Question About how to calculate Floatation of my design

Discussion in 'Boat Design' started by AdamOMahony, Sep 11, 2017.

  1. AdamOMahony
    Joined: Sep 2017
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    Location: Ireland

    AdamOMahony Junior Member

    Thanks SamSam,

    And don't worry the heavy mathematical accent goes both ways for those in Ireland brought up without the imperial system or when imperial measurements were on the way out.

    It's not really publicly funded as such just that it's spare money I earned from building website's online, I did it just for fun and now hoping to do something enjoyable with the funds as well. I had an account on a freelance site just building up with funds from making site's here and there so it's more just the funds were never really intended to do much with as such it was just some digits building up on a website and was enjoyable to make money this way.

    When we first started thinking of a house boat this is what came to mind MechanixIllustrated BudgetHouseBoat http://www.svensons.com/boat/?p=MechanixIllustrated/BudgetHouseBoat

    But with the low hanging bridges around here we didn't think it would fit under them.

    I suppose if going with the more flat bottomed hull it would end up similar to the flight CabinCruisers flight http://www.svensons.com/boat/?p=CabinCruisers/flight
    Not exactly like that but similar enough.

    No doubt that we will run into many situations where a cup of tea and a good think through will be needed. I see there is a section on the forum for builds in progress and when I reach the point of mind where I would like to continue with the build I'll get photo's along the way and post up there.

    I am waiting on the boil test as I have some epoxy glue laying around (it's not the resin but It's only for a quick test is all) that I will coat one piece of ply with and another without and see how they fair against each other in the test. I'll conduct the test outside so as to have good ventilation.

    I'll take the next two or three day's to have a good think about what to do before I get back to it.

    I've come up short for marine ply, this supplier looks good unsure of their prices too. Wallerwickham.ie http://wallerwickham.ie/product.php?prod_id=931#.Wb1yQMiGM2w

    I also found this supplier Woodworkers Prices - Plywood Sheets http://www.woodworkers.ie/prices/p_sheet_plywood.shtml

    It's a big jump in pricing from the general wbp ply I already have =/ (the one used thus far haven't ordered anything for the outer skin yet.
     
    Last edited: Sep 16, 2017
  2. Nick.K
    Joined: May 2011
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    Location: Ireland

    Nick.K Senior Member

    They are a marine supplier. I've used ply from them and it was good although the sheets were sent out by courier with no edge covers and arrived all broken at the corners. Builders providers often stock "marine" at extravagant prices which turns out to be rubbish. The quality standards are genuine but if they aren't enforced anyone can stamp a board with whatever they want and this often seems to be the case in Ireland.
     
  3. AdamOMahony
    Joined: Sep 2017
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    Location: Ireland

    AdamOMahony Junior Member

    Okay perfect, I'll give them a call on Monday and get a quote, down in Waterford though so I've no idea what the cost to bring them here will be =/

    If it's reasonable I'll probably go with them anything around the 400-500 for the entire outer skin would be okay :)

    Edit: any idea what would help with abrasion of the hull? Or would marine ply skin assist in helping the inner stay dry in case of a minor damage to the fibreglass
     
  4. osullivant
    Joined: Sep 2017
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    Location: cork

    osullivant Junior Member

    I am in Cork also and am interested in your project. Have been thinking about a house boat for years but too busy to settle down to building one, I often thought that I would will use a pontoon base using large pvc pipes but I was more interested in a house rather than boat

    I was a chippy/ building contractor and have some experience with fiberglass.

    The ply you are using looks like really poor quality, my roof was done with it a few years ago and a small leak has ruined it, it looks like the Chinese "marine" ply....even shuttering ply would be better, McMahons on Water Street sold me a sheet of proper marine ply about 10 years ago. it was not too dear but it lasted really well even exposed to constant rain.

    Why are you using epoxy? what is wrong with polyester resin it is cheaper and easier to use and for a beginner much safer, use your plywood hull as a mold to produce a fully fiberglass mono-coque hull, stiffen with internal tanks and stringers etc... buy the resin and hardener by the barrel it is much cheaper, it lasts and you will use huge quantities on a vessel that size,also buy rolls of chopped strand mat or some more exotic foams etc.. get advice here on thicknesses and so on.

    We used to buy in Midleton bu the UK/NI suppliers are much cheaper and especially now with sterling dropping but watch the NI crowd with the converson/ sales in Euros etc...

    If the hull is too unsteady consider adding some ballast in the lower portions concrete is a good option. ( you could of course build a concrete hull...)

    best of luck.
     
  5. Nick.K
    Joined: May 2011
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    Location: Ireland

    Nick.K Senior Member

    These are good points, especially that you could re-use much of the material you have bought doing the interior.

