Construction of a cutter

Discussion in 'Metal Boat Building' started by dskira, Oct 4, 2010.

  1. dskira

    dskira Previous Member

    I know, the builder unfortunately after giving me the scanting, I find he didn't follow the plan schedule. I started to mention what Ad Hoc mentioned, and I ends up receiving the new scantling with the frames far wider. I am on a pickle, the weight distribution as to be redone. When the builder change the schedule, it is not good news.

    The ballast reinforcement been inside was taking care very carefully. It seams not going that direction, but we have long telephone conversation and he will make the change to go back to the plan. He is a good guy, and I hope he will continue to send pictures, the only way for me to follow his work.

    Thank you for you input
     
  2. dskira

    dskira Previous Member

    The system designed was the one on the right of your drawing Ad Hoc

    [​IMG]


    It was not intended to be web system at the beginning, I designed with separate pieces and all welded, like I always do. He was on the trip to web and weld, since he find a way to have the offset put on a computer, and use the computer to cut the steel.
    My intention was for him to loft and the then do the framing the classic way, with the welding at the floors, at the gusset, and separate beams and floor.
    I am now trying to reconsider the whole plan since the builder put me against the wall. it is not fun, but it is always challenging to work with a builder at 3000 nm from my home. (I don't travel)
    Thank you for helping me, I will certainly come back with some specifics questions.
    For the moment I have to extract from him all the element already done, and redo the weight estimate.
    Then from there I will see the necessary changes.
    Thank you for your input.
    Daniel
     
  3. Ad Hoc
    Joined: Oct 2008
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    Ad Hoc Naval Architect

    It is not so easy working such distances for the first few times. I have been working remotely from yards for many years now. At my previous shipyard, we licensed out our designs to other yards, some being over 8,000 miles away. But once you recognise the pit-falls and establish and clearly define the scope and who has responsibility/authority, it all falls into place. So, whether you’re 3,000miles away or 3metres shouldn’t make any difference.

    If you have any questions, we're only too happy to assist :)
     
  4. MikeJohns
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    MikeJohns Senior Member

    Daniel hope you don't mind a bit of hijacking We don't get much opportunity for good technical discussion these days.
    :)

    John

    Yes that's one bracketed method, What does that Llloyds guide say about floor to frame non-bracketed, do you have it there?

    For others reading this; there is a distinction depending on the frame Z as to whether the ends require fixity or not. A lot of smaller vessels the web depth is dictated by other factors and they are beefy enough to not require fixity brackets. Then its more a matter of making sure the angles are less acute, or adding smaller curved brackets.

    John

    I think you'd be quite shocked to see some small boat framing that shipyards built and approved 100A1.

    The doubler on a web frame I meant as alongside the web across the weld as a cover plate fully fillet welded. Like normal commercial builds which just overlap the frame web over the corner bracket with fillet welds. The full butt welds take longer but will be stronger. Yes an insert bracket fully welded would be better still, if required. There are other doublers too, oval shapes circles and rectangles that are welded across as stress relief at the join.

    But with deep web frames on small vessels the loads are quite small. I've often shaved brackets off designs following analysis that would not be applicable in a larger vessel. I did a lot of analysis for one design of a very lightweight steel sailing vessel, it was quite illuminating to see just how much of the standard shipbuilding requirements were overkill when we looked at the actual reactions in a small vessel frame closely.

    On a larger vessel it's an entirely different story.
     
  5. Ad Hoc
    Joined: Oct 2008
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    Ad Hoc Naval Architect

    Concur with Mike, sorry for taking over the thread, but not often we do get the opportunity to discuss technical issues.

    LR generally don’t allow connections without brackets, as their rule state in Part 6 Ch.3. Sec4.,
    LR guidance notes corner joints-3.jpg

    but not necessarily consistent with their guidance notes, as they also provide alternatives:

    LR guidance notes corner joints-2.jpg

    Sadly no, I have seen some shocking stuff, but this too, is all slowly changing.

    Indeed.

    Small vessel tend to be at the ends of the “envelope” of Class rules and thus, the rule minimums do not generally produce meaningful results. However, if you have previous supporting evidence to reduce the minimum, they will review and generally accept this. I have done this on numerous occasions. Having a large database of previous designs and history does help though! :)
     
  6. dskira

    dskira Previous Member

    John and Mike please continue talking technical issue in this thread, it is very interresting and informative.
    Thank you both for your input and lets continue
    Daniel
     
  7. Ad Hoc
    Joined: Oct 2008
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    Ad Hoc Naval Architect

    We'd be happy for this to be a Q&A, we (Mike and I), and any others too (if they wish to chip in), would be more than happy to answer any questions anyone has, just ask away.
     
  8. Jack Hickson
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    Jack Hickson New Member

    Looks like a flat plate for keel and deadwood. I read an article in Latitude 48 a few years ago , about how racers were increasing their speed , by rounding of keels , and giving them a more airfoil section, to minimize stalling when sailing in rough water. When beating to windward , or sailing downwind in rough water, the sharp leading edges, and flat shape of some keels led to a huge amount of increased drag when they stalled.
    You could drastically reduce drag by giving this keel a bit of airfoil shape. This would enable you to drop your ballast a lot deeper, enhancing stability. When, as kids, we play with model boats, we quickly realize that the deeper the V, the tippier the hull. This boat has a super deep V shape ,and will need all the help it can get, when it comes to stability.
     
  9. MikeJohns
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    MikeJohns Senior Member

    Brent / Jack
    Lattitude 48 isn't really a quotable authority on Naval Architecture.

    Unfortunately you confuse a few issues in that post.

    Racing boats have had aerfoil sections for their foils for many decades becasue they have a lower drag while providing lift.

    Aerfoil shapes are not applicable to low aspect ratio keels since the flow has a high spanwise rather than chordwise component. For low AR foils flat sections are perfectly ok providing you round the corners on the leading edges.

    For example a full keel on a sailboat can have a flat leading edge and straight run sides and only a taper aft with a with no discernable difference to an expensive rolled parabolic LE . Just so long as you round the corners.

    As for flat plates; they can provide more lift and a delayed stall relative to an aerfoil section, just at the cost of greater drag.
     
    Last edited: Mar 26, 2011
  10. Jack Hickson
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    Jack Hickson New Member

    Not much rounding you can do on a plate edge
     
  11. MikeJohns
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    MikeJohns Senior Member

    There is, you don't leave it sharp square edged.
    You round those corners too even on a flat plate and it makes a significant difference in leading edge vorticity. Something most people would feel intuitively.
     

  12. Jack Hickson
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    Jack Hickson New Member

    It would be far sharper than a proper airfoil . You still have your ballast much higher, in a very slack bilged , tender hull shape, lacking initial stability.
    How many of these boats have been built? How many sailing craft of this size have you designed and built ? How many have done extensive ocean cruising ?
     
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