Multihull Structure Thoughts

Discussion in 'Multihulls' started by oldmulti, May 27, 2019.

  1. oldmulti
    Joined: May 2019
    Posts: 959
    Likes: 492, Points: 63
    Location: australia

    oldmulti Senior Member

    After comments about multi million dollar cats being unloved, I present a more a more humble cruising cat for study. The Raku 35 is a new design from Tony Grainger. The Raku 35 is 34.75 x 20.2 foot that weighs 8000 lbs and displaces a maximum of 11200 lbs. The 50 foot mast carries a 475 square foot main, 195 square foot self-tacking jib, 430 square foot Code 0 and a 715 square foot Gennaker. As with all Grainger cats the rig can be a fixed aluminium rig to a fully rotating Carbon fibre mast with fat headed main. The hulls have a length to beam of 11.6 to 1.

    The draft over the spade rudder is 3.1 square foot. The keel options are a fixed low aspect ratio or if you want more upwind performance a set of high aspect ratio daggerboards. The hull shape being a cruiser has its maximum rocker and more buoyancy further forward than eg the Livewire 28. There is still a reverse bow but it’s not as aggressive with more freeboard. The underwing clearance is 2.4 foot. The mast is 45% from the bow.

    The accommodation layout is good. It has a serious double berth in a good location aft of the mast and 2 single berths aft. The main cabin has 6 foot headroom where you walk and sitting headroom forward. The galley is in the hull with 6.5 foot headroom. The loo is forward in one hull. The cockpit/main saloon entrance is large allowing the semi outdoor living area feel.

    The structure is mainly foam glass flat panels with rounded chines. The hull bottoms are built on a male mould and mated to the flat panel hull sides and bulkheads. There are no specifications yet but similar cruising cats have 600 to 800 gsm e-glass triax on the outside 15 mm pvc foam and 600 gsm e-glass biax inside in vinylester resin, doubled e-glass below the waterline on the exterior. I suspect there is carbon fibre in the top and bottom flanges on the bulkheads.

    The design has minimal number of bulkheads and enclosed spaces. This is important. Each time you enclose a space, build a draw or cabinet door, put in an additional bulkhead your build time, cost and build hours increase. Do what is required for structural strength and minimum storage spaces, but if you want a fast build, do not get to elaborate with interior furniture, cabinet doors etc. EG the double bunk requires minimal framing to allow air circulation under and the aft bunks are a flat panels on semi bulkheads, simple and very fast build.

    I spoke to Jeff Schionning when he was building a 36 foot Comos cat years ago. He was very upset that the client had asked for a fold out lounge/double bed in the main cabin. Not only did this lounge/bed weigh a lot and could only be purchased with a steel frame which was going to rust, but a lot of simple storage space was lost. Build time, cost and maintenance up.

    I suspect the Raku 35 was designed due to “home builder” demand due to the Raku 32 being turned into a production cat. This will be a fun higher performance cruising cat that can travel anywhere warm that will be suitable for a family. The jpegs give the idea.
     

    Attached Files:

    Last edited: Sep 10, 2020
  2. oldmulti
    Joined: May 2019
    Posts: 959
    Likes: 492, Points: 63
    Location: australia

    oldmulti Senior Member

    Slingshot made comment that he thought a good cruising boat would be a Livewire scaled to 18 meters with a small bridgedeck cabin. Tony Grainger has not designed such a cat but has done a 40 foot version of the Livewire cat. The Livewire 40 is a very high performance cat that is 40 x 24.5 foot weighing about 5000 lbs and displacing about 7000 lbs. The Livewire 40 carries on a 55 foot rotating carbon fibre mast a 710 square foot mainsail, 235 square foot self tacking jib, 615 square foot Code 0 and a 1140 square foot Gennaker. The length to beam ratio would be about 16 to 1 with a 0.58 prismatic coefficient.

    To give a feel about the above numbers, the predecessor to the Livewire 40, a racing cat called Flat Chat OMR rating certificate shows a 40 x 25 foot cat that weighed 5860 ls and with crew displaced 6720 lbs carrying a 615 square foot main and a total rated sail area of 1100 square foot.

    Now we come to structure, not specified for the Livewire 40, but probably foam e-glass in epoxy with carbon fibre options. Flat Chat was built 300 gsm unidirectionals either side of 10 mm western red cedar strip planking in epoxy. The real issue with Flat Chat was the weight of the fiberglass crossbeams. They were put on a scale and the main beam weighed 625 lbs and the aft tube weighed 280 lbs. A Shockwave 37 cat beams were 208 x 161 mm aluminium tubes that weighed 5 lbs per foot. If the aluminium beams were used in Flat Chat they would weigh 125 lbs for the aft beam and 125 lbs + 70 lbs for the dolphin striker etc for the main mast beam. A possible weight reduction of 575 lbs (remember I am not a designer). The crossbeams on the Livewire 40 are Carbon Fibre tubes of about 380 x 300 mm which hopefully be a lot lighter than Flat Chat’s tubes.

