4,8m Skiff

Discussion in 'Boat Design' started by GraemeR, Aug 11, 2013.

  1. GraemeR
    Joined: Mar 2013
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    Location: Thailand

    GraemeR Junior Member

    Dear all

    I have built canoes and a 4.2m boat from 4mm ply, stitch and glue construction.

    Now I want to make a slightly larger boat as I have two small kids, I would like one similar to my last design, a photo of which I have uploaded.

    I would like to row it, use my windsurfer mast or small outboard.

    If I uploaded hydrostatic data, could anyone make any comments please?

    Many thanks

    Graham
     

    Attached Files:

  2. messabout
    Joined: Jan 2006
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    Location: Lakeland Fl USA

    messabout Senior Member

    Graham, we will be pleased to comment if you tell us more about the boat you wish to build. How big will it be? How many people is it to accommodate? Will you be using it in open water or only in sheltered areas. Is it to be primarily a sailing boat or a rowing boat?

    The picture of the pram looks pretty good as it is. The canoe/kayak is a bit odd and I'll wager that it is hard to tack.

    Four mm ply is a little bit on the thin side for a pram like the picture. If the new build is to be larger than that pram, perhaps 6 mm ply or more.
     
  3. El_Guero

    El_Guero Previous Member

    Double the length of your sailing kayak, widen no more than 30%. Make it a foot taller, use tumblehome where cockpit(s) are.

    Switch to skin on frame.

    Place the keel inside with the frame (i.e., strengthen the keelson and remove the 'keel').

    Use two cockpits, or three. unused cockpits can be closed, plastic tarp secured by a bungee cord will work.

    Attach an ama, about 10' to 15' long, 6" or 9" wide, 2' tall (maybe a little taller), think a sideways kayak.

    Place two masts on her, on whichever side the ama is .... placing on the edge of the main hull will give you some advantages.

    You can can build the main hull in ply, Okoume, Sapelle, or Meranti. But, you would double the weight of the hull .... I would suggest ply for the ama, but not the main hull, she would be getting too heavy for one person to handle on the ground with kids ...

    This would also allow you a small gas or electric between the hulls, for those times you want (need) to beat the rain home ....
     
  4. GraemeR
    Joined: Mar 2013
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    GraemeR Junior Member

    Hi

    The sailing canoe is about 10 years old and my favourite boat, it has outriggers and is small and fun.

    The pram is no longer with me after moving to Thailand. I lined it with glass and epoxy so it was quite solid. I plan to do the same idea, just larger.

    I want a small family boat to row, sail, with the unsupported windsurfer mast and to motor.

    Not too heavy, say 100kg as it's one man launching. 4,8m long.

    Intended for myself, two kids and occasionally my wife too,

    I use rivers and the coast. The sea is usually quite calm here.

    I've attached a first off linespan, ok for lower hull and hydrostatics text

    Many thanks

    Graham
     

    Attached Files:

  5. GraemeR
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    GraemeR Junior Member

    Gents,

    Just for comparison, this is my kayak in operation and a typical Thai open canoe, which is paddled short distances, very slowly.

    With sun and reflections every inch of skin needs to be covered!

    Graham
     

    Attached Files:

  6. GraemeR
    Joined: Mar 2013
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    GraemeR Junior Member

    4.2m Skiff - Hydrostatics

    Gents

    I've uploaded two hull designs. One with a flat bottom and one with slight lift on the keel and chines.

    Could anyone please comment on the effect on stability please?

    Many thanks,

    Graham
     

    Attached Files:

  7. Petros
    Joined: Oct 2007
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    Location: Arlington, WA-USA

    Petros Senior Member

    how about building a Great Pelican sailboat? it is a scaled up pram type hull, with a small cabin, 16' long by 8' beam. It can be motored, rowed or sailed. It has a junk type rig which would be perfect for your location. it is very safe and seaworthy, I know of someone that sailed one to Hawaii from California (though I would not recommend it). You can adopt modern stick-n-glue construction to it.

    [​IMG]

    [​IMG]

    plans from Murial Short, or:

    http://www.dngoodchild.com/5469.htm

    kits from:

    http://www.platypusboats.com/gpstore.html

    I have a set of plans for it in an old magazine that I can scan and post if you are interested.
     
  8. El_Guero

    El_Guero Previous Member

    I would be interested.

    It looks like Manie's Micro Cruiser he built.
     
  9. GraemeR
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    GraemeR Junior Member

    Yes please, that would be great :)

    Thank you

    Graham
     
  10. PAR
    Joined: Nov 2003
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    Location: Eustis, FL

    PAR Yacht Designer/Builder

    15' to 16' pocket cruisers are pretty plentiful. Your designs thus far show a lack of some hydrodynamic fundamentals, so honest comments about them would just likely piss you off. Many designers have low cost plans for this type of boat. You should look at Glen-L, Bateau.com, B&B Yachts, plus the older classics from Monk, Gardener and others. The Glen-L "Minuet" comes to mind for you. She's 15' (4.57 m) on deck.

    [​IMG]

    Nancy's China is another, 15' 3" (14.64 m) on deck.

    [​IMG]

    She's available with a Bermudian sloop, gaff sloop (shown and a sprit rigged main sloop.

