Foldable catamaran

Discussion in 'Boat Design' started by skatun, Nov 20, 2018.

?

Feasible?

  1. Yes

    3 vote(s)
    60.0%
  2. No

    2 vote(s)
    40.0%
  1. fallguy
    Joined: Dec 2016
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    fallguy Senior Member

    I don't know many designers that would recommend going across the oceans in folding cats.

    Not saying it can't be done, but you need to design it for serious conditions. Way outta my ballpark.
     
  2. skatun
    Joined: Sep 2010
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    skatun Junior Member

    1
    How much would that cost?

    2
    My budget is 2000h

    4
    Haven't done the math yet, depends a lot on range you want though, maybe 50nm is enough on electric, rest under sail...

    5
    Well it is experimental, and most likely you need to apply high lift devices, below lift off for 10kt:
    upload_2018-11-22_9-8-22.png

    6
    Not a problem where I live:)
    7
    Well the idea is to only be a like 5 hours on the way, then stop for dinner(recharge battery) then another afternoon sail...


    8
    I am on to it:
    http://rules.dnvgl.com/docs/pdf/dnvgl/ru-yacht/2016-10/DNVGL-RU-YACHT-Pt3Ch10.pdf

    9
    I paid 1700 euro last time from shanghai to Bergen,Norway, not sure what prices are across the Atlantic from hamburg or
    similar

    Thanks for the feedback, I never said it would be easy..!
     
  3. skatun
    Joined: Sep 2010
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    skatun Junior Member

    Bolted connections can be made strong when designed properly, the whole folding is just to make folding time quicker at the dock, so when unfolded all joints wil get bolts inserted to make it stiff enough, thats at least the idea. The two floaters will also be bolted properly on so that it will help to stiffen the hull.

    I am trying to do the catamaran calculations now:
    Catamaran Design formulas http://www.catamaransite.com/catamaran_hull_design_formulas.html
     
  4. rwatson
    Joined: Aug 2007
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    rwatson Senior Member

    Niclas Vestman likes this.
  5. Kai Rabenstein
    Joined: Jan 2019
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    Location: Hastings, UK

    Kai Rabenstein New Member

    Interesting thread ... I'm also a novice who is fascinated by the idea of building or converting a 10-12 metre catamaran as a liveaboard trawler/passagemaker in the Mediterranean and European inland waterways. Because of the latter's size limitations imposed by the 19th century French canal dimensions (max. beam 5m, max. air draft/bridge height 3.5m) I found to my disappointment that the vast majority of commercially available leisure boats are too wide beamed and - if sporting a flybridge - too tall.

    This got me thinking that adapting a workboat powercat design dispensing with most of the foredeck and sidewalks by enclosing them inside the hull structure so as to achieve full standing height in the sponsons, and having a deckhouse sporting an extremely shallow flybridge and folding navi mast should do the trick. I also envisage the boat acting as a technology demonstrator for green/regenerative propulsion modalities such as solar panels, wind turbines, electric engines (likely the most powerful Torqeedo or AquaWatt outboards) and kite sails - this might provide both ready interest as well as a potential source of income. Being able to run the boat up on any beach/stand on dry bottom would of course be a huge advantage in terms of accessing uninhabited islets and lowering marina mooring costs.

    Regarding the question of folding up a (smaller) boat and/or container shipping them I have come across designs that are specifically intended to facilitate this - Cheetah Marine have shipped one of their workboats to Canada in 2 shipping containers, and there are a variety of under 10m foldable designs available ... Woods Designs of Cornwall (UK) are even offering 28 and 36 ft designs (Sailing Catamarans - The Ideal Pacific NW Cruiser (a Skoota powercat!) http://www.sailingcatamarans.com/index.php/articles/11-technical-articles/278-the-ideal-pnw-cruiser) - check it out.
     
