Richardw's Narrow Boat Project- PLATE THICKNESS

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

  1. petereng
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    petereng Senior Member

    Richard - I looked at the sections published earlier. I'm still pushing for the fibreglass just for fun.
    Firstly FG is much tougher then steel or aluminium. I've done many impact tests over the years to validate impact properties of laminates for boats in survey. If you drop a 25kg steel impactor from 6m you generally go straight through steel or aluminium panels. But with FG it generally bounces upward nearly as fast as it came down. If you need weight then here's a suggestion. FG has a SG=1.6 say. Steel is 7.8 so the ratio is 4.8. So if you made the laminate say 4x thicker then the proposed steel hull you would be of near equal weight. I have also been involved in large houseboats and laminates of 20mm or 25mm are not uncommon. So the 8mm thick plate proposed in the dwgs would be 32mm which would be extremly thick for the job. But the advantage is that with the 8mm steel plate there has to be a bearer 100mm high, each 600mm. With the solid FG the bearer would not be needed so you gain 100mm in headroom which you are concerned with. Your dwg has a water draft of 0.61m and a width of ~2m so the displacement is 1.2 tonne per metre. Your 62ft boat is therefore 18.8m long ie its going to have a weight of 23 tonnes about. From the steel thicknesses you have 8.2 tonne of steel minimum. Say 9 tonne. so to achieve a 9 tonne FG shell we need a 30mm thick laminate. But I'm sure you can loss a considerable amount out of the 14 tonnes other stuff you intend to have around!! You will have a bullet proof boat, no corrosion and no maintenance. To move the argument towards your side you could build a 3 or 4mm thick steel shell and laminate over it. 1) You need a mould anyway which is usually the high cost item in this case, the 20mm laminate would be the corrosion barrier and you would not need bearers???? By the way I'm a yacht structures engineer so bring a bit of experience to this discussion but again just for the fun of getting creative juices going. My friend has a canal boat in France so have a bit of interest in this area. Cheers Peter S
     
  2. SukiSolo
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    SukiSolo Senior Member

    One UK example of a large fibreglass boat would be the Navy Minesweepers. Laminate is I believe 50mm. It is glass primarily to avoid magnetic mines. At 60m long I don't think GRP or FRP is a problem.....


    Googly Hunt Class minesweeper for more info. They have a reputation for being a bit 'rolly' down to their shape not construction.
     
  3. waikikin
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    waikikin Senior Member

    Peter, I get where your coming from..... I'm quite fond of melamine molding myself... and alliteration ... obviously;) gives a terrific cost benefit over "normal" tooling costs & gelcoat finish is as good as it gets on value/$perm2.
    The great thing about sheet products like ply & steel the product is Built once.... although steel usually gets a timber boat built on the inside.
    The terrific thing about these Narrowboats & other houseboat styles is the constant/strait sections for much of the length simplifying fitout details compared to usual yacht style fitout.
    Regards from Jeff.
     
  4. waikikin
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    waikikin Senior Member

    Tilt outs?


    Hi Tad, got any pics of the "tilt outs" we have some large power vessels here but I've never seen one opening something with that, is it like a tilt out "veranda/patio/alfresco" area?

    Jeff.
     
  5. richardw66
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    richardw66 Junior Member

    TANSL,

    Yes, 'Cut' is a very simple term that is difficult to explain especially to a foreigner like yourself. Basically it means that and object has had 'doo fangles and dingles' cut out usually as a cost saving exercise. Many UK Canal Boats are very traditional and can have lots of cosmetic features that are very intricate and therefore very expensive to reproduce and needing skilled craftsmanship in doing do.

    The point I was trying to put across was finding the balance between looks and practicality without the final result looking like something is missing.

    If you were to search on Google images for 'Canal Boat Fabrication' you will see many fine examples of intricate workmanship.

    For a good example of 'Cut': I very much doubt you would have heard of or seen a 'Bakewell Tart' before but the search for one on google images and then imagine a Bakewell Tart without the cherry on top. If you've never seen one before you probably wouldn't know if the cherry was missing but those that know would know. That's why it is difficult to define 'Cut' because not everybody can appreciate it; and the trick is to doing it well so that fewer people notice it.
     
  6. Ad Hoc
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    Ad Hoc Naval Architect

    That is an over generalisation and is incorrect.

    You may get 1 or 2 composites that perform well, in the high end exotic side, but in general, basic GRP is not better or worse than aluminium and not as tough as mild steel. As can be seen by this nice diagram that summarises such. Aluminium highlighted in red, mild steel in blue, and composites in green:

    Fracture Toughness of Materials.jpg

    Approx generic values are:
    Mild Steel is circa 100-140 MPA m^1/2
    Aluminium is circa 30-40 MPA m^1/2
    GRP is circa 30-60 MPA m^1/2
     
  7. richardw66
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    richardw66 Junior Member

    Come be serious SukiSolo & petering,

    It is just not practical in terms of cost to build a canal boat out of GRP. Regardless of cost and weight the shape of the boat would be very much dependant on it's ability to slide out of a mould. Then there's the cost of the mould; I might as well fit the mould out and sail it away!

    I know; Concrete! Why don't I use that because I have access to a lot of that in my profession. Before you laugh I read an article once who built a yacht out of concrete, if my memory serves me right it was called the Dexion Pheonix.

    Back in the war barges were built from concrete and some can still be seen on the side of the Thames River opposite Erith as per the photo below.

