Oil tankers

[cstunts]

Hello,

No idea at all. But I have the article hardcopied, and can put up relevant parts once I re-locate it. It has to do with Japan's pioneering efforts with the fast tanker fleet concept.

[Bronsky]

I think I already wrote this in this or another thread, but oil was the single factor accounting for growth in worldwide shipping. The other factor, and the one that every company focused on, was passenger transport (liners) but that went into long term crisis with the tightening of immigration quotas to the USA, was briefly revived with luxury liners in the 1930s but generally remained stagnant.

Were it not for the large growth in the tanker fleet, the world shipping stockpile would probably have been stagnant (this is all from memory but I have the figures somewhere and can dig them up if necessary). Tankers also changed the economics of shipping. The bulk of the pre-WWI shipping stock consisted of relatively small coal-burning tramps. So with short cruises, slow speed and range wasn't an issue.

Tankers were different, though: they would load to full capacity and then travel to their destination without any stopovers. Speed was therefore more of a factor given relatively longer cruises (especially for importing countries like Japan, Italy, France and Britain).

[takata_1940]

Hello,
No idea at all. But I have the article hardcopied, and can put up relevant parts once I re-locate it. It has to do with Japan's pioneering efforts with the fast tanker fleet concept.

Hello,
The Japanese were building fast tankers sailing 18-19 knots in 1938-39 but so were doing the other nations, at least the USA which had also build their T-3 with 18 knots during the same period and carried more petroleum. I think that it was a general tendency to build faster ship. The reason was that more powerfull diesel or turbine engines were available at this time. Economicaly, the tanker was also able to load/unload its cargo in a very short time by its own means and the greater speed would allow more turnover. Moreover, the life expectancy of a tanker was shortest than other ships type because of fast corrosion due to the mixed oil and salted water. So adding speed to tankers was a good way to increase their profitability with more service during their lifespan.

S~
Olivier

[Jon G.]

...
Were it not for the large growth in the tanker fleet, the world shipping stockpile would probably have been stagnant (this is all from memory but I have the figures somewhere and can dig them up if necessary). Tankers also changed the economics of shipping...

Just to add some numbers, if only of a more abstract kind. Measuring exactly how much tonnage Britain had at any given time turned out to be a demanding exercise - especially because wartime measures such as convoying, armament of merchantmen and port congestion would effectively reduce disposable tonnage. I recently picked up a nice little book by Martin Doughty Merchant Shipping and War which addresses the subject at length.

According to Doughty, p. 69, Britain (minus Commonwealth) had 17.3 mill tons GRT shipping on hand in 1936 as opposed to 19.26 mill. tons GRT in 1914. Additionally, as you say, tanker tonnage had increased from c. 675,000 tons GRT in 1914 to c. 2.7 mill. tons GRT in 1936, meaning that the drop in dry cargo tonnage was even sharper than the overall drop in tonnage would suggest.

[mescal]

According to Doughty, p. 69, Britain (minus Commonwealth) had 17.3 mill tons GRT shipping on hand in 1936 as opposed to 19.26 mill. tons GRT in 1914. Additionally, as you say, tanker tonnage had increased from c. 675,000 tons GRT in 1914 to c. 2.7 mill. tons GRT in 1936, meaning that the drop in dry cargo tonnage was even sharper than the overall drop in tonnage would suggest.

However, it should not be forgotten that these measurements of volume are only one point of view.

I mean, what really matters is less the transport capacity afloat at one given time than the flow of supplies over a given amount of time.
If you have in 1914 two 4000 GRT freighters on the line New York Liverpool and that their speed is 6 knots, it makes no difference, at least in peacetime and not taking into account the impact of maintenance, loading/unloading ... (which at first glance may go both ways) if you have a 1936 4000 GRT freighter able to sustain a 12 knots commercial speed.
Over a year, you will have shipped the same tonnage from NY to London.
So speed of the ships are also a non-negligible factor.

Admittedly, the risk in wartime is increased if you have a more limited overall transport capacity ...

[South]

Bonjour Mescal,

This is an excellent point-and 1 war later (excluding the Korean Conflict), this was NOT understood by America's RAND Corporation, the pseudo-intellectuals.

Transport capacity afloat is not a significant measurement when compared to the (liquid) cargo shipped. Speed is not relevant.

Re the last paragraph; it can be argued that in war time, "risk"- in the commercial sense - does not exist. In war time, it's really - chance -, something that canot be insured against. This is regardless of governments' subsidies called "war risk insurance". It's not really insurance, less the rhetoric. The hull is a pending reef.


