Multihull Structure Thoughts

Burger mentioned an X cat that Jeff Schionning, designed about 1996, called Growler 1150. We have spoken about the boat before but here is an article about the build. The cat is 37.75 x 24.6 foot with a “displacement” of 6000 lbs. The mast is 53 foot high carrying 805 square foot of sail. The hulls are about 15 to 1 length to beam.

The hull structure is 12 mm western red cedar with 440 gsm 45/45 double bias inside and out in epoxy. Any flat panels are duflex with carbon fibre reinforcement in the X beams and any high stress area’s. The mast base is on the top of the x beam intersection.

The accommodation is limited. There is enough horizontal space but limited vertical space with the headroom between 4 and 5 foot in the cat. This cat is aimed at high performance. I have not seen any comments about the cat actually sailing but the boat appeared to be nearing structural completion. Anyone know if it has sailed?
Sorry about the quality of the last 2 jpegs.

 

In 1986 Cruising World magazine held a design competition. The winner was a “cruising” catamaran by Michael Price. Michael Price was the developer and half owner of the Condor trimaran manufacturer. The catamaran is a semi bridgedeck cat of 42.9 x 28 foot weighing 7365 lbs and carrying 55 foot wing mast of 72 square foot, a 730 square foot main and a 280 square foot jib.

The hull length to beam is 17 to 1 with a prismatic coefficient of 0.56. Two judges of the competition were Dick Newick and Chris White, they said the hull ends were too fine and the prismatic coefficient should be about 0.60 which effectively makes the hull ends fuller by spreading the buoyancy more along the length of the hull. They were happy with the rest of the design.

The hulls are 5.5 foot wide at the gunnel level and are an inverted bell shape to obtain the narrow waterline with some accommodation. This cat has 10 "berths", 2 "double" berths aft under the cockpits, 2 "double" berths in the main cross beam, 2 single berths forward, 2 loo's, a galley in one hull and navigation location in the opposite hull. The internal seating is limited. There is sufficient accommodation for a reasonable cruise but the focus is more on performance.

The structure in the hulls is Airex foam with biaxial cloths in epoxy or vinylester. The main crossbeam structure is western red cedar with carbon fibre reinforcements. The wing mast is laminated from ??. The internal furniture is 3 mm ply on either side of a honeycomb core. A structure that has the potential to be light and strong.

The cat has a Bruce Number 1.79 which suggests high performance. The performance prediction programs said it should be able to average 17 knots and peak at over 20 knots. A set of numbers that I could believe. I do not know if this cat was built, or if the designed was modified as the judges suggested, but if one was built it would have been fun.

 

Roger Simpson gave up designing multihulls years ago and now makes guitars etc. But his plans are still available at Boatcraft.com.au ($1,100) including one of his really nice cruiser designs. The Sine Wave 9 meter is 29.65 x 18 foot with a 7000 lbs displacement and carrying a 43 foot aluminium mast with a 405 square foot main and 235 square foot jib. The hull length to beam is 11.3 to 1. The round bilge hulls have low aspect ratio keels with fixed spade rudders. Optional daggerboards were available.

The cats structure is strip plank cedar hulls and plywood decks and bulkheads with timber framing and stringers. The hulls are either 15 mm WRC or 13 mm Durakore with 580 gsm 45/45 biaxial outside and 440 gsm 45/45 biaxial inside. The decks are 9 mm plywood with 42 x 19 mm deck stringers and some deck beams. Any external surface above the hulls have a 200 or 330 gsm cloth covering to lower maintenance. The bulkheads are 9 mm plywood with timber edge framing. Internal furniture is 3 or 4 mm ply backed with framing. The cat will take about 180 to 200 litres of West type saturation epoxy.

The accommodation has 1 real sea berth, 2 forward “double” berths, a loo area and a galley in the hulls with full headroom. The main saloon has sitting headroom with a big dinette. The accommodation could be changed to allow 2 rear berths and the loo could be put forward. This will make the boat a more practical long distance cruiser. I have spoken to only 1 owner who was happy with its sailing ability saying it could go to windward well. He never pushed the boat and said it could average about 7 knots. He never sailed it over 12 knots but thought it could go faster. The 2 foot underwing clearance was OK with minimal wave slap.

