Multihull Structure Thoughts

A man who like entering the race to Alaska has developed a series of boats for the event over the years. He started with a narrow monohull called “Marsh Duck” that could be carefully sailed but was a good rowing craft. She’s was 18 feet long by 3.5 foot beam with wings for hiking out adding almost 6 inches on each side (to 4.5 foot wide). She weighs about 130 lbs, 170 lbs with all sailing and rowing gear. Construction is stitch and glue using 3mm and 6 mm ply with 6 oz fiberglass and epoxy. In 2013 he spent 3 months cruising the inside waters from Port Townsend to the north end of Vancouver Island.

Then he developed a new design for the race in 2014/15 which was a tri. This boat named “Sealark” and was 19 x 14 foot (with amas out for sailing, under 6 feet with amas in). She has small cabins fore and aft, a center cockpit. She weighed under 400 lbs including all sailing, rowing and paddling gear and a small solar power system for electronics. Maximum design displacement is 1000 lbs. Upwind sail will be about 260 square feet split between main (easily reefed) and genoa (also with one reef) – full sail only in light winds. The mast is a 22 foot carbon fiber, custom made by Forte Carbon Fiber Products, including mast base, gooseneck, masthead tri-light, boom and professionally custom made sails.

Sealark was stitch and glue, using 3 mm Okoume with 6 oz fiberglass/epoxy outside the hulls (plus an extra layer of 4 oz from high chine to high chine on the vaka) and 4 oz fiberglass inside the hulls and outside on the topsides. A small amount of 6 mm Okoume is used for the cockpit floor and side decks. There’s a little Kevlar and carbon fiber in key places for strength. Waterline beam of the mainhull is under 22 inches. Cabins are 35 inches wide at shoulder height (sitting on the bottom of the hull) and have shelves and mesh pockets for storage. The cockpit area is 27 inches wide to facilitate using a double bladed kayak paddle. The folding crossarms were metal. The metal crossarms were weak at the crossarm float joint which failed on one side during the first trials. From the jpegs This pivot joint is very short and would not take much to lever the joint out from the crossarm structure especially considering the beam and power the tri could generate.

After the problems with the 2015 version “Sealark” a new tri was designed in 2016. The new design 18 x 6 foot overall beam with a 19 inches waterline beam. The main hull is similar to an open-water rowing shell (similar length and waterline beam to a Mass Aero), flaring out above the water for an aft cabin.

Very lightweight construction, aiming at under 150 lbs including all sailing and rowing gear and 10 watt solar power for charging electronics: 3mm Okoume stitch & glue with 6 oz fiberglass outside & 4 oz inside for the hull, similar but 4 oz outside only for the forward storage compartment topsides, skin-on-frame for the cabin topsides. Amas may be extruded polystyrene foam core with some carbon and/or Kevlar outside on the forward 4 feet and 6 oz fiberglass over all. The amas shown are 8 feet long, but I’ll probably make them 10 feet if I use the foam core approach.

Sliding-seat rowing with oarlocks mounted on the amas. Sloop rig with almost 100 sq ft main with 2 reefs to under 30. Foresail will be very lightweight drifter/screecher style, about 55 sq ft, made of ripstop nylon with forestay built into the sail – used only in light winds. Mast top will be guyed to the amas to maintain better sail shape (foresail halyard and bottom line will act as forestay when using only the main). All sail management done easily from the cockpit. Lee-board on the starboard side of the mainhull, easily managed from the cockpit. Transom mount rudder with push-pull rod steering.

He recommends the use of the highest quality materials (for example, Lloyd’s 1088 rated marine plywood) and using fiberglass or Kevlar cloth throughout the inside of the hull rather than just taping the seams as I did. His experience suggests thinner plywood works just fine. My upper hull panels (all except the bottom) and the large cabin side panels are 3 mm ply. There is a lot of flexibility in the cabin top, but it never seems to be a problem, and the hull panels are narrow and the thin ply seems fine. So, if I were building one now, I might use 4mm ply for most of the pieces, though I think I’d still want 6mm for the cockpit floor and side decks, and maybe for the hatches and foredeck. And then there is fantasy: 6 mm CoreCell form core with 4 oz carbon fiber plus 6 oz S Glass on the outside and 5 oz Kevlar on the inside all done with vacuum bag or infusion techniques for maximum strength with minimum weight. I can imagine starting by applying carbon fiber to one side of full sheets of CoreCell, then cutting the panels and doing the stitch & glue more-or-less as with plywood, though that would be heavier than vacuum bag or infusion – but those are beyond my experience and current capabilities.

