An interesting concept. The jpegs give the idea.

 

The Wave 50 cruising catamaran is built by the Polish shipyard Wave Catamarans in Szczecin and designed by a team of designers lead by Agnieszka Bona. The Wave 50 is 49.1 x 27.3 foot of unknown displacement. The mast carries a 753 square foot mainsail, 743 square foot genoa, a 1,990 square foot Gennaker and a 2,370 foot spinnaker. The draft is 4.7 foot over the fixed low aspect ratio keels. The length to beam on the hulls is about 8 to 1 at best. The underwing clearance is low, it looks like about 2 foot at best. The engines are 2 x 60 HP Volvo Penta D-60 and two 18.5 kW electric motors. There is 840 litres (220 gallons) of fuel. The hull shape at the bow is unique, not the inverted bow but having an angled back “chine” to create the inverted bow is interesting. I could see a more conventional hull shape then some said lets do an inverted bow, OK, lets chop of the top of the bow and put a flat panel in, sounds good.

Now we get to the design concept. Accommodation is more important than performance. The base rig is relatively small for the size of cat and the topside windage is large. I cannot find a displacement number anywhere but I think it would be in the Lagoon 50 league (60,000 lbs all up). The visual style of the Wave 50 is your choice. I prefer performance over accommodation and minimum windage in a design but each to their own style.

The accommodation is Vast. Up to 6 double berth cabins with an ensuite per cabin in the hulls. The main saloon has a very large and well equipped galley, multi seating/table arrangements, entertainment area and direct access to forward and aft cockpits which can be “integrated” into a larger entrainment area. The we go to the flybridge control area located on the main saloon roof and extends over the lower cockpit. The saloon angled windows are mirrored to help reflect the heat but pity sailing to close to a Wave 50 on a sunny day the reflections could be blinding.

To quote one French test about sailing Wave 50 “The maneuvers come back to the helmsman, especially the sheets of the furling genoa, which are difficult to access in this kind of rostrum (flybridge). With only 140 m2 of sail area upwind, the Wave 50 has little sail area. Finally, it is difficult to access the mainsail. From the flybridge, you will have to climb on the rigid hard-top with hydraulic opening, and we wish you courage.” When you have wide stairways with minimal handrails to get between the various levels of the Wave 50, I begin to worry about the offshore suitability of this cat. Again, accommodation overrules the sailing requirements.

The Wave 50 is a vinylester carbon build using advanced and proven vacuum infusion technologies. The sandwich structure, consisting of a PVC foam core and carbon-fiber-reinforced sheathing, is assembled with vinylester resins. This structure guarantees the catamaran is both rigid, durable and strong, resulting in weight savings. The structure components may be light but if you have large amounts of light structures you end up with as much weight as a design with fewer heavier structural components.

My apologies but I suspect I am not the market for this cat. As I said I prefer performance and ease of handling over accommodation. The jpegs give the idea.

 

Seems like they were so focused on whether or not they could, that nobody stopped to ask whether or not they should. Interesting design choices, but we are getting dangerously close to Hanstaiger territory here.

 

Came across this Cat design the other day.

Kind of a classic fast Cat open deck layout but more modernly built.

Looks like a nice ride under power.

At about 1:56 in it starts pressing it’s leeward hull pretty good.