Multihull Structure Thoughts

An update. Tony Grainger worked with Corsair Trimarans when Corsair was looking to replace their C31 model. After 2 years, Corsair and Grainger Designs made a decision to "not go ahead". Tony Grainger scooped up the last 2 years of his life and walked away. Hudson yachts approached Tony Grainger for a production trimaran to fill a gap in the market. The Airplay trimaran was born from previous unused design work.

The Hudson Airplay Raw trimaran is 30.1 x 22.6 foot (folded 8.2 foot) The dry weight is 2,965 lbs. The 41 foot rotating carbon mast carries a 406 square foot mainsail, 230 square foot jib, 423 square foot Code 0 and a 968 square foot spinnaker. The draft over the hull is 1.5 foot. The outboard is 9 HP.

The hulls have flat bottoms on the main hull and parts of the float bottoms. The flat bottoms work like a water ski, the faster you go the more it 'lifts' and allows more speed. NOTE: the rocker profile on the main hull really kicks up aft the transom creating a suction aft lifting the bow of the boat making it easier to drive downwind fast.

Raw’s accommodation is reasonable with a berth forward and single settee berth in the main cabin and an aft berth under the cockpit. An initial version there was a slide out galley from under the cockpit seat. but later sports versions have a full length galley 1 side and a seat on the other side.

The initial Raw tris were built in infused carbon fibre foam epoxy. The cross arms are carbon fibre builds. The folding system is classic Farrier but with shape and structural improvements. The build jpegs give some idea of the structural cross beam arrangements. The later Sports version was built in E-Glass Vinylester with foam core.

The performance of the RAW 30 is very good. Reports include. “We had 12-15 knots of breeze when we headed out. Upwind the boat tacks easily, and we saw 12-13 knots of boat speed. Setting the kite is simple with the top down furling, and gybing is easy as long as the trimmers time the ease/trim correctly, just like any big asymmetric kite. We saw around 17-19 knots downwind, but we were using a gps app on a tablet for speed. Got to helm for a while both up and down, and the helm is very light upwind. Downwind she accelerates easily.” Delivery of RAW to Singapore. “Lightish wind so only cranked up to 16.5 knots. Boat was nice a steady in this configuration and would suit at 14-16 fairly easily in the 10-12 knot breeze. Feels like the boat likes 16 as just about then the leeward ama compresses enough to get the platform working.” And Paul Nudd an Australian racer “Day One testing in light 4-8 knots of true wind. The RAW rocked up to top 15.4 knots (GPS). 2-4 times wind speed. Translation, the full carbon versions are faster than windspeed in light to moderate conditions and has peaked at over 20 knots. The E-glass Sports versions are only slightly slower.

This tri started production in about 2013 and had several produced before production slowed but the Hudson site still shows several versions of the design are available. The jpegs give an idea.

 

Ever heard of the DH 50 catamaran by Dudley Dix? Dudley was asked for a 50 foot catamaran that CRW-Con in Edenton, North Carolina could build on spec for a potential customer. Dudley said he could extend and modify a Dix 470 design. Result The DH 50 (no it is not a DH 550 although it shares a lot of structure in common).

I cannot be sure about the following but Dudley said it is a Dix 470 extended so the numbers may be the DH 50 is 50 x 25.33 foot weighing 25,000 lbs and carrying 1100 square foot of mast head rig main and jib. This is basically a fast cruising cat with eg 4 double berth cabins and a main saloon containing the galley and seating.

If the design follows the Dix 470 structure, the hulls are 22 x 44 mm WRC stringers at about 225 mm centre lines on 12 mm ply bulkheads and 18 mm ply bulkheads for attachment to the main cross beams. 9 (10) mm ply covering the majority of the hull with radius chines. The chines are 3 layers of 3 mm ply over a short former then cut to size to fit the hull shape. The decks are either 3 x 3mm ply or 9 mm ply depending on the deck cabin curvature on very closely placed deck beams about 225 mm centre lines on cabin roof or deck stringers on fore and side decks. The underwing is 9 mm ply or forward 3 x 3 mm ply BUT it has an internal framing matrix and another layer of plywood on the inside for a total thickness 60 mm. There is Styrofoam inserts between the stringers in the underwing.

The cross beam structures are 18 mm plywood with 2 layers of 600 gsm biax on either face and an additional 2 layers of 600 gsm biax at 45 degrees on the joints between the 18 mm hull bulkhead and bridge deck cross beams. There is additional 44 mm wide by 88 mm deep timbers on the bottom and top flanges of the 18 mm ply beams. The rudder shafts are 73 mm schedule 80 stainless steel pipe. They are put inside a 90 mm PVC pipe wrapped in 8 layers of 450 gsm biax tape. Why the detail on the structure, because bthe Dix 430, Dix 470 and DH 550 have very similar wooden structures.

