Multihull Structure Thoughts

The EVO 60 is designed by Du Toit Yacht Design and is being built in South Africa by Evolution Marine Manufacturing. This is a high performance fast cruiser that is intended to provide: “A new benchmark in high-performance, luxury catamarans, designed to deliver exceptional speed, comfort, and versatility on the open seas” according to the company. OK.

The EVO 60 is 59.94 x 29.6 foot with a displacement of about 50,000 lbs The carbon mast is 74 foot high and the fractional rig carries a 1,962 square foot mainsail and fore triangle (760 square foot fore triangle, 1,200 square foot mainsail). The length to beam on the hulls is about 12 to 1. The draft over the hulls is 2.07 foot and with the hull daggerboards down 10.8 foot. The underwing clearance is 3.2 foot. Engines are unknown but think about 60 HP per side.

This cat’s interior is pure luxury. The configuration shown has an owners hull with a queen berth forward and seating etc plus a full size bathroom aft. The other hull has 2 double cabins with a bathroom in between. The bridgedeck cabin has a large galley, seating and table with a central forward navigation inside steering position forward. The integrated cockpit has additional seating and a fold down TV for entertainment. Hope the TV is waterproof. The external helming positions have a steering wheels that can be moved to 2 position to either be in the breeze or protected in the cockpit area.

The construction of the EVO 60 is an E-glass/carbon epoxy catamaran that features 80% carbon content. The catamaran features carbon appendages, rig, boom, longeron, and crossbeams. No detail of where the e-glass is placed but I could imagine it’s on the external hull shell especially under water as e-glass is more “flexible” than carbon fibre which has less elongation and can shatter under point loads.

There is no performance numbers as the first production cat will be delivered in 2025 but the numbers indicate peaks of over 20 knots and 300 mile per day averages in good conditions.

This is a well designed cat by a designer who understands multihulls. I hope the builder can meet the weight and “luxury” requirements customers want. The jpegs give the idea.

 

The Scape 30 is a 30 foot tube day racing cat was an outcome of a very similar design from De Toit Yacht design. The 30 foot cat is a day racer or limited range coastal racer. The Scape company is/was a South African company but its web site has died. They produced unusual 37 to 40 foot semi tube cats that had limited commercial success.

The Scape 30 is 30 x 16.9 foot with a displacement of about 4000 lbs. The mast is 44.5 foot high and carries a 148 square foot fore triangle with a 430 square foot mainsail. A 760 square foot spinnaker is available. The length to beam on the hulls is 18 to 1. The hull draft 0.94 foot and 5.7 foot over the hull based dagger boards. This adds up to an exciting power to weight ratio with thin hulls which should provide peak speeds above 20 knots.

The construction was foam fiberglass with aluminum cross beams bolted to the hulls. The main beam has a dolphin striker.

There are 2 storage lockers per hull but no significant accommodation.

The Scape 30 was designed and built prior to the foiling cats like the GC 32’s which limited its adoption with the serious racers, but if you want a good racer without the maintenance of lifting foils then a second had Scape 30 would be a good option.

The jpegs give the idea.

 

The following tri is a home designed, home built tri that was launched in 2005. The design was done by a Canadian, Leo Braun, who moved to Australia after completing a Westlawn naval Architecture course. This provided the foundation knowledge for the design and after building the tri it was improved to the owner’s satisfaction to be a good day sailing boat for the next19 years. The tri can sail with 3 to 4 crew.

The trimaran is 16.9 x 11.5 foot unfolded and can be folded to 5.9 folded for trailering. The weight is unknown. The mast is 17 foot high and carries a 50 square foot jib and about 100 square foot mainsail. The original rig was a mast aft with a large jib but the standard fractional rig was added latter. The main hull length to beam looks about 4 to 1 which is fatter than normal but it is a small boat capable of planning and carrying a 4 person crew when required. There is a main hull daggerboard and kick up rudder. My guess is a 4 foot maximum draft. There is an outboard bracket suitable for a 2 to 5 HP outboard or electric trolling motor.

The construction is described as a “wood fiberglass composite”. I suspect the floats are more plywood covered by a light layer of glass. The main hull has some interesting curves so it maybe a fiberglass structure with plywood components. The cross arms are aluminium box tubes with stainless steel hinges and reinforcing box sections at the hinge joints. This looks a reasonable approach for trailing.

The side decks are trampolines that can remain in position. It is a pity we don’t know more about the design as it looks interesting. The jpegs give the idea.

