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A view from the Engine Room: Endurance - 4/15/2010 4:34:25 PM   
steamboateng


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This is a two page, rather long read, so you might to go to the fridge and pop a cold one prior to diving in!
Definitions
Endurance is a measure of how far (in nautical miles) a ship of a given displacement and optimal fuel load, can travel, at a given speed (in knots). Simply put, its a vessel's operating range for a fixed set of parameters. This definition is valid for real navies, as well as WitP AE virtual counterparts.
The amount of fuel oil consumed to maintain a given shaft rpm is directly related to Endurance. This is the Fuel Rate and is defined as fuel consumtion per unit of time. During WW2, the (US) fuel rate was measured in gallons (gals.), barrels (bbls.), or tons (t. or l.t.). A standaed barrel = 42 gals. (This is a traditional measure dating from early in the century; not to be confused with our standard 50 gal. drum.) A ton, in marine usage, is a long ton, or 2200 lbs. (I know, damm sailor's can't call anything what it really is!)
Here are some more definitions to confuse and baffle you.
A propeller is basically a screw machine. It is defined by its diameter, number of blades, and pitch. Pitch is the ideal distance a prop will longitudinally travel if rotated one revolution. If you own a small boat (or big yacht), you already know from your fuel bill, that ain't what really happens! A propeller's efficiency, through water is a function of Slip. All props have slip, which is the distance it didn't move, expressed as a percentage of the distance it was supposed to move. Example: a prop with a pitch of 12 ft. is observed to move only 9 ft.; 12 - 9 = 3. It didn't move 3 ft.; 3 / 12 = .25; the slip is 25% This is called negative slip. 15% to 20% is an average range of slip for a large vessel on a calm day, with little or no current. But such days aren't always the case. A fully loaded ship, off cape Hatteras, heading south to Miami, nosing into a small gale fights not only the wind and seas, but is fighting the Gulf Stream current as well! If the ship hasn't seen a dry dock in several years, hull fouling (sea grasses and crusaceans, whch climb aboard for the ride) will also slow her pace. If the gale is strong enough, the ship may actually go backward for the day (slip in excess of 100% is not uncommon). Of course, the reverse is also true, a lightly loaded ship, being pushed by following winds, currents, and seas could warp speed you from Hatteras to Miami in far less than a day!
Trying to measure a consistant fuel rate over an observed distance, under varying weather conditions, is a useless task. That's why we sailor's invented another term, Engine Miles. Engine miles is the total number of turns of the propeller, over a given length of time, say a day, times the propeller pitch. Engine Miles less Observed Miles divided by Engine miles is Slip. Thus, using Engine Miles and shaft revolutions, at steady steaming conditions, allows us a method of determining Fuel Rates for a given class of vessel. The US Navy, of course, figured this stuff out a long time ago, and developed real time performance curves for their vessels. For most US ships engaged in WW2. this performance data, entitled War Service Fuel Consumptions of US Naval Vessels, FTP218, (from which I gleaned all relevent data) can be found at www.ibiblio.org/hperwar/USN/ref/Fuel, or you can simply Google 'USN fuel consumption' and follow your nose to the site.
Game Mechanics
In WitP AE, a ship has three speed states: stopped, which is 0; Cruising Speed (which is 15 knots for most combatants)and Maximum Speed (which varies by vessel class). In game terms, maximum speed is limited to an effective 30 knots, since no ship can move more than 9 hexes (360 n.mi.) per phase, 720 nautical miles total. In reality, most larger ships cruised at 17 to 18 knots. Due to fuel, machinery and hull considerations, maximum speed was used only to meet specific mission goals or in defensive manuevering. Maximum speed was in the 30-ish knots range for most latter built (DD through CV) ships. Of all US BB's, only the Iowa class could hope to reach this speed.
