Optimum Speed in Patrol Grid?

[Stiebler]

What is the optimum speed for patrolling your assigned grid square (eg BE65)?

The two plausible alternatives seem to be:
a) at one-third ahead (most efficient fuel setting to make progress);
b) at slow ahead (consumes least fuel to maximise time in grid).
[Alternative (c) - to use no fuel at all by remaining stopped - would not be permitted by BdU, since it endangers the boat in case of sudden air attack.]

If the target merchant ships appear truly randomly and instantaneously in the square, then there is no difference between (a) and (b), except that (b) will allow you to remain longer in the patrol grid.

However, the merchant ships do not appear randomly and suddenly. They move slowly through the patrol grid square. Moving faster through the grid may increase the chance of locating them as they move. Or it may take you away from the targets faster.

I'd guess that the answer depends on the (average) relative speeds of U-boat and target.

Quite an interesting statistical, or mathematical-modelling, exercise.
Does anyone already know the answer?

[Incidentally, wolf-packs patrolling the Atlantic moved at slowest speed in their grid, to conserve fuel. But they relied on their U-boat neighbours to patrol their flanks so that nothing could slip through. Their solution doesn't necessarily apply to a lone-wolf U-boat, as in SH3.]

Stiebler.

[Sailor Steve]

I always move at slow, to conserve fuel. I assume I have food for two months in a Type VII and try not to head for home until 50-60 days have passed. Of course if you're lucky you'll run out of torpedoes long before that...

[Deimos01]

I run at 1/3rd once I hit my grid. No use wasting fuel. Save that for chasing down convoys. When making contact with an unreported lone ship or convoy it is pretty much a matter of being in the right place at the right time and speed wont change that. Save yer fuel!

[Coda]

I stay submerged at 1/3 untill I use 20% of my battery, then surface and recharge at ahead slow. After charged, I go back down.

Reason I do this is the ability to hear much farther then see. It also save a ton of fuel.

[GT182]

I use 1/3 for the same reason as Deimos01 says. Plus 1/3 consumes more time for the required 24 hours. Now that I have a snorkel for my D2 I usually patrol submerged. If I come across a warship, they have less of a chance seeing us and we have a better chance of escaping if detected.

[Stiebler]

Many thanks for these replies, but unfortunately they state only how the respondents *do* patrol their grid areas, not how they *ought* to patrol their grid areas.

I've carried out a computer modelling simulation.

Results in the sticky NYGM Research thread:
http://www.subsim.com/radioroom/showpost.php?p=327125&postcount=66

Stiebler.

[Letum]

Historicaly 7-7.5 knots was the usual speed for a type VII

I stay submerged at 1/3 untill I use 20% of my battery, then surface and recharge at ahead slow. After charged, I go back down.

Reason I do this is the ability to hear much farther then see. It also save a ton of fuel.

This DOES NOT save fuel. You use more fuel to charge the battrys again!

[fxn]

1/3 all the way to the patrol grid, ahead slow once in patrol grid. That's how I do it.

[Ducimus]

Historicaly 7-7.5 knots was the usual speed for a type VII

I stay submerged at 1/3 untill I use 20% of my battery, then surface and recharge at ahead slow. After charged, I go back down.

Reason I do this is the ability to hear much farther then see. It also save a ton of fuel.

This DOES NOT save fuel. You use more fuel to charge the battrys again!


Acutally it does save fuel, at least, if you ahve the NASA battery fix in place. (only way you'd bring your bats down to 20% anyway :roll: ). But you have to do it for a long time to show fuel gains. Takes me about 3.5 to 4 hours to recharge a batter thats down to 30% to 40% .

The proof of it , is in the math, if we had the acutal figures.

Recharging bats, makes one engine run at flank speed for however long your recharging your bats, while the other engine is at around 100-200 rpms. How many RPM's your turning dictates your fuel usage.

So if we had the figures, you'd have to sit down and figure out how much fuel your using in a 24 hour period just running on the surface at ahead slow, vs running submerged most of a 24 hour period, surfacing for only 4 to 5 hours during that 24 hour period to run your diesals.

[Coda]

When I said I use 20% of the battery, I meant that I leave it 80% charged, only use up 20% of the full charge. It works for me.

[Tobus]

I go slow wherever I go, only using higher speeds in attacks. With slow speed, A VII can go from Kiel to New York and back with some fuel to spare.

In my patrolgrid I usually go under to 50 meters on slow speed, since you can hear much farther then you can see.

[Zero Niner]

My cruising speed, to the patrol area and within the grid itself, is 1/3.
I use faster speeds only to intercept targets, leave a dangerous area, or returning to port - if fuel situation allows.
I normally exhaust my torps before fuel becomes an issue (I'm a Type VII user).