Guide to fuel conservation

[Ducimus]

Fuel consumption, and its conservation is actually a big part of the game, and i believe a part that is not fully understood by everyone.

First, lets get the basics out of the way:

Things that lower your fuel capacity

- Damaged fuel tanks (obviously)

- Recharging batteries

- Battery damage. ( Once a battery is damaged the game doesn't always turn "recharge mode" off, and you have to do this manually, the kicker is, you may not always realize it, so always make sure you CE goes back to normal running after a battery charge)

- High speeds chases

- Putting around at excessively low speeds.


Things that effect your total surface endurance

- the state of the sea. High waves and wind will hinder you on the surface.


A bit more on charging batteries

In SH3, when you were recharging your batteries one of your two engines was taken off propulsion and switched to charge the batteries, and thats all it did. While doing so, this engine would be running at an RPM equivlant to flank speed. While i'm unsure exactly how engine configurations in SH4 handle the charge, it is reasonable to assume that while charging your batteries, you have one or more engines running at a higher than normal RPM, this takes fuel.

With this in mind, you would do well to conserve your batteries when you can by running at lower submerged speeds. With patch 1.3, assuming your running TMaru, battery recharge time averages around 6 to 7 hours. Running submerged at 2 kts uses less batteries then running submerged at 3 kts. Running submerged saves fuel, so long as you keep your battery expenditure to a minium to reduce recharge requirements.


Midway and sub tenders...
Use them. Plan on using them, their there for a reason. Infact, if your a pearl harbor boat, you NEED midway. Any patrol route that leaves pearl harbor that does not figure in midway both when going to your patrol area, and coming back from your patrol area, is a failure. Asiatic fleet boats should count on the tenders which appear later in the war.


Ploting the first half of your patrol route
So you've left pearl harbor, and topped off your fuel tanks at midway, (Tmaru does this for you, but thats besides the point).

The first thing I should do, is take the ruler tool and plot a line from my current location near midway, to my patrol area. This gives me the most direct route. What i do then is zoom in the map and actually plot the course using the line(s) i just drew as a guide. The purpose being to make sure i don't run the boat aground on some small island or reef that does not appear on the map when zoomed out. You may also have to plot around some large islands, and you should *try* for the closest route to the line you drew, geography and ASW concerns should be part of your decision. Once i've plotted my course to my patrol area, i wlll go to AHEAD 2/3's, and while i wait for the boat to build up speed to around 8 or 9 kts, i proceed to my next step.

Plotting the second half of your patrol route
So the boats building up to a speed of 8-9 kts and while its doing so , i will go ahead and plot my course back from my patrol area to midway or whatever refueling point i will encounter before my home base. Having done that, and the boat at now my normal cruising speed, i start jabber jawing with my navigator.

"Hey Jim, whats the range to course end?"

"Eh, i calculate about its about 10,500 Nautical miles Rich".

"hmm, ok, at our current speed, how far do you think we'll go?"

"Given our current speed, i reckon we have enough fuel to travel about 14,500 NM, give or take"

"Ok, thanks jim".

Figuring out your actual patrol allowance
Patrol allowance is a term i give to how much fuel you have to actually operate on. In the above example, you have an estimate of about 14,500 nm, and your round trip ticket costs you 10,500 NM. That's just coming and going. This fuel is commited, theres no flexing here. So what you acutally have is 4,000 NM of fuel to operate on.

However, theres other factors to consider. Primarily Battery recharging and the weather, both of which will reduce your operational endurance. Given this, ill take my above data, and round up to compensate. So i fgure 11,000 NM to get to and from base, with a 14,000 NM endurance, which gives me 3,000 NM of fuel to work with. In the interests of giving myself a bit more flex for the return trip to make sure i can make it home, ill take 1,000 off of that. So in reality, i have an operational endurance of 2,000 NM. Thats ALL im giving it. If i push it more then that (and i could with that built in buffer), i endanger my ability to RTB.

Establishing when its time to RTB
The easiest and simplist way is to always be mindful of how far you are from the closest refueling point (midway in my case), and your maximum range at current speed is. If you have a maximum range of 6,500 NM, and you range to midway is 5,000 NM, its time to RTB! Always allow a buffer.