His experience on the monohull Marsh Duck suggests that he needed far less stuff than he had aboard during his 3-month cruise. There was lots he never used. To keep all his electronics charged, even in cloudy, rainy weather he used a smaller solar panel of 20 watts feeding directly into the batteries of the various electronics. Therefore the tris were progressively lighter and smaller but still capable of doing the race to Alaska.

All the boats are capable of being rowed at a sustained 3 to 4 knots and the 2015 Sealark could sail at 8 to 9 knots before it broke its cross arm. The jpegs are of Marsh Duck then Sealark and finally the latest 2016 design.

 

I was asked for more information about Shotover 11, a 40 foot racing catamaran designed by Adrian Rogers. There is a mention on page 9 of this thread. But a little history first. Adrian Rodgers was interested in sailing and went to Lock Crowther for a line honours race winner. Lock had produced fast tris at this stage but thought a big cat would be faster. Adrian was willing to take risks and agreed to a mast aft 2 beam cat with a 70 foot rig. Result was Shotover, the 60 x 31 foot tube cat that displaced 16,000 lbs with 1650 square foot in the main and foretriangle. The main was only 530 square foot and the fore triangle was 1220 square foot on a very long forestay. The waterline length to beam ratio is 16:1. Now Shotover was fast on all points, bar upwind, where the forestay sag and the affordable sail techcnology was not good. Adrian home built Shotover (3 people about 2 years) and paid for it himself. Shotover took line honors in Australia’s premier ocean race the 310 miles Brisbane to Gladstone race. In 1982 it took 21 hour 21 minutes. In 1985 Shotover took line honors again in 63 hours 52 minutes. Yes, this race course can be a reaching downwind or light upwind course depending on the year. The outright record is 16 hours 46 minutes by a 60 foot french racing tri renamed Team Australia.

Adrian sold the 60 foot Shotover, then he designed/built a 40 x 25 foot light ocean racing cat Shotover 2. Shotover 11 is a tube cat that displaced about 5500 lbs. But due to Adrian’s experience of the 60 foot Shotover, especially it poor performance upwind, and the rating advantage of the IMOR rule given to mainsails he designed Shotover 11 with a 2 mast schooner rig for handicap wins. Shotover 11 has 2 equally high 40 foot masts with a 400 square foot fully battened mainsail on each mast. The 2 mainsails had big roaches when they were not normal at that stage and were placed close together. Before the boat hit the water, many detractors predicted the rig would be slow due to interference between the sails. Shotover 11 was fast on the race track. Shotover II twin mast rig keeps the centre of effort low, making her easy to handle and incredibly stable whilst providing maximum power. Upwind was meant to be a weakness but proved to be good because the forward mainsail, when sheeted correctly, smoothed air flow onto the rear wing mast mainsail unit. On a reach this boat was very fast and could go up wind very well. Adrian hoped it would be a line honors winner as well. It was. In the Brisbane Gladstone race in 1988 Shotover 11 won line honors in 27 hours 57 minutes, 1989 won in 45 hours 12 minutes and in 1991 won in 34 hours 13 minutes. Each Brisbane to Gladstone has about 20 multi’s of various designs with at least 50% being very quick boats.

I spoke to Adrian years ago about Shotover 11 and was told (memory, as I did not write it down on the day) it was foam sandwich with a 2 x 330 gsm cloth outside 15 mm foam 300 gsm Kevlar inside. Foam glass beams.

She has overnight accommodation with bunks forward in each hull and is great value for day sailing or inshore racing. The first 4 jpegs are of 60 ft Shotover, the rest are of Shotover 11.

