Multihull Structure Thoughts

This power cat is a Render, a tender to support Kokomo, a 24.4m (80-foot) Sunreef power catamaran (soon to be replaced by an even larger Sunreef). OK. So, the tender is part a toy carrier, has some accommodation and is fast for those rapid trips to shore from the mother ship as required. How fast, try 55 knots at peak speed. The designers are Morelli & Melvin and the builder is Lloyd Stevenson Boatbuilders of New Zealand.

The Catalyst 45 Render is 46.9 x 15.4 foot with a weight of 16,350 lbs. The weight fully fueled for offshore work is 29,100 lbs. The draft over the hulls is 1.6 foot. The engines are 2 x Mercury Verado V12 600hp outboards for a total horsepower of 1,200. The fuel is 3,200 litres, Cruising speed is between 20 and 43 knots with a peak speed of 55 knots. Render has serious range – 650 nautical miles at 40 knots (16.3 hours) or 800 nautical miles at 20 knots (40 hours). With delivery tanks, the range is extended to make long passages realistic EG Render made the 1070 nautical mile crossing from Auckland to Fiji on her own bottom. In good conditions, Render could have completed the voyage non-stop carrying deck-mounted delivery tanks in about 33 hours at 30 knots. It did average 28 knots in the prevailing conditions.

Render has bolt-on foils between the hulls that lift the hulls by around 300mm, reducing fuel consumption by up to 28%. With just the front foils fitted, Render planes at 10 knots under tow – rear foils are usually fitted as well when her displacement exceeds 12 tons.

Inside the hardtop and down below in the hulls, matte carbon finishes dominate, including for the galley, with lightweight furniture and clever touches throughout – like hidden magnetic tabs built into the laminate that hold clip-on covers and a reversible carbon table that converts into a daybed. The accommodation includes one cabin with a single berth and one double berth for guests and crew, a compact galley, and a luxurious head. Starlink connectivity ensures constant communication, while LED RGB lighting coupled with C-Zone automation lets you set the mood with a touch. A large TV in the crew/guest accommodation doubles as a multifunction display for both entertainment and navigation. There’s air conditioning throughout, and a misting system is under consideration for the cockpit – an understandable luxury given the boat’s hot-climate base.

The build is Carbon/E-glass and epoxy laminates with foam cores. Its composite construction is partial protected by inflatable tubes at gunnel level to allow the cat to attach to a pier or mother ship.

This is a very fast toy hauler and picnic platform that allows the guests to have a fun day away from the mother ship. This cat is a semi custom build (based on an America Cup chase boat design) to suit the owners' requirements. The crew live on this cat full time acting as a backup support vessel to the motherships crew and guests. Don’t ask how much it costs, the 2 outboard engines alone cost $250,000.

Th jpegs give the idea.

 

Fast, modern cruising catamarans tick every possible box to be FAST–SAFE–COMFORTABLE in equal measure. The “Matera 40” designer is Stephen Bull/Gary Pearson and the builder is Steven Bull Boat Builders from New Zealand. This lightweight fast cruising catamaran is an excellent example of what can be done.

The Matera 40 has a length over all (including bow sprit) of 44.3 foot. The hulls are 40 x 21 foot with a light weight of 8,960 lbs and a loaded displacement of 10,750 lbs. The 51 foot carbon fibre mast carries a 560 square foot mainsail, a 145 square foot staysail, a 322 square foot Solent and a 1,345 square foot gennaker. The draft is 2 foot over the hulls and 6.9 foot over the daggerboards. The engines 2 x 20 HP Honda outboards or 2 x 20 HP diesels.

There are 2 double berth cabins and a toilet shower in each hull. The main saloon has a galley forward with a transverse hallway to allow access to the hulls. Next is a seating table area with a navigation area and seat opposite. There are large glass doors that can be folded back allowing full integration with the cockpit. All sail controls and helming happens in the cockpit.