Being stingy with your operational fuel
So, now that we've established we have about 2,000 NM of actual fuel to play with, your going to encounter situations that will tax that, and your going to have to make decisions based on that.

For instance, is the target your pursing worth the fuel expenditure? Is that 2,000 ton freighter worth the fuel it would take to do an end around attack? Or would you hold your cards and hope 5,000 ton freighter?

Is a submerged approach more economical then a surfaced one?

etc etc, theres all sorts of hypotheticals.

Extending your stay in the area of operations
In short, in daylight, patrol submerged at the most battery economical speed of 1/3rd, or 1 to 2 kts. Use as little of your battery as possible, so you use less fuel recharging it, not to mention *some* fuel savings for having not used your diesals to begin with.



Now then, that clear as mud to ya all? :88)

if you read all that and understood it, now you know why ive always been saying fuel is a big part of the sim, and If your running out of fuel, well, you made some wrong decisions captain, better brush up!

[Ducimus]

edited a A BUNCH of times if you started reading it. I got over complex in some areas. :88)

[Go4It]

Never new SH4 had sub tenders, if so, were does one find one....

[Iceman]

Very good advice thank you for the post. :up:

[Von Tonner]

Never new SH4 had sub tenders, if so, were does one find one....

They are those striped anchors you see on the map. You can refuel and rearm at them but not effect any repairs. Just be careful, I have been attacked at one and sunk.

Thanks for that info Ducimus, I was under the false impression that the longer I stayed under travelling to assignment the more fue I saved. Now I see why I could never handle coming out of Pearl and resorted to always playing Asiatic Fleet. Thanks.

[Ducimus]

I was under the false impression that the longer I stayed under travelling to assignment the more fue I saved.

That was true in SH3, because the battery recharge only took around 3 hours. Now they take around 7 hours (give or take an hour). The 6-7 hour recharge being more realistic of course.

[THE_MASK]

Thanks for this awesome fuel summary :up: .

[PepsiCan]

I was under the false impression that the longer I stayed under travelling to assignment the more fue I saved.

That was true in SH3, because the battery recharge only took around 3 hours. Now they take around 7 hours (give or take an hour). The 6-7 hour recharge being more realistic of course.

There's also plain physics involved. If you burn diesel to charge your battery for the energy value of 100 kilowatts, then you will not charge your battery for 100 kilowatts. A lot of energy (as much as 50%) will be lost in the form of heat, friction (resistance in the .

So, the cycle looks like this:
- you start with a full battery and you use up 50 Kilowatts to transport yourself 50 miles.
- you then need to burn a 100 kilowatt to recharge your batteries (50% energy loss)
- so, you actually used up twice the amount of diesel to cover those 50 miles then you would have had to use if you'd run on the surface.

Conclusion: running submerged is very inefficient due to the way the recharge process works.

[Steeltrap]

Another thing to consider is this: do I have to go anywhere IN my patrol zone? In other words, having reached your patrol zone there is no actual need to go anywhere until you find a target or have one reported you wish to intercept. That's why I lie motionless on the surface in my patrol zone once I'm in a likely encounter position.

O'Kane did that in Tang...he said to lie to like that took some getting used to!

[Snuffy]

Good Tips Ducimus! Thanks! :up:

I for one have always been very conscious of my fuel, realizing that if I wanted to get the boys home to see the girls we needed certain amount of fuel for doing so. :yep:

Of course now that I'm in July 44 and tenders are showing up all the time as the allied lines advance over the Pacific, (the Marines just took Siapan yesterday! :rock: ) so having more places to refit before heading to home is allowing me to take on more and more assignments from HQ.

The only times I head home now are if I have damage to the point of batteries not reaching full charge or I have wounded that are taking a long time to recover. Also I don't go home unless HQ tells me too. (After sighting and reporting a contact sometimes HQ says RTB at your discretion.)