 

Rapido 40 is designed by Morelli and Melvin and is being developed built by Paul Koch and James Sganzerla, who ran the highly regarded and successful Corsair Marine from 1994 to 2010. They have 60 years of experience and 1,500 trimarans behind them. The first Rapido 40 will be launched late 2020.

The Rapido 40 is a performance tri of 39.4 x 27.25 foot that can fold to 15.1 foot. The weight is 9,000 lbs with a maximum displacement of 11,300 lbs. The aluminum wing mast (optional full carbon) is 55.75 foot high with a 818 square foot mainsail, a 463 square foot solent and a 1076 square foot reacher. The main hull length to beam is 8.1 to 1. The displacement, sail area and hull shapes indicate the tri will be a very high performance cruiser. Over 200 mile days and 20 knots plus should be very possible.

The main hull’s beam achieves a similar balance of desired interior volume for good accommodation without too much compromise on weight and drag under sail. The cross-sectional shape of the main hull tapers with elevation to create more volume. The stability advantage in Rapido’s comes in part from their high volume floats and a wide beam relative to their maximum displacement. Add the C-curved twin daggerboards on the Rapido 40 and the boat can be driven even harder.

The standard construction is infused carbon/vinylester laminates on closed-cell PVC cores for high-strength areas and E-glass where carbon is not needed. Vinylester is used in the hull and deck laminates for good adhesion and better compatibility with the gelcoat finish than with epoxy laminates, which are used in the structural elements of the boat. Construction meets ISO/CE standards and with CE Category A certification. There is an optional full carbon version available.

Paul Koch said ‘We use pre-preg carbon for the high-strength parts such as the cross beams (which are cured in the autoclave), chainplates and bulkheads,’ and Koch said ‘The cross beams are tapered on the ends so assembly is easy, the fit in the main hull is perfect and it’s strong as hell.’

Paul Kock said “The first 2 boats will be built in all Carbon and we will do the the next couple in all Carbon. We will also offer a base detuned version in glass with an alloy rig for the guys who don't want the performance . Obviously all structural bits will stay in Carbon . I realistically expect that we will be able to fold both the 40 and the 50 in under 10 minutes start to finish!”

As the jpegs will show you these guys are serious about producing a quality series of tri’s. The first jepgs are of the Rapido 40 and the final 5 jpegs are of parts of the Rapido 50 main hull, float structure (notice the internal framing of the forward part of the float) and carbon rudder blade and integrated stock.

But an owner of a F36 gives a warning about cruising in a tri with a limited payload. “We have scuba gear, two bicycles, three anchors, 85 meters of chain, 300 meters of rode, PT-11 dingy, quite a few spares, camping gear, water maker, fridge etc. I don't think the payload capacity that Ian Farrier envisioned included most of this gear. I stopped weighing it all around 3,500 pounds of added weight. We are lucky that Ian Farrier oversaw the building and outfitting of our hull and she floated on her design waterline before we started adding all that stuff. We went from a faster than wind speed tri to one that is only as fast as the speedier cruising mono-hulls we meet.”

 

I came across this design when looking at some Gunboat 66 information. The owner of the Gunboat 66 thought his boat was not fast enough (my definition of fast needs upgrading) so he employed David McCollough, of McCollough Yachts to design upgrades for more performance. David upgraded the rig and foils also reduced some weight out of the Gunboat 66. Result, a predicted 20% performance increase especially upwind. On the water, the cat matched the predictions. Ok let’s look at what David has done. Worked for some America’s Cup teams, has done custom work for several well-heeled owners including new designs etc. Let’s look at one example, the Gata 78.

The Gata 78 is 78 x 40 foot effectively open bridge deck catamaran. The weight is 35,000 lbs and the displacement is listed at 40,000 lbs. The Gata 78 carries a 100 foot carbon wing mast with 3230 square foot of upwind sail area. The mainsail wing is about 2,200 square foot and the jib is about 1,000 square foot. The length to beam on the hulls is 17 to 1.