    The Livewire 40 hulls are 4.8 foot at the gunnel and have about 5.5 foot of headroom. I am sure there are 4 single bunk spaces, a seat and a small galley/table space. Not exactly a cruiser, but sufficient for a weekend.

    Now we get to Slingshots idea of a “Livewire 18 meter”. If we use the existing Livewire design ratios as the base we would end up with a 59 x 36 foot cat that would weigh about 14,000 lbs and displace about 18,000 lbs and carry an 82 foot rotating carbon fibre mast and about 1500 square foot of mainsail, 1300 square foot code 0 and 2500 square foot Gennaker. Now this 18 meter cat would go like hell but at what cost. It would take at least 3 times the materials, 3 times as long to build and the rig would cost 3 times the Livewire 40 rig. The result is a 500 to 600 mile per day cat with peaks of 30 knots.

    A Livewire 40 could do 400 miles days in good conditions and peak at over 25 knots. So, we have an 18 meter cat with a bit more accommodation but it would cost at least 3 times the cost of a 40 footer, but only sail about 25 to 40% faster.

    The jpegs are of the Livewire 40 and a jpeg of Flat Chats OMR with the last 2 jpegs are of Flat Chat.
     

    Attached Files:

    Last edited: Sep 12, 2020
  3. oldmulti
    Joined: May 2019
    Posts: 959
    Likes: 492, Points: 63
    Location: australia

    oldmulti Senior Member

    The Raku 40 is a Grainger performance cruising catamaran design that is 39.33 x 23.5 foot weighs 11,600 lbs and displaces 15,500 lbs with a over load maximum displacement 20,000 lbs. There are 2 rig options. The standard rig has a 58 foot mast with a 645 square foot mainsail, 265 square foot jib, 485 square foot code 0 and a 870 square foot gennekar. An optional racing rig has a 62 foot carbon fibre mast with a 700 square foot mainsail, 710 square foot code 0 and a 1100 square foot gennaker. The hulls have a length to beam of 13 to 1. You can have low aspect ratio keels or daggerboards for better upwind performance.

    The accommodation layout has several options ranging from 3 double berths with 2 bathrooms, to an option with 2 doubles, 2 single berths and 1 bathroom. The main saloon has the galley, dinette and other seating in each option.

    The structure of the Raku 40 is mainly flat foam glass or Duflex panels with strip planked chines or a separate male molded foam glass hull bottom shoe. The bulkheads are foam glass with top and bottom carbon fibre flanges in them. Any bulkhead openings (eg doorways) have carbon fibre edging for reinforcement. Many internal furniture parts are structural so you have to be careful if want to make changes to the internal layout. There is a kit version available.

    The standard Raku 40 with a racing rig and daggerboards would be a fairly fast design but Tony Grainger has decided to introduce the Raku 40 Lite to increase performance and simplify construction.

    The RAKU 40 LITE is a sportier version of the RAKU 40. Now here is where the fun begins. Depending on the source of information depends on what the Raku 40 Lite is. One magazine says it is a “standard Raku 40” with the aft beam and end of the cockpit shifted forward 500 mm with the cockpit being shortened. The heads of the aft double bunks are pushed 500 mm forward into the main cabin area which reduces the standing space available in the hulls. The magazine article provides a “drawing” of the Raku 40 Lite as per attached jpeg.

    But Grainger’s web site says the Raku 40 Lite is a “Raku 40” with “The extra wide opening in the saloon bulkhead (2.3m) gave us the opportunity to compress the cockpit space and move the aft beam forward to trim some weight, but more importantly it moves the centre of gravity forward giving us more liberty with the shaping of the underwater hull profiles. The cockpit layout works well with tiller steering too. This is a rocket ship and a cruiser in the same package.” A Raku 40 Lite with daggerboards, racing rig and optimised hull shape will be a very fast performance cruiser.

    There is a big difference between the 2 concepts. Concepts one is the “standard Raku 40” with a quick redraw of a few bulkheads and simplifying the accommodation, the second concept is a redesign of the hull shapes, bulkheads and accommodation.

    If the Raku 40 Lite with a shorter wingdeck has a redesigned hull shape to take advantage of the reduced weight aft then the Raku 40 Lite may also have a slightly reduced displacement as well. Even if the displacement is reduced by EG a 1000 lbs and the centre of gravity is more centralised, it will provide a improved performance at a reduced coat and simplified build which should reduce build time. We are talking EG 5% improvement differences in performance cost etc.

