Richardw's Narrow Boat Project- PLATE THICKNESS

Discussion in 'Metal Boat Building' started by richardw66, Nov 27, 2013.

  1. JSL
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    JSL Senior Member

    From the "really out there" department:
    Another form of corrosion I heard about a couple of years ago is bacterial corrosion. Apparently, steel barges were being 'stored' in stagnant fresh water and the 'bugs' debris create an acidic byproduct which 'attacks' the plate. This was in the southern US so the water would have been warmer (and the 'bugs' happier, and more 'productive').
    I am sure there are some 'experts' than can provide more information.
     
  2. SukiSolo
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    SukiSolo Senior Member

    Don't forget that traditional craft will have used older imperial sized steel. The newer metric guage and sheet sizes are different. When did you last draft on double elephant paper?....;)
     
  3. richardw66
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    richardw66 Junior Member

    I think I've discovered the downfall to this design, it looks all well at first glance but is it possible to bend 8mm thick plate length ways just 60mm in from the edge or does it need a bit more meat to feed into the press. Anyone out there with knowledge of the minimum edge distance depending on plate gauge. All I know about pressed bends is the general guide that the internal radius ends up 1.5x the thickness of the material. (Nodoubt somebody more knowledgeable will dispute that and I'll stand corrected).
     
  4. richardw66
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    richardw66 Junior Member

    What about using stainless steel?

    With carbon steel around £1 per kilo and 316 grade stainless around £3 per kilo; could I build the bottom 5mm thick 316 stainless instead of 15mm carbon? 316 is apparently made for the petrochemical industry and is acid resistant so in a fresh water environment would it last forever?

    What is the advantage of building ships from aluminium; doesn't that corrode more easily than steel and more expensive? Would it be silly to build a narrow boat out of it?
     
  5. pdwiley
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    pdwiley Senior Member

    Given that you need to ballast the boat to get the air draft with standing headroom, what would be the value of using a lighter, more expensive material for the hull, so that you needed to add more ballast to get the hull down to the required draft? Remember, the ballast is going to cost you internal volume.

    WRT stainless steel, it doesn't do well in low oxygen wet environments. What's the oxygen concentration in those canals? It's also a right pain to weld without significant distortion and the welding consumables are far more expensive than for A36 plate.

    The plate thicknesses you're talking about, given a proper sand blast and epoxy paints, are going to result in a life span of many decades given even minimal attention to the barrier paints. I'd just go with plain A36 steel.

    PDW
     
  6. Ad Hoc
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    Ad Hoc Naval Architect

    Aaahh..i see now.

    That is not a "chine". Also butting 8mm into 15mm plate is not a good idea, not to mention that terrible kink at the bottom.

    Ideally you shall draw a line from the DWL (roughly) to to about 10mm from the end of the 15mm plate, So the "kink" in the hull side is very minor and easily formed. Secondly, about half way between the dwl and the bottom plate increase the 8mm to 12mm. Thus the 12mm to 15mm will give you a better structural welded joint.
     
  7. DCockey
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    DCockey Senior Member

    From ITTC dictionary:
    Chine: A more or less sharp corner or knuckle in the hull form, continuous over a significant length of the ship, as in the junction of side and bottom in planing craft. The chine is known as “soft” when the corner is rounded, and “hard” otherwise. http://www.ittcwiki.org/doku.php/structured_dictionary:shipgeometry?s[]=chine#chine​
     
  8. waikikin
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    waikikin Senior Member

    Generally looks pretty cool Richard, around 12 years ago we preliminary priced a Narrow Boat for import to England from Australia, cant remember the$ 'cos the premise was a little flakey(& as it turned out) but from memory the bottom was 8mm, sides 6mm, decks & cabin sides 4mm & cabin top was 3mm. A very small amount of flair in the topsides I think would be fine, the sheer/sides to cabinside intersection used a full pipe sponson, the bottom to topsides used about a 24mm round bar intersecting 1/2 each way(although twice the welding of the plate to plate ). The premise was to send to UK via container & ballast with concrete on arrival, after an extended holiday/base camp/cheap housing the vessel was to be sold to cover costs of international holiday. With your "cost engineering" as has been mentioned coating costs are the same for thick or thin, ballast costs are lower than steel costs so it really only needs to be built strong enough plus corrosion allowance, internal corrosion is usually due to poor coatings & structural detailing / drainage.
    Jeff
     
  9. richardw66
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    richardw66 Junior Member

    So what I was proposing IS a chine all be it a very small 60mm with a 45 degree deed angle and a 135 degree chine angle. Gosh I'm learning loads here with all these new words, tell me are any of them any use for impressing the ladies?
     
  10. SukiSolo
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    SukiSolo Senior Member

    Thanks Ad Hoc, very good advice. Richard you may find more use for the 'small' chine yet. If you study Ad Hoc's larger boat and especially the Section drawing he has used a larger chine for several good reasons. Many thanks Ad Hoc, many would not have released that information.

