Designing a wooden 7 meter open daysailer

Discussion in 'Boat Design' started by Peter Vella, Jul 16, 2018.

  1. Peter Vella
    Joined: Mar 2013
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    Location: UK

    Peter Vella Junior Member

    Hi to all on the boatdesign forum. I have been starting the design process for a daysailer/coastal cruiser. A few years ago I started off a build of a much larger blue water boat which I am unable to complete due to changing priorities in my life. As a result I already have aquired enough timber to build a smaller dayboat. I want to use the materials that I already have so that means it the hull will be of carvel construction and bronze/copper fastened.

    With ease of build in mind I have been working from the idea of a chine hull with a cross planked bottom. The topsides can still have some some flam, which will help with reserve stability and help soften the chine. To my eye this means a double-ended hull is desirable as it is hard to have a decent looking transom on anything other than a round bilged hull, and the double-ended hull ought to be simpler to build and slightly stronger. I accept that the double-ender will be slower due to having the run aft interupted by the chine where it bends back towards the sternpost, creating an area of turbulence. I am not completely against the idea of a transom, but not yet convinced that the lower drag that would be possible outweighs my other considerations.

    The design needs to be shoal draft and trailerable with mostly internal ballast in the form of lead pigs under the floorboards, which implies a low aspect ratio rig and a centreboard. A gaff cutter or sloop seems too complicated for a boat of this size, I am currently thinking of a lug yawl.
     
  2. Peter Vella
    Joined: Mar 2013
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    Location: UK

    Peter Vella Junior Member

    double ender REVISED AFT_Linesplan.jpg
    Length overall: 6.8 m
    Length LWL: 6.53 m
    Beam overall: 2.38 m
    Beam LWL: 2.04 m
    Draft: 0.46 m
    Disp: 1769 kg
     
  3. AnthonyW
    Joined: Oct 2012
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    Location: Cape Town, South Africa

    AnthonyW Senior Member

    Selway-Fisher is in the UK there. Maybe look at their website and contact Paul. Loads of designs, and he will convert the plans to open if needed. Active group of builders on the web of his designs too. Most of his plans could be build carvel or he could modify them to such for a small fee. (I have a modified plan from him.)
     
  4. kvsgkvng
    Joined: Jan 2012
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    kvsgkvng Senior Member

    Hello, Peter. Nice to see you here. In no way I am well experienced in building, but if I may add my two cents, the double ender hull's most attractive feature is supposedly well worth in following sea, while running in rough weather. Probability of this scenario is far less than one with pleasant sailing along the coast with a nice marina at the end. Double ender is more difficult to build with few benefits one of which is more pleasant looks. If you like it, by all means, go for it knowing it will add another chunk of change and building time to your finished project.
    Another thing to consider is centerboard mechanism and the housing box. In this small boat it will take a lot of useful space. And all of it for what -- to boldly go at 3 degrees sharper angle to the wind? and 0.347 knots faster? For long range cruiser, doing it for days, it is well worth it, for 22' coastal cruiser, or even day-sailor, I doubt it. Adding 10"-12" to the keel would serve well for normal sailing, it would allow to shift ballast down for better stability, make much more room under the deck (cramped as it would already be), simplify building, save on materials and rigging, make maintenance a breeze and look good too and still this sailboat would be able to gunkhole at most beaches except 6" deep wetlands full of mosquitos... Actually, a wine-shaped transom looks much "sexier" to my taste, adds more useful space and you will have a nice place for an outboard. Best of luck. JMHO.
     
  5. Peter Vella
    Joined: Mar 2013
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    Location: UK

    Peter Vella Junior Member

    AnthonyW - I have bought dinghy plans from Selway-Fisher before. I quite like the East Cornish Lugger if it could be shortened slightly to under 7m LOA. However, simply building that hull shape in carvel would not be a simple as the construction method I would like to use. A cross planked bottom would save having to either use all bent or laminated frames, or lots of sawn frames, and the bent frames I do use would only be on the topsides as intermediary frames to support the fore and aft planking between the main sawn frames at each station, therefore they will be much shorter and won't have to be tortured around the turn of the bilge as on a round bilge hull. Also that design seems very light - 500kg dry weight with up to 150kg ballast. Assuming another 250kg for crew and provisions that is a D/L ratio of around 100. I am sure that is achievable with the construction method Paul has designed but doesn't seem likely with traditional plank on frame construction.

    kvsgkvng - I do like the look of a double-ender but I agree it makes little practical sense the more I look into it. The initial idea to make it double ended came about from the first decision to have a chine hull and how to 'hide' the chine. The problem of having a smooth run aft on any double ended hull is made even worse with a chine running back athwartships into the sternpost, so I have been concerned about that, and while I have tried tweaking the run of the chine aft to minimise this, it will always be a problem.

    I am coming round to the idea of a transom:

    transom_Linesplan.jpg It will need some tweaking to get right, but this is an initial sketch. I am thinking that with a transom I may as well have a plumb stem also.

    As for the centreboard, I will be sailing in Cardigan Bay which is predominatly a lee shore so she needs to go to windward. I am not too concerned about the space the trunk will take up as there won't be a cabin there. I have thought about having a small external ballast keel, but I like the idea of having all the ballast removable so that the boat can be signifigently lightened for trailering. Also an external ballast keel of any depth would need to be supported by increasing the width of keel timber above it. Without a ballast keel I can make the keel timber the same siding throughout it's length which will save time, effort and material.
     

  6. AnthonyW
    Joined: Oct 2012
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    Location: Cape Town, South Africa

    AnthonyW Senior Member

    Perhaps lee boards? Aesthetically a matter of taste, and this seems important. But perhaps worth a thought anyway. Lifting they allow shallow draft. Could even suit the design depending on how they are finished.
     
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