    As a comparison the Seawind 1160 comes in a Deluxe version that displaces 15400 lbs (probably read weight), the Seawind 1160 Lite version displaces 14300 lbs. Seawind reduces the displacement by lighter infused hull layups and lighter interior furniture specifications. EG lighter tables, fabric liners not “timber” liners etc. Also, the engines in the Lite version are outboards versus desils in the Deluxe version and the Lite carries 90 litre less fuel which is a major weight saving. A 1100 lbs weight (7%) reduction helps performance or load carrying ability.

    The initial jpegs are of the standard Raku 40 jpegs. The second last coloured jpeg has the standard Raku 40 specs on the top half but the layout of the Raku 40 Lite in the bottom half of the jpeg. The final jpeg is a perspective of the Raku 40 Lite.
     

    Attached Files:

    Last edited: Sep 12, 2020
  4. catsketcher
    Joined: Mar 2006
    Posts: 1,288
    Likes: 136, Points: 63, Legacy Rep: 790
    Location: Australia

    catsketcher Senior Member

    Thanks as always Old Multi - great stuff.

    It is very hard to draw a good cruiser - in some ways a cruiser should be really heavy. Then you will reduce accelerations and improve comfort. But this slows you down. Getting the balance right between comfort when sailing and speed is tricky.

    When dealing with design numbers there is one number that is vital that no-one talks about - acceleration. This is probably because it is pretty tricky to measure due to differences in sea state but with CFD we should be able to produce numbers that show accelerations in different seas. Any accelerations produce a force and it these sea induced forces that make it hard to live on a boat underway.

    For most of my cruising in winds of over 15 knots I am slowing the boat down. This is because I want to arrive happy, refreshed, calm and with no breakages and a partner who still wants to go sailing the next day too. So when you need to start to hold on we slow down. Sailing an ultra light multi, with a huge rig is great for racing or for bay blasting but not for long term cruising. Going fast whilst not undergoing huge accelerations with little fuss and stress, that is clever design and is not found with huge rigs and high power to weight ratios. It is found with efficient rigs, easily driven hulls, well designed deck gear, well thought out deck arrangements and moderation in rig size and weight.

    I could make my mast taller, my boat lighter and potentially faster, but my wife already finds our modest boat a tad imposing to sail. I have made the systems easier to use over time but in reality a cruising boat should be designed and built so that the more timid and less strong crew can work the entire boat - otherwise you may find yourself cruising alone.
     
  5. oldmulti
    Joined: May 2019
    Posts: 959
    Likes: 492, Points: 63
    Location: australia

    oldmulti Senior Member

    For those who want a really fast proven ocean cruising catamaran that is capable of 700 mile days with peak speeds of over 40 knots. You will only need about $US 4 million. It started out as Club Med then was converted to a cruiser Ocean Pearl. The size is 111 x 54 foot and displaces in its modified form 50,000 lbs. The sail area is huge as is the over 150 foot wing mast. The advertisement says the boat will cruise at 6 knots. Look at MULTIPLAST Maxi Catamaran for sale in Spain for €2.490.000 (£2.305.598) https://www.rightboat.com/id/boats-for-sale/multiplast/maxi-catamaran/rb197079
     

    Attached Files:

    Last edited: Sep 13, 2020
  6. oldmulti
    Joined: May 2019
    Posts: 959
    Likes: 492, Points: 63
    Location: australia

    oldmulti Senior Member

    The RB 34 is part of a series of motor sailing cruising catamarans from a company in Thailand. This is about the cat NOT about the company that produces the cat, which has been subject to a 35 page thread discussion. The RB 34 is an Angelo Lavranos, naval architect design and is 34.3 x 19.5 foot displacing 16500 lbs and carrying a wooden mast (yes the mast and boom are in cedar/epoxy/biaxial) with 540 square foot of sail area in a sloop rig. The mast can be raised and lowered without crane. The length to beam on the hulls are 7.85 to 1. The cat has fixed keels. The underwing is 2 foot of the water.

    The RB 34 was a semi production boat of which at least 7 have been produced. They have 2 models with a delivery time of about 8-10 months. The models are the RB 34 Base built of plywood and outboard motors or the RB 34 Luxury built in honeycomb construction, luxury interior and 2 x 14 hp sail drive Yanmar inboard motors.

    Now we get to what this boat is all about. The accommodation is large for a 34 foot cat. How large, 4 double berth cabins and 2 heads in the 5.2 foot wide hulls at gunnel level. The 16 x 14 foot main cabin with 6 foot headroom contains the galley, dinette chart table and entertainment centre (see the jpeg). There are forward and aft cockpits and a flybridge.