    Agreed it is more of a long jouney boat (and larger) but he has created a sweet hull form with a good curve of areas (underwater volume curve) and pleasing lines. There are reasons for the slight panel curving. When you have a slightly better understanding of the shape underwater and just above the W/L you will find it easy to incorporate his suggestion of dropping sheet thickness slowly. It is similar even with thinner sheet steel fabrication - one guage apart is OK any more is not good practice.

    Nothing wrong with the thick 15mm base going to 12mm, then 10mm or 8mm. Note most existing builders do this too and for good reason.

    The above W/L flat cabin side, I might be tempted to put a slight curve in it. Simple with a roller and it fits the lower part of the side of ones legs better as well as giving a different visual feel. A fraction more space, though windows might be a little more fun!.
     
  11. waikikin
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    waikikin Senior Member

    Sorry mate, the ladies won't be impressed with your chine......
    better to invest in champagne & a picnic that they don't need to pack.
    The folded chine you've illustrated "may"(I'm not familiar with locks/canal construction/setup) be a potential wear point if your rolling a little against a concrete dock/lock/whatever, better to use a chine bar at the intersection of bottom to topside plate or the plate chine intersection that Adhoc has shown.. then there's a little back up for rubbing against things, in barges- at least in my experience there is contact, not so much like a moored yacht that gets nursed with fenders & rubber fendered marinas.
    Also the deck beams might be a little better in angle of slightly deeper section... just my take on it.
    Jeff.
     
  12. Ad Hoc
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    Ad Hoc Naval Architect

    Hmmm..well, what you're referring to is a knuckle, not a chine per se. Chine is normal nomenclature for planing hulls, and has a very specific understanding what it is and what it does. Some vessels have knuckles which are sometimes called a chine, mainly from an historical throw back, or by someone not familiar with the distinction between the two as in that link above.

    No planing hull has a 'soft' chine along its entire length, only 'hard', to aid flow separation from the sides; doesn't fully occur with a soft chine, i.e. it is a bilge radius like that of of a semi-planing hull. It is easy to understand, for example, how many 'chines' do you see on a super tanker, or how many planing hulls with a rise of floor? On a super tanker this feature is a knuckle, on a planing hull rise of floor is called deadrise. Each hull form uses its own set of nomenclature often for the same geometric feature, even though some may refer to both but is often incorrect usage. It is one of the first things a NA learns when working in a shipyard, use the correct terminology.

    As noted if you have a 60mm section, that is extremely difficult to fabricate into a quality joint. If you taper the knuckle much higher up and then down to the location you want, as another knuckle, it is far superior. But that's your prerogative.
     
  13. richardw66
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    richardw66 Junior Member

    What at first glance seemed so simple is actually quite complicated. From what I've seen Canal boats don't usually have chines or or knuckles but I can now see there are advantages to having them. It evolved on my design as a result of exploring the ways to increase the hull width of a flat bottomed boat to the maximum permitted width (2.1m) where for cost reasons the baseplate has to be narrower (2 m).

    I can't really change plate thickness on the knuckle because the whole hull side from baseplate and including gunwale is formed from a single 1250mm wide plate. How many times I press brake bend the plate is an added cost. Currently I am bending the sheet twice but I think I need to perhaps bend it 3 times, to form a knuckle from just below the DWL, then a vertical side before canting it in a bit before turning it flat to form the gunwale. I appreciate now the both the knuckle and the cant (what's that called?) will eventually blend into the bow give me a nice water slicing boat.

    I'm going to go away and sketch up several proposals for comment, this will lead on to what was going to be another forum titled 'The best shape to have a canal boat bow and stern' because I wanted to understand about canal boat builders call underwater swims. I guess I'm not quite ready for that though....I'll be back!
     
  14. SukiSolo
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    SukiSolo Senior Member

    When you get to your next phase,

    'The best shape to have a canal boat bow and stern'

    that is where you may find a real advantage to not doing the side in one 1250mm high sheet. That is why I have pointed you at Ad Hoc's excellent design of a larger version of what you are doing. An elegant solution carefully refined for a limited number of plates per side. May be cheaper to join another plate than press one especially as the bend has to line up along the length. Ad Hoc suggest this (unless I have misunderstood him) and I would agree. More freedom for a better shape plus better thickness tapers.

    Traditional boats were built for max cargo nothing else. You have the opportunity to refine the shape and use significantly less power for the same speed. Also to have much better turning and handling which is very important in restricted water. A horse probably did not pull a loaded boat at 4Kn either.

    BTW do not think of the bow or hull 'slicing' through water. It is displacing its own volume and moving through a fluid. The exact paths of the fluid flow are not blindingly obvious, and hold a few surprises to those who do not observe carefully, and note the behaviour of different shapes through a fluid. It is also why I suggest you look at the older Victorian and Edwardian launches and large commercial passenger vessels not too unlike the 'Marchioness' as they leave so little wash and disturbance as they pass through water. Their underwater shapes are what you need to study, also any barge lines especially known fast ones.

    Observe the 'sucking' or lowering of the level of a canal just prior to a vessel passing....
     

  15. richardw66
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    richardw66 Junior Member

    So the correct nomenclature is the Chine Angle and the Dead Angle. Not the deed angle that I copied of the glossary website or what the spelling checker tried to change it to; Dee Dangle! Fork Handles, that's all I can say.
     
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