Multihull Structure Thoughts

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

  1. Xpert
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    Xpert Junior Member

    It's actually a very good idea to use a combination of foam and honeycomb, foam for submerged area and honeycomb everything above WL or internal.

    Thanks.
     
  2. oldmulti
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    oldmulti Senior Member

    Xpert. Your hull layups are impressively strong and more complex than required. Assuming that you want to eg halve the 8000 lbs weight of a Catalac 9 meter then the layup your proposing is adding a lot of work. Similar sized cats intended for cruising have 600 to 800 gsm biax eglass external layups on 12 to 15 mm PVC foam and an interior layup of 440 to 600 gsm eglass in poly or vinylester. More aggressive layups go down to 440 gsm biax eglass on both sides of 12 mm PVC foam. All the glass layups are single layers filled and PU paints on the outside. A 31 foot cruiser racer had 300 gsm s glass 163 gsm kevlar on 12 mm PVC foam with 163 gsm kevlar inside in epoxy. This boat is 40 years old without a problem and weighs 5000 lbs displaces 8500 lbs. Have fun.
     
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  3. oldmulti
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    oldmulti Senior Member

    This post will focus on cost and maintenance, which effects total costs, of varying rigs. There is one certainty I know about boats, they have to be extremely well built with top quality gear to minimise maintenance cost initially. The alternative is to build a cheaper boat that will cost you more in maintenance. The only way to reduce these costs is to build a smaller boat or buy second hand in the knowledge that you may have to fix up many things.

    So, we will start with the common sloop rig be it fractional or mast head without roller furling/reefing gear. This type of rig depends many bits of equipment to hold it up and control the sail. If it is a large high load rig it needs good equipment checked annually and parts replaced. Good turnbuckles will last, 1x19 stainless steel wire has a limited life, halyards are under continuous loads and need replacing. Aluminium masts will last if well treated. But when you come to wooden, carbon fibre, wing masts etc with synthetic rigging they will need annual inspections and maintenance. The problems often appear at stay connection points, spreader bases and electrical lines for masthead equipment etc. The other problem area is luff tracks on masts. If the mast has a groove or a track the slugs or cars connected to the sails need constant maintenance or your mainsail may be jammed. If you have a luff rope on the sail it wears again causing problems. Translation of all this. Conventional sloop rigs are relatively expensive and high maintenance over the years. The higher the loads in the rig the more expensive they become.

    Next is any rig that depends on roller reefing or furling gear to reduce sails. Either buy the best or make it yourself so you can fix it yourself. Any reefing furling equipment needs/requires constant inspection and maintenance. Your life may depend on it. I have seen a headsail that deliberately destroyed by the owner because his furling gear failed. I have seen a broken rigging 1x19 forestay wire jam up a furling drum making it unusable etc. It’s not what’s visible that can cause problems but the underlying wire etc. If this means you have to take off the forestay/furling gear to disassemble part of it to do the inspection of the forestay do it! (sorry about yelling) Good furling roller reefing gear costs money and needs more money to maintain. Slab (manual) reefing is far cheaper and provides more sail efficiency although its often harder to use.

    Multiple sail, mast rigs that just drop sails for reefing are easier and cheaper to reef and maintain. BUT their initial costs can be higher and your reduced reefing maintenance cost are at the expense of additional mast/rigging initial and maintenance costs, especially if the rig uses wires spreaders etc to keep it up.

    Freestanding masts are cheaper to maintain but sometimes have higher costs. If you don’t need all the rigging wire, turn buckles, stay connections, spreaders etc but a lot of freestanding are made from carbon fibre epoxy etc. The advantage of the freestanding mast is in some boats the mast can rotate in its base and act as a “reefing/furling” unit. Again, reduced costs and easy to inspect for maintenance. As a total cost solution, I suspect this approach is cheaper than a conventional sloop rig.

    Speciality rigs like junk rig variations can be from cheap to expensive. Cheap in terms of the simple plain junk that can be home made including the sail even on larger boats. It is very maintainable and can be easily inspected. Sophisticated junk rigs with aerofoil shaped sails, booms etc can be more expensive and require much higher maintenance costs. I will not go into each specialty rig type but I will direct you to PHA 30 and 46 foot Tiki catamarans rig variations. Both boats have crossed oceans with the 46 footer sailing around the world. Bertrand describes some of his issues on the larger cat.

