Range curve

[Rosencrantz]

I might be wrong but I think range curve of Fleet boat in SH4 is a bit strange. What I mean is that for example gato's surface range seems to be only about 11 000 nm with one engine speed (1/3 or about 7 knt), 15 000 nm with two engine speed (2/3 or about 10 knt), 7 000 nm with standard speed (about 14 knt) and some 4000 nm with full speed (19 knt).

If we think that a typical WWII Fleet boat main diesel engine was constant speed type, running usually with steady rpm and at 80-90 combination (engine running with 80 percent rated load at 90 percent rated speed), then I think with given speeds the range diagram should not look like a curve, but more like a descending line. Look, that's the scale I got from my exec in SH4:

A) 11 000 nm : 7 knt = 1571 hrs
B) 15 000 nm : 10 knt = 1500 hrs
C) 7 000 nm : 14 knt = 500 hrs
D) 4 000 nm : 19 knt = 210 hrs

One engine on the line in case A, two in case B and so on... it just doesen't make any sense. Or am i missing something? :hmmm:

I think the previous table should look something like:

1/3 speed (one engine on the line) = 2200 hrs
2/3 speed (two engines on the line) = 1100 hrs = 11 000 nm at 10 knt speed (range taken from Wikipedia, could be wrong)
Std speed (three engines) = 550 hrs
Ful speed (four engines) = 275 hrs


BTW, does anyone know typical standard speeds for different bells of Gato? I assume mine are not off much, even if they could be...


Greetings,
-RC-

[Frederf]

I have a post with some engine-fuel data here. You will notice that the fuel consumption time rate (gallons per hour) basically flatlines between 0 RPM and whatever RPM is about 10 knots. The engine seems to burn just as much fuel (per hour) going 4 kts as 9 kts which is very weird.

http://www.subsim.com/radioroom/showthread.php?t=155945

[Rosencrantz]

Hello, Frederf!


Nice table indeed. You seem to be using RFB 1.52, while I'm using TMO 1.7 something (But I have done some editing in engine orders, so 1/3 bell is giving me 7 knt speed, 2/3 10 knt and so on...)

As far as I know real skippers preferred 80-90 combination to run engines most efficiently (clean burning, fuel used vs. speed etc). So I'm with you that there is something badly wrong in SH4 engines. If you are running one engine at 675 rpm (for example GM 16-278A and 16-248 were both rated for 750 rpm max, so 90 percent is something near 675 rpm), and using X gallons fuel oil, isn't it just logical that two engines at 675 rpm should use fuel oil 2 times X?

I think two engine speed might not be two times compared to one engine speed, but maybe somewhat slower, which means your "range per engine rate" decreases engine after engine on the line.

I think good start to solve this out could be finding original table of Gato's speed vs. rpm/engines on the line. I think my 7 knots from the first engine on the line could be a bit too much, but I think 10 knot speed for two engines is probably pretty close to reality. I have also found out that standard bell meant usually 13 - 14 speed, and three engines on the line, that has been mentioned in or between the lines in many original documents, memoirs etc. But how fast the boat went at full speed? Or at 1/3 speed? One solution could probably be:

1/3 = 6 knt
2/3 = 10 knt
Std = 14 knt
Full = 18 knt

But this seems to me to be pretty much too straightforward. Every new engine on the line would give some 4 knt extra speed... On the other hand, if we look increased speed in percents, then we'll see how every engine gives actually less and less...

I don't know...


Greetings,
-RC-

[SteamWake]

The part I dont understand is "one engine speed" and or "two engine speed"

As far as I know typically all engines run regardless of speed but the throttle setting is changed. Usually only time an engine is taken off a shaft is to charge batteries.

By the way the game considers your boat to only have two engines regardless of which boat your driving. :doh:

[Frederf]

It's true the game considers only 2 logical engines. Something like Engine 1 & Engine 3 are Engine A and Engine 2 & Engine 4 are Engine B. It also just goes slower or faster.

But I don't think the true diesel-electric boats had to do anything special to charge their batteries. Maybe with the old direct drive submarines you had to rig up an engine to charge the batteries. In the Gato class there's no physical linkage between the diesels and the screws. The fact that the engines power the electrical system and electricity is easy to adjust quickly based on propeller load is where the diesel-electric system gets all its benefits.

