Multihull Structure Thoughts

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

  1. redreuben
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    redreuben redreuben

    In case anyone is wondering why there aren’t many Kelsalls around a 26-28 footer plans fee is 3-4000 US.
     
  2. rob denney
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    rob denney Senior Member

    Some of it supports my post, some of it not so much. See inserted comments

    The difference between infusion and bagging wet laminate is that the air is sucked out of the former pre wet out, the latter post wet out. There is no reason why the air in the cut cells would not be sucked through the resin, except that if the resin has started to gel, which is often a problem with wet bagging. If the air isn't sucked out of the cut cells, it is unlikely it will be sucked out between the layers of cloth, resulting in a poor laminate. If an infused panel is heavier, it is due to poor matching of the panel edges or the bag not being pulled tight against the edges of the core. Intelligent infusion overcomes both these.

    Again, not if the resin runs freely. Both laminates will have minimum amounts of resin. The wet out one will have the extra in the absorber material, the infused one leaves it in the drum.

    If the laminate is not bagged under full pressure, it will contain air bubbles and excess resin. Both are likely to be stress raisers hastening any breakdown in the laminate.

    Absolutely.

    If the layout is logical, the laminate is wet out as the resin front progresses.
    Pin holes are the result of all or some of: air in the resin, inadequate vacuum, poor quality or excessively handled cloth (resulting in contamination) and mould prep.

    The carbon uni in the corners of the beam at Custom 20m/65′ – NORWAY – HARRYPROA http://harryproa.com/?p=726 is 20mms thick. Wet0ut was not a problem. There was no need to control the feed rate. No interlaminar material was used.

    For what it is worth, I am writing this in Majuro, Marshall Islands, where I am spending the next 70 days showing selected locals how to build a boat Mini Cargo Ferry – HARRYPROA http://harryproa.com/?p=2944 to replace their expensive to run and maintain outboard powered skiffs. They then return to their villages and build their own. Not a pretty boat, but exceptionally easy to build. Hulls are 2 and 3 sheets of ply long, half a sheet high and wide, with rectangular sections. Minimal cutting and measuring, no strongback or building frames. 6mm/quarter inch ply with 200 gsm/6 oz glass each side, stringers or fillets in the corners, frames as necessary.
    The income from this job goes towards a 24m/80' prototype cargo proa Cargo Ferry – HARRYPROA http://harryproa.com/?p=2561. Still a few tests to do, but the hull laminate will probably be 10 layers x 400 gsm/12 oz uni at various angles. Maybe a layer of thin foam for panel stiffness and to distribute the resin. Stringers and frames as required. I have managed a pretty cool deal with labour and shed. With a bit (lot) of luck, it will be sailing this time next year.
     
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  3. oldmulti
    Joined: May 2019
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    oldmulti Senior Member

    The attached is a listing of the multihulls we have spoken about in the first 15 pages of this thread. It is broken into simple categories of Trimaran, Catamaran etc. The name of the boat and a number appears, the number is the length of the boat in feet. Page number of the Thread appears in the right column or immediately after the length number. Hope this helps.
    I will do another one for the next pages 15 to 35 later. After 600 posts even I was starting to forget what had been spoken about.
     

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  4. oldmulti
    Joined: May 2019
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    oldmulti Senior Member

    The final in this Kelsall cruising cat series is a cat called TT 28. The TT 28 was 28.25 x 16.25 foot displacing 5600 lbs and carries 430 square foot of sail area. The hull length to beam is 7:1. This was one of Kelsalls Tonga range of which there was a 22, 25, 27, 28, 30, 36, 42 and 60 foot model of wide hulled tube cats of foam glass of ply epoxy construction. The concept was to allow people to build the hulls at home then transport the boat to the sea for final assembly. The accommodation in the hulls of all versions was impressive for there size. The 60 footer had hull accommodation that would have impressed even French cruising cat designers with walk around beds and full diner tables. To my knowledge none of the TT 28’s were built.

    The options for building a TT 28 hulls and decks included foam glass, ply epoxy and a solid glass option with foam stringers. The crossarm structure was ply timber. This boat had full headroom and just enough space for a face to face dinette in its 5.2 foot wide hulls. In my youth I had the IOMR rating program and rated this boat at 0.67 at 6000 lbs. This is not fast. Time Machine The 26 foot tri with long floats mentioned earlier rates at 1.01. This is a pure cruiser that is a minimum cat that is capable of crossing oceans if sensibly sailed. The Tonga Tini 25/27 proved much more popular as a design. Derek if you read this, is there any way that some of these older designs EG the ply Tonga 22 or the TT 28, could be made available at a reasonable rate because I think there is a small market available.
     

