Twin (double) Hull Tankers

Ferrous Phil
9th July 2007, 18:23
I would be really interested to know if anyone has experience or knowledge of a twin hulled vessel actually not spilling oil by virtue of the twin hull arrangement?
It strikes me as a tremendous amount of extra steel and cost, has it ever been proven to be worth it?

9th July 2007, 20:21
Do you mean double hulled?

Ferrous Phil
9th July 2007, 20:28
Yes, double hulled or double skinned. I guess twin hulled could be confused with a catamaran design and I definately wasn't meaning that!

14th July 2007, 11:26
In the '70s Mobil built VLCC tonnage with Double Bottoms. On 2 occasions the fact that these VLCCs had D.B.s was though to have helped retain these ships in one piece following explosions. "Mobil Pegasus" and "Mobil Magnolia" both mentioned in earlier threads.

Ferrous Phil
14th July 2007, 17:34
Thanks for the information. I was under the impression that twin skin tanker hulls were required to help prevent spillage following grounding or collision. It always struck me that this was a very expensive sledge hammer response to fixing the outcome rather than the cause of most oil spills.
I have always wondered if it has actually ever made a difference.

Jim MacIntyre
15th July 2007, 02:17
Hello Ferrous Phil
It's probably hard to come up with facts and figures. That sort of stuff only comes out when it 'hits the fan' and the press is all over it.
Bottom line probably the only place you would find any kind of hard information is through either the various classification societies or the P & I clubs if it is even available.
Maybe it does seem like a sledgehammer approach, but the cost of just a minor oil spill clean up these days, even the contents of a bunker or cargo hose, will set you back.
Certainly your double hull is not going to help in a major catastrophe but a minor collision breaching just one cargo tank in a medium size tanker is going to cost many millions to clean up and if the double hull has given you those few feet of extra space that protected the tank it was probably worth it.
All this before you even think about environmental issues....
I note your comment about 'fixing the outcome rather than the cause' - the cause of most accidents in any field is either human error or mechanical failure and sooner or later one or the other will get you. Ergo in this case - double hulls.
It's like sitting on the side of the road out of petrol saying 'I'm gonna get a bigger fuel tank in my next car'. Just a matter of perspective.
Jim Mac

Jan Hendrik
15th July 2007, 06:07
The first double hull ullc's were built by Maersk in Odense abt 5-6 years ago.
There are international arrangements in place now that countries will in future no longer accept single hull carriers, there is a period of grace until all tankers worldwide are of a double hull construction.

15th July 2007, 06:47
There's quite a bit from a Naval Architect and owner of several ULCC's here:

Including tank spillage in Appendix C.

Ferrous Phil
15th July 2007, 11:38
Thanks for the link Bill, judging by the preface the author seems to be well placed to have some very strong and well informed opinions on the matter. I will read the whole document with interest.
Regards Phil

17th July 2007, 19:32
Also, for some reason the author Devanney beats around the bush about his full background in the preface of the book. On the website the E-book comes from is his complete resume, which clarifies where his specific technical opinions about class rules, scantlings, & other technical matters come from. I'll post it here:

Devanney Resume

Jack Devanney obtained his education at M.I.T. where he received a Bachelors in Naval Architecture in 1962, a Masters in Naval Architecture in 1965, and a Ph.D. in Management Science in 1967. During his education, Devanney worked for Amsterdamsche Droogdok (fitters helper), Newport News Shipbuilding (carrier weight control) and Electric Boat (submarine operations research analyst), as well as mounting an unsuccessful campaign to represent the USA in the Olympic Finn class.

In 1968/1969, he worked for Litton Industries where he was responsible for the hull form and tank testing of the DD 963 (Spruance) class.

From 1969 to 1978, Devanney served on the faculty of the Department of Ocean Engineering at M.I.T. where he taught courses in marine transportation and petroleum engineering. While at M.I.T. he was the Project Director of the widely emulated Georges Bank Petroleum Study and co-director of the Atlantic/Gulf Of Alaska Outer Continental Shelf Study for the Council on Environmental Quality. He is the author of two texts and some twenty papers. He holds a patent in the field of fluidized bed combustion. He has been a consultant to the United Nations, the World Bank, the National Academy of Sciences, the Office of Technology Assessment, the Organization of American States, the Federal Reserve Bank, and several Latin American governments. He was the youngest person ever appointed to the Panel on Naval Warfare of the President's Science Advisory Committee and the youngest fired from that position.

