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Thread: 6.5 m SOF Kayak/Rowboat/Sail

  1. #1
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    Default 6.5 m SOF Kayak/Rowboat/Sail

    I posted something along these lines in the design section a couple of years ago. Decided to do some more thinking and build a couple of smaller kayaks first.

    I ended up building a smaller double (adult plus kid):

    Did some fishing:



    Built a 5.5 m folding kayak:


    The silver bag below now contains the red kayak above, ready to catch the bus home:


    I might post something on the above projects later.

    I now have a new design sorted, frames cut, stringers assembled, a bit of tidying up and I should have something 3D fairly soon.
    More in the next post.
    Last edited by IanHowick; 04-25-2020 at 12:09 AM.

  2. #2
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    Default Re: 6.5 m SOF Kayak/Rowboat/Sail

    So, some pictures of the design first:

    6.5 m x 0.86 m

    Aim is a big double kayak that can also be set up as a sliding seat rower, and possibly later as a sailer with outriggers. Some similarities in goals to the Angus Expedition and Rowcruisers, though a fair few differences in the design as well.
    These are a couple of views of the basic hull in sea kayak mode, a fairly long cockpit to fit me and two or three kids, it should also allow sleep on board for one.






    With a rigger and sliding seat for rowing, it should go pretty fast like this:


    Possibly with an aka further forward and a couple of inflated amas and a ketch rig. These amas are longer than those on the Angus Sailcruiser, but beam is less (about 1.7 m) so I can use the rowing rigger to support the amas.


    Pictures of some real bits and pieces next.
    Last edited by IanHowick; 04-24-2020 at 11:46 PM.

  3. #3
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    Default Re: 6.5 m SOF Kayak/Rowboat/Sail

    I like it, and I'm impressed by your previous boats.

  4. #4
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    Default Re: 6.5 m SOF Kayak/Rowboat/Sail

    Versitile and good looking! Following with interest.

  5. #5
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    Default Re: 6.5 m SOF Kayak/Rowboat/Sail

    Also following. I like the human powered aspects, a paddle or slide seat oar powered boat for solo camp aboard exploring. I'm happy with my Walkabout for this purpose, but at a meter longer and half the beam your boat must be faster. I'd like to test out such a boat, maybe I can borrow a rowcruiser someday, to get a feel for the tradeoff in a sleeker boat. My one trial of a CLC Expedition Wherry was about a knot faster, but that boat is not set up for on board camping.

    Rick

  6. #6
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    Default Re: 6.5 m SOF Kayak/Rowboat/Sail

    Looks good generally, but I really think you want more beam on the amas if good performance is expected as a trimaran. You could, of course, just put a sail on the hull without the amas and it wouldn't go badly. If you're going to add the weight and complication of making it a full-on tri, then I would suggest you want to plan for a high SA/Disp ratio. And to do that, you'll want more overall beam to stand up to all that sail. I don't think it would be too difficult to get the amas further out, and the improved stability would be signifcant.
    -Dave

  7. #7
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    Default Re: 6.5 m SOF Kayak/Rowboat/Sail

    Make the top of the Ama a little fatter so you can sit on it when pushing the boat hard? The non shunting single outrigger canoes do this with a plank on the ama side and a small platform on the non ama side. You might want to increase the prismatic at the stern if you plan to sail it a lot.
    Ben Fuller
    Ran Tan, Liten Kuhling, Tipsy, Tippy, Josef W., Merry Mouth, Imp, Macavity, Look Far, Flash and a quiver of other 'yaks.
    "Bound fast is boatless man."

  8. #8
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    Default Re: 6.5 m SOF Kayak/Rowboat/Sail

    Quote Originally Posted by Woxbox View Post
    Looks good generally, but I really think you want more beam on the amas if good performance is expected as a trimaran. You could, of course, just put a sail on the hull without the amas and it wouldn't go badly. If you're going to add the weight and complication of making it a full-on tri, then I would suggest you want to plan for a high SA/Disp ratio. And to do that, you'll want more overall beam to stand up to all that sail. I don't think it would be too difficult to get the amas further out, and the improved stability would be signifcant.
    Yes, something to think about. Trimaran sailing version is a ways down the track in any case - plan is to first get it on the water as a kayak, then get the sliding seat set up in it, see what makes sense after that. With the amas about where they are or a little further out, it looks possible to get a lot more righting moment by sitting out on the windward ama. It could be quite a comfortable sailing position with bum on the ama and feet in the cockpit. If the amas were significantly further out, they'd not be able to extend so far back without getting in the way of the rowing, then you wouldn't be able to sit out on them.

    Have to be a little careful, greater beam->greater stability->ability to stand up to more sail and you're vastly increasing the forces, especially torsional forces on the structure. Monocoque ply structure has huge torsional rigidity, that torsional rigidity is much harder to achieve in a lightweight space frame structure.

    By the way, typo in the second post now fixed, beam is 0.86 m, not 0.76 m.

    Narrower hull beam than Colin's boats, aim is to preserve the ability to paddle it efficiently as a kayak when it's in the sliding seat but no amas mode.