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  5. luff tension
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    luff tension Junior Member


    Your work is awesome old multi and the reference index is priceless, can it be pinned to the beginning of this thread?
     
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  6. bajansailor
    Joined: Oct 2007
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    bajansailor Marine Surveyor

    +1 re Luff's comment above - this whole thread is already a seminal work / treatise on every aspect of sailing multihulls.
    If you assembled everything into a book it would become very quickly the standard reference, and would no doubt sell for a small fortune.
    Thank you OM for all the work you have put in so far - I know that I will equally enjoy what is still to come.
     
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  7. Adrian Culda
    Joined: Jan 2020
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    Location: Edmonton, AB

    Adrian Culda New Member

    Wow.. finally made it to the end !!
    lots of knowledge in here specially for someone who has never built and was thinking of tackling such project!

    Thank you for sharing !!
     
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  8. oldmulti
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    oldmulti Senior Member

    As requested, the kind Thread moderator has inserted the first 15 pages index at the start of the thread. Adrian you are not at the end, you are only part way through there is more to come.
     
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  9. Adrian Culda
    Joined: Jan 2020
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    Adrian Culda New Member

    Can't wait.. I have an background in aviation, industrial maintenance as well as a mechanic. Plan is to build a 75' tri as a retirement project. I really like the NEEL 65 Evo however financially its far out of my reach unless I build it myself and slowly pick away at it.
     
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  10. redreuben
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    redreuben redreuben

    Old multi, do you have any specs on the Crowther International 23’ ?
    There are a couple here in Perth and one in particular is a project job and could be salvaged for rig and beams but I can’t find even basic specs on line like beam, sail areas etc Anything in your archives ?
     
  11. oldmulti
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    oldmulti Senior Member

    Redreuben. The International 23 basics are 22.5 x 11.5 foot that can compress to 8.2 foot sliding beams. The weight was meant to be 1000 lbs and it displaced 1700 lbs. The rig was fractional and had 320 square foot in battened main and foretriangle. The hulls were mainly solid glass with fixed keels. The mast and aft beams were Canberra lamp post section E 8150 (I think about 203 x 145 mm??) which is bullet proof for this size of boat. The same E8150 section is used on the Shockwave 29 (2500 lbs weight) and Schockwave 37 (4000 lbs weight) cats as full length beams (18 foot plus). E 8150 weighs 5 lbs/foot. The beam length in the 23 is exactly 8.2 foot long. It slid inside 6 mm thick wall solid fiberglass tubes. When at full sailing width 500 mm (19 inches) was left in the glass tubes. The hulls flexed a little when sailing as the builder went against Lock recommendation of on having a top entrance hatch. The build cut the hatchway down the side of the cabin. The hulls are only useful for sleeping. It was a reasonable sailor but took enthusiasm to drive it. Like all sliding beam folders I watched 2 strong men take over an hour to get it set up from trailer to water as the hulls bind on the beams unless they are pulled apart exactly parallel. The mast and rigging were strong. The brochure boat beam is wrong!! unless it is a fixed beam boat. The sliding beam models were 3.5 meters (11.5 foot wide).
     

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    Last edited: Jan 19, 2020
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  12. oldmulti
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    oldmulti Senior Member

    Dick Newick built a magnificent tri (with some assistance) that was intended to be a floating home for he and his wife. It was named Pat’s, it was Dicks view of what a cruising trimaran should be. Pat’s was 51.1 x 28 foot displacing 10,000 lbs and carrying a total of 740 square foot of sail in two mainsails on 48 foot (from deck) freestanding carbon fibre epoxy masts. The masts are 280 mm diameter at deck level. The sails were double thickness (Ljungtrom style) and down wind the 2 halves could expand to add extra sail area. The floats were “half moon” shape. The length to beam on the main hull was 11.5:1. The tri was demountable for possible shipping if required. The boat was eventually sold to a Swiss attorney and is now available in France for sale at 140,000 euro after a refit.

