Unmanned stability

Discussion in 'Stability' started by john.burnett, Sep 30, 2009.

  1. oralpiskin
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    oralpiskin Junior Member

    hi everybody
    ı am a ship engineering student and trying to learn about submarine design so ı need a useful document containing informations about stability and hydrostatic calculations for submarines because ı don't have any computer program. ıf there is one will help me in this subject ı will be pleased...
     
  2. Ad Hoc
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    Ad Hoc Naval Architect

    Try:
    "Dynamics of Marine Vehicles" by R. Bhattacharayya
    or
    "Mechanics of Marine Vehicles" by Clayton & Bishop
    or
    "Hydrodynamics of Ship Design - part III" Saunders, SNAME publication

    These do a reasonable over view.
     
  3. oralpiskin
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    oralpiskin Junior Member

    thanks for answer but do these books contain about submarines or under water vehicles?
     
  4. Ad Hoc
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    Ad Hoc Naval Architect

    They cover all...but have either chapters or subchapters related specifically to submarines.
    I've just grabbed them off my bookshelf, (big bulky books), to check..and yes, these cover all the basics and a bit more...so yes, these cover all and will suffice, for you.
     
  5. oralpiskin
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    oralpiskin Junior Member

    thanks gratefully...
     
  6. karabacak
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    karabacak Junior Member

    Ma huseyin from turkey and ma get some problem about designing submerged vehicle forms You know some software that can help me optimizing & analiyzing about ma ma project body. I need it as soon as possible because I do not have much time about my project.
     
  7. oralpiskin
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    oralpiskin Junior Member

    dear Ad Hoc,
    I couldn't find books you proposed cause our library is not enough, do u have any file you may share and if anyone has these infos ı will wait for documents...
     
  8. ancient kayaker
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    ancient kayaker aka Terry Haines

    -see, guys, I told ya we were scaring off people ...

    Stability (righting moment) is roughly proportional to the cube of the beam and is proportional to the length, for the same draft. That’s not all, obviously displacement is also effected, so if that is kept the same the ratios aren’t exactly as above, nonetheless you have reduced the stability by almost 2/3. This a completely different boat now.

    Because the displacement at the original draft is also reduced, but the load is not, it is a few inches lower in the water. It looks like you did not increase rocker, or bottom curvature, to raise the transom. This likely causes the bottom edge of the transom to be immersed. If this is the case, then as it moves through the water there will be turbulence, causing drag and noise, which you may have noticed.

    I estimate from the rigged photo that you have about 105 sq ft of sail area. That would suit the original design. However, the ability to bear sail varies as the 2.5 power of linear dimension; so it should also be scaled down to around 60 sq ft for your boat.

    Sailing canoes can carry a lot of sail area, up to 100 sq ft on a beam of around 3 ft or so but are usually 15 ft long or more and we are talking of a race boat here, weight kept low in the water and athletic sailor to boot; much less for a typical canoe, more like 50 sq ft.


    You should definitely be careful sailing this boat in its present state, especially if you are an inexperienced sailor. I would suggest you reduce the size of the sail, and you should always wear a lifejacket! A lighter mast might help, it looks more rugged than usual, but the rig you have is fairly low. I would not add ballast unless you have enough built-in buoyancy, and I don't see any in the photos. if it feels tippy, and it might, you can strap some plastic foam pool noodles a few inches above the waterline.
     
  9. messabout
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    messabout Senior Member

    AK has told it like it is. One of the ways that you might lessen the tiddly tendency is to lose the lug rig. The yard is a serious liability on a skinny boat. To a lesser extent the crash boat style outwales on your boat are kinda' big. Even that small amount of extra weight will contribute to the stability problem. It does have a rudder assembly that is probably overkill.

    AK has mentioned that the stability is roughly proportional to the cube of the beam. We are talking about the beam at the chines in this case. Be careful to note that it is a proportion. Example: compare 40 inch chine width with 48 inch chine width. The cubes of those numbers have a proportion of about 1,74 and sure enough the righting moment of the 48 inch one will be about 1.74 times that of the 40 inch one. You should not bet your life on a simple rule of thumb like this but it is a useful concept that can help the decision making process in the design stage.
     
  10. Ad Hoc
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    Ad Hoc Naval Architect

    oralpiskin
    If you ask your library, they should be able to get them for you, loaned from another library. (Well, that is how most libraries work).
    Other than that, you could buy one of those books? I have all of them, not cheap. But if you become a qualified professional naval architect, they are very good reference books which you shall use throughout your career, as such, a worthwhile investment.
    There is far too much to scan in...would take many many hours
     
  11. oralpiskin
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    oralpiskin Junior Member

    Ad Hoc,
    thanks for your suggestions, I will find....
     
  12. karabacak
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    karabacak Junior Member

    Ad Hoc
    but it is not the way libraries in Turkey
     
  13. yipster
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    yipster designer

    you may try your luck in university, some, like here in holland that have NA, have some hard to get books that they do not loan out in their library but you can read at their library for a small fee
     

  14. JLIMA
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    JLIMA crazed throttleman

    I agree with the fact that your mast is over robust and could be lightened considerably by just using a much smaller diameter mast. I got away with using a 10' 1by as a mast on an 9' gaff rigged cat and it never gave out or gave me any trouble as long as i had the boat.
     
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