16th-18th Century Cargo Vessels and Draft

[LM]

What was the displacement (in feet) on your typical late 16th to early 18th century wooden cargo vessel when loaded?

 

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[Salvor6]

12 to 18 feet depending on the size of the vessel.

 

[aquanut]

12 to 18 feet depending on the size of the vessel.

Correctomundo.

 

[LM]

Wowza! Bigtime.

So, a ship with an 18' displacement caught in a hurricane with a 10' surge could conceivably be carried into a depth of 8 surge-adjusted feet before it started bottoming out and breaking up? And in calm weather without the surge, that depth might be waist deep?

I have the History Channel DVD of 'Search For The Atocha'. On that, they talked about a big pile of silver bars (from the main pile, IIRC) and how they were found in essentially in the same location where they sunk (a large section of the Atochas planking was actually preserved beneath them), however, smaller items would obviously be scattered to wherever with each passing storm, etc.

Presuming you know where a vessel went down and any number of years have passed since that time without recovery, how wide is the 'target zone' for artifacts?

 

[mad4wrecks]

So, a ship with an 18' displacement caught in a hurricane with a 10' surge could conceivably be carried into a depth of 8 surge-adjusted feet before it started bottoming out and breaking up?

Conceivably, yes. But keep in mind, while there may be 10 foot waves or surge, there are corresponding troughs of the same height. So that ship with an 18' draft could also strike bottom on the top of a reef at 28'.

Tom

 

[Salvor6]

A tidal surge during a hurricane is different than the wave height. There is a dome of water raised up by the low pressure around the eye of the hurricane. The "target zone" of artifacts can be scattered for miles depending on where the vessel wrecked, high energy surf zone vs deep water. The Atocha was hit by a second hurricane which broke the vessel up. They are still finding artifacts 8 miles from the main ballast pile!

 

[LM]

Yeah, I'm talking tidal surge, not wave amplitude.

In recalling storms I've seen first-hand and how they turned out, it was pretty amazing, the number of boats (Shrimp Boats, pleasure boats, etc) that got deposited pretty far inland. I'm trying to think through the mechanics involved with a boat displacing 15' and how it would fare if it were forced inward towards shore in an area like the upper East Coast of FL.

It's not hard to imagine them breaking up in regions that, absent the tidal surge, wouldn't even be that deep, particularly from Cedar Key south to Tampa where you encounter large stretches of shallows pretty far out from the coastline itself (see noaa 11407 for a decent example). These would be very 'marginal' places for a heavy draft vessel being piloted by a Captain unfamiliar with the area even in the best of conditions. It probably wouldn't have taken much to push them from smooth sailing to stuck and breaking up... When you factor in storms and catastrophic losses of navigational control, well, interesting stuff.

 

[mad4wrecks]

I'm trying to think through the mechanics involved with a boat displacing 15' and how it would fare if it were forced inward towards shore in an area like the upper East Coast of FL.


Well stop thinking tidal surge and start thinking wave amplitude.

Those shrimp boats you refer to that were washed inland were sitting anchored when the surge washed them inland.

A ship sailing at sea in a hurricane is affected by wind, current and wave size, not storm surge. If that wasn't the case, the many galleon wrecks on the east coast of Florida would all be up on the beach (though several did end up there) or in the Indian River lagoon, and not offshore in 15 to 22 feet of water, where most of them are.

But hey, what do I know about east coast shipwrecks?

 

[LM]

A ship sailing at sea in a hurricane is affected by wind, current and wave size, not storm surge. If that wasn't the case, the many galleon wrecks on the east coast of Florida would all be up on the beach (though several did end up there) or in the Indian River lagoon, and not offshore in 15 to 22 feet of water, where most of them are.

But hey, what do I know about east coast shipwrecks?

There's no doubt you're immeasurably more knowledgeable about diving on shipwrecks than I am, but I'm having a hard time resolving how the ocean magically rising 10 feet doesn't impact the ultimate placement of a wrecked ship when the water recedes back down.

A lot of wrecks *did* get washed completely ashore. Uncovered remnants of very old wrecks have been found on beaches many times. Those probably wouldn't be much interest to us, though, since there wouldn't be much left worth recovering... Presumably, the wave action broke some up in deep water, too. Maybe the underwater terrain in Indian River Lagoon dictates that the 'sweet spot' for galleon wrecks is 15-22 feet, but couldn't we assume that in areas with different underwater terrain, the depth upon which these wrecks broke up would be different, too? And wouldn't the ocean rising 10 feet, carrying the ship inland, then receding play a role in that, even with the wave action on top of it?