    Translation of all this. Ultimately there is no substitute for good quality and good maintenance in rigging/sails. I have been on 2 boats when masts fell down. It is not fun and very dangerous. In both cases a little maintenance would have gone a long way to preventing these accidents.
     

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  4. brian eiland
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    brian eiland Senior Member

    @ catsketcher, oldmult,
    2 days ago I was presented with a viable posting about a serious error in my 'rigging force review' for my aftmast rig. Turns out they were correct and I was wrong,...for a number of years now. I posted new info on my discussion over there, and I will soon have some alternative rigging ideas to make it work.

    Regards, Brian
     
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  5. catsketcher
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    catsketcher Senior Member

    XPert - spend some time working on multis - there is no better way to understand boats than to fix them. The laminates you suggest are way over the top for a cruising boat. As old multi suggests something in the order of 400 - 600gm each side of a 15mm foam core is strong for most multis of this size. Your laminates will be heavier, much more expensive and susceptible to delam and water ingress.

    Cheers

    Phil
     
  6. oldmulti
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    oldmulti Senior Member

    The final on rigs for a short time. I will focus on one rig type that is not on the mainstream but is often used as a cheap effective cruising rig that can be repaired by an owner and easily used. The junk rig and its variations.

    The first user of a junk rig was Eric Debischop in 1937 on his ocean crossing cat followed by David Lewis on his 40 foot cat in the early 60’s. Lewis changed his cat to a sloop. Wharram tried a junk rig on his 51 foot Tehini, he claimed the leading edge of the sail fluttered and ruined the aerodynamics not making it efficient to windward. Wharram changed the cat to a ketch. All was not looking good, but people persisted. The Junk Rig Association members continued to work on the problem with one member converting his 26 foot “Fire Fly” performance tri to an improved junk rig. This tri could sail upwind well and match other tris boat for boat reaching and running under plain sail without spinnakers.

    Hundreds of junk rig multihull experiments have been done since with several sailing around the world. So, what is the “classic” junk versus the “modern” junk rig. The classic junk rig is basically a flat sail with no chamber. It required either a specialist helms person/crew or little desire to go to windward to make the classic junk rig to work across an ocean. Modern Junk Rigs have chamber either sewn into the sail or have articulated battens that induced chamber into the sail. Modern junk rigs can go to windward well and are reasonable all-round rigs.

    The next improvement was the development of the Split Rig junk which has small forward jiblets in front of the mast and on the same battens the mainsail components behind the mast. These split rig junks can match sloop rigged sloops around a triangular course. Slightly less performance upwind but stronger performance reaching and downwind. See the PBO article comparing 2 monohulls of the same design but one with a split rig and the other with a sloop rig. The performance is close. The article is Bermudan rig vs Junk rig - Practical Boat Owner https://www.pbo.co.uk/seamanship/bermudan-rig-vs-junk-rig-17481 There have been further developments with more aerodynamic batten shapes and jib/mainsail shapes which can match a sloop rig.

    So why the focus on junk rigs. Ease of use!! This rig can be reefed in 30 seconds by a man drinking a cup of coffee in reasonable conditions. Release the main halyard, the junk mainsail falls down to the required height then tighten a down haul. The major problem for most multi’s is the need for free standing mast or masts. If the rig can be designed in from the start its relatively easy to accommodate a Junk Rig but there are many samples of existing production designs being converted to Junk Rigs. There are Wharrams, Simpson 40 foot, Iroquois 30 foot cat with a folding mast rig etc. All of the jpeg boats have done many miles and most have crossed oceans.

    Now we get to the point of performance. If you are cruising you will get similar average speeds to sloops over any distance. Modern junk rigs will be able to go to windward well. If you are racing modern junk rigs will surprise you but a modern fractional rig with spinnakers and code 0’s will outsail you but they will be working a lot harder to achieve that performance.