[Inner Sound]

The screws have an optimum rpm to convert fuel to thrust, which I would guess would be somewhere between Full and Flank settings, on the surface. Pretty sure they didn't have variable pitch back then.

At Standard the screw may not be converting fuel to thrust quite optimally but the boat's drag will be considerably less by the square of its speed rule so you get the best miles per gallon.

At less revs the diesels are using up fuel to basically just tickover while the boat goes slow. Maybe sometimes they'd just work one screw for absolutely optimum mpg, doubt it tho.

[Rosencrantz]

SteamWake wrote:


The part I dont understand is "one engine speed" and or "two engine speed"

As far as I know typically all engines run regardless of speed but the throttle setting is changed. Usually only time an engine is taken off a shaft is to charge batteries.

By the way the game considers your boat to only have two engines regardless of which boat your driving. :doh:



Hello, Steam!

"One engine speed", "two engine speed" and so on comes from original patrol reports, and as far as I know those were part of standard phraseology in those days. And again as far as I know those phrases were really meant to be taken literally. If I'm not wrong the Big Idea was to run the boat for example at 10 knt speed with only two engines on the line, running at optimum 80-90 combination, and not run the boat with all four engines running at lower speeds. That's my conclusion after reading not only the war patrol reports but also The Fleet Type Submarine Main Propulsion Diesel Manual and several memoirs.

I think Inner Sound was after something, when talking about converting fuel to thrust.


Greetings,
-RC-

[ColonelSandersLite]

The screws have an optimum rpm to convert fuel to thrust, which I would guess would be somewhere between Full and Flank settings, on the surface. Pretty sure they didn't have variable pitch back then.

At Standard the screw may not be converting fuel to thrust quite optimally but the boat's drag will be considerably less by the square of its speed rule so you get the best miles per gallon.

At less revs the diesels are using up fuel to basically just tickover while the boat goes slow. Maybe sometimes they'd just work one screw for absolutely optimum mpg, doubt it tho.


I'm not a submarine or ship *expert*so I don't know how relevant it is, however, I do know a few things about propeller driven aircraft. Both being powered by piston driven internal combustion engines and propelled by propellers lends some relevance though. I do know for a fact that at least with aircraft, running multiple engines is *much* more fuel efficient at best cruise than a single engine (though at high power, fuel is burned much quicker). This is largely the reason you see an emphasis on multiple engines on larger aircraft, and less emphasis on building a single large engine that can provide the same thrust.

The reasons are complicated and have to do with propeller effiency and engine power bands. Propellers are more efficient at lower speeds as they have to fight drag less. Probably very important for ships as water is much thicker than air. Power bands are probably equally important in both setups. Bearing in mind that revs are a function of manifold pressure and engine load (loosely speaking) I believe that basically, to get higher manifold pressure, you're dumping more fuel into the cylinder, but the more fuel you throw into it, the larger the % that goes unburned. The reason slower is not always better though, is that at lower manifold pressure, the engine is using more and more of its produced power just to function. Balancing power consumed by the engine itself and the amount of fuel burned at a given manifold pressure is what it's all about.

Believe me though, I'm not a physicist and may stand to be corrected on a point or two.

[Wilcke]

Are you discussing boats configured with 4 diesels connected to generators which drove the two electric motors that were then coupled to the props via geared reduction boxes?

Currently the sim leaves much out regarding the engine management part and I believe most of the big mods have tried to interpret a semi realistic range and bell scheme for the boats.

Buried somewhere in the forums there is lengthy discussion on and how this was achieved and the rationale.

As Rosencrantz points out these diesels were run on a governor at preset RPMS, which delivers optimum power output at the most economical fuel consumption level. That is for a healthy running diesel. Now I have read some patrol reports about boats floundering around on 1 diesel while trying to get the other 3 online due to mechanical issues.

I would like to have the 4 diesels, generators and electric motors modeled with corresponding damage and unplanned problems appearing and thereby adding another wrinkle to the skippers ability to operate the boat in a tactical situation. It would definately add another challenging dimension to your patrols, especially in the early years when patrol transit distances were very long.

[ColonelSandersLite]

As Rosencrantz points out these diesels were run on a governor at preset RPMS, which delivers optimum power output at the most economical fuel consumption level. That is for a healthy running diesel. Now I have read some patrol reports about boats floundering around on 1 diesel while trying to get the other 3 online due to mechanical issues.

