Multihull Structure Thoughts

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

  1. Derek_9103
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    Derek_9103 Derek

    For my plans (foam sandwich) I've been leaning toward vinylester, mainly based on a statement in the middle of a long discussion somewhere I can't remember from someone who sounded knowledgeable - that almost all production boats use primarily vinylester, and what's good enough for "the industry" is good enough for him, and that epoxy, to the degree it gets a much larger percentage of discussion than it's percentage of use, is a prima donna.

    Hughes' quote above undermines the justification of my choice - so this seems like a good place to clarify:
    1. Is the statement true that most production boats use vinylester? If so, and the statement above that epoxy is easier to work with than vinylester is true, then WHY is vinylester then used more frequently than epoxy "in the industry"? (I wouldn't think cost would sway use percentages THAT much if the results difference is so clear, is epoxy THAT much more expensive?) (Or is this just a never-ending debate with 14 different answers?)
    2. If mixing together multiple elements is an integral part of using both epoxy and vinylester, how come the mixing is talked about a lot more for epoxy compared to vinylester? Especially since according to Hughes, it matters more for vinylester?
    3. Re: Hughes' statement "most room temperature epoxies post-cure at around 65C to 70C" >>>> Do most epoxies require this degree of heating to finish the cure? Or just for better results? How much better results? Cure for how long? What percentage of production boats have this high temperature cure? What percentage of home-built boats have this high temperature cure? (Ballpark answer okay, I can research whatever direction you send me.)
    4. Are there brands, or newer versions of vinylester for which the flaws Hughes notes have been fixed? Or are those already around, but more expensive?
    (For clarity, I removed any knock clearly about polyester from the quote, since I wasn't considering polyester anyway, I'm just talking epoxy vs. vinylester.)
     
  2. oldmulti
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    oldmulti Senior Member

    Derek. There are 3 distinct steps in foam glass (assuming you are using the same glass fabrics). Step one polyester cheap, relatively easy to work and controllable over a temperature range. Downside polyester is the weakest resin matrix and therefore the total glass resin matrix is the lowest strength. Step two. Vinylester stronger than polyester and in certain formulas as nearly as strong as low strength epoxies. Takes a little more care in mixing but is still controllable across a temperature range and still relatively easy to use. A very good half way house that is slightly cheaper than epoxy but its big advantage is it is more water impervious than polyester. Step three. Epoxy they range from low strength to very high strength, room temperature cures to some formula's that don't go off until cooked at 60 plus degrees for hours. The strength can be from slightly stronger than a Vinylester glass matrix to double the strength. The variable is cost the stronger the epoxy, the more likely to need controlled heated cure conditions the greater the cost. Epoxy if done correctly is the most waterproof. Your choice. If the designer is Derek Kelsall his designs will be polyester foam glass. If its Rob Denny its likely to be infused epoxy carbon fibre. Kurt Hughes will do you anything you want but prefers epoxy. Just make sure your design is suitable for the resin glass mix you want. PS yes epoxy requires mixing and often requires more accurate mixing than say a polyester or vinylester mix, but they all still need careful mixing and application.
     
    Last edited: May 16, 2020
  3. Derek_9103
    Joined: Oct 2019
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    Derek_9103 Derek

    Thank you for the summary oldmulti, great info. Given I'm looking for a 0.8 beam to length ratio, it seems to make sense to change my thinking FROM vinylester (I heard it was workmanlike, good enough for most applications) TO epoxy - specifically for the increase in strength, which I'll need to handle having the amas further out, plus obviously structural considerations and help from a pro designer. Obviously WHICH epoxy and fiber is a discussion for another day. My wife says stop boating and go to Home Depot to finish my project for today. :)

    I also just finished looking through all 69 pages of the whole thread to date. With that effort, I "ran into again" about 90% of the boats I'm taking inspiration from, but the way I did it took me many hundreds of hours to find them one at a time by myself, I'd have saved so much time if I found this forum and thread last August.

