Trimaran design for family cruising

Discussion in 'Powerboats' started by teamcallander, May 4, 2012.

  1. teamcallander
    Joined: May 2012
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    teamcallander Junior Member

    Hi all

    I have been thinking about a power boat for long distance family cruising for a while now and have finally started putting pen to paper.

    Some of the design parameters I used were long and narrow for good efficency at higher average cruising speeds. Multihull for stability on narrow hull form. Largest practical interior space. Sufficient range for circumnavigation.

    My best guess would be single engine around 250 hp for this application and overall length around 64'.

    Please take a look at the attachments for more details and note that each grid square is 2'. I have no background in boat design (obvious from the drawings I know) so please be gentle!

    Thanks.

    Mike's Tri Mk IV - Interior detail.jpg
    Mike's Tri Mk IV - Exterior view with transverse sectional views.jpg
     
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  2. teamcallander
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    teamcallander Junior Member

    Forgot to include the profile view...

    Mike's Tri Mk IV - Profile view with flying bridge detail.jpg
     
  3. Doug Lord
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    Doug Lord Flight Ready

  4. teamcallander
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    teamcallander Junior Member

    Thanks for the feedback Doug. Overall beam was something I was definetly hoping to get more information on. I guess I tried to comply with the 3 to 1 rule for stability without going too wide. Do you know of any formula that can be used more broadly for power trimaran design?
     
  5. Doug Lord
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    Doug Lord Flight Ready

    I think you could derive one from the Shuttleworth design above as well as boats such as Nigel Irens Cable and Wireless. But there is varied thinking on the subject so it will come down to you. I'd go with wider.....
    -- I read somewhere that there were considerations of placement fore and aft of a small ama other than how far from the main hull- like a boat with a small ama more or less centered could lose some degree of stability if the bow and stern of the main hull were supported by a wave crest and the ama was in the middle.
    There may also be gains in lower resistance by proper placement of the ama vs a vs the wave train from the main hull. I hope you would consult with an NA specializing in power multihulls before you made a firm decision on cat or tri, Irens type or Craig Loomes type(Edy Gil/Earthrace). There are designers who specialize in power cats, power tris or both. And whatever you decide an RC model(largest you can afford) would be an excellent way to observe first hand how the thing performs in waves.

    Nigel Irens power tris including Cable and Wireless(Adventurer): http://www.nigelirens.com/FRAMEpower.htm
    ---------------
    Another design philosophy for power tri's: http://www.cld.co.nz/earthrace.htm
     
  6. masalai
    Joined: Oct 2007
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    Location: cruising, Australia

    masalai masalai

    You have not specified the size of your family, - - where you intend to cruise, - - Cruising budget (how will you sustain this lifestyle)... All have significant impact on the style of vessel...

    I like the idea of sails (but I blew my budget and lacking stick and sails - I have to be content with motoring... You may find a tri, as you have sketched, to be very limiting on space (for a family and permanent live-aboard stores/tools etc) and range... Mine with 1200Litre tanks plus another 500litres in reserve will give a range around 3000 N Miles at 10 knots, being a cat, (40 ft loa and 21.5 ft beam), has plenty of space and each hull has a comfortable double aft and the forward section has a laundry on one side and toilet and shower on the other - galley is 'up'... I did not put doors as my children have children and some close to being grand-parents... My cruising region will be the Queensland and top end of Australia as well as Melanesia (all around the Coral Sea which is a bit over 1000 miles across)... I prefer to island hop and have only one major passage of 480 miles from Cairns, N. - to Samarai, PNG the rest are mostly less than 8 hour passages...

    Most live-aboard cruisers are at anchor or otherwise "not moving" for better than 80% of the time... There is usually no hurry, so 'weather windows' determine when a passage is made... Learn to become a sort of - "flanneur" - One who indolently observes the culture and society and absorbs and learns from the observations... Thence to become an active participant in those cultures enjoying the social interaction and appreciating the leisure time we in the west have lost...

    Do not get carried away with "romantic visions" but address practicalities of space, comfort, proven reliability and efficiency (2 miles/litre - ease of self repair and maintenance - careening on a friendly sandbar to change rudder - propeller or fix a hole from a nasty rock? :eek: ) Most of the time 12knots or less, is as fast as you want to go for long term comfort...

    - saying that a "flank speed" of 20+knots is necessary, - demonstrates inexperience and lack of competence/self confidence or appropriate knowledge/preparation for one who aspires to the remote live-aboard lifestyle...
    - 20+knot capability is perfectly appropriate for someone making a marina change to a new location some 100 miles away for the time constrained annual holiday... I do not like marinas - I do not need shore power (I may miss regular internet access :eek: :p ) - I carry supplies for 90 days and more...

    Your layout seems to have 7 bedspaces but nil space for tools, parts, fuel, or food for extended voyages? have I mis read?
     
