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, petereng, & DCockey,

    I'm very sorry but I don't understand any of that!

    Could I possibly have a fuller explanation without the abbreviations, please.

    I still don't know what SOR despite Googling it but I'm guessing its something to do with total weight?

    It has been mentioned on previous posts that in the past boats were weighed for toll fees according to the depth of draft. On 70ft boat that equated to 1 inch per ton, that's and imperial ton, not metric tonne.

    I have decided the boat will be 70ft long which is very approximately 20m, it is 2m wide so has an area of 40sqm. Divide one tonne or 1000 litres of water by forty and the answer is 25mm therefore the traditional one inch of draft per ton rule applies.

    I have a 22in (550mm) draft therefore the total weight of the boat will be 22 tonnes. Simple!

    Of that that: 10000kgs of shell, 400kgs of propulsion fuel, 750kgs of domestic fuel, 1350kgs of fresh water, 4800kgs of fixed ballast (thermal mass), 500kgs engine
    leaves 17.8 tonnes leaving 4.2 tonnes for fit-out that will be designed in a balanced way so as to reduce the amount of movable ballast needed.

    The shell weight was based upon 15-8-6 plate thickness but that will come down with 12-6-4 just in case you were thinking the allowance for fit-out was a bit light. Also a typical boat would have a typical 40gal fuel tank whereas I'm allowing for 85gals; a typical 150gal water tank whereas I'm allowing for 350gals. A typical boat would have storage for 2No 11kg LPG bottles whereas this boat will be 'gas free' and have a 170gal domestic fuel tank, that will top-up a further 5gal 'day tank'.
     
  2. SukiSolo
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    SukiSolo Senior Member

    SOR is Service Operational Requirements at least in my understanding. Others may correct me if I have the wrong end of the stick.

    You will need to place the ballast including all the main heavy stuff (ideally everything) to work out the metacentre. With computing these days it should not be too hard. There are also ways to measure it after the boat is launched by shifting known ballast distance X and measuring heel (angle). The reason the latter mode is/was important, was for measuring stability of the old wooden and steel warships as well as merchantmen under sail in particular.

    Definition of Metacentre

    The point of intersection between an imaginary line drawn vertically through the centre of buoyancy of a floating vessel and a corresponding line through the new centre of buoyancy when the vessel is tilted.

    See also this

    http://upload.wikimedia.org/wikiped...ricHeight.svg/350px-MetacentricHeight.svg.png


    So the height of all your heavy stuff, engine, fuel, water, woodburner?, etc etc matters in terms of stability which then impacts on ease of movement, handling etc of the vessel. If you get really pedantic about it you have to calculate the weight of the curtains(!) etc to get an accurate metacentre.

    Nice work Peter.
     
  3. TANSL
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    TANSL Senior Member

    This can be a little confusing if not explained. Metacentre position does not depend on weight of the curtains (or other object) and its location, but on the shapes of the submerged hull. But what is certain is that the value of GM depends on the curtains, as they influence the position of G (G is the center of gravity of the boat in the loading condition being studied).
     
  4. Ad Hoc
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    Ad Hoc Naval Architect

    Statement of Requirements.

    Basically what is the boat designed to meet/satisfy...in terms of speed, beam, length, engines, outfitting, water, range/fuel etc etc. So, what is it you're "aiming" at? The purpose of the SOR is to enable one to 'design' the boat. Without a target, where is the aim going?

    So, if the beam requirement is say 2.0m...yet in the SOR is it to meet the EU Directive for stability....one must 'design' the boat from the SOR to arrive at a final weight and centres and then establish via a preliminary stability check to establish whether the vessel satisfies such criterion. As an example.

    So without an SOR, it is just a drawing of just a boat just running on the water..anything else that occurs is by pure luck!

    This is called the inclining experiment is is important for ALL boats. It is required to establish the location of the VCG (vertical centre of gravity). From this the stability of the vessel can be calculated.

    Yep, a proper weight and centres estimate covers everything that goes on board, everything! :p


    I wager it was a tongue in cheek comment :p
     
  5. Stumble
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    Stumble Senior Member

    The one things. Would add to the SOR is that it is generally best if criteria are also prioritized either in order or by groups. In many cases deriving the SOR takes as much time as the boat design itself since they are interrelated, and compromises may need to be made as the design comes to fruition.

    As an example, you might want this to meet some class rules about stability for insurance purposes, obviously there is a box requirement (the outer dimensions), and you want 1350L of fresh water. But the narrowness of the box limits stability, so there could be a case where water weight has to be limited to keep stability inside the class rules or stability, and the extra weight shifted to ballast. This could then modify the SOR by changing the desire for simple systems by requiring the addition of a water maker.

