Multihull Structure Thoughts

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

  1. redreuben
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    redreuben redreuben

    I think a comparison of the Fish & Chips and the Woods Eagle would be interesting
    And perhaps the Siren 8.4 and the Simpson 8.2 Backslash ? They both seem interesting pairings.
     
  2. guzzis3
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    guzzis3 Senior Member

    I've been thinking the same about Eagle/F&C. Eagle has 5'6" headroom and is simpler and probably quicker to build. It offers the choice of LAR keels or daggers but not, in standard form anyway, swing centerboards. F&S obviously only offers centerboards. Making centerboards for Eagle would not be difficult. Likewise adapting F&S to LAR keels or daggers is doable.

    Both could be built in 8mm foam with 600gsm 45/45 each side. Eagle hulls are about 1.05 wide, and it offers a massive 2' bridgedeck clearance.

    F&S cabins extend well back so there isn't space on the hulls to sit, maybe 1 person each side but no more. I'd build a solid bridgedeck with a small cuddy and the cockpit integrated behind that, like Sango.

    Mr Woods has said he hasn't offered a round bilge version in order to give the european built Elf a chance.

    I'm not a fan of lightbulb hulls. Just personal opinion. They are a lot of work to build and it's easier to get width in a bridgedeck cuddy/sportsdeck/pod arrangement although I suppose it's hard to get standing headroom under 30' on a bridgedeck. The Gypsy solution to that dilemma is clever.

    I have a set of Mr Kendrick's trimaran plans and have seen some others. The detail is remarkable. He gives fully dimensioned drawings for every chine panel. drawings are A3 and can be printed and bound at officeworks etc for very little money.

    The Simpson designs are very nice but I'm not keen to do business with Boatcraft Pacific, and the plan prices aren't exactly bargain basement. There is a question over support and given there are other options....
     
  3. oldmulti
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    oldmulti Senior Member

    There is a request to compare Fish and Chips Scarab 24 foot cat with Richard Woods Eagle 24 and I am including Kelsalls old Tonga Tini 25 (now 27) catamaran. Each is described as a coastal cruiser that can sail offshore in limited trips.

    The Tonga Tini 25/27 is 25 x 16.5 foot and weighs 1900 lbs with a displacement of 4000 lbs. The hulls have 9 mm ply bottom and lower chines. The hull sides and decks are 6 mm ply sides with 200 gsm glass outside. Bulkheads are 9 mm ply. The main beam is 200 wide by 500 mm deep with 12 mm ply top, bottom and sides with timber framing. Internal bulkheads for main beam support are 9 mm ply either side with 18 mm ply where beam rests inside hull. The fore beam is 100 mm aluminium tube. The rear beam a wooden box beam. The 32 foot mast carries a 340 square foot. Hulls are 4.5 foot wide with 4.5 headroom.

    Fish and Chips is 24 x 15 foot with a 2,130 lbs weight and a 3,580 lbs displacement. Hulls and deck 6 mm ply with 9 mm bulkheads and ring frames. Inside is 300 gsm unidirectionals with 400 gsm biax outside around the entire hull. The fore beam is 100 mm aluminium tube, The aft beam is a 200 mm aluminium tube. The main beam has 9 mm ply faces and bulkheads with multiply layers of unidirectional glass top and bottom with some timber framing. The support bulkheads of the main beam are 27 mm thick. The 31 foot mast carries 325 square foot. Hulls 4 foot wide with 4.5 foot headroom

    The Eagle 24 is 24 x 14.5 foot and weight of 1450 lbs with a displacement 2800 lbs. Hull and decks 6 mm plywood with 200 gsm biax glass outside with 50 x 18 mm framing on 6 mm plywood bulkheads. The fore and aft beams are 150 mm aluminium tubes. Main beam is a version of either plan shown below. The mast is 160 x 110 mm and 31 foot high with 380 square foot of sail. Hulls 3.5 foot wide are with 5.5 foot headroom.

    The variation of structure are interesting. There is a lot of similarities between the Tonga 25 and Fish and Chips with both cats depending on the main and aft beam to resist twisting resulting in the need to has strong main beam support bulkheads in the hulls. The Eagle 24 depends on the 150 mm aluminium tube fore and aft beams to resist twisting. The Eagle 24 mast beam supports the mast and does little more. Richard Woods Eagle 24 was the recently created and has the advantage of using lighter specifications (but as equally as strong) than the other 2 designs but there is not that much difference. The Eagle 24 has a 1,350 lbs plus payload capability with the Tonga 25 having 2,000 lbs payload capability. The simplest and probably fastest build would be the Eagle 24.