    I am joking of course, I'm not going to use concrete either!
     

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  8. petereng
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    petereng Senior Member

    AdHoc - I've been dropping heavy steel sharp weights onto laminates for over 20 years and FG always does better then the metals. By definition generalisations are incorrect so no news there. The main reason for my comment was to inform Richard that its unlikely to find a FG boat on the bottom of the canal. The graph represents fracture toughness which is measured with small samples. As the sample gets bigger composites do much better then tests that are designed for metals. Cheers Peter s
     
  9. petereng
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    petereng Senior Member

    Concrete was the choice to build amatuer boats before strip plank became popular so don't laugh about concrete. I helped a friend build a 50ft concrete sailing yacht many years ago. How can you say its not practrical when you have not done the comparison exercise? white melamine sheet is cheap and your shape is simple. Cheers Peter
     
  10. Ad Hoc
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    Ad Hoc Naval Architect

    No, that's simple QA. If your scatter is large owing to sample size, then you have an issue with the QA. But your values will be no more different than those I noted above, large or small sample size.

    Fracture toughness is simply a materials ability to absorb energy, it is not size dependent, but material property dependent. Fracture toughness is a materials ability to absorb energy in the presence of a flaw.
     
  11. TANSL
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    TANSL Senior Member

    Richardw66, nobody on this forum will laugh to hear about concrete boats . Maybe you just had this idea but others long ago that had ( I did in 1969 ) and some have projected concret boats . You think you are located at a point of shipbuilding technique which only you can get . Not so, trust me and follow any advice that people give you .
    I do not understand the problems that you have with the thickness of the plates, the ballast , the loss of interior space, etc. ... All these are problems that naval designer use to fix . The design of a ship is always a compromise between multiple variables. A boat is like a house , subjected to earthquakes (waves) every 45 seconds. It is normal for a designer of boats have to size hes boat according to certain external parameters. Therefore, in my opinion, you do not need to discover the wheel. The wheel is already discovered . Maybe if you get to trust a NA, he can help you a lot.
    Cheers.
     
  12. SukiSolo
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    SukiSolo Senior Member

    I confess ferro cement construction had crossed my mind. Especially when screeded concrete floors were mentioned, as it probably eliminates the heat/cool contraction problem. I met a guy who built a 72' sailing vesel to go round the world out of this material, and he did....

    Richard, I don't think you have grasped the simplicity of a mould for this type of vessel. It would be incredibly similar to shuttering concrete except you use mfc or mf faced board (good face is inwards) to create the mould. No welds! no rust. I'm not averse to it and neither is Petereng.

    Steel's fine too, it is just different. I think Peter outlined some of the main benefits of an alternative glass construction. If you had the space, you could undoubtably build the thing yourself, and save the cost of the yard and welding.

    Still open about it to be honest. If anything the extra headroom from eliminating the 'bearers' would certainly tempt me towards the glass route. Nice quick calc Peter, shows what can be done with a bit of section size.

    BTW Richard, I think that is one of the old 'dummy' barges built to fool Hitler into thinking the Invasion would be across to Calais or nearby. There are still quite a few on the East Coast.
     
  13. richardw66
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    richardw66 Junior Member

    To All,

    I have worked up yet another mid section detail that hopefully will address several issued that the previous incarnation had.

    Firstly I have given thought the centre of gravity and the ballasting effects learnt in the other forum and have reduced the plate thicknesses to the top side. I have reduced the draft so it will require less ballast but hopefully the ballast will be further down so this boat design will have a lower centre of gravity and be more stable. At the same time of reducing the water draft of have also reduced the air draft by folding over the tops of the side which has had the added benefit of creating more internal space.

    The Hull Sides are still a 1250mm wide girth single plate but Ad Hoc would be proud of me in that it is now bent three times to form a vertical side and then a slightly angled chime from just below the waterline to inwards a bit from the edge of the base plate. I have kept the angles to simple 5 degree increments.

    The 500mm deep churn will blend into an important component on both the stern and the bow as it will be the height of the Uxter Plate on the back and the top level of an underwater feature known as an 'Eco Bow' on the front, (very rare on a narrow boat and difficult to find information on).

    All will be discussed a new forum subject of 'Below the Waterline' that I will start later on today.
     

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  14. TANSL
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    TANSL Senior Member

    You should place longitudinal elements in the bottom and below the roof of the superstructure. Some pillar will be inevitable.
    Consider supporting the sides of the superstructure on the horizontal piece of the deck.
    I canĀ“t see lateral frames but consider that the boat has. Their connection with the floors is very important, is usually done with brackets, and can reduce interior space.
    I suppose you made some calculation to derive the thickness of the plates and modules reinforcements. Flat bars have little stability when subjected to compression.
    A boat without deck may have major problems of torque. How do you avoid them?
    The configuration of the horizontal and longitudinal structural rings is very indicative of their ability to withstand working conditions. I would like to see the rest of the structure, if you think define.
    Thanks.
     

  15. Stumble
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    Stumble Senior Member

    I am curious what the steps in the sides are for other than tradition. It seems you loose about 10% of the interior volume there, and I can't imagine what good a 100mm step would be good for. I would consider pushing the sides outward, and reclaiming that space.


    Secondly, are there any restrictions on using the top deck as out door living space? So long as the stuff is removable/collapasable? I could see some fold out decks, and hinged furniture being valuable additions to the living space.
     
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