    C'est la vie.

    Thanks for all the effort and information, it's nice to have so much in one place.
     
  4. oldmulti
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    oldmulti Senior Member

    The Gold Coast 56 Trimaran “Virgin Fire” is the sixth vessel of veteran multihull ocean racer Joe Colpitt. The tri is 56 x 36 foot with a shell build weight of 14,000 lbs and displaces at full load 25,000 lbs. The normal payload is 4,000 lbs. The 72 foot rotating wing mast carries 1530 square foot of sail. The rig is a 3/4 rig with integral spreaders and rotators and Harken mast track for system C cars. It sits on a custom Teflon/stainless steel mast rotation cup and ball base. It has a Metalmast boom with outhaul car, tack hooks and three reef sheaves. Standing rigging is Norseman using Dyform SS wire terminating with Norseman fittings, turnbuckles and toggles to SS chainplates. All running rigging is Samson Dyneema to keep it light.

    The tri was built in 1996 in St.Croix by Gold Coast Yachts as a racer-cruiser. The tri has a Bruce number of 1.62 this is fast. How fast, Virgin Fire has proven capable of sailing one and a half times wind speed in most conditions with just her working sails. She climbs to windward at 80% of wind speed and has consistently won racing events.

    Construction of the hulls, decks, bridge decks, roof, cabin sides and cockpit are built of Corecell foam, glass and CPD epoxy resin using resin infusion and vacuum-bag processes. All primary structural components and amenities were built with West System construction methods. Interior has West System epoxy products and were painted with semi-gloss Awlgrip, teak trim varnished. The exterior of the tri is painted with Awlgrip Polyurethane paint systems.

    Virgin Fire was built for racing, but is set up for serious long-distance passage-making with 5 big spaces to sleep, private cabins, dinette and a galley with lots of working space. Her interior is simple, spacious, and functional with the structure built to knock off the miles with great safety and comfort.

    Virgin Fire with Finn (53 foot) and the Chris White Hammerhead 54 (54 foot) all have the same characteristics; they have reasonable accommodation and are very fast under working sail. Owners of big French cats may have accommodation but they would not understand just how fast and easily handled in a seaway these cruiser racer tris are. They do not depend on engines for maneuvering these tris can be sailed in light to strong winds upwind and down.
     

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    Last edited: May 16, 2020
  5. rob denney
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    rob denney Senior Member

    Not necessarily. The first big cat I built (38 years ago) was a 10.5m/35' race cat in polyester. We capsized it in the North Atlantic, were rescued by the Irish navy who tried to tow it at 8 knots (the rig was still in place) which sheered the alloy fore beam, which was glassed into the hull. They then decided it was a "hazard to navigation" so should be sunk. It was well insured and I had another project ready, so agreed. A huge Irish stoker attacked it with an axe, which just bounced off the hulls. Then they tried ramming it, but the ship rode over it, doing little damage, apart from to the frigate's bow thruster, when a sail bag got sucked in. The captain then gave an order and 2 minutes later all the doors on one side opened and the crew emerged with sub machine guns and fired them into the hull. Huge fun, but no result. They then uncovered the 50mm AA gun and fired 50 rounds into the cat, which eventually went down.
    Polyester worked fine, but in Aus at least, there is no infusion version available and infusion turns boat building from hard work to enjoyable.

    I have also built several Harryproas in vinylester, see attached. Drawbacks include waiting a week or so before secondary bonding with epoxy, shrinkage, shorter shelf liofe than epoxy and the stink, which rules it out for most home builders. Given the small price difference ($10/kg for VE vs $12.50/kg for epoxy), it is a pretty easy choice. However, if I was a commercial builder, using gel coat and watching every penny, I would be using VE.

    Answers to Derek's questions:
    1. Is the statement true that most production boats use vinylester?

