Multihull Structure Thoughts

Zeta 14 foot trimaran is a Richard Woods starter trimaran for an adult or some kids. The tri is 14 x 11.2 foot and weighs 200 lbs with a 20 foot mast and 100 square foot of sail area. The sail can be mainsail only or a main and a jib or a screecher are options. EG you could start with an old Laser rig of 76 square foot then upgrade to a larger rig as required.

Zeta is a small hard chine plywood trimaran which is a reasonable fast single hander with the emphasis on being simple and quick to build. The build is plywood and timber using stich and glue techniques. The main hull is a simple virtually flat bottom shape of 4 mm plywood with a 6 mm ply cockpit floor. Bulkheads are 6 mm.

The outriggers are simple V hulls of 3 mm plywood for the skin and bulkheads for easy building. The beams simply slot into the main hull and are joined on the boat's centreline. The beams are normally permanently attached to each outrigger, but can be unbolted for long term storage. A fast setup, especially as the dinghy skiff style mast can be left up even with the outriggers removed. The materials list is as follows, but I am always amazed at how small boats consumes quite a bit of (often cheap in price not quality) ply and timber.

6 sheets 4mm plywood, (or 3 sheets 4mm, 3 sheets 3mm)
1 sheet 6mm plywood
1in x1in 35 meters
11/2in x 1in 5 meters
3kgs epoxy
50 meters 50mm glass tape
1000 18mm (3/4in) number 6 stainless steel screws
wood flour and filler as required

The jpegs give the idea. A fun little tri for an afternoon sail or a little education for grandkids.

 

The lure of racing gets everyone. Here is a man who thought a pacific proa would be a winner. So, he did his design and built one using modern materials like ply and plastic film etc. The proa is 14 x 8.5 foot displaces 250 lbs and carries a 12 foot 52 mm aluminium tube mast that has 58 square foot sail made of exotic plastic film. The rigging is synthetic.

The proa performed well and after a few sails to sort out some issues did as expected. The issues included replacing the broomstick handle rudder shaft with something stronger. Replacing the cardboard helping to form part of the box cross beam. Stretching the cheap yellow poly “rope” rigging found at the hardware store. A cheap plywood seat was made on the cross beam for more comfortable racing. And finally, the biggest expense a 150 mm wide 400 gsm biaxial strip along the main hull keel line to stop leaks. Racing is expensive as we all know. When you spend $47.99 on the original, well designed racing proa, ready for the water you should not have to spend additional money to upgrade it.

The designer builder, Skip Johnson, constructed the proa "ACDC" from 2 sheets of 5.2mm luan underlayment plywood for the hull skins of the main hull and float. The bulkheads were thick stiff cardboard gotten from a trash bin. The decks were Tyvek plastic film covering. All glue was “liquid nails” polyurethane builder’s glue. The cross beam was a 52 x 105 mm timber beam which was made wider by stiff carboard to make it more comfortable to sit on. House paint was used to provide a professional finish. All rigging, control ropes, halyards etc was from a roll cheap poly rope. The initial sailing showed the boat had a small leak which threatened the integrity of the cardboard bulkheads which required the upgrade of the fiberglass on the main hull keel.

Now to the initial sailing and racing. Unfortunately, Skip’s proa came second to Ken Abrahams in a very small kayak with an umbrella sail in a downwind course. Skip upgraded his proa after this so it would be a better sailing machine. To quote Skip. “Damn that boat is fast, accelerates quickly and tracks like it’s on rails. Tracking straight is a very good thing. My carefully thought-out oar ball socket isn’t working at all and I’m flailing the steering oar around every which way trying to steer the boat and finally gain some control jamming the oar into the face (wrong) side of the socket and keeping it in place by brute force. Running parallel to shore, I pinch into the wind a bit to slow down for shunts.”

So, there you have it. A racing machine that has proven to be an excellent development platform to learn about proa’s at a cost most people can afford. Make sure you have a good life jacket and you can swim before sailing in water over 5 foot deep but go and have a lot of fun. The jpegs give the idea.

 

Another proa for consideration. Less on the rig design side more on the build and see what happens model. The main hull is OK. The proa is 14 x 8 foot displacing around 250 lbs with 1 person or 350 lbs with 2 people. The rig is a modified Crab Claw of 56 square foot polytarp sail on a short 6 foot x mast. When sailing the rig created problems when shunting. The hull is flat bottom with deep V sides to minimise the use of foils. There is rocker in the hull bottom to make tacking easier. The float is 150 mm PVC waterpipe.

