Weight capacity of new design

Discussion in 'Boat Design' started by Ron Skelly, Feb 25, 2014.

  1. PAR
    Joined: Nov 2003
    Posts: 19,133
    Likes: 473, Points: 93, Legacy Rep: 3967
    Location: Eustis, FL

    PAR Yacht Designer/Builder

    Ron, there's some physics involved you're just not getting (no offense intended). When working with materials to scale, it's usually best to work with common scales. For example 1/16" plywood is available, so at 1/4" scale, it's the same physical dimension as 1/4" plywood, but a 12"x24" sheet (a 1/4 scale of a 4'x8' sheet) doesn't have quite the same physical properties (bending, modulus, weight, etc.), plus the seeming conundrum of "mechanical similitude". It would be wise to read up on mechanical similitude, before continuing. In fact, it's the physics of mechanical similitude that cause small RC yachts to look so distorted, in regard to rudder, sail and appendage area, beam/length ratios, power to weight, etc., etc., etc.
     
  2. Ron Skelly
    Joined: Nov 2009
    Posts: 56
    Likes: 1, Points: 0, Legacy Rep: 23
    Location: Wasaga Beach

    Ron Skelly RonS

    I am reading up on this - thank you.
     
  3. rwatson
    Joined: Aug 2007
    Posts: 5,852
    Likes: 290, Points: 83, Legacy Rep: 1749
    Location: Tasmania,Australia

    rwatson Senior Member

    No - its not that straightforward.

    edit:
    PS - your 1 kilogram model at 1:10 scale, has a full size weight equivalent of 1000 kilos. 1 * ( 10*10*10)
    See the problem if the full size boat should only weigh 100 kilos.




    If you understood the formula I posted, the proportions are a Power of magnitude - ie. Cubed.

    For 1:5 scale -

    Weight of the model is Fullsize divided by 5*5*5

    Weight of the Fullsize is Model multiplied by 5*5*5

    For 1:10 scale - ( edited from 1:5 - trying to type too fast )

    Weight of the model is Fullsize divided by 10*10*10

    Weight of the full scale is Model multiplied by 10*10*10



    Its the same function when you calculate the volume of a pool 5 x 3 x 2.
    edited : a bit fuller explanation - 5 x 3 = 15, But then you have to have two lots of that to calculate the full volume of 30.




    Now, following on from Pars comments, take a sheet of plywood

    1200 mm x 2400 mm x 12 mm = 32 kilos


    If your boat used 3 sheets of plywood, it would weigh about 90 kilos.

    So a model of 1:10 scale, you could use 3 sheets of 120 x 240 mm . They would have to weigh ( 90/(10*10*10) = 9 grams ( 1/3rd Oz ) to match the scale weight. Almost tissue paper.

    At 1:5 scale, the weight equivalent = (90 / ( 5*5*5) ) or 72 grams ( just over an oz ), which is far easier to achieve without falling apart.

    PS - if you want to play with the math, dont go mad with pounds and ozs. The metric system is worth learning.
     
    Last edited: Mar 3, 2014
  4. PAR
    Joined: Nov 2003
    Posts: 19,133
    Likes: 473, Points: 93, Legacy Rep: 3967
    Location: Eustis, FL

    PAR Yacht Designer/Builder

    Simply put Ron, there's a fair bit more then meets the eye, when designing a boat. It's not hard really, only high school math and some understanding of general engineering principles, but the hydrodynamic stuff can take a long time if you're trying to "wing it" as you go. This assumes you'd like a boat with reasonably optimized hull forms, to suit your SOR criteria.

    You could save a lot of bother learning, head scratching and potential redo's and failure, with a set of plans. Pontoon boat (if you must) plans abound, from very simple plywood boxes to quite fancy asymmetric cat like hulls and everything in between.

    [​IMG]

    A set of "Huck Fin" "toons" being assembled. These can be built in 12' to 28' lengths. Of course these are designed for full plane mode boats, but displacement speed toons are also available too.
     
  5. rwatson
    Joined: Aug 2007
    Posts: 5,852
    Likes: 290, Points: 83, Legacy Rep: 1749
    Location: Tasmania,Australia

    rwatson Senior Member

    But I am sure Par would join in with me and encourage you to enjoy the challenge of learning, and the fun in discovering the principles.