The Matera 40 hull and deck panels were built using 400g carbon fibre cloth inside and outside, over a 15mm closed-cell PVC core. These were vacuum-moulded over MDF forms, resulting in remarkably smooth surfaces, needing almost no filling. Resin used was ADR 246, a West System product, with #28 Hardener and ‘cooked’ at 55o C. This build philosophy—and its practical result—is best shown in the wide, uninterrupted arch of the coach roof above the saloon. Stiff, too, as a crew member can stand there attending to the mainsail lazy jacks. The foils and mast are carbon fibre. Now please understand this is an aggressive build specification for a 40 foot cat. The details of the build would require additional reinforcement at keels, gunnels and on bulkheads/frames throughout the cat. Steve Bull is an experienced boatbuilder with carbon fibre, who helped with the construction of the first Team New Zealand 72ft foiling cat. He has built many other carbon fibre boats including racing and cruising cats over the years. The coach roof accommodates six 200W low-profile, flexible solar panels from Italian manufacturer Solbain.

Now we get to performance. This is a light cat for its size with a short rig but a lot of sail area. Result on one test was the cat did faster than wind speed. Quote “Our outing was in fairly light winds, and in two circumstances, with Code Zero or gennaker deployed, Aventador was sailing significantly faster than the wind. Moving at eight knots in just under six knots of breeze.” This cat according to my simple calculator will average 10 to 11 knots and will peak at over 20 knots. Impressive but the price you pay is a payload capacity of 2,750 lbs. Minimum toys, dive gear, fuel and water on board. The Matera 40 has modest ground tackle. A 20kg anchor hung from under the fore beam and 8mm chain, with remote control for an electric up-and-down anchor winch.

This is a seriously fast cruising cat that can be built for you on a semi custom basis. The jpegs will give the idea.

 

...now this is a seriously low bridgedeck!

 

The designer of the new L980 Emocean, Dan Leech and the builders Davie Norris/Randall Diggs from New Zealand decided to produce a semi displacement power cruising catamaran. Dan Leech had produced a few power cats along this line and opted for a slightly larger power cat that was still trailable if required using an oversize trailing permit.

The L980 Emocean is 32.1 foot overall with a hull length of 28.9 x 10 foot. The draft is 1.6 foot over the hulls. The engines can be from 2 x 90 HP outboards to on the test boat 2 x Honda BF150 outboards with 260 litres of fuel. A top speed of 34 knots and a cruise speed of 28 knots is possible with a fuel consumption of around 75 litres an hour, with an economy mode of around 20 knots and 30 litres an hour. The boat’s electronics have 3 lithium 120-amp house batteries which topped up by two 195-watt solar panels mounted on the cabin roof.

The accommodation has full standing head room throughout, a queen size berth forward, head and shower forward, quarter berth in the port hull (can have a second quarter berth in the starboard hull), large galley in the saloon and large L shaped settee with table that can form a double berth. The cockpit has a fold down hull side panel for side boarding, an aft boarding platform and optional built in seating. The aft cabin bulkhead has a large window that retracts down into a recess and a bi fold door so the saloon opens up to the cockpit to give good indoor / outdoor flow. To starboard, the cockpit gunwale hinges down with a swim ladder on the aft edge, which makes for an excellent swim platform. The aft deck and this side deck allow the central cockpit to remain clear and dry.

The construction is composite using E-glass epoxy laminate with a foam core. The pre-laminated composite panels were CNC machined at ASP Composites, making a tight-fitting structure that has resulted in a very strong, light boat. There are strong collision bulkheads in the bow, four watertight compartments aft. The hull form is a flat V section at the stern tapering into a tight V at the stem, with a small skeg that aids tracking and allows beaching. The hull is strengthened using a double chine format which keeps the spray deflected down and offers rigidity and more beam up high, where it is needed.

This is an excellent smaller cruising power cat that can be transported if required. The lower fuel consumption allows a 160 mile range at 20 knots which is good for a real cruiser for a couple and a friend or 2. The jpegs give the idea.

 

The following is how to turn your Sea-Doo jetski into a “cruising trimaran”. Sea-Doo are willing to try new things and have added a “Switch” option that provides “floats” and deck area to the standard model Sea-Doo jetski’s from 3.9 meter (12.8 foot) to 6.4 meter (21 foot) in length.

The model in some of the jpegs is the 6.4 meter which is 2.4 meters wide when set up (21 x 8.1 foot). This boat had an optional 230 HP engine in it. The weight is less than 4,200 lbs (depending on options) and can reach speeds up to 38 knots. Performance of the remaining range depends on the Switch size and engine power.

