Cruise Speeds

[engineer]

The resistance of a hull in the water is a complicated fluid dynamics problem, but a first order estimate is that the energy needed to move the hull varies with the cube of the hull’s cross-sectional area, adjusted by a number of factors that have to do with the geometry of the hull and the efficiency of the propeller(s). The bottom line as I understand it is that a ship can make about 80% of her top speed with about 50% of her motive power. If I misunderstand the math here, my apologies in advance, but I’m sure there are experts in the community who can verify or clarify the technical point that I’m raising.

The problem is with the numerous ships that have cruising speeds at a paltry fraction of top speed. Actually, I don’t have a problem that warships with high top speeds cruise at 10 knots. There is a good military reason for naval vessels to act in concert so a common cruise speed makes sense. Naval auxiliaries become the lowest common denominator here, and if you need to move faster, then you have Mission Speed. What does bother me is the merchant shipping. For example, this includes the 12 knot Allied AP’s that cruise at 4 knots and the 10 knot Allied AKs that cruise at 5 knots (but the 12 knot Allied AKs cruise at 11 knots).

The point here is that mission speed and full speed sailing accrue more systems damage than cruise speed. Merchant ships will be clogging the yards to have damage repaired unless they sail at cruise speed, but cruise speed in the stock scenarios is punitively slow.

I would suggest that warships cruise at 10 knots as long as their top speeds exceed 12 knots. Other ships (with a few exceptions noted below) would cruise at 75% of their top speed or 10 knots, whichever is lower. The main exception would be AP’s. Many of these vessels were converted passenger liners and routinely “cruised” at greater than 10 knots in their normal civilian roles. For AP’s I would recommend that they would cruise at 75% of their top speed (so a 14 knot AP would cruise at 11 knots and a 27 knot North Atlantic liner like the 59,000 ton SS Leviathan (an OOB oversight after allowing time for conversion into a troopship, a role she played in the Great War) would cruise at 21 knots. A player hoping to escort her would assign destroyers to follow at mission speed so as not to accrue unnecessary systems damage from having the liner sail at mission speed.

The recommendation would have one other benefit in indirectly comprehending the different complexity of warships and merchant ships. The warships had weapons, fire control equipment, ammunition handling equipment, and relatively high power engines for their higher speeds. Basically, there is far more to go wrong than in a merchant ship.

[JagdFlanker]

i run all my merch at full speed and i only accrue 2-5 sys dmg per month, which i don't think is too bad and totally worth it in my opinion. i find my warships at mission speed accrue about the same amount, but it jumps 10 X that at full speed so i rarely use full speed with warships unless they are chasing the enemy or there are merch's or replenishment ships in the TF to keep the warships slow. i must admit i never use cruise speed unless i have a replenishment TF loitering in 1 hex for a period of time, and even that might not be a good idea if there are hostile forces in the area.

[engineer]

Hmm, my experience is a bit different.  I've been seeing merchants on mission speed do a round trip from Karachi to Singapore and return with an average of about 5% systems damage.  On the Hawaii run, the Allied player has the advantage of the West Coast ship yards for quick repairs, but the dockyards on the Indian Ocean aren't as well developed.  Some AP's did a round trip from Pearl to Eniwetok on Mission Speed and returned with about 4% damage.  In any event those are anecdotes with off the top of my head figures. 
 
Certainly I can run some controlled experiments to verify performance of the game as currently coded.  Things like 12 knot AK damage at full, mission or cruise between various ports and 10 knot AK damage with similar speed settings.  Use lots of ships (at least five or six per cell) and long voyages then the randomization should even out.   At the end of the day, one would have a table of damage versus distance tables for the various merchant ships.  Certainly there is the possibility of perverse outcomes (a 12 knots AP that cruises at 4 knots accruing more damage at cruise than mission speed because it takes so long to get from point A to point B). 
 
Tactically, it also highlights the advisability of grouping like transports together.  12 Knot AKs lose out when convoyed with 10 Knot AKs and the like. 

[JagdFlanker]

the brits don't have near as much need to use transports since brunai is self-supplying and the rest is on the mainland. in all the games i play britain is neutral unless attacked by japan so there is not much need for a lot of brit activity. britain does have 2 20pt, 1 40pt and 2 50pt shipyards so they arn't doing too bad for shipyards! plus another 15pt and a 50pt in australia.

also you might be interested to know that 1-9kts goes 1 hex, 10-14kts goes 2 hexes, 15-19kts goes 3 hexes, and so forth (times 2 since there are 2 move impulses per day.) this means that a 10kt ship goes just as fast as a 12kt or 14kt ship - but should the 10kt ship take 1 sys dmg it then goes down to 9kts and slows down to 1 hex per impulse/2 hexes per day instead of 2/4 hexes. so yes it's better to split up TF's based on speed, but if you don't you can still get away with it for at least a little while.

