Designing a sailing dinghy for expeditions

Discussion in 'Boat Design' started by BoraBoats, Feb 25, 2019.

  1. JamesG123
    Joined: Mar 2015
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    JamesG123 Senior Member

    I can attest to the durability of Walker Bay's PE dinghy. :)

    IMG_9636.jpg
     
  2. sharpii2
    Joined: May 2004
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    sharpii2 Senior Member

    I have read this entire thread.

    The design shown here looks more like a sport boat than an expedition one. I can imagine this boat getting caught in a sudden squall. The skipper tries to crank in some reefing, but the CE (Center of Effort) of the sail moves forward. Now the boat suddenly has a lee helm. The skipper fights it, but the rudder stalls (as high aspect ratio rudders are known to do)--The boat broaches. Wind gets under the windward wing deck and flips the boat on its side. It is helped by the lee wing deck digging in. Now the skipper has no control. He must climb up the now vertical windward wing deck just to keep the boat from turtling. Or he at least thinks this will help. He's wrong. His instinctive action has only made matters worse The boat turtles.

    Now. How is he going to right it?

    For a less extreme scenerio, how is he going to sleep on board? I see less than 0.60 m of width on either side of the centerboard case.

    IMHO, you would probably be better off using real cross beams and maybe shorter than usual oars to keep clear of them. These cross-beams can be made of bent tubing to keep the floats out of the water when not sailing, as this is supposed to be a production boat. The floats can remain the same, but you may want to lengthen them, and maybe fill them with foam, or even make them out of foam. The open space between the floats prevents the wind from further flipping the boat in the event of a knock down.

    It may be possible to make the boat out of molded foam with vacuum molded PE skins on the top and bottom glued into place. This way, compartments can be molded in to keep some of the cargo separated from the crew. It may even be possible to have some heavier stores stowed beneath the crew.

    As drawn, the boat seems subject to some extreme torsion loads due to the mast placement and rig type. It may be possible to use a three-stay system with a bearing at the top of the mast, to allow it to rotate. I presume you intend to use the headsail only in light air. Anything above that will make the luff sag and kill its efficiency. With a stay system, this problem could be greatly reduced.

    If you want to stay with the mast-roller-furling, it is probably best to have the boat balance best at the smallest reefed SA, although the fore-and-aft pivoting board can help at least some in this regard.

    Just thinking aloud.

    P.S.-- The mainsail, as shown, will probaly not stand. The verical battens will hold the peak up but will not likely hold it out. The top of the sail could bag on you.
     
  3. Dolfiman
    Joined: Aug 2017
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    Dolfiman Senior Member

    The design is attractive but I am afraid I share the concerns about the wings, could be more a source of worries that a safety in rough seas (H > 1m) and wind force 5 to 6. Moreover the inflatable pontoons are very aft, in case of brutal contact with water when beam reaching or downwind at high speed, you can face a pitchpole capsize.
    An alternative to have significantly more stability without the wings complication and hazard could be just to add more beam overall and especially more Bwl (when comparing with RS Aero ones), together with a hull shape giving a significant hull contribution to the RM at 10° heel angle (illustration here attached). The DLR 100 to 120 (payload depending) is still light enough for sailing with planning speed occurences. The floatation surface leads to 34 kg per cm, to deal with various payload. An overall beam of ~ 1,60 m is already a good beam for oars holders, no need of outriggers. The internal cockpit is 80 cm width, to put it a berth at night in case of. The light weight in sailing consditions is here estimated at ~ 85 kg, but could be less with an RS Aero type construction + some extra thickness of the outer skin to cope with harsh grounds.
    By hoping this can be helpful,
     

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  4. BoraBoats
    Joined: Feb 2019
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    BoraBoats Emilie

    @sharpii2 and @Dolfiman, I appreciate that you share your concerns. This is definitly something I should work on and improve. I have not prioritized room for sleeping aboard. I think only a small percentage of the users would be interested in that. In scandinavia, you can put a tent up wherever you want (except in someones garden). The main reason to have the wings was for the boat to be easier to handle on land and to not take up so much space when stored. Also a narrower boat is faster to row. The boat ePoh seems to function well with outriggers as «support wheels». Maybe rigid outriggers shaped more like the ones that ePoh has would solve some of the problems? The trampoline/canvas on the wings is nice for giving various seating options, but it can be replaced with a mesh/net that does not catch the wind.
     
    Last edited: Apr 17, 2019
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  5. Dolfiman
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    Dolfiman Senior Member

    Ok, you have the point with this convincing video and concept (it is a French 2017 start-up !). To note (on the brochure) the longitudinal position of the floats in coherence with the centre of efforts, and the float shape for a progressive entry in the water (a mix of buoyancy and dynamic lifts). The weight of the 2 floats are given for 160-143 = 17 kg, so ~ 11% of the light weight.
    http://epoh.eu/wp-content/uploads/2018/01/ePoH-2017-GB_WEB.pdf
     
  6. philSweet
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    Location: Beaufort, SC and H'ville, NC

    philSweet Senior Member

    I suppose if you have snow-melt all the way, you can save a lot on the potable water. I had zero resupply opportunities in the Everglades and other coastal trips. I love the RS Aero, by the way. My concept for the Everglades Challenge is to use the Aero's rig and a custom hull with the underwater lines of the Aero. But there again, It's a short duration race with resupply opportunities every 12 hours or so, and even then, I want to modify the hull pretty significantly. A particular motive is to support navigation and electronics, which are needed in the race.

