40 ft cruising cat design. First steps.

Discussion in 'Multihulls' started by bscatam, Mar 28, 2016.

  1. bscatam
    Joined: Mar 2016
    Posts: 72
    Likes: 1, Points: 8, Legacy Rep: 16
    Location: Black Sea

    bscatam Junior Member

    I used Delft Ship for basic linesplan. After that continued with ACAD and Rhino.
    Building method strip planked huls. Flat decks. Materials: huls 12 mm end grain balsa with 1,5 mm layer of okume veneer both sides. 19 mm for decks and BD roof. 25 mm for bulkheads.
     

    Attached Files:

  2. bscatam
    Joined: Mar 2016
    Posts: 72
    Likes: 1, Points: 8, Legacy Rep: 16
    Location: Black Sea

    bscatam Junior Member

    40 ft cruising cat

    Basic design idea was live a board single handed catamaran for Med.
     

    Attached Files:

  3. TANSL
    Joined: Sep 2011
    Posts: 4,068
    Likes: 55, Points: 58, Legacy Rep: 300
    Location: Spain

    TANSL Senior Member

    A nice boat.
    You probably already know but I would point out that you must take care with special attention on scantlings of the bow of the hulls, in the area between the two hulls, as well as the wet deck. These are areas that need to be strengthened. Similarly bending moments between hulls must be taken into account for dimensioning the deck beams.
     
  4. bscatam
    Joined: Mar 2016
    Posts: 72
    Likes: 1, Points: 8, Legacy Rep: 16
    Location: Black Sea

    bscatam Junior Member

    Thanks. I know.:) Some additional drawings.
     

    Attached Files:

    • new.jpg
      new.jpg
      File size:
      159.6 KB
      Views:
      380
    • 8.JPG
      8.JPG
      File size:
      343.8 KB
      Views:
      282
  5. bscatam
    Joined: Mar 2016
    Posts: 72
    Likes: 1, Points: 8, Legacy Rep: 16
    Location: Black Sea

    bscatam Junior Member

    Drawings.
     

    Attached Files:

    • i6.JPG
      i6.JPG
      File size:
      254.7 KB
      Views:
      163
    • i7.JPG
      i7.JPG
      File size:
      341.1 KB
      Views:
      200
  6. TANSL
    Joined: Sep 2011
    Posts: 4,068
    Likes: 55, Points: 58, Legacy Rep: 300
    Location: Spain

    TANSL Senior Member

    I supposed, but, of course, in the photos is not possible to see if you have scheduled additional laminate/reinforcement for those areas.
     
  7. bscatam
    Joined: Mar 2016
    Posts: 72
    Likes: 1, Points: 8, Legacy Rep: 16
    Location: Black Sea

    bscatam Junior Member

    TANSL, I am calculating my lamnating schedule in separate table. So far I have for hulls, decks and bulkheads. Progressing construction drawings I will add all sensetive details. I think to put it in the forum. Probably somebody with more experience than I have, could correct me.
     
  8. TANSL
    Joined: Sep 2011
    Posts: 4,068
    Likes: 55, Points: 58, Legacy Rep: 300
    Location: Spain

    TANSL Senior Member

    If you think I can help with something, just say so. Not take too long to define scantlings because you are interested to know the weight as soon as possible, in as much detail as possible. Good luck with your project.
     
  9. catsketcher
    Joined: Mar 2006
    Posts: 1,151
    Likes: 70, Points: 48, Legacy Rep: 790
    Location: Australia

    catsketcher Senior Member

    Thanks for putting up something that shows thought and effort - looks good.

    You haven't put up any hydrostatics - LCB and displacement are the big ones for me. Cats often go down at the stern or just sink too much. If I look closely I am thinking (guessing) the immersed volume is about 3600 litres. She looks too fine underwater to cope with the build and cruising load.

