Multihull Structure Thoughts

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

  1. oldmulti
    Joined: May 2019
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    oldmulti Senior Member

    Fastcat 435 is a South African designed and built cat of 43 x 25.25 foot weighing 11200 lbs, displacing 14000 lbs at half load with an overload capacity to 22,000lbs. It carries 1360 square foot of sail with a genoa. The LB of the hulls 11.55 to 1. The boat is lighter and carries more sail than most cats of this size. It said to perform quite well compared to eg Lagoon cats of the same size. The boat is a 2007 design and was built with resin infusion and epoxy, divnycell foam cores in hulls, decks, bulkheads and some carbon fibre reinforcement in crossbeams etc. This boat is interesting because of its evolution of structure. Originally the hull had from the outside 1200 gsm E glass biax 20 mm foam 800 gsm e glass biax and 400 gsm Kevlar in epoxy resin. The hull/wing deck structure is done as one unit and is postcured for 8 hours at 80 degrees C. The remainder of the boat is also postcured. The decks and cabin sides had 1200 gsm E glass biax 20 mm foam 800 gsm e glass biax in epoxy. The underwing and cabin roof had 40 mm foam. The latest version of the cat has hulls etc from the outside 700 gsm biax basalt 20 mm AFC 47 foam 700 gsm basalt and 400 gsm biax Kevlar with additional Kevlar in the LAR keels. Basalt cloth is stronger than E glass but lower strength than S glass. Basalt cloth cost in most markets is half way between E and S glass costs.
     

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  2. catsketcher
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    catsketcher Senior Member

    Thanks OldMulti

    Below is a photo of a 38ft Newick Echo. I built the shell about 20 years ago and sadly she sat in a shed for 17 years with minimal work done on her. She has since been bought by a new owner and recently launched.

    She is Corecell foam with a combination of glass and carbon in the hull laminates. The hulls are 15mm corecell, which was built up on the mould using bead and cove strips (we tried vertical stripping but it didn't work). No vac bagging used on the main hull. The amas were made in half shells like Farriers which allowed us to put all bulkheads and reinforcements in before removal. It was really nice to do it this way.

    The wing is 25mm thick corecell. It is vac bagged as are all bulkheads. (We started the hulls first and so got more high tech as we went along.) Vac bagging was limited to 3m wide segments as we had to get the vacuum on before the resin gelled so the wing is made in three parts.

    When the whole structure was complete we post cured her to about 65 degrees for about 7 hours.

    Really glad to see her floating.

    cheers

    Phil
     

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  3. oldmulti
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    oldmulti Senior Member

    Catsketcher. Thanks for your kind words and contributions. I am impressed with your energy. I am aware of several cats you have built but did not know about the tri. Most Newick tri's are really graceful and after seeing the Newicks around the Cormoral Peninsula in NZ built by farmers, I was amazed at some of the performance claims.
     
  4. oldmulti
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    oldmulti Senior Member

    Tri X-5 was mentioned in Multhulls magazine nov/dec 1999. Andy Vavolotis created a 25 x 18 foot tri that weighs 800 lbs and carries 300 square foot of sail. Andy was the original owner of Cape Dory boats (fiberglass mono's) which he sold then decided, as he was getting older, he would like to have some fun building fast daysailing tris for himself. This was his fifth boat and he was going on to develop a 6 th tri that was lighter etc. He was 65 when this was sailing and you may just see a hiking plank in the lower quality photo so he could get his weight further out for more power. The tri could do 21 knots in 15 knots of wind. The floats were longer than the main hull and were designed more like a cat hull with wide stern etc as it was designed to be the only hull in the water most of the time. The hulls are built with 5 mm WRC bead and cove. The hulls have carbon fiber skins with epoxy. I can not find any more detail about this fun design.
     

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    Doug Lord likes this.
  5. oldmulti
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    oldmulti Senior Member

    We spoke about Basalt cloth in the Fastcat 435. So what is Basalt? This is literally an extraction of basalt rock with only a few additions. It has a better temperature, chemical and UV resistance than E or S glass and is compatible with most common polyester, vinylester and epoxy resins. The properties of Basalt are: A: tensile strength about 30% stronger than e-glass depending on manufacturer, about as strong as S glass. B: the same as to 25% weaker in tension than carbon fibre depending on manufacture. C: slightly heavier (about 3%) for a given tensile strength of e or s-glass. D: For a given tensile strength carbon fibre is about 55% of the weight. E: Basalt has better modulus than e or s glass but is lower than carbon fiber. F: Basalt has lower elongation characteristics the E or S glass but stretches twice as much as carbon.

    Translation/generalisation. Basalt is nearly as strong as S glass but slightly (about 3%) heavier, it is slightly stiffer and has less elongation than e or s glass. Carbon fiber has in most cases significantly better strength to weight ratios. The cost is higher than e glass but less than carbon fibre. A good material that can be worked the same way as fiberglass eg hand laid or vacuum bagging etc.
     