The Sea-Doo Switch isn’t a single model, but a family of boats available in three different lengths, and each with multiple engine choices. All ride on a scratch-resistant Polytec hull design that, from below, looks much like a small skiff with a sponson added to each side. The tri-hull design is deeper in the centre than on the sides, giving Switch tri-hull stability while retaining the ability to dig in on turns and handle very much like a traditional V-hull – or a PWC.

The engine options depend on the PWC you choose and can range from a Rotax 100 horsepower to a Rotax supercharged 230 horsepower unit.

Depending on the options you choose you can have a sporty version of the switch with PWC characteristics or a more sedate version that will be more of a fast pontoon boat with a lot of deck accommodation. BRP 9the manufacturing company) notes that while the helm console and seat always remain stationary, everything else is fair game, allowing owners to achieve more than 100 possible configurations. Items like additional seating or EG portable fridges can be clipped into various positions as required. This allows EG morning fishing, relaxing lunches and a bit of PWC entertainment in the afternoon. Then it can be all packed up and trailed home as required.

All Switch models feature Eco, Standard and Sport driving modes. BRP’s Intelligent Brake & Reverse feature also comes standard, providing greater confidence when docking or at the launch ramp, as well as allowing drivers to have some fun underway side-slipping and spinning the boat around in its own length.

The jpegs give some idea of the concept.

 

@oldmulti that is a brilliant way of repurposing (I won't say recycling) a jetski!
Every jetski that is converted is one less to cause mayhem on it's own.
(although this is assuming that the driver of the new trimaran is more sensible than the average jetski driver).

 

The Stryda 600C is an amphibious power catamaran. Typical of New Zealand they invent solutions to suit the local environment. So you want a nice 20 foot aluminium power cat to do fishing or cruising but there are no local ramps to launch it. All you do is put retractable power wheels on it so the boat can drive down a beach to launch itself. OK.

The Stryda 600C is 24.3 foot overall 9including motor and folded power legs. The hull is 19.6 x 8.5 foot with a weight of 5400 lbs. The draft over the hulls is 1.6 foot. The outboard engine power can be from 250 to 350 HP. The engine on this boat is the latest-generation Suzuki DF350A four-stroke outboard with a pair of counter-rotating stainless propellers and a relatively small gearcase for such a massive power output. A Suzuki electronic throttle to the right of the helm provides drive-by-wire control for the naturally-aspirated 4.39-litre V6 outboard. Suzuki says using two props spreads the torque and allows the gear diameter to be reduced. Counter-rotation also reduces the tendency to ‘prop walk’, making the boat easier to steer both at speed and when manoeuvring. The top speed for this engine is 40 knots for a 250 HP engine speeds of 34 knots can be expected.

The AMPHIBIOUS SYSTEM, ANURA S25 4WD Engine is a 40HP Briggs & Stratton EFI. The hydraulic 4 wheel drive has diff lock brakes which allows a land speed of 9km/h. The engine sits at the transom in front of the outboard. The power legs are raised and lowered by hydraulics.

The standard 600c has a double berth forward then an open cockpit which has a helming position, seating and space for a camp kitchen. There has been a cruise version built with a cabin forward that allows a galley, helming position, toilet shower unit and keeps the double berth forward under the foredeck. This model also keeps a fair large cockpit space.

The build is a very good aluminium structure designed to handle 40 knots speeds in rough conditions. There is an optional foil aft between the hulls to provide additional lift and better fuel economy which has proven to be very successful.

According to tests, the foil also combines with those asymmetrical hulls to provide handling that is more akin to a monohull than the outward-heeling action common to catamarans. The boat heels inwards in a conventional manner through the turns, but not quite as much as would a monohull. Despite the extra weight of the amphibious technology the boat rides well with predictable handling.

This has proven to be a very good design and build but as with all good things it costs about $300,000 New Zealand. I like the idea, the jpegs give an indication.

 

Merry Christmas Oldmulti. A huge thank you from me for your unending multihull education. For someone like myself, who is living in a place where multihull information is zero, you are the go to source. I'm not sure that you realise the impact and joy that you give others but it is greatly appreciated. All the best for the New Year.