    In this thread there are are three themes which are bit muddled and in the wrong order:
    The buoyancy and flotation aspects of the design coupled with the unfinished portions at the ends
    The suitability for purpose (SOR). Where will the boat go, what do you want from it etc
    The construction​

    Before ordering more material, why not as you suggested take some days to sort out the issues? However you do your project whether for the long or short term or whether it costs a lot or a little you'll still end up spending a lot of time on it and things like having bought and cut material only to change your mind...these will seem little problems compared to a finished project that may not deliver what you expected.

    I suggest
    First; that you make a statement of requirements, particularly addressing the different water areas for the use but also including the accommodation and boat systems.
    Second; See if the design needs to be changed (without being bound by what you have already done).
    Third; Decide on the construction materials and method.
     
  6. AdamOMahony
    Joined: Sep 2017
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    AdamOMahony Junior Member

    Really starting to think this is a good idea... Originally I was thinking the stitch and glue method was the easiest way to go however the arguments brought up here against my current methodology are quite valid.

    If I was to build the frame out of solid timber and glue + gusset the frame together with marine ply on the outer it sounds appealing to say the least.
    If I was to go with a shallow V as previously seen about what size timber would be recommended to build this farm out of? I have some 2 by 2 that I would ideally use but thinking they may not be strong enough. Any indication of size of timber would be appreciated. I will draw up a rough idea for the hull framing this afternoon or evening to give an idea of what I am thinking.

    Something along the lines of DIANNE'S ROSE, a "Tiny" Shanty/Camp/Houseboat 17' X 8' beam. http://www.diy-wood-boat.com/diannes-rose-a-tiny-shantycamphouseboat-17-x-8-beam.html is probably what I'm thinking but narrower and longer.
     
  7. Heimfried
    Joined: Apr 2015
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    Heimfried Senior Member

    Another idea.
    May be you should consider to build a professional designed boat and make a few changes to fit your needs. Sometimes it is not the best idea for a beginner to boat building to design his first boat himself. To deal with the first building is often challenging enough. (Not only beginners, also pros use sometimes plans of other pros: https://smallboatsmonthly.com/article/eco-cat/ )
    I'm just building a house boat (2,5 m x 6,2 m) for camals and lakes designed by Bernd Kohler and a friend started a modiefied version (2,5 m x 6,8 m) of it.
    ECO 62 Houseboat http://www.duckworksbbs.com/plans/kohler/eco62houseboat/index.htm
    boote-forum.de - Das Forum rund um Boote https://www.boote-forum.de/showthread.php?t=260166
    boote-forum.de - Das Forum rund um Boote https://www.boote-forum.de/showthread.php?t=260765
     
    Last edited: Sep 17, 2017
  8. AdamOMahony
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    AdamOMahony Junior Member

    Any idea how much the outer coating for steel may be? and does the steel have to be a specific grade etc?
     
  9. TANSL
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    Location: Spain

    TANSL Senior Member

  10. Nick.K
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    Nick.K Senior Member

    Tansl he's building an inland waterways boat of less than 7m length not a tanker (and the alternative is 6mm ply...). :)

    As Heimfried suggests
    This too is a very good suggestion IMO. In this case the steel will be specified for you.

    Important for you is the surface finish of the steel when you buy it and this is where you could have difficulties. Steel comes from the mill with a shiny black surface layer (mill scale) which is hard and brittle and will eventually cause the coating to fail and the underlying steel to corrode if left on. You would be best to buy steel that has had the mill scale removed and is pre-coated with a holding primer. Pre-prepared steel can be difficult to buy for thinner sizes and may have to be specially done.
    It is possible to 'sand blast' untreated steel after construction but not something you'd want to do if there were alternatives. If the primer is still in good condition when the build is finished then it can be washed and coated directly. As a very rough guess of the cost of coating, €1800 should be enough for a 7m boat for epoxy undercoat, two-pack top coat, anti-foul primer and antifouling. Remember the interior has to be coated too.

    There are of course disadvantages to steel too both for the build and the boat life.
    Steel work is very noisy and your neigbours may hate you by the end of the project if you are planning it at home.
    You will have to learn to weld. It isn't that difficult but it won't happen over-night, it's a skill that only comes from correct technique and practice.
    Steel boats can't be left without maintenance, coating damages must be repaired and the anodes must be changed before they are exhausted (though they should last at least a year and maybe two or three).​
     
  11. SamSam
    Joined: Feb 2005
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    Location: Coastal Georgia

    SamSam Senior Member

    For larger house boats here 10 gauge ( Standard Gauge for Sheet and Plate Iron, Ted Pella, Inc. https://www.tedpella.com/company_html/gauge.htm ) is a normal thickness. With steel, there is usually a size restriction in that the plating has to be thick enough to combat pinhole corrosion which usually means the plate is too heavy for smaller boats. But that seems to me just sort of a local (USA) thing as I believe in Norway etc steel dingies and small work boats with very thin plating are regularly made. Very tough but relatively heavy.

