[TEC] Unit of measurement fix for merchant ship slowdown

[nematode]

PROBLEM
Many of Silent Hunter 4's merchant ships, and some of its warships, slow down to a few knots when they turn, and accelerate back to speed very slowly. This problem appears whenever the ships turn at a waypoint, or turn during "evade mode", which is triggered when a player sub is detected.


INTRODUCTION
This article documents a unit of measurement bugfix to eng_power, which is a game measure of a ship's horsepower found in ships' .sim files.

This bug is UNRELATED to any "lost leader" or any other AI problem. This isn't a "rivet counter" issue, or a how-to for a realism mod. The UBIdevs gave us eng_power values for the game that they collected from historical references for the real life ships' sea trial horsepower. But apparently without the UBIdevs realizing it, one of the sources that they used put them on the wrong track with a badly flawed unit of measurement. I'll explain all that in a minute.

By posting my research here, I'm making it freely available to anyone who wants to incorporate it into SH4. If anyone uses my work and cares to credit me, that'd be nice, if not, I won't lose sleep over it.

All of my findings came from a non player modified version of SH4. Fresh install, completely stock, US CDROM plus v1.2 patch.

I would like to acknowledge Timetraveller and Nvdrifter for their work creating SH3 Mini-Tweaker and resource files, without which this article would not have been possible.


DISCOVERIES
While troubleshooting an SH4 custom mission, I noticed that the Kuma light cruiser would slow down to about 2 knots when it turned at a waypoint or started evading after it spotted my sub. Firing up Mini-Tweaker, I found that eng_power in NCL_Kuma.sim was 70. No wonder Kuma was having problems. SH4 was simulating trying to accelerate a large ship with the equivalent of a motorcycle engine.

The similar Naka cruiser in SH4 doesn't have those problems, and it has 90000 eng_power in NCL_Naka.sim. Opening my copy of "Warships of the Imperial Japanese Navy, 1869-1945" by Jentschura et al, I found that the real life Kuma and Naka were both rated at 90,000 shaft horsepower.

After editing 90000 eng_power into NCL_Kuma.sim and testing the fixed Kuma in an SH4 mission, it performs properly: no extreme slowdown on turning, with acceleration out of the turn that's consistent with other warships.

I next started checking other SH4 warships. There are several mistakes, but most warships checked out fine, and their eng_power values match real life sea trial horsepower values found in historical references. I've listed corrections for the mistakes that I came across in the table below.

That's when it dawned on me that one cause of the SH4 merchant ship slowdown might be eng_power problems. I started digging, and found that yep, all but one of the Japanese merchant ships in the game are underpowered, and some of them are extremely underpowered. After more digging, I spotted a trend...

It appears that the UBIdevs used Charles Hocking's "Dictionary of Disasters at Sea During the Age of Steam" (London: Lloyd's Register of Shipping, 1969) as a major source of information on the Japanese merchant ships. This book has been digitized and put online in PDF format, available at several websites including http://perso.orange.fr/cdasm.56/dico.htm

Hocking's book documented a ship's horsepower with a unit of measure called nominal horsepower. Basically, nhp was a system dating from the 19th century to measure steam engine horsepower by formulating together the engine's dimensions. For reasons that aren't entirely clear to me, Lloyd's Register, the merchant shipping information company whose databases Hocking used to write his book, continued to list nhp in its publications well into the 20th century.

While nhp was a useful way for Lloyd's Register to maintain "rule of thumb" style values for ships' horsepower, it's an extremely inaccurate way to measure it. The problem with nhp was recognized over a century ago by mechanical engineers. A typical criticism of nhp can be found in "The Mechanical Engineering of Steam Power Plants", by Frederick Hutton, published in 1908, which has been by digitized by Google (search for the title to find the online book if you care to). Hutton wrote, "Nominal Horsepower is an old term now properly disused, which was based on an untenable assumption that all engines of a given diameter and stroke (or cylinder volume) were of the same horsepower, whatever the mean pressure on the piston or the speed of its traverse."

Engineers have long since come up with improved methods of measuring sea trial horsepower, by installing a meter somewhere on the engine or drive train. These are known as indicated horsepower (ihp), brake horsepower (bhp), or shaft horsepower (shp), depending on the type of engine and testing method.