[pocatellodave]

Good job Ducimus.Thanks a lot.
Pocatellodave

[PepsiCan]

Another thing to consider is this: do I have to go anywhere IN my patrol zone? In other words, having reached your patrol zone there is no actual need to go anywhere until you find a target or have one reported you wish to intercept. That's why I lie motionless on the surface in my patrol zone once I'm in a likely encounter position.

O'Kane did that in Tang...he said to lie to like that took some getting used to!

I do that too. Near Kyushu or near Formosa/Taiwan the ships will come to you. So, wait and you'll get a contact :-) Waiting near busy harbours is also beneficial.

[ReallyDedPoet]

Nice Ducimus:up:, just saw this.


RDP

[SteamWake]

Good job D. Confirms alot of what I 'believed'.

About 'drifting' at your patrol zone. Its really not a bad idea but dont get caught out there at a dead stop in the day time by aircraft.

Also if the sea state is pretty rough it would be a good way to tear up your boat and make your crew pretty unhappy. But hey its just a game ;)

[Tom C]

O'Kane did that in Tang...he said to lie to like that took some getting used to!

Steeltrap, did O'Kane say whether he kept all or some diesels idling (instead of shut off), in case he needed to move in a hurry?

I'm still playing the archetypal over-cautious early-war skipper and I see Japanese periscopes under every whitecap!

[sqk7744]

Ducimus many thanks for posting, this is great! :up::up::up:

(so where's the Fuel Flow meter? ;) ) I guess the RPM gauges are not live.

Cheers!
:arrgh!:

[Ducimus]

RPM gauges are at the helmsman station in the control room (forward of the chart table), and behind you in the conning tower. Unfortunatly their not very accurate. Theres 4 of them and they range from 0 to 250. The needle starts measuring before it even hits 0. And then turns totally around ,and pegs soemwhere at what im guessing is around 540 (5XX soemthign) because that is what the max RPM in SH3 was. Im assuming its the same here, despite what the listed RPM in the sim file is saying. Anyway, point is, RPM gagues exist, and the scale on them is way off.

[Frederf]

I was under the false impression that the longer I stayed under travelling to assignment the more fue I saved.
That was true in SH3, because the battery recharge only took around 3 hours. Now they take around 7 hours (give or take an hour). The 6-7 hour recharge being more realistic of course.
There's also plain physics involved. If you burn diesel to charge your battery for the energy value of 100 kilowatts, then you will not charge your battery for 100 kilowatts. A lot of energy (as much as 50%) will be lost in the form of heat, friction (resistance in the .

So, the cycle looks like this:
- you start with a full battery and you use up 50 Kilowatts to transport yourself 50 miles.
- you then need to burn a 100 kilowatt to recharge your batteries (50% energy loss)
- so, you actually used up twice the amount of diesel to cover those 50 miles then you would have had to use if you'd run on the surface.

Conclusion: running submerged is very inefficient due to the way the recharge process works.

On the surface, applied physics would seem to indicate that running submerged on batteries would have less overall range than running on diesels alone, but this is not neccesarily the case.

While it's true that the energy in the batteries used for submerged travel is not "free" and has to be gotten from fuel reserves and that the fuel-diesel-battery-motor energy chain is not 100% effecient, it's still possible for battery / electric engine use to increase, not decrease the range of the submarine. I will try to explain using the most extreme case of diesel/electric mixed propulsion.

Version A: A stopped sub with 0% charged batteries will run the diesel engines strictly as a generator to charge the batteries. Once the batteries have a charge, the sub uses its electric motor to move 10nm.

Version B: A sub uses its diesel engines to drive 10nm.

Which version uses more diesel? You may be tempted to say Version A uses more diesel fuel since the recharging, eletric motor process has more steps and thus more chances for energy to be lost due to heat, friction, 2nd law of thermodynamics, etc but it is not neccesarily the case.

It is because the diesel engine does not have the same effeciency at all RPM! It is possible to charge the batteries at the RPM that is the most effecient for the diesel engine while maybe the best RPM for the diesel engine/ boat hull is not so effecient for the diesel engine. The convoluted fuel-engine-battery-motor process, despite having more steps CAN (in theory) be more fuel effecient than the diesel engine alone because of the variable effeciency of the diesel engine under various loads.