The construction is from plywood and timber. The mainhull is 6 mm lauan with 32 mm timber gunnels. The bottom and sides are joined by a 25 mm fillet cove of micro-balloons and glass taped inside and out. There are 2 bulkheads with a seat in the centre to shape the hull. A slightly tortured hull shape. The stem and stern piece are 12 mm ply. There is 900 mm long 6 mm ply deck at either end. The cross arms 2400 mm long with 9 mm x 80 mm wide plywood top and bottom flanges with 18 mm web blocks in between. The cross arms are tied onto the gunnels and around the 10 foot X 150 mm schedule 40 PVC pipe used for the float. All plywood had a coat of epoxy applied before latex house paint was applied.

The proa was only sailed a few times before being given away due to the owner having to relocate due to work commitments. His comments about sailing were: “This time I tried the shunting rig crab claw configuration. Not very successful due to a lot of back winding from turbulent air. Rigging lines also stretched making control a bit tough.” The proa could sail a straight course with moderate speed but it appears it needs some development in the rig for improvements in shunting and speed.

The jpegs give the idea. A reasonable hull in need of a better rig, but again not a lot of money and good fun refining making it work well.

 

On the last day of 2020 I wish to look back to a real pioneer of the ocean going “home built” multihulls. Eric De Bisschop sailed from France to Hawaii in a monohull Junk. He was ashore and lost the boat to a storm. After talking to local Hawaiians he saw many simple beach proa’s and cats and decided to create his version of a catamaran. Eric built a cat of 38 x 21 foot that weighed 16800 lbs and displaced 24600 lbs. The hulls are a wide V that are 8 foot wide at the gunnel with a 29 foot waterline length. The rig is a schooner with 420 square foot sail area which was mainly in a junk mainsail with bamboo battens. Oh, I forgot to mention Eric designed and built Kaimiloa on a Hawaiian beach in 1936 and launched it in 1936. He set off for France in 1937 arriving in late 1938.

All the numbers and rig do not indicate great performance. But “Kaimiloa” the cats name sailed 19,000 miles from Hawaii to France in 15 months averaging 150 to 165 miles per day. This was faster than most cruising monohulls of the day. The Chinese junk rig and rudders gave perfect steerage, “the bamboo battened Chinese sails gave drive and sail control.” The rudders when lashed gave self steering.

Eric De Bisschop began the construction of his catamaran in an open field near the beach. The keel and hull were solid planks of timber using carvel construction. The cross beams were solid timber and the hull deck cabins were timber framed canvas covered structures. The Junk masts were solid timber with canvas sails and bamboo battens.

In late 1939 Eric De Bisschop built a trimaran in France using a catamaran hull with 2 small floats again with a junk rig. The tri sailed from France to the Canaries where it was hit and sunk by a ship.

Thank Eric for his work, as he inspired James Wharram to build and sail his 23.5 foot Atlantic catamaran Tangaroa in 1955. James work was a major driver of the modern home built multihull movement. Secondly both Kaimiloa and Tangaroa show that even less than idea hull shapes and rigs can sail a long way at a reasonable speed.

Jpegs give the idea. Back to modern times tomorrow.

 

The MIRAGEM 33 (translates to Mirage in English) is a Brazilian designed catamaran by Fazanelli that is aimed to be a quick to build at a low cost. Good aim. The MIRAGEM is 32.8 x 17.7 foot with a 9000 lbs displacement and fractional sloop rig of 508 square foot upwind. The deep low aspect ratio keels and spade rudders will provide good foils for upwind work. The underwing has 650 mm clearance. I suspect the cat will be a good performance cruiser, if the numbers are realistic.

The cat is designed to be sailed singlehanded under adverse conditions with the correct selection of fittings and sails. The large cockpit is well protected with vision through the main cabin. The main cabin has a dinette and a chart table. The galley is in the hull. The hulls contain 2 aft double berths and either 1 or 2 bathrooms. Ahead of the mast base are compartments for electric generators which supplies power to the two electric 11 KW propulsion engines, air conditioning and an electric stove and oven. Headroom throughout is 6 foot.