In 1978, shortly after receiving tenure, Devanney left academia and emabarked on a 25 year career revolving around tankers. This included starting Martingale, Inc an engineering and economics firm specializing in tankers and the tanker market. Martingale has performed major oil related studies for OPEC, OECD, the Department of Energy, the Environmental Protection Agency, the State of Alaska, and the Sierra Club. The group has done ground breaking work in marine power systems, oil spill likliehood and transport, and oil futures trading strategies. Martingale maintains MARTINET, the most comprehensive model of the tanker charter market in existence, and has developed software covering all facets of tanker management and operation -- most importantly, MLOAD, a combined tanker loading, salvage and spill reduction package.

In the early 80's he was a founding partner of Atlantic Chartering, a successful tanker brokerage firm. He also started Three Blind Mice, a petroleum futures trading venture which implements Bayesian dynamic programming based trading strategies developed by Devanney and his partners.

From 1984 to 1990, Dr. Devanney was President and CEO of Majestic Shipping Corp, a company which he was instrumental in founding. During this period, Majestic purchased and operated seven large tankers with an aggregate deadweight of 2.25 million tons. Majestic, a subsidary of Loews Corp, was the largest independent American owner of very large tankers, carrying over 2% of all the oil imported into the United States in 1988 and 1989. In 1990, the Majestic fleet was sold in two transactions which valued the ships at over 315 million dollars. This fleet was purchased in the mid-80's for 42 million dollars.

Between 1990 and 2005, Devanney was a Director of Hellespont Shipping Corp, owner of as many as 14 very large tankers. In 1999, under his direction as Program Manager, Hellespont instituted the largest large tanker newbuilding program in the world at the time, four 305,000 ton VLCC's at Samsung Heaving Industries, and four 442,000 ton ULCC's at Daewoo Shipbuilding and Marine Engineering. The latter are the only ships over 320,000 tons built in the last 20 years. These eight ships were delivered in 2001/2002. Dr. Devanney was responsible for all facets of this program: specs, financing, yard negotiations, supervision, and all major technical and commercial decisions. The Samsung VLCC's were sold in 2001 and the Daewoo ULCC's were sold in 2004. While the projects were sold at a substantial profit, Devanney's decision to sell was, to put it politely, premature.

In 2005, Jack Devanney retired and founded the Center for Tankship Excellence. The CTX is a non-profit devoted to improving the badly deteriorated quality of tanker design, construction and regulation. Whether or not the CTX proves to be a success is very much an open question.


26th July 2007, 11:09
There is a certain view amongst many practical and experienced Tanker men that double hullled tankers are another form of disaster yet to happen. The maintenance inside of the double hull, where all the structure is will in all likely hood be a nightmare in future. Structural damage from berthing, tugs and general stress in a seaway will lead to paint flaking etc, sweating will bring out the rust and so on. Then there is the problem of any leaks into the void space gassing it up and those inherent safety worries. If the space is inerted then the quality of the Inert gas and its Cleanliness will cause further corrosion problems.

Nice idea and it probably will save some spills from groundings but .... what happens when she really hits the rocks or breaks up in a major???

By the way its not only for Tankers .... it applies to bunker tanks etc in most vessel newbuildings.....

Barnsey the pessimist

7th December 2007, 06:11
Solving tanker safety problems involves an different approach, both in ship design and hold design. This has been accomplished and is know as the HARTH Technology, which is a twin or multiple hull vessel - without the hold in the hulls. The hold is far above the waves - and the geometry of the vessel results in ultra vessel stability in elevated sea states. The bow wave is eliminiated in the design, and surface wetted drag reduction results in an 83%overall drag reduction. The obvious result is far greater fuel economies with consequent lower emissions and significantly greater speeds. Such vessel construction is currently and actively being considered.

7th December 2007, 09:04
Dr Devanney's book "The Tankship Tromedy" is a good read even for the non technical you can get a .pdf version at the c4tx Website here (
It has some interesting pictures and reports including one of the Sinclair Petrolore a Ludwig owned 56,000 ton self unloading OBO which blew up in 1960 "most likely cause - cargo leaking into the double bottom"

There is a chapter called "Rules of the Road Screw Ups". According to Dr Devanney there are only three rules - he may be right - would have been much easier to memorise!

