Multihull Structure Thoughts

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

  1. oldmulti
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    oldmulti Senior Member

    The Bali 4.0 or Catspace is a charter cruiser catamaran from the company that produces Catana catamarans. The Bali 4.0 is 39.5 x 21.5 foot with a weight of 20,600 lbs and a displacement of 28,600 lbs. The fractional rig has a 52 foot aluminium mast and carries a 538 square foot fat head main sail with a 355 square foot jib, a 600 square foot gennaker and a 970 square foot spinnaker. The hull length to beam is about 7.8 to 1. The low aspect ratio keels draw 3.5 foot.

    The manufacturer: Chantier Catana design team was Olivier Poncin with Lasta Design Studio. They designed a charter and cruising cat that is still capable of sailing well. The design has the accommodation of a 45 foot French cat in a 40 foot length. The accommodation is very creative on its virtually full length bridge deck. The forward cockpit is large, the window between the forward cockpit and the galley can be opened for conversation etc. This may be a problem upwind is strong winds but with 6.5 foot of freeboard on a full bow on a 39.5 foot cat helps reduce an problems. The main saloon and cockpit cab be integrated into one large space giving the impression of a much larger saloon. The hulls can have 3 or 4 double berth cabins each with their own bathrooms and entrances. This is a large amount of accommodation in a small package and requires the 8000 lbs payload to carry the stores, water and fuel tankage 8 people would want on a 2 week cruise. The main sailing steering and sail handling position is on the main cabin/cockpit roof.

    This excellent “open” accommodation has one downside. In really heavy or storm conditions you will have to handle this cat very carefully. I have sailed cats that have had solid water come over the bows and the side decks. I have also had the top of a breaking wave dump on top of a bridge deck cabin roof of a 37 foot cat. Storm window and cockpit door coverings would be a very good thing, especially at the front of the main cabin.

    So how does it sail? Well. It can go upwind at 45 degrees, it tacks without any backwinding and maintains a course easily. The roof top cockpit provides good vision and an excellent control location for all sail handling. According to a tester “Its position is delightful, and taking the helm reveals a special surprise: it is extremely light, precise and it feels as though there is a perfect contact with the rudder blades. The sailplan of the 4.0 follows the latest trends, with the rig set further aft, stepped on the coachroof. The mainsail remains effective with its moderate area (though a square-topped sail is recommended). However, it is the foresail that gives the power.” The test report said: “Any pitching moments are well dampened. The 4.0 doesn’t, however, have the waterline length of its bigger brother, the 4.5 and will start to have a bit of a porpoise effect earlier in big seas. There was no gennaker on our test boat, but with 12-14 knots of wind on the first afternoon, the liveliness of the 4.0 was already noticeable, and we easily picked up to 8.8 knots on a reach under main and solent. The following day, with the wind settling down around 8-10 knots, the other great revelation came when we were on the wind (less than 45° to the apparent, on a flat sea) with the solent allowing us to achieve a very good VMG. This type of sailplan gives a vitality to the foresail, which remains filled even at fairly tight angles. This leads us to assume that the performance under gennaker or spinnaker would be good.” Translation as with all accommodation cats they tend to sail at a speed of about half to two thirds of wind speed up to about 25 knots of wind speed. The good accommodation cats sail well on all points where as older designs/models had limitations. The Bali 4.0 is a 8 knot average with peaks of 15 knot sort of cat. The highest speed recorded in test sails I have read is 9.2 knots in 25 knots of wind.

    The structure is in 3 parts. The outer hull moulds are joined on the keel lines with the bridge deck platform and the inner parts of the hull are joined for a solid structure. Fiberglass hulls have been built with a polyester PVC sandwich resin infused. The Bali has fiberglass infused decks and topside with plywood supports. Bulkheads are multilayer plywood, laminated or glued. The main bulkheads in a polyester sandwich and secondary plywood multiply laminated or glued. The solid foredeck also serves as a structural member and is built of box sections and kept light in weight. The mast is supported partially by a nacelle under the wing deck. Now there is one issue, this cat is built in 2 locations. The charter version is built in Tunisia and other versions are built elsewhere. Result depending on which version I am reading about has slightly different structural components. One version claims to have no plywood in it.