 

Thanks for the kind thoughts. I will be on a short break until Jan 2 2026. May the next few days be kind to all.

 

I want to join in with the thanks of letting us profit from your encyclopedial multihullknowledge! Enjoy the summer!

 

Free Standing Mast in Multihulls

Early in this subject thread you made this posting of Shuttleworth's work with the AeroRig. At that time you also indicated you would be referencing other designs that utilized these free standing rigs,...Can you lead me to those other postings?

I was also very impressed with Shuttlework's work, and incorporated a similar structure in my Dynarig catamaran design,.
DynaRig MotorSailer https://www.runningtideyachts.com/dynarig/

Main BulkHead and Constructioin Specs https://www.runningtideyachts.com/dynarig/Main_BulkHead_and_Constructioin_Specs.php

I had plans to work with Shuttleworth if I should secure a client willing to go forward with such a project.

A few years ago there was a gentleman who showed a lot of interest in such a project, BUT upon his inquires to the Dutch designers of Maltese Falcon he was told there was not enough mast burial in my design to support such a notion.

 

The following trimaran is claimed to be the worlds fastest cruiser. The “Anahita 100” project utilises the high-performance skills of VPLP for design and build skills of CDK in Lorient. This 100 foot trimaran is designed from scratch to set a new bar of luxury performance sailing. The tri platform is also a more powerful, stable and safer one than a cat, its development team argues.

The ‘world’s fastest cruiser’ is in build being 101.75 x 68.9 foot with a weight of 62700 lbs (1 magazine report) and a displacement of 74,956 lbs. The 112 foot carbon fibre wing mast carries a cloud of sail. The draft is a minimum of 6.6 foot going to a draft of 17.7 foot with the float based daggerboards down. Engine power unknown, but think about 100 HP plus diesel in the main hull. There is 34 square meters of solar panels on the main saloon roof which will give about 8 KWH of power which is enough to run the power needs at anchor.

This tri is defined as the worlds fastest cruiser and it has the accommodation to back up the “cruiser” part of the equation. All accommodation is in the main hull, centred around the area of least pitching. Three or four double cabins are offered on the main deck, the former with the option for a vast owner’s suite forward. This looks set to create a new definition of a room with a view at speed. Crew quarters for four are situated on the lower deck, while the outriggers are only used for stowage. The main seating saloon and bar are on the upper deck whilst the large galley is on the lower deck with the crew accommodation. The finish is superyacht quality with light weight fabrics and internal fit out finishes. The internal space equals 120 square meters (1290 square foot). The sails controls are mainly done by captive winches and computer controls which minimizes the crew requirements.

The build is full prepreg carbon structure, combined with a Nomex core. For large multihulls, these benefits are significant. Reduced weight increases speed and improves motion. Greater stiffness sharpens foil efficiency and reduces hull flex. Stronger structural margins allow designers to build wider beams, taller rigs and more ambitious hull shapes. Better weight placement lowers pitching and improves balance. CDK is the best yard for such a project, having built leading Ultims such as the Banque Populaires and SVR Lazartigue.

The result of this design, engineering and build talent. Paek speeds of 40 knots and claimed cruising speeds of 25 knots. This means 6 day transatlantic trips. Just one small problem Ultim sailors often wear crash helmets when they are sailing very fast, as any boat sailing at 30 knots in a seaway motion is not always predictable.

This is the first of a 4 boat series and the first one already has a completed main hull and will be ready for assembly in March 2026. Launch will be in mid to late 2026.

If you want one put down about $30 million and you can have number 2.

The jpegs give an idea.

 

We have already done an item on the monohull Candela C 7 which is an electric powered hydrofoil. This is an item on the updated and much improved Candela C-8 power hydrofoil. The C-8 is a day boat for 6 to 8 people and short term cruiser for 2. The Candela C-8 hardtop was designed and built by Candela in 2025 and already has 100 sold.

The Candela C-8 hardtop is 27.9 x 8.2 foot with a weight of 4,140 lbs (includes the 1,100 lbs battery). The maximum payload is 1,435 lbs. The draft at rest is 6.25 foot with foils down, at speed the draft is 1.6 foot. The power is provided by a Polestar (from the car) 69kWh lithium battery which goes into a Candela C-Pod (45/50kW) twin 400 Volt electric drive unit. Recharge time, if you opt for a fast DC charger, charging takes between one and three hours (it’s quick to 80%, but the last 20% takes longer), or 12 hours/overnight on a conventional AC charger.

