Designing about 4.5m long trimaran

Discussion in 'Multihulls' started by TTTP, Feb 17, 2008.

  1. TTTP
    Joined: Feb 2008
    Posts: 13
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: Finland

    TTTP Junior Member

    I am interested in designing and building a sailboat. The reguirements are:

    - affordable
    - small enought that self building isn't too hard and it can be handled without engine
    - safe, confortable and easy to sail so that I can take family members and friends along
    - relatively fast and fun to sail.
    - transportable
    - can be sailed singlehanded but carries 180kg payload without sweat.
    - can handle some waves and decent winds.
    - can be used in a lake that contains quite a lot rocks at bottom.
    - something I can be proud of.

    My current idea of boat that fits the requirements is a small trimaran with following features:
    - length about 4.5m, floats about 4m, width about 3m
    - sitting place in center hull. About 0.5m freeboard.
    - float volume about 200% of maximum displacement.
    - single kick-up rudder and centerboard.
    - mainsain 10-12m^2 and gennaker less than mainsail. no Jib.
    - tunnel for gennaker
    - short pole for gennaker
    - two reefing points for mainsail
    - modest sail area.
    - glass-foam sandwich hulls with epoxy or vinyliester resin, aluminum mast, dacron mainsail, aluminum or carbon-glass-epoxy crossbeams.

    I have much questions, but this time I would like to know best sources of information. What are best books and articles to read for my design and construction needs? I would also like to hear comments about feasibility of my basic idea. I might later add drawings and renderings here to be judged.
     
  2. Fanie
    Joined: Oct 2007
    Posts: 4,603
    Likes: 170, Points: 63, Legacy Rep: 2484
    Location: Colonial "Sick Africa"

    Fanie Fanie

    First thing - are you taking the vessel to sea or strictly inland waters ?

    Designing and building is not as easy as it seems. If you've never built a boat before I would recommend you rethink and rather buy a tri or buy a 2nd hand one and restore it back to original condition. That alone is enough work by itself.

    One of my friends started building himself a boat too. Halfway through it he gave up - too expensive and too much work. He could have bought a new boat taken everything in consideration. There really are some stunning trimaran's out there, all sorted out already. Something to seriously consider. I have built 5 and is about to start the 6th, it is a HELL OF A JOB to do. Ask anyone here.

    The 4m500 seems much too short. Google for windrider, that's the smallest tri I've seen. You can make a comparason to the sizes on it too. I sailed one of them (not the smallest one) and they sail very nice and smooth, easy to handle.

    My personal opinion, if you're stuck on building it yourself, build the biggest you can handle single-handedly. A boat is always too big on land, and much too small on any water. Size does coun't, you can ask your wife :D

    It is my personal opinion that small kids should not go out on recreational boats. Many people does not share my view on this but I want to throw up if someone take their little kids out on the water with them, life jacket or not. I may have misunderstood the mention of family there.
     
  3. Pericles
    Joined: Sep 2006
    Posts: 1,948
    Likes: 106, Points: 0, Legacy Rep: 1307
    Location: The heights of High Wycombe, not too far from Rive

    Pericles Senior Member

  4. rayaldridge
    Joined: Jun 2006
    Posts: 581
    Likes: 26, Points: 0, Legacy Rep: 322
    Location: USA

    rayaldridge Senior Member

    Bear in mind that in these tiny sizes, a cat can carry substantially more weight than a tri, and the complications of a tri become more difficult, in proportional terms, than a cat's, which can be quite simple.

    Ray
     
  5. Doug Lord

    Doug Lord Guest

    Small Tris

    See page three of this forum for 14' singlehanded tri and heres a post from that thread:
    --------------------------------------------------------------------------------

    I think these two little tris (and the other two on the Astus site) are neat little boats and they offer a lot of fun in an easy to sail and easy to handle package. They're not powered up like the Exploder or most beach cats but they offer comfort and ease of sailing that seems like it could catch on. They're designed so that the main hull will plane and should give good speed particularly offwind without being at high risk for either pitchpole or capsizeEXCEPT IN VERY STRONG WINDS. They look great to me...
    I've sailed a 60lb tri with a planing main hull with 85 sq.ft. and it was a blast-a lot easier to sail with the ama's than it would have been w/o them.I think the niche of these boats is decent performance in a very ,very easy to sail platform.
    =========
    Weta Specs:
    LOA-14.4'
    Beam-12.13'
    All up weight w/o crew-211lb. main hull 132lb.
    SA-upwind 95.5sq. ft.
    -downwind 156 sq.ft. incl. screecher.
    http://www.wetamarine.co.nz/
    You tube video in VERY, VERY strong wind: http://www.youtube.com/watch?v=LHpJJNGmMVg IN A SURPRISING DEVELOPMENT THE WETA GUYS PULLED THIS VIDEO SINCE IT SHOWED MANY PITCHPOLES. It was in 35 knot winds and the boat handled it with no damage but did turtle. Most people in their right mind would not go out in such conditions and the factory posted the video thinking that people would understand that. They got a lot of criticism on SA under Dinghy Anarchy"I want a Weta" for the pitchpoling. Unjustified,in my opinion.
    =================
    Heres a new link to all the WETA videos including the high wind vid: http://www.norbanks.com/weta_video.htm
    ==========
    Astus Specs:
    Ex Aqua website with more complete info and details of a 16' and 20' Astus tri's:
    Astus Trimarans
    http://www.exaqua.co.uk/index.php