    Mainly as a tie coat to polyester to stop osmosis. Those who use it instead of polyester do so because it can be used with gel coat. Quicker cure, familiarity and no preparation for secondary laminating are other reasons.

    2. If mixing together multiple elements is an integral part of using both epoxy and vinylester, how come the mixing is talked about a lot more for epoxy compared to vinylester? Especially since according to Hughes, it matters more for vinylester?

    Vinylester has additives which the user can adjust. The ratios are important. But for the actual mix, a little more or less catalyst will only alter the speed of cure. As it is a snall amount, it is easy to measure in a squeeze bottle. With epoxy, one component needs to be accurately weighed, the other calculated and added, although there are pump systems which do this automatically.

    3. Re: Hughes' statement "most room temperature epoxies post-cure at around 65C to 70C" >>>> Do most epoxies require this degree of heating to finish the cure? Or just for better results? How much better results? Cure for how long? What percentage of production boats have this high temperature cure? What percentage of home-built boats have this high temperature cure? (Ballpark answer okay, I can research whatever direction you send me.)

    Home build epoxies do not need post cure to achieve adequate properties. It is a good idea to prevent print through, though. Very few boats are post cured, regardless of material, apart from high end race boats. The easy way to post cure is to cover the well supported components in black plastic and leave them in the sun for a day or 2.
     
  6. oldmulti
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    oldmulti Senior Member

    Jan Andersen designed and built Black Marlin, a tri of 32.3 x 26 foot with a main hull 31 foot long for himself. The boat can be folded to 11.5 foot or disassembled to 8.2 foot wide for transport. It displacing 3280 lbs ready for sailing without crew. The 50 foot high, 42 square foot self built carbon fibre wing mast that weighs 140 lbs carries a 495 square foot main, 215 square foot jib, 420 code 0 and 915 square foot genneker.

    Jan wanted a fast fun cruiser racer to replace his 30 foot race winning light WRC glass tri Barracuda. Black Marlin has several design improvements of better construction, a one meter taller mast, more sail area, more width, better foils, taller and narrower floats. This floats allow Black Marlin to sail better in heavy weather but heels slightly more, but the floats also allow the tri to push into light airs better compared to Barracuda. The boat can cruise at 12 to 13 knots and has peaked at 26 knots so far. Black Marlin can go upwind at 40 degrees. Result of all this, demand by other people to produce “Black Marlins” for them. Also, as Black Marlin is a swing wing tri, Jan has consulted with Dragonfly about their trimarans.

    The original “Home Built” version took 18 months including making his own mast. The hulls are built in molds and are carbon fibre infused epoxy on foam with PRO-SET epoxy, which belongs to the professional part of West-System. It is made with biaxial carbon fiber to produce high stiffness and lower weight. The carbon fiber mast use UD - Uni Directional (fiber in one direction only) and limited biax carbon fibre. Even the main cabin table and parts of the interior is built in Carbon Fibre with veneers to provide a finish. The racing versions has rudders on floats, cruising version has a rudder on main hull.

    This is one very fast cruiser racer designed and built by a man who has good boat building experience. His use of female moulded hulls simplifies the surface finishing and I think probably made the build faster. Sorry I do not have more detail on the build but the idea and result is very good.
     

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  7. oldmulti
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    oldmulti Senior Member

    Fabrovich designed an excellent 6 meter tortured plywood cat featured on page 7 of this thread. The Fabrovich cat featured here is the 9 meter, that is a cat of 29.5 x 20 foot weighing 2910 lbs carrying 667 square foot of sail with each sail in the biplane rig measuring 333 square foot. The 2 biplane 36 foot of deck free standing masts are 200 mm diameter at the deck base. The performance information is limited, but a video shows it sailing well in moderate conditions.