Now I am completely uncertain about the following two concepts:

1. Were real life WWII submarines more effecient under mixed diesel-electric propulsion compared to pure diesel? It's theoretically possible but was it actually the case? Unknown. I thought German U-boats benefit from the mixed propulsion.

2. Are WWII submarines as modeled by the game (vanilla, modded?) more or less effecient under either method? Again unknown.

MORE INFO AND CITE:

http://www.ossapowerlite.com/tech_library/fuel_efficiency/fuel_efficiency.htm

Not all of the points made in this article apply to WWII submarines as they are designed, but there are plenty of valid points made that do.

[Tom C]

Frederf, I don't know about SH4 but in RL I think you're on the right track. Not sure about the S-boats, but AFAIK all the fleet subs had the diesels driving the electric motors, i.e. the diesels never drove the propeller shafts directly. Any difference in efficiency must lie in charging efficiency versus motor efficiency, and I don't know which was the bigger loss-- as you said, if they were different the diesel rpm could be optimized in either direction.

But, the US WWII sub hull and propellers were optimized for surface running, not submerged running. IMHO if you're not losing efficiency in the drive train, you're losing it in hull drag underwater, and you still won't get the same mpg as on the surface.

[Sailor Steve]

O'Kane did that in Tang...he said to lie to like that took some getting used to!

Steeltrap, did O'Kane say whether he kept all or some diesels idling (instead of shut off), in case he needed to move in a hurry?

I'm still playing the archetypal over-cautious early-war skipper and I see Japanese periscopes under every whitecap!
I don't know what the great one actually did, but engines completely off should be no problem, as the electric motors can accelerate you pretty quickly and you'll want to be diving in that situation anyway.

[-Pv-]

When I'm eating time in a patrol area waiting for targets to show up and I'm also in an area agressively patrolled by the enemy, I will use 22ft deck awash and set 3 knots diesel speed. This lets me loiter a very long time without giving up mobility, fast acceleration and nearly instant diving time. The wake is minimal at this speed.
Conservation theory asside, it's my practice to conserve very aggressively on the way to the 1st patrol area so I can spend what I've saved being more aggressive and evasive in the patrol area.
-Pv-

[Torpex752]

Theres is one more variable that none of us has considered. The ballast tanks. There were 2 ballast tanks that were routinely converted to fuel tanks to extend the subs range capacity. This ability was never "advertised" when discussing the subs range, so most posted data leaves this out.
So I'll see what I can find on its capacity and then maybe that amount should be added to our fuel supply? Just a thought.

Frank "Torpex" Kulick
Subsim Staff :cool:

[Tom C]

Hi Frank, are you still involved with PTC? I haven't looked in on that in years.....

I just happened to be reading a chapter in Galantin's "Take Her Deep!" last night where he mentions the fuel ballast tank conversion added 24,000 gallons.

I don't know but that sounds to me suspiciously like an explanation for why the fuel capacity for Gato/Balaos is sometimes given as 115,000 gallons (more or less) whereas Tambors (with almost identical hull, only 2 feet shorter I think?) is usually given as 93,000 gallons (again more or less), around 22,000 difference. What capacities does SH4 use?

[Frederf]

What effects on diving performance would having ballast tanks full of fuel would there be?

[NEON DEON]

What effects on diving performance would having ballast tanks full of fuel would there be?

I suppose you could partialy flood negative in order to compensate for the difference in weight between oil and salt water.

I think the first bit of fuel to be used if part of the ballast was used to store fuel would be the oil from the ballast. So by the time you got into it the ballast should not have fuel left anyway.

Just guessing.

[Tom C]

What effects on diving performance would having ballast tanks full of fuel would there be?


Galantin says, "On the surface the ship rode a bit lower in the water, as it was without the buoyancy of an empty main ballast tank."

So if anything, dive time might be a bit faster.

Just before that he says that the fuel ballast tank was always kept full until the fuel was used up, which makes sense because blowing and venting that tank would blow away the fuel. "As diesel oil was consumed, seawater admitted to the bottom of the tanks took its place. This created the apparent anomaly of a ship becoming heavier as it burned up its fuel supply, since the fuel was lighter than the replacement water."