[engineer]

The manual says that the fractions eventually show up (so a nine knot TF will move two hexes for 4/5 moves and just move one square on the fifth move).  I've seen that in the operation of the game so this would seem to be case where the manual's right.
 
A few nights ago I forward deployed two battle squadrons with their escorts from Pearl to Eniwetok at cruise speed and had a good experience (3 ships out of 16 had only 1 point of systems damage and the others had no damage). 
 
One of the things that I like about WPO is the whole logistics problem of putting beans and bullets where it counts.  But the other, more subtle thing that's in the game is the whole operational wear and tear so you have to hit the right balance in setting an operational tempo that moves the campaign forward without running your forces into the ground. 
 
The Cautionary version of the historical War Plan Orange (from the early 1920s) postulated that the US forces would move on Eniwetok and then Truk in the opening phases of the campaign.  However, the return to the Philippines would depend on the construction of dreadnought sized dry-docks that could be towed to the forward bases to turn them into new main bases that would allow the fleet to proceed further west.  The operational wear and tear (the systems damage factor in WPO) was judged significant enough that keeping a sufficiently strong battlefleet at sea would not be possible when operating far forward of fixed repair yards.
 
On a related note, is there a switch in the scenario editor somewhere to adjust whether various countries are neutral or belligerant or does this depend on a "House Rule"?   Is there anything beyond an AR that represents mobile drydocks?

[Rysyonok]

To the two questions in the end: No and no.
 
In my experience transports can sail forever and still have little to no system damage. Remember, once they hit even 3 or 4, you might as well switch them to cruise speed anyway, as they'll be sailing at the same pace, 2 hexes a day, 0 speed or 9

[engineer]

I have some preliminary data from a late scenario game.  The results are based on sample sizes of about twenty ships (mostly merchants and destroyers but 8 battleships are in the cruise data set) sailing an average of about thirty hexes.  The group that sailed at Cruise Speed picked up an average systems damage of 0.0058 per hex traveled while the group that sailed at Mission Speed were picking up systems damage at a rate of 0.0090 per hex traveled.  I have a dozen more convoys, including some at full speed, that are still at sea.

The preliminary data leads to some preliminary conclusions:

• As the manual states, Mission Speed creates higher systems damage.  This data shows a ratio of about 1.5:1.  More data will smooth out any statistical aberrations due to small sample sizes. 
• For fast 12 knot AK's, one can sail at Cruise Speed instead of Mission Speed.  You get 33% less damage but only give up 8% of your speed. (Upon occasion the incremental damage will be worth the speed in getting food and fuel to some point on the map (Nathan Bedford Forrest's adage about being the "firstest with the mostest").).  Yard time is for the repairs is the critical variable on whether this is a better tactic or not.  If your yards are fairly empty, a few percent of systems damage can be repaired in a few days.  If your yards are clogged with other merchants and warships, then removing that damage will often take weeks.  In the latter case, sailing at cruise speed to postpone the yard time as long as possible is clearly the better strategy.   
• For 10 knot AK's, it's clearly a superior SOP to sail at Mission Speed instead of cruise speed.  You travel twice as far but only suffer 50% more damage.
• My impression of systems damage was overstated.  At 0.0090 systems damage per hex, it takes a voyage of 110 hexes (just over one round trip from Karachi to Singapore) to accrue an expected 1% damage. 
• The more valuable the ship, the more care should be taken in traveling faster than cruise speed.  It appears that the damage accrual chances are same regardless of the type of ship at sea.  However, the repair process does depend on the size of the ship (destroyers repair much faster than battleships).  The manual gives a precise formula.  I've started cruising to a waypoint just short of the target then making a mission speed dash for the final 24 hours to minimize systems damage prior to the first shorts being fired.      

My original point about the funky cruise speed values for the merchants is borne out by the third conclusion.  We have a perverse outcome in the simulation when traveling faster (putting more mechanical wear and tear on the propulsion system) results in appreciably less systems damage per distance unit travelled for the slow AK's.  Since the factor to control damage is buried in the game engine and not accessible, the free variable that we can adjust is the cruise speed value for the slow AK's.  They should come up to seven or eight knots. 

