Multihull Structure Thoughts

Tony Grainger has designed a high performance 57 foot cruising catamaran that according to the designer is: “She is designed around a persona focused on effortless blue ocean cruising. In yacht design everything flows from proportion, and proportion expresses persona. The combination of long sleek hulls, generous wing clearance and rig set well back on the platform provide comfort at sea and the capacity for long daily runs.”

“Marliese” is 57.25 x 27.3 foot with a displacement of 31,500 lbs to about a maximum of 43,000 lbs, depending on load. The 76 foot aluminium or carbon fibre mast carries a 1,055 square foot mainsail, a 516 square foot self tacking jib, a 1,355 square foot code zero and a 2,860 square foot asymmetric spinnaker. The length to beam on the hulls would be about 15 to 1. The draft ranges from 2.5 foot over the hull to about 5 foot over fixed keels or up to 9 foot over daggerboards. The engines are 2 x 75 HP Yanmar’s. The underwing clearance is 3.7 foot.

The accommodation is unknown as this is a speculative design but judging by other cats by Grainger around this size you can have 4 private double cabins (with berths partially on the wingdecks) and attached toilet shower units in the hulls. The main saloon has seating, table, galley, navigation, entertainment etc. The cockpit area also is large and has helming options. Grainger describes the helming options: “The helm is at a height that enables 360˚ visibility with all of the sail controls readily accessible from the helm station. Twin helm stations can be deployed as an option and an internal helm station at the forward bulkhead can be accommodated in the interior layout. Tiller steering is also an option for the ultimate in a direct feel at the helm.“

Construction of the cat is a lot of flat panel PVC foam cores, Glass and Carbon Reinforcements in an Epoxy Matrix. The hull bottoms are round bilge plus edges of cabin tops and gunnel edges are also rounded. Tony Grainer has developed a good build technique in foam glass that allows a lot of prepared parts to be constructed to form a “kit” that when assembled minimises the need for fairing etc.

I do not dout this cats performance capability. With a good rig an an experienced crew it will be capable of 300 mile days and peaks over 20 knots. 8 knot averages for comfort will be very easy.

The jpegs give the idea.

 

Today we will talk on a design that is featured in Woodenboat 300 (October 2024 page 96) magazine. JF Bedard was asked to do a motor sailor for an older client who wanted a simple trailable boat with a simple rig that could take he and his wife on mini cruises with a hybrid motor to help get home when the winds were to light or in the wrong direction.

Simple request as the client was upgrading from a 14 foot cruiser, but the client had some limitations included a length of about 20 foot, preferably the boat would sail flat and performance was not high on the agenda. Also he would like a sit down inside cabin and have an inside toilet.

At this point I will apologise for the one jpeg to show you part of the concept but either get Woodenboat number 300 magazine or visit the following website to get a drawing of the concept. https://www.woodenboat.com/sites/default/files/issue/WB300-toc.pdf

The solution was “Eccentris”. A motor sailing catamaran of 20.9 x 8.5 foot with a loaded displacement of 1900 lbs. The biplane rig has 2 freestanding masts are 12.8 foot above deck that carry 2 lug sails of 72 square foot sail area for a total of 144 square foot total sail area. The length to beam on the hulls is about 9 to 1,The draft is 1.2 foot over the hull and very mini keel. The electric motor outboard gives 10 HP output with a speed of 8.5 knots. Two 5KW lithium iron batteries will give a range of 27 miles. The underwing clearance is a maximum of 1 foot.

The internal layout of this full bridge deck catamaran is a double berth forward then the “main saloon” is a table with 2 seats on the wing deck with 4.5 foot headroom and a small stove sink (camping gear) in the starboard hull that has near full headroom. The 6 foot cockpit is comfortable for helming etc and has a canvas Bimini over the majority of the cockpit. As the sails are only 72 square foot each sail control is simple.

The build is plywood. The hulls are flat bottom with a step chine in the topsides for “extra space”. The hulls are 6 mm plywood sheathed either side by 200 gsm cloth in epoxy. The under wing is 18 mm Ocume plywood. The bulkheads are 9 mm plywood as are the seat tops. The cabin trunk and curved cabin top are 6 mm plywood sheathed either side by 200 gsm cloth in epoxy. Relatively simple and fast to build in the back yard and able to be trailed to and from home and maintained in your back yard

This cat is a halfway house between the 16 foot Miss Cindy and the 20 foot Jarcat 6. Eccentris is the motor sailor version of this “combination” and is a very good design for its purpose of a relaxed micro cruiser for an older couple.

Sorry about the lack of jpegs but contact JF Bedard for further detail. Edit, Extra jpeg from Waterbear, thanks.

 

The following is about a 2010 solar powered trimaran design concept that was intended to travel globally. The power tri was not funded or built to my knowledge but it had a few interesting ideas in hull shape and power configuration. The tri has semi-submersible hulls to minimise wave drag, wetted surface and windage.

The solar powered trimaran was to be 98.4 x 52.5 foot. The weight proposed was 22,400 lbs. The power comes from a 1,936 square foot solar array that provides 30 KW of power to the electric motor (this design was done in 2010 the same panel area would produce 40 KW of peak power using modern 600 watt panels). The average cruising speed would be 10 knots with a peak speed of 15 knots. The battery storage is Lithium Iron with sufficient capacity to maintain a 10 knot average overnight and semi overcast days.

Supposedly 12 people can be accommodated in the control pod and cockpit. There is no accommodation plan but the 98 foot tri has a 40 x 10 foot cabin pod which should provide enough space for a crew. One number I liked, is the control cockpit is 21 foot above the water line. Great view and unlikely to get wet in rough weather.