Merchant ships and Naval auxiliaries rarely could or would exceed their cruising speed for any length of time.
In game terms, WitP implementation of ships speed is adequate. Comparing the variuos Ships Information screen speed ratings, in all cases, was consistant with published data for Naval and Merchant vessels. The displacement tonnages were all fairly accurate and reflect the 'light' (unloaded) tonnage, in long tons. The listed fuel capacity is in long tons. The fuel capacities, as listed, often varied somewhat from FTP218 listings, and appeared to reflect the Maximum, or 95% capacity. For DD's and smaller ships this is not an issue, since space limitations clearly dictated dedicated fuel tanks. However, on larger ships, there are tanks which can carry fuel/salt water ballast and/or remain void for reserve bouyancy. Each class of ship has recommendations from BUSHIPS as to how these tanks should be maintained in combat areas. The implementation of these recommendations was at the discretion of the vessel's commander. This brings about a conflict, not only in the tonnage of fuel carried which can vary from 700 to 1300 tons (depending on class) less than 95% capacity; but also brings Endurance Ratings into question.
Also, each ship's rated Endurance, as it appears in FTP218, refernced above, is an Endurance Rating for Engine Miles In many cases the the Endurance listed on the Ships Information screen parallels (though exceeding) the FTP218 rating. Unless there is another reason, which I cannot easily ascertain with the available infomation; the data suggest rather inflated Endurance values present in the games code, for each vessel class. Propeller slip, weather, currents and hull fouling are not factored in.
To model fuel consumtion the developers use only one fuel rate for each ship class. That is the rate at Cruising Speed; which for most combatants, is 15 knots. Thus, a combat ship travering one hex will lose 40 (miles) Endurance; and the fuel capacity will decrese 40 times the tons/mile fuel consumption rate (or 1 times the tons/hex fuel consumption rate). If Endurance at cruising speed closely parallels FTP218 values, then it follow that the fuel consumption rates coded into the game, closely follow FTP218.
Wisely deciding not to encumber the game data base with a gaggle of class specific engineering data, and allowing one other ship's speed to be represented, that of Maximum Speed, the developers cleverly defined Maximum speed Endurance (i.e.fuel consumption) as a function of Cruising Speed Endurance. Maximum speed Endurance is is defined as Crising speed Endurance plus 240 Endurance. Thus a US combat ship at Maximum Speed consumes Endurance at 280 Endurance per hex traveled; which is a ratio of 7 times the cruising rate. We can safely assume that the fuel consumption rate is seven times that of fuel consumption at cruising speed. A close examination of the tables in FPT218 shows that from 15 knots to Max speed (30 - 32 knots) the fuel consumption rate of the various classes increases by a facto of 6 to 8; It seems that a factor of 7 times Enurance was a very valid choice.
Conclusions
Although the relevant data for each ship is pretty much in line with published Naval and Marad data; it seems the developers failed to account for propeller slip, weather, currents and hull fouling in their Endrance calculations. Also, fuel capacities for larger ships may be inflated. A reduction of enudrance in the range of 15% to 25% for each ship class is required to bring endurance in line with realistic operations.
Your comments, suggestions and insights on the above commentary is welcome.