Which in effect has the same purpose of a constant speed propeller unit and internal reduction gear on an aircraft, even if the exact mechanical linkages are somewhat different. Load is dynamically adjusted so that RPM stays the same while throttle changes, or in some types of systems throttle is governed to remain at the maximum allowable for a given rpm, while RPMs are controlled directly.

For fuel efficiency purposes, the batteries really don't need to be considered unless they're having trouble holding a charge. I'm sure there's a slight loss of efficiency there with normal operation (simple law of thermal dynamics) but for practical purposes it's negligible as unless you're wanting a power drain or surplus, power from the batteries to the propellers has to be equal to the power from the diesels to the batteries.

In effect, aside from things breaking, we would actually get no real bonus from more detailed engine operation as engines are run at prespecified levels (usually book listed form with handy reference charts available) to get desired power outputs. As submarine captains, not engineers, you just order up the power that the tactical situation demands and the guys in the engine room deliver it or tell you they can't (insert scotty here). Frankly, we don't need to worry about actively steering the boat in any dimension, which is as it should be as our heads need to be focused on either attacking or keeping the crew alive as the situation may be (not to mention the shear amount of micromanagement that would be. Too much for 1 player I think).

Anyways, I think what I'm really saying, and the only thing I've really meant to add to this discussion, is that there is no reason to ever shut down engines to save gas. That will just hurt your gas mileage. Running around on one engine is something to do only when the other three are seized up. I suppose I should qualify this and say that it is true that engine theory was not as refined in World War II as it is now, and it is entirely possible that they did not necessarily know this.

As an example of incorrect engine theory at that time, here is one easily identifiable example I can recall just off the top of my head. Charles Lindbergh flew with a P-38 squadron in new guinea as a technical adviser for a while. At that time, the USAAC's standard practice was to fly around at high rpm and low throttle. Lindbergh showed them that conventional practice was wrong and operating at high throttle, low rpm was much more fuel efficient, extending the range of the p-38 by a very large margin, and this happened in mid 44. I could probably come up with a few more examples of downright incorrect but accepted engine theory that persisted during and even well past the war, but I'm rambling anyways.

The entire point being, that multiple engines are more fuel efficient at their economy settings and shutting down engines to save gas hurts fuel economy. I'm not saying that it was or wasn't practice to do so in a submarine in the 40s, but I can almost guarantee that such a practice would not be accepted now.

Again though, I'm no physicist, and if someone who is cares to correct me, I would be interested in learning more about it myself.

[Hitman]

I would like to have the 4 diesels, generators and electric motors modeled with corresponding damage and unplanned problems appearing and thereby adding another wrinkle to the skippers ability to operate the boat in a tactical situation.

Well as long as they are NOt the HOR engines that will be fine! But if we are to model HORs in the game, better do not even start the patrol with them :damn:

[Rip]

Big difference in submarine diesel electric propulsion and airplane engines.

These big diesels are optimized to provide the best fuel efficiency at 80/90 not just based on the diesel but you have to remember they are just turning generators. Even if you throttle and that would somehow save fuel it kills the generator electrical efficiency. Most of them won't even work at all under a certain rpm. Once the battery is charged you are powering ship systems and the motors to turn the screw. Due to the diesel generator combination design two engines at 80/90 much more efficient than four at 40/45 IF you can even run them that slow. But even three at 50/60 or whatever would be less efficient.

[ColonelSandersLite]

So from what you're saying, I take it that each engine is linked to a separate generator instead of being linked in pairs or all to one central generator then?

I would think that would negatively impact fuel efficiency, but then again the added redundancy could certainly be a boon in an ocean going combat vessel.

[Inner Sound]

My understanding is that each diesel turned one generator. These provided the juice for two motors - one for each screw.

And the reason going slow gives you such poor mpg is the housekeeping load takes up so much if you're just running, say, one diesel. You need to get where you're going before the ice cream machine burns all your fuel. I think that's what Rip is saying anyway.

[Rip]

Yea each engine had its own generator as I understand. Redundancy in subs is everything. Even with four engines many of the HOR boats came close to being stranded by the failure rate.

Makes for an interesting difference in the U-Boats and their linking engines to the shaft. Although interesting Blair speaks of them occasionally running one engine but having the generator (which is also the electric motor IIRC) also engaged and using that power to spin the other shaft with the electric motor. This was to conserve fuel and he indicated this would give them about six knots one one engine.

