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Old 8th June 2016, 11:49   #121
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Default Re: Calling all TBHP Sailors - Post your maritime pics here !

Some more from the duffel bag -
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Old 16th June 2016, 10:49   #122
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Default Re: Calling all TBHP Sailors - Post your maritime pics here !

Why this sudden quiet on the thread? I was hoping for more of our sailing members to come up with their captures -
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Old 16th June 2016, 14:33   #123
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Default Re: Calling all TBHP Sailors - Post your maritime pics here !

Hi Shashanka,

I guess its a rather old thread - hence the lower participation at the moment. Hope it picks up again!


Regarding the anchor handling:
1) How common is it to need multiple attempts?
2) What causes the failure of the anchor hauling?
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Old 21st September 2016, 17:05   #124
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Got a chance to go for a 'ship launch' this Sunday

Calling all TBHP Sailors - Post your maritime pics here !-1-pano_20160917_105911.jpg


A battleship called the MORMUGAO, at the Mazgaon docks.

The date was chosen for good reason: A high tide of 4.67 meters would be unmatched until April 2017.

The next ship launch like this at MDL would only be after 2yrs.

Mormugao was scheduled to slide down the slipway at 1158 hrs.

The Navy had permission for a helicopter to hover for 1 minute, taking video footage of the launch, so timing was critical too.

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Anyone know why those silver pieces are present on the fins?
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We were in our seats by 1030hrs, and the supports holding up the ship were being periodically removed (and interestingly, the patches that were under the supports were being given a quick last minute anti-rust patch up job).

The supports themselves were interesting. They were propped up on containers of sand. To remove the support, a small flap at the bottom of the sandbox was opened, and the sand poured out. This lowered the part on top of the sandbox that was in contact with the ship, releasing the support.

In this (pretty bad) photo, you can see the sand-box (the black box with the white text on it) as it is being drained. The support shown is currently still pressed up against the hull:
Calling all TBHP Sailors - Post your maritime pics here !-5-img_20160917_114432.jpg

Finally, there were only 4 supports left holding the ship in place. All 4 were button-controlled solenoids, and at 1158, with the press of a button, the ship quietly and smoothly slid down towards the sea, gaining speed before it finally touched the ocean for the first time.

There she goes...



But that's not it.

The ship isn't much more than a hull at the moment! It doesn't even have it's own turbines, or even a rudder. Further testing and fittings will continue for a while, until the ship is finally ready to be handed over to the Navy in 2018~2020.

You can see that she has to be moved around by tug-boats:
Calling all TBHP Sailors - Post your maritime pics here !-6-img_20160917_120548.jpg

Another ship in the dry docks. Looks pretty stealth!
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The following 2 pictures are from IndiaTimes.com
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Last edited by Rehaan : 21st September 2016 at 17:20.
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Old 9th May 2017, 13:17   #125
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Default Re: Calling all TBHP Sailors - Post your maritime pics here !

Quote:
Originally Posted by Rehaan View Post
Hi Shashanka,

I guess its a rather old thread - hence the lower participation at the moment. Hope it picks up again!
Regarding the anchor handling:
1) How common is it to need multiple attempts?
2) What causes the failure of the anchor hauling?
Hello Rehaan - sorry for the l---o---n---g silence on my part! I guess you know the reason why, so I'll not dwell on it!

About the anchor handling operations on OSVs, its a pain at the best of times and a genuine nightmare if the weather picks up to any extent! This is why anchor handling in the Indian Ocean is restricted to the non-monsoon season. And why there are dedicated and skilled masters (captains) specialising in this operation and only these masters are usually sent on the anchor handling vessels. It is principally the masters job (not the C/E's, thank God) & the C/E must give precise & instant response to the master's orders on the commands on the anchor handling winches. It is a very delicate balancing of forces - the motion of the sea & the vessel, the tension on the anchor handling cable & most importantly ensuring that the anchor's flukes dont get entangled somewhere around the aft drum and that the flukes land on the deck in the perfect orientation for hauling up on deck. It is common for the anchor to be released back into the sea because it did not land on deck in the correct orientation, but flopped on to one side or the other! My description does not do justice to the high anxiety of those moments (injuries and even death to crew members are not uncommon)! I really wish we have an anchor-handling master among the members on this forum - he would be able to convey the finer nuances of the operation far better than a hammer & chisel engineer! But I hope I have been able to give a sense of the excitement & anxiety the operation calls for.
Regards,
Shashanka

Last edited by shashanka : 9th May 2017 at 13:26.
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Old 9th May 2017, 15:46   #126
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Default Re: Calling all TBHP Sailors - Post your maritime pics here !