    It's how the wood is to be used that determines the size and shape that is needed. In a frame the loads are more inward and outward as opposed to fore and aft. In a normal frame, a 2x2 would waste strength in the fore and aft direction. A better shape, with the same amount of wood would be a 1x4. That's just an example, not a recommendation.

    The house boat type boats on Svensons use 2x material for frames, budget hb uses 2x4, another with v bottom use 2x8 tapered on the ends to 3 1/2" and 4 1/2". At the bottom of the Svenson page are links to other boat building sites.
    Here's another site ( Plans | ShantyboatLiving.com http://shantyboatliving.com/category/designs/plans/ ) I think Bryan Lowe, the owner, is a member and posts here sometimes.
    Pinterest can give you a million ideas on just about everything.

    For such a simple boat you can study some free plans and adapt what others use. The advantage of having an actual plan to follow is all the little dilemmas have been worked out and the thing actually works - it handles ok, floats about right etc. You can also amalgamate all the ideas from others into your own plan and it's still basically your own plan. Re-inventing the wheel is hardly ever an improvement.

    Plenty of boats have been made using construction grade materials as opposed to marine grade, you just have to know what's good and what isn't with glues, number of plys, number of voids etc. Apparently that applies to marine grade also, as shysters are everywhere.
     
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  12. TANSL
    Joined: Sep 2011
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    TANSL Senior Member

    6mm ply looks like a very thin thickness, I do not think it can be an alternative :). A 7 mm steel hull may be too thick, may be correct or may be too thin, depending on the spacing of the inner reinforcements. To me it seems a very reasonable thickness considering, for example, that smaller thicknesses will give rise to many deformations when being welded. taking into account, in addition, that there must always be an over thickness due to corrosion, taking into account also the blows that can receive in the channels and the abrasion. Although it is not an oil tanker, there are factors of several types that, in my opinion, advise to give a greater thickness to the hull. This does not mean, at all, a greater weight of the structure as a whole. I would not lower the 6 mm thick for the hull.
     
  13. AdamOMahony
    Joined: Sep 2017
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    AdamOMahony Junior Member

    I've been busy at thought and after all the consideration the work I have already done will have to go else where in the boat...

    So based on the recommendation of solid frame with marine ply, here is what I've come up with, it's based around 2 by 4's with the keel being 4 by 4 (was just out of handy measurements not really definitive)

    After all deliberation the main focus of the boat is to provide a home for living along the canal's for some time.

    I've a lot of photo's here now but the dimensions I can elaborate on after if that's best?

    New design, same length and width, new design top right view.PNG


    Bow view bow view.PNG bow side view 2.PNG


    Bow dimensions 1 x 1.5 m rectangle. Bow dimensions.PNG

    Stern views Stern Side view.PNG Stern aboveside view.PNG


    Stern is just the first line of the bottom right continued on until it hits the outer part of the rectangle.

    Framing horizontal view. Horizontal of hull.PNG the plan is to have the chime logs be part of this farming structure.


    Hull Length-ways full view. Stern to the left Bow to the right :) Hull Horizontal..PNG

    I don't plan on re-inventing the wheel, I was wondering if there is any boat building books you could recommend as a nice way influence to the project and bring me more up to speed?

    May be steel for a future project unfortunately, might look into some classes on welding near by they run them in the evenings :)
     
  14. osullivant
    Joined: Sep 2017
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    Location: cork

    osullivant Junior Member

    Found this link by following others listed above but just in case you did not knock across it...

    Popular Mechanics ~ 1959 https://archive.org/stream/PopularMechanics1959/Popular_Mechanics_12_1959#page/n0/mode/2up

    page 160 of the magazine,

    https://ia601301.us.archive.org/23/items/PopularMechanics1960/Popular Mechanics-01-1960.pdf

    for part 2.

    Very interesting set of drawings easily built from materials available off the shelf, a few feet longer wider and taller would make a cool house boat with an outside patio area
     
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  15. DCockey
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    DCockey Senior Member

    How much headroom in the cabin is desired?
    What is the clearance from water surface to the lowest overhead obstacle (bridge, etc) you will want to go under?
    What is the maximum draft which will go where you want to go?
    What is the widest feasible beam?
     
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