Another owner builder “Aussiebushman” who owns “Little Bear” said “This is a Simpson Signwave and you are right in pointing out the difference between the design water line and the actual, though it has actually come up a bit since I removed building tools, construction materials and heaps of junk. Part of the reason it is overweight is that it was overbuilt - a common amateur construction fault. The scantlings were oversize, also the rudder stocks were 2" stainless, an inboard diesel instead of the 9.9 outboard specified and the decks and cabin roof were double-skinned to stop condensation and heat - all good ways to make the boat strong and liveable but certainly slower than designed.

It is worth mentioning that I have no interest in racing and the 7 to 9 knots I get from this boat is more than adequate, considering how comfortable it is. I lived on board for 3 months and loved every minute of it without feeling cramped or uncomfortable.” The first 2 jpegs are of “Little Bear” the Sine Wave owned by this owner.

A good fun design.

 

A short one on Kites for boats. About 8 minutes. This is a long developing story that may lead to some interesting outcomes, but Kites take a lot of control to optimize there performance.

 

Today we will talk about 2 similar cats. The initial cat is the precursor to the second cat. Designer, builder Mark Pescott built Summersalt 9.2 for his personnel use in about 1990, then put it out as a commercial design. The Summersalt 9.2 is 30.25 x 18.5 foot that weighed 4800 lbs and displaced 7500 lbs. The 38 foot aluminium mast carries a 310 square foot main, 165 square foot jib and a 210 square foot genoa. The hull length to beam is 11.3 to 1. This is a high performance cruiser that if built to weight would have no problems with 8 knot averages and 18 knot plus speeds.

The original design was specified for strip plank cedar with biaxial cloths inside and out in epoxy for the hulls decks and cabins. Mark found that foam glass hulls were easier to build than strip plank and specified foam glass hulls in later builds. The bulkheads were ply with the main cross beams being strip plank cedar with glass reinforcement. The underwing can be ply or durakore. The rudders are designed so the bottoms can be sheared off if they hit ground.

The accommodation again only has 1 sea berth with 2 “doubles” forward and a main cabin that has sitting headroom. The hulls have full headroom with a galley loo and navigation area. A single 9.9 HP outboard is the motive power.

Next came the Summersalt 10.1 which Mark built a version. The Summersalt 10.1 is 33.25 x 20.2 foot which weighed 6200 lbs and displaced 8000 lbs. The 42 foot All Yacht Spars IM 18 181 x 124 x 5.55 kg/m aluminium mast carries a 375 square foot main and a 205 square foot fore triangle. The winches to handle this rig included 2 Barlow 24 for headsails, 2 Barlow 21 for the mainsail and 2 Barlow 21 for halyards. The hull length to beam is 11 to 1. This high performance cruiser can average 8 knots and has done 2500 miles in 18 days on one passage. The cat has peaked at over 20 knots.

The original design was specified for strip plank cedar with biaxial cloths inside and Triaxle cloths outside in epoxy for the hulls decks and cabins. Mark built the 10.1 with foam glass hulls. The bulkheads were ply with the main cross beams being strip plank cedar with glass reinforcement. The underwing can be ply or durakore. The rudders are designed so the bottoms can be sheared off if they hit ground.

Several of these cats are still cruising racing after 25 years which speaks to their structural integrity. As you have seen with the Easy 32, Sinewave 9.1 and the Summersalt 9.2 and 10.1, 9 mm ply for bulkheads, hulls decks with 12 or 15 mm WRC or durakore 580 gsm biax outside, 440 gsm biax inside in epoxy and 12 mm ply or durakore underwings build ocean crossing cats at minimal cost that can perform well. The jpegs give the idea.

 

Petit Poucet PP17 (translates to “Tom Thumb”) is a demonstration of how to attract a designer’s attention. Eric wanted a small tri that was similar to a Scarab 16 but Eric wanted some modifications. The PP17 was just a modified Scarab 16 with more rounded shape, slightly longer hulls, added rocker to add buoyancy, shortened the cubby and give the possibility to sit more forward.

The first version of PP17 is 16.3 x 12.15 foot with a simple folding beam system then became 17 x 12.15 foot in the second version with a Farrier type folding system. The weight of the PP17 was estimated to be 450 lbs.

