S/V Sea Witch. Polynesian outrigger Inspired Trimaran.

  • 13 Feb 2017 08:01
    Reply # 4606295 on 4602302

    Hi Martin,

    i agree with David Thatcher wholeheartedly in advising against designing and building from scratch as a novice. I have been designing and building boats to my own design for over fifty years and look back with horror at some of my early efforts, they were absolute disasters!! I still make mistakes, it seems we never lose the urge to create from scratch even when it is the hardest route to follow!!

      My advice is to look at secondhand boat sales worldwide and see what is available. Here in New Zealand you can purchase an amazing amount of boat for your dollar and be sailing relatively quickly. Some designs such as Wharram catamarans can sometimes be purchased very economically here and are very seaworthy craft easily converted to junk rig. Other areas to look are the Caribbean, Southern California and parts of the Mediterranean. Of special interest in Southern California are Marina Lien sales, these can often deliver a boat into your ownership for 10-20% of its normal retail value and all it needs is a haul-out, removal of several years of growth and application of a couple of coats of anti-fouling . If you look wide enough I am sure that you will find something that ticks your boxes at an affordable price.

    Al the best with the project, David.

  • 13 Feb 2017 04:52
    Reply # 4606140 on 4602302

    Hello Martin, I have been following this post for a while and as an experienced sailor and cruiser of multihulls and monohulls, both offshore and coastal, and having built some boats I would certainly advise caution when hoping to design and build your own boat. Building a boat takes up a lot of money and even more time, and anything of 9 meters or more is going to take up some years of weekends and evenings. Unless you really know what you are doing this is a lot of time lost when you could be experiencing sailing and life. If you are building a boat to your own design there is a big risk that it may not work out so that will be a lot of your life lost for no good reason.

    People do spend years building boats. I know someone who spent 19 years off and on building a Newick trimaran, fortunately he was then able to spend almost a decade sailing around the world enjoying the fruits of his labours. We have also had a visiting boat in New Zealand which is Wharram Tiki 38 catamaran with a double Polynesian crab claw rig. So that is a good example of someone taking an existing well proven multihull design and adding a rig that suited him. It seems to work very well.

    So along with some others my advice to you would be to get out on the water in what ever you can afford and learn something about sailing and the cruising lifestyle. If you really want to build a boat invest what is really a very small amount of money in a set of plans by a reputable designer such as Bernt Kohler or as Graham has mentioned the John Marple trimarans.

    Hope you are able to get out on the water soon, David

    Last modified: 13 Feb 2017 05:00 | Anonymous member
  • 13 Feb 2017 03:13
    Reply # 4606053 on 4604798
    Graham Cox wrote:

    Pete Hill has a Bernt Kohler catamaran (see my Hall of Fame article about him in issue 72) and he initially built it with the anti vortex panels.  He found the boat had a seriously heavy helm and would not self-steer, so after crossing the Atlantic from England to Brazil, he cut them off and fitted mini keels.  This resolved his steering problems.  He did extend the design during construction, which may have affected the performance of the panels, but it is hard to see how.  I'd prefer the minikeel anyway, so you can beach the boat on it and scrub under the main hull.  With the vortex panels, the bottom of the boat would sit on the sand.  With dagger board in the amas (or aras as you call them) for windward performance, you would have the best of both worlds.

    Just to add to Graham's post. The anti vortex panels only work with a long dory type hull form and at more than 4 knots. Below 4 knots they seem to give little leeway prevention.
  • 12 Feb 2017 22:02
    Reply # 4605795 on 4602302

    I'm not discouraging you from designing it yourself, just pointing out issues that occur to me.  It is true though that a sailing double outrigger will have significant loads and requires good engineering.  I wouldn't know where to start working out specs like that.  Looking closely at existing designs is helpful and you could go down the empirical route, though there is some risk here, compared to a properly engineered structure.  Of course, you may have some engineering expertise, unlike me! If you are looking at existing plans, you should look at John Marples' trimarans.  His Seaclipper series (not sure if the plans are still available) is built from sheet plywood with a flat-bottomed main hull.  Aesthetically, they are more of the modern western trimaran rather than the exotic Polynesian/Philippino double outrigger type, but well-proven, easy to build, and as economical as it is possible to get.