    Be very careful and then more careful and then even more careful about your weight calcs. They are incredibly important. I would start with the built weight of a similar cat and use that as a base. Then work out if you would be heavier or lighter. EVERY first time designer gets this wrong. They ALL think their boats will be lighter than they end up. Only after a few boats do the underwater sections get filled out. Fixing this after the boat is built is expensive.

    Go visit a boatyard and see how many cats are floating on their lines. Then work out what type of interior you want. My cats' sistership floats 8cm lower because they have a beautiful interior and heavy stainless fuel and water tanks. Bit of a dog.

    I am guessing 3600 litres - Am I too far off? I think it needs to be closer to 6000 litres for a forty footer but then again you could get away with 4200 if you are very weight conscious.
     
  10. bscatam
    Joined: Mar 2016
    Posts: 72
    Likes: 1, Points: 8, Legacy Rep: 16
    Location: Black Sea

    bscatam Junior Member

    Thanks, CATSCATCHER. This is what I got from design parameters and calculations (in meters):
    LOA 12,21
    LWL 12,18
    BWL 1,12
    BH 7,08
    BCB 5,35
    Bridge Deck Clearance min 0,75
    Draft 0,58
    Light boat aprox 6000 kg
    Loaded aprox 7400 kg.
    LBRC 2,32

    I have very clear ideas for weight. As I am a furniture maker (factory) design of light, stiff and still nicely veneered panels for furniture is no secret for me. Of course it's still work in progress so I will apreciate any advices. My idea is to post regulary my work progress in the forum.
     
  11. catsketcher
    Joined: Mar 2006
    Posts: 1,151
    Likes: 70, Points: 48, Legacy Rep: 790
    Location: Australia

    catsketcher Senior Member

    That weight is very achievable. Looking at the renderings it looks to me that there is not enough volume there. So does each hull have about 3000 litres volume at designed waterline? (the grey part of the render).

    As to special scantlings for the bow areas and "wet deck" (I don't know what this is) - I don't think this is normal. Most of the boats I know just use a similar laminate all over with extra around the keel. Of course beams are very interesting and you need to copy someone's similar and well proven boat or do really good engineering based on something. Almost all the cats I know are based on simple rules of thumb - the one like this didn't break last time.

    cheers

    Phil
     
  12. bscatam
    Joined: Mar 2016
    Posts: 72
    Likes: 1, Points: 8, Legacy Rep: 16
    Location: Black Sea

    bscatam Junior Member

    Actualy - 3,4 m3. I think cross beam is not as big issue as bridge deck roof. As I have to reinforce it because of mast and mast post.
     
  13. Richard Woods
    Joined: Jun 2006
    Posts: 2,022
    Likes: 116, Points: 63, Legacy Rep: 1244
    Location: UK, USA and Canada

    Richard Woods Woods Designs

    I would try to slope the bridgedeck front more to reduce slamming. I am found that a slight Vee in the bridegdeck helps a lot. See my Transit 38 for more details. You will have to be very careful with the build to keep under 6T

    Richard Woods of Woods Designs

    www.sailingcatamarans.com
     
  14. TANSL
    Joined: Sep 2011
    Posts: 4,068
    Likes: 55, Points: 58, Legacy Rep: 300
    Location: Spain

    TANSL Senior Member

    Following the line of what advises Richard Woods, I recommend reconsidering the shapes of the forward part of the wet deck. In this area the sea produces huge hits and forms in "V" are a "very adequate" solution.
     

  15. bscatam
    Joined: Mar 2016
    Posts: 72
    Likes: 1, Points: 8, Legacy Rep: 16
    Location: Black Sea

    bscatam Junior Member

    This is how BD front actually looks like. Do you think that I should add some kind of nossele? I still hope that the minimum BD clearence of 750 mm will be enough. Originally its 780 mm.
     

    Attached Files:

    • tw1.jpg
      tw1.jpg
      File size:
      107.3 KB
      Views:
      188
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.