I need a folding Sailboat. Some ideas.

Discussion in 'Boat Design' started by heavyweather, Jul 5, 2014.

  1. heavyweather
    Joined: May 2008
    Posts: 30
    Likes: 1, Points: 8, Legacy Rep: 24
    Location: Austria

    heavyweather Junior Member

    I need a boat that can be disassembled for storage. I got a 256cm pram which I have equipped with the Mirage Drive.
    My sailing grounds are the "Alte Donau" in Vienna. There are no waves, no motorboat wakes (only electric trolling motors allowed) and no multihulls.

    The boat should perform better than the pram. I am looking for a skiff because I want to row it too when I am becalmed or need to go home against the wind fast.
    My inspiration are the MTW Delphin 140, Delphin 150, Scalare 250, the Mewa and the Delphin Pirat. All boats are in the 12' range.
    Their original hullweight was between 65kg and 85kg, I am aiming at something around 50kg.

    I am looking for some existing design with a balanced Lug. My favourite boat so far is the "Goat Island Skiff". Other designs I previously considered where Bolgers "Gypsy" and Iain Oughtred´s Skiff "Spike" (Pike)
    I then found the "Summer Breeze" and the "Ella" Skiff.
    The GIS is too big but I like the sail, the vertical bow and the skegless design.
    So I took those lines and blended them into a new design and called it "Blend"

    I could screw a skeg through the skin but I rather not.
    I have not yet decided whether to go with a daggerboard, off center daggerboard or leeboard. Any ideas on that?

    Here are my lines. Black is the original length GIS.

    [​IMG]

    What do you think? Will it sink?
     
  2. messabout
    Joined: Jan 2006
    Posts: 2,954
    Likes: 177, Points: 63, Legacy Rep: 1279
    Location: Lakeland Fl USA

    messabout Senior Member

    Heavy weather; Sorry to tell you that it does not work quite so simpliticly.

    Both the GIS and the Bolger gypsy are very competent boats. They are much different in design and purpose however. Gypsy has deeply beveled chines while GIS is a hard chined flattie. Gypsy will be easier to row and GIS will plane in a lesser wind than Gypsy. Different ball game. Depends on what you are aiming for.

    You can not successfully superimpose the lines of the various boats. Doing so will lead you to "shooting yourself in the foot".

    The first order of business is to make a careful estimate of the all up weight of the boat, the contents, and the occupants. That is only the beginning but every other feature of the boat depends on the estimate of displacement.

    If the boat is to row or sail well, the bottom of the transom needs to rise a little bit above the estimated waterline. (A planing boat is a whole different deal so let us not confuse the issue.)To determine how much the bottom should rise at the transom we will need to do some arithmetic. The vertical location of the transom is to be determined but so is the vertical location of the fore foot. The front end of the boat needs to be at or just slightly below the waterline. If it is too deep the boat will be difficult to turn and tacking under sail will be problematic.

    Your overlays do not take any of this stuff into account. You must estimate the load that the boat is to carry, including its own weight. Then you can decide how to configure the bottom rocker and even the plan view curves. Just a note; If the transom is too wide or the aft rocker is insufficient, the transom corners will drag under sail when the boat is heeled.

    Here is a cocktail napki design exercise that you can contemplate.

    Your little 12 footer will not be appropriate for a certain load so lets say, for arguments sake, that your best estimate for all up weight is 300 pounds. OK the boat needs to be designed for a displacement of 300 pounds when it is sailing or rowing on its lines.

    You have arbitrarily decided that he chine width will be 48(?)inches. Now put in an estimate of the draft of the boat which you need to know in order to get the transom bottom and forefoot elevation in an appropriate location. Talk a wild guess at four inches of draft. That tentatively sets the elevation of the bottom at each end of the boat.

    Four inches draft multiplied by 48 inch chine width, at the center of the boat, gives us 192 square inches of area for the center section only. The rest of the boat has smaller sections so we need a fudge factor to find the average section area. A simple skiff has a fudge factor in the neighborhood of 0.54. That fudge factor is called Prismatic coefficient (Cp) Multiply center area by Cp and we get 192 x 0.54= 103. so now we have an educated guess about the average area of all the sections of the boat. Now we need to find the cubic volume of all the underwater sections of the boat so we have to multiply by the load water line. The LWL is shorter than the overall length of the boat so let us guess at .......144 minus 14 inches and we get 130. Good!
    Multiply by 130 times the average area, 103, and we get 13,390. Dandy! we have the total cubic area of the immersed part of the boat. How much weight does that support? Use the constant 0.03611....that is the weight, in pounds, of one cubic inch of fresh water. 13,390 x 0.03611 = 583 pounds. we are way over our draft estimate so we go back to the drawing board and modify the rocker and other stuff.

    Can you see where we are going with this? If you are up for all the tinkering with the lines of your boat and all the calculations that go with it, then have at it. If you just want to build a boat then get a set of plans from any the of our numerous pro designers here on the forum.

    (disclaimer:I am not in the boat design business. )
     
  3. heavyweather
    Joined: May 2008
    Posts: 30
    Likes: 1, Points: 8, Legacy Rep: 24
    Location: Austria

    heavyweather Junior Member

    The above lines are a blend of a scaled version of the GIS and the Summer Breeze. There are a lot of boats that I am looking at that are not designed by navel architects.
    I don't really care about the rowing abilities, I might even put in the Mirage drive instead of rowing.
    I would love to take a proven design, I just can't find one that really suits my needs.

    I need a boat that can carry 1-2. I will be sailing alone most of the time. Sometimes my 3 kids will hop aboard. No racer, just medium performance is required.
    A flat bottom with little rocker and no skeg would be great for converting the hull to a folding SOF boat. Unstayed mast, balaced lug rig. free plans or some drawings on the internet would be great.