    The hulls are built of tortured Okume plywood (guess 6 mm ply in hulls) with stringer and plywood bulkhead support. As you will read in his smaller design (in the attached word document) he joined the keel lines together poured in bog, glassed the keels at a predetermined angle and tortured the hulls into shape around the bulkheads. The original design had aluminium tube cross beams but this version is built with box (guess) timber ply cross beams. The centre pod is a tortured ply construction and can accommodate a single berth in front of a covered area and cockpit for sailing. The hulls are 5 foot wide at the gunnel level. The accommodation has 2 double berths, 2 single berths a galley, dinette and loo.

    The cat is demountable (not easily trailable) for transport to new locations. A 9.9 hp outboard powers the boat and ground tackle of 15 kg CQR and 15 KG Danforth anchors each has 25 meter of 8 mm chain with 150 foot of rope keep the cat stopped. The cat has 2 by 100 litre water tanks and a 70 litres fuel tank.

    I have included the word build document of the 6 meter (20 foot) version of the cat, as this boat would have been very similar in design and construction of the hulls rig etc. The 9 meter is a big transportable, relatively easy to build, useful cruising cat that could go long distances with minimal effort. Interesting design.
     

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  8. redreuben
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    redreuben redreuben

    I just thought I'd throw my 2cents in on the resin issue.
    I worked a substantial part of my life as a fibreglass laminator with the latter part being mostly yachts.
    All vinyl ester production boats are rare, we built one as a special for the boss to race and it was given a light post cure in a tent with a gas space heater, it went to windward like a witch and he won his championship ( Farr 9.2's).
    As mentioned most production yachts have vinyl ester behind the gelcoat and the bulk is then an iso polyester. I think out of 50+ boats 3 were 100% VE.
    IMHO if I was going to build a composite boat that wasn't designed or required to be the latest and greatest I would use vinyl ester because it has the properties to complement higher end fabrics but has the usability of decades long techniques and skills and tooling.
    Epoxy on the other hand, cost aside, requires more specialised training and technique but worst of all it's slow. Very very slow.
    Long gel times, long cure times all add up to a job that take minutes taking hours, hours taking days and days taking weeks, this can be ameliorated by space and planning and running multiple components at the same time but few home builders have that luxury, most are cramped in a shed or tent concentrating on one component at a time.
    Further, the expense goes beyond the laminating resin, if you are moulding in a production or one off mould you can use gelcoats and flocoats - cheap.
    Epoxy needs epoxy hi builds and 2 pack paint high cost and high maintenance.
    Disclaimer, I haven't worked in the industry since the mid 90's so I'm sure materials and technique like infusion have changed things but I believe the above is still basically sound.
    I hope this provides food for thought.
    P.S. And my best piece of advice - Peel ply-Peel ply- Peel ply ! :D
     
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  9. catsketcher
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    catsketcher Senior Member

    Gday Red
    I will bow to your knowledge on poly and vinyl but I still like epoxy. I don't find it too slow for my building as I am usually doing lots of individual parts if they are small and a big job takes me all day anyway. It makes great custom boats when there is no moulding to use and you have to fair and paint anyway. Secondary bonding is excellent. Then you also have its great ability to protect timber, which I like using. It is also a wonderful one chemical system, being able to be used for gluing and laminating.

    I think that one problem with the moulded approach is one of weight. It seems that with gelcoat and tie and print through layers, poly boats are appreciably heavier than custom epoxy boats. Epoxy boats are covered with filler but it is rare to see a moulded multi look light. This could be due to the fact that epoxy boats are usually racier designs.

    cheers

    Phil
     
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  10. oldmulti
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    oldmulti Senior Member

    This is about a man who entered a race around Victoria Harbour Canada in 1984 to win $100. The race is associated with the Swiftsure event. The only requirement, you had to prove that the entire boat cost $100 to enter the race. So, what fine vessel did he build? A foil stabilised canoe. The tri is 16 x 18 foot wide. With 90 square foot of polytarp sail on a wooden mast.

