Way down man - Davey Jones

A ship "displaces" a volume of water. I beleive that this displacement is how ships are size rated, in tons. You would need to overcome this displacement, assumably with the weight of water, for the ship to lose it's buoyancy. If the ship is "water tight" as it would be in a storm, I think it would be difficult for the deck to hold enough water to offset the bouyancy of the ship. I would imagine that this would be taken in to account in the design. Although, in a storm, I would assume that even getting close to matching the displacement of your boat could be quite detrimental.

Simply put, a ships' structure is designed with the considerations of supporting the vessels' structure (primarily longitudinally) by the buoyancy of the water it displaces. Most all ships are quite flexible and that is also taken into account in design, but as with most all steel structures, there are limits to that flexibility which must be maintained to prevent over working and failure. This is most important in the loading and ballasting of the vessel.

In the understanding that a vessels keel is designed longitudinally straight, there are two conditions of deviation to that straightness. If the vessel (relative to the keel and draft marks) is concave downwards it is in a state of 'HOG' (banana with two ends down); if it is concave upwards it is in a state of 'SAG' (banana with two ends up). These conditions can be a result of construction, loading and or dynamic flexing while in seas and or underway.

Certain sea conditions coupled with loading conditions will cause significant HOG and SAG underway. This is dependent on the length of the vessel and the moment (distance of peak wave to peak wave) of the seas. Hence, you can have a condition where a ship is supported at both ends with little or no support amidships, or support amidships with no support fore and aft. Either of these conditions in the extreme (and considering vessel loading) can cause a ship to break in half. It has been a well documented occurrence.

In the case that you ask about, a ship would not drive itself under, rather it would drive itself in and be forced upwards by buoyancy and likely break up in the extreme.

That is what happenned to the Edmund Fitzgerald!

There are still several theories about the Fitzgerald. The most likely, in my opinion, is that she hit bottom at 6 fathom shoal, which later was found to be a little less than 6 fathoms deep, and took on water as a result. Her navigation radar was out and her course took her very close to the shoal.

Dear Mareng,

Your explanation was very concise and accurate, I would add only that : in the majority of cases of ships hulls failures and/ or sinking, these come from shifting of cargo. This generally exacerbate the dangers of heavy seas and stresses on the sructures of the hull. These effects are almost impossible to forecast in the design or stability calculations

"In the case that you ask about, a ship would not drive itself under, rather it would drive itself in and be forced upwards by buoyancy and likely break up in the extreme."

Agree with you Mareng, this is born out by the damage to ships such as the Benchruacan that experienced a freak wave off Durban, her forward section was bent downward by about 15 degrees. I may not have the name right, but there was a "Neptune Sapphire" I think she was called that had her entire fore-peak ripped off under similar circumstances, also off the East coast of South Africa.

Many other documented cases exist - Edinburgh Castle amongst others. All survived but suffered severe damage to the forward section due to the upward force of the ships buoyancy and the downward force of the mass of water.

Which Endinburgh Castle and when, I sailed on her in the early '70s?

Davah,

I think her encounter with this wave phenomenon was in 1962, so the same ship that you sailed in.

Thanks. I did the last trip before she went to scrap. Also the Pendennis, Oranje, Windsor, nice ships all.