These methods weren't perfect, but they were light years more accurate than the nhp formula. When compared to ihp, bhp, or shp, nominal horsepower underestimates the sea trial horsepower of ship engines by anywhere from 400% to 1500%.

I've been able to locate ihp, bhp, or shp sea trial horsepower values for most, but not all - I had to make several "best guesses" - of the Japanese merchant ships, and they're listed in the table below. I've included notes to document how I came up with my numbers, as well as showing where I believe UBIdevs got their nhp numbers.

By replacing the incorrect eng_power values in SH4 with my numbers, the game's merchant ships and merchant convoys will no longer come to a screeching near-halt. Or rather, if they do, it's because of AI problems, whether they are "lost leader" or bad pathing/collision avoidance stuff. Hopefully that'll be attended to by the UBIdevs. Data follows in next post......

[nematode]

THE DATA

THESE eng_power VALUES CHECK OUT OK, NO CHANGES ARE NECESSARY
---------------------------------------------------------------
Ship Name................SH4 v1.2 eng_power value
---------------------------------------------------------------
NBB_Fuso........................78000
NBB_Ise.........................81000
NBB_Ise2........................81000
NBB_Kongo......................136000
NBB_Yamato.....................150000
NCA_Maya.......................130000
NCA_Mogami.....................152000
NCA_Takao......................130000
NCL_Agano......................100000 -- see Note 1
NCL_Naka........................90000
NCV_Hiryu......................163000
NCV_Shokaku....................165000
NCV_Taiho......................163000
NCVE_Akitsu......................7500 -- see Note 2
NCVS_Chitose....................44000
NDD_Akizuki.....................52000
NDD_Asashio.....................50000
NDD_Fubuki......................50000
NDD_Minekaze....................38500
NDD_Mutsuki.....................38500
NDD_Shiratsuyu..................42000
NSC_SubChaser....................1700
NMS_No13.........................3200
NBB_Iowa.......................212000
NBB_North_Carolina.............115000
NCA_Kent........................80000
NCA_Northampton................107000
NCL_Brooklyn...................100000
NCL_Dido........................62000
NCL_Omaha.......................90000
NCVE_Bogue.......................8500


THESE eng_power VALUES ARE INCORRECT, RECOMMENDED CHANGES LISTED HERE
---------------------------------------------------------------------
Ship Name......SH4 v1.2 eng_power.....Correct eng_power value
---------------------------------------------------------------------
NCA_Furutaka........52000.............102000 -- see Note 3
NCL_Kuma...............70..............90000 -- see Note 4
NCVE_Taiyo..........10000..............25200 -- see Note 5
NML_Okinoshima.......2250...............9000 -- see Note 6
NBB_New_Mexico......31197..............40000 -- see Note 7
NCA_Baltimore.......12000.............120000 -- see Note 8
NCL_Cleveland.......10000.............100000 -- see Note 9
NKLCS_Nagara.........9325...............6700 -- see Note 10
NKLSS_Hakusika........704...............5461 -- see Note 11
NKMCS_Akita...........342...............2899 -- see Note 12
NKMCS_Heito...........500...............3786 -- see Note 13
NKMCS_Zinbu...........532...............2500 -- estimate, see Note 14
NKMSS_Biyo...........2000...............2800 or 3973 -- see Note 15
NKMSS_Kinposan........250...............2324 -- see Note 16
NKSCS_Taihosan........110...............1000 -- see Note 17
NKSSS_Kasagisan.......181...............1633 -- see Note 18
NOL_Nippon...........2250...............9773 -- see Note 19
NOM_Buzyun...........2000...............2900 -- estimate, see Note 20
NOS_Haruna............126...............1414 -- estimate, see Note 21
NPL_Conte_Verde......3650..............20000 -- estimate, see Note 22
NPL_Horai............1370...............7400 or 8132 -- see Note 23
NPL_Kiturin..........1250...............7800 or 8395 -- see Note 24
NPS_Tyohei............225...............1000 -- estimate, see Note 25