To understand ROTR screw-ups, you must understand the Rules of the
Road. The Rules are simple. There are basically only three.
1. Overtaking vessel must keep clear.
2. In crossing situations, the ship that has the other ship on her starboard
side must keep clear. This ship is called the give-way vessel. The other
ship is called the stand-on vessel.
3. In head-on situations, both ships should alter to starboard for a port
to port passing.

7th December 2007, 16:42
Tacho is right, The Tromedy is a very interesting read and if you don't want to print off the .pdf version it can be bought from Amazon for abot $30. Davenney's polemic is primarily about the deterioration of tanker structures and construction over the past several decades and for Ferrous Phil should cover evething he asked on double hulls. He's a highly qualified Naval Architect with eons of experience so his thesis is very convincing. Chris Allport

7th December 2007, 17:04
Don't forget one big advantage of double-hulled tankers is that all of the stiffeners can be placed inside the ballast tanks and above the main deck. Therefore the internal surfaces of the plane and corrugated buklheads, inner botton and deckhead are flush to facilitate tank cleaning. In chemical tankers the bulkheads and inner bottom are sloped to a sump for the deep-well pump, in order to maximize the recovery of valuable cargo.

7th December 2007, 18:53
Below from the CT4X Casualty Database (

type D

On December 30, 1975, the oil/ore carrier M/S Berge Istra (Solberg, 1981) sank in the Molucca Sea. Two of the crew were rescued. They reported a rapid series of three massive explosions followed by the immediate sinking of the ship. In October, 1979, the sister ship M/S "Berge Vanga" disappear in the Atlantic Ocean. Practically nothing is known about that incident. No one was rescued.

The rapid sinking of the Berge Istra indicates that a gas explosion in the double bottom of the ship ripped the ship structure open, and water flooded the double deck and the engine room.

source CTX
type D
volume Y
dead 38

These two sisterships ships were VLCC-sized OBO's; ships that can handle both oil and dry cargo. They had a structure that is very similar to a double hull tankers. The double bottom is for all purposes the same.

A Norwegian Master who had served on these ships told djw1 they did have leaks into the double bottom. Surveyors check for such leaks by shining a mirror down the ullage hole into the double bottom when it has ballast in it. If there is any oil on top of the ballast water, a trained eye can see it in the beam of sunlight. To fool the surveyors, the crew would put a large bucket of water under the ullage hole. The surveyor's mirror would see only the clean water in the bucket.

After the Vanga disappeared, Bergesen the owner took all the sisterships out of the crude oil trade. Henceforth, they traded only as dry bulk carrier. A little monument to these two crews used to stand in the entrance of the Bergesen office. Don't know if it is still there.

These two casualties indicate the hazard associated with cracks from double hull cargo tanks to double hull ballast tanks are real. Double hulls have already killed 80 people.

Spill would have consisted of bunkers plus slops, but we have no volume. Need to know if ship was loaded (iron ore) or ballast.

8th December 2007, 11:58
OBO's do have to withstand the uneven stresses imposed on the hull when carrying ore, and also may suffer damage to the stools and inner bottom by grabs and bulldozers. Oil will always find a crack, but it is far more difficult for surveyors!

Long ago I did read the findings of research by the classification society into the losses of these OBO's. If I remember the gist of the conclusion correctly - and contradict me by all means if I am wrong, because the grey cells have been proved to be faulty with age in a previous Ships Nostalgia thread - when vapour from an oil leak ignites, expansion accelerates the gas cloud successively through the lightening holes of floors in the double bottom, until the fireball has sufficient energy to tear the ship apart.

Derek Roger
8th December 2007, 14:56
Double hull vessels are not that new .
The Mv Arctic built in Port Weller Drydock in 76/77 was the first vessel to be built to the Canadian Arctic Pollution Regulations which required a double hull .
I was the Owners new build surveyor at the time .
The vessel is still in service ( I understand presently being refitted ) the voids and ballast tanks between the hulls were given a good paint system to reduce corrosion .
As mentioned in a previous thread there are few single hulled tankers if any left ( After the grandfather clause ) which are allowed into US and Canadian waters .
Certainly a major step forward in limiting grounding pollution.