Will add some pics soon.
The thing with this thread is the usual problem with sailors.
Being away for long and then coming back and trying to catch up on everything.
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Old 11th May 2017, 09:22   #127
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Quote:
Originally Posted by Rehaan View Post
Anyone know why those silver pieces are present on the fins?
R, those are the sacrifcial anodes which are used for preventing corrosion. The extremely corrosive sea water acts as an electrolyte and will eat way the ship's hull which is made of mild steel. So this piece of metal which is made of Zinc or Aluminium will sacrifice itself first before affecting the hull. Thus the name sacrificial anode.

Btw, this particular long flat metal plate is called a bilge keel which aids in preventing rolling of the ship by improving the hydrodynamic resistance.

PS: Will let you know when we launch our Coast Guard OPVs (there are seven of them) and a floating dock for the IN. You can have a look at a different kind of launching which uses a ship-lift.
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Old 11th May 2017, 12:09   #128
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Originally Posted by Gannu_1 View Post
R, those are the sacrifcial anodes which are used for preventing corrosion. The extremely corrosive sea water acts as an electrolyte and will eat way the ship's hull which is made of mild steel. So this piece of metal which is made of Zinc or Aluminium will sacrifice itself first before affecting the hull. Thus the name sacrificial anode.
Very interesting, thanks!

However - how does it work? How will having a zinc/aluminum anode there help prevent corrosion on the whole hull?

Or do they just make a very minimal difference?
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Old 11th May 2017, 12:25   #129
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Very interesting, thanks!

However - how does it work? How will having a zinc/aluminum anode there help prevent corrosion on the whole hull?
The quantity of the anodes to be welded onto the ship's hull are determined using a calculation using the life of the anodes, material of anode (Zn, Al) etc.

As to why Zn or Al is used, there's something known as the electropotential series which lists down the order of the materials in terms of reactivity. In this list, steel comes above zinc and aluminium. i.e zinc and aluminium are more prone to corrosion (they become the anode) than mild steel (becomes the cathode) when they both come in contact with sea water (which is the electrolyte) thereby consuming the anodes first. During the course of the ship's voyage, these anodes get worn out and have to be replaced from time to time when the ship gets dry docked to repairs and under-water hull painting.

Quote:
Originally Posted by Rehaan View Post
Or do they just make a very minimal difference?
Oh no, they do make a difference. Of course, this is what we call passive protection. There's also an active protection for the ship's hull also known as the ICCP or Impressed Current Cathodic Protection wherein the system is connected to a DC supply.
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Old 2nd August 2017, 06:44   #130
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The corrosion of the hull is due to the presence of dissimilar metals in an electrolyte like in a battery.
Presence of a propeller made of an alloy based on bronze (Bronze, nickel, aluminium) around a steel hull in sea water makes for all the ingredients for flow of electric current. This type of corrosion is called galvanic corrosion and as Gannu mentioned the series is also called as galvanic series (or electro-potential series).
All the metals which are lower in the series loose ions to the ones higher in the series, means they corrode. Gold, silver, copper, brass, titanium etc are higher in the galvanic series so steel corrodes in the presence of these metals. As zinc is below steel it is used as sacrificial anode to protect the hull.
The sacrificial anodes are usually fitted only to the aft and forward section of the hull of a cargo ship, placement can be different based on the presence of dissimilar metals around the hull. It protects only the areas closer to dissimilar metals. A rudder made or steel has its own sacrificial anodes fitted on to it due to its close proximity to the propeller.
The ICCP (impressed current cathodic protection) system is based on DC current which is used to generate ions which do not let the hull to generate ions from its surface.
The problem posed by this galvanic process is that the current flows through the sea water to the propeller and back to the hull through the bearings, which causes pitting corrosion on the bearings. To prevent this the propeller shaft has a shaft earthing device (grounding) based on carbon brushes slipping on a steel ring attached to the shaft.

A galvanic series can be found on the web by typing the text on any search engine.

Hope that clarifies how the whole system works.

Regards
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Old 31st August 2017, 00:44   #131
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The corrosion of the hull ............Hope that clarifies how the whole system works.
Regards
+1 Brumby - That was very well and succinctly put! I was still struggling to compose a comprehensive reply! Very happy & relieved that one of the forum members has done the needful.
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Old 31st August 2017, 09:48   #132
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+1 Brumby - That was very well and succinctly put! I was still struggling to compose a comprehensive reply! Very happy & relieved that one of the forum members has done the needful.
Thank you Shashanka. Are you home or on-board? I signed off just few days ago and enjoying the incessant rains since the day I came back.

Regards.
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Old 31st August 2017, 12:45   #133
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Thank you Shashanka. Are you home or on-board? I signed off just few days ago and enjoying the incessant rains since the day I came back.
Regards.
Hi Brumby! I am fully retired now since 2015 and trying to catch up with all those things I put off while in harness. And also being an occasional pain-in-the-neck for the rest of the household - which they are too polite to bring up!

The rains here in Mumbai too have been bad recently and have eased up since last night. So, what are your plans for the break?

Regards,
Shashanka
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