    I was looking a Bolger's Teal the other day but I guess it is not the boat I want. His Windsprint is a little to big.

    Any more suggestions for a hull?
     
  4. messabout
    Joined: Jan 2006
    Posts: 2,954
    Likes: 177, Points: 63, Legacy Rep: 1279
    Location: Lakeland Fl USA

    messabout Senior Member

    Consider that a displacement boat responds in proportion to the input force applied. An upper limit of speed exists for a given hull depending largely on the length of the boat. The point is, that whether rowing or sailing the amount of force needed to propel the boat is of some interest to the user.

    To minimize the force required for a specific performance envelope, there are several design features that are involved. Getting the transom clear of the waterline is one of them that need not be ignored.

    Try to avoid choosing a design that suits your perception of what a boat should look like rather than what will best serve the purpose. That is a common mistake that frequently results in poorer than hoped for performance.
     
  5. heavyweather
    Joined: May 2008
    Posts: 30
    Likes: 1, Points: 8, Legacy Rep: 24
    Location: Austria

    heavyweather Junior Member

    I ordered Michalaks Book with the plans to the Mayfly 14. I am not sure if that is the hull I want, it's a little to long but other than that it would suit the idea.

    I don't really know which design would suit the purpose. A multichine hull probably won't. A double-ender would suit it most I guess.
     
  6. heavyweather
    Joined: May 2008
    Posts: 30
    Likes: 1, Points: 8, Legacy Rep: 24
    Location: Austria

    heavyweather Junior Member

    Some progress.
    I took the Mayfly 14, cut the sheerline down and set the transom to vertical.

    Here is the last drawing.

    [​IMG]

    I still need some idea to fix the 2 cassettes aft to the spine and the frames so that the whole thing won't twist. I only came up with bolts so far...

    [​IMG]

    Then there is the rudder.
    Option one is mounting it inside the hull.
    Option two screwed through the hull and transom.

    [​IMG]
    [​IMG]

    I also tried glueing some PVC with Pattex Contact/Kraftkleber ...that works...when I tried to pull my samples apart (I hammered one and clamped the other) only the 2mm PVC tore up on both samples.

    I guess I will start building it soon.
     
  7. bother54
    Joined: Aug 2014
    Posts: 2
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: Singapore

    bother54 New Member


    Goat Island Skiff is my favorite boat too. I have seen a while ago about this boat. But I think we should also look for the best Marine Electronic Equipment to use in our boat. Right? :)
     
  8. heavyweather
    Joined: May 2008
    Posts: 30
    Likes: 1, Points: 8, Legacy Rep: 24
    Location: Austria

    heavyweather Junior Member

    Whaaaat? The only electronic thing in my boat is my mobile for GPS tracking.
    [​IMG]
     
  9. Petros
    Joined: Oct 2007
    Posts: 2,937
    Likes: 139, Points: 63, Legacy Rep: 1593
    Location: Arlington, WA-USA

    Petros Senior Member

    I have built a number of skin-0n-frame kayaks and sailboats, including a folder. You need to have a means of tensioning the skin both lengthwise and cross wise. You can fold the skin over the gunwale and have it lace or attach to the floor or bilge stringer to tension the skin crosswise. lengthwise you either have to have a device up in the prow that can lengthen the frame to put tension on the skin or have adjustable length stringers so after it is assembled you put lengthwise tension on the skin by adjusting the length of the stringers. There is no simple way to make the skin tight over the hull, you will need a means of pulling on the skin or enlarging the frame width and length or you will have lots of loose and wrinkled skin.

    Also consider that you need to design your frame to take torsion loads from your mast, using just stringers will allow the mast to twist the frame, so you need some diagonal bracing around the mast area back to where the crew sits.
     
  10. heavyweather
    Joined: May 2008
    Posts: 30
    Likes: 1, Points: 8, Legacy Rep: 24
    Location: Austria

    heavyweather Junior Member

    Hi Pedro.
    I have also built some open SOF boats, both rowing and sailing boats. The skin can also be tensioned by inflatable bladers along the inside of the skin. That's how the old Klepper boats work.
    I will ad more diagonal pieces as I go, I don't want to overbuilt. Two more bamboo members should work or just some belts. The hull will also zip over the bow/deck and around the mast to add more tension and stiffness.
     
  11. gonzo
    Joined: Aug 2002
    Posts: 13,413
    Likes: 333, Points: 93, Legacy Rep: 2031
    Location: Milwaukee, WI

    gonzo Senior Member

  12. minno
    Joined: Aug 2014
    Posts: 88
    Likes: 0, Points: 6, Legacy Rep: 10
    Location: Canada

    minno Junior Member

    what's the reasoning behind the no multihulls rule? too wide?

    minno
     
  13. heavyweather
    Joined: May 2008
    Posts: 30
    Likes: 1, Points: 8, Legacy Rep: 24
    Location: Austria

    heavyweather Junior Member

    "Alte Donau" is very small and sailing multihulls is prohibited (though a folding multihull would probably work.)
     
  14. heavyweather
    Joined: May 2008
    Posts: 30
    Likes: 1, Points: 8, Legacy Rep: 24
    Location: Austria

    heavyweather Junior Member

    Thank you Gonzo,
    I did not know that boat. Looks good but a little too small after I have embraced the 14' boat. I also like the untwisted side panels on the Mayfly 14. This should make the skinning easier and I can use heavier PVC without getting wrinkles from just draping it over the shape.
     

  15. MikeyBrat
    Joined: Aug 2016
    Posts: 1
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: Phoenix

    MikeyBrat New Member

    Folding boat?

    Maybe Google Sea Hopper?
     
Loading...
Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.