The Scarab 16 was 16 x 11.25 foot and could fold 7.9 foot. The Scarab16 weighs 400 lbs.

The sail area of both designs is EG a Hobie Rig. The mainsail 124 square foot, jib 48 square foot and a 97 square foot screecher.

The structure of both designs is intended to be mainly 6 mm ply with 84 gsm or 200 gsm e-glass cloth on the outside. The ply is taped together with 400 gsm biax tapes. A foam glass version uses 10 mm foam with 400 gsm biaxial on either side in polyester or vinylester. The crossbeam are e-glass uni and biaxial components that are home built.

So how do you get Ray Kendrick to respond to you. Mention you are going to modify the hull shape to improve its load carry capacity aft. Ray chimed in stating the design was correct to carry a lightweight outboard (5 HP max) and 2 medium sized crew in the cockpit. At 16 foot, the design was never intended to carry 4 crew in the cockpit with a 10 plus horsepower outboard aft. Very valid points.

Now I will say the PP17 is a very nice modification of a Scarab 16 that I hope was built by Eric (he never intended it to be a commercial design). The Scarab 16 is an excellent design for fun day sailing and overnight bay cruising for 2. Good fun. The Scarab 16 design is available for $150 Australian from the Team Scarab site.

PS The Scarab 32 x 24 foot trimaran displacing 5600 lbs design full plans (and I mean the genuine full PDF plans to build the 32) are available for $100 Australian on special for August 2020.

 

That is a VERY GOOD link to a LOT of photos of Elf Acquitaine !!

I first became acquainted with that vessel during the first the initial days of the Formula 40 racing over in France. It later inspired me to think of an X configuration of crossbeams for a vessel design for the first round the world races. I even recorded such back in 2006-2007.

X-Beam and the Gaint
X-Beam and the Giant https://www.boatdesign.net/threads/x-beam-and-the-giant.14679/

excerpted quote

 

So that boat was designed in 1996,....and is still not sailing?? Is that the correct date?

 

The Somersault 26 tri was also known in later life as the Outrigger 26 which started production 1987. This tri was a Dick Newick design that is liked by those who own them. The tri is 26 x 21 foot weighing 1400 lbs and displacing 2000 lbs. The 31 foot aluminium mast section is 165 x 104 mm with a wall thickness of 3.2 mm with 365 square foot sail area drove the tri well. The tri was could be disassembled for trailer transport but it’s a four-hour process to assemble or break down.

The tri’s performance is very good with one owner saying “She sails at wind speed till 15 knots, and thereafter her limit is 18 – 19 knots. Sailing up to 16 knots is no big deal. In the recent Dutch nationals, she was as fast as the Farrier F-28’s and F-82’s. Her Achilles heel is wave action with little wind, in which she tends to Hobbyhorse.” Since, according to the owner, the hull/outrigger shape is dated the tri loves hobby horsing the owner changed his rudder to add a wing to minimise its hobby horsing. One issue, the 26 in racing configuration including bedding etc. weighed 2200 lbs with a crane, for a Texel rating of 1.42 and Mocra TCF 1.20.6. With a couple of degree angle of attack on the “swivelling” daggerboard, she tracks 90 degree tacking angles on GPS.

Later Newick designs have fuller ended main hull and float shapes which would help minimise pitching.

Now the reason for the discussion. Although the whole boat is a production foam glass vessel with unidirectional, biaxial and some carbon in its structure there have been some issues with the cross arms. The tri has 3 hulls which are connected with 4 half crossarms that push into slot sockets in the main and float hulls. The trampolines and rig caps hold the hulls onto the half crossarms. On the beam ends at the main hull there is a bolt through the hull socket to prevent “working” in and out in rough seas which in the end would cause wear on the beam and beam socket.

One owner found significant cracks around the main hull socket slots and a degradation of the crossbeam inner ends. The beam specs from the plans from an owner showed the beams all come from a single mold with the rear beams cut short from the outboard end. The aft beams are sealed while the forward ones are not. Layup specified: 8 plies of orcon s-500 (unidirectional s-glass, 2 plies at a bias) + 8 oz woven roving inside & out of a “blue core” assumed to be a heavy density PVC core. The sockets are thick solid glass layups attached to bulkheads in the main and float hulls.