I do not know any performance figures but the numbers indicate 10 knot averages and near 20 knot peaks. If anyone knows anything more about this build please advise.

The jpegs give the idea. The first 2 are of the Dix 470, the rest are of components of the hull and underwing build.

 

The DH550 catamaran was designed by Dudley Dix as a family cruiser. He now have a new version of the DH550 , named the DH550 Charter. It was commissioned by a charter and has features that are better suited to charter service, in the cabins, bridgedeck accommodations and rig. This version has four equal double guest cabins, each with en-suite heads and shower. There is also a compact single crew cabin in the bows of each hull and a shared crew heads with shower in the starboard hull.

The DH550 Charter is 55 x 28.6 foot with a weight of 27550 lbs. The fractional furling rig has a high fixed aluminium mast with a vertical furling mainsail and jib of 1293 square foot. There is an optional more conventional rig of 1435 square foot. The length to beam of the hulls is 8 to 1. The draft over the fixed keels and rudders is 3.4 foot. The power is 2 x 50hp diesels.

As mentioned there are 4 equal double berth cabins in the hulls but the saloon is smaller than the DH550 cruiser version with more emphasis on the outside deck area. It has two galleys, one internal and the other in the cockpit. The forward cockpit, a working area in the cruising version, is changed to a social area with seating and folding table. The working cockpit has moved aft to above the outside galley, with helm and engine controls. All sail control lines, except halyard and reefing lines, are led to a pair of electric winches mounted on the cabin roof. This cockpit has large cave lockers to keep the ropes tidy and out from underfoot. This cat lives up to its name of a charter cat, guests first with space to view the world.

The construction is ply and timber with glass sheathing as required. To give an idea of the materials required to build a cat this big, look at the following list.

CHIPBOARD (for setting out bulkheads if building from offsets) 1,83x2,74m 16mm [6'x9'x5/8"] - 2 sheets

MARINE PLYWOOD 1,22x2,44m [4'x8'] or 1.22x2.50m [4'x8' 2"]
4mm [3/16"] - 90 sheets, 6mm [1/4"] - 55 sheets, 10mm [3/8"] - 81 sheets, 12mm [1/2"] - 119 sheets, 18mm [3/4"] - 12 sheets

PINE or similar (for building stocks) - 38x152mm [1 1/2"x6"] (rails) - 40m [132'] 50x75mm [2"x3"] (bulkhead legs) - 33m [109']
100x100mm [4"x4"] or 100mm [4"] dia (posts) - 20m [66']

WESTERN RED CEDAR or similar
22x44mm [7/8"x1 3/4"] (stringers, joinery framing etc) - 2300m [7546']

HONDURAS MAHOGANY or similar
25x50mm [1"x2"] (laminated beams for main beams) - 150m [492'], 25x76mm [1"x3"] (beams for bridgedeck & cabin) - 61m [200']

SUNDRIES
Epoxy laminating resin for coatings, reinforcement and fillets. If you use pre-mixed filleting epoxy, that will come out of this quantity. - 1100 litres (290 US gal).

I just love the 7,546 foot of western red cedar and the sundry item of 1100 litres (290 US gal) of epoxy. This should help explain why it may be cost effective to do foam glass boats in Australia as these items and the 335 sheets of good quality plywood are expensive in Australia.

Thee jpegs give the idea of the design.

 

The plywood is not just expensive - it is virtually unobtainium.....

 

The final on the Dudley Dix DIX 470, DH 50 and DH 550 series. Dudley was asked to do a smaller version of this series of cats and after a couple years he designed the DIX 430. A you will see Dudley took the basic DH 550 design and just shortened it to 43.2 foot. So, lets look at the DIX 430.

The length 43.2 x 23.6 foot with a weight of 12,100 lbs and a displacement of 22,700 lbs. The 51 foot fixed aluminum or carbon mast carries a 667 square foot mainsail and a 303 square foot self tacking genoa. The length to beam on the hulls is 6.6 to1. The draft over the fix keels is 3.25 foot. The power is 2 x 30hp diesels.

The accommodation is 4 double berth cabins in the hulls, a fore and aft cockpit and a main saloon with galley, navigation area and inside helming area. This cat has a very good layout for long term cruising.

