Multihull Structure Thoughts

A request has come in for some information about some Andrew Simpson designs. Simpson did a lot of multihull design work in the 80’s and 90’s before he left the industry to pursue other interests. His portfolio of work is mainly plywood and timber or strip plank cedar and ply. He did some foam glass tris but mainly stayed with catamarans. His main work was in good solid wholesome fast cruisers. Although some owner builders built some lighter versions with good rigs and those boats performed very well. Simpson had a knack of drawing boats that a broad range of people wanted. Of the people I spoke to as they built his designs most were happy and finished their boats.

The first cat we will talk about is the Woodwind 9.1. The cat is 30 x 18 foot displacing 4100 lbs and carrying 275 square foot in the main and 153 square foot in the jib. Its plywood (guess 9 mm) and timber stringers with ply bulkheads. It has a multi chine bottom. The crossbeams are box plywood and timber. The boat is covered with 330 gsm glass and epoxy resin. The jpegs are of a boat for sale in Cairns for $65000. It will give a good idea of the structure.

I have only sailed on 2 Simpsons. A 40 foot full bridge deck cruiser with a very average rig. It would sail OK and tack consistently but I suspect it was capable of more. The other was a 26 foot F1 production cat. Now that could really sail.

 

Awesome boats .a Simpson Formula One was surprisingly roomy with the open Bridge deck

 

That's Roger Simpson, not Andrew. He and his wife are now making world-class banjos and mandolins, brilliant wood skills.
I had a daysail on an F1 with a gung-ho skipper. Very quick little boat with reasonable interior space.

 

My apologies to Roger Simpson (his first name is not Andrew), who designed a production catamaran called the Formula 1. It was a 26 x 16 foot open bridge deck production fiberglass and foam fiberglass cat that had roomy hulls for its size. The boat was originally built by a Frenchmen in QLD. Claude Desjardins had sailed across the pacific in a 19 foot boat with his wife and though a 26 foot cat was going to be roomy. There were several F1’s built by several manufacturers and they still can be gotten for $40000 to $50000 second hand. A very close cousin to the F1 is the Backlash 8.2 meter. The Backlash is a 1990 home build version of the F1.

The Backlash is 26.75 x 15.75 foot open bridge deck cat that weighs 2425 lbs and displaces about 3300 lbs. It carries a 40 foot aluminium mast with a 3 wire rig and a set of diamonds 363 square foot heavily roached main with a 280 square foot genoa. The hulls are 4.2 foot wide at the gunnel and 2.2 foot at the waterline giving a length to beam ratio of 12:1. The hulls are either strip plank Duracore or WRC up to the hull knuckle then the rest is mainly plywood as are the bulkheads etc. There are some timber stringers and deck beams etc. The cabin roof is cold molded plywood. The 3 cross beams are at least 150 mm aluminium tubes.

As I said and several others have supported the statement, the 26 foot F1 production cat could really sail well, especially if it was lightly loaded. The Backlash has a bigger rig and if built lightly could be fast. I am still trying to find the test articles on the F1 and will summarize when available. The jpegs are of a Formula 1 and of the Backlash 8.2 meter.

 

I am currently going through my library of paper to find more detail of the Simpson designs. No small task when your sailing books, magazines, photocopies, design books etc cover over 100 foot of shelving and I also have about 15 boat plans. As you can see this thread may go on a little longer. So I found more information about the Simpson designs we have already discussed. Sorry about the quality of some of this but its better than nothing.

The jpegs are of a Formula 1 bridge deck (I don’t know if any were built), a further Backlash 8.2 meter detail of bulkheads and two more details of the Woodwind 9.1 meter.