    Personally, I think boats this size with a cabin are just too small to be very practical and they increase boat weight a lot too.

    For an open boat, consider a Core Sound 15 or a Bay River Skiff, both from B&B Yacht designs. They are in the weight range you desire, practically sail themselves and a light fabric dodger could be arranged to provide some shelter if a thunder shower rolls through.
     
  11. GraemeR
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    GraemeR Junior Member

    I admit I know almost nothing and it takes a lot to piss me.

    I am after a light stable boat as I have two small kids and difficult launch sites., so many of the

    If you could make any comments, I would appreciate it.

    What is the effect of raising the keel at the bow and stern?

    What is the effect of raising the chines to make a more V hull?

    I was a civil engineer and now teach maths, so I understand about fluid mechanics. What I lack is the background in hydrodynamics/ hydrostatics.

    Thanks

    Graham
     
  12. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    The first design posted above has zero "rocker", which means she'll row and sail terribly and maneuver poorly. The amount of rocker in the centerline and the distribution of the volume are application specific. Speed targets, performance envelop, weight and loading expectations, etc. all will require a different "belly" profile to this little boat.

    Making her a V bottom will have the same requirements, though will add a little complexity to the build, while detracting from initial stability too, compared to the flat bottom, which has a higher initial stability. A V bottom can soften the ride, but requires more displacement and build effort. For your needs, this complication isn't necessary.

    If you must self design, pattern closely after a well known design, so you don't have to take a short course on the dynamic aspects. Ed Monk had several of these, most of which are in the public domain now. Ted Geary, Bill Jackson, John Gardener and many others, who's plans are now public domain or very low cost are some of the ones you should look at. Styling can be updated, as can rigs and building methods.

    I still think a Bay River Skiff or CS-17 would be ideal for you. Both are V bottoms, quite stable, easy to sail, light weight, can take to a beach on their bottoms and the divided rig gives the kids a string or two to tug on. If you want a flat bottom, I have a few, as well as most designers, so again check with Glen-L and the other sites. Lastly don't ask for too much from a 15' boat. This is what makes them heavy and poor sailors. Cruisers need cabins, day boats really don't.
     
  13. GraemeR
    Joined: Mar 2013
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    GraemeR Junior Member

    Dear Par

    Many thanks for the advice.

    I based the design on this 4.2m skiff (attached).

    The beam may be increased to 1,6m to increase stability.

    I was considering 10 or 15 degrees rocker at the bow, tapering to 0 at the stern. Does that sound OK for tidal rivers/calm coastal sailing.

    I will probably motor to a location then sail, or row depending on the situation. So probably 40% motor, 30% sail and 30% row

    What about raising the bow and stern? Other than reducing the metacentric height and reducing stability, does it improve manoeuvrability much?

    How much is it worth raising them?

    With the pram I increased them about 75mm and added a 75mm skeg,

    Many thanks for your advice, no offence taken, it's just the help I need :)

    Graham
     

    Attached Files:

  14. philSweet
    Joined: May 2008
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    Location: Beaufort, SC and H'ville, NC

    philSweet Senior Member

    I agree with PAR 100% on this one. At 15' of 16', cuddies are more of a hassle in the tropics than anything else. A covered foredeck is always nice, and a little hatch to get at the stuff stashed there. The Core Sounds are spot on, but might be biased towards sailing compared to what you want for river work. But I think a slightly lighter version with reduced rig would make a wonderful river boat. A mostly open boat with raised floorboards to keep the kids out of the bilge. Versatile seating to allow you to face away from the sun. This also suggests a bit more initial stability than strictly necessary. I like to be able to move around in a river boat. (I mucked around in the Everglades for ten years). One feature from sailboats I would borrow is sidedecks around the cockpit. Big enough to sit on, say 8" wide. Getting your butt out of the boat helps a great deal when it comes to not stewing in your own juices on a steamy day. I dressed exactly as in your picture in the 'glades in the summer. Had to considering the bugs. This restricts the activity level to very low and changes everything about how you operate a boat.

    On a pure sailboat, the centerboard housing is not a huge inconvenience because you're pretty much stuck sailing from one position. In a mixed use boat, one quickly begins to resent the darn thing when not actually sailing.

    Although it adds weight and complexity, I personally feel it is worth the effort to build two centerboards - one into each side seat - and leave the middle of a small boat open. I never once in twenty years thought "gee, I really miss that centerboard case in the middle of the boat".

    <sorry, we cross-posted. This wasn't a comment or rebuttal of your last post GraemeR>
     

  15. GraemeR
    Joined: Mar 2013
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    GraemeR Junior Member

    Phil

    Many thanks for the advice. I was intending to use a daggerboard. I have several different lengths for different sails with the kayak.

    Doubling up sounds a good idea. I have seen lee boards work too, but better not with kids.

    I like duckboards to keep the kids dry and add a pump with a pipe below.

    I want to use my existing windsurfer mast and sails. I think the biggest is about 4 sqm,

    A tent made with a spar makes a good cover for a rest out of the sun or if it rains.

    The Bay River Skiff looks super :)

    I think I would prefer my own design as it's half the fun and the other two boats, though largely based on guesswork, seemed ok.

    Many thanks

    Graham
     
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