    Also, camera gear has gotten a lot more convenient in the digital age. My partner and I used to both carry fairly basic camera kits that weighed about 3o pounds each. We had modified tripods for setting up in the water that were about 15' tall. And we had lots of flash power for night photography of wildlife. These days, a drone and a GoPro could do as well at half the price and a tenth the weight.

    Solo, I can go for just under 1 month on 3o kg in the conditions of the Norway coast if I have a reliable supply of fresh water. But it's a fairly bulky 30 kg when all the seabags and hardpaks are accounted for. Also, I used to carry six sails for my 16' dinghy. All were 6 oz nylon or heavier. My mast was a Dwyer DM 375. It's spreaders were heavier sectioned than the RS's mast. I could cartwheel up the beach in the surf without damage. You can't do that in an RS.

    So if you want to beef up an RS, add lots of hull volume forward. You need an isolated deck access for mooring gear and spares in the bow, and an open, but securable cuddy for waterproof containers and for hiding electronics. Beef up the bow and transom a lot. You should be thinking about 10,000 - 20,000 pound rated hardware being mounted to the bow and transom, and it should snap and not pull off the boat. I'd use 1" hardwood ply with glass over it. The ends of little boats take a beating. I've had an old outboard literally beaten to pieces hanging on my dinghy when a houseboat tore apart a fuel dock in a storm, and the houseboat and a lot of the dock ended up in the slip with my dink. There was nothing left of the outboard except the clamp, but the dink was fine. It took me a week to patch the all the holes in the houseboat.

    Use a stronger mast - like ten times stronger. Set up the boom on a slide so it can be raised and lowered on the mast. Your first reef is rolling the boom up and leaving the sail topped out on the mast. Make a self-tending boom jib for the boat. It should be about 3/4 as big as the standard jib. It can also be flown at different heights off the deck by using a tack pennant. I prefer full battened mainsails for this job also, and have had good luck resizing Hobie 16 mainsails, which can be had for a song.

    Use bigger boards and rudder and make them stronger. This is the number one problem with production boats. Since these bits are expensive, they are always too small and too weak for running up onto a beach in the surf. I'd use about 28 mm thick for the board (solid wood or glass, no lightweight foams), and about 22 mm thick for the rudder. The rudder kickup mechanism can't be too strong. I used 1" SS bolts running in 1" boiler pipe sleeves for all my pivots. These were built into solid heartwood mahogany cheeks 5/4 thick. This is what took the hit from the first Honda Civic that hit me while trailering. The Civic was totaled but my rudder was fine and I continued to go sailing that day. The transom and rudder sheared the A pillar of the Honda and the car's engine went between the hull and the trailer, straightening the hooks of the tie downs out and launching them a 100 feet in the air, according to a witness. The car was doing about 50 mph and I was stopped. I had a rudder gudgeon give out when I was a kid, and I plan to not ever let that happen again. Imagine the boat completely filled with wet sand, standing on its rudder and board. It needs to be able to do that. Because if you get the tide wrong, or the wind wrong, that's what happens when the surf plays with your beached boat for a few hours.

    I'll be interested to see what that fellow's RS looks like after 20 years of doing this. I've already posted pictures of my dinghy at 20.
     
  7. Squidly-Diddly
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    Squidly-Diddly Senior Member

    yipes. I wonder why the front spar doesn't run through, surely they didn't break it at the gunnels just to keep the boat more open.
     
  8. BoraBoats
    Joined: Feb 2019
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    BoraBoats Emilie

    More about the floats of ePoH:
    "D’Armancourt didn’t want to design a trimaran. “There is nothing like steering a monohull,” he says. The problem was gaining sufficient buoyancy from the two floats without adding too much weight. The aim is to rely on the stability of the floats if there is a sudden gust – or the crew make a mistake – but not to sail with the floats in the water. So he played around with the position of the floats, moving them fore and aft, from touching the water surface to sitting high over it. In the end, the hardest part was finding the right shape. Now D’Armancourt doesn’t speak of floats, but uses the word ‘ski’ to define these outriggers.
    They are rather strange skis, but on the water, I have to admit that the comparison fits. There is a vertical part, very narrow, that slices through the water like a knife. But, more importantly for stability, is the horizontal part, which is flat like the sole of a ski, but wider. So when the float hits a wave, first the vertical part cuts through it and then the water hits the flat part, creating a vertical lift. The faster the boat sails, the more powerful the lift."