The cat hulls and underwing is built from strip planks of yellow pine (pinus taeda) covered with bi-directional fiberglass fabric and epoxy resin on either side. Western red cedar could substituted. The bulkheads, wing frames and decks are plywood covered with e-glass. The main crossbeam structures have timber framing. The entire boat is designed to meet the ABS American Bureau of Shipping Offshore Racing Yachts rules.

The cat appears to be well designed to fit the minimum comfortable performance cruiser market. The jpegs give the idea. Also, the last 3 jpegs are of a plywood trimaran also designed by Fazanelli. I do not have any details of it but it appears to be a good basic structure.

 

Hello all and especially oldmulti.

I stopped reading this thread back in July as honestly sailing is a bit above my paygrade, ftmp.

And I see you mentioned my build. Thanks. I think a few points of clarity are in order.

The reason the build is multi chined is it is all a vac bag build. The reason for foam is to offset other factors the build required.

The boat is demountable. And so; instead of the hull sides going straight up the the deck; we had to turn them back to stay below a 48" planned constraint so the two hulls could side by side on a semi. Insert chine. And all these pieces and parts coming apart add weight which goes against some basics for an economy cruiser. Insert foam.

Not sure how well we will end up on weight, the raw weight of the painted hull is about 1600#. I could have saved maybe 125-175 pounds by not using biax with mat tapes and I also used a bit more glass than needed inside up to dwl.

Fairing the first hull was a bit tough. The guy I had help me did not go about it right. We were true amateurs. The second hull went far better, but still lots of work.

The build is progressing and working on cabin interior this winter. Hope is for a June launch. Lots to do.

There is some cruel irony to the demounting aspect. The Mrs wants to move to Texas and so I might have been able to Huck Finn my way in a 17' wide boat.

But I still want to take the rig to Alaska.

 

Fallguy, I admire your persistence and work. You are building a cat to suit your needs and using good problem solving skills getting the job done. I hope you can launch soon.

Today, here is your chance to build a Nigel Iren’s design yacht from free plans. Nigel Iren’s has designed many ocean crossing racing cats and tris. He has designed a few cruising monohulls with lug rigs and only one dingy sized boat. This is the 14 foot skiff design that can be a rowed or sailed, but as with all Irens designs it rows or sails well and you can claim you own a Irens designed boat!

The is a slender 14ft clinker plywood dinghy, with an upright stem and elegantly raked transom. Although primarily a rowing boat, it was fitted with a modest lug rig (just 61sq ft/5.7sq m), complete with daggerboard and rudder. The boat is 13.7 x 4.4 foot that weighs 154 lbs and has a 61 square foot lug sail. The designer and builder want a boat that would perform well as a row and sail boat. Result the design is a little tippy under sail especially downwind. In short, it’s a normal racing type monohull dingy. Reports on its performance rowing and under sail are very positive.

The build is from plywood and timber with the following materials.

4.5 sheets of 6mm ply

1 sheet of 9mm ply

1 sheet of 15mm ply

0.25 sheet of 12mm ply

2 sheets of 12mm MDF for mold build

Solid timber (eg. 1in Douglas Fir) for thwarts, etc

The full plans (mainly PDF’s) and other build information is available at the following web address:
Free boat plans – Build your own Nigel Irens 14ft rowing and sailing skiff - Practical Boat Owner https://www.pbo.co.uk/boats/free-boat-plans-build-your-own-nigel-irens-14ft-rowing-and-sailing-skiff-60770

A fun design for you and the kids. The jpegs here are just a start. The plans are mainly PDF’s (all under 1 meg and less than 40 pages) with a full build description PDF also available. There is also 7 PBO magazine articles available with many pictures to guide you in the build.

 

I think this is an appropriate thread to introduce a series of five youtube interview videos involving a French Multihull Naval architect with a catamaran owner. The NA's name is Anton Richeu (?) and he works for a French catamaran manufacturer. Obviously these videos are aimed at expensive high end catamarans, they do however go into a lot of detail. The NA has a very thick accent and the videos could be shorter, however it is unusual to here a Naval Architect describe the details of multihull design and construction. IMHO the series of five videos is very good, even more so if you are in the market for such a boat

 

This is about some good research by a Tiki 26 builder when a new bridge deck was required. Robert Hughes already owns a foam fiberglass Tiki 26 with carbon fibre cross beams (from C-tech NZ) and wanted to replace the timber ply bridge deck. The research Robert did was to laminate up several groups of test strips, then he added weights to the test strips and measure the deflection of the strips.