[Rosencrantz]

Inner Sound wrote:

And the reason going slow gives you such poor mpg is the housekeeping load takes up so much if you're just running, say, one diesel. You need to get where you're going before the ice cream machine burns all your fuel. I think that's what Rip is saying anyway.


I think that was a good point again, Inner Sound. However, I think one of the very first and biggest problem is that we lack more detailed range vs. speed information about the real life fleet boats. After reading originals I still know nothing much about the subject. From patrol reports you can definetly find something, but not without problems: at least you have to consider boat's type, loadout, operational tempo etc. Manuals are handy but their information is still limited.
Another big problem is probably the way the engines are modelled in the sim. Present two-eniges solution comes clearly from SHII/III and U-boats. Easy, but somewhat harmful way to get the sim more flexible.


Greetings,
-RC-

[Wilcke]

Oh yes, the HOR engines were rubbish, that was engine type in the patrol report I read that was just nightmare as the plugged along on one engine. Occasionaly they could get a second or third engine up and running for about 24 hours or so and get the AC up for a bit.

I think that the time limiting factor for patrols in the 40's was more the endurance of the crew than the fuel consumption. I have to go into my notes and look at average days for the type of boats that went out and how long they were on patrol.

To model the HOR engines would be an absolute nightmare and as Hitman so aptly stated I would just stay in port.

[Frederf]

http://www.squick.org/ffa/bin/GatoCharts.png

Just wanted to drag this image over from the other thread. I think it shows what's going on with the fuel consumption in SH4. Look at the gallons-per-hour consumption... perfectly flat from 0.5 knot to 10 knot. It's around 12.5 hrs endurance per % of fuel below 10 knots. That means 52 days of fuel if you go any speed at all, less if you exceed economy speed. A 70 day patrol just plain ain't happening unless you sit still for days. Did submarines ever just sit still in the ocean with their engines off for long periods of time, just bobbing up and down?

[nubse]

Think about this: if you're heading straight north at 10 knots while an ocean stream is hitting your entire starboard side (heading west) at 10 knots, the ocean stream will influence the direction of water sucked in by your propeller, pushing your boat westwards, thereby also lowering the speed of the water being sucked in by the propellor to 2/3 or so. The propellor-size greatly impacts the amount of water that can be moved, which obviously has something to do with the fact that surfaced submarines never goes that fast.

I guess there's only rarely a situation where the current runs the same way as you, which probably WOULD put the propellor-wings at their optimal angle - and even more fascinating: try to put your sub into a coffin and measure the volume of water around the sub compared to the volume of the sub... you need to move this water. Therefore it must be propellor-size related to common ocean-currents, since there's always a current.

[Inner Sound]

And let's not forget the influence of the full moon - which is tonight, funnily enough. Awooo!

I like that water in a cofffin round a sub image.

[ColonelSandersLite]

WOW. That's incredibly wrong. Current has nothing to do with the propeller. You drift at a constant rate with the current unless anchored. True speed is calculated with trig.

Your true speed in relation to land is calculated thus:

The angle at which your submarine is hitting the current becomes the basis of the triangle. Current and and submarine speed are the legs of the triangle. The hypotenuse is true speed. The angle at the corner representing the submarine is true direction of travel.

Examples:

If your boat is pointing north going 10 knots according to the speedometer, and there's a 10 knot current heading east to west.

http://i3.photobucket.com/albums/y91/ColonelSandersLite/Currentexample1.jpg

Suppose now that you know there's a 4 knot east to west current, and want to head north at 10 knots true speed. In order to determine what speed you need to order up you use some trig and get this:
http://i3.photobucket.com/albums/y91/ColonelSandersLite/Currentexample2.jpg



Note that currents and tides are not in the game at all. Honestly, that's a big oversight for a naval sim. If you want to know more about it though, consult any trig guide to find out all the boring information you could possibly want about sines and cosines and crap.


Note that for the tacticle purposes of an engagement current is effecting your submarine, your torpedoes, and your target in exactly the same manner. Meaning that for the purposes of a targeting solution, as long as the current is constant it can be ignored. In real life, it might be an issue for harbour shots, but not gonna be a big problem for open water engagements.

