Richardw's Narrow Boat Project- PLATE THICKNESS

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

  1. DCockey
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    DCockey Senior Member

    Annex 8 provide two alternative stability requirements. One is to meet ISO 12217-Part1:2002 Small craft - Stability and buoyancy assessment and categorisation - Non-sailing boats of hull length greater than or equal to 6 metres. The other is to meet the relatively simple requirements directly set out in Annex 8, 1.1 to 1.3 . If I was designing a boat which would need to meet the RCD I'd use the ISO standards.

    One confusing aspect of the RCD / ISO standards and the Inland Waters Small Passenger Boat Code is that both use the terminology Category A, Category B, etc. but with very different meanings. RCD Category D corresponds to IWSPBC Categories A and B.
    Inland Waters Small Passenger Boat Code

    ANNEX 8

    MOTOR VESSELS

    STABILITY

    For the purposes of this Section, where vessels are to operate in fresh water, the stability tests defined within this Section are to be conducted in the area of operation, as appropriate.

    1. Motor Vessels

    1.1 A vessel should be tested in the fully loaded condition (which should correspond to the freeboard assigned) to ascertain the angle of heel and the position of the waterline which results when all persons which the vessel will carry are assembled along one side of the vessel. (The helmsman may be assumed to be at the helm.) Each person may be substituted by a mass of 75kg for the purpose of the test. Annex 10 gives guidance on how to carry out a simple heel test.

    The vessel has an acceptable standard of stability if the test shows that:

    1. the angle of heel does not exceed 7 degrees, and

    2. in the case of a vessel with a watertight weather deck extending from stem to stern, the freeboard to downflooding is not less than:

    100mm for Category A vessels

    175mm for Category B vessels

    275mm for Category C vessels

    375mm for Category D vessels,

    and additionally, the freeboard to deck is not less than 75mm at any point.

    3. the angle of heel may exceed 7 degrees, but should not exceed 10 degrees, if the least freeboard to downflooding in the heeled condition is in accordance with Annex 9 of the Code for the upright condition.

    1.2 In all cases, the maximum permissible weight of passengers derived from the tests conducted should be recorded for reference. Vessel loading should be restricted by the position freeboard mark and maximum permissible weight, and thus for the purposes of this test, attention should be paid to any activity related equipment where this may be significant, e.g. diving equipment.

    1.3 It should also be demonstrated that an open boat, when operating in Category C and D waters, when fully swamped, is capable of supporting its full outfit of equipment, the total number of persons which it will carry, and a mass equivalent to its engine and full tank of fuel.

    1.4 Vessels complying with ISO 12217-1 Small craft - Stability and buoyancy assessment and categorisation - Non-sailing boats of hull length greater than or equal to 6 metres, or ISO 12217-3 Small craft - Stability and buoyancy assessment and categorisation - Boats of hull length less than 6m, may as an alternative to 1.1 to 1.3 above, be assigned an area of operation as follows:

    IN CATEGORY A and B WATERS, ISO 12217 Design Category D applies.

    IN CATEGORY C and D WATERS, ISO 12217 Design Category C applies
     
  2. Ad Hoc
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    Ad Hoc Naval Architect

    If the vessel at sometime in the future may be sold on, I would tend to agree. Since it provides the seller/buyer more confidence and greater cover. However, it also depends on the type of boat, since the ISO definitions are more in-depth, and may not be wholly applicable.

    ISO Cat C is Hs=2.0m and BF>6, that is somewhat different.

    Just means you need to be very careful which rules you are applying and be very careful using the correct definitions and not assume Cat A in one set of ruels is the same as Cat A in another.

    Cat A, for small commercial workboats is "unrestricted" area of operation! As with any set of rules, read them and understand them and don't assume.
     
  3. brian eiland
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    brian eiland Senior Member

    Canal Boat Designs

    Interesting. I will be interested to see what design options you come up with.

    My personal favorite canal boat is Roi Soleil. I made this posting on a long subject thread about canal boats:
    http://www.boatdesign.net/forums/boat-design/dutch-barge-long-distance-cruisers-11316-20.html#post455644

    This is another one I like:
    http://www.boatdesign.net/forums/boat-design/dutch-barge-long-distance-cruisers-11316-20.html#post455651



    oops, didn't notice how long this subject thread was. will have to do some reading when I get some time.
    Brian
     
  4. Simonosteopath
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    Simonosteopath Junior Member

    Hi,
    I've just joined this thread and have read most of it but I may have missed some points so please forgive me and nudge me in the right direction if I've a lot to catch up on.

