Cruising cat - Final design

Discussion in 'Multihulls' started by bscatam, Jun 6, 2017.

  1. bscatam
    Joined: Mar 2016
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    bscatam Junior Member

    This is my final design renderings of 12.75 m (42 ft) cruising catamaran 1.jpg 2.jpg 3.jpg 4.jpg .
     
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  2. groper
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    groper Senior Member

    Your lower shroud gets in the way of walking past the cabin and will be an annoyance - consider revising by putting the lower shroud chainplate on the side of the deckhouse to rectify. Otherwise, looks like a comfy cruising boat. For styling - i dont like the reverse bows, the rest is nice :)
     
  3. UpOnStands
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    UpOnStands Senior Member

    Nice looking but as grouper notes fwd access is rather constrained. Shifting the chainplates inboard should do the trick.
    Repeating an earlier comment? Isn't it possible to mount the dingy davit arms onto the bimini posts and make them horizontally swivel so you have a general hoist system. Mono's like to use the boom but not possible with most cats.
    Given the height of main deck above water a robust lift system that you can swing out to pickup and then swing in to release would be nice selling point.
     
  4. jorgepease
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    jorgepease Senior Member

    Nice Detail!! What about steps going down into hull, looks like it will be tight, what is the Bridgedeck clearance?
     
  5. John Perry
    Joined: Nov 2003
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    John Perry Senior Member

    Nice rendering and lots of detail, at least for the external 'skin'. I wonder if the shrouds are swept a bit far aft? and will the spreader sweepback be enough to stop mast inversion with the lower shroud pulling back half way between the spreaders. A rig/mast specialist should be able to advise. Otherwise, as Groper says, comfy cruising boat which is what quite a few people want, not Groper's style I think and far too big for me!

    A comment that is no critism of your design - why do people model things with 3D computer design then put the results in old paper style 'frames' with old style title blocks. I would hope that this is going to be used as a computer model, which will be stored as a computer file, not a big sheet of tracing film in a polished wooden chest of draws. Have it on a screen on the shop floor and take all the dimensions, with tolerance data, straight off the model with the 'tape measure' function in the CAD software. The information on the title block and drawing frames would then be better stored in a text file associated/linked to the model. Just my view!
     
  6. bscatam
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    bscatam Junior Member

    Thanks Groper. Still working on rig design. This is one of solutions. Anyway will consult with specialist.
     
  7. bscatam
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    bscatam Junior Member

    Davits are designed to be used as platform for solar panels as well. All from 8 mm aluminium.
     

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  8. bscatam
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    bscatam Junior Member

    Thanks. Steps opening is 60 cm. Will post drawings. BD clearance is designed on 75 cm fully loaded. Probably it will be around 78-80 in normal conditions.
     
  9. bscatam
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    bscatam Junior Member

    Actually I am using Delft Ship, ACAD and Rhino. It seems than Rhino is the best software for that kind of work. You better design in 3D because you can see all mistakes you made in almost real time. Putting on paper is for production. Also cat is very complex design task. You have to many details and parts. Most of them will be produced by others. For example to make perfect cable steering I made at least 15 drawings. Just st1.JPG st2.JPG for example
     
  10. catsketcher
    Joined: Mar 2006
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    catsketcher Senior Member

    Your CAD skills are incredible.

    I would agree with many of the comments here. You must put the lower shroud on the cabin top or risk decapitating yourself every time going forward. The rig designer will be fine with the slightly narrower staying base which is still much wider than monos. I have been on cats where you had to swing yourself around the lowers every time you went forward - "Who was so stupid to do that?" - you say to yourself every time you go forward or aft.

    I don't like the reverse bows as you have had to distort the bow region to cut away the upper stem. I think a bow shape should be the result of the hull flare and not an add on. You have slightly flared hull sides and so the bow developed from this shape is one of modest normal rake. I think it will date the boat when people eventually realise that reverse bows are for low drag racing cats and have no advantages for cruisers. In a marina you lose a toehold to jump off the bow and onto the dock. You have to position your bow cleats further back so that the bridle does not work as well. In tidal conditions the bridle will be rubbing the bows more than with the normal bow for this hull flare. Same for any reacher bridle. No advantages except for dubious fashion and I think that form should follow function.In some ways it is like slopey front windows. They used to be the rage because they looked cool. But they were silly to live with. Now all the cats with slopey windows are easy to pin down to 1990-2005. And no-one puts slopey windows on cruising cats anymore.
     
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  11. bscatam
    Joined: Mar 2016
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    bscatam Junior Member

    Thanks Catscatcher. As I am steel in process of rig design, probably the best way is to put lower shroud on cabin top slightly forward to free boom movement. The upper shroud will be on composite chainplate on main cabin bulkhead. Probably you are right about reverse bows. Still I like the stile and there are some positives in less weight and wandige with same LWL. As to mooring in marinas I am not worried at all. The cat will be sailing in Med, mostly in Aegean Sea where the only way to moore is medmooring -stern to pier. Anyway all your remarks already helped and still helping to improve the design. Generally I am almost ready and hope to start building soon.
     
  12. sailhand
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    sailhand Junior Member

    Hi Bscatam, nice work. I agree with catsketcher about the reverse bows I think they're ridiculous. Impractical and unnecessary. Why have a boat that you take away buoyancy from the bows just for a fashion statement. I suppose it will help to increase bridgedeck slamming to windward if that is the goal. I think it has just followed on from the off the beach cats as a bit of a style thing I don't see any practical advantage only disadvantage. Some people believe they help the bows rise up after being submerged and that was there original purpose I believe. Not really applicable to cruisers just distribute your buoyancy well and you shouldn't have a problem with submerging your bows your not doing 40 knots more likely closer to 4 on average. My other bug bear is saildrives. They are fantastic for production boat builders as they provide a drop in solution. No aligning shafts and shaft logs and seals etc. Cheap to install and quick, the ultimate builders solution. The only downside is for the owners. Different antifouls, electolysis, growth in tight and hard to access water gallery's, rubber flapping seal things,expensive props, 150 dollar anodes, deep draft, drag etc. I have cruised on a cat for 14 years now and I will never have saildrives. I have shaft drives and i can sit on the beach whenever I want, and I dont have Mini keels. I have boards and kick up rudders with shallow shaft angle and i wouldn't go any other way. I have been tempted to go with outboards but just put brand new diesels in my boat. Outboards offer many advantages but some disadvantages like cavitation and a lack of reverse grunt when you want it. Like everything in boats it's about compromise and that is for you to decide but definitely do your research on saildrives. A guy I know with a pregnant lagoon thingy has twin Volvo saildrives and he has to lap the cone clutches every 100 hours that is just ridiculous.
     

  13. Mr Efficiency
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    Mr Efficiency Senior Member

    Interesting comments about saildrives there.
     
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