[vanjast]

AFAIK there are no curents modelled in the current SH3/4 series..
:D

[ColonelSandersLite]

AFAIK there are no curents modelled in the current SH3/4 series..
:D


Correct, sit with engines off for a week and your boat will not move 1 millimeter.

Tides are not modeled either.

[nubse]

I'm no sailor, I'm only guessing. Is it called Aqua-dynamics? Aero-dynamics in cars count a lot on downforce, but there's no force pushing a boat down - a u-boat is very much the same as an airplane, the propellor/turbine draws in air/water, to propel the plane/sub ahead, but when the air/water is influenced by a current or wind, the angular heading of the water or air being sucked in by the propellor, should influence the speed of the sub greatly - simply because the propellor/turbine would turn towards the current, while the rudder would have to make up for the difference.

[ColonelSandersLite]

Big difference between what you're thinking and reality. A car is connected to the ground, a boat is not unless anchored. Since the boat is in no way connected to the ground, it moves with the water at the speed of the water. From the perspective of the boat's mechanics, the water is stationary and constant current has nothing to do with anything with a couple of exceptions. Mainly, if the current changes, inertia will resist this change. "Gusts" (I'm not sure what they're called in water terms) effectively end up being averaged out, with some rocking of the boat. Going from one current to another results in a more pronounced jarring, which then stabilizes.


A perfect example to think about is what happens if you drop a log into a river. There's no thrust, but the river carries it down stream.

This exact same thing happens with a plane as well. Since, in flight, a plane is in no way connected with the ground and is actually held aloft by the air, an aircraft drifts with the wind at at the speed of the wind. Instruments register airspeed, but not speed over the ground.

One notable incident, which nicely illustrates this, I can recall just off the top of my head was in WWI. I can't remember his name, but I'm pretty sure he was British. Anyways, the guy was flying around in his very slow biplane in a very strong wind. The wind was in fact so strong that that he was actually moving backwards, in relation to the ground but not the air, when he landed. I seem to recall that he was rewarded with a broken airplane for his efforts as it was never designed to land in reverse ;).

For a more visual approach, consider a plane landing. A plane must land on a runway going a specific direction (namely the direction the runway goes :D ). If the wind is blowing at an angle to that runway, you have what's called crosswind. Since a plane flies forward and not sideways in relation to the air, this must be compensated for with rudder, making the landing *look* crooked. Since I promised a visual example, here's a *perfect* example of how it looks:
http://www.youtube.com/watch?v=n9yF09DMrrI

If you don't know what you're looking at, that may seem to be a terrible landing, but it's actually extremely brilliant.

Several more crosswind landings, some good, some bad:
The one at 1:01 is an especially neat clip as it looks like the aircraft is coming right at you, but isn't.
http://www.youtube.com/watch?v=4RdxU-0W-RE


For yet another way to think about this to help you understand this. You are (most likely anyways) on dry land when you read this. The land beneath your feet is moving at roughly 1,000 miles / hour (slightly wrong but just run with it). With your logic, this would have some kind of effect on the tires of your car, but in reality, it has absolutely 0 effect on your car (or feet) regardless of whether your are driving east, west, or in any random direction. Your speed in relation to the ground is the same either way. However, suppose you where, for some reason, navigating by the earths core.

If you sit stationary in your car, your speed is about 1,000 miles per hour in relation to the earth's center. If you drove east at 60 miles an hour, your speed would be 1,060 miles per hour in relation to the core, and if you drove west, your speed in relation to the core would be 940 miles per hour. For any other direction, your speed would be solved with simple trigonometry as stated above. Thankfully, there's practically no need to ever know your speed in relation to the center of the planet, so it's not a worry! Well, maybe for astronauts...

Hope that clarifies matters some.

To muddle them, wind can effect the boat as well (assuming it's not below water), pushing it off in that direction. Honestly though, even the "fast" ships are slow compared to your average car and even "light ships" are very very heavy. Unless you're in a sailing ship or very small vessel, wind effects are likely to be somewhat negligible for practical pruposes.



Side note, if you want to try some *really* tedious math, try figuring out what a ship's speed in relation to the center of the sun is at any specific time, date, current speed, and boat speed.

[Munchausen]

I'm no sailor, I'm only guessing. Is it called Aqua-dynamics?

:hmmm: I think the correct term is hydrodynamics.