The C-8, available in three configurations – Day Cruiser, T-Top and Hardtop as reviewed – is a major upgrade on the C-7, with improved software and hardware, a completely new hull design, and a new, much quieter, more efficient twin-motor 400-volt propulsion system. The foil design is also new.

The accommodation is 2 bunks under the foredeck. The cabin can be configured for sleeping or sitting while a toilet, shower, sound system, swim platform, backdrop, sunshade, and underwater lights are C-8 options. There is a large open cockpit that has optional roof arrangements depending on the crafts use.

The build is vacuum-infused carbon fibre epoxy. The finish is in two-pot epoxy paint rather than gelcoat to save weight and provide UV protection. This is a very well engineered structure with every item aimed at light weight. EG cushions are thin to reduce weight; there is no standard fairlead forward for anchor ropes etc. This is not for cost saving but minimal weight.

The performance is good. At displacement speeds, the C-8 rides on its stepped hull like a normal boat, but with the foils in the down position and the throttle applied, it lifts off the water at around 15 knots, riding on a single full-beam transverse C-foil amidships and a steerable winged T-foil aft. The cruising speed is 20 knots with peak speed about 27 knots. The C-8 is efficient consuming one kWh per nautical mile at 20 knots cruise speed. In the C-8’s case, the effective range on a full charge is around 50 nautical miles (2.5 hours run time at 20 knots). A limp home mode gives 3nm at 4 knots. Travelling above the water’s surface at 20-plus knots in near silence except for a bit of wind and water noise is deceiving.

An array of radar sensors monitors the height above the water in foiling flight. The flight controller (computer) uses actuators to make constant adjustments to the foiling surfaces’ angle of attack (including warping the C-foil), to maintain stability and elevation, controlling pitch, roll, and height. The vessel also utilises GPS, gyroscopes, and accelerometers to monitor its position relative to the environment. Optimum flight height is about a metre above the waves. The user interface (UI) has a large touch screen display providing access to the boat’s many modes of operational and environmental information.

This is an excellent hint to the future of boating. The jpegs give the idea.

 

The following is a conceptual idea created by a student of a French naval architecture education institution. It has a combination of good ideas that could be developed into a practical design. The cat is a daysailer that has some limited cruising ability. It can be outboard powered or with a simple rig day sailed for a bit of fun. The hulls are inflatable supporting a pod body.

The Boboat 5 is 16.4 x approximately 10 foot wide (the main hull pod is about 16 x 7.5 foot wide). The 13.5 bipole aluminium folding masts carry about 95 square foot of sail on 18 foot long yards. The hulls are inflatable tubes that are 16.4 x about 2.2 foot diameter. The remaining details are unknown. The design is trailable with the inflatable hulls deflated. The trailing wheels can just be seen raised in one jpeg, aft under the rear of the pod.

The accommodation is flexible. It has a double berth in the bow of the pod with windows on the side. The next is a seating area with a raisable roof to provide some inside seating and camp type facilities. Aft is the open cockpit.

This is a limited cruiser for rivers lakes or bays and speed is not its primary goal but for having fun for a day it would be great.

The jpegs give the idea of the various configuration options for a very flexible design concept. There would be a lot of engineering issues to work through, but the basics of the concept are good.

 

The following is a design students work so the details are not refined. It appears to be a large (guess 80 to 90 foot) fairly open cruising catamaran with semi swath hulls (if there is such a thing).

No power details etc have been provided but the hulls could easily handle large diesel engines for high performance or smaller engines and larger tanks for long range cruising.

The bow has a raised helming and entertainment cabin with what looks like 2 luxurious double berth full ensuite cabins on either side of the main bridge deck below the helming cabin.

The bridge deck is left open from virtually the bow to the stern. Aft there is a full lounge area or dinning area. In the remaining area you could set a ping pong table, dart board, coits game etc and still have room to spare.

This cat looks more about have a floating fun island than a long distance cruiser. I wonder if it was developed. The jpegs give the idea.