[GT182]

Great info as always D. :up: Unless it was needed I always kept my speed to what was most efficient in SH3. That ment checking the range often as related to the speed you were using. If lowering you speed ment a great range, that was the way to go. Or stop and filler up wherever you had the chance at a friendly base or "tender".

And to what Torpex say, would it be possible to make a mod to use these ballast tanks for fuel?

[Ducimus]

And to what Torpex say, would it be possible to make a mod to use these ballast tanks for fuel?

*shrug* use stock fuel settings! All boats save the porpoise and S boat in stock have a 15,000 NM range at 10 kts. When it should be in the neighborhood 12,000 @ 10 kts. In TMaru i fudged it and gave in the neighrborhood of 12,000 @ 10.95 kts (may as well say @ 11 kts). That little fudging of the numbers i did, in action increased max range by 1000 to 2,000 NM, which is still less then stock. :88)

edit:

As anyone coud guess, im a big stickler on fuel. Its an important gameplay aspect to me. That said, if someone links some hard evidence of how much extra fuel was carried in the ballast tanks, ill adjust for that in TMaru 1.5.

[Ducimus]

Meh, this threads worth a revisit:
http://www.subsim.com/radioroom/showthread.php?t=114746

Im wondering if i should just stop counting rivets and bring it back to stock, but it really bugs me not having to worry about fuel.

[Frederf]

I thought that having fuel in a tank that was designed to help surface and submerge this submarine would limit the captain's ability to do certain things, lest he risk blowing out precious diesel like it was bilgewater.

[Captain Scribb]

As Galantin explained in "Take Her Deep!", it was only a small hindrence, and was usually consumed well before reaching any area of enemy activity. As the fuel was used, sea water would replace it, since the fuel wouldn't mix and would float on top anyway. So it didn't really do anything but make the boat sit a little lower, and any fuel inefficency caused by the increased drag from that would be well compensated by the extra fuel that was available that originally caused it. And dive times would actually be slower at first because the oil weighs less, thus less ballast, but it would soon be neglible as it became more and more seawater in the tanks.

Galantin did mention that once the extra fuel in the ballast tanks were consumed, the sub would repeatedly dive and surface, to flush out any trace amounts of oil that would leave a "tell-tale slick" when diving in a combat situation. So in that effect, it effect combat operations. No reason to add that into game though, before adding in diving at least once a day to adjust trim in the ballast tanks. That's more of a day-to-day thing missing than a one-time flushing.

[Torpex752]

And to what Torpex say, would it be possible to make a mod to use these ballast tanks for fuel?

*shrug* use stock fuel settings! All boats save the porpoise and S boat in stock have a 15,000 NM range at 10 kts. When it should be in the neighborhood 12,000 @ 10 kts. In TMaru i fudged it and gave in the neighrborhood of 12,000 @ 10.95 kts (may as well say @ 11 kts). That little fudging of the numbers i did, in action increased max range by 1000 to 2,000 NM, which is still less then stock. :88)

edit:

As anyone coud guess, im a big stickler on fuel. Its an important gameplay aspect to me. That said, if someone links some hard evidence of how much extra fuel was carried in the ballast tanks, ill adjust for that in TMaru 1.5.

After doing some looking around, I would say that as long as the fuel capacity we use includes the fuel/ballast tank capacity included in the calculation, then 12KNM @ 10.95kts is fine IMHO.

Frank "Torpex" Kulick
Subsim Staff :cool:

[Torpex752]

I thought that having fuel in a tank that was designed to help surface and submerge this submarine would limit the captain's ability to do certain things, lest he risk blowing out precious diesel like it was bilgewater.

I am sure that the tank was isolated from the others. A simple valve line up is all would be needed.

Frank "Torpex" Kulick
Subsim Staff :cool:

[SteamWake]

Saltwater mixed into the diesel even in tiney amounts would absolutly wreck the engine. Ive seen a 750 HP diesel generator that inhaled some rain water and ended up siezing the engine. The cylinder walls looked like they were scrubbed with 80 grit sandpaper.