    LOA-14.1'
    Beam-8.2'
    Main hull weight 83lb.
    SA-upwind 86 sq.' main only
    -downwind 161sq.ft. incl. genaker
    ---------------
     

    Attached Files:

  6. TTTP
    Joined: Feb 2008
    Posts: 13
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: Finland

    TTTP Junior Member

    Thanks for comments. The reason for thinking trimaran over catamaran is that in small catamaran it is hard to find decent place for cockpit. I know that for same money and weight catamaran can be made longer.

    I haven't build a boat before but as a kid I watched and helped as well as I could when my father build his own design catamaran. It was far from production boat but I still remember sailing it among best things in my life. When I was younger I wanted to be a boat designer. That didn't happen, but I still like thinking these things. I have read some older books about yatch design and have MSc in technical field so designing shouldn't be impossible with enough good information. The small size of the boat should make finishing it easier. I know it would still be huge work.

    Youngest of my nephews will be 7 at summer. I sailed with my father at that age. I would also like to sail with my parents and sisters.

    In fact I have read about Astus, Weta and Magnum trimarans. They seem interesting but have quite low volume floats. Of course bigger floats would weight more which worries me. Those production boats are very hard to find used. I watched videos of Astus trimarans and they seemed to move fine even with their tiny floats.

    4.5m tri wouldn't be very fast, but If it could be build to 120kg it would have more sail/weight than e.g. laser when sailing singlehanded. It would also have higher aspect ratio rig, longer waterline, gennaker and better stability.

    The boat would be used both in a lake and for coastal sailings on Gulf of Bothnia. There are islands around to limit waves and I have often paddled a sea kayak there. On average day the waves are about 30cm high. I haven't hit 1m wave yet.
     
  7. TTTP
    Joined: Feb 2008
    Posts: 13
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: Finland

    TTTP Junior Member

    Weta seems fun boat but I still would like to design my own. It seems top and bottom halves of floats in Weta are mirrored. That could make building easier. Make one mold and laminate four panels in it. There are many websites about boat design and construction and I am going to read many of them too, but I prefer good books over internet.

    I just found out that our library has "Principles of Yacht Design", which I am going to read. I have also read following books that are more than 25 years old:
    - Kinney, Francis S. Skene's Elements of Yacht design
    - Marchaj, C. A.: SAILING THEORY AND PRACTICE
    - Phillips-Birt, Douglas: SAILING YACHT DESIGN
    What other design books shoud I read? would "The Elements of Boat Strength: For Builders, Designers, and Owners" be applicable for small trimaran?

    I have eyed through Farrier marine study book and I am going to read it more througly. I also downloaded PDF:s from: http://www.marinecomposites.com/ but haven't yet read it. Is there other building books I need to read?

    About software:
    - I have started learning Freeship and have downloaded Michlet. I also have QCad for 2D design and Blender for rendering. Is there other free or cheap software I'd better get?
    - How much would the cheapest program that can calculate polars for a multihull cost?
    - Is there any free or cheap program for analysing sailplan aerodynamics?
    - Is there any free or cheap program that can calculate strength of crossbeams?
     
  8. Fanie
    Joined: Oct 2007
    Posts: 4,603
    Likes: 170, Points: 63, Legacy Rep: 2484
    Location: Colonial "Sick Africa"

    Fanie Fanie

    I'm buzy putting tohether the web pages of the little tri I built in December this year. I'll put a link up to it when it's up for viewing - it will be found in the 'sailing experience' thread.

    If I would do the centre-hull over again, I'll make it more like the farrier's hull that flares open above the waterline to gain more deck space. Personally I don't like trampolines.
     
  9. TTTP
    Joined: Feb 2008
    Posts: 13
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: Finland

    TTTP Junior Member

    Your trimaran will be interesting to see.
     
  10. TTTP
    Joined: Feb 2008
    Posts: 13
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: Finland

    TTTP Junior Member

    Is there nobody here, who has read most books about boat design and construction and can give recommendations?
    :confused:
     
  11. Pericles
    Joined: Sep 2006
    Posts: 1,948
    Likes: 106, Points: 0, Legacy Rep: 1307
    Location: The heights of High Wycombe, not too far from Rive

    Pericles Senior Member

  12. Chris Ostlind

    Chris Ostlind Previous Member

    Sharing Some Thoughts

    This is a trimaran I have designed that is pretty close to the boat you describe above. It is designed to be built in marine plywood in a stitch and glue build style with glass/epoxy laminates inside and out.