The jpegs give the idea of the sockets and inner ends of the beams. The first jpeg gives the idea of the beam and socket placement. The sockets are seen in the accommodation shot. There are cracks around the edge of the socket. The beam inner end appears to have cracked due to use. Both parts have been repaired and reinforced with no further issues. Please understand that this tri did not fail whilst sailing BUT if it was not repaired it had the potential for a major failure.

This is a fast fun boat but like all boats, needs to be inspected and maintained.

 

The Vuot Song 76 cruising catamaran is an impressive vessel. What you have not heard of the Vuot Song Shipyard. It was established in 2000 in Vietnam and is among the 5 top shipyards in Vietnam. It has completed 178 different boats from heavy duty commercial boats to yachts and cruise vessels. The Vuot Song 76 is amongst the smallest boats they build. The Vuot Song 76 is 77 x 32 foot, weighs 72,000 and displaces 110,000 lbs full loaded with 12 passengers and 4 crew. Its 95 foot mast carries about 3000 square foot of sail. This cat lives of electric winches, furling sails and a crew to help sail it. But the two 130 HP engines that can drive the cat to 15 knots if required with a 700 miles cruise range at 12 knot.

Why do Vuot Song produce a cat? Because there main business is producing 140 to 160 foot river commercial cruise boats for the Asian market. Clients liked what they saw and asked for this cat.

The Vuot Song 76 is built from steel and has a reasonable design hull shape with 12 to 1 length to beam hulls and low aspect ratio keels which will help it get to its claimed 16 knot maximum sailing speed. After have steered an 84 foot charter cat I can assure you these large cats can get to 15 knot speeds, but unless they have big rudders they have a mind of there own when working through a seaway. Vuot Song 76 draught of 3.25 foot indicates you need to anticipate what will happen next in a seaway as the rudders would not be deep or large.

The comfort level in this cat is high if you can afford the fitout. I am a little confused by the 12 passengers when I can only count 2 double and 4 single berths in the vessel but that’s nit picking. Interesting concept that was built in 2019.

 

CM 52 catamaran is a product of Current Marine from South Africa. The CM 52 is a Schionning design which is 52 x 25.25 foot weighing 14,800 lbs and displacing 19,200 lbs carrying a 65 foot carbon fibre mast and about 1300 square foot of sail. The length to beam of the hulls are 13 to 1 at full displacement. The marketing claims for performance are impressive but I suspect 12 knot averages and 20 knot peak speeds maybe the reality.

Bows are long and slim with an A-symmetric hulls flared inboard giving reserve buoyancy when driven hard reducing the hulls from burying at high speeds and larger waves action. The centre of buoyancy is located aft of the middle of the hull with the weight concentration located close to mid ships with water and diesel tanks located mid ships below cabin soles. Also shifting forward the inboard shaft drive diesel engines reduces the pitching motion at sea and giving the optimum hull rocker starting further forward. The bridge deck living area has been shifted aft with the bow section proportionally lengthened with a shorter over hang at the stern reducing bridge deck slamming. Also the cross beams are curved for increased stiffness and increased the wave clearance when pressed hard under sail. The angled inward carbon dagger boards are standard.

The structure of these boats is interesting. The Standard CM 52 built uses epoxy resin infused composite E-Glass, 80 to 130kg cubic meter PVC Foam core achieving optimal weight and strength. Carbon is used extensively in locally reinforced structural areas. There is also an all carbon version available. The cat has externally-spray finish Awl Craft 2000 in light solid colour of choice/Anti-slip/ Antifouling barrier coatings. They also fair and paint the majority of the internal surfaces. This does add many man hours but does not to pay the weight penalty of paneling to cover up the internal hull.

The hulls are infused in a female hull mould in a 3 stage process by doing this allows us to use a core that has no infusion grooves or slots to feed the resin which increases the resin content. The first stage being the outer skin which is infused in a first stage on to the epoxy primer coating in the mould. The second stage the core is carefully tailored and vacuumed in place with the optimum adhesive paste, once cured the core is then long boarded prior to the final internal laminate is stacked and infused. The advantage of infusing the final internal laminate instead of wet lay-up and bagging is that we will not have creases and folds in the fibre which does not allow the fibres to load evenly therefore not getting their full benefit.