Regards
steamboat




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RE: A view from the Engine Room: Endurance - 4/15/2010 7:30:23 PM   
findmeifyoucan

 

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Very interesting and valid points but don't forget that this is a strategic game with tactical variations. This game also has to be playable and to put all the individual currents into the game and wind variations I think the work needed would be quite extensive. Other factors which you haven't taken into account is on how streemlined the bow of the ship was. A ship built like a ball in the front would be more energy efficient and use less fuel and the same speed as say a ship built like a knife. Contrary to earlier belief. I know these things as my father was the one who invented the ball for ships and now they all have them built that way!

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RE: A view from the Engine Room: Endurance - 4/15/2010 8:15:48 PM   
Panzerjaeger Hortlund


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quote:

ORIGINAL: findmeifyoucan

Very interesting and valid points but don't forget that this is a strategic game with tactical variations. This game also has to be playable...


In what way would that change in your opinion, if all the endurance ratings were lowered 15-20% across the board?

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RE: A view from the Engine Room: Endurance - 4/15/2010 9:38:18 PM   
JWE

 

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Woof! Nice big post Steamboat. Too much there to hit all your points, so lemme just give you the game philosophy, and we can go from there.

Ok, there's two speeds the game engine recognizes; full and cruise. Game engine can calculate a "mission" speed, but it's just a math % of curise and full. When you make a TF, the TF moves at the slowest cruise speed of the constituent vessels (nominally). Ok, so what? So the designers did was normalize warships (and the merchies) into cruise speed bands. It was utterly stupid to set ships at 16, or 15, or 14, 13, 12, whattheheck, so we normalized warships to 15 knots, cruise. Any marine engineer with half a brain that can read a power chart can figure out, pretty darn quick, just how to normalize things to 15 knots cruise. Ok, so Navy TFs wander about at some nominal speed - cool.

Merchies are same/different. Don't want TFs to care about if cruise is 7 or 8, so the same bands apply. Some are 14, some 10, some 8, but it all depends on specific classification. The bands are important, not the individual ship specs. And we also normalized ships into their respective bands.

Ok, so what is endurance? Well ... top level it is the "fuel mile" parameter that the design specs specify, given the nominal bunkerage, noted in the base paper. This ain't deep tanks, this ain't wet bow, this is in your face bunkerage. But individual ship class endurance is tagged and flagged to its position in the speed band. Endurance is a parameter that depends on fuel and a mathematical calculation as to how that fuel/speed may be used to implement an imperative.

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RE: A view from the Engine Room: Endurance - 4/15/2010 9:51:28 PM   
steamboateng


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In no way do I suggest that weather, hull fouling etc. be implemented as individual factors in game mechanics; thus complicating and bloating an already sizable game data base. What I am saying is that propeller slip was a real and unavoidable loss in efficiency, through the water. Rarely would the value of observed miles approach engine miles. In reality, an average day's progress would almost always be 15% to 20% less than recorded engine miles. This can easily be handled in game, by reducing the value of Endurance, as indicated on the Ships Information screen, by a percentage which would more reflect prototypical operating parameters. In game terms, all this means is your TF's must refuel more often. Of course, the availability of fuel within the game, be it a scenario or a full campaign, is a separate factor. Refueling more often could very well affect game balance negatively.
Regards
steamboat

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RE: A view from the Engine Room: Endurance - 4/15/2010 10:38:28 PM   
AlaskanWarrior


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Good analysis, although as far as the game code goes I am afraid you fall on deaf ears. Most of this has been hashed over repeatedly. I mod for 20kts Allied and 18kts Japanese for most warships cruising (shown to be historically verifiable), which significantly increases their fuel consumption and the speeds are more realistic fleet cruising speeds, as well as allowing for the increase of auxiliaries such as turbo-generators, pumps, and inefficient steaming practices such as the necessity of having most of the boilers hot. When playing my mods there is a grater attention to where the nearest fuel station is, and how well it is provisioned.

< Message edited by AlaskanWarrior -- 4/15/2010 10:39:44 PM >


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RE: A view from the Engine Room: Endurance - 4/15/2010 10:56:15 PM   
sdevault


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I thought Japanese ships where faster than Allied, so would your statements mean that Japanese commanders, on average, sailed slower? Fuel conservation perhaps, or is it that the Allied ships were damn near always on the move (more sorties). And in some cases, in a hurry to get the job done...

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RE: A view from the Engine Room: Endurance - 4/15/2010 11:41:56 PM   
pompack


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quote:

ORIGINAL: steamboateng

In no way do I suggest that weather, hull fouling etc. be implemented as individual factors in game mechanics; thus complicating and bloating an already sizable game data base.


Outstanding post Steamboat!.

I will add my two cents in here with the thought that hull fouling could be considered to be modeled into the SYS damage that accumulates through normal steaming. Now admittedly, this point gets a little soft when the SYS damage can be repaired at pierside instead of a drydock but at least there is some mechanism to produce slower speeds with increasing time without maintenance.

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RE: A view from the Engine Room: Endurance - 4/16/2010 4:35:19 PM   
findmeifyoucan

 

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I don't think it would be fair to reduce endurance ratings accross the board as every ship is different. Even ships with the same exact design could perform differently. Engine Crew experience also should be a factor in performance. Some crews maintain their engines better than other and as a result better performance.