 

To remind people that boating should be fun. This design is a cheap way to get on the water for a bit of running around. Crawdad is a 7'6" parody of coastal workboats. It is an effort to create a usable knockabout with 3 sheets of ply and some scrounged lumber. She's cost less than $50 so far and, when done, should tilt the books for no more than $100. Think about 6.4 mm or 9 mm plywood sides and flat bottom with a few keel strips fore and aft plus a stringer on the sides EG 18 x 40 mm. Tape seam joint chines. At deck level do a gunnel strip with a few deck beams. Transom will need a 75 x 40 mm edging to handle a minimal power outboard. Just fun, don’t try and go out in strong weather conditions.

 

The following is a conceptual idea for a small camp cruiser proa, be it a Pacific, Atlantic or tacking proa. The designer has done many proa concepts as he works to get a small, trailable, reasonable version of a proa that he can do limited cruising in. He is not after outright speed but a craft that can be trailed and used on mini cruises in his sailing area. Result he is willing to think about unusual hull shapes to achieve an easy to build mini cruiser.

The “Scow Proa” is 18 x 10.5 foot overall length. Load waterline is 13.5 foot. Displacement is estimated to be 650 lbs but this hull shape can carry a large overload EG a displacement of 1,100 lbs. The schooner lug rig has 2 free standing solid wooden masts are 15.5 foot above deck and a total length of 18 foot overall. The total sail area is 112 square foot. The length to beam main hull 5.25 to 1. Float length to beam is 12 to 1. Hull draft is 0.45 foot with rudder board down is 1.8 foot.

The cabin is 6.75 foot long by 4 foot wide at its widest point with a maximum of 3.3 foot of headroom. Enough room to sleep one with storage available for camping gear.

The performance of this proa will not be as good as EG a Mbuli 20 foot proa but the scow proa will be more comfortable. The rudder board solution is elegant and the shape will be easy to achieve in a plywood timber construction with eg taped fiberglass seams. The limited jpegs will give the idea.

 

It seems someone followed the suggestions to Guzzi's dilemma. Should be affordable for him to try one.

 

The following is a simple plan of a tacking outrigger racing canoe that was used around the Tahiti area. This is a 1985 design based on some research of original designs but uses modern readily accessible materials. The design was done for FAO, Food and Agriculture Organization of the United Nations.

The tacking proa is 24.6 x 18 foot with a 21.6 foot waterline. The length to beam is on the main hull is 16.5 to 1. The length to beam on the 25.5 foot float is 22 to 1. The draft is 0.5 foot. The weight is about 700 lbs. The wooden mast is 85 mm diameter by 27.9 foot high and is held up by wire rigging. The sail area is 323 square foot with a 258 square foot mainsail and a 65 square foot jib.

This is a racing canoe with no accommodation beyond a couple of storage areas.

The construction nis plywood, timber and some galvanised steel components. The main hull is a simple box structure with 6 mm plywood sides over 19 x 52 mm timber frames. The chines and gunnels are 19 x 64 mm and the bottom frame timbers are 60 x 70 mm. The bottom plywood is 10 mm. The outrigger is a 160 high x 350 wide 6 mm plywood with 40 x 70 mm fore and aft edges. The central spine beam is a 170 x 35 mm timber.

The forward beam is 130 x 130 mm laminated beam to 6 foot width with an additional laminated beam of 10 foot that is lashed on to the main hull beam (or laminated to full width beam if not trailable). The down pipe from the beam to the outrigger is a 30 mm galvanised pipe with an angled 8 mm solid rod angled from the outrigger to the beam for stiffening. Aft beam is 70 x 90 mm high across the hull with a 27/34 mm galvanised pipe lashed to the hull beam that is bent down to the outrigger. The rudder is on the aft end of the main hull and is a solid blade that is wide and fairly shallow.

This tacking proa would be a relatively fast for its level of technology. An inproved rig, construction and hull shape would produce a very fast boat for a low cost. EG a 4 mm tortured ply main and float hull, lighter cross beams and a used Hobie 20/21 rig could produce a very fast tacking proa that would surprise many Farriers etc.

The pdf has more detail.

 

I have

Sailing Catamarans - Saturn - 8.8m hard chine performance cruiser with central cuddy https://sailingcatamarans.com/index.php/designs-2/3-25ft-to-30ft-catamarans-designs/173-saturn

and

Plans for the Avalon 9 metre folding trimaran http://www.teamscarab.com.au/Avalon9Des.html

at 10% can trailer in Qld!

saturn traler at 10% can trailer. Very nich!

reed and write more importin, then build a boat.

Have:

Plans for 7.3 catamaran http://www.teamscarab.com.au/7.3Des.html

code trailer

Plans for8.4 catamaran http://www.teamscarab.com.au/8.4Des.html

to big to trailer.

EX40 HARRYPROA

Mabe on trailer, maybe.

 

I know very little about the first of 2 jpegs I found recently. The drawing is from a person who wants what looks like an Evergreen 6 metre concept with more headroom in the hulls. Martin Moermel is playing around with the design od a small cruising catamaran with accommodation in the hulls.

