Multihull Structure Thoughts

Ezifold is a 30' Trailerable Catamaran that is 30 foot long and can fold to 8.2 foot wide for trailer towing. The height on the trailer is 13.75 foot high. There is also a 10 foot wide version for trailering. The cat is 30 x 16.5 foot unfolded on the water. The following are educated guesses. Displacement is approximately 6000 lbs. The mast is 32 foot high with a sail area of approximately 400 square foot. The hulls length to beam is 10:1.

A 30 foot cat that is trailerable and has full standing headroom in hulls and bridge deck. At 30 foot the cat has a700mm bridge deck clearance at DWL so it has a full size bridge deck. However even with all systems designed to make trailering launching rigging and sailing Ezifold we would still suggest these are trailerable not a trailer sailer. The design has had in house testing at 20 foot, all working well but we are incorporating a new folding locking system into the beams so its design evaluation and refinement is ongoing with complex design solutions.

Ezifold are a Christchurch NZ based design company who have developed a novel beam reduction system for use on multihull vessels, power or sailing, in new build and retrofit solutions. There is a patent pending on the design. The jpegs give an idea. The first is a side view of the hull. The following are further overviews. Finally the last jpeg is a drawing of a similar concept with the attached 1991 Patent PDF document by Dennis Conner (YES the America Cup winning skipper) multihull variable folding system patent that used a very similar approach. Excellent work by Ezifold for “transportable” full headroom bridge deck cat. But folks towing a 13.75 high load with a high centre of gravity down a road would be a challenge especially in a strong wind.

 

Thanks for that OldMulti (it seems strange to call a person that). This looks a little like Richard Woods Wizard designs. It would require a quite deep ramp to get the trailer structure under the bridgedeck. It is also somewhat similar to Len Surtees cats (he sailed one to Western Australia from Tin Can Bay) but he folded the larger ones arms up. The smaller one folds down like Richard's designs but uses a lifting trailer to get around the deep ramp issue. Nice and strong but has limited room in the hulls.



It looks like both Ezifold and Len have not found buyers for their folding cat designs as Ezifolds website is missing and Len has stopped updating his.

 

Catsketcher. Ezifold the business folded a few years ago but the design of Ezifold has been taken over by another company that intends to push through the patent. The company is https://www.gestaltgroupltd.com/ezifold Len sold his Surtees 22 to a doctor after it was not a sales success. He then designed a home build foiling tri called Stinger which I will feature in the near future. Len Surtees is a creative inventive designer that deserves some sales success.

 

That 22 footer Surtees cat is a nice looking vessel, and it looks like it sails quite well.

Some of his other videos...


I'd have some questions about his mast raising in that video.,...particularly sideways support as its being raised up. I ran into a number of challenges when I was designing a similar system for the Firefly 26 tri.

 

That Surtess 22 was a nice looking vessel, with a number of good ideas.

When I saw it in the video, my mind wandered off to something a little bigger,..do you recall Earthling ?



Perhaps simplify this design to become a candidate to become a ,
Weekender/Picnic and Gamefisher Catamaran

 

Thanks for this super interesting discussion. What point am I missing in thinking akas can be super strong & light if made as extensions of cabins. For example, if a trimaran main hull is 7'deep with 3' extensions to the amas at the 4' level, creating a 3' deep beam. I wonder if there is such a design?

 

JW,

Do you mean like EARTHRACE or ADASTRA?
It's been done.

 

Jonathon. Horstman trimarans are the best example of cabins extending to the floats with associated cross beams integrated into the cabin/beams. Cross beams are just a function of depth, tensile strength of top and bottom flanges and fore aft width of beams to act as a torque box. In extremely simple terms, you have a choice, separate the top and bottom flanges (of the same thickness and material) of a beam further apart and you gain more stiffness and "strength" or separate the top and bottom flange further apart but make the flanges thinner (which often means lighter weight) and maintain the same "strength" and you will also get a slight increase in stiffness. This is the reason each designer has there own approach to cross beam design. I have seen 35 foot cats, of similar displacement, with 160 mm high aluminum mast cross beams, 300 mm high timber box beams or 900 mm high "I" mast cross beams to do the same job. Each has its advantage and down sides in material weight, availability, ease of building and the intended purpose of the design. This is a subject that requires a clear understanding of the intended purpose of the design, then designing a beam to suit. Example Lock Crowther told me he spent 3 weeks trying 4 different approaches to Twiggy's (32 x 29 foot open wing tri) original wooden box cross beams with wire water stays underneath. Years later John Bastion who worked with Crowther designed a much simpler, lighter foam glass cross beam that was only slightly deeper than the wood version. This was used on the MK 2 version of Twiggy. There is no simple answer, this is the reason a good designer is valuable.