    The canoe construction was a sheet of plywood 16 x 4 foot tortured in shape with 50 x 100 mm timber for frames and cross beams. The cross beams were lashed onto the “framing” in the main hull and foils. The foils were 12 mm plywood, semicircular shape, 3 foot long by 2 feet deep. The foils are angled at 60 degrees which end up at 45 degrees when the tri heels. When the boat sails the centre of effort of sail line goes through the centre of “lift” of the foils so the tri heels to a certain point then heels no more. This means increased sail force means more speed if the hull and rig can take it.

    This fine vessel won after his third attempt due to stronger winds which allowed him to sail faster than other but blew the top of his sail apart. The first 2 jpegs show the concept, sorry about the words but I am respecting the original authors rights.

    The foil stabilised trimaran concept has been tried for years after a gentleman called Edmund Bruce popularised the concept in the AYRS booklets. Some samples of the types of tri’s are shown in the jpegs. Sabrina 1 and 2 is from NZ and worked relatively well under many conditions including NZ version of a light sailing day. Holtham foil stabilised tri was the first commercial version of the concept, very few were sold. The 35 foot tri is Joe Dobler Australian built version that eventually ended up in Europe and still can be chartered. The final jpeg attempts to explain the concept.
     

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  11. redreuben
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    redreuben redreuben

    Hey Phil,
    My post was tilted towards the production boat question of Derek, your absolutely right regarding epoxy being the only resin of choice for timber of course. And it is superior to poly and VE in all aspects except price and I would argue useability way from timber.
    One thing I’ve noticed is that many foam sandwich boats still have ply bulkheads and furniture, I don’t get this, foam sandwich all the way, brings the weight right down and is far more homogeneous.
    In my experience epoxy is no guarantee against print through, especially with strip plankers.
    Weight, is always cost/benefit and in the hands of the customer/ builder, to this end production boats tend to be lowest common denominator meaning the builder makes the boat idiot proof to cover his arse !
     
  12. Derek_9103
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    Derek_9103 Derek

    Thanks for the alternate opinion, redreuben.
     
  13. oldmulti
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    oldmulti Senior Member

    In 2017 the Millennium Yacht Design Awards were presented with a special mention (1 of 8 given out) given to the following cat. Details beyond its 60 foot length are unknown as this cat is about style and grace with some functionality. It’s basically a design study by a design company that does older style house interiors etc.

    The award winning Contemporary Classic 60 foot cat design is for those who want classic styling in their modern 60 foot cat. This design stems from the desire to have a sailing catamaran that is free from the common “plastic floating caravan” aesthetics. Extensive use of wood and chrome epitomise a timeless style and elegance. Flush fitting curved glass surrounded by wood is ‘classic’ and unusually for a catamaran, the stern is raised as in classic old yachts.

    The rear stern structure has built-in steps, which pivot at the touch of a button to lower the steps down to the jetty or water level for a more dignified boat access. Careful floor deck height manipulation results in perfect sight lines from the outside seating area with visibility all around yet maintaining a secure and comfortable space for guests. The two large sliding glass doors retract into the sides for unimpeded visual and physical access to the interior.

    The dining table is the focal point of the interior. The rear portion is movable to completely seal the dining table for intimate meals. The port side has a fully equipped galley. The starboard side has an internal chart table and the boat can be helmed from the comfort of the saloon. Custom details such as the skylights and hull windows add to the narrative that this is indeed a very special yacht for the discerning owner that desires individuality and style.

    The jpegs show it all. I would not recommend the hull shape and short waterline or the potential displacement unless it had a lot of very thin veneers on foam carbon fibre everything. But as I said it’s a design study to attract interest.
     

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  14. Derek_9103
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    Derek_9103 Derek

    Thanks Rob!
     

  15. rob denney
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    rob denney Senior Member

    Best indeed. For anyone interested, I have 85g/m2 red stripe peel ply, width 1.8m, 200m rolls for $AUS900 each ($2.50 per sqm), ex Brisbane Australia. harryproa@gmail.com
     
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