The real issue with this design is how much performance you want. The 6.6 to 1 length to beam will limit its peak speed. This cat will probably do 8 or even 10 knot averages under good conditions but its peaks will be in the 15 – 16 knot range. For a cruiser it will not be a problem, for the occasional racer you may be frustrated. For a cruiser, this cat will handle overloading better than most.

The build again is plywood/timber and you have had a hint from the Dix 470 and DH 550 Charter build of the type of plywood and timber sizes required.

A good cruising design. The jpegs will give the idea.

 

An update of the Threefold 6 is designed by Dudley Dix to be a safe small cruising trimaran to be used as a day sailor or gunkhole cruiser. The accommodation is simple with 2 wing berths, a forward berth, a small galley and a small seat area. It has 4.5 foot of head room but with the moving hatch, when open will allow 6 foot headroom at the galley. It is a plywood timber build.

The Threefold 6 is 19.66 x 16.25 foot in sailing format with a dock beam of 10.9 foot and a trailing beam of 8 foot. The weight is 990 lbs. The 27.5 foot mast (could be a Hobie mast) has a mainsail sail area is 152 square foot and the genoa is 113 square foot. The length to beam of the main hull is 5.5 to 1 on the 18.33 LWL. The draft is 0.66 to 2 foot. Engine can be a small outboard or electric trolling motor.

The performance of the Threefold 6 is best described by Oleg Zelinskiy built in Russia. “In November 2008 he went out in extreme storm conditions to test his boat. With winds of 15-22m/s (30-40 knots) and gusting to 32m/s (65 knots), they sailed with storm jib and deeply reefed main. He reports that she handled perfectly, even with seas washing over the deck through to the cockpit. She achieved speeds of 15-17 knots and was responsive and under full control at all times. He says that stability was perfect and there was no hint of the boat ploughing in. Oleg is very satisfied with his testing of the boat in storm conditions.” And “In September 2009 Oleg reported that in 15-25 knots of wind he and one other crew had sailed 15 miles in one hour, with speeds sometimes exceeding 20 knots.” Brave.

The tris construction is plywood, timber and an aluminum cross beam structure. The materials list is as follows:

MARINE PLYWOOD 1,22x2,44m (4'x8') (preferably Gaboon or Okoume plywood)
4.5mm (3/16") - 11 sheets (use 4mm if 4.5mm is not available)
6mm (1/4") - 14 sheets and 9mm (3/8") - 3 sheets

CEDAR or similar, selected, free of knots, shakes fractures etc
15x30mm (5/8"x1 1/4") - stringers, framing - 80m (262')
15x40mm (5/8"x1 1/2") - beams, framing - 20m (66')
20x20mm (3/4"x3/4") - framing - 94m (308')
20x30mm (3/4"x1 1/4") - framing, tiller - 67m (220')
20x40mm (3/4"x1 1/2") - framing - 70m (230')
20x50mm (3/4"x2") - keelson, sole bearers - 9m (30')
20x60mm (3/4"x2 3/8") - framing, sole bearers - 4m (14')
20x200mm (3/4"x8") - companion ladder - 1m (4')
25x50mm (1"x2") - beams, posts - 9m (30')
30x30mm (1 1/4"x1 1/4") - sheerclamps - 10m (33')
30x40mm (1 1/4"x1 1/2") - framing - 6m(20')
50x50mm (2"x2") - stem, beams - 3m (10')

This is a relatively easy to build small cruising tri that can sail well and is trailable (with a bit of effort). The jpegs give the idea, the Orange tri is Oleg’s, the build jpegs are of a Michigan boat.

 

Cruickshank Design Studio in Western Australia had naval architect Erik Lerouge design a pocket cruiser suited for the Australian coast and its estuaries. The pocket cruiser is named the Pulsar 20. In 2024, the design went into production in Fremantle Western Australia.

The Pulsar 20 is 19.6 x 16.9 foot and can be disassembled to 7.5 foot. The weight is 1,120 lbs and the displacement is 2,130 lbs. The carbon rotating mast is 31.5 foot (spar requires no diamond spreaders) carries a fractional rig with a 205 square foot mainsail, 97 square foot jib and a 420 square foot spinnaker. The length to beam on the main hull is 6.25 to 1 and the length to beam on the floats is 13.8 to 1. The draft is 1.12 foot over the fin keels on the floats. The power is a 1 KW electric outboard.

The beams are bolt on: The beams and floats are designed to be light and easily manageable, secured with just a few bolts. Each beam is made using prepreg epoxy/carbon in a vacuum autoclave moulding process, weighing only 20kg each. This reduces weight, complexity and cost of folding systems according to the builder.