    I have a background in engineering and may be able to help with the materials questions.
    Stainless steel would be a fantastic material but expensive and fewer builders have good experience in welding it; it is normally at welds that problems occur with stainless.
    Aluminium is actually good as far as corrosion goes and builders who use it (Otter Boats) say it can be left untreated for use in canals.
    The oxigenation of canal water varies but is higer near weirs and locks due to the churning of the water.
    Balasting a boat of aluminium would be more of an issue as you point out!
     
  5. Simonosteopath
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    Simonosteopath Junior Member

    Just a few notes on earth-bonding, galvanic/electrolytic corrosion and anodes:

    Anodes first. Any two dissimlar metals incontact with eachother, immersed in water that is not completely pure, ie- distilled water, will create an electric current; The basic priciple of a bettery.
    In the case of a narrowboat the two metals are normally the steel hull and a bronze propeller. The hull forms the cathode and the prop forms the anode. As this 'battery action' takes place, the anode is gradually corroded. The less pure the water, especially salty water, like the sea, the faster this action takes place. Zinc or even better, Magnesium 'sacrificial' anodes are fixed to the hull as they are more 'anodic' that bronze, and therefore they are corroded in preference to the prop. I haven't looked it up but some forms of stailess steel may have a similar electrolytic property to mild steel. In which case it would be very sensible to fit a stainless prop and overcome the need for sacrificial anodes? Maybe.
    The point is that anodes are only required because there are dissimilar matals that form the wet parts of a boat. On that score, an aluminium boat could have an aluminium prop, except a small part of the steel shaft would also be exposed to the water. So maybe not so good.

    Galvanic isolators are only require if you are moored and taking power from ashore, the reason being that mains neutral is normally close to, but not actually at earth potential, so a current may develop between the boat and the water, causing the same problems as above, prop and maybe even hull corrosion.
     
  6. Simonosteopath
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    Simonosteopath Junior Member

    Hi Richard,
    I like your idea of using the ballast as a thermal mass but for one reason. Thermal lag. Such a large mass could be slow to heat and then slow to cool should the sun come out; Boats can heat up so quickly with a change in weather. A lot faster than a house.
    However I stronly agree, from an engineering point of view, that water shouldn't be allowed to accumulate, in any quantity, in the hul/bilge. People who have been in the boat business for a long time seem scared of blocking this area off, but if it can be sealed and insulated at the same time I don't see why condensation shoould become a problem!
     
  7. Simonosteopath
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    Simonosteopath Junior Member

    Very nice of you to submit all the plans at finalisation! I am reading all of this with great interest as I plan to get a 65' boat built to my specification, as yet not finalised, and this idea sharing is very conducive!
     
  8. Simonosteopath
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    Simonosteopath Junior Member

    This lack of insulation also gets me! Here, for what it's worth, is my view on why it now should be and also why it isn't.

    Why it isn't:-
    Traditionally, old insulation materials used to be absorbent and could also 'breath', ie, they were not air-tight. Even when expanded polystyrene became available, it was only in sheets or beads. This is non-absorbent but still allows water vapour to get behind it and onto metal surfaces. Once there it would condense and collect and because the sheets would impede free airflow it would have more chance of increasing rather than evaporating. This is particularly the case in the bilge area as the bottom of the boat is nearly always cooler than the interior (I can't think of a time when it would ever be warmer, unless abandoned in winter) and so will always be a condensing surface!
    So, having no insulation will at least allow collecting water to drain to the lowest point where it can be pumped out, if it never dried out naturally.

    Why it should be:-
    Nowadays we have high performance, spray on, self-adhering insulation that forms a vapour barrier. The most common form is polyurethane foam, sprayed on with a two-part mixing system. It adheres well to almost any sound surface, forms a vapour-proof seal/barrier and has a much higher insulation value than even polystyrene sheets.
    The inside surface of the hull finished in such a material will always be a lot warmer than the hull itself and would rarely, if ever, form condensation on its surface.
    I spoke to a guy at the Crick boat show this year, selling such a system, and I asked him about the ventilation issue and he also agreed that the traditional trend seemed wrong with what is now available. Okay, he may be biased but he's been installing this for some time and I've not been able to find any gripes on forums yet.

    Does anyone else have a view, taking the above into account, as to why hulls are not insulated?
     
