4,8m Skiff

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

  1. LP
    Joined: Jul 2005
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    Location: 26 36.9 N, 82 07.3 W

    LP Flying Boatman

    You need to look close at your volume distribution and your entry and exit designs. Here is a link to another skiff type design.

    http://www.duckworksbbs.com/ProductDetails.asp?ProductCode=JD-Presto_16

    I'm not promoting it, but only using it as an example. Look at the transom on this and the Pelican design. You'll note that the bottom of the transom is right at or just clear of the waterline. This helps to give nice clean flow as the boat passes through the water at displacement speeds. Both of these boats are flat bottom so the chine at midship is at it's deepest. This contributes greatly to stability. It gives you displacement where it is needed to help the boat stand up.

    If you look at the skiff MP posted in post #35, it has a very immersed transom. This skiff is intended to be powered and operated in planing mode. Once the boat falls off plane, it becomes very inefficient.

    You mention rowing, sailing and maybe a small motor that leads me to believe you are tying to develop a displacement hull. The depth of your transom looks more like the planing model than the displacement models.

    If you are looking at rowing, sailing and low powered motoring as the primary means of propulsion. I would pull your chine down at mid-length on your boat and then pull it up towards the waterline at the transom. Pulling the chine up at the forward transom would give you a little more V forward to help cut through chop.

    Just some thoughts.

    Happy designing.
     
  2. GraemeR
    Joined: Mar 2013
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    Location: Thailand

    GraemeR Junior Member

    Many thanks

    I'm playing with different options this weekend.

    Graham
     
  3. GraemeR
    Joined: Mar 2013
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    Location: Thailand

    GraemeR Junior Member

    Gents

    Things have been moving. I have drawn out and done analysis on 4 more different hulls including Pelican Snowgoose and SchockPram. Not sure what the name of the 4th is. All were kindly uploaded.

    I scaled all to 5m and set the draft to 0.150m for comparison. I will upload the data if anyone is interested a little later.

    What I want a boat for is:

    1 Estuary, river and light coastal trips
    2 Sail using my existing wind surfer mast and suite of home made sails. These range from 4.5 sqm to 0.75 sqm and include a spinnaker.
    3 Able to be sailed and launched by one man
    4 Stable for kids
    5 shallow draft for estuaries
    6 Centre board with shock cord may be better than dagger board
    7 must be able to ro, sail or motor
    8 2hp and 6hp motors available
    9 ply stitch and glue construction with taped joints and epoxy coating and lining
    10 Built in buoyancy
    11 Easily demountable mast - bridges
    12 quick to rig - kids waiting
    13 possible swimming platform for kids - rear access?
    14 able to have tend over as surprise storms occur
    15 max load 2 adults and 2 kids plus equipment, though usually one adult and 2 kids

    More later

    Graham
     
  4. rwatson
    Joined: Aug 2007
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    Location: Tasmania,Australia

    rwatson Senior Member

    "13 possible swimming platform for kids - rear access?"

    On a small boat like this ???? - the whole boat is an easy access into the water. Getting back in without tipping it over will be the trick.

    "15 max load 2 adults and 2 kids plus equipment, though usually one adult and 2 kids"
    This is approaching the upper limit for this size boat.

    What you want from a boat is looking to exceed a light weight dinghy here.

    One option that sprung to mind is the Phil Bolger Brick

    Its two hulls that create either 2 x foot dinghys, or an 18 foot schooner, using two "windsurfer" type sails.

    I remember reading some rationale about it "Big enough to sail the whole family and their picnic gear to a remote beach. Disconnect the two halves so the kids can chase each other around the bay for a couple of hours, then reconnect together for a trip back to the car. Disconnect each hull, and easily lift the components onto the trailer or car top."

    http://hallman.org/bolger/isometrics#Brick

    also check out

    http://www.pdracer.com/articles/bolger-brick/

    for some comments on the design. You may be able to modify the design to improve it.
     

    Attached Files:

  5. GraemeR
    Joined: Mar 2013
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    Location: Thailand

    GraemeR Junior Member

    I did consider a twin hull, that would be easier to transport without a trailer too.

    Graham
     
  6. GraemeR
    Joined: Mar 2013
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    GraemeR Junior Member

    My kids are 4 and 7, so I hope with a rope over the stern, covered in a hose pipe, they may be able to clamber in if I site in the bow.

    My wife doesn't go out often. So not a huge priority.

    Am I over optimistic?

    Graham
     
  7. GraemeR
    Joined: Mar 2013
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    Location: Thailand

    GraemeR Junior Member

    Gents

    If anyone is interested, I've uploaded hydrostatic data for 4 of the prams that people have kindly sent drawings for.

    Each has been scaled to 5m with 0.15m draft for comparison.

    The Pelican is flat bottomed and probably not suited to my uses.
    The Snow goose seems more designed to plane with the aft design.

    I may play with the other two.

    Graham
     

    Attached Files:

  8. GraemeR
    Joined: Mar 2013
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    Location: Thailand

    GraemeR Junior Member

    Gents

    Can I ask for any initial comments about this hull please?

    I mentioned the criteria a little earlier.

    Many thanks

    Graham
     

    Attached Files:

  9. rwatson
    Joined: Aug 2007
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    Location: Tasmania,Australia

    rwatson Senior Member

    Length over all : 5.000 m
    Design beam : 2.351 m

    7 must be able to row, sail or motor

    how are you going to row that ? Its wider than I am tall ????
    Its nearly to wide to be legally trailerable !

    nor are you going to be able to launch it yourself - you will need two people

     
  10. LP
    Joined: Jul 2005
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    Location: 26 36.9 N, 82 07.3 W

    LP Flying Boatman

    Graham,

    You're making progress. I see a lot of improvement with this version. Watson is right about it being so wide. I see you are keeping your chines high. If you lower these, you'll gain stability (on a narrower boat) and displacement...and you'll be able to narrow your beam.

    I'm attaching a linesplan that imbodies my suggestions and also the hydro information for it. It still has your desired displacement, but the beam is less than 2m and it has an entire m^2 less wetted surface. Also the transom is running clear of the waterline for clean flow.

    I've also put the section cuts into the model and you can see how it helps to define and visualize the hull shape. Both lines plans represent the same boat.

    Just some ideas for.

    Regards.
     

    Attached Files:


  11. GraemeR
    Joined: Mar 2013
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    Location: Thailand

    GraemeR Junior Member

    Many thanks for all the help
    I'm comparing this against a twin idea.

    Thanks again

    Graham
     
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