Reverse Engineering (conversions And Modifications)

Discussion in 'Boat Design' started by viking north, Dec 25, 2010.

  1. daiquiri
    Joined: May 2004
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    Location: Italy (Garda Lake) and Croatia (Istria)

    daiquiri Engineering and Design

    I was just making my observation about the costs issue. It comes from my building experience, had to open some 2 yrs old excel files before writing. No intention to question your passion, which is very visible. ;)


    And this:
    is what I call a winning argument. I can't think of any credible counterreply to it... :D
     
  2. Submarine Tom

    Submarine Tom Previous Member

    Geo, you've just alienated some of the most knowledgeable folks on this forum with your broad brush stroke there my friend. I'm not really following your logic. Maybe that's just your point.

    Well, good luck to you.

    -Tom
     
  3. Scunthorp
    Joined: Dec 2010
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    Scunthorp Hull Tech

    Hi Tom are you converting a lifeboat or am I the only one. (I have the hull in the back yard and the wife is in the kitchen bare foot I might add) I like my hull it cost me very little (a few hundred bucks). I figure if I bought the ten or so barrels of polyester to make it well that would be more than a grand a barrel plus the cloth (Canadian funds sorry a barrel here is about 1000$ each) Then there would be the mold for the one off even if I made it cheep and nasty that would be more money. I might have to pay a grand or so to get the engine overhauled properly. Perhaps I will end up buying one of those brand new Isuzu engines fully done at the Luneburg foundry(8000$). If I junk rig her (even though I think it looks ugly) I know it is a great cruising rig for shorthanded sailing (Read Ann Hill voyaging on a small income) Well I still need to find 4or 5 thousand pounds of wheel weights that or shell out the same in dollars as well lead too has gone up. I have the good fortune of having the best friends in the world who seem to know just what I would like for birthdays and Christmas(got some nice winches and other equipment even 800lbs of lead one year) I don’t know mate. It’s a hobby so I can’t deprive me kids of too much. A smart dude would chip away at a project like this collecting the necessary electronics as he go’s. I think when she is painted up smart I will not be embarrassed to take her out in public I might actually be a little proud. Perhaps there should be a thread on frugal sailing and fiscal restraint. Maybe there is something quite honorable in recycling an old boat in a world where so many have much less. What do you think? John
     
  4. Ad Hoc
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    Ad Hoc Naval Architect

    If this is a “theoretical” exercise, then why oh why have a “limited” budget from the outset?

    If your raison d’etre is to “learn” the processes involved, why bring money into the equation? When I was studying at university, and when we did, say stability calculations, for example, the solutions did not depend upon how much money I spent on the investigation, same with structures, hydrodynamics etc etc the result is independent of money/finances. The methodology remains the same.

    Yet for some bizarre reason you feel that introducing
    will enable you and others to short circuit everything and have a “cheaper” boat at the end.

    You fail to grasp the significance of your throw away comment of “on a tight budget”.

    Whose budget, how much...what is tight for you may not be tight for me...and so on. The cost of materials where you may be very different from where I live, the cost of second hand eqpt may be prohibative, the cost of NA fees non-existant as non about...and on it goes. The definition is rather meaningless in this context of:-

    If you wish this thread to be a hypothetical mental exercise into understanding what is required, then remove money from this exercise and learn what process are involved and required to fulfil your gaols. It is then for you, and YOU ALONE to judge whether you have the finances or not for each step that must be undertaken.

    I took my wife out for a birthday lunch last week, we had sushi and sashimi. How much would you feel is a “on a tight budget” expected cost for this?? I can guarantee you, whatever figure you come up with does not equate here, nor the money I paid. Ergo, take money of this debate and focus upon the facts which are common to all, not one.

    Those that do not understand, talk numbers, as numbers are “measurable” in their frame of reference and hence palpable. Those that wish to learn and understand talk about the theory.
     
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  5. Scunthorp
    Joined: Dec 2010
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    Scunthorp Hull Tech

    The students of bumblebees theorized that they should not be able to fly. And yet how much for a poem, a song, a boat, a passion. I like it. John
     
  6. Ad Hoc
    Joined: Oct 2008
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    Ad Hoc Naval Architect

    Q.E.D. :eek:

    You can continue to "talk numbers" but it won't alter the facts.


    BTW:
    http://www.straightdope.com/columns/read/1076/is-it-aerodynamically-impossible-for-bumblebees-to-fly

    "...the problem was--a faulty analogy between bees and conventional fixed-wing aircraft. Bees' wings are small relative to their bodies. If an airplane were built the same way, it'd never get off the ground. But bees aren't like airplanes, they're like helicopters. Their wings work on the same principle as helicopter blades--to be precise, "reverse-pitch semirotary helicopter blades," to quote one authority. A moving airfoil, whether it's a helicopter blade or a bee wing, generates a lot more lift than a stationary one...."
     
  7. Scunthorp
    Joined: Dec 2010
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    Scunthorp Hull Tech

    "The real challenge with bees wasn't figuring out the aerodynamics but the mechanics: specifically, how bees can move their wings so fast--roughly 200 beats per second, which is 10 or 20 times the firing rate of the nervous system. The trick apparently is that the bee's wing muscles (thorax muscles, actually) don't expand and contract so much as vibrate, like a rubber band. A nerve impulse comes along and twangs the muscle, much as you might pluck a guitar string, and it vibrates the wing up and down a few times until the next impulse comes along."