There is a gizmo called a fuel / water seperator on the fuel feed lines of the engines to try to avoid this catastrophie. In the above example generator the water was sucked through the wall vents, through the air filter, and into the engine. (the mechaincal engineer had undersized the intake louveres and there was too much air velocity literally sucking rain into the room). I imagine that air intakes for a subs engine has some sort of way of avoiding that.

I belive the ballast tanks and fuel tanks had no interaction with one another.

That being said a full fuel tank would most likely help to dive a tad faster but then again the ballast tanks would have to be ... uhh... emptier to keep the ship afloat.

It has been known that at least in game that if the 'ballast tanks' are partially filled from either running decks awash or a recent dive the ship dives faster.

[Mylander]

On the surface, applied physics would seem to indicate that running submerged on batteries would have less overall range than running on diesels alone, but this is not neccesarily the case...

Is the above some kind of cruel pun?

All kidding aside, great thread and great info.

Mylander

[Frederf]

Saltwater mixed into the diesel even in tiney amounts would absolutly wreck the engine. Ive seen a 750 HP diesel generator that inhaled some rain water and ended up siezing the engine. The cylinder walls looked like they were scrubbed with 80 grit sandpaper.

There is a gizmo called a fuel / water seperator on the fuel feed lines of the engines to try to avoid this catastrophie. In the above example generator the water was sucked through the wall vents, through the air filter, and into the engine. (the mechaincal engineer had undersized the intake louveres and there was too much air velocity literally sucking rain into the room). I imagine that air intakes for a subs engine has some sort of way of avoiding that.

I belive the ballast tanks and fuel tanks had no interaction with one another.

That being said a full fuel tank would most likely help to dive a tad faster but then again the ballast tanks would have to be ... uhh... emptier to keep the ship afloat.

It has been known that at least in game that if the 'ballast tanks' are partially filled from either running decks awash or a recent dive the ship dives faster.

From another post recently apperantly there was a series of several tanks between the "open ocean fuel tanks" to the actual engines. They apperantly scrubbed the fuel oil real well before the engines to remove the damaging water.

[Torpex752]

Saltwater mixed into the diesel even in tiney amounts would absolutly wreck the engine. Ive seen a 750 HP diesel generator that inhaled some rain water and ended up siezing the engine. The cylinder walls looked like they were scrubbed with 80 grit sandpaper.

There is a gizmo called a fuel / water seperator on the fuel feed lines of the engines to try to avoid this catastrophie. In the above example generator the water was sucked through the wall vents, through the air filter, and into the engine. (the mechaincal engineer had undersized the intake louveres and there was too much air velocity literally sucking rain into the room). I imagine that air intakes for a subs engine has some sort of way of avoiding that.

I belive the ballast tanks and fuel tanks had no interaction with one another.

That being said a full fuel tank would most likely help to dive a tad faster but then again the ballast tanks would have to be ... uhh... emptier to keep the ship afloat.

.

US Subs had what was called a clean fuel oil tank, and in fact even modern submarines have a similar setup with diesel on top and seawater on bottom. No high tech gizmo here just a simple seperator tank. So, not blasting you, but there is more than one reference in the books about this fuel/ballast tank. It did exist and was used for fuel & once empty, ballast tank.

Frank "Torpex" Kulick
Subsim Staff :cool:

[SteamWake]

US Subs had what was called a clean fuel oil tank, and in fact even modern submarines have a similar setup with diesel on top and seawater on bottom. No high tech gizmo here just a simple seperator tank. So, not blasting you, but there is more than one reference in the books about this fuel/ballast tank. It did exist and was used for fuel & once empty, ballast tank.

Frank "Torpex" Kulick
Subsim Staff :cool:

Amazing... although it makes sense because the oil would 'float' above the seawater. I guess they pull the fuel off the top of the tank.

Probably have some damn good fuel/water seperators. I can imagine that in rough conditions the two might mix up to some degree.

I can see filling the 'empty' tank with sea water to keep things balanced too makes sense.