  6. skatun
    Joined: Sep 2010
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    skatun Junior Member

    I have done quite a bit of work over Christmas and I think I have now a concept that might work. I met up with a guy from Oma båtbyggeri which makes catamaran passenger ferries, and he gave me some useful input. So I think I will make the frame itself of aluminium and the hull of fiberglass. I was a bit worried about thermal expansion between the two materials, but he was confident that it will be enough flexibility to avoid this. More info to come, but I am getting some inspiration from this one: Sunreef Supreme 68 Sailing - Sunreef Yachts https://www.sunreef-yachts.com/en/supreme-68-sailing ...
     
    Last edited: Jan 7, 2019
  7. skatun
    Joined: Sep 2010
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    skatun Junior Member

    So here is some sketches of my design which currently have a displacement of around 10 tons.

     
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  8. fallguy
    Joined: Dec 2016
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    fallguy Senior Member

    How is starboard not heavy?
     
  9. skatun
    Joined: Sep 2010
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    skatun Junior Member

    @fallguy , should be port heavy... I am just showing one sided folded and the other side unfolded..

    I am getting pretty close now to make a 1/10 scale prototype(Gonna take some time to make it though..) . For this I have a few questions.

    So weight scaling will basically be fullscale weight/ 1000 i.e 10tons= 10kg modell weight.

    How do I scale power requirements for electric motors and speed through water? I guess this needs to be scaled based on the Froude number or?

    Second question is the large side windows. How would people make them. I assume that it will be best to use double glazed windows out of acrylic with aluminium frame right? Where can you order large boat windows?
     
  10. fallguy
    Joined: Dec 2016
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    fallguy Senior Member

    I recommend Bomon in Quebec. I have not used their product; so the recommendation is weak. However, they were very professional with me when I sent them boat pictures and I like the way discussions went...

    I am buying from them in July.
     
    Last edited: Jan 21, 2019
  11. fallguy
    Joined: Dec 2016
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    fallguy Senior Member

    Your design appears to have a weakness that my gut tells me; not facts, but the forward beam is aft of the for and aft vessel center.

    What will keep a beam sea hitting the starboard hull from applying a force the port hull does not reconcile? Or rather, what will stop athwartship forces from moving the hulls this way and that? Or an upwards force on one hull will not transfer to the other hull without first passing to the back of the ship. Under adverse conditions, the seastate might rapidly affect one hull very differently and my gut tells me you have not properly accounted for these forces.

    The boat looks stern heavy as a matter of appearance as well.

    Kind regards even if it seems otherwise.
     
  12. skatun
    Joined: Sep 2010
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    skatun Junior Member

    There is several elements missing still, I will post some updates next week. I have just worked on the stern so far, because thats where the folding mechanism will be, the fixed part in the front is still to come. So dont worry @fallguy it will be according to DNV standards.
     
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  13. skatun
    Joined: Sep 2010
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    skatun Junior Member

    upload_2019-1-24_10-38-42.png


    Are these heatloss calculations far off? Seems like it should be possible to heat the boat with a 2kw oven at winter times...
     

    Attached Files:

  14. Heimfried
    Joined: Apr 2015
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    Heimfried Senior Member

    The value of 0.05 W/(m² K) may be appropriate for a well heat insulated building with thick (about 1 m) ceilings and floors. My calculation (as an example for boats) shows other values:
    Plywood: 0.15 W/(m K), two panels, inner and outer surface each 8 mm thick, inbetween rigid foam (or an similar insulant): 0.04 W/(m K), 12 cm thick.
    Lambda 0.15 W/(m K) / 0.016 m = 9.4 W/(m² K); 1/Lambda = 0.107 (m² K)/W
    Lambda 0.04 W/(m K) / 0.12 m = 0.33 W/(m² K); 1/Lambda = 3.0 (m² K)/W
    alpha = 40 W/(m² K); 1/alpha = 0.025 (m² K)/W
    (0.107 + 3.0 + 0.025) (m² K)/W = 3.13 (m² K)/W
    -> 0.32 W/(m² K), which is about 6 times more.
     

  15. skatun
    Joined: Sep 2010
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    skatun Junior Member

    @Heimfried Thanks for the input, I will add it to the calculations, however it will still only be 1/3 of the windows.. But important to take into account. I probably will update it during next week. And do a full FEM in a month or so...
     
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