Now a small warning provided by the late Bill Roberts designer of the Supercat 27 and 30. Once you have hulls that have length to beams of over 16 to 1 the lateral bending loads on the bows of hulls becomes significant and requires additional reinforcing. This is the Pete Goss Team Phillips 120 foot cat problem. The hull width was very narrow on the 25 to 1 plus hull shape. The bow snapped off, partially due to design, but mainly due to structural build problems.

The draft with boards down is 14.8 foot. Be careful where you sail or you could be paying over $100,000 for a new set of boards. Also there are small lateral foils (DSS type) to provide lift at higher speeds.

The Gata 78 is according to the design information is a “HIGH Performance Cruising Catamaran. She bridges the gap between a dedicated Racing Multihull, and the existing Performance Cruising Catamarans on the market. Capable of staying ahead of the fastest monohulls in the world on the race course, the Gata 78 still carries her crew in comfort.”

My performance calculations indicate this boat will be very fast, we are talking a 400 miles plus per day boat if you have the crew. The Gata 78 should be able to top 30 knots under the right conditions. By the way, the accommodation would indicate this boat is more a limited course racer/cruiser than a cat that you will be taking on a month long cruise. This boat will require a good multi person crew to sail it to its full capability.

The structure of this boat will require a lot of infused carbon, foam, nomex and very good engineering. This is not a home build.

I hope this cat will be built and sailed to its full capability as we all will learn something. Good work David McCollough. The jpegs give an idea.

 

The following is a comparison between 2 “cruising” cats that are “owned” by a person who can afford the $5 million per boat. The reason for the comparison is this person can afford what he wants without compromise and as a result the resulting second boat generally is more suited to the task intended, in this case, a long term high performance global cruiser.
The person has circumnavigated a Gunboat 66 in “cruising mode”. A Gunboat 66 is 66 x 28.5 foot weighing 36,000 lbs and displacing 45,000 lbs with a 90 foot mast and 2250 square foot of sail. The length to beam is about 13:1.

Gunboat 66 hulls and deck are vacuum bagged, post-cured in an oven and built of epoxy carbon with 25 mm Corecell foam. The core is thermo-molded into the correct shape prior to lamination and is then sheathed in carbon fiber. Sacrificial false bows, collision bulkheads in the bow and stern, and several independent watertight bilge areas provide further collision security. The lay-up involves a “wet-preg” process, in which carbon cloth is run through an epoxy bath and then pulled through high-pressure rollers before being set in place. The cabin and cabin soles are epoxy carbon skins on a Nomex honeycomb and Corecell sandwich. The deck joint is laminated, vacuum-bagged with SP epoxy and post-cured, so there is no evident flange, creating a monocoque hull and deck structure. Bulkheads and all other structural members are tabbed with epoxy and carbon fiber, then vacuum bagged and post cured as well. The Marstrom rig is carbon, and all standing rigging is either carbon or unidirectional Aramid. The foils are also carbon.

In flat water, the Gunboat 66 tacks through 95 degrees. It can sail comfortably 300 miles in a day and in racing conditions do 400 miles days. The Gunboat 66 generates her own apparent breeze, meaning that the entire sail wardrobe is flat-cut. A self-tacking jib track allows for easy upwind sail handling, and a lifting daggerboard in each hull facilitates close-winded performance and good VMG.

The owner of a globe circling Gunboat 66 then requested David McCollough of McCollough Yachts to design a live aboard serious cruising cat design for the next part of is life. The resulting cat, the BN 72 is 72 x 30.5 foot cat that displaces 65,000 lbs carrying a 90 foot mast and 2640 square foot of sail upwind. The length to beam of the hulls is 12 to 1. The BN 72 will still have to be lightly built of foam glass with carbon fibre in stress points.

Now the comparison begins. Notice the BN 72 displaces 20,000 lbs more, has slightly more beam and 400 square foot more sail area. Translation, for a serious cruiser, the owner required more displacement which requires more sail area to drive the boat. The Gunboat 66 will be a faster boat due to its relatively higher power to weight ratio.