[Spruence M]

Very nice fuel walk-through. Thanks for the effort.

[Fearless]

I was just wondering in the .sim file of the sub, distance is shown as "miles". Now 1 nautical mile = 1.15 mile so does that mean for example in the .sim file lets say for the Gato class, 11,800 miles should in fact read 11,800 nautical miles therefore the setting should be 13,570 in the Gato.sim file :hmm:

Just wondering.

[Frederf]

I was just wondering in the .sim file of the sub, distance is shown as "miles". Now 1 nautical mile = 1.15 mile so does that mean for example in the .sim file lets say for the Gato class, 11,800 miles should in fact read 11,800 nautical miles therefore the setting should be 13,570 in the Gato.sim file :hmm:

Just wondering.

Pretty much all "miles" in game should be "nautical miles". It's a good eye and an obvious possibility. The only statute miles should be given in terms of weather visibility which the game doesn't do.

[Torpex752]

US Subs had what was called a clean fuel oil tank, and in fact even modern submarines have a similar setup with diesel on top and seawater on bottom. No high tech gizmo here just a simple seperator tank. So, not blasting you, but there is more than one reference in the books about this fuel/ballast tank. It did exist and was used for fuel & once empty, ballast tank.

Frank "Torpex" Kulick
Subsim Staff :cool:

Amazing... although it makes sense because the oil would 'float' above the seawater. I guess they pull the fuel off the top of the tank.

Probably have some damn good fuel/water seperators. I can imagine that in rough conditions the two might mix up to some degree.

I can see filling the 'empty' tank with sea water to keep things balanced too makes sense.

Even though they did it then & we do it now, and I know how it works...it still amazes me how well it works. :rotfl:

On the nuke boats I was on, we had a waste oil collection tank that the bilges would get pumped to. It has a mixture of seawater & oil leaks from the bilges. We could pump it after so many hours of being pumped into, to allow it to seperate. We'd pump just the seawater out at sea, and in port the waste oil to a tanker on the pier.

Frank "Torpex" Kulick
Subsim Staff :cool:

[PepsiCan]

Try the following:

1) Get a glass or cup that you can see through so you can observe the effect.
2) Poor some salad or olive oil in the glass
3) Add some water
4) Observe the effect
5) Stir the mixture with a spoon
6) Observe how long it takes for the oil and water to be separated again
7) Poor the olive or salad oil back into the bottle
8) Drink the water

Have fun! :know:

[dean_acheson]

I guess, what I am wondering is what is the best speed to use from and too area in different boats, using only the patched game and TM 1.4.

Now, how lazy is that?

[WernerSobe]

not sure if that has been already said.

There is always an optimum speed for every engine, so called "cruising speed". Cruising speed slightly differs but it seems to be between 10 and 11 knots for most boats. Try setting 10,5 knots and ask for maximum range. You can go about 20% further then at a speed of 8 knots (2/3).

I always try to go on cruising speed over large distances. And then switch to slower speeds when patrolling. Thats the best way to save fuel.

[Ducimus]

I would increase the 2/3rds throttle percentage in TMaru, except that throttle settings apply to both submerged and surface. Maybe i should change ahead standard?

[WernerSobe]

i think what is calles "standard" should be the cruising speed.

There is no cruising speed submerged. At least theoreticaly electric engines are indeed the slower the further.

[Ducimus]

Well again, my problem is in terms of submerged performance 2/3rds is right where i want it, and 1/3rd is about ok as well. 2/3rds on the surface is 8 kts. Standard is 12, full is 18, flank is 20+.

So i suppose i could make standard around 10 kts, full around 15, and flank at 20. Just feels redundant and silly have the throttle settings so close to each other.
5, 8, 10, then 15 20.

[Von Tonner]

y heart nearly stopped when I was told we were out of diesel. I couldn't understand it as the sub came to a complete stop even though the calculations read that I had a range still of 654nm. But when I asked for 2/3s the engines kicked back in and we were under way again. Reserve maybe?

