Designing a trailer sail boat

Discussion in 'Sailboats' started by Bioptica, Nov 18, 2004.

  1. Bioptica
    Joined: Nov 2004
    Posts: 1
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: Australia

    Bioptica New Member

    I am considering designing and building a small sail boat that can be transported by trailer.
    I already have a 22 foot Duncanson trailer sailer but need a challenge!

    I want to build a boat that is between 26 and 28 foot (max 8.2 foot wide)with partial water balast and lead swing keel to make transport lighter.

    My questions at the moment are:

    - Would a hull built in marine grade aluminium be much heavier than fibre glass?

    - Is there anyone out there who knows how to design a trailer boat with a combined water and swing keel balast in aluminium? And how much would the price of such plans be?

    The main purpose of the boat is for safe family sailing with a strong emphasis on utilisation of space, camping and ruggedness.

    All the best,

  2. Doug Lord

    Doug Lord Guest

    Trailer Sailor

    Pete, in some magazines over the last few years-especially Seahorse- the words "swing keel" have been used to mean a canting keel. I would assume you're using the "traditional"(and correct imho) definition to mean a ballasted keel that swings fore and aft like a centerboard?
    You might want to consider ditching that idea given the plans you have for the boat. Most swing keels are pulled up or let down by a wire that is attached low down on the keel and immersed in the water while sailing.If(when) the wire breaks you have trouble.Also the pin retaining the keel is usually in a wet, hard to get at location... A better solution might be a vertical lifting "daggerboard" keel with,perhaps a bulb on the bottom to get the weight as low as possible.
    Last edited by a moderator: Nov 18, 2004
  3. tspeer
    Joined: Feb 2002
    Posts: 2,311
    Likes: 282, Points: 83, Legacy Rep: 1673
    Location: Port Gamble, Washington, USA

    tspeer Senior Member

    Why not build a multihull? There are a number of designs in that size range, including the
    Ian Farrier F-82 (
    Kurt Hughes 27 ft cat (
    Kismet 24T (
    Marples/Brown Searunner 25 and Seaclipper 28 (
    Woods Skua (
    and many more.

    Personally, I recommend the Farrier boats - they are arguably the finest trailer sailers ever designed. There's a reason why the F-27 is in the sailboat Hall of Fame.
  4. sorenfdk
    Joined: Feb 2002
    Posts: 511
    Likes: 27, Points: 28, Legacy Rep: 394
    Location: Denmark

    sorenfdk Yacht Designer

    Tom - didn't you forget the Dragonfly 800? Sorry - I don't have any URL!
  5. K4s
    Joined: Nov 2004
    Posts: 68
    Likes: 2, Points: 0, Legacy Rep: 29
    Location: New Zealand

    K4s Junior Member

    tspeer has it in one.If room and lightness that doesnt overly detract from performance is the aim,multihull is the way to go.
    Although a dagger type board and bulb is better,in my opinion,than a lifting centre board the trade off is the room the centre case takes up in the middle of the cabin area.Thats one consideration.Another is performance.
    Getting room inside a short monohull really means width pushing well aft and forward in the hull shape,outcome of this is you end up pushing water around where ever you go,this is slow.Getting these dimensions correct with regard to sailng performance would be on the top of my list at design/build stage.
    Down here in NZ there are some truley awful trailer boats that spend more time motoring than sailing because they just wont go to windward,but they have huge interior space.I guess the choice is yours.For me the boat has to sail well.
  6. tspeer
    Joined: Feb 2002
    Posts: 2,311
    Likes: 282, Points: 83, Legacy Rep: 1673
    Location: Port Gamble, Washington, USA

    tspeer Senior Member

    I thought the Dragonfly was only available as a production boat - I didn't know the Dragonfly was available as a homebuilt boat (that was the original question). So I only listed trailerable boats that had plans available.

    If the object is to have a trailerable boat to sail, but not necessarily to build, then the best way is to buy a used production mulithull. And in that category, I don't think there's anything close to the performance, utility, and just sheer enjoyment for the money of a used F-27.

    With regard to cost, these boats are on the flat part of the depreciation curve and hold their value really well. So the net cost of ownership is low, although the intial cost is higher than for a monohull of the same length.

    Interior space is comparable to a monohull due to the flared topsides, but the storage space in the main hull is minimal. However, the amas are a good place to put anything that can get wet. For a family, the aft cabin makes a great, safe playhouse for the kids. And the real estate of a trimaran makes it possible to have room to stretch out or just get elbow room and not be crammed together in a small cockpit when cruising.

    The boats are easily launched. When you get the routine down, you can be sailing away half an hour after leaving the roadway - I've seen it done.

    Performance is roughly along the lines of a racer-cruiser monohull in the 40 - 50 ft range. Even upwind.