Regards Derek

8th December 2007, 15:13
Double bottoms may have had a major impact on the number of spills
from bottom damage, but they have had almost no impact on the volume
of oil spilled. Almost all oil spilled from tankers is spilled in a handful
of extremely large spills. In these spills, the double bottom would
have been pentetrated and becomes a non-factor.
Double sides on the other hand have the ability to collect lots of oil
no matter how badly the bottom is damaged,
as long as the top of the damage is below the waterline.
See Tromedy for the complete argument.
In tanker spillage, we must be very careful to distinguish
between number of spills and spill volume.

Keep the faith,

Jack Devanney

8th December 2007, 18:53
What's the score with this one ( - is she double hulled?

Bill Davies
8th December 2007, 19:12
OBO's do have to withstand the uneven stresses imposed on the hull when carrying ore, and also may suffer damage to the stools and inner bottom by grabs and bulldozers. Oil will always find a crack, but it is far more difficult for surveyors!

Long ago I did read the findings of research by the classification society into the losses of these OBO's. If I remember the gist of the conclusion correctly - and contradict me by all means if I am wrong, because the grey cells have been proved to be faulty with age in a previous Ships Nostalgia thread - when vapour from an oil leak ignites, expansion accelerates the gas cloud successively through the lightening holes of floors in the double bottom, until the fireball has sufficient energy to tear the ship apart.

There is an interesting piece of software primarily used in the petro-chemical industry called FLACS (Flame Acceleration Simulation) and its sister FRED are excellent in the in depicting consequence explosions in OBOs.


9th December 2007, 13:21
The Hebie Spirit IMO 9034640 is a Marpol single hull.
I think in this discussion it is important to distinguish
between double bottoms and double sides.
In my view double bottoms involve an unfavorable trade-off,
reduction in number of small spills from minor bottom damage
versus an increase in probability of a very bad casualty from a double bottom explosion.
Double sides are a favorable trade-off, protection from moderate side damage
plus ability to collect oil from bottom damage.


Jack Devanney

9th December 2007, 16:22
From the initial photos, it appears the barge bounced along the port
side punching holes as it went.
This may be one of those rare collisions involving a major spill
in which a 2 m double side would have made a difference.
Normally, of course in a major collision the struck ship suffers
much more than 2 m penetration.
However, we should keep in mind that on this Marpol ship,
two of the five port wing tanks are ballast
which probably made a difference.

The crew appears to have listed the ship to starboard
another indication that the damage is all above the waterline.
In this case, a double bottom would have done nothing
but sink the ship deeper which in this case would have been
a bad thing.



12th December 2007, 17:20
I know this maybe slightly off topic a bit and my appoligise for it, but isnt there a legislation stateing that single hulled tankers are not allowed into european waters? i heard that after the prestige sinking they banned all single hulled tankers, and the US were going to do the same.

Any truth in it?

Sorry for hijacking


John Briggs
13th December 2007, 04:36
Shouldn't the name of this thread be changed to 'Double' hulled tankers? Very annoying to keep seeing 'Twin' hull tankers popping up - makes me think of a high speed cat!

non descript
13th December 2007, 08:09
Shouldn't the name of this thread be changed to 'Double' hulled tankers? Very annoying to keep seeing 'Twin' hull tankers popping up - makes me think of a high speed cat!

Yes, a very reasonable point; but if we try and sanitize every posting and thread we achieve a result that none of us really want and we then lose part of the magic that is SN.

If we were to edit the thread title, then what of the reasonable a friendly comments that have been applied to it in its innocence? - You can see the problem.

So all in all, whilst I too trip up every time I see it, there is good reason to allow it to trundle on in its uniqueness.

Possibly not well explained, but hopefully you get my drift.

John Briggs
13th December 2007, 08:16
Very well put Mark. Far be it from me to turn into a miserable nark. I agree, we don't want to lose the magic. I will give myself a quick kick up the backside and get a bit of Christmas spirit into myself. Thanks.

non descript
13th December 2007, 09:59
Thanks, very nicely put and to be frank, I had thought exactly along the same lines as you originally and even reached for the edit, but then remembered why we were all here.

K urgess
13th December 2007, 12:26
I've made a small change to the thread title to include the word (double) to remove any confusion for those that haven't visited before.
Those that have visited before will know the reason for the change [=P].