    The jpegs give the idea of a good accommodation cat that can sail well.
     

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  2. oldmulti
    Joined: May 2019
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    oldmulti Senior Member

    Mark Gumprecht not only designed tri’s but also wanted to look after your health. He designed an excellent catamaran for recreational rowing. The Glider is 11.9 x 3.5 foot as the basic boat with row support outriggers that extend 1 foot either side of the cat for a total width of 5.5 foot. The cat can have a small sail rig for those days you feel lazy. This is a one person cat in most situations.

    Again, its constructed from 3 mm and 6 mm plywood with some timber stringers and gunnels etc. The rowing outriggers and rowing seat are extra work but are relatively cheap to build and effective compared to commercial units.

    Again, limited jpegs but the PDF is the full free plans that Mark has released. Thank you, Mark for your thoughts for our health.
     

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  3. guzzis3
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    guzzis3 Senior Member

    Have you found a way to access that forum again ? I thought it was still inaccessible...
     
  4. oldmulti
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    oldmulti Senior Member

    Guzzis3. If I remember I think I found the quote on a Wharram forum quoting Scott Browns forum. If anyone knows how to access themultihull please advise.
     
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  5. oldmulti
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    oldmulti Senior Member

    The Class 6 is a performance cruising catamaran that has a few interesting design concepts. The Class 6 is 62.5 x 29.5 foot that comes in 2 versions. The first is a performance version that weighs 33,600 lbs and displaces 43,700 lbs that carries a 77.5 foot mast with a 1170 square foot main, a solent of 602 square foot, a 1130 square foot genoa and a 3000 square foot gennaker. The next version is the racer model (the performance model needed an upgrade) with a weight of 30,250 lbs and a displacement of 40,300 lbs. The mast is 84 foot carbon fibre rotating with a 1,540 square foot mainsail, a solent of 645 square foot, a 1,323 square foot genoa and a 2,850 square foot code 0. Translation the performance is very fast, the racer version with the same hull deck shell is absurdly fast due to its 8% lighter weight and 24% more sail area in the main and genoa. The length to beam on the hulls is 13.7 to 1. The curved daggerboards draw 8 foot.

    The main design feature of the Class 6 is the “spine” which runs the length of bridge deck and then extends to act as the prodder supporting the forestay. This is a significant structural item that carries the main rigging forces and allows a base for a rigid set of forestays to handle the fraction sloop/cutter rig depending on the situation. If the spine concept is done well, it can also house anchoring arrangements and engine mountings etc. The design team claim the spine can provide wave piercing in heavy seas for comfort and security, extra buoyancy to lift “nose up” in heavy sea and easy sailing with reduced main sail and large front sails on furlers.

    As the Class 6 is a semi production boat, the accommodation layout can be tailored to suit from a 3 double berth cabin arrangement to 6 double cabins with attached toilets. The saloon area is large with galley, navigation and dining. There are large doors between the main cabin and cockpit for an open plan living arrangement. The cockpit can be setup for short handed sailing or racing. Please anticipate very big and hopefully electric winches to control this sail plan. Even hauling up the main would be no simple task, let alone sheeting in a 1300 square foot genoa in a strong breeze.

    The performance version is built from a Gelcoat, vinylester resin infused PVC foam glass, Kevlar and carbon structure. The spine has up to 24 layers of carbon fibre in it to carry the loads. The racing version is built from a painted (much lighter than gelcoat) epoxy resin infused PVC Foam sandwich, mainly carbon fiber and Kevlar structure. There are less loads on the forward hull structure with the spine concept. The forestay loads go onto the spine not a crossbeam then down the forward hulls. Result is you can lighten the forward structure.

    The performance claims cannot be verified as I have not read supporting tests but the statement that the cat “can easily match wind speed with Main and XL Genoa (104m2) in light air (3 to 10kts). If you to fly a Code 0 or Gennaker you could go faster than the wind!” It is a very believable claim. This is a 12 to 15 knot average sort of boat in favourable conditions and would have peaks of 25 knots plus. There are at least 2 in existence.

    An interesting design for those with large wallets and a need for speed. The jpegs give the idea.
     