Details of a “live-aboard cruiser” can be found throughout the BN 72. Form follows function with the BN 72 design never loses sight of the goals of comfort, safety, and speed. With the forward raked Portuguese windows, the BN 72 displays her work-boat sensibilities. The galleys are on the bridge deck in both designs and both have inside steering positions with easy access to forward cockpits. Both also have aft cockpits. Both have similar accommodation layouts with the main bunks aft of the mast. Both designs have their engines centrally located to centralise weight although the engines on the BN 72 is 2 x 125 hp versus 2 x 75 hp engines on the Gunboat 66.

Yes, these are dream cats but the experience of the owner of the Gunboat 66 has been translated into a new design, the BN 72 that has more load carrying capability, slightly less performance but much of the same layout and function to achieve its goal of a global live aboard cruiser. The first 3 jpegs are of the Gunboat 66 the rest are of the BN 72 design.

 

The Triptyuqe 20A is a coastal cruising trimaran of 18.5 x 14.9 foot which can be folded to 5.9 foot or 7.9 foot. The 20 weighs 1075 lbs and carries a 25 foot mast which carries 322 square foot of sail. The tri is unsinkable with floats the same length as the main hull. The main hull length to beam is 6 to 1. The floats length to beam is 22 to 1. The float buoyancy appears to be less than 100% due to the requirement of trailing but the wide beam would help stability.

The folding system is interesting with 127 mm sliding half aluminium beams that slide into transverse slots in the main hull. The beams are slightly curved to push the floats down to provide extra stability as the tri is folded. The beams have water stays underneath the beams.

The designs construction is plywood with an epoxy saturation covering. The designer specifically tries to reduce the number of parts in his design to simplify construction. The floats flat bottom and simple box shape indicate the attempt to simplify the structure.

The 20 has an impressive amount of accommodation for a 18.5 foot tri. It has a real cabin that is 11 foot long by 5.75 foot wide. The cabin includes a 6.5 x 5.2 foot at the head double berth, a dinette area with water point and stove, transverse table, a retractable toilet, with 5.4 foot headroom.

The 20A Triptych is fitted with the hull retraction system which allows its width to be reduced by the simple handling of the ends without dismantling and in the water: The maximum width of 14.9 foot and can be reduced to 7.9 foot for motoring and to 5.9 foot for transport. This trimaran is fitted with a mast raising and dismasting system using 2 support poles that hold the bottom section of the mast in position as it is moves from the horizontal to the vertical.

The jpegs give the idea. Tomorrow we will do a larger version.

 

The Triptyque 28 is a semi-offshore cruising trimaran offering all the comfort for 4 to 6 people. It is a larger sister of the Triptyque 20A trimaran featured yesterday. The 28 is 28.7 x 22 foot able to be folded to 11.5 foot or down to 8.35 foot for trailing. The weight is 3700 lbs and a displacement 6250 lbs. The 36 foot aluminium non rotating mast carries 535 square foot of sail. The main hull length to beam is about 6.5 to 1 depending on load. The 27 foot long floats have a length to beam of 16.5 to 1. This tri will sail well but is not a high performance racer.

Like all Triptychs, the tri although bulky has retractable hulls allowing trailering without disassembly and is unsinkable. Its light weight of 3700 lbs allows it to be towed by a family car.

But what this tri is about can be seen in the accommodation plan. To quote the designer “The interior space is very large for the size of the boat and comparable or even greater than that of a monohull of the same size: With 1 separate aft cabin with a berth of 1.90 m by 1.45 m, a Breton bed at the front (2 m X 1.50 m) that can be isolated to form a separate cabin, a comfortable saloon convertible into a double berth (1.88 m X 1.25 m), a 2 m long fitted kitchen with the possibility of a 65 l fridge, a bathroom including WC, sink and shower, a comfortable chart table, this trimaran is a successful cruise ship that will satisfy families with 2, 3 or 4 children.”