 

The Stinger or Sting 600 is a Len Surtees home build trimaran design that will be able to be converted into a foiling tri at a later stage. The tri is 20 x 15 foot able to be folder to 8.2 foot for trailering. The boat weighs between 924 to 1067 lbs depending on its confifuration. It is capable of carrying 500 lbs of crew weight. The 31 foot high mast carries a 183 square foot main, 93 square foot jib, 230 square foot screacher and 395 square foot spinnaker. The boat folded on a trailer is 25 foot long (excluding the mast).

The boat can be built in plywood with foam lass cross beams or timber plywood cross beams. The folding cross beams are the same as the Seaclipper 20 approach but are much lighter. The boat was designed and intended to be a foiler from the outset and has been progressively developed over a couple of years. The foil development has been delayed by Covid-19 but the actual non foiling tri has been raced and is fast. Foiling trials have been done but the final package has yet to be fully tested.

I hope that Len can finialise the foils soon as this could be a real fun boat.

 

There was a request for more detail on Looping cats designed by a Frenchman, Mr Luscher. I now understand the request as he has done designs aimed at amateur/professional designs from 42 to 60 foot. In the first item I will list the designs and show study plans. In the second item I will give some structural details. In general, the designs are modern bridge deck cat shapes built from WRC strip plank and epoxy glass hulls with foam glass in other areas. The designs I have found are:

Looping 42 a 42 x 25 foot cat weighing 12300 lbs and displacing 16800 lbs with 915 square foot of sail.

Looping 47 is a 47 x 26.25 foot weighing 12350 lbs and displacing 18000 lbs with 980 square foot of sail.

Looping 50 is a 50 x 26.25 foot weighing 12770 lbs and displacing 18400 lbs with 1160 square foot of sail

Looping 50 Sport is a 50 x 26.25 foot weighing 12350 lbs and displacing 17470 lbs with 1290 square foot of sail

Looping 54 is a 54 x 27 foot weighing 15250 lbs and displacing 21000 lbs with 1400 square foot of sail

Looping 60 is a 60 x 28 foot weighing 16000 lbs and displacing 24000 lbs with 1500 square foot of sail

This is not all his designs just the easy to find some detail on. He also has done a power cat. The jpegs give some study plans. From what I can find several boats have been built for each model both home and professionally built.

 

There was a request for more detail on Looping cats designed by a Frenchman, Mr Luscher. He has done designs aimed at amateur/professional designs from 42 to 60 foot. In this item I will give some structural details. In general, the designs are modern bridge deck cat shapes built from WRC strip plank and epoxy glass hulls with foam glass in other areas. The structure of most of the designs are very similar to the Looping 50 which is a 50 x 26.25 foot cat weighing 12770 lbs and displacing 18400 lbs with 1160 square foot of sail.

The common build for hulls is from the outside 2 layers of 420 gsm e glass unidirectionals at 45 degrees, 19 mm WRC strip plank, a 650 gsm e glass 45/45 biax inside in epoxy. From waterline to waterline underwater is a 450 gsm of Kevlar is placed on the outside for additional knock resistance. A later optional build in the jpegs is similar but slightly heavier glass layup with 25 mm strip plank corecell foam core.

The underwing, decks and bulkheads can be foam glass or plywood. The build in jpegs is ply bulkheads, decks and foam glass underwing. The original 50 had foam glass decks , roof (with some carbon fibre reinforcement) and bulkheads. The main cross beams are timber reinforced box beams with carbon fibre assisting in the main beam. The foil boards are foam glass with carbon fibre reinforcements. If the boat has a low aspect ratio keels they are plywood timber.

The 42 foot version is mainly foam glass. From 47 foot up the hulls are WRC glass with options of ply or foam glass for the rest. All the high performance models are mainly foam glass. This man has options to suit most builders. His web site is Document sans titre http://looping.luscher.free.fr/

A few details of the build process is from TomCat custom boat building. http://tomcatboats.com/custom-projects/ Another site featuring the same build is Building: The Looping 50' — Steemit https://steemit.com/blog/@thebongdruid/building-the-looping-50 The boat is a corecell build with plywood box beam with timber strips for rear beam and a plywood timber frame build for the main beam.