The first group of test strips was a 400 gsm biax, 225 gram CSM in polyester either side of a 5 mm or 10 mm or 25 mm PVC core. The 5 mm core deflected 8 times more than the 25 mm core. The 5 mm core deflected 3 times more than the 10 mm core. The 10 mm core deflected 2.5 times than the 25 mm core. Translation thicker the core the stiffer the panel with the same glass layup.

Next was a test of polyester resin with glass and carbon fiber. Compared with epoxy resin with glass and carbon fiber. The glass layups were 400 gsm biax, 225 gram CSM either side of 10 mm foam. The carbon fiber layups were 200 gsm carbon twill either side of 10 mm PVC foam. The result was the polyester glass and the epoxy glass deflected the more than the polyester carbon fibre. The least deflection was the epoxy carbon fibre combination. The carbon epoxy 10 mm deflected only 60 % of the 10 mm glass polyester test strip, and the carbon epoxy test strip was half the weight of the polyester glass test strip.

Translation of the testing in the web site below is, carbon epoxy on the same thickness of foam can either be significantly lighter than polyester glass mat construction or can be significantly stiffer (and stronger) than polyester glass mat for the same weight.

Please read the article for more detail at the following web site: EXPERIMENTS WITH FOAM SANDWICH CONTRUCTION MATERIALS http://wharrambuilders.ning.com/forum/topics/experiments-with-foam-sandwich-contruction-materials

A very good piece of research that is applicable to wing decks and carries more general conclusions. Some jpegs below are from the test series results.

 

Does anyone have any links to research comparing polyester v epoxy that tests to destruction ?
The accepted wisdom is that with high end fabrics like Kevlar and Carbon the polyester shatters before the fabrics reach their potential thereby demonstrating the value of epoxy.

 

Redreuben. I will do some research but an initial statement is buried in a very long blog by a professional builder of 18.5 ft power skiff boats with 70 HP on the stern 1400 lbs displacement. The guy did some tests with glass, carbon fibre and basalt cloths with polyester, vinylester and epoxy. I can lead you to the site but I cannot remember where he made this statement like this: Basalt vinylester is stiffer and slightly stronger than e glass. Epoxy/vinylester both the fabric and resin broke. The polyester resin broke down before the fabric failed. Reading this web site is a long process with a lot of detail by a man who started working with Gold Coast over 30 years ago before doing his own thing. Testing stuff is mentioned on page 2 and 3 and additional mentions on later pages. The web site is Starting Beryllium 18.5, Boron 17.9 and Puffer fish 19... https://www.microskiff.com/threads/starting-beryllium-18-5-boron-17-9-and-puffer-fish-19-skiff-builds.72870/page-2

 

The bigger problem, from my understanding is the elongation of carbon @2% does not match well with epoxy @8% and foams of sim to epoxy and thus the carbon is the place where something would fail. But for the Americas cup; they boats are basically disposable, so the failure is acceptable.

But why people would build in carbon and epoxy and foam eludes me some.

And I understand carbon and ply share elongation characteristics, but are opposites in the weight game.

Perhaps our friend can shed some light on the subject, especially how a carbon fiber vessel on foam is better than glass, or how the industry is dealing with the deltas.

 

Fallguy, I think a builder has to use a version of the fast, comfortable, cheap trichotomy and apply it to the requirements of the intended use. For a multihull solid glass is heavy, foam carbon epoxy is expensive and basalt vinyl-ester is a good compromise for a home build but maybe not for production.
It is clear to me though that polyester and carbon is a waste of materials except perhaps to the marketing department.
And while there are generic properties to all resins in a group like epoxies, different formulations can vary properties like elongation to better suit the materials or purpose.
Combinations also work, like solid glass around hull penetrations and all carbon for masts etc. For the club racer looking for an edge a carbon mast has real benefits, whereas carbon everything is a bridge too far.

 

Is not the post above yours exactly that?

 

No it isn’t. He tested until noises were heard, and being a cored panel the core is bound to shear first before the resin/fabric bond is tested to its limits.