Pod cat square rigger cold weather cruiser project

Discussion in 'Multihulls' started by Autodafe, Feb 4, 2012.

  1. Autodafe
    Joined: Jun 2008
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    Autodafe Senior Member

    After a couple of years of reading and saving I've (sort of) finalised a basic design and just started building a hull.

    Layout and accommodation drawings attached for anyone interested.
    Basic Specs:
    LOA 12m
    LWL 11.7m
    BOA 7.8m
    Cp 0.78
    Displ ~1200kg empty
    Displ 2300kg loaded at DWL

    SOR:
    -Ocean going cruiser, for couple or single-handing.
    -Cheap to build and run.
    -Enclosed wheelhouse and easily heated interior for cold weather.
    -Low effort sailing

    I've ended up putting so many unusual (odd?) features in the design that the current build is basically a prototype, and all the major components will be demountable. If some part doesn't work, I chuck it and put in a more conventional design.

    Whacky features:
    -Square rig with dipping yards
    -No outside cockpit
    -Planar open frame truss crossbeams
    -High Cp hulls
    -Low freeboard hulls
    -Fore and aft steerable daggerboards/rudders outboard on one hull only
    -All accommodation in pod
    -Hull section shape - I've ended up after much fiddling with a regular decagon.

    Enjoy,
    George
     

    Attached Files:

  2. spidennis
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    spidennis Chief Sawdust Sweeper

    Had you built a scale model of this yet? Maybe tested out that sail plan? It's an interesting looking design but of course I like cats and multis in general. It kinda reminds me of my design, but mine is MUCH smaller at 16'.
     
  3. pogo
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    pogo ingenious dilletante

  4. cavalier mk2
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    cavalier mk2 Senior Member

    Years ago in England the AYRS did extensive research with a sail very much like this. In fact they called it The AYRS Sail. It worked but there were turbulence issues. Their issue from 1963, Basic Research AYRS publication # 45 shows the details of this sail and has other interesting information. They can be reached on line and I've been told can now send these over the internet though they may have some booklets on the shelf still. Nice to see other peoples extensive research to compare notes.
     
  5. Wavewacker
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    Wavewacker Senior Member

    Can't help you with the sail plan, but I like the cat! NICE!
     
  6. Autodafe
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    Autodafe Senior Member

    Spidennis, I've made some 16 foot scale hulls, but haven't tried the rig out at all. I am planning to make a scale model rig, but I won't start that till the main summer building season is over here.

    Thanks for the link Pogo, I hadn't seen Othmar's designs. They look good, remind me of Kurt Hughes 'cat 38' and some of Lock Crowther's designs such as X10. Google translate is a bit iffy, but he seems to have a very good discussion of the benefits of pod cats for low cost lightweight sailing.

    Cavalier, thanks for the info, I was familiar with some discussion of the AYRS Sail as the "Bolger" rig on Proa forums, but I wasn't aware of the AYRS work on the design. I'll try to get hold of #45.
    On my version all the yards rotate with the mast, so the issue that some proa builders had of the top part of the sail gybing will not apply, however leading edge turbulence may be a problem for pointing close.
    Aerodynamically it's very like the DynaRig also.

    Wavewacker, thanks, glad you like it. I grew up around workboats and it shows in my aesthetics.


    George
     
  7. ImaginaryNumber
    Joined: May 2009
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    ImaginaryNumber An Imaginary Member

    What materials and building technique will you use for the hull and pod, given your SOR that it be cheap to build. How will you insulate the pod?

    The pod almost looks like you could detach it from the hulls in a capsize, and it would become a life raft – though it might need ballast to be stable.

    If you sail in ice-filled waters will the outboard daggerboard and rudder be vulnerable?

    Thanks for posting your ideas.
     
  8. Autodafe
    Joined: Jun 2008
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    Autodafe Senior Member

    Build is marine ply with glass sheath, both hulls and pod. Beams are planned as solid laminated timber, but if the budget looks ok I may save some weight by adding carbon.
    The pod will be a fairly conventional frame and then skin.
    Hulls are a stitch and glue variation. I'm setting up temporary female half frames, in to which I'll assemble a half hull with stitch and glue chines. I can then put a continuous FRP sheath on the inside of the hull skin which should give me better than average impact resistance. Once the inner is sheathed I put in half bulkheads, then remove from mould. External sheath goes on when each pair of half hulls are joined.