I'll have more data in a few days that should characterize how the engine is handling all of this so final conclusions can be drawn. 

[Tankerace]

Finally have time to comment on this. Been having to do field research for a thesis. Good stuff.
 
The Cruise speed, in terms of damage, should really only matter with regards to warships. Merchant ships, with a max speed of only around 12-13 knots, will usually not rack up enough damage to put them out of action. When I run my merchant ships, they usually get yard time every 7 or 8 months. They do rack up damage, but not enough to be a true hassle.
 
The primary effect of cruise speed with regards to merchant ships is to illustrate size of ships. Moreover, fuel efficiency. It takes more fuel to go 12 knots over a "standard" merchant run of 3,000 miles than it does to go at 9 knots. If playing as Japan and hitting a fuel crisis by 1924, this can become a critical factor. For long runs, going 3,500 miles at 5 knots is twice as long as going 10 knots, but you won't burn nearly as much fuel. For the smaller cargo vessels, this is a necessity for using them in the Pacific.
 
This won't be an issue on runs from Hawaii to Wake, for example, but going from the United States to Australia, or Australia to China, or India to Australia it is a must to effectively use the small AKs on routine convoys without making a ton of stops.
 
For instance, a large US AP travels at 15/10 knots, and has 4,450 tons duel. A Small Ap can do 10/5 knots and has 1,000 fuel. If you continually run the small AP at 10 knots, you cannot use it for backwater convoys, thus taking your large APs you need to haul troops. But if you set it to 5 knots, it can probably make the distance. When the values are tweaked (range and cargo capicty), it will be more clear and necessary.
 
As to taking damage, what was the weather of your test? Doing 10 knots in a calm sea will not put as much damage as 10 knots in a heavy swell.
 
Finally, the cruise speed difference is to help differentiate class. You don't want to put Small, Medium and Large APs all in the same convoy, as running at full speed your large APs will be handicapped, or going long distances (admittedly not so much a factor now. But in the new patch the ranges are getting cut by over half, as is fuel and capacity, so it will then) you will want to use each merchant type within it's speed grade. Using examples from the 1.3 OOB set (still working on it... been delayed because of school), the Transport class ships have max speeds of 9, 13, 14, and 16 knots. You can run full speed if you want, but that 16 knot TP has a range of only 11,000nm (versus 14,000 in 1.205) with 3,500 fuel. That is at cruise speed (10 knots). At full speed it will only get you about 7,500 nm. Not to bad for that type of ship.
 
But, the 9 knot TP has a range of 6,000nm/6 knots with 2,000 tons fuel. At full speed, it will only go about 4,500. Not good if you need a regular convoy from Aussie land to the U.S.
 
Remember, cruise speed is what affects range and consumption. When you see a given range, that is at cruise speed. If wish to run at full speed, if it is twice the cruise speed your range will be cut down by about half.
 
They may seem funky when taken only in one context, but consider cruise speeds have affect on damage, convoys (i.e. how fast/slow a convoy can go), fuel consumption, damage at speed, and damage for being at sea (i.e. continual use), and interception, it really makes sense.
 
Yes, interception. By knowing relatively how fast a merchant ship can go, you can plot a mid ocean intercept. 5 knots (cruise) * 12 hours = 60nm, meaning it will be one hex away in the night phase, or *24 hours = 120 nm = 2 hexes away in the day phase. 9 knots (cruise) * 12 hours = 72 nm, meaning it will be two hexes away in the night phase, and *24 hours = 144 means it will be three hexes away. 10 knots (cruise) *12 hours = 120nm means 2 hexes away at night, 240nm or 4 hexes away during the day. 12 knots (full) means it will be 144nm, or 3 hexes away at night, or 288nm or five hexes away during the day. This variation in cruise speeds (besides being taken from reality...) allow you to change it up, so while it is possible to get an MOI and blast the bejesus out of a convoy, the player controlling the convoy can adjust speeds so that the enemy can not concentrate his entire force to get it.

[engineer]

Doh!  Still learning the system and have only played Allies so I made the mistake of mirror imaging an absence of fuel problems for the Allies without considering the Japanese - and my initial paragraph waaaaay up top started off with speed vs. power.  You're absolutely right about the fuel consumption versus speed issue.  Half speed is only about 10% power on a straight cube law calculation so this is very much a fuel economy measure that is much more important to the Japanese player than the Allies. 
 
I was playing with realistic weather, but I haven't noticed sea-state data, just the clouds (which saved the Shokaku from a well-deserved dose of wrath, but that's another story).  Do the sea-state effects only accompany storms?
 