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RE: A view from the Engine Room: Endurance - 4/16/2010 5:10:05 PM   
JWE

 

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quote:

ORIGINAL: steamboateng
Your comments, suggestions and insights on the above commentary is welcome.

Regards
steamboat

Ships evolved from the original WiTP database. IIRC four different people worked on the ships; one did Allied warships, one did Japanese warships, one did submarines, one did auxiliaries and merchies, and other people chimed in from time to time. The data came from Jentschura, Watts, Lacroix, Conway, etc .. and had a bunkerage figure and a figure of endurance at x-kts (usually 14, 15 or 16). Since consistency was an object, and since that’s the way it was done in WiTP, it was a straight forward matter of simply entering published data. 15 knots was chosen as cruise speed because the majority of the endurance data was given as ‘umpty-ump’ nautical miles at 15 kts (where it was 14 or 16, a linear adjustment was made to normalize to 15).

While 18 19, or 20 might be economical for larger vessels, it is moving right up the power curve for smaller combatants and requires a disproportionate reduction in DD endurance, for example, which causes issues when factored with the code multiplier for the ‘full’ speed differential. It makes DDs very problematic with respect to endurance when escorting 12 knot merchant TFs. A TF moves at the speed of the slowest ship. Fuel consumption is on a hex basis. There is no consumption benefit given to ships with a high cruise speed that are moving much more slowly. It’s one calculation applied to all. So 15 was retained because it works adequately over all the movement and consumption models.

As to endurance, well, when you have published numbers, and don’t have a lot of naval architects on the team, you use the published numbers. FTP218 is very nice, but it’s only for about 1 in 100 of the ships in the game, leaving the other 99% losing suction. A uniform reduction in endurance wouldn’t be that hard to do. There is a program provided with the game that allows scenario files to be exported in an Excel readable format. Just multiply everything in the Endurance column by 0.8, or whatever, re-import, and presto.

Try it, and let us know what happens. Be very interested to see how it works out.

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RE: A view from the Engine Room: Endurance - 4/16/2010 7:00:59 PM   
witpqs


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And as you point out, the game already de facto performs the endurance reduction in most use cases for DE's and many use cases for DD's, because they are 'cruising' at less than their cruising speed by escorting tankers, merchants, transports, and so on.

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RE: A view from the Engine Room: Endurance - 4/16/2010 7:15:06 PM   
CarnageINC


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I needed 2 cold ones to get thru that 

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RE: A view from the Engine Room: Endurance - 4/16/2010 11:40:27 PM   
steamboateng


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Ok Guy's. Seems I may have opened a can of worms on this topic!
JWE, it seems you got a bit of 'Navy Special' or 'Bunker C' in your veins; your comments are well taken and to the point.
You got the old gears turning again. From your last post, it seems you agree somewhat, based on FTP218 data, that at least some US warships may be over rated for Endurance. My point being simply that comparing WitP US warship data vs. FTP218 data, Propeller Slip was not factored into Endurance ratings for the game. (FTP218 was a reference document for navigators and engineers; it was up to the ships navigators to factor in slip, under their current weather and sailing conditions, to accurately project ETA for meets or destinations) You are quite right in stating that I can't make that assumtion for all ships in the game. Particularly since several folks were involved in collecting the relevant information.
I'm sure my 'Google' goggles will get a work out in the next few weeks, tracking some data down for other ships. Ships engineering data (and construction, armament data) is not easily come by over the internet. Hat's off to you guys who must have searched a gazillion pages for reference documents.
Please understand I'm not trying to poke holes into WitP AE. My original quest was to research data, to more fully understand how the game mechanics translate reality to virtual reality. It was purely an accident that I bumped into FTP218 in my search.
CarngeINC: I hear ya! It took me a lot more pops than that just to type it!!
findmeifyoucan: Point well taken. I was quite surprised, over the years, how different engine room performance varied, given the same class of ship. (Hint: the Navy, nor the Merchant Marine, operates as a democracy.)
witpqs: Endurance, in game, as well as real world, greatly decreases as ships speed increases. Increasing speed from 15 to 20 knots, on the average, will double a ships fuel consumtion rate, i.e. half its effective Endurance. At full speed, in the 30-ish knots range, fuel consumtion is increased by a factor of 6 to 8 times. At 32 knots, your Essex Class carrier is reduced to an effective Endurance of about 1/7th its 15 knot Endurance.
pompack: Thanks for the kind comments. Calculating propeller slip inherently ecompasses hull fouling. In fact, the daily noon calculations for slip will slowly increase as hull fouling increased. Slip was a major factor when determining when its time to 'get her bottom scraped'. System damage, during a voyage, at least in my newbie mind, would cover normal wear and tear breakdowns (somethins' always breakin') and occasional storm damage.
sdevault: The relationship between a ship's speed and her Endurance is reiterated, above.
Alaskan Warrier: Afraid I misled you a bit there. As my comments to JWE indicate and he has confirmed, Endurance is a data base entry, therefore modable. Its not hard coded. Sorry!
Thanks all again, for your input. I've got an Excerin headache now, and will quietly retire to the comfort of my couch to tend my potatoes.
Regards
steamboat