    I for one am vibrating

    "You can't change the world
    But you can change the facts
    And when you change the facts
    You change points of view
    If you change points of view
    You may change a vote
    And when you change a vote
    You may change the world"
     
  8. viking north
    Joined: Dec 2010
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    viking north VINLAND

    Thanks TAD, that was the next area i wanted to get into, Center of Balance as it's location plays a role in winward abilities and this with the prismatic coe. number will seal the faith on a decision of what a hull will be most efficient at. I.E. if the CP number is up say 50 or so and the L.C.B. is say midship or even slightly forward of this the hull would suffer windward ability and would be better suited in the motorsailer range rather than say a heavy crusing sailer. Am I correct in my interpretaion of this info?.This is an area i am weak in, i have an understanding of what it is but absolutely no knowledge of how to calculate it on paper thus on my build which was started 12 months ago i rely on the outputs of my designers computer. Getting late here now have to be up in the A.M. and away for a couple of days but will get back to explore this area more. Tnx. Geo.
     
  9. viking north
    Joined: Dec 2010
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    viking north VINLAND

    OPS, was making a small edit of my last post and deleated the entire thing, man thats like cutting a 180deg. wrong angle in an expensive piece of teak. Pressed for time but let me try to re construct, Lets see,Tom the submarine guy, be nice, as an electronics specialist in the RCAF(ARGUS aircraft) we tracked Russian subs. Welcome to the thread and try not to judge what others are thinking, brain processes are like boats and submarines(your project) alike but vastly different. To Daiquiri and Ad Hoc, two reasons re the tight budget, the reality of most people doing conversions or completing abandoned projects,and once the thread build is completed maybe work out the costs(that should be a debate, however having gone thru it several times I have a reasonable idea.) Over the next couple of days Mr.X will get the results of two of the magical numbers, CP and LCB and from these make a decision on what route he will take on his build. The idea of the make believe build (conversion)is that as such it becomes a build condensed in time and challenge to create a reasonable outcome. It would be easy to end the thread at the point where the decision is make on what the conversion will be built into by simply saying ok from here on in treat it as a straight forward build, say a heavy crusing boat, sloop rigged with a full keel, get the following remaining magic numbers from you desidners computer, refer to the following reference books and have fun. However(and i should know better) i would like to expose MR.X, myself and others to a better understanding of the basic engineering involved, not how to calaulate the magic numbers but to have a good grasp of what they mean and to better work within their parameters thus maximizing the build whatever it is. The next magical number LCB, and TAD, has already opened the topic. At this point in time and if my understanding it's location does play a role in windward ability is correct,( it's the old cods head mackerals tail profile comparison,) then it is a factor that should play a role along with CP in determining what a hull is more suite for or if you're dabbling in designing a new boat an important thing to keep in mind. Ok next question,#1 "Longitudional" LCB basically what it represents,(some input already posted but more is better) If calculated before installing a full keel and ballast do we use it as a rought fulcrum/referance point distributing equal amounts of ballast weight fore and aft of it and then once launched hopefully use only a little trim ballast(the truth will be in the pudding) to attain the desired water lines. I know there is a way to calculate this thru something called "moments" but is the statement basically correct as calculations are one thing but doing is another. Have fun gone for two days,Geo.
     
  10. frank smith
    Joined: Oct 2009
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    frank smith Senior Member

    Dose the hull have a water line? Can you level the hull , and take basic measurements ?
    what is the nature of the hull, it basic shape? Collecting data is the first thing I would do .
    Eight stations on the waterline would tell you a lot , and could be loaded into freeships .
    Do you know where the boat was built and used ? Was it registered with a gov. agency, that might have info?

    If you are going to DIY , take a tape measure into the back yard and get on with it. I am sure someone here would be willing to load info int a program for you. it may not be very accurate but would give you some idea of the direction to head in.

    Good luck , Frank
     
  11. gonzo
    Joined: Aug 2002
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    gonzo Senior Member

    Prismatic coefficients and other numbers like that only make sense if you have the knowledge and experience to interpret them. A burdensome hull can have a lower number than a beamy hull with fine ends.
     
  12. Tad
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    Tad Boat Designer

  13. Scunthorp
    Joined: Dec 2010
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    Scunthorp Hull Tech

    "The cubic foot capacity for the 30 ft. lifeboats was 30x9x4x.6 = 684 cubic ft. That means to fill the inside of the lifeboat with 648 cubic ft. of sea water would result in a weight of that water of 648 x 64 = 41,472 lbs. If you took an arbitrary average man as 150 lbs. that would mean that it would require 41472/150 = 276 occupants of 150 lb. weight each to sink a 30 ft. lifeboat" If a 648 cubic ft Lifeboat = 41,472 lbs (= 18.8113 mt) then Lifeboat X would = Xlbs
     
  14. gonzo
    Joined: Aug 2002
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    gonzo Senior Member

    That is wrong. Lifeboats are designed for rough conditions. The boat will swamp with a much lesser load. That is what numbers without understanding the concept to be able to interpret them do.
     

  15. Scunthorp
    Joined: Dec 2010
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    Scunthorp Hull Tech

    ok so what do you get?
     
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