Saluations,

Bob

[LWD]

...
So speed of the ships are also a non-negligible factor.

Admittedly, the risk in wartime is increased if you have a more limited overall transport capacity ...

On the otherhand faster ships were less vulnerable. Indeed if fast enough U-boats became marginal as far as a threat goes.

[Jon G.]

According to Doughty, p. 69, Britain (minus Commonwealth) had 17.3 mill tons GRT shipping on hand in 1936 as opposed to 19.26 mill. tons GRT in 1914. Additionally, as you say, tanker tonnage had increased from c. 675,000 tons GRT in 1914 to c. 2.7 mill. tons GRT in 1936, meaning that the drop in dry cargo tonnage was even sharper than the overall drop in tonnage would suggest.

However, it should not be forgotten that these measurements of volume are only one point of view...

Very true, net GRT will only tell you so much. However, it is one variable which you can predict with reasonable accuracy ahead of time, whereas losses to effective available tonnage due to convoying, evasive routing, port congestion and enemy action can only be estimated. For example, the net gain of your 12 knot freighter will, for purposes of speed vs. effective GRT tonnage only, be cut to 1/3 if your fast ship for some reason finds itself in a slow 8 knot convoy.

[mescal]

Very true, net GRT will only tell you so much. However, it is one variable which you can predict with reasonable accuracy ahead of time, whereas losses to effective available tonnage due to convoying, evasive routing, port congestion and enemy action can only be estimated. For example, the net gain of your 12 knot freighter will, for purposes of speed vs. effective GRT tonnage only, be cut to 1/3 if your fast ship for some reason finds itself in a slow 8 knot convoy.

Exactly, and that's why I explicitly excluded wartime constraints from my reasoning -- the logic behind being that the size (volume) of the commercial fleet in 1936 is mainly drived by economic logic and only marginally by future possible war constraints.

Now, if we want to compute what would be an "adequate" commercial fleet for Great Britain in 1940 wartime (under the assumption that France falls), it will require a quite complex model and a lot of assumptions -- and probably only to re-create something that was empirically designed by that time and must lie on a shelf in the Admiralty's archives.
(and such a model designed today would most probably not have been possible by that time, because I strongly suspect that it requires dynamic programming results from the 70's and 80's, and would anyway be untractable without a computer).

On the otherhand faster ships were less vulnerable. Indeed if fast enough U-boats became marginal as far as a threat goes.

I think that the vulnerability does not decrease in a linear way according to the speed. Rather, there must be a sharp threshold, most probably at speed just inferior to the max speed of the U-boot and then, something with this shape :

Tanh.gif

err..., it looks like I inverted my plot ... let's say it's not the vulnerability, but the security of the merchant ship which is plotted along the horizontal axis

it can be argued that in war time, "risk"- in the commercial sense - does not exist. In war time, it's really - chance -, something that canot be insured against.

Actually, I must confess that I did not think of this distinction when typing my post.
Now, I would say that it depends on the point of view chosen : for a crew member on a random ship, it may be chance.
However, for the admiralty of whatever service in charge of a large number of convoys, it's risk ... On a large scale and a long imte period, a measure of probability can be constructed, and hence you can ground an "insurance" system at this aggregated level.

[LWD]

...

On the otherhand faster ships were less vulnerable. Indeed if fast enough U-boats became marginal as far as a threat goes.

I think that the vulnerability does not decrease in a linear way according to the speed. Rather, there must be a sharp threshold, most probably at speed just inferior to the max speed of the U-boot and then, something with this shape :
....

If we look at the actual war time vulnerability it's even more complex. Consider the following speed catagories
1) Too slow for even slow convoys - better use this one on internal waters or the US Pacific coast.
2) Fast enough to travel with slow convoys but not fast ones. In this case there is only a very slight improvement with speed (ie given warning of if the convoy scatters or it's in areas without convoys.
3) Fast enough to travel with fast convoys but not independint sailing. Probably a significant step up from slow convoys but then very gradual until you reach independent sailing speeds.
4) Fast enough for independent sailing. Here I think it will continue to increase but you are correct probably not linearly. A faster ship is harder to target and too hit as small aiming errors are magnified and a faster ship especially operating on its own can maneuver more/faster if a sub or torpedeos are spotted.

[cstunts]

Hello,

Let's examine this:

"I mean, what really matters is less the transport capacity afloat at one given time than the flow of supplies over a given amount of time.
If you have in 1914 two 4000 GRT freighters on the line New York Liverpool and that their speed is 6 knots, it makes no difference, at least in peacetime and not taking into account the impact of maintenance, loading/unloading ... (which at first glance may go both ways) if you have a 1936 4000 GRT freighter able to sustain a 12 knots commercial speed.
Over a year, you will have shipped the same tonnage from NY to London.
So speed of the ships are also a non-negligible factor."