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  6. oldmulti
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    oldmulti Senior Member

    Othmar Karschulin has launched Kalapuna, a 26 foot proa of his own design. The new boat is a Pacific proa with crab claw sail, flat bottom hull, and two retractable rudders similar to Russell Brown’s Jzero. Kalapuna is 26.25 x 12.5 foot displacing 900 lbs with 2 crew. The crab claw sail was initially 215 square foot on a home made 23.3 foot GRP mast and two 23.4 foot carbon fibre spars. The main hull has a length to beam of 17.5 to 1. The float has a length to beam of 17 to 1. Othmar Karschulin has deigned other proa’s one 16.4 foot long and another 10 foot version featured on page 108 of this thread.

    Kalapuna was designed for coastal sailing and is a camp cruiser at best. Construction is plywood, fiberglass and epoxy. This story will be in 2 parts. The first item will be about the hulls, crossbeams and rudders. Tomorrow will be about the mast, spars, rigging and sailing capability.

    Both main hull and float are built from 6 mm plywood with 20 x 30 mm stringers. The main bulkheads are 6 mm ply reinforced with 20 x 30 mm timber strips. Hulls are completely covered with one layer of 200 gsm fiberglass, and reinforced on keels with one layer of 300 gsm fiberglass. The stem (stern) is made of solid chestnut on the main hull are 30 mm wide at the bottom and 70 mm at the top. To form the bow (stern) the front edge of the 6 mm plywood is screwed onto the stem after they have been pressed together. Trying to hold the plywood with ties as the bows were pressed together was difficult.

    The floats were made from 16.3 foot long 6 mm plywood side panels. Holes were drilled 200 mm apart along the lower edge, as well as vertically along the frame line. Cable ties will later be threaded through there to pull the whole thing together. The cable ties should be at least 3-4 mm thick, otherwise they will tear under the load. Thickened epoxy is poured along the keel line and the bottom is taped with a layer of 300 gsm glass.

    Beams are also made from good quality plywood covered with 3 layers of 650 gr uni-directional glass. The profile of the beams is a hollow box girder with ribs for stiffening of a box with a cross-section 140 x 75 mm. The beams are mounted on the hulls with rubber mounts. The beams were later reinforced with a fiberglass cover.

    The platform between the hulls is 7.4 x 5 foot 6 mm plywood panels on either side of 60 mm thick construction foam to form a stiff base. After trials the mast base was moved from a hull gunnel onto a part of this panel. It needed to be stiff.

    The Proas rudder system works in both directions. The plug-in rudder concept has two sword boxes are built into the boat to accommodate the steering gear. A simple plywood box is built in the hull ends to store the rudder. The rudders are connected to the 25 mm diameter rudder shafts. If the rudder is aligned fore and aft the rudder can be pulled into the sword case by the rudder stock. This allows the forward rudder to be raised when sailing.

    The jpegs give the idea. Othmar has done a good build and development of a fast cruising proa. part 2 tomorrow will focus on the rig and sailing performance.
     

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  7. Dejay
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    Dejay Senior Newbie

  8. oldmulti
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    oldmulti Senior Member

    Othmar Karschulin has launched Kalapuna, a 26 foot proa of his own design. The boat is a Pacific proa with crab claw sail, flat bottom hull, and two retractable rudders. Today will be about the rig and performance.

    The mast is a multi part fiberglass structure. The mold is a 75 mm diameter PE water pipe. The pipe is wrapped in a layer of corrugated cardboard, which is cut off precisely at the longitudinal joint edge. The mast is made from three pieces, each 8.3 foot long. A plastic film is wrapped around the cardboard. A layer of epoxy is put on the plastic film then 3 layers of 300 gsm cloth is wrapped around the tube and any additional epoxy is put on the surface and smoothed. In this way three blanks were made. Each piece of pipe was built about 300 mm too long. The reason for this were short sections that I wanted to use to connect the individual parts to the 23 foot mast mast.

    Then all blanks were connected to the 23 foot raw mast. The 300 mm inter connection sections connect the long sections were inserted into the longer sections and initially screwed together. Now it was also possible to sand the whole mast for the first time (80 or 100 sandpaper) so that a good surface is created for the lamination of 3 layers of 650 gsm of UD glass (UD = unidirectional) in epoxy on the raw mast. The mast is wrapped in one layer of 300 gsm cloth, sanded and smoothed. The mast weighed about 23 lbs.

