mardi 24 avril 2018

For Sea-Farers ....

I have been looking at a book about "stability and trim", editor William E. George.*

Transverse Metacentric is an imagined but localisable point in the middle of the vertical axis, affecting the radius of a circle segment in which smaller variations of centre of buoyancy occur, around the longitudinal axis.

It is calculated as BM (radius of B, centre of buoyancy, around/below M, Transverse Metacentre) = I/V.

I is calculated in relevance to water plane as Length * Breadth3 / 12, for a rectangular water plane, which Ark arguably had.

Assume 1 cubit = 2 feet.

300 cubits * (50 cubits) 3 / 12 =

600 ft * (100 ft) 3 / 12 = 50 000 000 ft4.

V involves Length, Breadth and Draft, and I assume the latter is 15 cubits = 30 feet.

600*100*30 = 1 800 000 ft3.

Now, I/V = BM = 27.777 ft. Or 27 ft 9' 4".

If Draft was 30 feet, then centre of buoyancy "initial" (before any rolling) would be 15 feet above "keel" (if any), meaning, Height of Transverse Metacentre (KM) is 15 ft + 27 ft 9' 4" = 42 ft 9' and 4".

So much for transverse stability.

Now, longitudinal hull strength ... how do we avoid hull breaks ...

First, how do we not avoid hull breaks? A ship progresses through waves and especially waves that are the length of the ship are a strain on the trim. When waves have crests near two ends of ship, a sagging tendency if there in structure is enforced. When one wave has the crest midship, a hogging tendency is enforced. The periodic enforcing of either a sagging or a hogging one can case a break of hull.

Now, how long were waves in the Flood?

I would imagine, a very typical seascape during the Flood would have been long dunes.

If they were very much longer than 600 feet, like 1200 feet, ark would not have had to deal either with hogging or with sagging, even if progressing through the waves. But more importantly, it was arguably not even doing that. The main motion except rolling would have been swaying - moving with waves and having the length of the Ark confortably between two of them, so moving sideways.

Progress would have sunk the Ark, fortunately there was none.

Indeed, one Swedish dialect would translate progress as "framstega" - and in block letters and ASCII values, that adds up to 666.

But, there was no progress, no surge, for the Ark. No progress, no hull break, no sink.

Hans Georg Lundahl
St Fidelis of Sigmaringen**

PS : I was out, I calculated that total weight of Ark with load when waterline was 15 cubits up was 50,970 metric tons. I took into account that there were three storeys on Ark, and considering foot tons and calculating for even distribution of weight over three storeys, I got it to a centre of gravitation of either 21.37 feet above keel/bottom, if lowest storey count as ten feet up, or if the foot tons are zero because the height is zero, 18 feet above bottom.

I also considered that lifting a ton in pulleys from its resting on floor of one storey to its hanging from its roof, twenty feet higher, ten cubits higher, would add twenty foot tons on that side. Note, with pulleys, even one man can lift a ton, especially if he only needs to lift it one inch.

And this would imply a possibility of leaning a floor (with all "ship", or if it has independent slant from that of whole Ark), when cleaning or food distribution can be facilitated by that.

Supposing the lowest floor counts as ten feet for weight position, and lifting is done at one side between second and third floor, the sides would then have a momentum of 594,150 foot tons on one, and 594,170 foot tons on other side - for all of Ark. Independent movement of a floor would add agility to occasional slanting and a floor could be secured to the side except when this is done./HGL

* Stability and Trim for the Ship's Officer, Third Edition, based on original edition by John La Dage and Lee Van Gemert, Third Edition, ed. by William E. George Cornell Maritime Press, last copyright 1983. ** Sevisii, in Rhaetia, sancti Fidelis a Sigmaringa, Sacerdotis ex Ordine Minorum Capuccinorum et Martyris; qui, illuc ad praedicandam catholicam fidem missus, ibidem, ab haereticis interemptus, martyrium consummavit; et a Benedicto Decimo quarto, Pontifice Maximo, inter sanctos Martyres relatus est.

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