Multihull Structure Thoughts

[Russell Brown]

My old G-32 just won the WA 360 race in 2 days 16 hours. The new owners beat a number of monohulls, very competitive Farriers, and a Seacart 30.
Here's a short video of them from yesterday:

 

[Karstan]

My old G-32 just won the WA 360 race

Such a fantastic boat! Someone should take some lines and measurements of a G-32 one of the days (since, if I recall correctly, the original plans were lost).

 

[oldmulti]

I am always amused at what can be done in catamaran design. Here is a british version of a fun cat. Its 8 foot long about 6 foot wide with really strong hull to bridge deck connections. Looks like some old table legs. The bridge deck structure is some spare aluminium tubes with a lose netting “bridge deck”. I don’t know if the motive power is a sail, paddles or motor. Definitely an inshore short journey craft for 1 or 2. The fishing rods hanging of the side may give a hint as to its real purpose.

Life can be simple for those who can swim to shore.

 

[oldmulti]

Domi Montesinos is a man who likes cruising on his power cat but wanted a more functional tender than a common RIB tender. He wanted a stable low power tender that could also be used for fun if required. He choose a catamaran tender and after a bit of trial and error built one for himself refined it a little then wrote a book about its construction which can be purchased from his web site. The book cover in the jpegs is only for illustration not a link.

The tender he designed can be built either 8 foot or 10.75 foot x 5.9 foot wide. The weight is about 170 lbs depending on the length and type of plywood used in construction. The optional free standing mast is 12 foot above deck and carries about 60 square foot in a lug sail. The outboard can be a 3 HP petrol or a “1 HP” electric motor which will give about 5 knots under power. The "economical" speed of 4 knots is obtained at 260 watts and gives a range of 18 nautical miles (more than 30 kilometers). The sail will drive the cat at about 6 knots.

As you can see the 10.75 foot version can carry 2 people well and have storage for additional items. This appears to be a very functional tender.

The simple hull shape allows a nearly frameless plywood build with taped seams and some timber reinforcing at the chines and gunnels. This would be a fast easy build but to get the stiffness in some components I suggest 6 mm and some heavier plywood would be needed. By the book and you will get full details. The mast step is a very neat arrangement.

The jpegs give the idea.

 

[oldmulti]

Raraka is a Tony Grainger design that started with the owners of a 40 foot ex racing trimaran Spirit. The owners are full time cruisers but they wanted more of a floating home that an ex racing tri. They approached Grainger about a larger trimaran and he did the initial design for them based on their and Tony’s experience. Before the design was completed the owners of Spirit purchased a second-hand Hammerhead 54 (Chris White design) so the Raraka design went into the bottom draw. It is available now as a design for completion.

The Raraka is 52.4 x 37.4 foot with a displacement of approximately 25,000 to 30,000 lbs. The carbon mast would have beam about 70 foot tall. Length to beam on main hull about 9.5 to 1. Main hull 13 6 foot at gunnel main hull. Length to beam on floats 15.25 to 1. The draft over the float based fins is 4 foot.

The fixed fins on the floats is an excellent idea. As the tri is driven harder in stronger winds the fins are driven deeper providing more effective lateral resistance when needed. The fin floats could also be angled to provide lift in stronger winds. The fin floats also do not take up space the main hull as a daggerboard or centreboard would. Fins on floats would require stronger cross beams.

The accommodation can be changed to suit your needs. There are 2 accommodation layouts shown but it can be optimised. The basic layout is a double berth forward, toilet shower next then the main saloon has a full galley forward, 2 seat dinettes followed by the cockpit. Aft of the cockpit is a double berth cabin with a toilet shower. There is more than enough accommodation for a couple to live comfortably for a global trip.

The basic structure would be foam biax or triax cloths in S glass or carbon in epoxy or vinylester. Grainger employs top quality engineers to design the structure of these tris. The final builds is often controlled by the budgets of the owners.

The performance of this tri is unknown but I would not be surprised at 15 knot averages and peaks of over 25 knots.

A very good design that deserves owners who would appreciate and use the concept. The jpegs give the idea.

 

[oldmulti]

We mentioned the Chris White designed Hammerhead 54 trimaran yesterday. We have done an item on the trimaran previously, so this will be short reminder. The Hammerhead 54 is a very fast sailing cruiser that is capable of sailing at 24 to 25 knots without surfing and without a spinnaker.