    The top and bottom spars of the crab claw sail are made from carbon fibre using a similar technique to the mast. Spars are made three GRP kernels of two layers of 300 gsm glass and covered with 3 to 4 layers of 150 gr UD carbon and a 300 gsm glass top layer. Each spar weighs about 8 lbs. As UV protection, they were covered with transparent polyurethane varnish. Both spars broke at attachment points of halyard and mainsheet so were additionally reinforced with at least one additional layer of 160 UD carbon fibre and 300 gsm glass over the mid 10 foot.

    According to the designer builder “The boat is very stable, so that you have enough time to do everything. In general, KALAPUNA sails very safely. Straight ahead as if on rails, rather leisurely. And with two men on the platform, the Ama is only raised a little even in stronger winds (15-20 knots) and otherwise remains well-behaved in the water. That gives a good feeling of security. According to GPS, it “tacks” (shunts) between 90 and 100 degrees. I was really pleasantly surprised. This can only get better after correcting the mast position and getting better with the winch. The speed - wind estimated at 15 knots and speed on the GPS just under 8 knots - but the whole thing pretty close to the wind. If there is enough space we have been traveling well over 10 knots. The quick start with the slightest breeze or gust is nice.”

    The angle between the yard spars were reduced, the sail was cut and now is about 193 square foot. The initially 214 square foot of sail area were too big for single-handed sailing, despite the skipper's 180 lbs weight. A new sail with an incorporating a slight belly was ordered from Elvström in winter 2011. The proa now sails about 5 degrees closer to the wind with more speed in light winds.

    An interesting proa that appears to sail well. Good work. The jpegs give the idea of the rig.
     

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  9. guzzis3
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    guzzis3 Senior Member

    Were there really only 2 built ?

    I went to have a look when he started building them and was interested. I've still got the brochure. I thought he made more than 2!

    I recall one being advertised that looked like it had a central dagger going through the middle of the cabin. I didn't think that was a good idea. The design was brilliant. The hulls straddled the trailer and was carried on the bridgedeck.
     
  10. ThomD
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    ThomD Senior Member

    That was a fun forum. For quite a while I had something like 1/3 rd of the posts there.
     
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  11. oldmulti
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    oldmulti Senior Member

    There was a request for some thoughts on power trimarans. This is a wide topic and I will do a few examples today to show the difference styles of power tri’s. Nigel Irens was the first to popularize this concept with the Ilan Voyager trimaran. Since then, it has broken into 3 basic types. The small (8 to 25 foot) day use fun or transport outboard power trimarans that are designed to either have a displacement or a planning hull main hull.

    The example chosen is done by JBwatercraft, the Eagle 4.6 which is 16 x 6.9 foot. The main hull is 15 x 2.9 foot with the short floats positioned aft with the float sterns 1 foot behind the main stern. The Eagle is plywood construction, weighs 225 lbs and can carry 3 people. The builder states “The slender, deep vee main hull cuts through chop easily, gives a much smoother ride than most monohull powerboats and requires less power to propel. With an 8hp outboard motor and outboard mounted hydrofoil, the Eagle has a maximum speed of around 15 knots, but is happiest and most efficient when cruising at around 10 - 11 knots. The Eagle is most suitable for outboard motors form 5hp - 15hp but can be used with smaller motors. In Initial testing the Eagle achieved over 9 knots with only 3.3hp*.”

    In larger sizes (up to 200 foot) there again is a choice between displacement versus planning main hull shapes. I have chosen 2 examples.

    Kurt Hughes displacement hulled, home build, 38 foot power trimaran. The 38 x 16.9 foot which can be compressed to 8.5 foot (by sliding beams) for transport with a weight of 4,125 lbs and a displacement 5,278 lbs. The standard power is twin 15 HP outboards which can power the tri at 12 knots. 6.5 HP will push it at hull speed. There is a jpeg that described the structure of the 38 foot power tri which is mainly plywood skins over a balsa or PVC core. The sliding beams are mast sections.

    The planning hull version is a production power tri the Azzum 12 meter. The Azzum is 39.5 x 16.4 foot tri has 3 planning hulls which was originally powered by an inboard diesel engine in each float. After a short time the builder changed to an outboard on the stern of each float to provide more performance and cheaper initial and servicing costs. The 200 HP outboards can push this boat along very quickly EG 30 knots. This is a foam glass structure.

