8 foot wide shanty boat

Discussion in 'Stability' started by jrl5678, May 4, 2007.

  1. jrl5678
    Joined: May 2007
    Posts: 68
    Likes: 0, Points: 6, Legacy Rep: 31
    Location: New York NY

    jrl5678 Junior Member

    I am designing and then building (I hope) a shanty boat. I am thinking about making sure I can trailer it so 8 feet is the widest it can be. I am wondering how long I can make it also I am planning on using 90 degree chines.
    what is a good length to width ratio?
     
  2. SamSam
    Joined: Feb 2005
    Posts: 3,825
    Likes: 161, Points: 63, Legacy Rep: 971
    Location: Coastal Georgia

    SamSam Senior Member

    Welcome! You don't want to make it less than 3 to 1 for effeciency, but it sort of depends on the hull shape too, what sort of bow and how fast you want to go. Sam
     
  3. jrl5678
    Joined: May 2007
    Posts: 68
    Likes: 0, Points: 6, Legacy Rep: 31
    Location: New York NY

    jrl5678 Junior Member

    more info

    I am thinking of treating it like a barge and not powering it. As far as basic hull design I am leaning towards a Johnboat feel. I am at a lose for the words a squared off bow and stern with a gentle roll sweep up on the bow and stern.
     
  4. jrl5678
    Joined: May 2007
    Posts: 68
    Likes: 0, Points: 6, Legacy Rep: 31
    Location: New York NY

    jrl5678 Junior Member

    More shanty boat questions

    Thank you for the three to one ration. I would like to know if three to one is for speed or stability or both. I am fascinated with the Dutch and other European narrow boats. I would like to know what ration would keep a flat bottomed boat up right with little ballast to keep the draft low.

    Like I said I am thinking of either a double ender or a squared off bow with sudden rise and a flat transom. I would build the whole thing out of ply wood and glass using stitch and glue.

    I think double sheets of 1/4 Exterior grade ply covered with glass and epoxy any Ideas?
     
  5. dick stave
    Joined: Dec 2004
    Posts: 144
    Likes: 1, Points: 18, Legacy Rep: 12
    Location: MISSION B.C. CANADA

    dick stave Senior Member

    As far as I know, max width is 8 ft. 6 inches in most states for trailering. I bought a set of plans for a 25 ft. shanty boat from Mother Earth News a while back that are very close to what youre looking for. Google " Return of the Brandy bar" and you will find them. They are pretty good prints (3 "D" size drawings detailing pretty much everything. "Atkins " boat plans also has some pretty good shanty boat designs...
     
  6. jrl5678
    Joined: May 2007
    Posts: 68
    Likes: 0, Points: 6, Legacy Rep: 31
    Location: New York NY

    jrl5678 Junior Member

    I have a set of study plans from MacNaughton for the "Evening Hush" (32'x12' (almost)). If it were not for the terrible customer service from MacNaughton and the really bad study plans I would be working with them. I have found several shanty boats designed and built by amateurs on line. I also really like the Dutch Narrow boats and wanted to try my hand at a little design work. I choose to use this Forum because I was am npt sure of a length to width ratio for stability and safety. 3 to 1 was mentioned but what about a longer length to width ratio.
    How long is too long verses width. I have turned many a small sail boat in to a submarine, I have no desire to design and build a turtle.
     
  7. Guillermo
    Joined: Mar 2005
    Posts: 3,644
    Likes: 185, Points: 63, Legacy Rep: 2247
    Location: Pontevedra, Spain

    Guillermo Ingeniero Naval

    3:1 lenght/beam ratio is commonly used for small boats, specially commercial fishing ones, but it can be bigger than that, dpending on the uses.
    Narrow boats are also very common even for commercial fishing. Have a look at this FAO document: http://www.fao.org/docrep/007/y5649e/y5649e00.htm.
    You have to be careful with the high CG of 'house' weights in a shanty boat.

    You'll find lots of info on shanty boats at: http://euler.sfasu.edu/Shantyboats/

    Here some trailerable ones from a reputed designer, with the same beam (7' 11" - 8') but different lengths:
    http://www.glen-l.com/designs/house/gypsy.html
    http://www.glen-l.com/designs/house/quest.html
    http://www.glen-l.com/designs/house/deltaq.html

    Cheers.
     
  8. jrl5678
    Joined: May 2007
    Posts: 68
    Likes: 0, Points: 6, Legacy Rep: 31
    Location: New York NY

    jrl5678 Junior Member

    Thank you for the links.
    I think I want to go for a long low look.
    I am thinking a small Pilot House Aft lots of clear stuff (not sure glass or plastic) may try to meet the British standards for narrow boats which is something like 6' 11" to 7' something I found it once on one of these forum pages. I am looking at a 30 foot length over all.
    I am not sure if I will power the boat and make it a house boat. I have seen several work boats in a johnboat configeration with big push bumpers on the forward end and big out board power pushing small barges around on job sites. I like that Idea I could knock together a plywood top for a johnboat and make it look likt a tug.
    My new question is ballast in a long flat boat. If the basic demension is 8'X32'
    I need 6'6" of head room but would like some of that to be below the water line can I make the draft 24" and fill 4" of the inside of the boat with cement and lead?
    Also since I have gotten way off on tangents.
    Has anyone experience with the composting toliets.
    I have found several on line and a few say they have a model desinged to go in the Head of a boat.
    It does not help me out with the grey water but it is moving towards the right direction.
    Also is there a good place to tlak about solar cells on a boat?


    This is the best place on the web!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
    If you are in NYC go to 72nd street and the Hudson on a weekend and take a kayak on to the river it is free and I should be there helping out.
     