Over a year's time, on the route from say, Yokohama to Seattle, [or, as in the war, from Singapore or Miri to Yokohama] how many trips can the 6 knot tanker of X GRT make and how many can the 16 knot tanker of X GRT make? Therefore, speed IS the critical factor.

This, at any rate, was precisely the thinking behind the Japanese decision to go with smaller, faster tankers in the early 1930s, well before Western nations. The article I noted was from 1937, but Japan's first high speed tanker had been launched around 1933 IIRC.

[mescal]

3) Fast enough to travel with fast convoys but not independint sailing. Probably a significant step up from slow convoys

I quickly checked the losses of the fast vs slow convoys on uboat.net.
I have HX & ON as fast convoys and SC & ONS for the slow convoys. I chose those because they are the most statistically significant convoys, and because they are on the same route and in both ways.

Here are the numbers I found :

losses_convoy_1.jpg

The number of convoys is the number of convoys attacked and which lost at least one ship.
So these numbers do not measure the relative vulnerability of slow vs fast convoys, since there is no info regarding the convoys that went trough unscathed, but gives an idea of the relative vulnerability once the battle is under way.

Therefore, speed IS the critical factor.
This, at any rate, was precisely the thinking behind the Japanese decision to go with smaller, faster tankers in the early 1930s

Are those Japanese high-speed tankers purely commercial tankers or (potential) fleet tankers ?
Actually, my question is more : does this increase of speed come just from purely commercial/economic incentives, or did the IJN subsidize those ships in exchange for requisition should a war begin ?

[Bronsky]

I'm not sure I understand Jon's remark about convoying. Convoying forces a 30% loss of efficiency across the board, which isn't the same as a 30% in average speed, though of course the faster ships will be at a disadvantage in a convoy. On the other hand, is a ship capable of doing 12 knots and sailing at 8 more penalized than a WWI ship with a theoretical speed of 6 knots and sailing at 4?

I also share Olivier's failure to understand the rationale behind the fast, small tanker equation. From a theoretical starting point of a 8,000 tons tanker doing 10 knots, it seems easier to build a 16,000 ship with the same speed than build a 20-knot one of similar size. Both allow the same theoretical throughput, and the higher investment (storage capacity at both ends of the trip) for the large tanker is recouped by savings in fuel and crew expenses given how it only makes half the trips. Also, fast ships require high-pressure turbines and these are expensive.

[Jon G.]

I'm not sure I understand Jon's remark about convoying. Convoying forces a 30% loss of efficiency across the board, which isn't the same as a 30% in average speed, though of course the faster ships will be at a disadvantage in a convoy. On the other hand, is a ship capable of doing 12 knots and sailing at 8 more penalized than a WWI ship with a theoretical speed of 6 knots and sailing at 4?...

Well, my remark wasn't so much about convoying, but more about how we can measure the effect of wartime efforts to reduce shipping losses. I mentioned in passing that Britain had less tonnage on hand, in absolute numbers, in 1936 than she did in 1914. Olivier, perfectly reasonably, pointed out that there are clear limits to how much a simple mass GRT figure will tell you. He did that by making a theoretical example showing that a 4,000 ton ship with twice the speed of two 4,000 ships will deliver the same tonnage, if we let other factors be equal.

In turn, my objection to ship speed as a factor is that wartime efforts to reduce shipping losses - evasive routing, convoying and resultant delays and port congestion, and perhaps also reduced maintenance and repair afforded in wartime - will also diminish the benefits of fast ships over slow ships. Total GRT on hand is something that you can calculate fairly accurately, but speed as a factor will be difficult to nail down, especially if you're going to factor in wartime expedients as explained above.

[Bronsky]

Ok, thanks for the explanation. In terms of tanker tonnage, part of the problem was how in wartime supply was struggling to keep up with demand.

Looking at UK imports of petroleum products gives the following:
1940: 11,381,000 tons
1941: 13,051,000 tons
1942: 10,232,000 tons
1943: 14,828,000 tons
1944: 20,176,000 tons

The 1944 surge was largely caused by increased avgas imports: 9.4 million tons against 5.3 the previous year. Yet, British fuel stockpiles were reaching dangerously low levels during the last winter, the combination of a full-tilt strategic bombing campaign and an active land front with motorized armies was proving too much for even the vastly expanded tanker fleet in the priority theater. The average tanker was both larger and faster than it had been when the war began, too.