  9. #9
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    Default Re: 6.5 m SOF Kayak/Rowboat/Sail

    While it's a little tricky, canoes and kayaks can be sailed without amas. I sail one that is only 28" wide.

  10. #10
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    Default Re: 6.5 m SOF Kayak/Rowboat/Sail

    Some pictures of some real bits and pieces:

    Cross frames:


    Keel, stems and sides ready to go:




    Some cable ties to hold things together at the bow and stern:




  11. #11
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    Default Re: 6.5 m SOF Kayak/Rowboat/Sail

    And suddenly we have something that looks like a boat:




    Detail of how the cross frames and gunwale/lower chine go together:


    A stringer will go in halfway between the keel and the chine, and a second chine will go in above the one you can see above.
    Midships cross section like this:



    Still a bit of work to do, taking it apart, tidying up and chamfering all the ply and stringer edges before putting it together permanently with epoxy and some lashings.

  12. #12
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    Default Re: 6.5 m SOF Kayak/Rowboat/Sail

    Wow! No steam bending or strongback. Very clever. I think lots of people will be asking for your CAD file.

    Looks great!

    Woody
    Last edited by Woody Jones; 04-25-2020 at 09:34 PM.

  13. #13
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    Default Re: 6.5 m SOF Kayak/Rowboat/Sail

    Detail of how the additional stringers will fit in place:




    >No steam bending?
    Actually, I'm thinking I will probably steam bend an additional thin rib in-between each of the ply frames. Those stringers are pretty light (18x18mm). Main strain on them is when pulling the skin tight, trying to get it wrinkle free without bowing the stringers in can be tricky. (Gunwales are 18x40, Keel is 25x25).

    Mock-up with a strip of MDF:


    Yes, no strong back needed, just accurate cutting and measuring and faith in the numbers that come out of the CAD.

    The girder formed from pre assembling the gunwale and chine has a lot of vertical stiffness, and putting it on an angle locks in the gunwale sheer and keel rocker.

    The big advantage is I can potter away in the garage and garden making bits that can hang on nails along the garage wall, then in one session I can go straight to a 3D boat that can be hung from the rafters in the garage. (Though said rafters are getting a little crowded, this will be number 5 up there). No annoying my wife by parking the car outside and taking over the whole garage floor for months on end...

    Nice also that the structure remains portable at all times, I can take it out of the garage and work on it on a sunny winters day in the garden rather than being stuck in a cold garage.
    Last edited by IanHowick; 04-25-2020 at 10:08 PM.

  14. #14
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    Default Re: 6.5 m SOF Kayak/Rowboat/Sail

    Ian,

    Sent you a PM.

    Woody

  15. #15
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    Default Re: 6.5 m SOF Kayak/Rowboat/Sail

    Wow, great idea!

  16. #16
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    Default Re: 6.5 m SOF Kayak/Rowboat/Sail

    Some Progress, the main hull structure is all glued up now:





    A bit of structure going in to allow attachment of the rigger for sculling. A stringer runs parallel to the long axis under the skin between the gunwale and the cockpit rim. Once the deck skin is on, I'll screw/bolt a stringer on top of that and outside the skin with a line of captive nuts at about 16 cm spacing in it. That way I'll have the ability to bolt the rigger onto that external stringer at whatever position makes sense. The sliding seat rails will primarily attach to the rigger and rest on the cross frames. Aim is to be able to take the boat off the roof rack and bolt the sliding seat/rigger set-up in whatever lengthways position makes sense depending on whether I'm rowing solo, taking my wife out sitting in the back, or have the kids sitting up the front with their fishing rods.



    Some fairly solid structure towards the front of the cockpit rim to take the loads of a set of akas if I go in the direction of a serious sailing mode.

    The deck between the gunwale and the cockpit rim will get some diagonal 18x15 mm timber bracing, the sides will get some zig zag spectra cord bracing, the floor will have some ply inserts bolted between the cross frames. Between all of that it should be torsionally rigid enough to take a decent sailing rig while hiking out.

    Weight of the frame so far is just over 20 kg, shooting for a final full weight of about 30 kg including rowing but not sailing rig.

  17. #17
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    Default Re: 6.5 m SOF Kayak/Rowboat/Sail

    Your workmanship looks good. What are you going to skin and coat it with?

    Woody

  18. #18
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    Default Re: 6.5 m SOF Kayak/Rowboat/Sail

    The hull will be covered in polyester fabric, I have some I think I got from Kudzu Craft some time ago. The deck will be done in a proofed awning/tent canvas.

    Similar to how I did the smaller blue and white kayak in the first post.

    I have thought of doing the deck in PVC truck tarp type fabric, the advantage is it's easy to glue a patch or cover a hole with some duct tape. I'll end up with a couple of holes in the deck where bolts go through to the underlying structure to hold the supports for the Akas for example, with PVC it would be easy to stick a square of duct tape over the hole when I wasn't using the outrigger set up. I'll probably stick to plan A, have a subsequent project for the PVC.

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