    As a good rule of thumb, the better and more detailed the SOR is when first speaking to a NA the less the boat will cost in the design stage, and the quicker it will be complete.
     
  6. TANSL
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    TANSL Senior Member

    The weight of water need not decrease the stability. It may be that the free surface of water in the tanks interferes with the stability, but this has a solution, without reducing the weight of water.
     
  7. DCockey
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    DCockey Senior Member

    One thing to keep in mind is that Richard is not designing and building a completely unique boat. Every year there are many welded steel narrow boats built and sold in the UK which satisfy the basic dimensional box constraints, contain accommodations, meet regulatory requirements including the relevant parts of the EU RCD. (Presumably most narrow boats are Category D, Sheltered/Inland. My understanding is the stability requirements for Cat D are much less stringent than even those of Cat C.)

    It appears that Richard is using these boats as examples to base his requirements and assumptions on.
     
  8. TANSL
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    TANSL Senior Member

    The intact ship stability Code, resolution A.749 (18), provides the stability criteria to be met by various types of vessels. None of these criteria seems to be affected by the área of navigation of the ship.
    The category of design, for pleasure boats (CE), provides stability criteria more difficult to meet, from the category "D" to "A".
    Richard's boat will have to meet some criteria or others as it deems as cargo ship, passenger ship or recreational vessel.
     
  9. richardw66
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    richardw66 Junior Member

    Is it really that complicated? Does it need to be that complicated

    I can see I may need to do a lot research into CE and it's implications. Is it a set of compulsory rules that have to be adhered to or does it only cover boats professionally built for clients?

    Is it a minimum standard?
    I ask because my new Nate Len White who built his own eco bow boat as mentioned in the 'below the waterline' forum knows quite a bit about boats being a retired merchant sailor did a practical demonstration. We both stood in the side of his boat that has a 22 inch draft and as we are both big blokes it listed over an inch or two. The boat moored next to his was fairly new and classy in a very fancy traditional style with lots of 'doo-fangles and dingles' and a 33inch draft. When we did the same test it listed a good 6 inches and apparently that boat was compliant with CE.

    The point I am making is that if there is a CE stability rule then it can't be very stringent. I need to do more research on the subject as it may effect whether or not I am able to publish the final plans free into the public domain.

    Why do that and not sell them? Because I've already made my money doing other things that's why.
     
  10. petereng
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    petereng Senior Member

    Richards Stability

    Hi Richard and All - Since I had a section model I imported into Rhino and made it 10m long. I also have Orca so I produced the stability info using it. Since I'm not into stabilty I can't comment from the numbers but some of you out there can. I didn't get the water draft quite right as I have to change my settings to fresh water but its close enough to get an idea. I also presume that the bow and stern shape on this vessel will not change the numbers much as its very long. Cheers Peter S
     

    Attached Files:

  11. SukiSolo
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    SukiSolo Senior Member

    The CE standards can be a bit of a moving target, they do change sometimes. We even have a situation (in the UK) where one sailboat class is being asked to license amateur builders!....:p

    I don't even bother sticking in the exemption plaque....in my own boats.

    However your narrowboat will have to comply with the relevant directive. It would be wise to check out which one actually applies. As it is not fully commercial it should not be too hard to meet. There is of course no guarantee that a boat with a marking (CE plaque) is any better and could be worse than one without but that's bureacracy. Aim for the best you can achieve.

    Worth checking to see if any draft standards are in the pipeline which may apply come 2015 even if not in force now. The RYA may be able to help on this.
     
  12. TANSL
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    TANSL Senior Member

    petereng, yours is a laudable attempt to help. Keep in mind, however, several things:
    - Make a model that looks like, but is not like the boat is very unreliable.
    - Stability curves to be studied are the righting arm, GZ, and dynamic stability.
    - At least you have to draw the curves up to the value of the angle of flooding, which should exceed 25º (+-).
    - Curves alone are not enough. Check whether the ship for various load conditions, meets the stability criteria applicable to that type of vessel.
    - Can not, not worth it, study the stability of a boat when its height cog is unknown.
    If Richard provides us the shapes of the boat, maybe someone could do some calculations to help him.
    Cheers
     
  13. petereng
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    petereng Senior Member