    The jpegs are Eric 1937 cat, Lewis 40 cat (2), dragon wings 34 foot cat with tree free standing masts, 34 foot wharram Atlantic crosser, 40 foot China Moon global sailor, Simpson 40 ocean crosser (2), 40 foot tacking proa, Iroquois 30 foot retrofit with folding masts (2), 34 foot wharam masts, cambered junk sail, advance swing wing junk sail, PBO boat comparison.
     

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  7. oldmulti
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    oldmulti Senior Member

    Ocean crossing multihulls have been built from many materials. Some are very common such as wood, fiberglass, foam, aluminium, inflatable in smaller cats etc. A few larger ones are built from steel (the smallest design I know of that has sailed successfully is 36 foot full bridgedeck cat), but the ones that are interesting are the often done by people who want cheap.

    One British couple crossed the Atlantic in a 35 foot animal skin on wooden frame tube catamaran with a fairly technically advanced reefable wing mainsail. Not overly fast but it worked. Another guy welded 44 gallon drums together for his trimaran hulls and did some basic angle iron crossbeams with a second hand rig. The tri sailed about a 1000 miles before failing due to weak crossarms and faulty welding. I know of a 48 foot long trimaran that had a slim central hull of ferro cement. It had small floats but still made a 2000 mile coastal voyage.

    But the guys who really do interesting things are those who care about the planet. De Rothschild built “Plastiki” a fully recyclable ocean-going 60ft catamaran, that sailed for four months across the Pacific Ocean from USA to Australia. The vessel was built was kept afloat by 12,500 discarded plastic bottles lashed to its sides. Now this is an excellent marketing exercise. The underlying boat has many other components acting as its framework and crossarms that are from manufactured components (hopefully recycled re manufactured plastic) and the boat took 3 years from design to final build by quite a team of volunteers. The boat sailed OK but I very strongly suspect you could build a 40 foot cat with less total environmental impact.

    The next cat along the same lines I suspect inspired or was a prototype of Plastiki as it uses a very similar construction technique. The cat is again made from 1-liter pop bottles, PVC tubing, I beam cross beams and a Hobie Cat trampoline with an oar as a rudder. The boat is just 2 hulls, simple ketch rig and headsails on rigging to the forward part of the hulls. Seen in San Francisco.

    The final boat is “Junk” is a conglomeration of 15,000 plastic soda bottles, PVC tubing, plastic sheeting and the fuselage of a Cessna 310 and a mess of good intentions that left Long Beach bound for Honolulu. The cat was built for self-described "eco-mariners" Dr. Marcus Eriksen and Joel Paschal. The boat moved but was not refined. This cat probably was truly the most “recycled” boat here but I suspect would be the least capable of the group.

    I fully support the message they are trying to pass but for real world builders a wood cat using green epoxy and green structural cloths will achieve a more viable boat whilst being ecologically sound.
     

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  8. oldmulti
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    oldmulti Senior Member

    I recently spoke to a young guy who went for a 2 day trip in the Whitsundays with 14 others on a charter yacht. He said it was on a 39 foot catamaran. He didn’t care about the boat but focused on the fun he had and some of the girls. I thought he got the cat size wrong and didn’t think about it for a while. Then I ran across this cat. I rang him he said yes that was the boats name and it was fiberglass. He didn’t know much more. So, what are we talking about?

    Tongarra is a 39.5 foot catamaran which can take a maximum of 24 passengers and 2 crew. Tongarra offers a 2-day 2-night (yes up to 24 people can sleep overnight) social sailing experience that’s perfect for the young, fun and adventurous backpackers. Translation, your young enough to put up with 2 toilets for 24 people, have up to 6 people sleeping in a 6 x 6 foot space and have virtually no privacy for 2 days. But as a young person between 18 and 25 for $500 you get to visit some of the better destinations in the Whitsundays including Whitehaven Beach, Hill Inlet Lookout and snorkelling at pristine locations on the fringing Great Barrier Reef.

    Why is the cat 39.5 foot. Because in Australia the charter rules allow a boat under 12 meters to be controlled by a Coxswain not a fully registered Captain required on larger boats. Now, the rules do not specify how many people you can load aboard provided the vessel meets the require seaworthiness and safety requirements. Result 24 people spending 2 nights on a cat.