    Read more at ep0h, a skiff with stabilisers – Yachting World https://www.yachtingworld.com/yachts-and-gear/skiff-stabilisers-meet-ep0h-skiff-anyone-can-sail-76090#3MXQluGTZQkCrmBS.99
     
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  9. Angélique
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    Angélique aka Angel (only by name)

    It looks to me like the deeper vertical part of the ‘‘skis’’ provide extra leeway resistance when ‘‘skiing’’ on the horizontal part, but it also looks to me like the vertical part creates the chance the boat trips over it, so I think I would rather have the ‘‘skis’’ to be only horizontal on the water surface, and relying solely on the centreboard for leeway resistance, which might require a deeper and/or wider centreboard...

    — pic from Emilie's link
    [​IMG]
     
  10. Doug Lord
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    Doug Lord Flight Ready

    Angelique, in the set-up of the "ski's" now the vertical portion only works when it needs to-if you made a bigger centerboard you'd have that extra area-drag- all the time. In my opinion, I think it is an excellent design as is.......
     
  11. Angélique
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    Angélique aka Angel (only by name)

    — the post #98 pre start still of the video has the vertical part of the ‘‘skis’’ nicely marked —
    [​IMG]
     
    Last edited: Apr 23, 2019
  12. Angélique
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    Angélique aka Angel (only by name)

    Yes, on second thought indeed the centerboard as it is would be OK, since the ‘‘skis’’ are only meant for emergency stability, but when the lee ‘‘ski’’ hits the water in a gust, then I think one don't want to have the extra leeway resistance of the vertical part of the ‘‘ski’’, as I think it's then better to have the boat slide sideways a bit then having the boat tripped over the ‘‘ski's’’ vertical part.
     
  13. Angélique
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    Angélique aka Angel (only by name)

    Emilie just for info, there are recently ancient Sápmi expedition canoes posted on the thread 1811 Lapland Canoe, maybe you can shine your light on it, or post the link on Nordic forums for more info . . ?
     
  14. BoraBoats
    Joined: Feb 2019
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    BoraBoats Emilie

    I will take a look!
     

  15. BoraBoats
    Joined: Feb 2019
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    Location: Norway

    BoraBoats Emilie

    Project Update 6: Problems and possibilities

    I have been thinking a lot about the problem with the floats. The placement of the oarlocks prevents the floats from being placed further towards the bow (they are pushed as far forward as possible). If I remove the floats, the wings will still be a nice feature because they provide a large area to sit on and they give the user a greater moment of force when hiking out. The wings are also creating an aesthetic lightness, the boat looks slimmer and faster. The characteristic wing shape and the combination of the centerboard case and the sliding seat are making the boat stand out from the other boats on the market. Removing the wings will also take away a lot of the boats identity. Therefore, I have decided to keep the wings. I am okay with the boat being more of a sports boat rather than one that can be used for extreme expeditions. I am more interested in presenting a design that looks interesting and original. But I think it should be able to handle the same conditions as an ocean kayak can. The main goal is that this boat can enable more people to experience nature powered by the wind.

    I will probably increase the beam a bit to 1.2 m (with wings 2.3 m). The beam at the waterline will then be 1.13 m. The displacement will be 243 kg, and a very rough weight estimation gives a bare hull weight of 43 kg if it is made out of GRP.

    The hull goes almost straight up from the chine, which makes it look nice and narrow, but it does not have a lot of secondary stability, which I really want to do something about. What if I replace the floats under the wings with fiberglass skis (a bit like ePoH)? The skis will not provide a lot of buoyancy, but they will create a surface that, if designed correctly will lift the wing out of the water and prevent the wing from digging in. This will hopefully give the crew a bit more time to right the boat. It will be difficult to include the vertical part of the ski because it will not make it possible to fold the wings (the vertical part will stick out too much). Do you think the skis can work, or is there no point in having them? They will still be placed quite far back, will this cause a problem?

    bdn.jpg

    Another idea I have is to attach curved hydrofoils on the wings (or on the sides of the hull), not for flying, but for stability. They will not be submerged unless the boat heels. The idea is that they will generate more righting moment and resist leeway. I think it will be possible to place them in line with the center of effort without being in the way of the oars. If they are detachable, it will still be possible to fold the wings in. But I don’t know if this will work at all. You would need some speed for it to work. What do you think?

    bdn3.jpg

    As for the rigging, I still want the roller furling main and I have improved the batten design. I have angled the mast more backwards to get the center of effort further back. Is it angled too much or is it ok? The high clearance between the mainsail and the cockpit is to make it possible to row with the sail up, but I am concerned that the center of effort too far up on the sail. Will this be a problem and cause the boat to heel too much?

    bdn2.jpg

    I would like to have your opinions on the front sail. Right now I have three options:
    1. Furling gennaker - Anti-torsion rope for making the sail furl. I have not seen a lot of dinghies with this solution, but here is one example:
    2. Screacher – something in between a gennaker and jib. Can be used to sail upwind in extremely light wind (but that will cause a lee helm – problem?). Not as good as a gennaker downwind. Might be easier to furl because it is flatter than the gennaker.
    3. Gennaker with sock – the most common solution for dinghies. Might be a problem with the sock taking up so much space in the cockpit when you also want to have room for camping equipment. It can be a problem if the sock gets squeezed by the camping gear.
    So, summed up, I would appreciate your opinions on the rig and on how to improve the stability, but still maintain a slim look.
     
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