    Go for a ride on an F-27 - you won't look at trailerable boats the same way again.
  7. PAR
    Joined: Nov 2003
    Posts: 19,133
    Likes: 479, Points: 93, Legacy Rep: 3967
    Location: Eustis, FL

    PAR Yacht Designer/Builder

    Bioptica, there are many trailer born designs available, ranging from the sturdiest of small passage makers to all out race machines. You've voiced interests in healthy construction, good storage space and the ability to camp cruise or over night her if you wise. This plays out the racers as most don't have a lot of room in them and are on the light side in terms of the beating they'll take. So a good performing cruiser, with a shoal option.

    In spite of what Doug had to say about centerboard pendants and pivot pins, they are a well proven time tested way of reducing draft and easing trailerability. The pendant doesn't have to be in the water and most good designs will last many years before renewal is necessary, the rig will have had it's wire replaced, maybe more then once before this is needed. The guy I regularly race with has a early 70's Catalina 22 with the original pendant holding on to the 900 or so pound centerboard, and it does go in (the pendant) the water.

    A dagger board really only belongs on a craft small enough to push off whatever you've run aground on. A dagger will not naturally retract when it hits a sand bar, oyster bed or etc. like a centerboard will (most of the time) and this requires the sailor to try and raise the board that is usually jammed in the slot or has the weight of ship and crew centerstanding on it. It is an efficient type of appendage, but not on a 28' cruiser. Centerboards can jam too, but are much less likely to do so. I design my centerboards to be "over the top" tackle or winch operated in this displacement range. This permits the board to be lowered without the pendant being in the water.

    I'd think 'glass or one off wood construction would be the most practical and cost effective in this class of pocket yacht, when compared to aluminum.

    I'd also reconsider the water ballasting requirement, unless you intend to build to a rule or get a rating and go racing. A fine craft can be had and not kiss off valuable stowage space or accommodations. This would be a good sized trailer boat at 28' but quite do-able with an average pickup or SUV and tandem trailer. Unless you insist on dragging her behind a Toyota Celica or intend to win races, water ballasting is more trouble then it's worth in a cruiser.

    Multihulls are an option and they offer a number of advantages, but like everything else there are the disadvantages too. You'll have to have a folding boat to trailer. The unfolding operation has become quite refined in this last generation, so this doesn't have to be a draw back. There is a decided speed advantage, but the living space is tight. The tramp is fine, in nice weather, and provides a lot of options not open to mono hull designs.

    In the end, you could consider one of the stock plans sets available from the world's designers. Prices range from free or near so to the cost of a good used yacht. You'll find the free and cheap plans are dated (generally) and possibly lacking in one or more of your requirements. Another idea is a custom design. One that suits you and your needs perfectly, possibly drawn around your building skills, certainly your budget. This would be the best value for the money, though quite a bit more then a set of 30 year old stock plans from a catalog store. The last option is to acquire the skills to design it yourself. This would be the least cost effective way of getting it done and would take the most amount of time. This would entail what would amount to an engineering degree (without the required English lit, or civic studies) and the experience to do it right. Most of us take a number of years to gain the skills necessary.
  8. sorenfdk
    Joined: Feb 2002
    Posts: 511
    Likes: 27, Points: 28, Legacy Rep: 394
    Location: Denmark

    sorenfdk Yacht Designer

    Oops - I didn't see that! You're right - The Dragonfly is only available as a production boat.
  9. Peter Bowen

    Peter Bowen Guest

    Thanks for all the replies,
    I might try to get the hull designed by a designer and then go from there. I am not fond of multihulls for trailer transport and they are cramped too.
    Anyway, I will see how I go and get back with my progress.
    Again thanks for all the great replies!
  10. dougfrolich
    Joined: Nov 2002
    Posts: 661
    Likes: 21, Points: 28, Legacy Rep: 225
    Location: San Francisco

    dougfrolich Senior Member

    how about this,
    28' loa
    standing headroom

    Attached Files:

  11. BrettM
    Joined: Apr 2002
    Posts: 204
    Likes: 1, Points: 0, Legacy Rep: 16
    Location: Australia

    BrettM Senior Member


    My first suggestion to people wanting a boat in this size is to look at the second hand market as you may well get want you want for a lot less than building your own.

    If building your own is your desire, then good for you. The satisfaction seeing your own work slide into the water and sit as designed is not to be underestimated.

    If price is a factor then the cheapest/roughest method would be plywood/glass. but then you will get a boat that looks like it has been made from ply/glass and poor resale value.

    I would suggest that for a one off construction then perhaps a hull of epoxy/cedar/glass or epoxy/duracore/glass would be worth looking into. Deck could be fashioned from premade grp/balsa sandwich panels and taped together.
    Note that I have no financial interest in any of these materials.

    Where in Australia are you? Perhaps I can help.

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.