Must admit that the idea of a catamaran tanker is fascinating. Maybe Steve, who drives a pleasure version in his spare time, could comment.

non descript
13th December 2007, 12:58
Neatly done Sir, a better result than I had woked on - well done (Thumb)

Ferrous Phil
17th December 2007, 22:06
My apologies! When I wrote the phrase 'twin hulled' I knew what I meant (honest!) although I can plainly see why it is confusing, so consider me chastised.
Moving on, the information that I got from my original posting, particularly the link to the Jack Devanney book was really very interesting and I used some of that data (and with referenced due credit of course) to produce a short report for an Open University degree course that I am undertaking.
The general point I tried to make in the report was that double hulls seemed to me to be an expensive regulation introduced as a means to prevent an oil spill after an accident rather than addressing the cause of such accidents in the first place (usually running aground).
To anyone that is interested (and can bear seeing the phrases 'twin hulled' and 'double hulled' used frequently and constantly interchanged !) then please feel free to email me and I will gladly send a copy. (I will try to attach it to this post but as I cannot get it below the site size limit I suspect this plan will fail !)
Of course having said that an oil spill is frequently (nearly always?) the result of running aground, then I acknowledge that this in turn must be due to something else and perhaps shipowners money and legislation may be better directed at addressing this 'something else' aspect rather than concentrating on soon to become rusty double hulled vessels?

non descript
17th December 2007, 22:47
No apology needed and you have made a very valuable point. It (the idea of having more than one hull) is an emotive issue, and like so many things largely misunderstood and even a knee-jerk reaction, possibly based on little genuine logic. Of course the odd newspaper article, complete with diagram of inner and outer hulls makes for compelling reading and adds fuel to the fire of misunderstanding; certainly newspaper editors rarely worry too much about the facts, after all they do tend to get in the way of sales (Jester)
Kind regards

Mike Robinson
25th January 2008, 15:41

At virtually the same time as the Berg Istra disaster,Shell had explosions on the Mactra and Marpessa and another VLCC,King Haakon also exploded.Much research went into these losses and I believe that static generated by the tank cleaning machines was the most likely cause.
I visited Mactra in Durban after she limped in,and she certainly was not double hulled.What saved her was that the deck plating,by design was thinner than the hull,and the force of the explosion was vented upwards.
I have sailed on numerous double hulled tankers-have never seen a spill averted by them,but can state categorically that,with the ballast winged out in the double hull,they are a pure bastard to sail in in bad weather-or even moderate weather for that matter.After a period of time there have been many small stress fractures evident in these spaces,and,despite the International requirement for them,and as far as I am concerned,the jury is still out.

Mike Robinson. Master rtd

16th February 2008, 14:14
I can confirm Capt Robinson's experience with the poor
roll characteristics of double hull tankers.
Even on our 445,000 ton DH ULCC's the crew
often had to alter course to keep the roll down,
both loaded and in ballast. This was almost never
required on our SH tankers. Lightering off California
weve had 5 to 7 degrees roll in conditions that were so
calm you could not see the swell. This is due to
the high position of the cargo loaded and the
high radius of gyration of the ballast in ballast.

With respect to the pandemic of fatigue cracking,
this is not the fault of the DH. The last generation
of single hulls were horrible crackers. The cause
here is the steel is simply to thin. To avoid
cracking, you will need to increase Class minimum scantlings
by abt 15 pct. We did this on our DHs, and there has been no cracking.


Jack Devanney

16th February 2008, 15:40
Just revisiting this thread on DH tankers to find where its leading. Jack's book and comments probably collates most of what can be said on the subject including operational problems. But what about survivability in the event of a grounding, collision or explosion? To my knowledge it was the DH ULCC Limburg which survived the first and only terrorist attack on a merchant vessel a few years ago. It can be argued that this 300KDWT vessel which was half loaded with crude oil as she approached the SBM only survived the bomb explosion due to the Double Hull. Some of you may, or may not have seen the photgraths taken during and in the few days following the terrorist attack off the coast of Yemen. They are very convincing. I have a DVD with 250MB DVD of photos and videos taken during the event and subsequent follow-up which illustrate the point. The thumbnails illustrate how both outer and inner hulls were penetrated. In the subsequent repairs at Dubai, 3500 of steel had to be replaced. Rgds Chris Allport