 

We will now talk about 2 very good Chris white tri’s. The Hammerhead 54 and 34 series. The Hammerhead 54 came first, it is 54 x 34.5 foot displacing 17,000 lbs at half load and carrying a 858 square foot main with a 492 square foot jib on a 59 foot mast.

The tri was designed as a fast cruiser, something I will let you assess with this quote. “Hammerhead's 54 sailing performance is extraordinary. She can lope along at an easy 20 knots with mainsail and jib alone. I have seen 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. Steering in these conditions is a one handed affair. At high speed the helm is easy and balanced with absolutely no feeling of losing control. Hammerhead is capable of sailing at 24 to 25 knots without surfing and without a spinnaker. Hammerhead will easily out sail production catamarans and trimarans, in any conditions. Hammerhead's windward ability is excellent. With her centerboard down draft of 9' she has the ability to drive to windward like a freight train. 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.” Several other test reports have had similar performance outcomes, this boat is a "cruising flyer" very capable of 300 mile days.

The 54 is constructed from foam glass hulls, bulkheads and crossbeams with carbon fibre added as required as required.

A few years later there was a request for a smaller tri with a bit more accommodation than the Explorer 34 so the Hamerhead 34 was designed. It is 34 x 23 foot with a weight of 5,000 lbs. A 46 foot fractional rig mast with a 377 square foot mainsail and a 230 square foot jib. The smaller Hammerhead incorporates a folding crossbeam structure so that the boat can be transported over the road for winter storage - or to a new cruising ground. This boats performance is very good from all reports.

The construction consists of thin epoxy laminated plywood and foam. The decks of the amas use plywood and the top-side use foam. The hulls are cored foam glass. There is a combination of foam and thin layers of plywood laminated with Epoxy for bulkheads and topsides. The builder used carbon fiber in high stress areas such as crossbeams and the attachment points of the beams and the G10 tangs where the struts attach. The standing rigging is wire and the laterals are synthetic. The boat is painted with Awlgrip 2 part polyurethane.

To control the centerboard, there is a fiberglass tube bonded to the top forward end of the trunk and the other end of the tube attaches under the deck adjacent to the mast. The control lines run up the tube to a double block attached to the mast and back to the cockpit. Along the top of the trunk there is a length of G 10 that is fastened around the perimeter.

 

A few simple French plywood tri’s from Giles Montaubin. He is popular in France for raid boats both mono and multi’s. His mono’s are very well designed and are light weight long lasting structures. His multi should be similar but I have little information on the builds of the smaller boats. He entered into a WoodenBoat design competition for “raid” boats was Triboulet is 23 x 14.5 foot weighing only 790 lbs carrying 260 square foot of sail. The main hull is 3.6 foot wide. This boat has won European Raid events.

The next design is a slightly larger “mini cruiser version called Tricky tri. The tri is 23.5 x 14.75 foot weighing 810 lbs with 260 square foot sail. The “cabins” are simple berth arrangements with some additional storage. The main hull is foot wide.

Both of these designs are demountable for transport having simple laminated timber cross beams with water stays. The hulls are plywood with minimal stringers and timber frames. The rigs are free standing carbon fibre masts that often rotate to reef the sails. Giles has literally designed many of these masts for both his mono's and multi's and they can be home built or purchased.

The larger design today is the Trimar which is more of a cruiser with berths, galley and headroom. It is 29.5 x 21 foot weighing 3100 lbs carrying a 300 square foot fore sail and a 150 square foot mizzen. The main hull is 8 foot wide at bunk level. The cross beams are plywood timber box beams. The rest is plywood timber with minimal stringers, timber frames and plywood bulkheads. The boards are in the floats.

Tomorrow I will show you a 33 foot long term cruiser version that has varying thickness of plywood in the hull panels which will give a hint how the smaller boats are built. Simple jpegs more later.

 

I was also a great admirer of the ketch rig, and Chris White's Hammerhead tri,...

brian wrote:

Thought I had lost these images, but here is that mastaft rig with the genoa-mizzen deployment,...a ketch rig attribute

 

Check out this 'unusual ketch rig',...
Aftmast rigs??? https://www.boatdesign.net/threads/aftmast-rigs.623/page-7#post-198608