quick dinghy

Discussion in 'Boat Design' started by catsketcher, Oct 15, 2009.

  1. catsketcher
    Joined: Mar 2006
    Posts: 1,306
    Likes: 148, Points: 63, Legacy Rep: 790
    Location: Australia

    catsketcher Senior Member

    Gday all

    I have been thinking about a 4 plywood sheet sharpie style dinghy for our cat. Around 3.5 metres long with 1.2 metre beam. Too fat to be a real sharpie I know. My kids are growing and I need more volume in a dinghy for them and for friends sailing with us. We have real trouble fitting in the extended Bolger Nymph.

    My question is - Are there many boats out there that have gone flat bottom for a dinghy? I would like this thing to be able to plane and take an 8Hp outboard too. It will be for protected waters (Pittwater, Lake Macquarie) and getting to the beach. Much of the time it will be on the duckboard of the cruising cat.

    Flat bottomed would really suit sitting on the duckboard of the cat and for putting sailboards and kayaks on the thing when upside down. I was thinking a little Sneakeasy style thing would be nice. I would guess about 5 degree side flare would be nice - 10 seems too much in my first drawings.

    I can't seem to find much on flat bottom skiffs that aren't punts. I don't want a punt - it doesn't look boaty enough and would really pound. We have lots of quasi punts in OZ.

    cheers

    Phil Thompson
     
  2. gonzo
    Joined: Aug 2002
    Posts: 15,189
    Likes: 925, Points: 123, Legacy Rep: 2031
    Location: Milwaukee, WI

    gonzo Senior Member

    There are more than you can shake a stick at. The transom should be about 14 degrees to take a standard outboard. You don't need any flare. Sides can be vertical, I had a dinghy in my cat like that, if it will fit better. If you give some rake to the bow stem, there will be flare on the bow and keep it drier.
     
  3. messabout
    Joined: Jan 2006
    Posts: 3,137
    Likes: 302, Points: 83, Legacy Rep: 1279
    Location: Lakeland Fl USA

    messabout Senior Member

    You are describing a tubby little boat but a utilitarian one. You can build an entirely serviceable boat to those dimensions. It is not likely to row as well as a more sophisticated design but it will get the job done. This boat will pound enthusiasticly when planeing. You will need either a thick bottom to span the width of the chines or you must have generous interior framing to keep the bottom from panting. Ten degrees is not too much flare but as Gonzo says, you do not need flare at all. Make it with plumb sides if you can tolerate the appearance. Generous flare is sexy looking but not necessary for the purpose that you describe. The punt will be more commodious than the pointy hull and it will be more capable of carrying weight. Not sure of the semantics here but if punt is the same as pram in yankee speak then I'd want to use the pointy design if planeing and kid operator is anticipated.
     
  4. waikikin
    Joined: Jan 2006
    Posts: 2,378
    Likes: 147, Points: 73, Legacy Rep: 871
    Location: Australia

    waikikin Senior Member

    Hi Phil, check out Michael Storers Goat Island Skiff for some inspiration, it sounds like a similar concept Just a bit bigger, I'm sure a bloke of your talents will have little trouble sorting a nice result, also up your way around 15 years ago there was a kit builder or collective putting something really similar out, the boatshed I kept my cat at bought one already build but not painted & it rowed quite nice. All the best from jeff.
     
  5. narwhal
    Joined: Aug 2009
    Posts: 68
    Likes: 1, Points: 0, Legacy Rep: 45
    Location: Nashville, TN

    narwhal Junior Member

  6. catsketcher
    Joined: Mar 2006
    Posts: 1,306
    Likes: 148, Points: 63, Legacy Rep: 790
    Location: Australia

    catsketcher Senior Member

    Thanks

    I really like the GIS. Maybe later I will do something like it. I have always liked Sharpies. I am more interested in a power boat that can plane and be stable. We will be hanging around Broken Bay and have friends with us and maybe our dogs. That means I have to have a dinghy that can plane to take the dogs to Cottage Point or a secluded beach to run around early morning and evening and maybe to deliver friends to a ferry etc. The GIS is a little too much of a sailer and has the extra rocker needed in a sailer.