The production method of these boats is labour intensive to reduce the weight of the structure. EG No gel coats, no internal liners etc but if it is done well you have a 52 foot boat that can displace loaded under 20,000 lbs. Should be fast fun as a cruiser. The initial jpegs are of the CM 52, then a carbon mast shot and finally a CM 40 foot hard chine cat build shots.

 

Razor 52 is a cat built by Pacific Seacraft who were very good quality monohull boat builders. Pacific Seacraft most famous design was Flicka, a 20 x 8 foot monohull, that could genuinely cruise the Pacific with 2 people in a full headroom main cabin. Over 400 were built and are still lusted after by many. BUT Pacific Seacraft has been sold to a new owner who shifted manufacturing across the US.

Back to the Razor 52 catamaran, it is 52 x 26.33 foot weighing 17,000 lbs and displacing 19,700 lbs with full tanks. It can carry a 5,700 lbs payload. The 64 foot mast carries an 860 square foot main and a 420 square foot jib. The hulls length to beam is 13.7 to 1. The advertising claims that weighing less than 20,000 lbs (with full tanks) makes for a truly light performance cruising catamaran, which is easily driven with routine cruising speeds of 15 knots+ and capable of 25+ knots.

This sounds familiar. Again, it is a Schionning design the same as the CM 52. The structure of the hull, deck, and structural bulkheads are built with foam cores utilizing carbon fiber and kevlar layers in high load areas to achieve optimum strength with minimum weight. There is a variation of accommodation layouts, especially the internal steering and winching station on the Razor, but the overall shape and structure is similar to the CM 52. The Razor is more suited to what the US thinks is required for cruising, Th CM 52 is more appropriate for South Africa sailing. Take your choice. The jpegs give the idea of the Razor 52.

Next topic. There was a 13 page discussion on Boat design net in 2014 on the build time to build a 40 foot cat. The discussion is wide ranging with many good contributions from people who know what they are talking about. I do not intend to repeat the conversation but the conclusions were interesting. Build time 40ft catamaran https://www.boatdesign.net/threads/build-time-40ft-catamaran.49339/

You can build a 40 footer shell fairly quickly but fairing and finishing the shell will often take more time than building the shell. The material choice to do the build is yours. According to the experience you have you can build in plywood or infused foam glass panels in similar time but in each case joining things together requires time and fairing which slows down the entire process. The quality of the fitout will dictate how long it takes to build the entire boat. A full fit out can double or triple the hull shell build time. One sailor built and launched the shell and literally went cruising with airbeds and camping equipment until he could afford the time and money to finish the boat. A short build time was the benefit.

The actual quality of materials came under discussion. It ranged from a cheap 10 year boat built of exterior ply with a 200 gsm cloth covering to high quality 4 mm ply unsheathed hull on a 25 foot cat that has lasted over 25 years. Fiberglass ranged from polyester e-glass to infused epoxy carbon fibre. Each had supporters and detractors but the only real conclusion you could draw is resale value of a plywood based boat is lower than a glass based boat.

 

That is one of the best threads on this forum and it doesn't just apply to Multihulls. It is a must read for any amateur that wants to build any type of vessel.

 

Now we will talk about a very specific racing trimaran designed for coastal sailing. “Mosquito” is a 22 x 16 foot overall tri that was built in 7 months. The tri weighs 350 lbs without crew or stores. The 35 foot rotating carbon fibre mast (30 lbs comes off a Bimare Javelin 2 HT 18 foot cat) that carries a 215 square foot mainsail, 100 square foot foretriangle and a 215 square foot screacher. Main hull 22 foot long and 2 foot wide with rudder on main hull only. Daggerboards in the floats. Warning some of the numbers are approximate.

Main hull is a partially tortured 3 panels of 4 mm ply with 11 x 25 mm wrc stringers, 2 stringers per hull side plus a keel batten. The 3 panels of 4 mm ply are shaped and angled at about 70 degrees bogged and glass taped before lightly torturing the side and centre bottom into shape. There are temporary 25 x 50 eternal gunnels strips to help form the shape of the main hull. The bulkheads are put in, bogged and glassed into position. The main hull has 25 x 25 mm gunnels. There are 4 mm ply crossarm bulkheads and half bulkheads for the bunk floor. The stringers are then slide in from aft into the length of the hull into slots precut into the bulkheads. Bows have a 10 degree half angle. Decks are 12 mm durakore (1.5 mm wrc skins on 9 mm end grain balsa) that is slightly curved over 4 mm ply deck beams around openings.