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  6. rxcomposite
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    rxcomposite Senior Member

    Basalt fiber was originally developed for high temperature applications of automotive mufflers. Due to high cost of high temperature resin available, it became impractical for use in other purpose.
     
  7. oldmulti
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    oldmulti Senior Member

    Seaclipper 16 is a nice design for daysailing. It comes in several formats from a tandem sailer to an open cockpit version. The tri is 16 x 11.3 foot folding to 7.5 foot. The dry weight 400 lbs with a 400 lbs carrying capability. The sail area is 146 square foot with a 21.5 foot mast. Standard Hobie 14 mast, boom and mainsail with “Turbo” jib Hobie 14 mast step. The material list is below for the open cockpit swing wing version. The decks are 9 mm ply because Marples thinks by the time you do framing and stringers for lighter ply you end up with more work for only a small weight saving. The swing wing material is 2 laminations of the 19 mm material. The lumber for stringers etc gets cut down to stringer width. The kickup fixed rudders system is very good. An owner I have spoken to enjoys the boat as its more comfortable than a day sailing cat although not as fast. He described it as an old age fast cruiser. The major Materials List

    Plywood – marine grade, solid core, water proof glue, 4’ x 8’ (1.219M x 2.438M)
    7 sheets ¼” (6mm)
    5 sheets 3/8” (9mm)
    Lumber – straight, clear, dry, vertical grain fir or equiv.
    3 pcs. ¾”x 3 ½” (19 x 89mm) x 16’ (4.88M) stringers, glue strips
    2 pcs. ¾” x 5 ½” (19 x 140mm) x 15’ (4.57M)stringers
    3 pcs. 1 ½” x 3 ½” (38 x 89mm) x 8’ (2.44M) coamings, stems
    Hardwood – mahogany or other
    1 pc. 1 ½” x 3 ½” (38 x 89mm) x 3’ (914mm) tiller
    Western red cedar
    5 pcs. ¾” x 3 ½” (19 x 89mm) x 8’ (2.44M) daggerboard
    Akas – straight, clear, dry, vertical grain fir or equiv.
    3 pcs. ¾” x 7.5” (19 x 191mm) x 8’ (2.44M)
    2 pcs. ¾” x 7.5” (19 x 191mm) x 10’ (2.54M)
    3 pcs. ¾” x 9.5” (19 x 241mm) x 8’ (2.44M)
    2 pcs. ¾” x 9.5” (19 x 241mm) x 10’ (2.54M)

    Epoxy
    12 gallons including hardener.
    6 lb. wood flour filler
    3 lb. silica thickener
    misc. supplies – gloves, mixing cup and sticks, squeegees, etc.

    Fiberglass cloth – 4 ounce (135 gr./sq.M), plain weave or twill
    75 yds. x 38” (965mm) wide
     

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  8. oldmulti
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    oldmulti Senior Member

    The following aluminium tri is claimed to be 20 x 20 foot full expanded (I think it more likely to be 16 foot) and 20 x 8 foot folded. Maximum displacement of main hull 2000 lbs but the tri weighs 650 lbs. It is intended for 2 crew so the sailing displacement is probably 1000 lbs. Although not a great hull design, the interesting part is the build material in the hulls of 1.52 mm aluminium skin with 50 mm Styrofoam formers every 300 mm. The aluminium skin is riveted and glued together with butt plates at any joins of sheets, bow and stern. The deck is thin checker plate aluminium. Welding a 1.52 mm aluminium skin would require a very skilled specialist to prevent distortion, not practicable for a home build. The crossarm structure is agricultural but can be slide together to reduce the beam. The rig is very simple and probably only about 150 square foot. No idea of performance but the build technique is interesting.
     

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  9. oldmulti
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    oldmulti Senior Member

    A fun little design for the big kid in us all. This 10 x 9 foot trimaran is was design by Eric Henseval, a man who knows how to design smaller multihulls (designed Sardine Run tri). A Mr Proserpio paid for the design and sells build plans but the PDF’s are freely available on the web at Growing the 10 Foot Trimaran Class | Small Trimarans http://smalltrimarans.com/blog/growing-the-10-foot-trimaran-class/ PDF #5 of 10 foot trimaran class is the preliminary structure PDF that gives some structural details. The photos of the final boat built by Mr Proserpio has modified the cross beams. The tri weighs 100 lbs and can carry 200 lbs. The sail is an ex Moth of 85 square foot with a 85 square foot gennaker to suit the Itialian 10 foot class rules. The top speed recorded by these 10 footers is 11 knots. This boat has done 10 knots in initial sails. Pure fun for the "kids".
     