Damage (wear and tear) would still seem to accompany speed (Scotty on the Enterprise and all that) but those are just variables in the engine. 
 
The AP category does seem to be missing one category for the North Atlantic greyhounds.  I haven't got around to digging into the details of the Cunard-White Star, United States Lines, the Los Angeles Steam Ship Company, Matson Line, etc., circa 1922-1926, and all the rest, but the pride of the German merchant marine were mostly sailing under the US flag in the 1920s.  The US had the experience from World War 1 of modifying these as troopships and using them to take hundreds of thousands of soldiers to Europe.  Leviathan was one of a kind (in Newport News being refitted for passenger service at the outbreak of the early scenario and on the North Atlantic run in 1926).  She was clocked at 27 knots following her 1922 refit.  But there were a number of other former 1st class former German passenger ships that had a top speed in the low 20's and high teens that would filter into a real conflict with Japan.  The UK and Canada had more liners, too.  The other thing I've run into was the US practice of converting her coastal passenger ships to minelayers.  But I digress . . .

[Rysyonok]

ORIGINAL: Tankerace
If playing as Japan and hitting a fuel crisis by 1924, this can become a critical factor.

Is this how scenarios are set up when it comes to supply/fuel generation?

[Tankerace]

The scenarios are set up so that Japan will always have fuel. However, if excessive Fleet operations are run, after about 2 years the fuel problem will arise. You will always have fuel, but you will probably have to scale back operations. After a year of that, depending on whether you have built up a stockpile, it will become a matter of saving up enough fuel to deploy the battlefleet. (In force, as in a dozen or more TFs).
 
So, in those situations, ever know of speed and every ton of oil will matter, to the point where cruising speeds will become a necessity. This also plays into the feel of the game, in the sense that if you can accomplish your objectives within the first two years, you can stockpile fuel while the United States goes on the counteroffensive, thus building back enough reserves to launch a counter offensive of your own.
 
For the United States, running at full speed won't really hurt that much (unless we are talking operating from an isolated PI). But for Japan, or fleets operating out of a secure and steady supply line, too much full speed can turn a hefty fleet and merchant marine into 10,000 ton paperweights.

[Helpless]

Have a feeling that in 2 years Japan shouldn't have much of their battlefield left... Would be interesting to see a PBEM survived that long.

[engineer]

Here are the results with larger samples sizes.  The basic unit is a "ship-hex", the distance covered by ships.  For example, 50 ship-hexes could 1 ship travelling 50 hexes or ten ships going five hexes.  Then I add up the incremental systems damage incurred over the voyage and divide by the number of ship-hexes to get the expected damage per hex travelled.
 
Cruise Speed - Sample size 1655 ship-hexes - Result 0.85%/ship-hex
Mission Speed - Sample size 1210 ship-hexes - Result 1.16%/ship-hex
Full Speed (Auxiliaries and Merchant Ships) - Sample size 409 ship-hexes - Result 1.71%/ship-hex
Full Speed (warships) - Sample size 269 ship-hexes - Result 10.78%/ship hex
 
Final Conclusions:

• There's not a lot of difference in the rates of damage accrual between cruise and mission speed.  Mission is worse, but that meets a common sense test that faster travel will create more wear and tear on the ship.  As Tankerace explained above, this will end up making the major difference between the two turn on fuel consumption. 
• Full speed did see a somewhat higher rate of damage on merchants/auxiliaries.  At 1.71% you can expect your merchant ships to get about 1% systems damage for a one way trip from Karachi to Singapore or round trip from the West Coast to Pearl Harbor.
• I sent two destroyer groups on a sprint to see what happened and ships in both scored between 10% and 11% chance of accuring a system damage point per hex of travel.  Flanker Leader was right on target in his estimate that full speed was an order of magnitude increase in systems damage.
• Variations in damage from task force to task force were common but I didn't bother to calculate standard deviation data.  One variable that I did not control was the task force commander's administrative ability.  That suggests a potential exploit if you would gather an enormous fleet on a transport mission and give the command to your administrative genius.  Then the fleet could stage to an advanced operating base with a minimum wear and tear in the course of moving forward.    

The bottom line is that when you sail ships, things break.  The faster you go, the more they break.  In planning your operations you'll need to take this into account.  For combat units, cruise speed on non-combat missions pays big divindends by avoiding damage that takes a long time to repair.  For the merchantmen, allowing for periodic yard time to repair damage is a necessary part of understanding the real supply capacity of a given volume of shipping from a supply head to an operating base.