  7. Corley
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    Corley epoxy coated

    You might like to read this Nigel Iren's interview he goes into his views on "why a tri" for power boat application. It might help with defining what you want from your boat design and what compromises your willing to accept. For a 60' trimaran powerboat consulting with a multihull designer/naval architect makes sense it's a lot of dollars no matter what way you slice it if you want a good, efficient result.

    http://www.stevencallahan.net/images/proboat/irens-feb2000.pdf
     

    Attached Files:

    Last edited: May 4, 2012
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  8. teamcallander
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    teamcallander Junior Member

    Hi Masalai - normal "crew" will be Mum and Dad plus two younger children. There is a lot to like about cats, especially as many of them are available in the size range you are talking about - needless to say I have looked at them extensively and prefer the tri platform overall.

    In terms of storage space you will note from the cross sectional drawings that there is quite a lot of space beneath the lower cabin sole which will not be totally filled with tankage. Also, if you look at the first drawing there is a large stores area below the galley - a washing machine is also located here.

    The top speed is simply a reflection of wanting to have my cake and eat it to. Why bother to go long and narrow if you also sacrifice go fast? If displacement speeds are acceptable to you then a diesel duck type would be more appropriate in my view.
     
  9. teamcallander
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    teamcallander Junior Member

    Hi Corley

    Could not open the link you provided? Do I need to be a member to look at it?
     
  10. Corley
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    Corley epoxy coated

    I've added the interview as an attachment. The link seems to work fine but it is a bit slow to load (large .pdf with lots of photos).
     
  11. teamcallander
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    teamcallander Junior Member

    Corley, that must be why, our internet speed is the pits here on the Island.

    Interesting article - thanks very much for posting.
     
  12. HASYB
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    HASYB Senior Member

    Attached Files:

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  13. teamcallander
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    teamcallander Junior Member

    Hi HASYB

    The Alchemist surely looks beautiful as it skims through the water with near zero wake, exactly the end product I am trying to achieve. Unfortunately at nearly 30m it's much bigger than I want to go. I have already looked at the boats from Kasten and Kurt, nice designs. I especially like the way Kasten managed to get a trimaran to have a more classic style - not easy to do.

    My design goal was to stay below 20m (due to international regulation) while providing very comfortable accomodations on a very narrow boat. Most say you get 30ft interior on a 60ft tri but I think I've shown that it doesn't have to be so.

    The main problem with what I've drawn is the overall freeboard but its almost required with two full head height decks. I was also interested in people's thoughts on the wing clearance of just under 3ft? Given that the span is just over 5ft it will probably work ok but what happens if I widen it to 7ft or 8ft as suggested by Doug to increase stability?
     
  14. teamcallander
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    teamcallander Junior Member

    Trimaran length to beam ratios

    So looking at some boats already out there we find:

    LOMOcean design
    Patrol One - 22.4m x 8.3m (2.7:1)
    Azzum - 12m x 5.4m (2.2:1)
    Earthrace - 24m x 8m (3:1)
    Moonset - 148.7m x 47.5m (3.1:1)

    Nigel Irens
    iLAN - 21.3m x 10m (2.1:1)
    C&W - 35m x 16m (2.2:1)

    My design
    Mike's tri - 64' x 20' (3.2:1)

    So it seems that ocean going power trimarans range from length to beam ratios of 2.1:1 to around 3.1:1. Its interesting that LOMOcean tends to be skinnier (primarily power boat designer) while Nigel Irens tends to be wider (sailing background).

    By comparison mine seems to be a little skinny at 3.2:1 so taking it out to 24' or 2.6:1 would split the difference.
     

  15. longcours62
    Joined: Jul 2011
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    longcours62 Junior Member

    As we wrotte here (http://www.trawlerforum.com/forums/s3/power-trimaran-5988.html)
    or on our blog.
    During the phase of the concept of our actual boat we thinking power trimaran.
    But our first 'drawing" was moe narrow than your for the main hul .
    As you I am not a designer!
    Our first project was 21m loa, 21lwl, beam at water line less than 2m, beam of the main hull at deck level 3 m, beam oa, 7,5m and the air draft maximum under 3 m.
    It means from the bow she lok quiet different than your 3m hight on 7,5m beam.
    But we just know metal work and always we get a problem with the weight 20/21 t loaded for a volume of hull (under wl ) of around 17m3 ....may must navigate only on the "Mer Morte" ?
    In this type of hull if I want kept the sleek profil and reasonable weight I have 40/45 ù less volume in the arrangement than our actual boat (for a couple it still sufficient) but for a family it depend of the size of the family !
    We can fit : forward cabin, nice toilette, salon/kitchen, wheelhouse, af cabin (small) and engine room.
    Sure if we can sold our actual boat and don't find potentials customers for built two evolutions of our actual boat we will try built a power tri ...for see.
    If we found an architect for make the hull lines and check our structural choice.
    It could be interesting to discuss with people with same project for at less definite a same platform .
    On our old project we try to get (at less) 1,10m gap between the water surface and under part of the "arms"
    The "bouge"(in french it is the bouge ) i don't find in English ) it's mean the élévation of the deck at the center line compared to the side level of the deck(not clear at all!!) around 5% in this case the hight of the deck of outriggers could be no more than 1,24m not bad for looking by side , and 'bouge curvature' of the deck it is not too much and we can walk on the wings and not use them like a "tobogan".
    Long time ago we discuss with Nigel Irens and he said he was not sure the 3 hulls was better than 2 hulls of a catamaran for efficiency.
    And if the center one is too beamy at the water line it could be worst .
     
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