Tank Top Deck


Nov 14, 2005
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A simple question I think. And it might fall into the dumb question category. I've read some articles and looked at the prints. The obvious answer would be yes but its not entirely clear to me. Is the tank top deck the actual caps to the ballast and other tanks? Or is there a space between the deck and the tanks? I was wondering that because I was thinking how they did repairs/maintenance on the equipment mounted to the deck such as pumps ect. As in if they had to access the underside of the deck to get to bolts...ect. Or did they just crawl into the tanks to get get to stuff? Mr Halperns article below is a really good read on the deck but if the answer is in there I missed it. Read it twice. Anyway was curious about it.
 
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Nov 14, 2005
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I thought there might be something like that but after thinking about it I don't know. If there were spaces it would reduce the capacity of the tanks. Maybe tank space is more valuable. But thats why I asked. I don't know.
 
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Sec'

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I believe the construction is the same as ships have today. The framing, Hull, and tanktop form the tanks. The pumps, pipework, etc. Is all on top of the tank top. All of those are mounted on frames and stands permanently fixed to the top of the tanktop plates. So there is no need to access the tanks apart from tank inspections
 
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Ok thanks for the reply. Sound right what you said. Was wondering about how they did it because from what I've read over the years there was little to no welding used on the Olypmpic class ships.
 

Sec'

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Ok thanks for the reply. Sound right what you said. Was wondering about how they did it because from what I've read over the years there was little to no welding used on the Olypmpic class ships.
Yes no welding was used, it was fully riveted construction. All of the plates snd frames were riveted, machinery and anything that needed to be removed would then be bolted to them. Hopefully some drawings of crossections through the engine room show this :)
 
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Yes no welding was used, it was fully riveted construction. All of the plates snd frames were riveted, machinery and anything that needed to be removed would then be bolted to them. Hopefully some drawings of crossections through the engine room show this :)
I recently watched a documentary where they stated that minimal welding was used during construction. But I question that because I haven't read or seen that anywhere else. I've never seen a riveted ship. Closest I think I've come to it is maybe the Eiffel Tower. I was impressed on how they built it.
 
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People did not walk directly on the tank top plates for the most part. For example, in the boiler rooms there were stokehold plates that were two feet above the tank top upon which the workers walked on.
Ok thanks. I need to go check as I don't think anybody has gotten that low on the Britannic. But I don't know as I haven't read up on any ROV missions inside her.
 

Stephen Carey

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Pumps are attached to stools or seatings on the tank top - welded these days but probably riveted in 1912. The only part of any machinery that pierces it are the holding down bolts for the main engine(s) and thrust blocks. That's current practice in ships today, so would have been the same then.
I sailed on a 110,000dwt ore carrier where most of the holding down bolts were slack and many were broken. To rectify this meant removing the broken ones (the bolt end had fallen into the double bottom (DB) in way of the cofferdam round the engine (ie it's not a water or oil space, it's supposed to be dry, as there are grommets on the bolts to stop bilge water running into the cofferdam. As so many bolts were broken though, we pumped the bilges by pumping out the cofferdam as the water was running through the slack and broken bolts...
The double bottom on that ship was the standard 3m, with lightening holes to allow passage round the engine bolts, which were 1m+ above your head if you were 1.82 like I was (it was a job for the tallest engineer you had). To replace a bolt you took the new ones into the cofferdam with you (they were heavy, believe me), with a grommet fitted round the bolt head. Standing on the lightening holes meant your feet were around a metre or more above the bottom plating, so astride two lightening holes with the bolt in your arms, you had to proffer it up to the hole - which you could see because your oppo above had a torch shining down it... Once into the hole, your oppo fitted a flat washer and then the nut, as you were sweating like a piglet in a confined space with your arms outstretched holding the thing in place (you made sure the threads were clear and the nut would spin on before you disappeared into the rather claustrophobic space). With some 160 bolts to hold down the engine and with at least 20-30 broken, this was an arduous task undertaken by the 4th engineer (up top) and the 3rd Engineer (me) in the cofferdam.
On completion we went round and flogged up all the loose bolts.
Attached is a sketch of the arrangement where I've marked the cofferdam. You can see where the holding down bolts project into it through the chocking arrangements.
 

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Nice info. Thanks for that. Where I worked we had a lot of mounting pads for pp's, mtr's ect. We always called them skids. Basically identicle to what you described but with slots for alignment. Power plants and ships have a lot of similar systems. Probably why half the maintenance and operating depts were ex-navy.
 

Arun Vajpey

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I sailed on a 110,000dwt ore carrier where most of the holding down bolts were slack and many were broken. To rectify this meant removing the broken ones (the bolt end had fallen into the double bottom (DB) in way of the cofferdam round the engine (ie it's not a water or oil space, it's supposed to be dry, as there are grommets on the bolts to stop bilge water running into the cofferdam. As so many bolts were broken though, we pumped the bilges by pumping out the cofferdam as the water was running through the slack and broken bolts...
The double bottom on that ship was the standard 3m, with lightening holes to allow passage round the engine bolts, which were 1m+ above your head if you were 1.82 like I was (it was a job for the tallest engineer you had). To replace a bolt you took the new ones into the cofferdam with you (they were heavy, believe me), with a grommet fitted round the bolt head. Standing on the lightening holes meant your feet were around a metre or more above the bottom plating, so astride two lightening holes with the bolt in your arms, you had to proffer it up to the hole - which you could see because your oppo above had a torch shining down it... Once into the hole, your oppo fitted a flat washer and then the nut, as you were sweating like a piglet in a confined space with your arms outstretched holding the thing in place (you made sure the threads were clear and the nut would spin on before you disappeared into the rather claustrophobic space). With some 160 bolts to hold down the engine and with at least 20-30 broken, this was an arduous task undertaken by the 4th engineer (up top) and the 3rd Engineer (me) in the cofferdam.
That sounds quite physically demanding but I was even more nervous thinking of working in narrow, confined spaces. Was there any danger of becoming trapped or something?
 

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