The Hammerhead 54 is 54 x 34.5 foot with a weight of 17,000 lbs and a 60 foot mast. The mainsail is 858 square foot, jib area is 492 square foot and a 250 square foot jib. The draft is from 2.5 foot to 9 foot over the swing centre board in the main hull. The power in a 62 horsepower Yanmar turbo charged diesel engine with a cruise speed of 10 knots.

The Hammerhead can sail at an easy 20 knots with mainsail and jib alone. Extended periods of STEADY 19 to 20 knots of boat speed with a single reefed main and full jib, beam reaching in approximately 20 knots of wind have been seen. Steering in these conditions was a one handed affair. In moderate conditions she will tack inside of 80 degrees making 8 to 10 knots through the water. As wind speed increases the fastest way to windward is to open up the tacking angle slightly to build more speed- which offsets the greater distance. Boat speeds of 11 to 12 knots hard on the wind can be achieved with proper sail trim. In a single handed trip from Chesapeake bay to Bermuda Hammerhead averaged 235 miles per day.

All this speed with accommodation as well. A large saloon with galley, seating and good views all around, a double berth cabin with ensuite forward and a double berth cabin aft with ensuite.

These big well designed big tris can be very comfortable while crossing oceans very fast. The jpegs give an idea.

 

[oldmulti]

Tony Grainger new 42' LOA “single handed” trimaran design was largely inspired by Venom R42 trimaran but destined to live in Mediterranean waters. The prospective owner had some very specific ideas for the design. Ideas that were grounded in the desire to sail mostly single handed, and to be able to safely reverse into the marina spaces along the shore front of the typical Mediterranean port facilities where boats tie stern to with access on and off the boat.

At the heart of the design concept was a cockpit arrangement that allowed the skipper to pass quickly and safely across the boat when tacking and gybing without having to step down into the cockpit. The boom had to be high enough that it didn't pose the threat of a serious head injury.

In addition to the port and starboard helm stations on the aft beam there would be a central helm station in a more sheltered cockpit forward of the platform between the beam mounted helm stations.

The tri is 42 x 34.1 foot with a weight of 8,450 lbs and a maximum displacement of 10,080 lbs. The rotating wing mast is about 66 foot high. The sail area is about 700 square foot mainsail and 400 square foot jib and an about 1500 square foot gennaker. The main hull length to beam is 11.6 to 1. The float length to beam is 17 to 1. The draft is 4.5 foot over the main hull rudder to 6.3 foot over the main hull daggerboard. The engine is 15 HP inboard with sail drive leg. There is also a forward raisable sail drive leg to act as a bow thruster.

The accommodation layout is a double berth forward, a toilet then the main saloon with a galley on one side and a seat table that can be converted to a single bench on the other side. The cockpit is vast and setup for single handed sailing. There out board helming on the rear beam which with the rudders on the floats and main hull allows excellent control (hopefully) under many conditions.

Performance is unknown but I would suggest 10 knot averages and if you are courageous enough single handing over 20 knot peaks. This tri is going to be about the deck gear and sail controls. If correctly set up a very fast single handed tri. If not set up correctly, a boat that could become a handful in stronger winds.

The build is foam glass throughout. I suspect a fair bit of carbon fibre in the mast and crossbeams.

I hope the owner has fun. The jpegs give an idea.

 

[oldmulti]

This proa was spotted on a Saipan beach and is an example of a simple sailing solution. The proa is set up to be either a pacific or Atlantic proa depending where the crew weight is placed. I would suggest it would be an Atlantic proa in light winds as the float shape is rudimentary. This proa would be faster as a Pacific proa. The proa has solid mast and I assume a crab claw sail. I do not know the dimensions of the craft but would guess it is 20 to 25 foot.

The simple planked sides (joined by a lot of ties and I assume some waterproof joint material) of the doubled ended narrow flat bottom hull will cut through the water well. The steering is by an oar aft of the decking structure at either end of the craft.

The cross beam structure is timber beams. At the float there are several timber verticals that have ropes to lash the cross beams to the float posts. The extended wing deck opposite the float is a substantial structure that appears to be able to be removed when required.

An interesting view of old style construction on an old design concept but was produced in the last 50 years. I would suggest cheap and relatively fast. The jpegs give the idea.

 

[oldmulti]

Burghard Pieske, a sailor and adventurer from Germany, and Ignacio “Nash” Camacho, a member of Guam’s Traditions About Seafaring Islands, are shown on the dock in Palau next to their proa, Ana Varu, after ending their voyage from Taiwan. They had planned on sailing to Guam. The ultimate destination was to be Easter Island.

