Interesting discussion here. :hmm:
Let me chime in with some comments.
UBI
It is worth to note that UBI got equiped not with the engines they were supposed to be equipped by design. However the engines could not be delivered in time with the commission of the boats so they simple used dinghy motors. This explains the weak engine performance. Engines were such a rare good at that time and delivery delays were quite common. They used what ever they got.
This is also not the only case where improper engines were used on u-boats. Some times an engine was available suddenly from somewhere and the submarine was build around it. The U 57-59 was a serie for example where the pressure hull had to be widened in the engine room to fit in the engines that were originally not made for this boats. Not all of the improper engines were even designed to be on an always moving platform. The UE boats were boats that were equipped with such engines that were made to be operated on land. This gave regular troubles on an always rolling and pitching boat and the performace was. And of course such engines were always of a weaker performace. You can spot this unlucky boats by looking at their performance.
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Originally Posted by Chock
The UB1 types (known as 'Tadpoles' in the Kaiserliche) had a range of 1,600 miles, with a top speed of just five knots (4 knots submerged),
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I think the top speed of the UB 1-UB 8 was 6,47 nm on the surface and 5,51 submerged
For the UB 9 - UB 17 of the UBI serie it was 7,45 nm on the surface and 6,24 nm submerged. 5 knots was maybe the cruise speed. But the speed of course varies with the load of the boat an buoyancy of the water.
But yes, the speed was so slow and as i know from first hand accounts this boats regularly miss targets because of it. Overtaking targets was not possible with this boats unless your target was a slow sailor.
You had to be in the way of your target when you spot it. But their operational area surely gave them planty of opportunities.
Average patrol time
I think there was no such thing as an average patrol time, as chock already pointed out quite well. The petrol times were very variable indeed. Generally you can say that it began with patrol times below one week and as the war was progressing and especially after some incidences where a boat was forced to stay MUCH longer then it was considered at all possible, the patrol times got longer and longer. Soon the boats were at sea for weeks and even months. I think in the medeterranien you would have patrols of typically maybe two weaks for the UBII types for example.
The torpedoload and deck gun ammo are of course the dominating factors for a patrol duration. On a UBI you could be done in one day if you had luck. In an UBII you could stay out for a week or two, easily, especially when you consider that in flandern, where you operate so close to the british coast, all hell will brake loose when you sink a ship, so in a UBII you had to shift your patrol area after the attack pretty far. That was a very serious thing being caught there, in the shallow water, and so close to the coast you are right in the air threat zone. Air attacks became a srious subject for WWI u-boats as well in the second half of the war. UBII operations were surely more formidable. Besides 3 times more torpedos than the UBI it also got a 8,8 cm gun later. But this was a troublesome affair since this small boats were to small for the hard recoil that caused the neats of the fuel tanks to leak somewhat and the thin oil slick you would give out the boats positon in daytime when submerged. Even the big boats had all problems with the recoil. I don't even know whether this problem was ever solved sufficiently.
Ahh, it would be great to have all this in a subsim but it will take me a while till i arrive there.
Anyway, in the north sea 2 weeks was surely rather the minimum for a patrol if you consider that the boats had to travel around the north coast of england and all the way back again. The fleet type boats built in prewar times had only 6 torpedos initially. So they were done faster too. As most boats got equipped with deck guns the patrol time surely increased then even more.
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Of course there were also the U-Cruisers, with a range of up to 15,000 miles and endurance that could easily be two or more months.
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Pardon, up to 25.000 miles(U 151- U 157)
Anyway nice discussion again.