Its epoxy plywood construction ensures longevity. The Triptych's hull retraction system has no articulation between the arms and the side hulls. The cross arm halves are one unit and can withstand significant shocks without deformation. The cross arm halves slide in slots beside each other in structural units in the main hull. The guides and rollers used during the retraction of the side hulls are not subjected to any load once the safety pins are in place. The rigging forces are taken up through the side hulls by retaining sea stay cables taken from structural bulkheads of the central hull to the floats. Once the sea stays are stretched, the arms only work in compression. However, the cross arms have been calculated to resist the bending generated by the boat's maximum righting torque to provide maximum reliability of the system. The rollers are interchangeable without disassembly other than removing the retaining cable and releasing the arm from the slide: just remove them and put the new ones back in place. A visual verification operation must be carried out every year (without dismantling), and the change of the rollers is no longer necessary since the use of a plastic resistant to heavy loads. The curving of the 180 mm cross beam half tubes will require a specialist to make it consistent over the 4 tube halves. The reason for the curving is to push the floats down for more stability in the folded mode. The same could be achieved by slightly angled straight beams but it will require some designing to maintain the cross beam length and not to interfere with the other float when folded.

The Triptych 28 when folded for port is about the size and has the manoeuvrability of a monohull. Launching and getting onto a trailer is very easy. From the trailer to the water takes 1 hr 15 minutes with release of the straps, to water, mast lifting and installation of the sails and boom. Recovery from the water to the trailer takes 45 minutes. There were 2 adults and a 15 year old child doing the work according to the designer.

This tri is for those who like trailable trimarans but want more accommodation. It a very interesting approach which sacrifices some performance (this boat is still fast) for the accommodation. The jpegs give the idea.

 

This was very interesting to me as Lock did this sometime around the time he did that sportfishing cat Tara Vana . Tara Vana inspired me to draw up my sportfishing idea with its aftmast as well. Then when I later argued for that mast aft idea I made reference to Shotover. Lock eventually attended the Annapolis Boat Show one year shortly after and we met meet,...but never got the chance to sit down and discuss the aftmast ideas in more detail.

Thanks, ....well presented. I was unaware of that gentleman's second boat with the double mast.

PS: Another Tara Vana article
RunningTideYachts, Ltd. - Archives http://www.runningtideyachts.com/archives/TaraTour1.php

 

Fallguy 1000 is an occasional poster on this site and has his own blog started in August 2017 which after 160 pages is still going today. Why is it of interest? Because the blog teaches you something on every page.
Woods Skoota 32DM - Bateau2 - Builder Forums https://forums.bateau2.com/viewtopic.php?f=12&t=62495&sid=3aac2475d41ecde244583c1f68c16a09

Fallguy choose Richard Wood's designed Skoota 32DM (a power cat 32 x 16 foot that can be demounted into a 40 ft container for transport). The build is getting done with 12mm corecell and Silvertip System 3 epoxy from bateau.com using developable panels built with vacuum and a full female frame. Richard Wood's designed the boat when Fallguy told him it was going to cost Fallguy $55,000 to move a fixed Skoota 32 to San Diego and when Richard decided the Skoota 28 was a little small for his wishes. So, Richard designed the Skoota 32 to suit. Fallguy is building the boat in Minnesota, near Minneapolis, in his garage.

Fallguy explains not only what he has done, but what he could have done better and writes about what has failed. He is learning as he goes. What you gain by reading the blog is hard won experience and solutions to many problems you may not have even thought of. He also has made some interesting thoughts on the overall project.

EG. “The Skoota 32 is only specified in foam. The Skoota 36 is only specified in ply. The Skoota 28 and Skoota 30 are specified in plywood. A sheet of 12mm 5# corecell is about $150. A sheet of 9mm ply is ???. But the differences are much larger. The corecell laminate is 800-900gram glass and the glass for the Skoota 28 is ? 200 gr glass on the plywood. The Skoota 28 does not require a vac table even. And vac bagging is super tricky. I think a lot of my problems bagging were related to peelply. I digress, sorry. Anyhow, the laminates are about 4 times heavier. And then the epoxy used is much higher, despite it being less at the end. Typically epoxy is 1:1, so a 12 oz/yd or 200gr glass uses 12 oz of epoxy per yard. But a 21 oz glass uses more like 29 oz glass in the bag to yield 11 oz resin at the end. Or a staggering 18 oz of waste. I am using a bit much resin for sure, bit waste rates of 14-18 oz are typical.