 

The next Simpson design we will do is the Woodwind 10.3 meter a plywood multichine boat. The cat is 33.75 x 20 foot open bridge deck boat that displaces 10750 lbs carrying a 227 square foot main and 308 square foot genoa. The waterline beam is 3.7 foot with a length to beam on the hulls is 8.5:1. This boat was relatively popular as it was a realistic size that you could build in the back yard and cheaply transport to the sea for final assembly. The maximum hull width with the mini wing deck edge is 7.5 foot. The boat has some real accommodation for 2 people to cruise in, probably matching a Wharram 38. The hulls are 9 mm ply with a 12 mm ply flat panel bottom. The chine logs are 60 x 19 mm with stringers 42 x 19 mm. Internal keel is 2 layers of 90 x 19 mm. Bulkheads are 9 mm and some 12 mm at bulkhead points. The wood main cross beam is plywood and timber. There are 3 x 12 mm plywood webs with a 350 mm x 35 mm top and bottom timber flanges. The jpegs give some idea of the boat structure. I have only heard but cannot confirm these boats sail well and achieve OK averages even when carrying a reasonable payload. We will do a few small tris next before we return to Simpson bridge deck boats.

 

OldMulti,
Firstly, thank you for this thread! It is an unbelievable source of information.
Second, I was wondering if you had any info on any of Team Scarab's multihills?

 

Burnside Style. Yes, I have some information about the tri's and cats and have some material lists etc on pages 5, 8, 9, 11 of this thread. Team Scarab's web site is informative and there are some good build blogs about a 22 foot tri built by a Canadian etc. Most of his tris sail well according to what I have seen and read. His cats have also had positive reviews. These boats are strong. The build process is OK but the cross beams take a lot of time and effort to build and align properly. If its done well they match a F22 for trail-ability etc. I will do further stuff on Scarab boats later but I have a bit of a backlog of other stuff to get through first.

 

John Westall was an original thinker in the early days of trimaran design. He went against convention and designed tris that were very good cruisers and capable of being moored in monohull berths. Most of his tris had folding beams. His first big tri was a 40 footer that entered an early Around Britian race. A float fell off breaking the steel cross beam tubes at the folding float cross beam connection. He learnt from this and designed in 1970 a 30 x 22.5 foot which could fold to 11.5 foot production tri called Oceanbird. These boats may be heavy at 12000 lbs displacement (this was a time of solid glass and CSM builds) but are loved by their owners and are still available second hand 40 plus years after they were produced. After the success of Oceanbird came a series of designs intended for production that had varying levels of success as people became more interested in performance.

Thalassa was one of those designs. Thalassa is 34.5 x 26 foot and can fold to 12.1 foot. It weighs 7300 lbs and carries 375 square foot of sail in the main and 425 square foot in a genoa. The length to beam of the main hull is 5.2:1. All this adds up to good light air performance but limited top speed. The tri is solid glass and foam glass. The cross beam structure is glass with pivot bolts the same as the Dragonfly series of tris. The jpegs give an idea of Thalassa. The 3 start photo’s are of an Oceanbird tri. The last jpeg give a plan view of an Oceanbird.

 

Paolo Bisol is a designer who won an award in a 2002 design competition for his trimaran of 23.7 x 19.5 foot weighing 1590 lbs displacing 2580 lbs. The tri carries a 32 foot mast with a 260 square foot mainsail and a 130 square foot jib. The sail plan includes a large full batten, heavily roached mainsail, a small blade jib and an asymmetric spinnaker set on a canting bowsprit. Upwind performance is assured by the single daggerboard on the main hull.

This tri was advanced for a home build for its time with full high buoyancy floats and rudders on each float providing full control in every condition. This boat could be pushed hard with a good rig and the right crew. As you can see from the hull lines, the main hull has a lot of flair providing a simple interior with sleeping accommodation and sheltered seating for four crew. A chemical toilet can be installed, as well as a cooking stove and sink.

The trimaran is foam glass with vinylester resin and some carbon fibre in the cross arms. Tritium is made in a sandwich of 80 Kg/m3 PVC foam, 15 mm thick, with symmetrical skins in Glass bi-directional, 2 x 300 g/m2 layers each skin, and vinyl ester or epoxy resin.

The PDF’s give a lot of detail. The Intro describes the boat, the brochure does an overview and the interior and side gives study print views. The hull lines how a good hull and float shape for a cruiser racer.