The sailors decided to dock in Palau and send the flying proa – traditional canoe - via cargo to Guam in time for the opening of the Festival of Pacific Arts after high winds caused damage to their proa. It took 15 days to sail 1000 miles. Camacho said they are not disappointed at ending the journey in Palau where they were warmly received. “It was a decision we made in the ocean, not to quit but to change our course to Palau,” Camacho said. Pieske said that the journey was part of his goal to get to know the Pacific seafaring culture.

Ana Varu is a pacific proa. Burghard sailed her from Taiwan to the Marianne’s where he successfully supported the local boat building and sailing communities. Unfortunately, “Ana Varu” capsized and was lost to the big blue.

Ana Varu is a pacific proa 36.5 foot long with a crabclaw sail with its clew foot is attached to a sail track running the length of the main hull on the outside gunnel. Winches are used to move the crabclaw foot during “tacking” requiring less crew for the task. 2 people can sail this 36.5 foot proa.

The accommodation is either end of the central cockpit and is adequate as the asymmetric flared main hull is wide at the cockpit.

The construction uses modern material EG foam glass for most components.

Ana Varu performance based on its initial sailing was not good. An average of 67 miles per day in moderate to “strong” winds suggests either the crabclaw sail was not efficient or the crew were being very conservative. Access to some of the trip information is in sites that have virus software, so I did not get much detail.

The jpegs give the idea of a modern version of an old concept.

 

[tane]

Pacific Proa - clearly not a concept for everyone, only for extremely competent seamen...

 

[Skip Johnson]

It looks like the sail is more a lateen than a crab claw.

 

[oldmulti]

We have done this design before but additional information is available. The David DeVilliers designed 52.5 foot aluminum catamaran is a performance cruising catamaran capable of global cruising in comfort. There are 2 versions of the design ie. a ketch rig as well as a sloop rig. DeVilliers provides either full plans or plans and kits to build this cat (assembly drawings and nested CNC cutting files). There are companies willing to build the entire cat for a client. This design will give good sailing performance if the owner does not over load the boat.

The 525 is 52.5 x 25.5 foot with a “displacement” of 32,900 lbs (likely to be weight). The aluminum mast is 67 foot high and carries a 1052 square foot mainsail (10 oz US Dacron Crosscut with Twin Ply Leech), a furling staysail of 350 square foot (10 oz US Dacron Crosscut Luff Foam), a furling genoa of 760 square foot (10 oz US Dacron Crosscut Luff Foam) and a 1615 square foot spinnaker (1.5 oz Nylon Full Radial Cut). The hull length to beam is 11.3 to 1. The draft is 2.2 foot over the canoe body and 4 foot over the fixed fin keels. The underwing clearance is 2.8 foot. The engine power is 2 x Volvo Penta D2-50Hp Mechanical Propeller- 2 or 3 blade - Gori or similar folding x 2 Propeller Shaft Coupling x 2 Propeller Shaft- 38mm minimum 316 L standard SAE Taper. Hull Speed under power is 10 Knots and the cat carries 860 litres (227 USG) of fuel. Engine Room Soundproofing Perforated Stainless or Aluminum wall sheathing. Electrics are a DC-AC Inverter/Charger-Victron 3000W with 8 x Solar Panels at 365W each feeding 6 x 100Ah 12V LiFePO4 Deep Cycle Battery. Mechanical engine starting Batteries 2 x 100 Ah.

Accommodation has a saloon/lounge with a L-shaped dinette table (converts to a bed), galley navigation position and inside helm. There are double bed cabins aft [port and starboard] with attached shower toilets and a forward double berth cabin in one hull. One hull cab be converted into an owner’s hull. This cat can be set up as a charter machine with 4 double berth cabins if required. The cockpit is large and can provide additional seating to the main saloon through a wide cabin door.

The structure is a durable, rugged alloy cruising boat with inherent safety features (6x watertight compartments, skeg protected rudders and props, exceptional underwing clearance etc) which will appeal to anyone wanting to cruise far and wide. The hull, bulkheads, deck and superstructure constructed using certified (DNV or similar class) marine grade 5083 H116 aluminum with extrusions being 6061 T6 with mill certificate. Welding wire to be 5183 with ABS certificate. The hull finishing Primer- Epoxy- Maestria, 2 coats exterior only Fairing Compound. The final paint is Enamel, Maestria, 2 coats, yacht finish Antifouling paint Jotun 2 coats.