And then the labor is also astronomical. A ply boat is laid up with a frame and the glasswork is external. So the cost difference between a foam boat and a ply boat is truly astronomical. Had I understood this better, I would have certainly built a plywood Skoota 30, but lost the use of the hull spaces as sleeping berths.”

This is a long read but worth it. Please also understand this is a power cat capable of powering into 10 foot seas at 20 knots plus in the Pacific Northwest of the US where there are occasional floating logs etc. The hull structure is strong with heavier layups than sailing cats of similar size would have. But the build issues are similar, especially the beams etc. The jpegs give the idea of the cat.

 

I just had a quick look at the site. It is interesting that he built the boat in foam but with chines. IMHO that is snatching defeat from victory unless you need to because you use a vacuum table. The poor guy then has to fair a sharp edge where the foam panels meet on the boat. Then he doesn't seem to use anywhere near enough filler. One of the first things I learnt in boatbuilding was to avoid sharp creases wherever possible. We tend to think of building as just popping together pieces but fairing is a huge part of any job. So reducing fairing time, by getting away from sharp lines saves time. I would have gone round bilge for foam construction or used ply from 300mm above the waterline with heavily radiused joins. The boatbuilder is a huge variable in construction. Some people take a huge amount of time whereas someone like Peter Snell from Easy catamarans, could knock a great boat like the Skoota in ply in about 4-6 months full time. He built a ply 38ft Piver in 4.

 

I will get back to sanity tomorrow but I saw this and said “I use to draw boats like this when I was a teenager”. The boats I drew were roughly the same shape, 60 foot long, had similar accommodation and were steel. Not very practical or fast. As I matured, I understood there were 2 paths in multihull design. Reasonably to very fast boats that did not depend on engines to get places, and floating accommodation units that satisfied those who wanted a hotel accommodation, air-conditioning, daily showers and go in any direction wanted, in spite of the wind direction.

THE SAILING RESORT is a 86' x 41.9 foot trimaran design fulfills the clients brief of literally a sailing resort very well. There is going to be 5 of them operating by late 2022 (ignoring Covid). They are designed for a very intensive charter program. The tris will “Offer high-end hotel services comparable to a 45 meters motoryacht and can accommodate 12 to 18 guests in 6 VIP cabins ; she has a dedicated crew quarter in the central hull. THE SAILING RESORT has also hybrid propulsion to allow the guests to discover protected natural areas, where the others yachts can't access.” According to the advertising the tri will have “Equivalence of 4 Star hotel service and quality.” And be “High profitability on charter activity with a living room area (main state room) of 830 square foot, a main deck area of 2700 square foot and a flying bridge of 1350 square foot.”

This floating resort is 86 x 41.9 foot weighing 112,000 lbs and displaces 146,000 lbs. It carries a schooner rig with two 92 foot masts and about 6500 square foot of sail with full sail including the fisherman sail between the masts. The hull length to beam is about 9.2 to 1. But the real issue is the underwing clearance and the wave interference between the hulls and underwing when even sailing/motoring in even a slight seaway. The total wetted surface on this design in a seaway would be high. This tri will probably motor faster than its capable of sailing and to maintain its hotel status it probably will not go over 10 knots as the passengers may have their wine glasses fall over. The power is two 110 KW (about 150 HP) electric motors with two 28 kilowatt thermal generators providing the electrical power. And this boat will require electrical power even when anchored to drive fridges, aircon, TV’s, Internet, water systems, air compressors for diving gear etc.

I do not know what is structure is but my guess would be aluminium lower portion and foam glass from deck level up. The furniture alone would probably cost more than most of our boats.

Do not get me wrong, the designers PHR design and Naval Architecture have done an excellent job meeting the clients brief. And from PHR web site their other work indicates they know how to design a fast cruiser racer multihull or monohull. It’s just I prefer multi’s that can sail upwind not use engine power to go upwind. Jpegs give some detail.

 

Catsketcher. I agree with you, which is in part the reason I put up Fallguys site. He is doing good work but there are alternate ways to build a cat. Fallguy acknowledges this with his quote about building in ply versus foam glass.