    Our caution is over you being severely disappointed with the time/money of embarking on a quite complex task - when you can 'get there' with proven, workable designs without major dramas.

    Keep up the research.
     
  6. PAR
    Joined: Nov 2003
    Posts: 19,133
    Likes: 473, Points: 93, Legacy Rep: 3967
    Location: Eustis, FL

    PAR Yacht Designer/Builder

    Agreed, we've "brought along" a number of budding designers, but learning "on the fly" is difficult and time consuming. This reminds me of an email reply I need to make, about another forum member's latest set of "harebrained" ideas.

    Given the very basic nature of your questions thus far Ron, taking the plans route, at least on this project, will get you there much quicker. You'll need the time to work up the necessary understanding across several subjects anyway, so it might as well be puttering along on something you built, with visions of the next greatest project, possibly of your own design.
     
  7. Fanie
    Joined: Oct 2007
    Posts: 4,603
    Likes: 170, Points: 63, Legacy Rep: 2484
    Location: Colonial "Sick Africa"

    Fanie Fanie

    Ron, these two are lying through their teeth ! Designing boats is HELL ! It NEVER works the way you think and those that say so lie also.

    It is ALWAYS any amount of times more expensive, a LOT more work, takes years longer and and and. Murphy was an amateur at problems.

    Furthermore, boat building is seriously addictive - it NEVER ends with one or two or three or four or five or... "Boats are like rabbits; you can have one boat or many, but you can't stop at two" - A. Onassis

    I've had serious marriage problems because every time I only talk, note, ONLY TALK, about another boat the wife wants to know how many more boats do I plan to get, and she does't fall for the Noah story any more.

    Get out while you can mate ! Don't get sucked in !!!

    The rest of us are stuck here forever...
     
  8. rwatson
    Joined: Aug 2007
    Posts: 5,852
    Likes: 290, Points: 83, Legacy Rep: 1749
    Location: Tasmania,Australia

    rwatson Senior Member

    Hahahaha ... you sound like my ol' mate PDW, nearing completion of his 30+ foot steel yacht.

    "I am very happy to advise new boatbuilders - and the best advice is one word. .... DONT !!!!"

    Fanie may sound like on old, deluded curmudgeon - but dont let that fool you. He is being overly optimistic, and has no place offering such enthusiastic encouragement. Shame on you Fanie :p
     
  9. Fanie
    Joined: Oct 2007
    Posts: 4,603
    Likes: 170, Points: 63, Legacy Rep: 2484
    Location: Colonial "Sick Africa"

    Fanie Fanie

    "Go for it" in boating actually means "lets see if you have what it takes".

    I think the most difficult thing for humans to do is think. No, not think the way you think you think, I mean really think. Boating can do that to you, once, maybe twice in a lifetime it gets someone to think. Almost like landing in some death defying moment where you have to come up with a brilliant solution or it's tickets. Since we apparently use only like 6% of our brain capacity, what is the rest there for ?
    LOL, boat building of course :D or shall I say, I think so.
     
  10. Fanie
    Joined: Oct 2007
    Posts: 4,603
    Likes: 170, Points: 63, Legacy Rep: 2484
    Location: Colonial "Sick Africa"

    Fanie Fanie

    It's a matter of fitting a sophisticated physical shape into a part hydraulic, part pneumatic environment, subject to gravity, temperature, humidity, weather, wind, seasons, day or night, and of which it's existence and performance depends on mechanical interaction with all the above, all depending on your skill, - or lack of it. Least of all is the measurements and values are either US, the damn Brits or metric. That's just the obvious - add electrical power, radio's, satellites and anything else you can think of.

    This all you mix, add catalyst, cure and see what comers out.

    If it doesn't look good you start again with changed ratio's.
     

  11. rwatson
    Joined: Aug 2007
    Posts: 5,852
    Likes: 290, Points: 83, Legacy Rep: 1749
    Location: Tasmania,Australia

    rwatson Senior Member

    Great summary of boats.

    That old myth 'we only use x% of our brain for thinking' is a misquote of something Albert Einstein was credited with, but its incorrect. Brain scans show we use every bit of our grey matter - but not equally at the same time. Anyone who build boats knows its a whole brain effort ;)

    And of course - there's the alcohol damaged bits .... :rolleyes:
     
Loading...
Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.