    The plywood version is covered with e-glass in epoxy. The sandwich construction is in Nidacore (honeycomb), biaxial and epoxy resin. Either cat has a light filler of epoxy/microballoons covered with epoxy paint. All stainless steel used is all AISI 316, tig welded and polished.

    I have a small problem with Nidacore used in hulls. In comparison with commonly used PVC and similar foams, Nidaplast shows similar values for compression strength and slightly lower values for shear and tensile strengths. Being more flexible, it has lower stiffness (modulus) properties. Therefore, design and application of composites using Nidaplast must take into account these parameters. But the main issue is the Nidaplast approval from Bureau Veritas which says: “Application / Limitation of use: Decks, superstructures, and accommodations for yachts, fishing vessels, service and working ships, and inland boats according to the Society’s rules”.

    The reality is several boats have used Nidacore construction throughout but I also have seen a person trying to get water out of individual 8 mm cells that had mysteriously gotten into a monohull hull structure.

    This is a pure cruiser as I suspect 15 knots would be a rare event in this cat. Catsketcher comment about acceleration is accurate, the comfort of a multihull depends on many factors but having the balance between performance and cruising capability is one of the harder things to achieve. This boat is about the cruising end not the performance end. The jpegs give the idea and please study the hull shape which for what this cat is good. Angelo Lavranos is probably over 70 and appears to be retired.
     

    Attached Files:

  7. oldmulti
    Joined: May 2019
    Posts: 959
    Likes: 492, Points: 63
    Location: australia

    oldmulti Senior Member

    Today is not as much about the specifics of the catamaran but what is required to sail the catamaran in higher winds. The cruising catamaran chosen is the Nautitech/ Bravaria 40 open designed by Marc Lombard. The 40 Open was chosen because over 100 have been produced and reflects a fairly modern version of a cruising cat. The Open is 39.3 x 22.5 foot weighing 17300 lbs and carrying a 58 foot VMG aluminium spar and sail plan of 979 square foot. It has a self-tacking jib and a gennaker on a continuous-line furler attaches to the bowsprit. The cat has fixed keels and a “high” underwing clearance (for a production catamaran). The boat is fairly light for a 40 foot production cat, with solid glass below the waterline and a cored infused laminate above.

    When in cruising mode, the Nautitech 40 Open can average 7.5 knots in EG 18 knots and do 11 knot averages in 35 knots. It can tack through 100 to 110 degrees.

    Now what to do in higher winds. In general, in a cruising mode, you should reef your sails to the maximum gusts you expect. This means you are often under powered but in cruising mode with a reasonable cat you will still be able to average a good speed. EG the Open 40 may average a knot slower when well reefed down, but you will be much more comfortable and rested.

    So, the Open 40 sees a true wind speeds of 18 knots its time to put in the first reef in the mainsail, when the true wind gets to 22 knots it is time for the second reef in the mainsail. In a true wind speeds of 22 knots to 28 knots progressively reef the furling solent jib by up to 60%. When the wind is hits 28 to 30 knots true wind speed put in the third reef in the mainsail. Please remember the True wind speed is a lot less than the apparent wind wind speed upwind. When you read the jpeg charts below for the Open 40 they are talking about the Apparent wind speed.

    When the true wind speed is 30 Knots and gusting, it is time to furl the jib away and sail with a fully reefed mainsail only In very windy conditions the fully reefed main can be set to luff and spill wind (going upwind) or sheeted in going down wind which will allow you to sail in very strong winds without damaging the rig or sails. Or get the mainsail down and run before the wind bare poles, trailing a drogue.

    In a Squall / Gust. If you spot a nasty squall coming, prepare early. Furl the jib in and head onto a beam reach. Spill the wind by luffing the main and keep it on a beam reach through the squall. Unfurl the headsail, once the squall has gone through.

    The above guide is when a person is sailing in fast cruising mode. In the real world if you are me or Catsketcher you hit about 8 knots boat speed and you are going fast enough. You reef down the boat down to maintain the 8 knots of speed even though you may be able to average 12 knots. I have sailed on many cats that could average 15 knots boat speed in stronger wind conditions but only when racing. You are personally thrown around at 15 knots boat speed and you are always on edge to react to any wind or course change that may be dictated by wind or sea conditions changes.

    When you start reefing early your sailing life becomes easy. You have time to make changes as required to meet the wind and sea conditions. BUT this all depends on you having a well set up boat that can be reefed easily under all conditions. Reefing equipment is the one area you spend money on good quality gear. Good correctly sized furling equipment, properly sized ropes and blocks for slab reefing and good winches for adjusting halyards etc. Also PRACTICE reefing as when your trying to reef in 30 knots plus wind speed as you are likely to be hanging on with one hand and only have one hand available for the reefing task. This a lot harder than practice reefing in 15 knots of wind.