    I'm not sure about insulation. XPS is cheap and light, but fireproofing it would mean adding a substantial ceiling in the pod which would add quite a bit of weight.
    My current idea is to use an elastomeric foam and simply paint the interior surface, but I may think better of that after some durability testing.
    Option 3 if the others don't look viable is to build the pod as a PVC foam sandwich, with either ply or glass skins.

    The pod would be buoyant on it's own, but I think that in conditions that would cause a capsize of the whole vessel the pod on its own would turn over so often that it would be totally uninhabitable. Putting water ballast tanks under the floor is a thought.
    Detaching the pod at sea is theoretically possible with just a spanner and something to cut the plumbing and wiring looms, but getting it clear of the wreckage after a capsize sounds like nearly as much work as righting the whole boat.


    Plan A for capsize is to hide in a hull until the weather moderates and then right the boat using a long pole attached under the wingdeck, a large canvas bucket and a winch.
    Because the boat is pretty light, and the pod and masts will prevent it from floating flat on its back the mechanics of the operation look very straight forward on paper. A 6m pole, a 1000L bucket, two temporary stays and a small hand winch will do the job in theory.
    If I have a rush of enthusiasm right after launching I may put this to the test, in calm waters at least.

    The exposure of the boards is a bit of a worry, but I felt that the advantage of having kick-up boards and absolutely no holes in the hulls was worth the risk.
    For major impacts the boards will kick-up, minor impacts should be shrugged off.
    If ice gets jammed between the hull and the board it can be easily cleared from on deck with a pole.
    If there is so much small ice that jamming is a constant problem then I can get some steering with just the biplane sails.

    I'm not fitting inboard diesels, so I won't be going into the ice too much with this boat.

    Cheers,
    George
     
  9. ThomD
    Joined: Mar 2009
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    ThomD Senior Member

    - The center pod looks way too large for a boat intended to sail. Windage is enormous.

    - Center pod design has a number of design benefits for sure, but I prefer arrangements where one does not have to leave the pod to operate mechanicals. Putting the sails way out there, and the daggerboards in unsafe areas is going to make it very dangerous, cold, and wet to run this thing when bad stuff happens

    - The conventional board and rudder arrangement has the advantage of being able to divide the loadbearing aspect of dealing with leeway from the complexities of dealing with steering, it is also well sorted out and can be tuned for a variety of sailing styles. Some very interesting steering boards have been worked out, but some of these break when scaled up, others have features that have simply not been worked out. A 4 board system with ackermans, kick up, ease to defoul, and reasonable steering will be interesting.
     
  10. Autodafe
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    Autodafe Senior Member

    ThomD, appreciate you taking the time to give me your thoughts.

    I hope you're wrong about the sailing performance. The combination of low hulls and upright pod shape make it look huge, but as a measured frontal area it is very low by catamaran standards. Compared to the average 12m cruising cat it only has about a third the accommodation space, mostly in an attempt to reduce windage and weight.

    My impression is that by having very low hulls, open beams and a compact central accommodation the windage will be lower than average for comparable size and comfort. However I'm not an aerodynamics expert, so I may be in for a shock. I know that raking the windscreen aft would help, but can't find any data on how much, so it doesn't seem worth a very definite loss of visibility.

    If you (or anyone else) have suggestions about how to reduce windage with evidence to back it up then I would be very grateful.
    Otherwise I'll have to wait and see how I go on the water.


    In theory the only thing I'll have to leave the pod for when sailing (other than checking the weather) is reefing, which is done inside the guardrails and should feel at least as secure as any other boat I've reefed.
    If the steerable boards fail and I have to go along the hulls then I agree it looks not so good, but most common operations such as raising, lowering and re-setting the kickup can be done from on deck.

    I don't disagree that new ideas are seldom as straight-forward in practice as they look on paper, but I can always retrofit fixed boards in the hulls if these don't work out in testing.

    George
     
  11. ImaginaryNumber
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    ImaginaryNumber An Imaginary Member

    George,
    At one time you were exploring the idea of making the hulls of aluminum. I would think that aluminum would resist abrasion from ice (or coral :) better than wood/fiberglass. What changed your mind?