Experience comes in 2 ways, you either do a lot of up front research and learning from others or you go straight in and learn on the job. Sometimes if you are creative and not locked in by the past you create new fast techniques (EG Denny) but for the majority of us we learn from other's or our errors on the way. The reason for this thread is to provide knowledge to help people understand multihull structures. Your thoughts Catsketcher are invaluable as you come from an education background and think through an issue before starting.

Yacht designers also think a design through before a person builds it and if they have the experience can make it simpler to build. But a home builder does not always understand their are ways of simplifying the build and a little extra work up can front save a lot of fairing latter. As one older boat builder told me when I asked "Whats the easiest way to build a boat?" His response "The hard way!". In short do it properly first time and don't take short cuts.

 

Having had more of a look through Fallguy's blog I dips my hat to him, but would caution anybody in following his lead. Again it has to do with all over build time. There are just a few things that cause heaps of issues. Vac bagging all parts as panels is one headache I would rather avoid. A good worker with a squeegee and peel ply can get close enough to vac bagging to get by. I get that you get nice finsihes from the table ( I did this 20 years ago) but you still have to fill the weave anyway. What worries me is that bending foam with curved hull shapes with vertical strip foam will allow you to laminate up the whole hull side in one go. Sure you have to fair the hulls but in reality, and this may surprise people, fairing the outside of hulls is rather fun and it is pretty easy. As long as there are no creases! Give me 10 square metres of hull side rather than a 1 metre of a chine. Do what Schionning and Oram do and hide the chines under water. Schionning even goes so far as to have a chined boat there there are multiple chines under the water and then strip construction for the deck radius. Because fairing is easy and fast when you don't have creases or chines. If I was Fallguy I would have asked Richard for a round bilge design to make out of foam or just gone ply. Ply is lovely to work with and a great material with epoxy. Use foam for decks but for hull sides where there are no stringers ply is great.

Vac bagging is a good way to save weight but with the money you put into making plastic waste you could just make a slightly larger boat, or save money for more fuel, or buy lithium batteries, or something. I loved bagging in one way but it did slow me down. You could bag a vertical strip foam hull all at once if needed but large parts are harder to bag. I have never bagged a boat for myself, I could never justify the cost when I was paying.

I wouldn't build a boat like this, the sharp creases scare me silly. I would want to build a vertical strip foam, better looking and better performing hull or at least in sheet with large radius edges. Which is not much more hassle to fair and which will have better resale and probably be faster to make. But Fallguy is smarter than me in many ways - he didn't design and build prototypes for over a decade. Boats are traps for the unwary and once you get in deep you have nowhere to go but ahead. Anyone who finishes a boat project may not have the best method but they sure are super stubborn workers and deserve plaudits from all.

 

I do not have enough experience (or education) to understand it (plus, it is a huge project, very detailed description, maybe I missed a lot), but it seems that the "Poor guy" has an ply design "adapted" for foam composite. Flat sides, chines etc. but he build the panels, instead of cutting them from 4x8 sheet material. He went for the vac bagging as a way to make the best panels, then it logically has to continue with fairing to get to the desired quality finish, the way a ply builds go? I admire his work, but hope to find a better way.

 

There was another builder who built a Scarab trimaran out of foam panels. He could have built nice smooth and easy to fair curved shapes with a Farrier design but did similar to fallguy and made flat sheets that then were joined with many above water chines. The joins needed secondary bonding strips and lots of fairing and so he ended up as Fallguy has with a chined boat that is may be a little weaker than a smooth non vac bag foam boat. I can understand Rob Denny with his flat panel construction because like Oram and Schionning he hides the chines, but I don't understand using foam, that can so easily be made into any shape and then making it into flat panels with sharp edges - to be so close to a seamless and smooth hull panel and then make it in sections - I don't get it. If you want flat panel, go with ply or Duflex, it is a great material. But ply would be well rounded at each chine making it easier to fair. With a chine log at each chine you can grind off huge amounts of ply to give a very nice and rounded edge - sort of like a Searunner or Crowther Twiggy chine.