The cat is 19.7 foot long and has a by plane rig with 2 free standing masts carrying a total sail area of 246 foot. The length to beam on the hulls is 10 to 1. The keels are low aspect ratio. I know nothing more but a guess displacement would be about 1700 lbs. I do not know if this design was ever completed.

The second plan is of a tri that I may have done before but it is interesting as it looks like a swing wing possible home build. Fiftri 37 appears to be a cruiser with a mast aft headsail and staysail rig. The chine hulls indicate a plywood timber build with fiberglass over. The swing arms would be interesting in design but not difficult to do in timber or composites.

Fiftri 37 is 37.7 x 21.65 foot that folds to 13.9 foot. The small beam is compensated by L foils on the floats to help with stability. The mast aft rests on the rear cross beam and has a 485 square foot genos and a 300 square foot self tacking reefing stay sail. The length to beam on the main hull is about 6 to 1. The length to beam on the floats is 14 to 1. The draft is 2.5 foot over the hull foils and rudder on the main hull.

The accommodation is a double berth aft, a cockpit, a single berth and seating in the maion saloon, a galley and toilet forward with a single berth in the bow.

Sorry I don’t know more but others may be able to help. The 2 jpegs give the idea.

 

The following is about building your own day sailing cat or tri. It was prompted by seeing Revintage trimaran which has a {I think) Tornado main hull and Nacra floats. The first jpeg shows the Revintage tri.

I then searched out what this size of hulls are structurally made of. EG Tornado hulls were originally 3 mm tortured plywood with a light e-glass cloth over with a foam spacer in the hulls, next came 3 mm strip plank cedar hulls with 200 gsm uni’s on both sides of the core. Finally Tornado’s were foam glass of various weights and types of cloth over 3 to 6 mm foam cores.

The next jpeg is of a Hobie 20 hull, bulkhead and internal stringer/foam spacer shelfs. This is a complex layout for a small cat but the Hobie 20 is designed to take the knocks of less skilled sailors.

The next jpeg is the hull lines of a 18 square meter catamaran. This is similar to A Class catamarans. These cats structure can vary as it’s a development class. The simplest is a 3mm okume tortured plywood hull sheathed in 4.7 oz carbon. There is a forward 50 mm Styrofoam shelf and bulkheads under the cross beams. Later cats had 9 mm 4 lb core cell core with 190 gsm carbon fibre cloth and 190 gsm Kevlar on the outside and a 190 gsm carbon fibre cloth inside. The latest versions have 6 mm 6 lb core cell with 2 layers of 132 gsm unidirectional carbon fibre at 45/45 degree (all in epoxy) with a 190 gsm carbon fibre cloth inside. Be careful as you need to ensure the fabric and surface of the hulls are fully wet out as light cloths can be porous.

The cross beams can be done by EG using a 75 aluminum tube as a mold and wax it very well. Lay up 10 layers of uni directional 132 gsm carbon fibre with a couple of layers of 190 gsm carbon fibre cloth (acts as a binder for uni directionals). This will require a dolphin striker to support the mast. Yes you may have problems getting the aluminum tube out. Some people put a thin layer of cardboard around the aluminum tube first.

As you can see even small cats can be complex to build and if you want to build a light cat or tri it may be better to find a designer who can give you a completely integrated design.

 

@oldmulti - do you remember a crazy Kelsall design that looked like a cross between an alien spaceship and an elephant trunk?

This was a 16m weekend racer for 2 people - very slim hulls, flat keels, giant sail area on a rotating mast, the pod was extended forward (just like an elephant's trunk) to hold the forestay ... When I saw her for the first time - what an ugly monster. On second glance, ohh interesting. And on third glance - what a fck**g cool boat!

Anyway, I was so fascinated that I ordered the study plan and the KSS DVD. Unfortunately, both got lost somewhere along the line... if you find any information about it, that would be very welcome

 

ropt. You may be thinking of VSD a 60 foot Kelsall pod cat built by Nick Kieg in foam glass in about 1985 and raced. The following 2 jpegs will give an idea, if its the design your interested in. Yes I have a little more detail if its the right cat.

 

Not the right cat, unfortunaly. But i found her in the wayback-machine. She called FastKat KSS-FK47.

From here: Catamarans - Kelsall Catamarans - KSS FK47 (FastKat) https://web.archive.org/web/20161025133320mp_/http://kelsall.com/Designs/KSSFK47.htm

 

ropf. Nice concept but I have no information on that design. Lock Crowther did a slightly more radical version in the X 10 design (Windswept) and several 50 foot cats EG Triple 8 (for sale NZ).

 

That’s probably the most attractive KSS boat I’ve ever seen !