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    Last edited: Sep 8, 2019
  10. Dolfiman
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    Dolfiman Senior Member

  11. oldmulti
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    oldmulti Senior Member

    Details are always amusing in multihull design. John Shuttleworth gives options for benches, shelves etc of 400 or 600 gsm glass on either side of 12 mm foam or 4 mm ply depending on circumstances for 28 and 31 foot boats. In a F22 tri a step for a ladder was made as follows. On top is 300 gsm 90/90 carbon fibre, 10 mm corecell foam, 300 gsm 90/90 carbon fibre. Additionally there are two 20 mm foam stringers covered with 600gsm triaxial, 0/-45/+45 and a piece of unidirectionals. All vacuum bagged. Should take even heavy crew members. On the same boat the back rests are 6 mm H60 foam with 200gsm carbon fibre 0/90 each side. The amount of work and cost for a small weight saving is amazing.

    Another F22 builder whilst working on the second float half, noticed some lettering on the edge of his corecell foam that said "A550". This surprised him since he had ordered and previously gotten A500 foam but upon checking the rest of the foam it turns out that it is all A550. He did some numbers. Using Farriers figure of 950 sq ft of foam to build the entire boat, he came up with the following total weights for the different weights of foam:

    Pure A400 boat: 119 lbs (A400 density=4.0-4.6 lb/cubic foot) standard build recommendation.
    Pure A500 boat: 140 lbs (A500 density=4.7-5.4 lb/ cubic foot)
    Pure A550 boat: 181 lbs (A550 density=6.1-6.7 lb/cubic foot)

    The builder went to a company that was selling large offcuts of foam cheaper so he said OK I will buy A500 offcuts instead of the standard build A400 foam not realizing the consequences of the additional weight. He used the standard glass layup fortunately, as any carbon fibre layups would have been negated by the additional foam weight.
     
  12. catsketcher
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    catsketcher Senior Member

    The ladder details scare me. The vac bagging of such a complex shape would be really hard. I think that sometimes designers get caught up in their own bubble and forget about details like the fairing required on complex foam shapes (like the ladder). This could then negate any advantage the foam has over say a cedar ladder done in nice varnish in terms of weight. Picking out the peel ply in the nooks and crannies developed when bagging the step joins would be a pain. Or you could have some fun and make a nice cedar railed and stair tread ladder with a vac bagged veneer of a hardwood on each step. It would take less time, look really nice and weigh about the same after filling.

    I prefer to use 4mm-5mm ply for the benches in the boats I have built. It is tough and stiff (the 5mm is a 5ply). I do like foam but for me, ply is great until you have to use stringers to stiffen it, then I prefer some sort of composite.

    As to foam always being a great material, I once ran into a foam cat which had a light laminate (it was on port, very light wind and they stopped in front of me - with a Twiggy tri I would have hit them harder with my float if I tried to bear away). When we touched their laminate just deformed - no cracking sound, no thud, just a divot in their topsides. It was a bit disturbing.

    The lightweight laminate multis of the 80s could be globally fine, but could have issues with localised loading - I think this is one of the reasons we go heavier today.
     
  13. oldmulti
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    oldmulti Senior Member

    https://forum.katera.ru/index.php?/topic/43381-davaite-narisuem-parusnyi-mnogokorpusnik-dlia/page-133

    For those who need an additional fix of multihull design. The Russian web site above is interesting as it intended to design a multi on the web. The site is over 140 pages of “online Katamaran design”. Russians do reasonable thinking but occasionally speak in code (or it could be the English translation engine)! It has many potential designs some of which have been built. I have put up a few of the design proposals, some good and some needing refinement. But the Rus Cenpn 3 and 5 attachments are of a design that tried to use conical plywood sheets to skin a hull. The advantage of a round bilge hull shape built with flat plywood sheets slightly tortured.
     

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    Last edited by a moderator: Sep 8, 2019
  14. oldmulti
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    oldmulti Senior Member

    Catsketcher. Your comments and experience are very welcome. Each designer has their own approach but few people who build the one off boats understand that often there are easier ways of achieving a result for often minimal weight gain. Home building a boat is hard enough without having build a complex high tech part (eg a step of seat back) for very little gain.

    Many years ago I ran across an English guys attempt at a 26 foot home design cat. He turned the concept into a public domain development of the catamaran and the attached PDF gives you the latest version of the cat. The cat is 26 x 13.8 foot with 300 square foot of sail area. The boat is mainly ply with 6 mm hull sides 9 mm bottom and decks and 12 mm bulkheads. The design is more of the old English style cat but probably could be updated. I have no idea if any have been built. Information only.
     

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  15. oldmulti
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    oldmulti Senior Member

    An interesting tri of which I know nothing beyond it is in Russia. Ply and timber. Name is Trim.
     

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