Floats 4 mm tortured ply with 4 mm ply bulkheads. Ply panels wired together with sheets held at 20 degrees (angled apart at 140 degrees) and a 90 mm radius epoxy bog keel placed in before folding. The ply panels are folded to the gunnel line and bulkheads are epoxy bogged in. During the process hot wet towels were placed against the plywood to try and reduce the stress build up in the plywood.

Fiberglass daggerboard cases were installed into the floats then the floats were decked with durakore. The daggerboards are wrc with glass. West Epoxy saturation throughout.

The crossarms are about 140 mm diameter aluminium tubes with wire waterstays under. The crossarms run through a fiberglass tube attached to the main hull bulkheads and are bolted onto the floats. PS Yes, the floats have an opening in the float sterns but there is a watertight bulkhead at the rear beam. Something to do with the race rules.

So how fast, try 15% faster than a Tornado cat (with racks to get the crew out further) over a leg of extended coastal race course of 300 miles. This is a fast boat because it has 80% more stability than a Tornado cat. The tri can do wind speed or better up to 15 knots and has topped 20 knots. Again, a very fast home built boat that can handle coastal conditions. The tri has done several extended coastal races over a number of years with very few problems. The accommodation is a little lacking, but it can genuinely sleep one in comfort and store some gear. Every thing else is done on deck. The jpegs give the idea and the web site is Sailing Adventures of SOS: 2011 http://sailnaway.blogspot.com/2011/

 

Yesterday we spoke of a 22 foot 350 lbs coastal racing tri. Now we will discuss the tri that is 15% faster than yesterdays tri. Yes, its up to 30% faster than a Tornado in light to medium weather. But first we will talk about the races the tri has entered around Florida. The Everglades challenges rules state you have to finish with everything you start with (exception food and water). If you launch with EG a beach trolley it has to be onboard for the whole journey. During the race you may have to traverse very shallow waters for possibly tens of miles, cross land pushing or carrying our boat for miles, go up and down narrow channels with overhanging trees and low bridges etc so a removable mast etc is required. In short, a light boat that can be moved on land is mandatory.

So, we now discuss “Scissors” (Sew Sew), a tri designed, built and modified by Randy Smyth (he has done America’s cup, global racing cats, the odd Olympics etc). His tri is 20 x 18 foot weighs 168 lbs (the complete boat ready for racing) carries a cut down 26 foot carbon fibre A class wing mast with 185 square foot of sail upwind and 337 square foot of sail down wind. The tri has a water ballast system in the floats to add to the stability. The tri can easily drop its mast and slew its float hulls to narrow the tri beam for rowing for narrow channels and bridges. This boat has raced for a decade and has many upgrades with differing floats and rigs.

The original boat started with an A class carbon fibre foam main hull extended to 20 foot and lower the freeboard, add 2 very light 18 foot carbon fibre cross arm tubes (less than 50 mm diameter) with fabric waterstays under, 2 very small carbon fibre floats and a very deep daggerboard and rudder in the main hull. An A class hull has EG 200 gsm carbon fibre 6 or 9 mm PVC foam and 200 gsm carbon fibre inside in epoxy. An A class mast weighs under 30 lbs. Starting to understand the 168 lbs all up weight. Remember, Scissors under full sail with its screacher, has more than a square foot of sail for each pound of boat and crew weight when fully loaded for its races.

“Scissors” depends apon the very great skill of its skipper, Randy Smyth, to keep it in one piece, sailing fast and treading very lightly around the boat to use his weight to keep the tri upright. The original tri had a single ply batten mainsail and round bilge floats. The last jpeg shows the tri in a later version with a semi reefable wingsail forward with a single ply “flap” aft and hard chine floats. Scissors went from fast to very fast in light to moderate airs. Finally to allow Randy to have the odd nap whilst racing, "Scissors" has electronic self steering for those longer legs in coastal sailing. A single handed "cruiser"?