Shanty type boat need advice/opinions

Discussion in 'Boat Design' started by BuildingaLemmy, May 2, 2010.

  1. BuildingaLemmy
    Joined: May 2010
    Posts: 7
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: Ottawa, Canada

    BuildingaLemmy Junior Member

    So in the fall a my friend and I decided to build a shanty boat to putt around in the Rideau Canal/ Lower Ottawa River with. At first we decided on the 'Lisa B Good' but decided it seemed a little too top heavy and we ended up with a design that was a mix between the the 'Lisa B Good', The Bayou Belle, and the Bolger Brick. Basically we liked the general look of the centre (ish) cabin of the Lisa B Good, the hull shape and simplicity of the Bayou Belle, and the sail of the Bolger Brick.... Any we ended up with something like this: (i'll up load it in a second message).
    We're just looking to gather some feedback or constructive criticism so I'll give you guys a run down of the basics.
    Its a scow(ish)/ gundeleon type of hull.
    Length 19ft
    Length at water 17ft
    beam 7ft3in
    Hull depth 2ft5.5in"
    Overall height 7ft.

    Ok so here are a few things we'd like to know. A/ are there any glaring screwups with the design? B/ is it absolutely ridiculous to put a sail on this thing (with side boards) C/ whats a decent a wgt of fiberglass to use..., (I can get a good deal on 6 oz biaxle, but are two layers of 6 oz the same strength as 1 12oz layer? Is 3/8 ply too thin for the hull? I'll post a mock up of the boat in a message below.
    Cheers,
    Adam
     
  2. BuildingaLemmy
    Joined: May 2010
    Posts: 7
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: Ottawa, Canada

    BuildingaLemmy Junior Member

  3. messabout
    Joined: Jan 2006
    Posts: 3,073
    Likes: 245, Points: 63, Legacy Rep: 1279
    Location: Lakeland Fl USA

    messabout Senior Member

    No need to complicate the front end by beveling it in plan view. Put some rocker in the bottom as in the Bolger Brick. You will need to use much thicker skin. Three eigths is ok for top sides but not for the hull. I would consider two layers of half inch ply for the bottom or maybe three layers of 3/8.. That means that the bottom will be one inch thick or more. See Bolgers scantlings such as Birdwatcher where he uses one inch bottoms. A broad bottom, such as this one, will need some frames to support it even if the bottom is one inch thick. Avoid unnecessary complication, use a small outboard rather than the inboard shown on your sketch.

    You could use a sail on this boat for downwind work. I would not expect much from the sail when going any other direction. It is possible to make the boat go to windward but that would involve a lot of complication and considerable expense.

    Have you read the book; Shantyboat... by harlan Hubbard.? The book does not provide any plans or anything technical, but it does describe the true essence of a shantyboat along with wonderful tales of adventure and self sufficiency.
     
  4. BuildingaLemmy
    Joined: May 2010
    Posts: 7
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: Ottawa, Canada

    BuildingaLemmy Junior Member

    I've seen the Hubbard book and leafed through it but I didn't read it all. See the problem is the hull frame is basically complete so I can't really work more of a rocker into the hull. I maybe should've been more precise, it does have a frame made of 2X4s strap butted for the length and braced vertically every 18 in. The beam braces are 2X4s every 18in as well these are horizontally length wise braced in a 3-4 design so there is no gap on the hull wider than 18in by 21in. (i'm going to draw a quick diagram to better describe what I mean.) I also plan to fiberglass it well so I don't think i'll need to go to full inch ply. (at least I don't think so maybe 1/2 or 5/8?). You basically outlined the exact use I wanted for the sail. But I think i'm going to keep the inboard, since I already have a 15 hp horizontal diesel and I personally dislike the ease at which outboards go 'missing'. Anyway, thanks for the feedback!
    Cheers.
    Adam
     
  5. BuildingaLemmy
    Joined: May 2010
    Posts: 7
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: Ottawa, Canada

    BuildingaLemmy Junior Member

    Last edited: May 3, 2010
  6. Paul A
    Joined: Apr 2010
    Posts: 16
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: Florida

    Paul A Junior Member

    You bracing is way over the top for the loads you'll impose on this boat. You honestly should stick with a set of plans for the structure parts of the build. 3/8" plywood is thin but not too much, 1/2 will be more then enough if it's good marine plywood. You do not need 1" thick bottom planks, Bolger does this to add ballast, which you just don't need on this boat. Lastly, don't bother putting a sail on it, there's too much wrong with the design to consider much more then flatting down wind with this thing. It's a shanty, nothing else, so don't try to make it into something i could never be. A little rocker would help maneuverability at the displacement speeds this will motor at. Don't get fancy, just apply similar structural reinforcements found in the other plans you have. Weight is the enemy in this type of boat. Every effort to keep it light and strong will reward you with more load carrying capacity and and more economical operation. So far you're building it like a house, which it's not and it'll float at her gunnels this way. Longitudinal stringers should be 1x3 or 1x4 at most, athwart stiffeners the same, possibly smaller. Buy the book "Elements of Boat Strength" and stick to the guidelines in the book. The boat will be safe and not too heavy, which is the road you're traveling down now.
     
  7. SamSam
    Joined: Feb 2005
    Posts: 3,900
    Likes: 196, Points: 63, Legacy Rep: 971
    Location: Coastal Georgia

    SamSam Senior Member

    If you look here http://www.svensons.com/boat/ or here https://www.boatdesigns.com/Houseboats/departments/7/ you'll see 3/8" ply is not unusual. It seems a little thin to me, though, especially for point loads like submerged objects.

    The fiberglass is for watertightness and not for strength.

    Maneuverability will be a struggle with your design, removable daggerboards on the sides will give some help, somewhat akin to rocker, in that they would give a central point of resistance around which the hull can rotate. They would also help against side drift in a wind from the side.

    Rethink the inboard. Again, maneuverability will suffer drastically and you introduce problems of through hulls, noise, vibrations and fumes, cooling and exhaust systems and loss of space.
     
  8. BuildingaLemmy
    Joined: May 2010
    Posts: 7
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: Ottawa, Canada

    BuildingaLemmy Junior Member

    "The fiberglass is for watertightness and not for strength" -Sam Sam

    Really? I thought added strength that was a main purpose for fiberglass/epoxy! Why do they talk about tensile strength, and strength to weight ratios on all the sites where you can buy fiberglass cloth?? I'm confused...
     
  9. lewisboats
    Joined: Oct 2002
    Posts: 2,329
    Likes: 126, Points: 0, Legacy Rep: 1603
    Location: Iowa

    lewisboats Obsessed Member

    A single layer of cloth doesn't have much strength against point loads like sharp rocks etc. It provides a measure of abrasion resistance though. What SamSam means about watertightness is that it holds the epoxy in a matrix of wood, resin and glass which provides a strong barrier against water penetration. Additional layers do add stiffness and impact resistance to a hull though.
     

  10. tugboat

    tugboat Previous Member

    the lisa b good is a great desighn i built one almost identical to it but at 20 ft and 10 wide..trust me it wont be top heavy..and its very simple and extremely strong!! better than the other designs i have seen...another good design is the atkin retreat!..btw i grew up in ottawa...split my time between there and muskoka. /georgian bay area...rideau is a nice relaxed body of water so the lisa b good i your best bet...also you could build the hull for around 500.00 glassed!
     
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.