Richardw's Narrow Boat Project- PLATE THICKNESS

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

  1. richardw66
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    richardw66 Junior Member

    Ad Hoc,

    There will be side frames, I just haven't decided what yet, (hence question marks). Before when the side was straight, but slanted there angle side frames and the starting example had them made from 75x50x8mm RSA. The bottom had 100x75x10mm RSA, which does seem rather heavy but will have a positive effect on lowering the CG.

    Frankly I don't know what sections to use for either but I don't need the top face of the angle to act as bearers for the linings so I don't need to use angles. I drew the horizontals and that's as far as I got. The vertical frames will need to be done in 3 parts so I could infill between the horizontals but then perhaps if I had a special vertical frame profile specially flame cut to suit in one piece I wouldn't need the horizontal members if they were at close enough centres.

    It's understanding the ratio between weight an cost that's my problem and it will probably have knock- on and knock-back effects on plate thickness as the design progresses.
     
  2. TANSL
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    TANSL Senior Member

    My opinion is that you should not go much further in the project without defining the structure that will have the boat.
    It is likely that the frames and the floors have to be T shaped (or angulars). That may save you weight and interior space.
    The frames should be continuous and longitudinals, bottom and side, adapt to them. But with the structure you can always make many variations.
     
  3. richardw66
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    richardw66 Junior Member

    That's a lot of downsides being pointed out above and much of it I agree with!

    I've said many times before that Windows, Insulation & Condensation in a Narrow boat are all interconnected, very problematic in current designs and above all; I my view, fully addressable given the right approach.

    Be patient, this is a full ground up rethink about the subject and all will be revealed all in due course...
     
  4. richardw66
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    richardw66 Junior Member

    Ad Hoc,

    I'm having a closer look and think at what you wrote earlier but I'm finding if a difficult to comprehend the names and locations of what part the Web would be and what Rider Bar is. Are we taking specifically floor now in that you're saying reduce the 'Floor Stiffeners' down to 5mm thick and then have an addition 50x6mm flat plate across the top so that it effectively makes a 118mm deep structural bottom length ways rather that just the 12mm thickness of the baseplate. (As per my rough sketch), And the two thinner smaller components are lighter and therefore cheaper than the one thick component that is only strong in one direction.

    That's a good idea and another stage further on from my idea of using flats instead of angles. Thank you.

    For the side frames the idea I have in mind is to use a width of flat plate thin enough to guillotine down to suit the outer hull profile and still be vertical on the inner face. Because of how the churn slopes inwards and in order to make the most of the floor area the bottom of the side frame narrows. I was going to weld them side by side with the bottom frame but may be the best way to do it is to do them inline and have a strengthening gusset either side. In a way its greedy really because I only got the extra width because of the churn so I never had it before but trying to make best use is difficult as the baseplate has to remain the same old width. I could slop the sides but I rather not.

    Another way I could do it is get some construction reinforcing bar bent to suit and use those instead either side of the side frames for extra stiffness.
     

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  5. Stumble
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    Stumble Senior Member

    12mm bottom plate seems awfully heavy. I appreciate that you may need plate thickness to add ballast, but I wouldn't worry about it at this point. I would probably design it for what it needs, appreciating that you may come back and add some extra mass at the end. This way your weight budget remains intact, and you can do things like add extra large fuel tanks, water tanks, ect. Without needing to worry about the overall displacement growing to fast.
     
  6. Ad Hoc
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    Ad Hoc Naval Architect

    A Tee bar is simply that, shaped like the letter "T".

    The vertical part, is the web "|" the smaller horizontal part is the rider bar or flange "-", which sits on top centrally, and is called a Tee, "T".
    http://www.roymech.co.uk/Useful_Tables/Sections/Tee_Prop.htm

    If the rider bar is offset to one side, it is an angle bar.

    So, in your sketch/diagram, the 50x6, is running athwartships and on the transverse FB, to make a Tee bar.

    BTW..only Americans or big ships uses the terminology "floors". They are called frames, and transverse frames at that. But in this case, they are the 'bottom transverse frames'.

    Agreed. Unless you have fully designed the boat and completed a proper and detailed weight estimate, you shall fall fowl of the same mistake that occurs to everyone when designing/building....it'll grow in weight. Boats always get heavier during build never lighter. Plus you may add extra things later from an after though, and in say 5 years time add a nice pot belly etc etc...thus, better to use movable/removable ballast, like sand bags of sorts, as you can move/remove them if you boat gets too heavy or you add things in the future.

    As I noted way way back, and also Tad mentioned this too...what is the SOR of the boat? Without that, you're trying to hit a moving target.
     
  7. SukiSolo
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    SukiSolo Senior Member

    An interesting link to a boat built with a thick 12mm baseplate. Looks like they have used both T and box sections on this one. I note it has relatively few side ribs or braces if you prefer.

    http://www.nbtheantidote.info/hull.html

    Pity there is not an under the hull shot to see if there are any longditudinal members acting as stiffeners, and for grounding reinforcement.

    Also a link to an older wooden boat that was rediscovered in 1981.

    http://freepages.history.rootsweb.ancestry.com/~carrleith/images/lock33-6-1.jpg
     
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  8. richardw66
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    richardw66 Junior Member

    Suki Solo,

    If you look closely at the photo you will see that they are all angles. Each boat builder does their own thing but generally all use angles. I don't know what size the ones in the photo are and Reeves are no longer in business to ask but what does look strange is that there is no connection between the bottom and side frames. The horizontal struts are temporary and there also appears to be a circular object in the corner which I believe may be a conduit for the routing of cables. There are not many vertical side frames either; difficult to say but if bottom framing is at 450mm (18in) centres then verticals would be approx 1800mm centres. There will be no other steelwork underneath the baseplate, just a flat bottomed boat.