    The accommodation of the Tonga 25 is good as long as you don't want to stand up. Fish and Chips foot hall walk ways are narrow and some of the bulkheads need a thinner person or some slight contortions to get past. The Eagle 24 has the least accommodation but the best headroom. Take your choice. they are all practicable for 2 to 3 people over a week cruise.

    The Tonga 25 is the highest displacement and widest waterline beam on the hulls, Fish and Chips is in the middle. The Eagle 24 is the lightest with the narrowest waterline hull beam. The Eagle 24 also has the largest sail area. But the Eagle 24 has the simplest hull shape. Overall, I think the Eagle 24 would be faster than the other 2 but I think over a day cruise you would not notice that much difference. I have sailed on and against Marine Timbers Tonga. It goes surprisingly well in light to moderate airs but will not get near a EG Buccaneer 24 trimaran whereas the Eagle 24 would at least see the Buccaneer.

    The jpegs give the idea. The PDF’s need to be viewed.
     

    Attached Files:

    Last edited: Aug 31, 2021
  4. redreuben
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    redreuben redreuben

    What bothers me about all of them is the size of the flat bottoms, I know it gives internal beam and displacement for the size, a decent footwell etc etc. But it just grates with me. Am I being irrational ?
    My thoughts to date have been to take Fish&Chips to 26’ with a Woods cuddy and Eagle headroom.
    Alas I think my boatbuilding window has closed.
     
  5. guzzis3
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    guzzis3 Senior Member

    Why has your building window closed ? :(

    F&S has chined round bottoms doesn't it ??

    Eagle is well V'd forward so I don't think it'd slam, but I would prefer a multi chine or round bottom option. You get a round bottom option on gypsy of course. Mr Woods deliberately did not do that with Eagle as I said above due to the production boat (Elf). IMO both Eagle and F&S would want the mast further forward, bigger main smaller jib, to accommodate a decent bridgedeck pod cabin (cuddy, whatever). I can't speak for Mr Woods but I would not be surprised if he was willin to supply sango/wizard rig and cuddy details with Eagle. Actually the wizard items would probably fit nicely on Eagle.
     
  6. Teamscarab
    Joined: Aug 2021
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    Location: Glenwood Queensland

    Teamscarab New Member

    Hi, after all the discussion about my cat designs I have decided to extract the digit and finish off the SIREN 8.4. I have recovered all the drawings except the panel dimensions so there will be a few drawings to complete. I intend to do this between painting jobs on my Scarab 32 tri starboard float. Fran will put the design up on the <teamscarab.com.au> website when I have the drawings complete.
    Regards
    Ray Kendrick
     
  7. oldmulti
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    oldmulti Senior Member

    Ray. Thank you very much, it will be appreciated and hopefully purchased by many.
     
  8. guzzis3
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    guzzis3 Senior Member

    I hope you sell a lot of the plans. Both boats are pretty interesting. I was just about to suggest you send me F&C in leu of a refund but you were too quick for me.

    You could almost buy all the materials to build for what Mr Kelsall charges for plans.
     
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  9. redreuben
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    redreuben redreuben

    See, nagging does work ;)
    Good Job Ray, I hope its worth it.
    Thats too sexy a hull to stagnate on a hard drive.
     
  10. redreuben
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    redreuben redreuben

    I agree.
     
  11. redreuben
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    redreuben redreuben

    When I first saw the pictures of the Marine Timbers, Tonga 27 I had a discernible rush of blood ! But alas Mr Kelsalls prices soon killed that.
    I think its sad that such a capable and prolific designer priced himself out of the market the way he did.
    Multihull sailing would have been immeasurably better off with more of his boats on the water. :(
     
  12. guzzis3
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    guzzis3 Senior Member

    There are other designers who try to sell plans for big money. I don't know how many customers they have these days. Presumably there are still people buying from Schoining etc.

    But at the pragmatic end of the builder market there are plenty of very good quite cheap options.

    Presumably there are still people buying Wharram plans so the market is unfathomable. (couldn't help myself)
     
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  13. oldmulti
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    oldmulti Senior Member

    Redrueben, the comparison between the Backlash and Siren 8.4 became redundant after Ray Kendrick of Team Scarab kind offer to finalise the Siren 8.4 design yesterday. So today, something different.

    You need to get places quickly in some comfort? Try the MN Centurion Interceptor which is a long-endurance fast patrol boat designed and manufactured by South African defence solutions provider Milkor to serve the requirements of the military and coast guard forces. The Milkor s a 39.5 x 15.7 foot power catamaran. The cat has a full load displacement of 22,500 lbs. The cat features a hydrofoil-assisted stepped catamaran hull design and offers enhanced seakeeping performance. The engines can be either two 440hp diesel inboard engines or two 350hp outboard engines. The cat can carry up to 6600 lbs of fuel (940 gallons or 3600 litres).

