The mouth of the Tagus River

[Alexandre]

A peek at the the verification dive done on the reported finding of an iron cannon on the mouth of the Tagus river, Lisbon, Portugal.

The sea fortress you see is the pivotal place of where more than 300 treasure-carrying ships, maily Portuguese and Spanish, have sunk.

 

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[old man]

Alexandre, Great video, thanks for sharing. I was actually more impressed with the fortress. ( I also like History ). Good luck on your dive site. We may not always agree with the Political aspect of Treasure Salvage, but hey that's what makes the world so interesting. ( Different Opinions)

 

[pcolaboy]

Alexandre,

That is AWESOME! Thank you for sharing that.

 

[Salvor6]

Alexandre that is soo cool. I noticed the visibility is not so good. Is it always like that? Are you going to bring up the cannon or leave it "in situ"?

 

[Alexandre]

Alexandre that is soo cool. I noticed the visibility is not so good. Is it always like that? Are you going to bring up the cannon or leave it "in situ"?

We were "downwind" of the low tide, meaning that a lot of that water was from the river.

We are almost certainly going to leave it "in situ". There are a lot of those scattered all along the shore, not really defining any shipwreck site - no other remains associated with the guns, I am afraid.

Old man: that fortress was last used by the Duke of Wellington as his main escape route, in 1810, should the Napoleonic army of Marechal Massena breach the Torre Vedras lines. Some 200 years before, one of many Portuguese Eastindiamen lost in the Tagus was wrecked there: it was the "Pepper Wreck", the Nossa Senhora dos Mártires (1605):

http://nautarch.tamu.edu/shiplab/index-PepperWreck.htm

 

[Salvor6]

We are almost certainly going to leave it "in situ". There are a lot of those scattered all along the shore, not really defining any shipwreck site - no other remains associated with the guns, I am afraid.

Alexandre, that is sooo sad. It would be nice to recover the cannons (all of them) and conserve them and put them on display for everyone to enjoy the history. Eventually they will be consumed and disappear forever if left in the sea. Then, all the information they could tell us will be lost forever. Unfortunately that is the same idea that our ignorant Florida state archaeologists have. They would rather have our cultural heritage rot away forever than have greedy treasure hunters recover it for profit.

 

[Alexandre]

Actually, I pretty much doubt that all those iron guns are going to go away just like that - the ones I have seen in conservation vats have even retained all their inscriptions behind all that concretion gunk they have gained.

And, being left "in situ", they can be visited by all divers. Real wrecksites. Not stuff in a museum, stuff that, by being conservated, would consume time and money and not provide a lot more of archaeological information.

Now, if they are in any way endangered - a pier, dredging, whatever, then we would remove them...

 

[bronzecannons]

We recovered an iron cannon that was at a depth of 100 feet and it was in excellent condition due to this depth. However, if that iron cannon is in shallow water (like others I have seen) then there's a good chance that its highly corroded already.
TW

 

[Alexandre]

And what did you do that cannon? Did it went into conservation?

I am curious to what happened to it if it didn't. I have seen first hand the results of botched salvage attempts by divers on iron cannons and the results, though pretty and nice when you break that gunk (as in your photo), were horrific after the first two weeks...

 

[bronzecannons]

Unfortunately, you are absolutely right, Alexandre, this was a classic example of a botched recovery. We were unprepared to recover it that time and made the stupid mistake of leaving this newly recovered iron cannon out on the deck of the ship and after several days it had corroded so badly that you couldn't even recognize it was a cannon anymore. Till today I really regret that because it was a beautiful specimen of an English 6-pounder iron cannon. Even though I wasn't in charge of that operation, I should have insisted we immediately submerge it in a tank of seawater.
TW

 

[Alexandre]

Yep, that's what usually happens. Iron cannonballs have been known to explode, due to the intensity of the heat released by the oxidation process.

In your case, this could have come in handy:

http://nautarch.tamu.edu/crl/conservationmanual/

 

[Salvor6]

Alexandre I printed out Donnie's entire manual. Its like a bible to me. Good stuff!