Boatnerd Discussion Forum

[quote="Douglas Bob" post_id=254111 time=1686321662]
Found below at: https://cultofsea.com/ship-construction/shipboard-plate-and-construction-terms-2/

Tank Tops – Tank tops are the covering deck plates over the double bottom structure and are found at the bottom of the ship’s holds. They are often covered by a protective wood shield known as the ‘ceiling’ which has a tendency to protect the plates from heavy duty cargoes being landed either intentionally or accidentally.
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I can add the wooden covering is not common. I have seen this for finished paper products but not every time, it depends on condition of the hold and value of cargo. Certainly any bulk cargo is loaded direct onto the tank tops. Diminution (thinning) of the T/T plates is normal and service life depends on the vessel's trade. More frequent cargo operations will wear the steel faster. 10-15 years is normal service life for a ship engaged in bulk cargos with grabs for discharging. Lower hoppers and stool plates will also wear but to a lesser extent. If the ship carries corrosive cargoes like salt or petcoke and lime washing is not performed well, the wastage rate will increase.

This should answer your questions:

https://www.marineinsight.com/naval-architecture/design-of-ships-bottom-structure/

Found below at: https://cultofsea.com/ship-construction/shipboard-plate-and-construction-terms-2/

Tank Tops – Tank tops are the covering deck plates over the double bottom structure and are found at the bottom of the ship’s holds. They are often covered by a protective wood shield known as the ‘ceiling’ which has a tendency to protect the plates from heavy duty cargoes being landed either intentionally or accidentally.

The tanktops are the tops of the center ballast tanks that contains the keel, keelsons, frame-webbing, etc. Over time, the tank tops can be badly distorted and thinned by repeated unloading at docks that use grab-buckets, the type of cargo the vessel carries (if it's abrasive) and the vessel's original design - such as using light steel to save weight and increase a vessel's carrying capacity.

Depending on the trade, the tanktop and sidetanks may need to be replaced - 25 - 30 year service life was common at one time. It was at that point that some owners would take the opportunity to convert the vessel to a self-unloader as the tanktop and sidetanks would need to be rebuilt in any conversion anyway.

In 1989, the Senneville required major tanktop repairs at Port Weller Drydock and spent the Summer in the graving dock. I recall that the issue she had with her tanktop was discovered at Chicago when a grab bucket put a hold in it while unloading.

Are they he steel sheet separating the cargo hold from a ballast tank directly below?
If so is that just one thick piece of steel or is it a double wall or floor?
If it the floor of the hold I suppose over time it gets beat up and stretched form the weight of the cargo being dumped in.
Tell me about tank tops and cargo hold floors.
Tanks, RCRVRP