    How are you making your doors/hatches/seals on the pod? I would think that their being towards the front of the pod would expose them to wave strikes.
     
  12. Timothy
    Joined: Oct 2004
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    Timothy Senior Member

    I hesitate to post this as it is probably not germane but attached is a short animation of a concept for a 40 foot sailing pod cat I toyed with and then abandoned .It was to motor using a Torqeedo electric outboard at at least 6 knots for 4 hours. All electric loads were to be handled by two 26 volt Torqeedo batteries charged only by solar panels . It had to fold to be legally trailer-able and to fit in a 20 ft container with trailer for shipping. I didn't do much work on it as I decided to take a different approach ,but you may find it worth looking at as I ended up with basic proportions and structure similar to your design. I like your design and agree that the windage is no more problematic than it is for a bridge deck cat.You might want to check out the yahoo proa files group as there has been a lot of discussion about the rudder configuration you propose. Also Rob Denney a member of this forum has a lot of experience developing this style of rudder.
     

    Attached Files:

  13. Autodafe
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    Autodafe Senior Member

    Weight was a factor - 6kg/sqm is considered quite heavy skin plating for a 2.5ton wood-composite boat, but very light (2mm) as an Aluminium boat.

    Fear and ignorance was a factor too. While I agree that Al would be better in a number of ways I could never convince myself that I could design and build a aluminium structure that would go the distance. I don't doubt that others can, but I would always be wondering if I made sufficient allowance for the HAZ, if my welds were penetrating fully or if the frame was fatiguing in places I couldn't see.
    If I had more experience with Al and less experience with wood I would probably have ended up building differently.

    Good point.

    I decided to put the doors at the front to make going from helm to deck and back was as quick as possible, but it is fair to say that they will leak during wave strikes.
    Electronics will be mounted high and forwards, while the electrical switchboard has its own doors with rubber seals. I've been considering putting drains in the floor, but that could lead to geysers every time there's a wave strike under the pod. A bilge pump may be safer.
    Another possible problem is if greenwater more than a foot deep is over the wing deck it will be untenable to open the door, but I believe that this should be pretty transitory, even in extreme weather.

    The doors (fibreglass/plywood/wood-frame/plywood) will open by sliding from front to back. I am planning to experiment with UHMWPE runners top and bottom. See attached sketches.
    The latch will pull the door forward into the main seal on the front and rear edges, but the bottom edge isn't very well sealed. In order to avoid jamming there will be a reasonable clearance on the runners within the channel.

    Cheers,
    George
     

    Attached Files:

  14. Autodafe
    Joined: Jun 2008
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    Autodafe Senior Member

    Thanks for the suggestions Timothy. Thats an impressive piece of folding you had there.

    I admire Rob's work and he's pretty generous with his time, so I'll ask his opinion once I have drafted up the detail drawings for my boards.
    Proa files is a good idea as well, I'll poke around there.

    I'm considering electric auxiliaries myself, but Torqeedo is out of my price range.

    George
     

  15. Ilan Voyager
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    Ilan Voyager Senior Member

    1200 kg empty for a 40 feet cat, cruiser ocean going? Are you sure of your calculations? We made in 1986 a batch of 5 Formula 40 catamarans designed by Irens. Good boats, "Data General" skipped by Le Maout was 2nd of the F40 world championship in 1987. Ocean capability. Made in Airex, Kevlar, Carbon fiber, with all the niceties of advanced composites (vacuum, oven etc etc) in a shipyard known for its quality (making also composites for aerospace applications). The top of the cream of the French Flying Circus. No amenities, just a trampoline, no engine, no generator: as empty as a race boat can be. Just the sails, the minimal alu anchor and a few meters of rope. 1725 kg for "Data General"...we had to lest to meet the 1800 kg minimal weight requisite. We got the lighter boats of the fleet at Brest. The F40 "Renaulac" weighted 2560 kg...
    2300 kg loaded is simply totally impossible with your SOR.

    An example; 38 feet Kat http://www.multihulldesigns.com/designs_stock/38cat.html 2087 kg empty (optimistic... I would add 300 kg more). Loaded 2512 kg. Lets's say not far of the 3 tons with all the things that we put in a boat. Cargo 500 kg. One teeth brush and only 2 pairs of socks allowed by person. Cans forbidden, only lyophilized food allowed. LOL
     
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