    The attached jpegs are first of the Open 40 then the final jpegs are of the reefing charts and diagrams. the final jpeg is the Beaufort wind sea scale.
     

    Attached Files:

    Last edited: Sep 14, 2020
  8. oldmulti
    Joined: May 2019
    Posts: 959
    Likes: 492, Points: 63
    Location: australia

    oldmulti Senior Member

    A little detour into monohulls. The IMOCA monos are very impressive if fairly dangerous beasts now. The mono’s can top 30 knots and require crash helmets to be worn when travelling fast as they throw there crew around fairly badly at speed. One example is Sébastien Simon’s Arkea-Paprec. Arkea-Paprec is a Sam Manuard design. The monohull is 60 foot long by 18.7 foot hull beam wide and displaces 18,000 lbs (yes 18,000 lbs) as the foils do most of the stability work. There are also water ballast tanks to assist stability. The keel is required to right the boat from 100 plus degrees but little else, so the keel is quite light at around 6000 lbs. The 92 foot rotating wing mast carries up to 2800 square foot upwind and 6500 square foot downwind. And remember on some occasions these boats are sailed single handed across oceans and around the world in eg the Vendée Globe.

    The 5 key points that help make this boat fast are (1) Large Foils. They are essential in high speeds. There are different sets depending on the race to be undertaken. A set of these foils can cost hundreds of thousands of dollars. (2) The cockpit is equipped with several "windows" that allow Sébastien to see his sails and the front of the boat. On the previous generation of 60 footers with no forward windows “It was like driving a car with your eyes closed! " (3) The hull is flat and rigid to exploit the full performance of the foils. The bow shape is very full and flat on the bottom with an axe type shape to try and promote early take off for foiling with minimum windage whilst flying. (4) The centre of gravity lowered with the mast foot "sunk" into a "seagull wings" bridge. Also, the keel weight and adjustable ballast tanks which help lower the centre of mass allowing the boat more be more powerful. (5) Versatility. ARKÉA PAPREC is optimised to perform at around 15 knots, the average speed encountered in the Vendée Globe. It is not a typical boat IMOCA designed for certain conditions, it is designed to go fast in many types of weather.

    There was a hint of the speeds these boats can get to. They are designed to average 15 knots around the world. On the Defi Azimut fun trial day many IMOCA’s were put over a straight line course. Arkea-Paprec was the fastest taking 3 minutes and 5 seconds to cover the 1.2 miles at an average speed of 23.35 knots. As I have said these boats top out at over 30 knots. The fastest I have read is 34 knots.

    These boats are carbon fibre, foam, epoxy and nomex. They are very well designed and engineered using high strength carbon fibre and resins. They are 50,000 hour plus builds. The stresses in the keels and foils, especially in the mounting points, on these designs make them harder to engineer than cross arms on high speed multis. They are teaching multi designers a bit about structures and material capabilities.

    The jpegs give the idea.
     

    Attached Files:

  9. oldmulti
    Joined: May 2019
    Posts: 959
    Likes: 492, Points: 63
    Location: australia

    oldmulti Senior Member

  10. oldmulti
    Joined: May 2019
    Posts: 959
    Likes: 492, Points: 63
    Location: australia

    oldmulti Senior Member

    The Minimus 11 project mentioned in this thread page 21 number 303 and page 66 number 976 has been developed further and has its masts and rig on. Details are at Untitled 1 https://www.omick.net/adventure/minimus_ii/building/building.html

    She's an open deck design, 23.75 x 13.3 foot which is about as small as one can go in an ocean-crossing multihull with enough weight-carrying capacity for a crew of two, around 1200 pounds of crew, gear and provisions for 4 to 6 weeks at sea. The launch jpegs have ground tackle, dinghy, battery, all the rigging, personal gear and 500 pounds of food and water. Minimus 11 was just 25 mm over her designed waterline when loaded.

    The materials we're using in the hulls of Minimus II are 1/2" MDO plywood throughout with 25 x 50 mm lumber for chine and sheer stringers. 50 x 50 mm lumber is used for bulkhead reinforcement and deck beams. Raka epoxy with medium hardener and epoxy additives, including wood flour, chopped fiberglass, microballoons and silica.

    The reason for this update is the boat has been launched and had initial sea trials. From trailer to launch took several hours with the installation of the crossbeam rope wrapping being time consuming. The installation and set up of the mast and junk sails also took time. Minimus is not intended to be a trailer sailor but an ocean cruiser. It is very transportable for home storage when you are not cruising.

