For Himanshu and others who may be interested

Dear all,
I finally found that someone does follow me - well this gentleman did and he asked me some questions, to which I've tried to answer. For others to think over, I'm reproducing them here.

1) Can U give a note(guidance) on making loading plan for an aframax/vlcc,Where loading rate is fast (10,000 m3/hr.)


My Ans:

Loading or discharging plans for smaller / bigger vessels is the same. Most important is for you to know the limitations of the vessel. Check your stability booklet for such. If you’ve U-shaped ballast tanks etc.

Every vessel’s pumping / loading arrangements are made basis the same consideration or ratio; rate of loading / discharge vis-à-vis the tank capacities. Accordingly, if you go on a small tanker of 30000T DWT, the max. pumping rate for homogeneous cargo will be about 3000 m3/hr, while if you go to a 100000 T DWT tanker, the pumping rates will be 10000 M3/hr.

This is always designed keeping in mind the filling rate and/or so the vapour displacement rate (P/V valve throughput etc.).

For developing any cargo plan, the most practical approach will be, in my opinion, as this is what I used to do –

1)    Work out your initial (ballast, no-cargo) stowage and stability and the final (all cargo) stowage and stability conditions.
2)    Your job is half done, once you’ve the above two conditions in hand.
3)    Next, assuming your question is for VLCC / Suezmax etc., means homogeneous cargo, start first foot loading in all tanks, that is work out a stage, where all your tanks or the first set of cargo tanks are filled about 0.5 – 1 m innage. During this time, you can start the loading at slow rate as per your ship’s design and shore agreement. Also you’ll start deballasting by gravity. Work out this condition on loadicator and compute the result, always keeping stern trim and maintaining vessel stability. Drafts should always agree with MARPOL criteria of max trim and minimum propeller immersion draft.
4)    At the next stage, you can start filling up tanks and reducing ballast slowly, always approaching your final condition, which you’ve already worked out earlier in stage 1. Continue deballasting keeping in mind the draft / favourable trim and stability.
5)    Always keep the amidships tanks slackest, available for the end. This would ensure that your ship does not develop sag, and towards the end, when you’re completing cargo loading, you’ll not have to keep resolving unusual trim.
6)    Multiple conditions will have to be worked for intermediate stages of loading, and this has nothing to do with time. As you work out, each stage will tell you, how much cargo has been taken in, and you’ll find that you have the time for each stage in hand, basis the available rates.
7)    At each stage, you’ll have to be careful about de-ballasting rates, since that has to be kept up with loading condition / stage too.
8)    In case, if you find that de-ballasting may be a problem, the best solution is to commence de-ballasting as soon as possible and prolong the initial slow loading rate stage and gradually increasing the rate of loading to max. Also towards the end, you can ask for decrease of rate in view of topping off.
9)    Keep an eye on the IG rates etc. to ensure it is coping up.
10) Actual topping off can be done towards the end. From my experience of stage loading, I’ve found its relatively easy to top-off tanks without having to reduce rate right until the end. What you have to do is plan your loading in such a way that each tank has a different level towards completion. This means on a bar graph if you see, you’ll have the cargo tanks filled with max. cargo on the extreme end (foremost and last) tanks, and gradually reducing to the centre. As you start topping off the end tanks, you can continue loading in the next set of tanks, changing over as you continue topping off, and as you reach closer to the last set of tanks, ask terminal to reduce rate. However, try this only if you are sure you are able to do this.

I’ve attached the cargo plan documents that I’d made during my own service as Chief Officer and now incorporated as company docs in my present company. You’ll have to amend the wordings, as these are more suitable in the present form for the chemical tankers.

Further questions:

Pls clarify on following pts-

1)Ford most & aft most tank will have least ullage,in case of heavy wx,during pitching oil/vapours may come out from ford tanks.

2) At discharge port,I can discharge those set of tanks which are nearly same,till all the tanks have come to nearly same level.

My Answers:

1)Ford most & aft most tank will have least ullage,in case of heavy wx,during pitching oil/vapours may come out from ford tanks.

The simplest explanation for this in layman terms is the principle of moments. Consider the fact that when a vessel is making way, its centre is the pivot point. Right? Now this Pivot point gets displaced or basically you can say that the loads along the scale passing through the pivot point keeps changing, causing the vessel to roll, pitch etc. Now the closer you are to this imaginery centre of the vessel, during her movement, you’ll feel less force of movement. However, the furthermost you are from this, the higher will be the resultant motion, with smallest exertion of force (think of Leverage). This would surely explain you, why?

However, it is important for you to understand also, that this is more importantly observed on vessels, where the Cargo tank PV valve orifice is on deck plating (remember normally it should not be constructed this way; it must be in the tank dome above the level of deck plate). With a trim in heavy pitching , cargo from forward will enter the PV pipes with orifice on deck platings and cause splashing on to deck. This would also cause rapid movement of vapours, being forced out of the P/V Valves.

Due to the same leverage, it is probable, in case of poorly maintained manholes on deck, that cargo or vapours may seep through it on deck.

2) At discharge port, I can discharge those set of tanks which are nearly same, till all the tanks have come to nearly same level.

What do you think, will happen (typical of vessels with pumproom ships and COPs in pumproom), when you commence discharge from tanks with different ullage level of cargo? You always commence discharge slowly, and increase it slowly too. Assume you started discharge from two tanks with ullages 3.6m and 1.4m. You will find that most of the cargo is being discharged from the second tank, while the 1^st tank may actually not change or may show an increase only. This is because cargo is getting transferred internally. Your expectations go for a toss.

It is always prudent to discharge the more filled cargo tanks until you are able to achieve a level lower than 88% in all tanks. This gives a safety margin too, in order to act, should there be internal inadvertent transfer of cargo.

Next question:

I noted that' There are numerous blogs, nautical institute site, various flag of registry sites, which provide you a lot of information.' Can you please name some of them for which I will be very grateful to you.

My Answer:

For Nautical Institute try www.nautinst.org

Various Classification societies have their own news feed, check them on their websites BV/LR/DNV/ABS etc.

For various Flag news, check

http://www.mantamaritime.com/

Marshall Islands: http://www.register-iri.com/

Liberia: http://www.liscr.com/liscr/

Panama: http://www.segumar.com/

Other sites:

http://www.safety4sea.com/

http://shipsbusiness.com/

http://gisis.imo.org/Public/

http://www.shipinspection.eu/

http://gcaptain.com/

http://pinoymaritime.com/blog/

http://mymaritimeblog.wordpress.com/

Blogs check as follows:

http://barratry.blogs.lloydslist.com/

http://ajitvadakayil.blogspot.com/

http://internationalshippingnews.blogspot.com/

http://theworldofshipping.wordpress.com/

http://kennebeccaptain.blogspot.com

http://www.lawandsea.net/maritime

http://www.themaritimesite.com/the-best-nautical-and-maritime-blogs/

Finally, anything you wish to get the knowledge on, just do a google search on it. I personally believe people blog for the reason of sharing the knowledge and experience. 

Remain objective in your search for a query, do not be judgmental, and you'll find the answers you are looking for.