    The little portugese skiff looks good but is a little too small. I have about 4.2 metres available on our duckboard and with an outboard ( I already have an 8 hp) I reckon the longest I can go is 3.5 and still safely pull it up between the hulls. The width of max 1.2 is due to the ply sheet.

    Even on the mooring it would be nice to have two dinghies. Our little one is that - little. I usually just push Kankama on the shore and heave people over the forebeam. I have a design on Rhino but I just want to learn from others first.

    As an aside I got started on sharpies/dories long ago. In 1983 I sailed a Gloucester gull built by Cathy Hawkins on the Tweed river where my mums C 10 was being built in the same shed as Bullfrog. It was the only boat I could tack and gybe under its little sprit with no rudder. Later a crazy guy at Castlecrag used to make sharpies on the waterfront out of construction ply and aquadere. He would bang them together and then dismember them. I have been coveting them since.

    cheers

    Phil
     
  7. lewisboats
    Joined: Oct 2002
    Posts: 2,329
    Likes: 128, Points: 0, Legacy Rep: 1603
    Location: Iowa

    lewisboats Obsessed Member

    So basically you are looking for something like this...a simple flat bottomed skiff.

    [​IMG]
     
  8. catsketcher
    Joined: Mar 2006
    Posts: 1,306
    Likes: 148, Points: 63, Legacy Rep: 790
    Location: Australia

    catsketcher Senior Member

    That is pretty much what I had in mind. Have you built one? Does it go okay?
     
  9. lewisboats
    Joined: Oct 2002
    Posts: 2,329
    Likes: 128, Points: 0, Legacy Rep: 1603
    Location: Iowa

    lewisboats Obsessed Member

    I have built similar and they are all pretty much the same. The flat bottom will pound whether you like it or not...regardless of whether you have a pram bow or a pointy bow. At the draft shown this displaces .184 tonnes but add 25 cm draft you are up to .255 tonnes (both disps in salt water). Initially the bow will go up fairly high with most of the weight in the back but then will settle down some as it comes up on plane. Putting a bit of "hook" to the bottom aft run would act as a trim tab...keeping the nose down a bit but knocking a km or two off the top end. This would run well with up to a 15 or so horse motor...or a 10 horse 4 stroke (weight issues). High speed turns are discouraged with this kind of hull as the chine sometimes digs in and it "trips" and dumps over. Seats filled with flotation, flotation in the bow area and in the corners of the transom would keep things bobbing in the event of a capsize.

    You could build the hull only out of 3 sheets of 6mm and 1/2 sheet of 19mm for the transom but you would need another sheet of ply for the interior seats and such or you could use solid lumber. Breasthook and knees should be of 19mm thickness (solid or ply). You would want a couple of athwartship frames (stand alone or part of the seating) and a couple of runners underneath to help stiffen the bottom.

    If you are good with tools you could bang the hull out in a weekend and have it in the water a couple of weeks later (curing times, finish work etc)

    Basic specs on this are:
    LOA 3.478
    Beam 1.216
    Draft @ .075m 0.184 tonnes
    Draft @ .1 m 0.255 tonnes
    LWL @ .1m disp 3.225 m
    BWL @ .1m Disp 1.054 m
    LCB 1.231
    Transom rake 15 deg
    Side panel flare 15 deg

    If you have freeship I can email you the .fbm if you want.

    Edited to add: go to Duckworks magazine and download the plans for DuckSkiff. It is very similar tho a bit longer and has some building tips in it.
     

  10. catsketcher
    Joined: Mar 2006
    Posts: 1,306
    Likes: 148, Points: 63, Legacy Rep: 790
    Location: Australia

    catsketcher Senior Member

    Thanks for the help everyone

    I will have a look at the skiff stuff
     
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.