    I show the boat with a unirig (no jib) and a modest screacher flown from a bow pole. This contributes to simpler sailing and rigging, though the addition of a self-tacking, blade jib would be an option for a hotrod version. I see the boat (A16 Sport) using a furler for the screacher, rather than your idea to use a retrieval tunnel. The sail rig is a modest 130 sq. ft. and the screacher is 118 sq. ft.

    It has rather large volume amas for a boat of this type at 180%, so that the boat can be sailed from the cockpit without the need to move around on the trampolines for ballast should the owner chose that method. The beams, mast and boom are seamless aircraft aluminum in 6061 T6 alloy. They will anodize inexpensively and be very low maintenance.

    Foils are both flip-up style (centerboard and rudder) for ease of beaching, as well as handling underwater obstacles. Both foils are high aspect in planform with sections designed to give the best performance at the widest range of potential boat speeds.

    The forward volume in the vaka hull can be used as a cabin for one, should the weather turn poor. The aft volume is perfect for gear storage out of the elements.

    The displacement can handle two adults for day sailing, or one adult and a whole bunch of gear including a small outboard engine. The coastal cruising/exploration potential for this boat is terrific when sailed solo. It can take to very shallow water and is decently light, allowing the boat to be pulled up on a beach. A 2 hp outboard is sufficient to drive this boat and will run all day on a tiny tank of fuel.

    If this boat helps you to visualize the style of craft you are looking to design for yourself, please feel free to borrow ideas if they will also work for you.
     

    Attached Files:

  13. TTTP
    Joined: Feb 2008
    Posts: 13
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: Finland

    TTTP Junior Member

    Nice looking boat. It has many similarities with drafts I have made.

    Am I right in my guess, that mast is designed to stand without diamond shrouds or lower shrouds? That would be a good reason for low reacher top point.

    Do you have plans ready? How much is the price?

    I saw pictures of your A18 trimaran. The floats seems to have two little hatches. Is the float separated to two watertight compartments?

    What software did you use in design?

    What section profile do you recommend for trimaran centerboard and rudder? It should resist ventilation and work well even though home builder can't match the accuracy of CNC milling.
     
  14. Fanie
    Joined: Oct 2007
    Posts: 4,603
    Likes: 170, Points: 63, Legacy Rep: 2484
    Location: Colonial "Sick Africa"

    Fanie Fanie

    Now you can. For some reason I couldn't find the thead to post the link, sorry.

    http://www.faze.co.za/Little Tri.html

    I have again looked at the tri I build. If I have to do it over again I'll flare the bow out sideways outward from the deck so it has a flat squarish 'deck' one can walk on and have that run right up to the transom.

    If this was going to be my only or main boat I'll make it as large as I can handle. I see a lot of people just wants a 'small little' boat. Small is too small on the water. Even big on land is too small on the water. You will pick the same up everywhere on this forum, bigger is safer.
     

  15. Chris Ostlind

    Chris Ostlind Previous Member


    Thanks. Small multihulls like this tend to take on many similar attributes as there are only so many ways you can solve the issues present with the fixed size of the human form and the weight locations in which it can operate with the boat.



    There will be shrouds, as well as a recommendation for diamond wires on the mast, depending on section used. A carbon, self-supported mast this size begins to get expensive and it would virtually eliminate any functional use of the cabin as the hatch would be just four inches away from the spar when the hatch was opened.

    The fractional location for the screacher on the mast was done to keep the Center of Effort of the sail relatively low and not over-power the boat. This is a small, light boat which could have a tendency to pitchpole in a big gust if the screacher were too large, or too high.

    I left out a lot of the detail elements in the design as it is only at the point of being a study right now.



    There are no plans for the boat at present. This design is on the list of things to do and I'll probably be able to get to it in another month, or so.



    The deck hatches are there to give access to the mounting bolts for the aka beam ends on the amas. There are watertight bulkheads in the bow sections of each ama in case the boat hits something hard at speed. These are, more or less, large volume crash boxes to provide secure flotation or serve to isolate the damage and entry of water.



    I use Rhino3D with RhinoMarine, principally, with a host of other packages for specific parts of the boat.



    NACA 0000 profiles are very good all-around foil sections and are pretty easy for home builders to complete. For a daggerboard/centerboard on a boat such as this one, I suggest a NACA 0009 section. For the rudder a NACA 0012 is a very good solution. Neither of these foils are going to give you that last knot or two in high speed use, but they will function extremely well in low-to-mid speed work.

    I suggest the use of a set of simple plywood templates for regular intervals down the length of the foil planform to aid the shaping process. At the bottom of this post there is a photo of a centerboard which I built in this exact fashion. The board has a shaped, Sitka Spruce core and was then skinned with two layers of carbon twill cloth in a vacuum bag process. The board is strong, light... and it looks pretty cool as well.
     

    Attached Files:

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.