  • 12 Feb 2017 18:44
    Reply # 4605578 on 4602302

    I agree with Graham and David.  The structural and design requirements for an engine-powered multihull are quite different from those of a sail-powered multihull.  Compare Nigel Irens' Ilan Voyager (http://www.nigelirens.com/boats/power-boats/ilan/)or Cable and Wireless Adventurer (http://www.nigelirens.com/boats/power-boats/cable-and-wireless/) with a sailing trimaran by the same designer: http://www.nigelirens.com/boats/sail-boats/paradox/.  The sailing boat has far greater beam, far more volume in the outer hulls, and correspondingly greater loads on the connecting structure.  Adapting a powerboat design to sailing looks to me a greater problem with multihulls, especially trimarans, than with monohulls.  

    What is your reason for designing from scratch?  You mentioned financial constraints.  The price of plans is generally a small proportion of the price of the finished boat, and unless you have prior experience in design and building, that is not where I would try to save money.  Besides, good plans likely save you time and expensive mistakes, so they may pay off even in purely financial terms.  Finally, good plans and instructions may introduce you to building methods that you would not otherwise consider, and that may be cheaper than what you are planning now.  Rob Denney says that the resin infusion method he uses is both cheaper and lighter than plywood.

    Last modified: 12 Feb 2017 19:22 | Anonymous member
  • 12 Feb 2017 12:01
    Reply # 4605208 on 4602302

    Just to keep you smiling, try this Google Images search 'junk rig trimaran image'. Somehow it pulls in monohulls and cats as well, but plenty of Tris too.

    Last modified: 12 Feb 2017 12:02 | Anonymous member
  • 12 Feb 2017 09:56
    Reply # 4605093 on 4602302

    Martin,

    I know nothing about designing trimarans, so I thought I'd have a look at what resources there are for the home designer and builder. Are you aware of http://smalltridesign.com/ ? 

    But really, there doesn't seem to be too much need to reinvent the wheel. There are home-build trimaran designs from the likes of Ian Farrier, Kurt Hughes, etc, etc and catamaran designs from James Wharram, Richard Woods, Bernt Kohler, etc, etc. Your declared aim is to sail the oceans, and it's such a technical structural challenge, starting from zero, to design a multihull that's fit to do that, that it's a challenge I wouldn't want to accept.

  • 12 Feb 2017 00:10
    Reply # 4604799 on 4602302

    I just looked at the photos and sketches on your profile page.  I assume you are aware that you will need much bigger amas (aras) than the motorboat version, which looked like a Philippine Banca design.  For a sailing double outrigger, the amas need at least 100% of the main hull's bouyancy, and many modern cruising trimarans have used up to 200% (measured when the ama is submerged to deck level, which you should try and avoid in reality!).

  • 12 Feb 2017 00:02
    Reply # 4604798 on 4602302

    Pete Hill has a Bernt Kohler catamaran (see my Hall of Fame article about him in issue 72) and he initially built it with the anti vortex panels.  He found the boat had a seriously heavy helm and would not self-steer, so after crossing the Atlantic from England to Brazil, he cut them off and fitted mini keels.  This resolved his steering problems.  He did extend the design during construction, which may have affected the performance of the panels, but it is hard to see how.  I'd prefer the minikeel anyway, so you can beach the boat on it and scrub under the main hull.  With the vortex panels, the bottom of the boat would sit on the sand.  With dagger board in the amas (or aras as you call them) for windward performance, you would have the best of both worlds.

  • 11 Feb 2017 16:54
    Reply # 4604317 on 4602302

    We have created two albums. One of Aurora Delfin, the boat that inspired us. The other are some of the planning whiteboard madness and the MS Excel drawing. Don't take these drawings as the plans, they where done early on with just a base idea of what the Sea Witch would look like. We most likely start the build, stand back and say "we don't like that" and change it. Best part of building you own boat, you get to change a few things here and there. Nothing major....we hope.

    To Graham:

    We are thinking of a mini/micro keel on the main hull and Centerboards on the Aras. Centerboard will most likely be use too when beaching the boat to keep her level.

    We are also looking in on Bernd Kohler's (a designer we found on Duckworksbbs.com) Anti Vortex Panels as a option. We want to keep our draft as little as possible, so this might be the option.

    To Antoine:

    Thanks for the correction. We weren't sure what it was called (didn't do our homework all the way it seems), so we started calling it Twin Sails so not to confuse it with the schooner or ketch.


    By the why we think it is the sail plan we will be building. The Schooner rig with identical sails....our Twin Sails. Now with our minds pointing this way we can start piecing things together.

    (But still busy moving, so will have to wait)

    Last modified: 12 Feb 2017 06:46 | Anonymous member
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