  9. Simonosteopath
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    Simonosteopath Junior Member

    I think the comment on concrete being heavier than steel applied to the whole boat. Concrete boats have a much thicker skin thickness due to its relatively brittle nature. So a 60' concrete narrowboat would be heavier than a steel one.

    I'm not surprised that the boats you mentioned with the poured concrete were rusting internally around said concrete. Cold, good for condensation, and a small gap to trap moisture. I'm sure the thermal coefficient of expansion is different between steel and concrete too!
     
  10. petereng
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    petereng Senior Member

    Hi All,
    Reading all the bits about corrosion and heat gain and loss etc brings me back to fibreglass. The comment about FG not being tougher than steel is incorrect. If you had a 15mm thick FG shell it would be exceptionally tough. The only drawback from the calcs I did was being much less dense then steel you would need quite a bit of ballast. Worth a revisit I think. Peter
     
  11. Ad Hoc
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    Ad Hoc Naval Architect

    Im sorry but you keep getting this wrong. Composites (in green) at the lower end are worse than aluminium and steels in toughness. At their mid level range the same toughness as aluminum (in red). And the 'better/advanced' composites are only as good as steel (in blue) in terms of toughness.

    Fracture Toughness of Materials.jpg

    You seem to consistently misunderstand the definition of "toughness" for some reason. I have no idea why.
     
  12. petereng
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    petereng Senior Member

    Well Mr AdHoc thank you for the interesting graph. I'm fully aware of the meaning of the engineering term "fracture toughness'. When most people in the boat industry talk about toughness they mean the ability to survive daily chores such as berthing and grounding. The notion of fracture toughness in terms of the engineering value "fracture toughness" is not what they are talking about. I've been impact testing laminates and metal panels for over 20 years for clients building commercial vessels and the composite panels always outperform the metal panels. A fiberglass narrow boat hull will give longer service, provide better impact and thermal properties than a mild steel boat will. There is a long term argument about comparing composites at very small test coupon size verses real structure size. There is clearly a scaling problem otherwise various industries wouldn't use composites. In my opinion for an amatuer builder it would be easier to build a fibreglass hull then a steel hull. Plus it would not need internal framing so you gain space. No need to discuss further just stating an opinion. Cheers Peter
     
  13. Ad Hoc
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    Ad Hoc Naval Architect

    That is strength, not toughness.

    Then why are they/you incorrectly using the term toughness to describe strength?

    Sorry, no. That all depends upon the EI of the structure. This it is a strength and flexibility which is applicable to any material for any hull.

    No there is not. Eeach material must stand on its merits against the SOR. You making a woefully incorrect assumption of others’ SORs with such a carte blanch statement.

    Sure opinions are fine, everyone has one. Just don’t subvert opinion as fact or attempt to redefinition words with an already known definition to suit an argument.

    But you are repeating the same incorrect use of the terminology As noted here depsite the above image being shown again here.

    I'll quote the values again for ref:

    So im not convinced you do know what is toughness.
     
    Last edited: Jul 20, 2014
  14. pdwiley
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    pdwiley Senior Member

    You can state all the opinions you like but you're still wrong.

    Name me one, just one, icebreaker that's ever been built with a f/g hull.

    Name me one composite panel widely used in boat building with superior abrasion resistance to A36 steel plate.

    Name me one vessel of over 50,000 tonnes displacement that's been built out of composites.

    I know, you'll say these are all big ships and it's a different game. But the point remains, a narrowboat has a pretty severe life in those canals and a steel hull with decent rubbing strake is going to be a lot more robust *and* easier to repair *and* cheaper to build as a one-off than a composite hull.

    Now if you were going to build 10+ hulls maybe a f/g composite might be cheaper using a mould. Maybe not too as there's not much shape in those hulls and getting say 6mm plate rolled or pressed to a nice U shape then welding a pile of them together would go pretty fast.

    I'm really tired of this argument about the toughness of f/g type structures. Rub a f/g hull against a timber piling and you get a hole in the hull. Rub a steel hull against a timber piling for the same length of time and you get polished metal.

    PDW
     

  15. SamSam
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    SamSam Senior Member

    What is the basis for that chart as far as comparing the materials? The same weight or the same thickness?

    As an example, say maybe a square foot of 1/8" steel weighs the same as a square foot of 1/2" composite, are they comparing the same thickness steel and composite or the same weight of steel and composite?
     
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