For various reasons, I didn't evaluate NLCVP, NPT_Br, NCVE_Casablanca, NCV_USEarlyWar, CMD_small_boat, JPFish01, JPFish02, JPGunBoat01, JPGunBoat02, NAMC, NATF, NBB_KGeorgeV, NDD_Clemson, NDD_Fletcher, NDD_Somers, NDD_Tribal, NDE_Buckley, NDE_Evarts, NDE_JCB, NFD, NFishingTrawler, NF_boat, NKSQ_, NKSs_, NLifeboat_01, NLifeboat_02, NLL, NLST, NOTMs_, NSampan01, NSampan02, NSampan03, NTR, NTRW_, NVV, Sub_Depot_Ship, NS_Ko_Hyoteki, NSS_Sen_Toku, NSS_Balao, NSS_Gato_sim, NSS_s18, NSS_s42, NSS_Salmon, NSS_Sargo, NSS_Tambor, NSS_Porpoise, or Survivor


BIBLIOGRAPHY

Jentschura, Hansgeorg; Dieter Jung; and Peter Mickel. Warships of the Imperial Japanese Navy, 1869-1945. Annapolis: Naval Institute Press, 1977

Noma, Hisashi. Japanese Merchant Ships at War. Tokyo, 2002

Fumio Nagasawa's "Nostalgic Japanese Steamships" website at http://homepage3.nifty.com/jpnships/ In Japanese, but with many statistics in English, can be read using a translator program

Jon Parshall's "Imperial Japanese Navy Page" at http://www.combinedfleet.com/

Andrew Toppan's "Haze Gray & Underway Naval History Information Center" at http://www.hazegray.org/navhist/


Notes from the table follow in next post.

[nematode]

NOTES

Note 1 -- Agano's center of gravity is high, needs reducing. It almost lays on its side in a high speed turn. CG is beyond the scope of this post, so, I'm just sayin.

Note 2 -- Akitsu is seriously broken. Its rudder is displaced off the model by about 100 meters, and it gets stuck trying to turn. I don't know how to fix it, so, once again, I'm just sayin.

Note 3 -- Furutaka class Heavy Cruisers had 102,000 shp. See Jentschura page 79. Is it just my PC, or is part of Furutaka's rigging missing?

Note 4 -- Kuma class Light Cruisers had 90,000 shp. See Jentschura page 106.

Note 5 -- Taiyo class Escort Carriers Taiyo, Unyo, and Chuyo were converted from brand new NYK steam turbine ocean liners Kasuga Maru, Yawata Maru, and Nitta Maru, respectively, and had 25,200 shp. See Jentsura page 58. Andrew Toppan lists 25,200 shp for Taiyo class at http://www.hazegray.org/navhist/carr...cv.htm#taiy-cl Fumio Nagasawa lists 25,200 shp for class leader Nitta Maru at http://homepage3.nifty.com/jpnships/...1_oshu_nyk.htm

Note 6 -- Okinoshima Large Minelayer had 9,000 shp. See Jentschura page 200.

Note 7 -- BB New Mexico and sister ships received a refit in the 1930's, upgrading engines to 40,000 shp. See http://www.hazegray.org/navhist/batt...s_dr.htm#nm-cl

Note 8 -- Baltimore class Heavy Cruisers had 120,000 hp, see http://www.hazegray.org/navhist/cruisers/ca-cl2.htm

Note 9 -- Cleveland class Light Cruisers had 100,000 hp, see http://www.hazegray.org/navhist/cruisers/ca-cl2.htm I'm assuming that SH4 v1.2 eng_power values for Baltimore and Cleveland were data entry errors.

Note 10 -- NKLCS_Nagara = Large Modern Composite Freighter. The one merchant ship in the game that's actually overpowered. In real life, Nagara Maru was a 1933 built diesel powered fast passenger/cargo vessel. Ships of this type were built to government specs for private shipping lines under subsidy programs and heavily requisitioned by the Japanese military as troopships and auxiliary naval vesels. Fumio Nagasawa lists 6700 hp at http://homepage3.nifty.com/jpnships/...okubei_nyk.htm 6700hp is consistent with values found in Hisashi Noma for similar vessels.