05.33 CE We're out of diesel fuel sir!
05.33 NA Range to end is 654 nm
05.33 NA Maximum range at current speed is 648 nm

Had to creep into Freemantle at periscope depth for the last 10nm:oops: I'm getting there Ducimus, had I not read your fuel post I would again have been stranded.
http://i200.photobucket.com/albums/aa130/shazavaar/fuel.jpg

[dean_acheson]

I'd been running around 8ish, so I'll adjust that.

[Steeltrap]

O'Kane did that in Tang...he said to lie to like that took some getting used to!
Steeltrap, did O'Kane say whether he kept all or some diesels idling (instead of shut off), in case he needed to move in a hurry?

I'm still playing the archetypal over-cautious early-war skipper and I see Japanese periscopes under every whitecap! I don't know what the great one actually did, but engines completely off should be no problem, as the electric motors can accelerate you pretty quickly and you'll want to be diving in that situation anyway.

They remained on the surface without any motors running. As Steve points out, the batteries could deliver power immediately. O'Kane's orders were to manoeuvre on batteries only to alleviate any unpleasant motion caused by the swell. In short, they sat dead in the water and moved slightly on batteries if required. O'Kane demonstrated in a training period pre-patrol that this would enable them to hear an approaching sub before it could get to good attack range. It's also the ONLY circumstance under which the hydrophones should work on the surface.

I actually have taken to remaining dead in the water at 80' depth. It's impossible to remain on the surface without using fuel, even at 'all stop'. You can, however, hover at any depth without using battery power, so you need only surface periodically to replenish the air supply. It's silly, but works as a response to a probelm in the sim vis a vis remaining motionless without using fuel AND being able to 'search' using the hydrophones. I find a good spot where shipping should travel then remain at 80' for long periods of time. It's the same as remaining on the surface and allows using the hydrophones and no fuel, as was actually done in real life, so I accept that hovering was not really possible......

[captiandon]

In short for those who wonder Take how I run. At night I am on the Surface and running at 2/3's Day time I run submerged at 2 kts. I have burned over the same milage half the fuel I would have if I ran on the surface at Standard most of the distance. I have gone from Fremantle to The southern Part of the Celebras Sea on less then 15% of my fuel load. Of course I fueled at The tender at the North east side of Austrailia as well. Figure about a Quarter of your fuel to get to your patrol from Fremantle and I would use about a Quarter on the Patrol its self leaving you with another Quarter to get you home. The Last Quarter should be reserve only in case of Emergancy.

[Powerthighs]

Has anyone quantified the degree to which sea state affects your fuel usage? I assume it increases with wind speed, which to my knowledge is the only thing that affects sea state.

I'm looking for some data points that define the curve of how fuel usage climbs with wind speed. Does the wind direction versus your sub's direction factor in?

[sniperdoc]

I actually have taken to remaining dead in the water at 80' depth. It's impossible to remain on the surface without using fuel, even at 'all stop'. You can, however, hover at any depth without using battery power, so you need only surface periodically to replenish the air supply. It's silly, but works as a response to a probelm in the sim vis a vis remaining motionless without using fuel AND being able to 'search' using the hydrophones. I find a good spot where shipping should travel then remain at 80' for long periods of time. It's the same as remaining on the surface and allows using the hydrophones and no fuel, as was actually done in real life, so I accept that hovering was not really possible......

That's pretty much what I end up doing a majority of the time.

If I'm not sure where the shipping lanes are at, I'll submerge to about 80 - 100' and just listen. When I hear faint noises, I'll head there at ~2kts until my air supply runs low, I'll surface replenish the battery and air to 100% and then dive to 80' again and listen until I get a travel pattern of contacts.

Once I have the approximate travel lane figured out, I'll head topside and head out there at Standard speed diving periodically to see how close the contacts appear. Once about 2500' out from the travel lanes, I end up bobbing up and down from 100' to the surface (replenishing my air supply) just listening for contacts and refining my target search.

In the past, if I was trying to conserve fuel, I've always been under impression that going Standard or Full while under diesel, then diving to 50 - 80' and doing electric at 1/3 until my battery is about to run dry and then recharging topside at Standard or Full again, was the way to go... but I guess not?