    Pat’s could comfortably cruise at 10 to 15 knot averages under the right conditions. The boat was a genuine single hander or two people operation. It even had a modern inconvenience of an anchor winch. Dick intended to live aboard for several months a year but the boat took 10 summers to complete (could not work on it in winter) and he and his wife decided living on land would be more sensible. Dick would sail to a vacation location and his wife would drive there and stay aboard. The hull panels were made in about 1979 and the boat was launched in 1988 and is still sailing today with minimal maintenance. Constant chamber if well built will last a long time.

    The tri was constructed from 3 layers of 6.4 mm white cedar for the main hull, decks and floats. The keels are epoxy glass fillets. There are strong sheer clamps on all hulls for stiffness and to support cross arm connection points. Bulkheads are taped to the hull sides. There are no intermediate frames or stringers and furniture provides additional strength. The exterior is covered with E glass and a layer of polypropylene for protection. The mold was the same as used for Chris Whites 52 foot Juniper tri and Pat’s panels were built at the same time. The 2 cross arms were 450 x 250 mm timber boxes reinforced with carbon fibre top and bottom and had waterstays. This is one fast cruiser that would carry 2 people a long distance very comfortably.
     

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  13. redreuben
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    redreuben redreuben

    Thanks, Multi answered my questions beautifully. Beams are too short, back to the drawing board. Was considering wether the beams and rig could go on a Richard Woods hull.
    I think basket case Seawind 24 would be a better candidate.
     
  14. oldmulti
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    oldmulti Senior Member

    We have dealt with the Scarab 22 previously but this boat is interesting because of the rig it carries. The Scarab 22 is 22.4 x 18.5 foot folds to 8 foot weighing 1100 lbs displacing 2000 lbs and carrying a 380 square foot main and genoa. The French builder built a basic foam glass Scarab 22 with one modification. Instead of a fractional sloop rig he got Gilles Montaubin to design a freestanding 2 mast schooner rig for the tri with the same roll the sail around the mast reefing approach used by Newicks Pat’s. The Ljungstrom rig masts are 29 foot carbon fibre tubes and weigh 25 lbs and 22 lbs. The 2 sails weigh of 10 lbs each and the mizzen wishbone 11 lbs. Translation to stand the masts and sail up you are lifting a maximum of 43 lbs. Doable if it’s not too windy. PS all the add on sailing gear weight over a basic boat including the rig, electric motor, safety gear, battery and anchor etc but no personal stuff is 260 lbs in weight. The owner also modified the cabin by raising the roof 180 mm to obtain more room.

    Now the fun bit. This guy sailed with his mate who also has a Scarab 22 with a conventional fractional rig on a few occasions. This was not a racing situation but both guys could sail and liked to push the boats in side by side sailing. The results were interesting. The schooner rig will give 13- 14 knots reaching with peaks of 16 knots in force 4-5, sails reefed by 2 rolls on mast it will do 11-12 knots. Compared to a fractional rig Scarab 22 the schooner will sail 5 -10 degrees further off the wind-up wind (tacks trough 100-110 degrees) and the fractional rig is “much more powerful”. The schooner rig also suffers in a light wind and choppy seas with its tacking angle going to 140 degrees as the heavier mainsail cloth not holding its shape in light airs as a light weight genoa would. The difference between the two rigs is marked after a long day’s sail in a variety of conditions where the sloop rig will arrive an hour earlier at a destination. The big difference is the ease of sailing and reefing of the schooner rig but at the expense of some speed especially upwind. If you are a cruiser, the schooner rig is cheap, easy to reef and works well. If you are a racer cruiser then the sloop rig will add, guess, 10% more performance overall. The jpegs give the idea and my idea of cruising.
     

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  15. oldmulti
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    oldmulti Senior Member

    Cobra catamaran is a beach cat that was designed in the early 70’s and is still going strong. Its 16 x 6.9 foot and weighs 175 lbs with 160 square foot of sail and can be sailed single handed or dual handed. It is a tortured ply design using 4 mm ply hulls and decks with 75 mm tubular aluminium cross beams (these are optional beams). The original mast was a E5308 90 x 55 mm 24 foot long section and the main beams were also the same section with a stainless steel dolphin striker.

    The full plans are available at Cobra Catamaran documentation page https://www.cobracat.com/cobradocs.html

    The plans are in the Zip file at the end and describes in detail the hull shape, tortured ply technique and the full build details. The building instructions and parts list are in the PDF’s below. There are 2 samples of the PDF plans also. These cats are fun and relatively fast. Fiberglass versions also exist.
     

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