    Once on the water there was an early morning light breeze where the owners sailed downwind with both mains up. They could hardly feel any breeze and she was still moving through the water at about 2 knots. The next time they sailed in around 15 knots, gusting to 18 knots of wind and they experimented with taking down all sails. Surprisingly, she was still going around 2-1/2 knots downwind under bare poles.

    The 4 masted rig makes her easy to balance and she's very light on the tiller. Another pleasure, inherent to junk rigs, was the lack of flapping sails. Coming about when tacking to windward takes finesse and there working on the best strategy to tack. Getting accurate data on how she sailed upwind was almost impossible given the current in the bay, but she isn't designed for that, so our expectations aren't high for that point of sail.

    There was testing of pounding of the flat hull bottoms. They found that going to windward it didn't prove to be an issue.

    The accommodation there is sitting head room in each of the 4 cabins. We used one hull as the galley with one person cooking in one cabin and the other person in the other cabin. The 2 people can see each other, converse and pass food through the open center bulkhead in the galley hull. They sleep in the other hull, head to head. The bunks are about 24" (61cm) wide and have found the hulls comfortable to sleep.

    The jpegs give the idea.
     

    Attached Files:

  11. oldmulti
    Joined: May 2019
    Posts: 959
    Likes: 492, Points: 63
    Location: australia

    oldmulti Senior Member

    The ELF 25/26 is a Richard Woods design that has been a production catamaran. The ELF 26 is 26.3 x 16.4 foot (can be disassembled to 8.2 foot width for transport) that weighs 2460 lbs and displace 3800 lbs. The 36 foot aluminium mast carries a 246 square foot mainsail, 110 square foot jib, a 160 square foot genoa and a 490 square foot spinnaker. There are other specifications listed for this design by different builders but the above is the most realistic I can find. The cat can be obtained with low aspect ratio keels or daggerboards. The low aspect ratio keels are an integral part of the hulls. They simplify sailing and beaching enormously, yet windward performance (according to the designer) is only a little less than with daggerboards. The hull length to beam is about 10 to 1.

    The Mark 1 Elf 25 was built in Germany. Only a few were made, but some sailed long distances. The Mk2 was an open deck boat and was built, very heavily in solid glass, in South Africa and was extended to 26ft. It was a well proven design. In the 1990's a few were built in the UK with an added a removable cuddy cabin but still transportable. The Elf 26 is now produced in eastern Europe updated, with a modern, lighter laminate and rig. Once again it is an open deck design and available with daggerboards or LAR keels. The transom has been shortened to allow for the simpler transom mounted rudders. Although it is a big boat it is still trailable, each hull is under 4 foot wide. Result, you will see a variety of jpegs of different builds but the underlying design (and molds) are the same.

    The accomodations are basically hull based with 6 foot headroom. It has 4 single berths, a galley and a loo across the hulls. The removable central cuddy available from some builders had a dinette/double berth with in one case a small galley available. The cuddy only has 5.3 foot headroom unless you are standing under the open hatch.

    The construction of this cat varies enormously. The South African model was solid glass with aluminium fore and aft cross beams and a glass main beam. The other versions had foam glass structures with aluminium forward beam and glass main and aft beams. The latest European version has a lighter laminate being built with a claim of 1900 lbs weight and a displacement of 3000 lbs. The real truth is out there somewhere.

    To give an indication of the sailing capability I will quote some owners comments. “At the end of March 2007 I sailed single handed the 900 miles back from the Canaries to Almeria in Southern Spain. On the last day, after three and a half days at sea, a storm of wind of a steady force 8 with gusts to F10 caught me and my Elf catamaran. The Woods Design made 5 to 7 knots without sails and I also used a car tire to slow down somewhat, and to keep control.”

    “Two Elves stopped off at Dassen Island. The trip was a total distance of about 115 nautical miles. The average speed attained during this trip was 12 knots. The boat had 4 adults on board plus stores and provisions for the same for 5 days. I estimate that we had 800kg load. After a slow start the wind slowly picked up to 25/30 knots on the beam. We upped the kite but when it started gusting 35 knots and swells were running at about 4 metres the boat speed was 18 knots with creaking, groaning and flexing but overtaking monohulls like I crazy.” A 6 HP outboard provides 6 knot cruise speeds.

    This is a capable smaller cat that can sail very well. The jpegs give the idea.
     

    Attached Files:

    Last edited: Sep 18, 2020
  12. oldmulti
    Joined: May 2019
    Posts: 959
    Likes: 492, Points: 63
    Location: australia

    oldmulti Senior Member

    Today a small annoyance. Production cats in the mid 20 foot range divide into those that have big accommodation with minimal performance and those that sail fast with minimal accommodation. The “fast cruiser” production cat market does not often commercially succeed. Designs for the home builder market tries to fill the “fast cruiser” gap.