Note 11 -- NKLSS_Hakusika = Large Old Split Freighter. In real life known as Hakushika Maru, built 1917, triple expansion reciprocating steam engine. 5461 ihp is from http://homepage3.nifty.com/jpnships/...ano_aclass.htm Notice that Fumio Nagasawa lists both nhp and ihp for this vessel. UBIdev nhp number can be found at http://perso.orange.fr/cdasm.56/dictionnaire/295.pdf

Note 12 -- NKMCS_Akita = Medium Composite Superstructure Freighter. In real life Akita Maru was built 1916, triple expansion reciprocating steam engine. 2899 ihp is from http://homepage3.nifty.com/jpnships/...akitaclass.htm
Notice that Fumio Nagasawa lists both nhp and ihp for this vessel. UBIdev nhp number can be found at http://perso.orange.fr/cdasm.56/dictionnaire/016.pdf

Note 13 -- NKMCS_Heito = Medium Modern Composite Superstructure Freighter. In real life Heito Maru was built 1934, steam turbine fast cargo/passenger ship. 3786 shp is from Hisashi Noma page 117, confirmed by Fumio Nagasawa at http://homepage3.nifty.com/jpnships/...taiwan_osk.htm UBIdev nhp number can be found at http://perso.orange.fr/cdasm.56/dictionnaire/310.pdf

Note 14 -- NKMCS_Zinbu = Medium European Composite Superstructure Freighter. In real life known as Jinbu Maru, built 1894 England, later sold to a Japanese shipping company. An antique by the time of WW2, Jinbu Maru was sunk in the Sea of Okhotsk by submarine S30. I've found no technical data on Jinbu Maru, 2500 hp is an estimate based on comparisons with similar vessels. UBIdev nhp number can be found at http://perso.orange.fr/cdasm.56/dictionnaire/360.pdf

Note 15 -- NKMSS_Biyo = Medium Old Split Superstructure Freighter. The real life Biyo Maru was built 1920, member of the numerous Yoshida Maru No. 1 class, possibly with a different power plant than its triple expansion reciprocating steam engine powered sister ships. I don't have a horsepower figure for Biyo Maru, but Hisashi Noma page 279 lists 3973hp for sister ship Havre Maru, and Fumio Nagasawa lists 2800 ihp for Havre Maru at http://homepage3.nifty.com/jpnships/...ano_bclass.htm

Note 16 -- NKMSS_Kinposan = Medium Modern Split Superstructure Freighter. The real life Kinposan Maru was built 1936, triple expansion reciprocating steam engine with turbo supercharger. Requisitioned by the Japanese Navy and converted into an auxiliary gunboat/minelayer with 4x120mm guns and 2x7.7mm MG along with its sister ship Kinjosan Maru. The only ihp info I could find comes from a dissertation in Japanese at http://ci.nii.ac.jp/naid/110003879646/ which translates to "The engine develops a normal output of 1950 I.H.P.at 82 r.p.m. The trials were carried out at a light loaded condition and the results were quite satisfactory. The maximum speed of 14.5075 Knots was recorded at 89.75 r.p.m.and 2,324 I.H.P. ..." , It's not the authoritative source that I wanted but it beats no sources at all. Having said that. 2,324 ihp looks believable for this ship. UBIdev nhp number can be found at http://perso.orange.fr/cdasm.56/dictionnaire/385.pdf

Note 17 -- NKSCS_Taihosan = Composite Superstructure Freighter. In real life Taihosan Maru was built 1938, triple expansion reciprocating steam engine with turbo-supercharger. During wartime Taihosan Maru was used as a fresh water tanker bringing water to garrisoned islands. Hisashi Noma page 95 lists 1000hp. UBIdev nhp number can be found at http://perso.orange.fr/cdasm.56/dictionnaire/680.pdf

Note 18 -- NKSSS_Kasagisan = Small Old Split Superstructure Freighter. In real life Kasagisan Maru was built 1925, triple expansion reciprocating steam engine. Hisashi Noma page 445 lists 1633 hp. UBIdev nhp number can be found at http://perso.orange.fr/cdasm.56/dictionnaire/374.pdf

Note 19 -- NOL_Nippon = Large Modern Tanker. SH4 bug limits this ship to 9 knots, should be 20 knots. In real life Nippon Maru was built in 1936 as a diesel powered fast tanker. This ship and many of its sister ships were requisitioned by the Japanese Navy for use as auxiliary fleet oilers. Fumio Nagasawa lists 9773 bhp at http://homepage3.nifty.com/jpnships/..._showa1_02.htm UBIdev nhp number corresponds to that of sister ship Genyo Maru, which can be found at http://perso.orange.fr/cdasm.56/dictionnaire/267.pdf

Note 20 -- NOM_Buzyun = Medium Old Tanker. I have no useful info on the real life Buzyun Maru (aka Bujun Maru). My estimate of 2900 hp is based on comparisons with vessels of similar date of build and displacement.

