SH3 -- should I be able to run on batteries on surface?

[aj906]

I'm currently reading Feindfahrten by Wolfgang Hershfeld and in it he describes a trip down to ET89 in U-109 and the concern there was over the fuel requirements getting them home. From memory (The book is not by my side at the moment) there was something like 38 cubic metres of oil left in the bunkers when off Freetown and that was apparently sufficient only for a trip to the Azores. U-109 is eventually resupplied by U-460 but again there is anxiety over whether they will reach Lorient. He states that the only option then available to them would have been to jury rig a sail (quite how, and from what, he doesn't say). I can't imagine this would have been the most useful method and the question would then become one of rations about the boat and how long they would last as opposed to how quickly landfall could be made.

Similarly he notes that during the northerly trip home as much running on batteries as possible was employed and that the engineers transferred the oil around the various tanks to change the boyancy of the boat, thereby lowering the draft and thus improving fuel economy. This raises a peculiar question - at ahead 2/3rds I get 4knots underwater in calm seas in a IXC. I wonder what you could get with a 1/3 of the boat (and thus resistance) out of the water Nevermind that extra few feet of draft saved by the loss of the weight incurred by all those eels!

[Sailor Steve]

Originally Posted by aj906

I wonder what you could get with a 1/3 of the boat (and thus resistance) out of the water Nevermind that extra few feet of draft saved by the loss of the weight incurred by all those eels!

Actually drag is worse on the surface due to wave resistance. As the hull moves through the water waves build up along the waterline, and the waves create more drag.
http://www.mecaflux.com/en/ship%20Hydrodynamics.htm

[Gangrene]

Try and hit escape and end the patrol / mission. You might end up back at base... Sometimes when I was really far out from base and didn't want to sail all the way back I just ended the patrol.

[Raticon]

Originally Posted by Sailor Steve

Actually drag is worse on the surface due to wave resistance. As the hull moves through the water waves build up along the waterline, and the waves create more drag.
http://www.mecaflux.com/en/ship%20Hydrodynamics.htm

Is this mimiced in SH3 or with GWX in some kind? My first thought is the Schnorkel, and by using that you should technically be able to save lots of fuel for long voyages.

[TorpX]

Originally Posted by Sailor Steve

Actually drag is worse on the surface due to wave resistance. As the hull moves through the water waves build up along the waterline, and the waves create more drag.
http://www.mecaflux.com/en/ship%20Hydrodynamics.htm

I don't believe this is true for WW II boats. Modern nuc subs are slowed by the bow wave on the surface, but most of the WW II boats were designed for surface travel. At least this is what I've read.

My first thought is the Schnorkel, and by using that you should technically be able to save lots of fuel for long voyages.

I doubt this would be the case. One of the results of the snorkel was that fewer boats were 'on station'; that is it took longer for them to go to and from their patrol areas. In other words it's only advantage was in avoiding aircraft attacks/detection, in every other way, it was a disadvantage.

[Sailor Steve]

Originally Posted by TorpX

I don't believe this is true for WW II boats. Modern nuc subs are slowed by the bow wave on the surface, but most of the WW II boats were designed for surface travel. At least this is what I've read.

He was talking about running on batteries. It's true that WW2 subs were designed for surface running, but hydrodynamic drag is what it is. If surface running on batteries changes anything, it will be for the worse.

One of the effects of wave propagation is that as speed increases the bow tends to lift. The bow wave cuts under the ship and the ship is forced to climb a hill made of water. The faster the speed the steeper the climb, the more power required and the more fuel used. At four knots there won't be much difference, at eight a little more. All I was trying to say is that using batteries on the surface won't increase the range. On the other hand running decks awash doesn't help even though the hull is submerged because that close to the surface the hull creates a boundary layer that tends to cause even more drag. This, coupled with the drag from the sail, just makes it worse. It's a no-win situation.

[aj906]

Originally Posted by Sailor Steve

Actually drag is worse on the surface due to wave resistance. As the hull moves through the water waves build up along the waterline, and the waves create more drag.
http://www.mecaflux.com/en/ship%20Hydrodynamics.htm

But at 4 knots (as your latter post implies) this will not be a problem. And, with batteries engaged, it is not like you would want to do much more than about that for the sake of economical cruising. Also, if it is such an issue - and I'm not for one minute questioning you - why would it be a viable option related by veterans? Perhaps their recollections refer to mill-pond conditions only and I missed that implication

[Sailor Steve]

Originally Posted by aj906

But at 4 knots (as your latter post implies) this will not be a problem.

Absolutely true. I was only answering his idea that it should be better.

And, with batteries engaged, it is not like you would want to do much more than about that for the sake of economical cruising.

True. That said, you're only going to get six-to-eight hours doing that and then you'll have to recharge them. Since the engine doing the recharging has to run at full speed it will actually cost more fuel than if you just ran at 4 knots on the diesels. Unfortunately the game has this wrong and you can actually save fuel by travelling on batteries. Also they will recharge even if you are out of fuel. SH4 fixed this.

Also, if it is such an issue - and I'm not for one minute questioning you - why would it be a viable option related by veterans? Perhaps their recollections refer to mill-pond conditions only and I missed that implication

I was unaware of submarines using batteries for long-distance travel. Decks-awash surface approaches, yes, especially where silence is important. Maneuvering in port, yes. But travelling? I've not read those accounts.

[aj906]

According to U-Boat Far From Home. The epic voyage of U-862 to Australia and New Zealand:

"One shaft was kept running at half speed coupled to a diesel while the batteries were charged using the diesel dynamos. The remaining shaft was coupled to the motor with current from the batteries. With this arrangement the greatest range could be covered while proceeding at approximately 7 knots."

[Mittelwaechter]

As far as I understood the most efficient (fuel vs.range) way to sail the U-Boot was using one diesel directly, making revolutions for about 8 to 10 knots.
With the necessity to recharge the batteries, they used your quoted setup for recharging, sacrificed 1 or 2 knots but kept the fuel vs. range efficiency as high as possible. The low charging rate may have been a welcomed feature either, to keep the overall lifetime of the batteries up.

Running the second diesel to recharge the batteries would have used definitively more diesel fuel.

[Mittelwaechter]

Post under reconstruction...