    Now we get to the issues. These designs are all very efficient in either displacement or planning versions and have reasonable seakeeping characteristics. But they have limited accommodation and payload capacity, which means you will have limited cruising range and ability to carry the stores required to support eg 4 people for any period of time. Next power tris have their own issues. I spoke to a man at Monty’s marina a few years ago who had a 50 foot displacement power tri powered by a diesel engine. The diesel engine is mounted in a lightweight build structure and required a lot of vibration and sound deadening control. Even so, you still could “feel” the engine as you were voyaging. There were also certain sea angles there were short sharp side to side movements which required course adjustments. Also, for a 50 foot boat he had limited accommodation but was still paying 50 foot mooring fees etc. The fuel economy was very good but the downside is the handling required in close quarters due to the tris overall shape. Mooring alone side is fun.

    The jpegs give the idea. I would prefer displacement power cats but power tris have their place.
     

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  12. Dejay
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    Dejay Senior Newbie

    Thanks oldmulti! I've found two threads about KH38 (1, 2) and as my thinking is now back to a trailerable it's a good starting point.

    About mooring fees for the desired lengths for power tris, are there any multihulls that have been designed so the front falls off? Or maybe hinge sideways?
     
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  13. waynemarlow
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    waynemarlow Senior Member

  14. oldmulti
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    oldmulti Senior Member

    Dejay, look at some of the designs of Gary Dieking who has proa’s up to 32 foot that can be broken into component parts. Also, Phillip Bolger designed a 48 foot mono hull sail boat that could be disassembled into parts for trailing. The extreme 45 foot racing cats have removable bows for transport as does a 44 racing monohull. Yes, it would be possible to have a folding bow but speak to a designer please as the loads are not small and it’s not about the hinges as there has to be secondary connectors to ensure strength around the full joint.

    Today we will look at one nice example of a power tri to finalise power tri’s for a while. Turning Point designed a 24 x 8.5 foot power tri for Nigel Oswald who wanted an efficient powerboat to get around in the San Juan islands with his family. Russell Brown was consulted on the design as he had designed and produced a single outrigger motorboat which inspired Nigel. It is 24′ long and built fairly ruggedly. It uses a 20 hp Yamaha four-stroke and goes about 18 knots with three people on board. A few jpegs of the outrigger are attached.

    Although the Turning Point power tri is 24-feet long it only weighs 250 lbs (500 lbs with motor, fuel, and all other bits). They were sure that we could get to 20 knots with a narrow displacement hull shape and 20 hp. The goal was to make a power boat that was as efficient cruising at 20+ knots as possible. It must be able to operate comfortably in small chop where many planning boats of this size become very uncomfortable. The boat would be for transporting people on the water from point A to B as efficiently as possible in most weather conditions quickly and efficiently.

    The boat is designed to carry 3 adults or 2 adults plus two children. There is a provision for turning the seats into a berth, or taking them out and turning the whole cockpit into a long storage area/ pickup truck type bed.

    It took Turning Point about 3 months of work (spread out over 8 months) to complete the prototype. The structure is from CNC cut flat panel foam/glass construction with the aim of making the build cheap, efficient and fast.

    The owner reported “Turning was never going to be its strong point but it did ok. When we first launched, we where running in a new engine so were not going above 50% throttle and it was blowing about 25 knots. It was not easy to keep the bow in the wind or turn into the wind from a 90 degrees without a decent amount of throttle in those conditions but once we broke the engine in and could go to 3/4 it was not a problem.” And “Its a REALLY smooth ride heading upwind as it has such a long bow, fine entry deep v until a fair way back.”

    The boat later had an ama extensions and a flap/foil on the outboard. There were also had lifting foils added as an experiment but initially were not successful. I do not know if the foils were developed further.

    The jpegs give the idea. Interesting boats.
     

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  15. Tony.Ellen
    Joined: Nov 2019
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    Tony.Ellen Junior Member

    A Kiwi guy designed his own after seeing something on Rob's site. Folding bow as per your question
    http://harryproa.com/?p=1987

     
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