    For example the Prout Ranger 27, Heavenly Twins 27, Catalac 28 etc all have been very successful commercially but in each case they have large accommodation and less than stellar performance, especially upwind. The Hirondelle variations come the closest to a fast cruiser performance cat with reasonable accommodation that was commercially successful.

    There are 3 issues here. The first is internal accommodation space sells because the spouse often holds half the voting rights and is interested in comfort, not upwind sailing capability. If you can put a double berth, 2 singles, a dinette and full headroom galley and separate loo into a small bridgedeck cat it will sell if priced correctly.

    The second problem was described by the builder of the Formula One 26 foot cruiser racer tube cat. People perceive a value of dollars for a given length. A 26 foot boat may sell for $100,000 which would be seen as expensive, but if the cat is 30 foot long, there is no problem of selling it for $130,000. All he had to do was extend the bow and put sugar scoops on the stern and put a larger headsail and fat head main on his cat and his boat would sell and he would make a larger profit margin.

    The third problem is the ease of building a full end to end bridgedeck cat especially from female molds. A Catalac for example is basically a full 2 hull underwing mold and a full deck mold. The hulls are solid glass with a balsa core in the underwing but using the same layup as the hulls. The deck is solid glass with again a balsa insert on the cabin roof and for deck. The “bulkheads” are 18 mm ply panels. This is a monohull type structure and in early cats had CSM chopper gun layups. A fast way to build a cat but produces a heavy cat. No need to make separate fore and aft beams and associated attachment points, netting, specialised rigging attachment points etc. A performance cruising cat will generally have a shorter wing deck require a fore beam and forward net walkway etc. The hull and deck structural layups require foam glass which have to be formed and cut to size before being put into a mold. Attachment points for fittings have to be pre planned and inserts fitted etc. There have to be top and bottom flanges fitted at major bulkheads etc.

    Result, a dumpy full bridge deck mid 20 foot cruising cat has a lot of accommodation and by its very nature and often is easier to build and cheaper to produce. Result they can be sold at a perceived value for money proposition. A performance cat has less accommodation, cost more to build and often has a more expensive rig to provide the performance. Result more expensive for a given length.

    The best example I have of the problem has been done by Pat Patterson who designed the Heavenly Twins, a 27 x 14 foot short waterline, 6.5 length to beam hulls, heavy cruising cat with 2 double berth aft cabins, central cockpit and forward galley, dinette and loo cabins. Over 400 sold. Pat decided to design the Summer Twins a 25 x 16 foot still full bridge deck but with 9 to 1 length to beam hulls with lighter displacement and better foam glass structure. There was less accommodation but still had 2 double berths. Not a commercial success. Why? The sale price was higher for slightly less accommodation, and owners loaded up the Summer Twins with “modern” conveniences so the underwing had less than 1 foot clearance. Result was the performance of the Summer Twins was compromised to the point that over a distance a Heavenly Twins could almost match the newer sister. The Summer Twins had a stern extension to create the Summer Twins 28, which has had some sales success. The extra length made the cat more acceptable for its price but virtually nothing else was changed.

    Jpegs give an idea of some cats.
     

    Attached Files:

    bajansailor likes this.
  13. bajansailor
    Joined: Oct 2007
    Posts: 1,162
    Likes: 307, Points: 83, Legacy Rep: 37
    Location: Barbados

    bajansailor Marine Surveyor

    Just some random scribbles.

    I think there was a thread on here not too long ago by a chap who was wanting to extend the waterline of his Heavenly Twins and make the bows finer by adding an extension to make a sort of 'axe' bow. I guess that this would help a bit, but would it be worth the considerable amount of time, effort and $'s required?

    I remember seeing a Heavenly Twins 26 arrive here some years ago from the Canaries with a family of three on board (I think there was a dog as well). Even when she arrived here after spending perhaps a month at sea the underside of her bridgedeck was kissing the water. So she must have been more laden / deeper in the water when she set off. But she did arrive here ok, after a 2,700 mile passage.

    There are 3 Catalacs here, an 8 m. and 2 x 9 m's. One of the 9 m. cats has been laid up ashore for many years and is in very poor condition - the rig might be salvageable, but I don't think it would be economically feasible to try to rebuild the boat.
    The other 9 m is owned by a small hotel on the west coast, and they use her to take their guests out on complimentary day cruises along the coast - she has been doing this for almost 40 years now.
    The 8 m. has a pair of small diesels with saildrives in her and she was being used as a live aboard fishing boat, but she is also now laid up ashore.
     