The accommodation is 2 single berths and an area between with shelving and storage for a minimal galley. A porta potti can be put under a berth. There is 4.6 foot headroom but with an open hatch you can stand full height.

The boat is sold as a kit or fully constructed and is basically foam glass with vacuum infused e-glass and Kevlar in grounding areas in the hulls. The beams and mast are infused carbon fibre. The components are listed below.

Main Deck two moldings- 8-10mm PVC foam core fiber glass and epoxy vacuum infusion molding .

Main hull- 8mm PVC foam core fiber glass and epoxy vacuum infusion molding. Reinforced grounding zone Kevlar

Side hull- 6mm PVC foam core fiber glass and epoxy vacuum infusion molding. Reinforced bottom/keel Kevlar.

Side hull deck- 6mm PVC foam core fiber glass and epoxy vacuum infusion molding. Reinforced beam sockets Kevlar.

Rudder- PVC foam carbon fiber and epoxy vacuum infusion molding

Composite Spar- Innovative spreader less Spar 9.6m wing section carbon fiber and epoxy vacuum infusion molding.

Beams- Prepreg epoxy/carbon vacuum autoclave molding, only 20kg

Bulkheads/internal joinery- PVC foam core fiber glass and epoxy vacuum infusion molding.

Bowsprit-Prepreg epoxy/carbon vacuum autoclave molding. Deck fittings-on request

Entrance hatch/ ports/side hull hatch- PMMA/plexiglass- flush mounted ports and entrance hatch. storage hatches on side hull decks ABS plastic

Boom- Aluminium

The jpegs give an idea of the design and the kit components. An interesting pocket cruiser design.

 

Going back to the post about the Grainger designed Airplay Raw Tri, I have to say after reviewing/comparing the specs to Corsair’s current offerings and looking at the photos, I would much prefer the Raw.

Knowing that some of the design work he did for Corsair likely made its way into the Airplay Tri, and looking at what Corsair ended up producing (designed by someone who worked for Grainger if I remember correctly), you can’t help but wonder what it was about the Grainger design that they didn’t like?

Im sure it would outperform what Corsair is currently offering, and in my opinion it looks a whole lot better. The 760 has some nice lines, but the 880 just kinda looks fugly IMO.

Of course there’s a lot more to the story I’m sure, but it’s interesting to see the direction Grainger was going/pitching in comparison to what Corsair ultimately went with.

 

SolGato, my guess is they didn’t like the bill.

 

This is one to test you all, especially since many on the forum have a depth of knowledge re most old cat designs.. eg. Simpsons and Tennants, maybe Ed Horstmann..

Would you say the following photo is a Simpson cat, if it is, which model is it..(seems to have the customary Simpson stripe down the side) Its approx 11m LOA Max beam is 5,5m, from center of hull to center of hull is 4,4m, Hull width is 1,2m at widest narrowing to 1,1m in front of the cabins, 2 cabins upfront, transom extensions of 0,6m added recently. Initially I thought it was a Simpson 10.2, but the windows at top of the hull (which have been covered in ply, then made me reconsider.

It was an open deck with motor in the center originally, but seems to have been converted (the saloon is not original)since I can still see where the hatches were aft inside the hulls (hence was thinking it may be a Woodwind 10.3), however, seems to be rounded hulls, and no chines. There are some 9 stringers from hull bottom to top longitudinally in the hulls. Ply and glass.
Some have said its a Malcolm Tennant Shilo design due to rounded hulls which seems to have been moulded at bottoms of the hulls. Brown areas are where osmosis has been removed..It was apparently originally built in Queensland. The boats name is Blase'.

Any help in identifying will be appreciated gratefully.

(I know she is ugly and I will be reducing heights of saloon and bimini, last owner was 6ft 4", he raised heights of all, or maybe I will convert it to a power boat)
Will also be epoxying hulls over ply this time too.
Without identification, its difficult to know payloads and possible performances, the boat looks very bouyant too so she may be able to carry a good payload.
Any comments or opinions would be appreciated if anyone has any idea of the original design and also with these hulls, what will pitching etc be like?.

 

In 2022 White Tip (company) commissioned Yacht Design Collective to design a trimaran. They then asked Cape Performance Sailing in South Africa to build the tri on a production basis starting in 2025. The first of the 3 initial orders was done by Thomas Wilson's new regatta school, the White Tip Race Academy, based in Haslar, near Portsmouth in southern England. So, if you want some fast sail training this may be the place to go.