This cat is going to provide 10 knot type of averages and peaks of 20 knots with the fractional sloop rig if not overloaded. A very nice cruiser concept that could be home built by an experienced home builder who has a few years available.

The jpegs give the idea.

 

[oldmulti]

Splice (or design number 58) is a 31.5 foot catamaran David Devilliers design (from New Zealand) that is designed to be a minimum sports cruiser that can be disassembled for transport. The philosophy of this cat is to be simple to build and maintain, devoid of complicated and costly systems, offer “camping” style accommodation for up to six people and will be capable of exciting coastal passages.

Design number 58 is 31.2 x 18.7 foot with a displacement of 4,960 lbs. The 39.5 foot rotating mast carries 533 square foot upwind and a 685 square foot asymmetric spinnaker added down wind. The hulls are 4.3 foot wide at the gunnel and about 2.4 foot at the waterline which would give about a 13 to 1 length to beam. The hull draft is 1 foot with 4.7 foot when the hull daggerboards are down. The bridge deck clearance is 2.75 foot. The outboard power is 10 HP.

The accommodation is a double berth aft in each hull and a table seat forward in one hull. The other hull forward has a galley. Forward of the main beam is a toilet area.

The construction is mainly plywood with plywood and timber frames and timber stringers. The hull shape is a simple chine structure. The external shell is covered with e-glass and epoxy. The plywood appears to be thicker EG 9 mm as the frames and stringers are spread apart. The internal furniture of this design adds to the structural strength of this design, so discussions with the designer may be needed if you wnat to change the internal layout. The cross beams are either a built structures or aluminum tubes. This is a relatively easy structure to build that would get you on the water sooner than other methods.

This cat should be able to sail well and should be relatively fast coastal minimal cruiser as it has all the requirements of a reasonable rig, good foils, a lighter displacement and narrow waterlines. The jpegs give the idea.

 

[oldmulti]

I know very little about this power cat but a 6 foot headroom helming cabin on an 18 foot cat is unusual. This looks like a small charter fishing catamaran or someone has quite a maximum of 5 friends as the capacity of the boat is 6 people.

The cat is 17.9 x 8.2 foot with a weight of about 2,500 lbs. There are 2 Johnson outboards (Model: J115VXSSS) of 115 HP manufactured in 1999. The boat was manufactured in 1985 with structural modifications of the forward cabin done sometime in the 1990’s.

The helming cabin forward can accommodate the helmsman and a few people for weather protection. The cockpit is large and open with a roof allowing excellent fishing etc. The looks are not good but the cat is very functional for its intended use.

There is a video of this cat in calm waters doing at least 25 knots. It can move very well with its 2 x 115 HP engines but may I suggest it fuel economy will not be good.

The base cat hull build is aluminum with an additional aluminum cabin structure done at a later stage. The trailer was home built at a later point.

An interesting cat that was sold in 2024 for $A14,700. The jpegs give the idea.

 

[oldmulti]

Alloy Boats formally from Texas did a power catamaran that pairs electric propulsion with innovative autonomous software to simplify cruising on the high seas. The 28-footer was intended to be able dock itself, navigate around other boats and beeline to any spot you point it to. In addition, the vessel’s three-pronged sensor suite combines radar, lidar and computer vision to give you greater situational awareness. The sensors will pick up everything from a swimmer next to the hull to a superyacht in the far-off distance, for instance. Stopping is a cinch, too, thanks to the built-in brakes.

I said formally from Texas as I cannot find any evidence of the company still being in business. This cat made big promises, but I suspect the company found out the development cost and time of the software etc was greater than expected so we only see promotional material, not reality.

The alloy cat was to be 28 foot long and probably 8.5 foot wide. The power was to be a zero-emission cruiser equipped with twin 300 hp electric motors and dual waterjets that enable a top speed of about 35 knots. Alloy says the battery is “rated for all-day use” and affords a range of approximately 50 to 55 miles. Translation 1.5 hours of use.

The cockpit has 2 chairs up front and bench seating for six at the back. When the vessel is still, you can press a button, and platforms expand both forward and aft to create a little extra space. A table also pops up at the center of the vessel if you fancy a little alfresco dining at sea.

The cat was to be built using marine aluminum but no further details are available. The limited jpegs give the idea.