    The performance is interesting. The typical cruise speed of the vessel is from 30 knots to 40 knots, whereas its maximum speed is 54 knots (depending on the engine power) and loitering speeds 7 knots. The hull design allows high speed as well as stability and fuel economy – maximum range is between 600 to 1000 nautical miles with an endurance of 5 days at a surveillance patrol speed of 7 knots.

    A test of the Milkor produced “Milkor said the vessel was pushed to its limit, encountering sea states with swells of four to eight feet high and the crew intentionally buried the nose in waves coming into St Francis Bay harbour to see how it would handle. The boat averaged speeds of 25 to 30 knots in sea states 3 and 4 (up to eight foot swells) and 30 to 40 knots in sea states 1 and 2 (up to one foot swells). A top speed of 47 knots was achieved.”

    OK so it genuinely fast but what about the crew? The crew members are seated in shock mitigation seats housed in the air-conditioned command and control bridge located amidships. The cabin is totally separate from the hull and is on an air suspension with shock absorbers to reduce the slamming forces in rough seas and effectively negate it. There are two hot-bunking sleeping berths, sleeping at 40 plus knots would be very interesting. The bridge also has armoured glass and ballistic protection features to protect the crew from bullet firings. Huh? Did I mention the vessel is compatible with a 12.7 mm machinegun, a 40 mm grenade launcher and could also accept a 20 mm cannon and a missile system on the aft deck? Need to intimidate those pesky interlopers at your favourite anchoring spot.

    The vessel’s PVC foam carbon fibre-reinforced composite skin and frame with built-in counter-radar material gives it a stealth capability. Any power cat that can do 50 knots under moderate horse power, requires a really good structure.

    There are video’s online of the Milkor performing at high speed. It is very interesting. The jpegs give an idea of the a very good high speed cat.
     

    Attached Files:

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  14. oldmulti
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    oldmulti Senior Member

    Andromeda is a 1980 hydrofoil cat that whose design was started in 1967. The Russian design was done by Yu. Chaban and I. Matveev from the Central Design Bureau for hydrofoils as a small project to develop a 40 knot sailing hydrofoil. The basic cat is 18.8 x 8.5 foot with a weight of 404 lbs. The mast is 27 foot high and carries sail area of a mainsail 210 square foot and a 59 square foot jib. The length to beam is 10 to 1 on the single chine hull.

    The hulls are 0.8 mm thick of light alloys D16 and AMg-61. The frames and I-beams of the connecting bridge, and all the joints are riveted. The frames are made of 15 X 15 X 1 mm corner sections, longitudinal stringers are made of 20 X 20 X 1.5 mm corner sections. In the middle of the bridge there is a centerboard (also made of light alloy) with a symmetrical profile with a 9% thickness. The rudders are 5%.

    The surface piercing foils are welded metal: The bow foils are from aluminum-magnesium alloy, the stern foils are from stainless steel. The foils are attached to the deck and are fixed on the axles, which allow the foils to raise the out of the water. I won’t go into the maths but the design was modelled for wind strengths from 5 to 40 knots and wind angles from 40 degrees to 150 degrees. The design settled on “self correcting” surface piercing foils to minimise any crew intervention required when sailing across a wind range. T foils were considered but considered but would need more control than was thought to be practicable by a crew. The foils section are a variation of an ogive section, symmetrical fore and aft with a near flat bottom.

    The design theoretically is capable of 2 times wind speed, in testing the cat only achieved about 1.5 or 1.6 times wind speed under certain conditions. The testers described it as “Thus, several test trips of the catamaran confirmed the expediency of using hydrofoils to achieve high speeds on a sailing vessel. However, as follows from the comparison of the thrust, drift and drag forces, qualitatively confirmed by tests, the movement of the catamaran on the wings was possible only in a certain range of heading angles with respect to the wind.”

    An interesting design done as a government funded project. The cat sailed for 2 years before it was lost in a factory fire. Sorry about the limited jpegs.
     

    Attached Files:


  15. jamez
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    jamez Senior Member

    The thing I like most about the F & C is it has some thought put into cruising amenity for instance a small galley etc., whereas most are just shown with a bunk at each hull end and don't necessarily have width for anything else to be added. I've sailed on a small (4.8) bi plane rigged cat, it was great and sailed well, and not difficult to get used to the differences in trimming the sails in relation to a normal sloop. I think the owner spent as much on the revolving carbon masts/vertical batten sails as building the rest of the boat. Neat to pull a string and have the sail roll up around the mast though. Easy and quick to rig too. I can imagine doing a similar rig on a larger scale could be eye wateringly expensive.
     
    Last edited: Sep 2, 2021
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