  9. Guillermo
    Joined: Mar 2005
    Posts: 3,644
    Likes: 185, Points: 63, Legacy Rep: 2247
    Location: Pontevedra, Spain

    Guillermo Ingeniero Naval

    Yes you can. I recommend you to do some stability calculations before going any further. Aren't they mandatory in the USA for this kind of boats?


    Have a look at this one. No composting but air drying: http://www.airheadtoilet.com/Air_Headx.html
     
  10. jrl5678
    Joined: May 2007
    Posts: 68
    Likes: 0, Points: 6, Legacy Rep: 31
    Location: New York NY

    jrl5678 Junior Member

    I was posting on the Forum because I am looking for help with the stability calculations.......
    In general if you are a back yard boat builder and you do not take passengers or at least not more than 1 you do not need a cost guard inspection or you might need one but they are over worked and understaffed.
    Also I am not building this boat for large waterways.
    But I am trying to get a handel over the calculations.
    Length to width
    area to displacement
    I have no Idea how to predict theoretical water line.
     
  11. Guillermo
    Joined: Mar 2005
    Posts: 3,644
    Likes: 185, Points: 63, Legacy Rep: 2247
    Location: Pontevedra, Spain

    Guillermo Ingeniero Naval

    You have to figure out how much your boat its going to weight. That's a tedious (as you have to go item by item, noting their weights and coordinates of their CG and then calculating momentums to find out the position of the overall CG), but most important task. Youll get data for the boat itself, this is for what it's called the 'lightship condition'
    Once you know the total weight and CG of the boat for lightship condition, you add cargo (intended people, consumables, equipment, etc) and calculate again for full load condition. This will give you how many weight your hull has to float up for the boat not to sink.

    If your hull is boxy, as it is usual for a shanty boat, volume calculations of the inmersed hull are not difficult to calculate and can be approximated very easily. Volume of the hull times the density of water will give you the 'upwards' force needed to match your 'downwards' weight. This is the Archimedes principle.

    Once you know how many hull you need to have under the water, you have to allow for enough freeboard for the boat to be able to resist some heeling and waves without capsizing, its amount depending on the waters where you want to use the boat, as well as maximum shifting allowed for weights aboard (movement of persons to the side, i.e.).

    The CG position will tell you also if the boat will have a tendency to tilt (if it's not in the longitudinal plane of symmetry of the boat), or not. Also it will tell you the tendency to trim by the bow or by the stern, if it's forwards or backwards of the center of buoyancy of the leveled hull.

    From the position of the CG, center of buoyancy of the hull and freeboard to the lower flooding point, you may derive the transverse stability curve for each load condition (for this kind of boats the one for the maximum load should be enough), and so know what you can expect from your boat from the stability point of view.

    I'm afraid (and strongly recommend) you should hire the services of a local NA if you are not able to perform such calculations by yourself.

    Cheers.
     
  12. jrl5678
    Joined: May 2007
    Posts: 68
    Likes: 0, Points: 6, Legacy Rep: 31
    Location: New York NY

    jrl5678 Junior Member

    I have done a few weight and balances on airplanes and can follow your line of calculations
    8'X32'
    is 16 sheets of 1/4" AC exterior grade ply wood (X) from Lowes (Y)gallons of epoxy/hardener (Q)weight of glass cloth (256squre feet not sure of the width of standard cloth but I bet 64' liner feet would do maybe another 8 sheets of 1/2 for the sides and topsol (Z)
    that would give me a basic weight to start out with.

    so Q+X+Y+Z (I should be able to find all the actual weights on line some where)= (f)
    so
    the volume of water I will displace is calqulated by using (f) (L*W*H) (8*32*6) cause i am not using fractions right now (1536 feet cubid) (please forgive my spelling I lost my spell checker and I am tired)
    I think water weighs 6 lbs per gallon I do not know the metric equivlent specfic density you said
    so the formula is volume of the hull (Vh) times the specfic density of water (Dw) which gives me upward thurst
    so (f) = (Vh)(Dw)
    or
    (f) = (1536 feet q)(Dw)or did I miss understand you completly

    also I have read a lot of your post you are a very knowledgeable poster and very funny when apropreate
    I also want to design and build it myself that is the point
     
  13. jrl5678
    Joined: May 2007
    Posts: 68
    Likes: 0, Points: 6, Legacy Rep: 31
    Location: New York NY

    jrl5678 Junior Member

    Ike
    Senior Member Join Date: Apr 2006
    Rep: 106 Posts: 433
    Location: Washington

    If these are air chambers then they will support 62.4 lbs per cubic foot.

    200/62.4 = 3.2
    3.2/2 = 1.6

    So each box needs to be about 1.6 cubic feet.
    __________________
    Peter D. Eikenberry
    "Please pray for my husband. He spends most of his time playing with boats!"

    if Ike is right the quote is from a thread on john boats
    then the basic 1536 cubic feet I have would support
    95000 lbs
    so in theory that is flat on the water
    if my boat is a simple box with no shape
    32 X 8 X 6 (length X width X height)
    if it weighed less than 95000 then the draft would be almost zero
    I have to do some more calculations
    Also I guess I need ot figure out how much concreat weighs
    another trip to the internet.
     
  14. timgoz
    Joined: Jul 2006
    Posts: 1,079
    Likes: 32, Points: 48, Legacy Rep: 277
    Location: SW PA USA

    timgoz Senior Member

    JRL,

    Water weighs 8.345 lbs. to be more specific. Thats fresh H2O.

    Welcome.

    Tim
     

  15. jrl5678
    Joined: May 2007
    Posts: 68
    Likes: 0, Points: 6, Legacy Rep: 31
    Location: New York NY

    jrl5678 Junior Member

    right gas weighs 6 lbs per gallon
    I will look it all up and write it down before I start running numbers for real
    thank you all
     
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.