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RE: A view from the Engine Room: Endurance - 4/17/2010 1:39:52 AM   
witpqs


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quote:

ORIGINAL: steamboateng

witpqs: Endurance, in game, as well as real world, greatly decreases as ships speed increases. Increasing speed from 15 to 20 knots, on the average, will double a ships fuel consumtion rate, i.e. half its effective Endurance. At full speed, in the 30-ish knots range, fuel consumtion is increased by a factor of 6 to 8 times. At 32 knots, your Essex Class carrier is reduced to an effective Endurance of about 1/7th its 15 knot Endurance.


Understood! My point is that DE and DD endurance is calculated at 15 knots for the game database. When they are tethered to slower ships, the game will still charge a hex at the 15 knot rate. Hence, the 'built-in penalty' for many DE and DD missions, which probably makes up for the lack of slip being calculated in.

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RE: A view from the Engine Room: Endurance - 4/17/2010 4:41:13 AM   
steamboateng


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witpqs, o.k, i see what your getting at now: a DD escorting a 10 knot convoy is still tied to its 15 knot endurance rate; this is due to how Endurance is implemented in game mechanics. Sorry, I was partaking of my evening ration of salt pork and biscuit, and overlooked your point.
Well, that just threw a few more worms in the can, didn't it.
Thanks for the insight
Regards
steamboat

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RE: A view from the Engine Room: Endurance - 4/17/2010 5:28:56 AM   
witpqs


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That is a large part of what John (JWE) was getting at - they had to pick only two speeds for each ship, cruise and full. And cruise is what the calculation for endurance is based off of.

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RE: A view from the Engine Room: Endurance - 4/17/2010 10:26:50 PM   
JWE

 

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Oh, gosh, no worries guys. I just thought to explain how and why it happened as it did. Once all our little ducks are lined up, then the shooting gallery can have a fair chance to knock 'em down.

hi steamboat. Not much Bunker in my veins, mostly rum. I'm a rag-bagger, do racing sailboats, but Forude is Froude and a hull is a hull, yeah? I did take most of my elective courses at the Pratt School and am a member of SNAME. Takes a while, but I can usually figure out that stink-pot stuff. I just happend to be fortunate and grow up in Tampa with a bunch of Howells and Lykes, so had contacts with the international community and got access to stuff that just isn't on the internet. That's about it for me - salt water sailor, but need some big breeze to get excited.

< Message edited by JWE -- 4/17/2010 10:27:56 PM >

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RE: A view from the Engine Room: Endurance - 4/17/2010 11:25:20 PM   
steamboateng


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I'm jealous, JWE! I'd love to have a 36 foot motor sailor to run away from home, in.
However, knowing how it can get out there, especially in the Gulf during Hurricane season, I'd prefer sumthin' 'bout 900 foot long, 105 foot wide, with a big, brassy wheel at the back end.
godspeed, sailor!
Regards
steamboat


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