The designer had an understanding of the hull shapes required for an efficient and reasonably comfortable ride. The only issue would be the build weight. Even with a good carbon fibre foam glass build, the 22,400 lbs weight would be hard to achieve. EG high efficiency solar panels alone would weight about 4000 lbs, the batteries would weight at least 3000 lbs and the wiring, the inverters, motor infrastructure etc would add another 1000 lbs. Even 60 foot OMRA tris weighed 11,000 lbs. and this solar tri has a much larger total surface area than and OMRA 60 tri.

If this tri was built great but I suspect it wasn’t. The design concept looked good and deserved to be tried out. The jpegs give the idea.

 

“Deserved to be tried out”

Nice one OldMulti!

With a design like this where the solar array are mostly large flat areas, it would probably make more sense to incorporate the cells into the surface/skin structure rather than mount individual ridged panels.

That way you could reduce some weight, minimize failure points, streamline the surface, etc..

 

It's nice one but also quite high on the sides.Rigid sail.

 

This is about a concept trimaran where the guy wanted a tri that could have a tent up for sun protection etc. He had canvas tents on boats before and was not happy putting them up and down especially when he was doing a short sails in sunny conditions. A little bit of thinking came up with this solution.

The thought was to integrate a fixed tent like hardtop into the structure of the crossbeams etc. Good thinking for a daysailer in sunny environments with the possibility of acting as a camp cruiser. The tri size here is not important, the concept is the important part.

The tri in the diagrams is about 30 foot long which aligns with the fact the creator originally had a Cab SIB 32 Marples design that was extended to 41 foot.

I suggest the hulls may be constant camber, the cross arms and roof structure would be foam glass with unidirections on the edges.

An interesting idea with many advantages of providing shade and ventilation whilst sailing whilst strengthening the overall structure. The jpegs give the idea.

 

Oldmulti, here's an image that shows the whole craft.

 

When you manufacture 1000 Lagoon 42’s you would suspect the Lagoon company would be careful about the replacement cat for the Lagoon 42. So, Lagoon employed VPLP to produce the Lagoon 43 design with specific exterior and interior designers to optimize and improve the concept.. The 43 is a very similar cat to the 42 but has more fullness forward below and above the waterline and the mast further forward to improve the structure and provide slightly more room overall. The hulls remind me a lot of the Excess 13 which is manufactured by a Lagoon subsidiary.

The Lagoon 43 is 42.1 x 25.25 foot with a weight of 30,900 lbs and a displacement of about 40,000 lbs. The 56 foot carbon or aluminum mast carries either a 646 square foot main or a 732 square foot square top mainsail with a 400 square foot furling genoa. The length to beam on the hulls is about 7.8 to 1. The draft is 4.33 foot over the fixed low aspect keels. The engines are two 57 HP diesels with shaft drives.

The accommodation is spacious with a choice of an owners cabin version with 2 double berth cabins with ensuites in the other hull, or the 2 double berth cabins in each hull. The main saloon has an integrated seat table unit, navigation entertainment area and a forward galley. The cockpit under a fixed roof is integrated with the main saloon through large glass doors. There is a control cockpit for helming and sail control half way up to the flybridge on the main saloon roof. There is also a forward cockpit in front of the main saloon.

The structure of the cat is foam glass through out with some solid glass below the waterline. The Lagoon 42 has the mast in the middle of the main saloon supported by a beam structure under the wing deck floor. The Lagoon 43 put the mast further forward onto a forward full cross beam. This made the cat easier to manufacture slightly lighter and structurally stronger. It also probably made the 43 cheaper to build.

On performance, one test report said “The boat was not memorably great to sail but it was good in the 12 to 16 knot wind conditions and relatively flat water. Hard on the wind we were sailing at an angle of 45-50 degrees true and we were doing 7kts. Easing off the wind with the big Code 0 set we were touching 9kts and that’s pretty decent. A good speed without being scary. The boat was simple to handle and I liked the steering position which struck a fairly decent compromise between an out and out fly bridge, which can leave the helm feeling quite isolated.”

The Lagoon 43 is a solid cruising cat not designed to be the fastest cat in its size range. It aimed at real cruisers or the charter market who want comfort and reasonable performance.

The jpegs give the idea.

 

A short one about a new material for boat building that is claimed to be a substitute for plywood. Three British guys liked the concept of plywood as a build material but were unhappy with its maintenance and deterioration requirements. They developed a material that is an engineered extruded sheet crafted from plastic waste that’s 100% recyclable, waterproof, and rot-proof. It also will not splinter, split or warp. We understand production can easily be scaled up and at the end of life the material can be returned to pellet form to be recycled into other products.

“Supercede” has a hollow matrix to improve strength and reduce weight (see first jpeg). At the moment, it’s available in ½in (13mm) and ¾in (19mm) thicknesses that can be used as a direct replacement for marine ply. It’s also available in any custom length over 4ft (1.2m), which has potential to save boatbuilders a considerable amount of wastage. On the downside its density of 1,400kg per cubic metre is at least double that of most marine plywood.

The cost is about the same as good quality plywood. The Supersede Marine Board, a true 1:1 replacement to marine-grade plywood according to the developers has already won an IBEX Innovation Award for Boatbuilding Methods and Materials in Florida in October.

I am advising you of the product but have some issues. Is it better to have plastic recyclable marine board sheets or sustainably grown timber plywood that can have a WEST saturation technique to provide a sealed surface reducing maintenance and rot. Also the weight of the Supercede board is a concern in light weight builds.

The jpegs give and idea.

 

First question is how to glue it.