    Let’s look at the boat, Tongarra is a 39.5 x 26.3 foot single-masted catamaran with fat 6 foot wide hulls at the waterline. Result length to beam of 6.5:1. The underwing is 1.75 foot off the water. The charter area this cat sails in rarely has any large waves during the charter season, in the areas the cat sails. I would recommend a higher bridge deck clearance for offshore work. The mast is a 45 foot aluminium section with about 800 square foot of sail. From the limited information I have this is a chined flat panel foam glass cat with very washable vinyl surfaces inside.

    This a pure guess, but by basic calculations, the displacement is about 45,000 lbs. This cat offers hot showers to its charter guests which means at least 7000 lbs of water, 6000 lbs of people and personnel belongings, provisions and drinks would weigh another 1000 lbs. The toys and dinghies they have would weigh another 1000 lbs plus anchors gas fuel etc which would weigh a further 3000 lbs.

    The result is a cat that according to the young guy, could sail but it didn’t “go fast”. My guess is a maximum speed of 12 knots with maybe averages of 7 to 8 knots in the Whitsunday winds.

    Why does one need a 60 footer when a 40 footer will give you all the accommodation you need for an overnight party and a short cruise. I am trying to learn more about the boat but the jpegs will have to suffice for the moment.
     

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    Last edited: Jun 28, 2020
  9. oldmulti
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    oldmulti Senior Member

    The Puddlecat Adventure Catamaran Specifications is 13.1 x 6 foot (can be made wider) with a bridge deck clearance of 1.3 foot. The boat weight is 390 lbs with a total displacement of 890 lbs. The rig can be a single mast with 75 square foot sail area. An optional biplane rig of 2 lanteen sails has a total sail area of 150 square foot. The hulls are asymmetric requiring no boards allowing 180 mm draft but the central kick up rudder requires 1.5 foot draft.

    The performance of these boats proves small heavy boats have their limitations. Peak speeds of 10 knots, cruising speeds of 5 to 6 knots. The motive power could be a small outboard but an oar is preferred and can get 2 knots speed and save you a trip to the gym. The cabin has 2 foot “headroom” with enough room for one and half people to sleep. The cockpit can handle 4 people.

    The Puddlecat Adventure Catamaran was developed for day trips or weekend cruising for two people and supplies for 30 days. It was also developed for a single sailor to attempt the 300 mile Everglades Challenge boat race (Tampa bay and sailing to Key Largo). It requires a large enough boat to carry food, water and equipment for 8 days. The rig can be reefed by a single handed sailor and the boat is unsinkable as long as the watertight bulkheads remain intact.

    The cat is built from plywood with fiberglass and epoxy coating protecting the plywood bottom of the boat. The boat also is very affordable and easy to build. The prototype Adventure was put into operation for slightly over $1100 dollars with twin masts and brand new sails. It was constructed starting mid Nov. 2010 and its first sail was Jan.15th 2011. It was built by one person during nights and weekends while working a full time job. Construction plans are $20 US dollars and available for instant download from PuddleCat Adventure | PuddleCat Catamarans http://rogermann.org/puddlecat/designs/puddlecat-adventure/

    This cat is about the minimum cabin cat that has proven itself capable of travelling a distance in bay and well chosen weather for coastal sailing. The bi plane rigs lower the centre of effort for safer sailing. This is not a performance boat but is cheap fun to get away for a few days.
     

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  10. oldmulti
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    oldmulti Senior Member

    We spoke of the Puddlecat 13 footer yesterday, now we talk of the Islander a 20 x 8.5 (optional 9.5) foot bridgedeck cat that weighs 2000 lbs and can carry a load of 1500 lbs. The mast is 26 foot high and can be eg a Hobie 18 sail plan.

    The hulls have 6.1 foot standing headroom and the bridgedeck 3 foot (later increased to about 4.2 foot by lowering the bridgedeck). It has 2 singles and a double berth.

    The boat is plywood on stringers with solid timber crossbeams. External surfaces are done in epoxy glass. The designer does home built aircraft designs as his normal work.