    Tansl - I do realise the devil is in the detail. As Richard is in the early stages I think we may have down flooded him with too much information! But out of interest since I understand the maths, Orca does not ask for the CoG to do the stability calcs. This is not a free floating calculation but a calculation that is driven from a defined geometry so CoG (or weight ditribution) is not needed. We assume that in practice the weight distribution will be acheived (this is called the design spiral) Plus the section shape is to Richards latest dwg so it is accurate as it can be at this stage. Orca can do the free floating calc if the weight distribution is known or I can do this in FE if I'm interested in stressing or structural info plus the stability info. ... Cheers Peter S
     
  14. DCockey
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    DCockey Senior Member

    RYA web page on RCD: http://www.rya.org.uk/infoadvice/re...ssafety/Pages/recreationalcraftdirective.aspx
    RYA guide to RCD: http://www.rya.org.uk/sitecollectio...ents/RCD Documents/1 RCD Compliance Guide.pdf
    RYA website of RCD documents with updates through August 2013: http://www.rcdweb.com/ Subscription is 550 pounds for first year

    Looks like relevant section on stability for Richard's design is:
    A.3.2 and A.3.3 Stability and Freeboard and Buoyancy and Flotation
    Doc ID : 12217-1:2013 Doc Status: EN ISO
    Non-sailing boats over 6 metres hull length

    From the guide:

    New Design Category D boats do not required Notified Body involvement and certification. RCD Compliance
    confirmation is a matter of self certification solely for the builder.

    Engine certification generally is by the engine manufactuer/supplier:

    For the engine

    The engines of all boats (requiring RCD assessment. See first paragraph above) are subject to Notified Body
    exhaust emission assessment and certification. The engine manufacturer is (normally) responsible for such with the
    “boat” builder including the engine manufacturer’s certification within the boat Technical Documentation and
    Declaration of Conformity.

    Engine (and boat) sound (noise) assessment and certification is also a mandatory requirement but in a similar way
    to exhaust emission this is (normally) the engine manufacturers responsibility for outboard engines and inboard
    engines where the exhaust is an integral part of the engine (this is because the noise of these engines may be
    tested without the boat). Where the fitted engine is a stern drive or inboard without integral exhaust then the sound
    assessment and certification for the combined engine and boat is required.

    In some case sound assessment and certification is required to be undertaken by a Notified Body subsequent to
    physical “testing”. Generally this relates to fast planning power craft. For slower, high displacement boats like sailing
    craft the may be assessed by simple calculation and can be self certified by the builder. Similarly when an
    “equivalent” method of assessment is used this again this may be self certified. For full details see the RSG
    Guidelines and the section below on Engine Noise Emissions.​


    Noise self-certification should be simple for a narrow boat:

    9.1.2 As an alternative to sound measurement tests, recreational craft with inboard engine configuration or stern
    drive engine configuration, without integral exhaust, shall be deemed to comply with these noise requirements if
    they have a Froude number of ≤ 1.1 and a power displacement ratio of ≤ 40 and where the engine and exhaust
    system are installed in accordance with the engine manufacturer's specifications.
    9.1.3 "Froude number" shall be calculated by dividing the maximum boat speed V (m/s) by the square root of the
    waterline length lwl (m) multiplied by a given gravitational constant,
    (format didn't work)
    "Power displacement ratio" shall be calculated by dividing the engine power P (kW) by the boat's displacement D (t)
    = P/D​
     

  15. DCockey
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    DCockey Senior Member

    RCD Category definitions from RYA guide:
    Design categories (as in the amended Directive)

    Category A - Ocean: Designed for extended voyages where conditions may exceed wind force 8 (Beaufort scale)
    and significant wave heights of 4m and above but excluding abnormal conditions, and vessels largely self-sufficient.

    Category B - Offshore: Designed for offshore voyages where conditions up to, and including, wind force 8 and
    significant wave heights up to, and including, 4m may be experienced.

    Category C - Inshore: Designed for voyages in coastal waters, large bays, estuaries, lakes and rivers where
    conditions up to, and including, wind force 6 and significant wave heights up to, and including, 2m may be
    experienced.

    Category D - Sheltered: Designed for voyages on sheltered coastal waters, small bays, small lakes, rivers and
    canals where conditions up to, and including, wind force 4 and significant wave heights up to, and including, 0.3m
    may be experienced, with occasional waves of 0.5m maximum height, for example from passing vessels.

    Craft in each Category must be designed and constructed to withstand these parameters in respect of stability,
    buoyancy, and other relevant essential requirements listed, and to have good handling characteristics.​

    Catergory D appears to be the appropriate category for narrow boats to be used on the UK canal system.
     
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