  14. oldmulti
    Joined: May 2019
    Posts: 959
    Likes: 492, Points: 63
    Location: australia

    oldmulti Senior Member

    The Dazcat 995 is designed by Darren Newton who designs fast cruiser racers as a way of life. The Dazcat 995 is 33.9 x 20 foot weighing 5800 lbs and displacing 7300 lbs. The fixed aluminium mast carries a 495 square foot mainsail, 240 square foot jib and a 645 square foot spinnaker. The hull length to beam is 11 to 1. The hull shape was optimised with slightly finer forward sections and slightly fuller sterns to try and minimise pitching which was helped by the centralisation of weight in the design. The daggerboards and rudders are carbon fibre.

    The weight in this design has been centralised as much as possible with water tanks, batteries etc close to the centre of gravity. The 995 does not have a fore beam but a prodder again to reduce weight forward. The galley is also down in the hulls to lower weight. The main cabin only has sitting headroom with the dinette floor lowered in a central pod to lower the main cabin roof line which allows the mast base to be lower etc. The focus on lowering and centralising weight helps upwind performance especially in smaller cats.

    The Dazcat 995 (33’10”/10m) was offered as a “structural shell” for owner completion to “fully kitted,” ready for cruising and racing. The basic shell is a vacuum bagged sandwich using PVC foam cores, biaxial, triaxle and unidirectional e glass and Kevlar cloths. The majority of the cat is built in isothalic polyester resin. There are carbon fibre reinforcements in bulkhead cross beams and for foils. All internal surfaces are hand finished and painted to reduce lining weights. The external of the cat comes from a gel coated female mold.

    Dazcat (Multimarine are the builders) however has moved “to infused hulls, but we still hand-lay the deck, as there are lots of individual carbon aspects to the laminate, including uni-directionals, so we find it more controllable not to infuse this,” says Darren Newton the designer.

    The jpegs show the Dazcat 995 being sailed hard as several of the model have been used in racing. The Dazcat 995 has been superseded by the Dazcat 1095 which has the same beam but more displacement and sail area.
     

    Attached Files:


  15. oldmulti
    Joined: May 2019
    Posts: 959
    Likes: 492, Points: 63
    Location: australia

    oldmulti Senior Member

    On page 28 of this thread number 417 we mentioned Frenchman Sébastien Roubinet and a crew plan to sail a hybrid iceboat/sailboat 1,620 miles from Alaska to Spitsbergen. The boat featured there was Babouche 11 which achieved the task in 2013. But as mentioned on page 28 an earlier protype of Babouche was built in 2007 and completed the 4500 mile North West passage over the top of Canada and Greenland in 3 months 21 days. The entire trip was made under sail with no engine assistance. Babouche is unusual. She is part sailing boat, part ice yacht, with metal runners on her hulls so that she can ‘skate’ over ice if her way is blocked.

    Babouche is 24.7 x 16.5 foot weighing 1100 lbs and displacing 2200 lbs. She has a 33 foot mast which carries 590 square foot of sail upwind and can carry 1200 square foot downwind. The rudders and under hull skates are a combination of carbon, Kevlar and metal. There are daggerboards in the hulls.

    The first version of Babouche which had accommodation in the hulls is being discussed here was deemed too heavy at 1100 lbs. 3 later versions (from 18 foot to 22 foot and about 8 foot wide with small bridge deck cabins and inflatable hulls) came after with the 22 foot model featured on page 28, Babouche 11, weighed 440 lbs and carried 484 square foot of sail.

    French composites company Resoltech has provided materials for the several versions of the boat, called Babouche. Nearly all versions of Babouche employed basalt fibers, Innegra (a lightweight high-performance olefin fiber; www.innegratech.com), and Resoltech’s “flexible epoxy system” R1600/1606 helped reduce the weight. For sailing on ice, the boat rides on two slides made of carbon/Innegra/basalt, and Resoltech 1020, engineered for flexibility and elongation. The skins of the hulls were laminated with Innegra and basalt fibers, using 1600/1606 epoxy. The hulls must be able to withstand significant impacts as they bounce over cracks and sharp ice features.

    Sébastien made the floats by hand, shaping a large piece of foam, and then laying up carbon reinforcements all over with a soft epoxy matrix. He then had to destroy the polystyrene plug from the inside to get an empty float and close the transom. Everything—mast, cabin, rudders, and skis—is carbon, made with wet laminations by Sébastien but with the help of some prepreg fabrics, in eg the mast.

    The original version of Babouche succeeded in its North West passage task but was considered too heavy for moving over ice etc for other tasks such as “sailing” to the North Pole.

    The jpegs show the original Babouche could sail very well in relatively flat water. An interesting concept which shows that an unusual concept may work better than people think especially if it is light and has a big rig.
     

    Attached Files:

    BlueBell, Zilver and bajansailor like this.
Loading...
Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.