 

Marc Louis Rifflart was an early French multihull designer that drew a range of relatively easy to build multihulls. His cats were mostly plywood and timber and often had simple symmetrical dory shapes hulls that could carry a reasonable load. Most of his cats had a beam about 50% of there length. The design featured here was Marc’s personal boat and had fairly wide asymmetrical hulls to maximise accommodation. The Catfly catamaran is 26.25 x 12.25 foot weighing 3000 lbs and displacing 4400 lbs. The hulls have a length to beam of about 9.7:1. The 33 foot mast carries 380 square foot of sail in the main and fore triangle. Result 6 to 7 knots upwind 10 to 12 knots downwind. The cat was built with plywood with glass cloth epoxy covering on the outside and judging by his other boats glass cloth on the inside up to the waterline. The boat took 1400 hours to build or 5 months at 10 hours/day with only a few days off.

The other jpegs are of a Rifflart 23 x 12 footer built and sailed by a guy who later built PHA (30 foot Tiki biplane rig) and Grand PHA (46 foot Tiki biplane rig). Also a study plan of Echo, a 32 x 16 foot liveaboard cat that crossed the Atlantic from France to USA and has been through a hurricane. All his designs worked well as cruisers but were not racers. These boats show that simple home build designs with basic hull shapes can sail well enough to satisfy a lot of people. And in a lot of cases the build time of these simple boats is often shorter. The final jpeg is other Rifflart designs. If anyone has any more detail it would be welcome.

 

John Westall produced many tri designs in the 70 and 80’s but one of the more interesting following the Oceanbird and Thalassa theme was his micro racing trimaran. The tri was aimed at production and had a cruising version available. The tri was 25.75 x 21 foot capable of being folded to 8.66 foot. The cruising version displaced 3100 lbs with 403 square foot of sail on a mast head rig. The racing version displaced 2300 lbs carrying 432 square foot of sail on a fractional rig. The length to beam on the main hull is 6:1. The hull and float shapes were the same on both versions. The racing version had less accommodation furniture and fittings (eg no fixed loo etc) inside and had a lighter hull layup. As a production boat it had a single skin hulls of unidirectional and biax fabrics in polyester. The decks were balsa core sandwich. The folding cross arms are glass fibre with metal pivot pins.

John choose to have a fixed fin on the main hull and an angled fin on the floats for a semi hydrofoil effect. This may have helped righting in heavier airs but you are dragging around a lot of wetted surface in light airs. The major advantage of this design for racing is it had a very wide beam overall and therefore could carry a lot of sail in strong winds but its downside was it weight, fat main hull and high wetted surface which would have slowed it down in light to moderate weather. I don’t think this boat made production but it would have made a nice transportable cruiser with some real berths, a galley, sitting room and 4.9 foot of headroom.

 

Froggy dans try is for sale , he’s fallen in love with another boat apparently . Great guy and Multihull family his son Ben also built a Whitehaven

 

Just a short one. I found this interesting approach on how you can recover a Woods Wizard 22 (will also apply to a Sango and Skoota series) from eg a build situation on land and get it onto a trailer for trailing. Normally Woods trailer cats “self” fold when they enter of leave water when the trailer actually sinks down. This approach to getting the boat on or off the trailer is able to be done on land. Good thinking Mr Woods. The Skoota picture is the power version of the Wizard.

 

Roger Simpson Wildside 10 meter is part of a series of Wildside full bridgedeck cabin catamarans. The cat is 32.8 x 19.5 foot weighing 7000lbs and displacing 8750 lbs. The aluminium mast is 42 foot high with a 400 square foot main and a 150 square foot jib. The hulls have a knuckle midway up the hull allowing a smaller waterline beam. The length to beam on the hulls are 10.6:1. The Wildside is listed as a performance cruiser and the numbers support this claim. The hulls are built with WRC or Duracore cored with biax cloths in epoxy. The decks, wing deck and bulkheads are all plywood with timber framing and stringers. You have a choice of minikeels or dagger boards. There is some basic information in the study plans and I have not personally seen one of these cats but if they are built in a standard way they will be strong and capable of sailing well.