    The Islander catamarans goal is to be large enough and capable enough to take a couple on long trips to remote Islands comfortably. (It is as big as it can be and still towed home for storage). It was built with open water passages of 50 miles (Fla to Bahamas) in mind. This boat is build without the use of forms or a strongback so every thing you build goes into the boat and not thrown away after used. A set of hulls can be built in roughly one month.

    The cat had a very high wingdeck clearance, fat hulls and minimal beam for a 20 footer resulting in no wave slap on the original underwing so the designer decided to make a change to the bridgedeck. He decided that having so much water clearance was not a concern and that having the extra space and storage was worth the modification so he cut the underwing floor out and lowered it so he had an extra step to get down into the boat hulls. It added approx. 15 sq feet of living area and 6 sq feet of storage both forward and aft in drawer lockers that will be built.

    Now this boat is not on the performance end of the scale but is a very big 20 footer. I would suggest you would need to pick your weather windows for any coastal work but with prudence you could cruise for many weeks. The jpegs give more information.
     

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  11. oldmulti
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    oldmulti Senior Member

    Some additional Puddlecat Islander 20 jpegs
     

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  12. Burger
    Joined: Sep 2017
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    Burger Junior Member

    Re. Tongarra (the almost-12 meter floating backpacker party palace), she's steel. A crew member told me the sails were for auxiliary power, shade, and "that sailing vibe." Under sail alone, she'd need a gale to get over 5 knots.
     
  13. oldmulti
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    oldmulti Senior Member

    Burger. Thanks for the additional information. If this boat is steel my displacement calculations would be way off. A 36 x 18 steel cat (Catrina by Bowden design) with less bridge deck has 18,000 lbs of steel in its hull structure. Best guess Tongarra would require 32,000 lbs of steel to build the hull shell to the specs as Catrina, but knowing some of the survey rules I would suspect it would be heavier than this. Tongarra's displacement could be 60,000 lbs. Result, I can understand the lack of speed and the dependency on an engine.
     
  14. oldmulti
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    oldmulti Senior Member

    Simpson 40 cat Seadragon is 40 x 23.3 foot weighing 11400 lbs and displacing 16800 lbs. The sail area is a biplane junk rig with 512 square foot of a junk sail on each free standing mast for a total sail area of 1024 square foot. The junk sail is a classic style, which is a flat sail with straight battens. The sails were made by Lee Sails in Hong Kong. Gary and Frances Aro (the builder owners) found the rig to be a great cruising rig with the ease of handling and reefing associated with junk rig. And the cat tacks unassisted in all of the conditions that he had encountered. The original Simpson 40 design had a sloop rig of 820 square foot.

    Seadragon was built and launched in Maryborough, Queensland in May 2011 after a 6 year build. After launching it did some coastal sailing then in April 2012 was sailed up the east coast around Cape York, across the Gulf of Carpentaria to Darwin, where it sailed in the 2012 Sail Indonesia Rally. Gary Aro cruised through Indonesia and Singapore for 4 months before heading up to Malaysia. Seadragon sailed in and around Malaysia and Singapore for the next 3 years, logging around 7,000 sea miles.

    The owner, Gary Aro, took a stock Simpson 40 hull plans and designed his own superstructure, increasing the bridge deck space. He also designed the and built the Bi-Plane Junk Rig. The hulls are 9mm ply above and 12mm ply below the waterline with 3 layers of 300 Double Bias glass over above the waterline and 4 layers under the waterline. The decks and cabin are constructed from Polycore, a honeycomb cell structure material, glassed on both sides. The original Simpson 40 design had plywood and timber crossbeams and bulkheads. The whole boat is built with epoxy. The engines are two Tohatsu 18hp two stroke outboards.

    This cat is a basic design modified to suit the owner’s needs. It appears to be easy to handle and sails well covering enough sea miles to prove the idea. An interesting concept.
     

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  15. catsketcher
    Joined: Mar 2006
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    catsketcher Senior Member

    I am pretty sure we met the builders of Tongarra back in the 90s when she was just new. They were a Swiss background family and he was an engineer who decided the fastest way to build a boat was to make it as rectangular as possible. He was also a hydraulic specialist and the boat featured a single engine powering hydraulic props in each hull. He later built a much more streamlined boat that sat for a while off Airlie but I can't remember it now.
     
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