The CAPE-WT 10M is 32.9 x 27.5 foot and can be folded to 11.5 foot with a Farrier type folding system. The “displacement” is 4,630 lbs (more likely weight). The rotating (assume) carbon fibre mast carries a 452 square foot mainsail, 312 square foot genoa and an asymmetric spinnaker of 1017 square foot. the draft ranges from 1.4 foot to 5.95 foot over the float based daggerboards. Power is with an outboard.

The accommodation is 2 double berths, a separate toilet shower area and the main saloon which contains a galley down and minimal navigation aft with a seat table combination forward which can convert to a single berth. The main saloon has 6 foot headroom. The cockpit is large and capable of sailing with 6 people.

The aim of this tri is to be a high performance racer cruiser of which the designer/builders claim its capable of 30 knots. Seacart 30’s have a very hard time reaching 30 knots and Seacart 30’s are lighter and capable of carrying more sail. When I read a real test, performance report, I will accept 30 knots otherwise my guess is maybe 25 knot peaks and 10 – 12 knot averages in good conditions.

The construction by CAPE, if it follows the same structure as a 30 foot monohull racer CAPE build, is infused e-glass vinylester resin. There will be some carbon fibre in the cross beams and other stress points and foils. CAPE knows how to build a light fast boat that is structurally sound.

Yacht Design Collective also have designed a lot of the latest Corsair tri’s and understand what is need to get a good cruiser racer, so hopefully the CAPE WT10 will perform very well.

The jpegs give the idea.

 

Peter Dale. Try this site it may help as it still sells Roger Simpson design plans. It list many plans including a 11 meter round bottom model, But I cannot find a near match to your dimensions.
Simpson Design Catamaran Plans https://boatcraft.com.au/Shop/index.php?main_page=index&cPath=32_33&sort=20a
Boatcraft Pacific has been around for years.

 

I have a question.
Who or where is the next generation of designers, the next Woods, Grainger or Wharram ?

 

Redreuben. There are designers out there but they are mainly European and if French, designing for the home builder market, are often using plywood. Composite is often cheaper than ply in Australia. The second problem is designers are starting to understand the value of their time and are charging accordingly. Schoinning is widely know but is expensive as are Grainger etc. Very few designers have used the Ray Kendrick model (TeamScarab) of low plan cost high volume. Also the latest design trends in hull shapes, materials and structures is very different from even a few years ago. Finally, the real issue is people are time poor and their are many second hand multihulls available which means there is a smaller market for plans home built boats. Designers make better money designing for manufacturers with less questions about how to build a boat after they have done the plan. Remember a custom plan is worth about 6% of the final value of the boat. The home market gets scared paying 2% of the final cost of a boat and expect a designer to answer all questions and do plan modifications for free. Also every major designer I know have been sued (with out much success) for boat failures that were builder problems often, not design issues. Home builder designs especially in the 20 to 40 foot market is a hard place to be successful in as you build a reputation. Later today I will give an example of a home builder plan by a European guy.

 

Hi Old Multi

Thank you for your reply.

I have looked at all the Simpson designs on Boatcraft, the closest I could find was the Windwood 10.3 , however, the beam on this boat is 5,5m (not 6m and plus) as per Simpson study notes and it seems all Windwoods had hull chines. Apart from method of construction and the bouyant bows, I would have guessed a 10.3.. and was pretty convinced originally it was the Windwood 10.3 until the construction method on Blase', the more convex hull than typical Simpson's and more bouyant bow (hull toward front which seems deep) was highlighted to me.

The 11m Simpson the beam is too wide and it shows aft cabins under the deck, (and a few other differences) mainly beam is too wide, so I don't think it is the 11m Simpson.

I am thinking that the Malcolm Tennant Shilo specs are quite similar, same beam and rounded hulls.. (Original specs 30 ft before xtensions to 32ft/ 34ft, 5.6m beam- which is roughly correct) I have tracked down 2 Shilos, one named Perfection and another named Windzang (a cat that you placed on your design forum) and was wondering if perhaps you had more photos of Perfection (I only have one), which was a normal beam Shilo (unlike Windzang which was narrower for mooring purposes) I am particularly looking for photos of Perfection on the dry. The Shilo's are rounded hulls too.

There was also another Malcolm Tennant open deck design called a Northern 37 and Northern 38, that may be the exact original design since these cats were originally an open deck. That LOA seems right..
Again, wondering if you perhaps have any info on those in your archives? Cannot seem to get any history on the Tennant designs since he passed.

Hope you are not too busy, and can scan your records for me as regards Perfection, any more info on the Shilo's and the Northern's will really help..
Thanks again for helping..