Re: [bolger]over ANALysis of Calculating Buoyancy
In a message dated 5/13/01 11:39:37 PM Central Daylight Time,
rocwandrer@... writes:
rocwandrer@... writes:
hows that for easy, now, if you take the good advice from Bill, you will
plan to use twice the number of barrels needed to support the weight you
plan to put on the dock......
Richard <----- picked on Bill :-)
There is need of a new "Bolger Rule": "Don't make fun of the handicapped."
:-)!
Granted, determining the displacement of a one-half submerged, horizontally
disposed cylinder is as trivial an exercise as calculating that of a fully
submerged one. Anyway, there are situations where a semi-submerged cylinder
or its equivalent may make sense, although a small private dock is probably
not one of them. The "surface-piercing" catamarrans used as an inter-island
ferry between a couple of islands in the West Indies being one example. These
reduce the "bounce" that would otherwise be caused by wave action because of
their lack of increased bouyancy per depth of immersion compared to a
conventional hull, or hulls. The 1970's vintage "FLIP" ship was an extreme
example of this principle. It is not inconceivable that a floating dock
might be constucted on similar principles.
Bill (how could I be ANAL(y) retentive when I poop regularly?) in MN
um, it is just a dock.....docks bounce. :-) less bouncing will result
if you figure to use half of the max load rating of your dock as the
average "in use" loading. what this guy is probably saying is that you
might not want to submerge the barrels more than half way to avoid
bouncing......
i am sure your question was already answered, but here it is
3.14 (3.141592654 <---- for Bill Page?) anyway
use feet for units
(3.14) x (half the diameter of the barrel) x (half the diameter of the
barrel) x (the height (or length if it is lying down)) x (about 62) =
(lbs of bouancy)
hows that for easy, now, if you take the good advice from Bill, you will
plan to use twice the number of barrels needed to support the weight you
plan to put on the dock......
Richard <----- picked on Bill :-)
wmrpage@...wrote:
To invent, you need a good imagination and a pile of junk. --Thomas
Edison
if you figure to use half of the max load rating of your dock as the
average "in use" loading. what this guy is probably saying is that you
might not want to submerge the barrels more than half way to avoid
bouncing......
i am sure your question was already answered, but here it is
3.14 (3.141592654 <---- for Bill Page?) anyway
use feet for units
(3.14) x (half the diameter of the barrel) x (half the diameter of the
barrel) x (the height (or length if it is lying down)) x (about 62) =
(lbs of bouancy)
hows that for easy, now, if you take the good advice from Bill, you will
plan to use twice the number of barrels needed to support the weight you
plan to put on the dock......
Richard <----- picked on Bill :-)
wmrpage@...wrote:
> In a message dated 5/12/01 4:33:32 PM Central Daylight Time,[Click Here!]
>j.c.ewing@...writes:
>
>
>
>> I want to calculate how much dock weight I can support by floating
>> plastic
>> drums, 1.75' dia. by 2.66' long/high.
>
> This is not a trivial question. Calculating the displacement of an
> immersed
> cylinder is a trivial problem, as someone will probably point out.
> Your
> problem is not so simple.
>
> I think that as far as mathematics are concerned, you need to be able
> to
> calculate the areas of the portions of a circle circumscribed by
> chords and
> arcs, where the chords are parallel to the waterlines of the
> (partially)
> immersed float and the arcs described by the immersed diameter. This
> is
> probably a trivial exercise to a numerate human, but I don't know that
> I
> would be able to figure it out. The computational methods used to
> determine
> the displacement of vessels from plans would certainly suffice, but
> with so
> simple a shape as a cylinder there is certainly a simpler mathematical
>
> solution.
>
> You have an engineering design issue here, not just a mathematical
> problem.
> I think the issue can be more precisely stated as: "How do I achieve a
>
> tolerable level of vertical movement of the structure for a given
> load?" As
> you have not specified your tolerance for vertical movement, nor the
> maximum
> load, I don't think there is any simple answer to be derived from any
> mathematical formula.
>
> Any floating drum is going to sink until the weight of displaced water
> equals
> the supported weight, or sink until it strikes bottom or implodes.
> Since you
> do not want your dock to sink, and you want walk along it dry-shod,
> the
> relevant inquiry is probably the increase in displacement per unit of
> vertical movement that will keep your platform at the desired minimum
> height
> above water when subjected to the maximum load.
>
> If the drums are to be conventionally mounted under the dock, with
> their long
> axis' (axes?) parallel to the waterline, you face an interesting
> phenomena.
> As long as the waterline is below the diameter of the drum parallel to
> the
> waterline, each increment of immersion reflects progressively greater
> displacement of water, or conversely, each increment of weight results
> in
> less vertical movement. Once the waterline passes that diameter, the
> opposite
> result would obtain, with probably undesirable results.
>
> In the unlikely event that you plan to mount the drums with their long
> axis'
> (axes?) vertical, the familiar "Pi x R^2 x L" formula will give a
> displacement per unit of vertical position solution which even an
> innumerate
> such as I could calculate, but that does not address the practical
> engineering considerations your question raises.
>
> If I were in your shoes, I would look to the empirical experience of
> my
> neighbors and adjust my plans accordingly, as local conditions and
> expectations probably have been and will continue to be adapted to a
> host of
> empirical factors, not readibly reducible to mathematical resolution.
> Failing
> that, I would use 1/2 the immersed displacement of the drums, reduced
> by a
> very substantial "fudge factor", to allow for the density of the
> drums, the
> weight of the supporting structure, marine growth, imprecision in
> estimating
> the "live" loads, and other "factors of ignorance".
>
> I am curious about the source of your "drums". Would you care to share
> with
> us what your source is (after you secure an adequate supply for your
> purposes, of course)
>
> Ciao for Niao,
>
> Bill in MN,
>
> contemplating whether he can calculate the area between a chord and a
> circle
>
>
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To invent, you need a good imagination and a pile of junk. --Thomas
Edison