    The starting example I was given by another constructor had a 10mm thick bottom plate, the base frames were 100x75x8mm rolled steel angle. the hull sides were 6mm thick and the vertical framing was 60x60x8mm rolled steel angle. The both sets of framing were at 450mm centres and verticals though not all the way down to the bottom did overlap the floor framing so I assume there was a welded connection. On that arrangement there was no horizontal side framing.

    They all use angles because that's how it's always been done and the insulation can be tucked in behind it. The floor and side linings are fixed through the horizontal / vertical face usually via a 2x1 timber section on the side with 12mm veneered ply and a 3x2 timber on the base framing with an 18mm plywood deck over.

    The stupid thing is that it's standard practice to not put any insulation in the floor!
     
  9. boat fan
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    boat fan Senior Member

    [​IMG]

    This is a wooden boat 32 ft x 10 ft Barge .
    I don`t see why this could not be built narrower.

    Wood may well be a viable alternative , it has better insulating properties.
    and you don`t need to build another wood liner inside a steel shell.This may actually save internal space.


    The hull can be strip planked , using lesser grade , lower priced stock....


    A Steel hull design also available.

    Paul Fisher has steel narrow boats too.[​IMG]

    http://www.selway-fisher.com/Mcover30.htm#32
     
  10. richardw66
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    richardw66 Junior Member

    Ow Much???

    You show an example of a typical narrow boat design complete with all the nasty bits; anybody could draw one of those. I'll probably get slated for saying this but Living on a typical Narrow is like camping outside but on a canal. Too hot and sweaty in the summer with solar gain; freezing cold in the winter with condensation, damp & mildew. If it weren't for those inherent off puts I'd have bought a ready made boat already and not even contemplated designing my own.

    My boat will be built from steel in order to survive the inclement English weather and a tough life on an English canal bashing into locks and other boats. Granted it's never going to get T' boned given the length of the boat and the width of the canal but it needs to be tough, tougher than wood and tougher than Fibreglass, (but not as heavy as concrete!).

    I envisage at least a 1 year in-depth design followed by a 1 month shell construction closely followed by a 2 month fit-out.

    But wait, there's more! The full complete set of working drawings will be made available to download absolutely free for anyone wishing to build one for themselves and I would consider licencing the design to any established constructors who want to build for profit.
     
  11. SukiSolo
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    SukiSolo Senior Member

    A bit more worrying is the Selway-Fisher plywood version, with 32 sheets of 6mm ply so the sides and topsides presumably. Whilst I think a ply boat is OK, I would be looking for quite a bit more stiffness than that on the sides, at least 12mm and 9mm for the 'side' deck and end decks. 6mm even 5 ply and glass sheathed would last a short time on colliding with another steel behemoth!

    Actually I had the SG (or SD if you prefer) of cement down at approx 2.5 and steel around 7.8 for quick rule of thumb calcs. So cement is heavier than steel?.;)

    Personally I think the bow and stern sections are the tricky bit. Partly to design well and partly to make it reasonable to fabricate. I can easily see a 'lifting' part roof working well and it may well suit a part FRP roof structure.

    I think a lot of air is allowed to circulate around the steel internally and deliberately for ventilation, see Michael's earlier post. I have noted problems ie rotting of 5-7 year old boats from the inside being mentioned on certain forums when concrete is poured into the bottom of this type of steel hull.
     
  12. petereng
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    petereng Senior Member

    Narrow Boat

    Hi Richard - Just for fun heres your boat in section. Plus some FEA on it. The 500mm spacing with 100mm deep beams is very stiff and very low stressed. One video shows the 12mm bottom unstiffened. I've applied a 1m head to the bottom plating. The CofG of the structure is about waterplane height. So if you floated it empty it would flip over!! As the centre of bouyancy is at about 250mm under the water. If you had a 12mm unstiffened hull it would deflect about 35mm inward at 500mm head. See video. The pdf is 3D so click on it and you will be able to swing it around etc. Cheers Peter S FYI - Solid modelling done in Geomagic Expert, FE done in Strand7 and FE premodelling done in Rhino3D.
     

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  13. DCockey
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    DCockey Senior Member

    The Center of Buoyancy is below the Center of Gravity for most boats. What is important for stability is the location of the Metacenter, not the Center of Buoyancy. CoG at the waterplane height does not mean the boat will flip over.

    Submerged submarines need the CoB above the CoG but the canals are a little shallow for a submarine.
     
  14. petereng
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    petereng Senior Member

    Hello David - Yes you are correct. I was a bit quick in discussing the CoG & Cb. It would be interesting to calculate the metacentre. For those out there, this indicates the tendency fo the boat to correct itself in heel. The centre of bouyancy pushes up, the CoG pushes down and at stablity they lie in line with each other. When the boat heels the CoG stays in the same place. The CoB moves stbd or port and this creates a mom
    ent. A stable boat has a unstabilising moment a stable boat has a "righting moment" The metacentre is a way to describe whether its stable or not. I'm used to working with racing sail boats that have huge amounts of lead in deep keels. As I work with structures I'm not usually involved in stability so I'll brush up in that area. ta & Cheers Peter S
     

  15. Ad Hoc
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    Ad Hoc Naval Architect

    Indeed.

    A quick back of a fag packet calc shows the KM for this boat to be circa 1.0m, not much.

    But this then needs to be put in context of how much restoring moment there is when heeled, and the magnitude of a heeling moment. A narrow boat is narrow..which immediately implies poor stability anyway!...so QED really.
     
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