Note 21 -- NOS_Haruna = Small Old Tanker. I'm at a loss for what this is modeled after. There was a Haruna Maru, but it was a 10,000 ton NYK ocean liner that foundered on the rocks in 1942. Maybe it's a model of Haruta Maru, which was a 1515 ton Norwegian merchant ship built in 1925 named Halldor captured by the Japanese in December 1941, and used until it got sunk in 1945. It's driving me nuts but, I found 1414 ihp for this ship somewhere, and didn't write down where. Now I can't find it again. Goes to show I shouldn't search for things at 4am. That being the case, 1414 ihp is my estimate.

Note 22 -- NPL_Conte_Verde = European Built Liner. The real life Conte Verde was a 1920's-built Italian ocean liner that was trapped at Shanghai in Dec 1941. It remained there until the Italian armistice in 1943, when its crew scuttled it. The Japanese raised it, repaired it, renamed it Kotobuki Maru, and it got sunk for good in 1944. I could find no technical specs on Conte Verde. My estimate of 20,000 hp is based on comparisons with other 1920's era passenger liners.

Note 23 -- NPL_Horai = Large Old Passenger Carrier. The real life Horai Maru was built in 1912 in Great Britain with a quadruple expansion reciprocating steam engine, sold to Japanese shipping line OSK in 1923. Sunk by friendly fire in 1942. Hisashi Noma page 16 lists 7400 hp, Fumio Nagasawa lists 8132 ihp at http://homepage3.nifty.com/jpnships/...taiwan_osk.htm UBIdev nhp number can be found at http://perso.orange.fr/cdasm.56/dictionnaire/328.pdf

Note 24 -- NPL_Kiturin = Modern Passenger Liner. In real life known as Kitsurin Maru, built in 1935, steam turbine engine. I don't have much useful on Kitsurin Maru, but it had a sister ship named Nekka Maru, and there's good info on that ship. Hisashi Noma page 141 lists 8395 hp for Nekka Maru; Fumio Nagasawa lists 7,800 shp for Nekka Maru at http://homepage3.nifty.com/jpnships/...dairen_osk.htm UBIdev nhp number matches up with Nekka Maru at http://perso.orange.fr/cdasm.56/dictionnaire/498.pdf

Note 25 -- NPS_Tyohei = Small Passenger Carrier. I don't have any info on what this ship was in real life. My estimate of 1000 hp is based on comparison with Taihosan Maru.

[CaptainCox]

WOW that's some serious research! Anything for realism hey Brilliant work, keep it up!

[Jace11]

I believe you, I always wondered why the old light cruisers lagged behind in the Palawan Passage mission.. now I know. Center of gravity is editable too.

[U-Bones]

This is absolutely outstanding work.

[tater]

You must have a good library in whatever sinus you are curled up in

Wow. Well done.

tater

[Jace11]

Also nematode,

Note the minitweaker file for NKSSS_Kasagisan actually reads values from the landing craft.. NLCVP folder.

The dev NKSSS_Kasagisan power is still wrong though, at 181

CG of Taihosan is 5 - too high for that size, comparable ships like the other small freighter are at least half that value. It rolls too much with a CG of 5. Agano is set to 8 I think. Same as a large top-heavy BB. Both are easily lowered with MiniTweaker.- Can;t think of any nasty side effects of changing these.

[MONOLITH]

Bravo!

*Applaudes*

[nematode]

Thanks guys! What with 1.3 being worked on, hopefully between their efforts and our efforts, we will have the sweet little PAC subsim of our dreams.

tater -- the "heavy hitters" for my research were the Jentschura book, which absolutely rocks...and Hisashi Noma's book, which I ordered from the author, who lives in Tokyo. It's full of great Maru pictures, data, and stories that I've never seen before in an English publication. Surprisingly, or maybe not these days, I was able to pull together a lot of the work from the internet, in particular old books that've been digitized & put online. Website-wise, Parshall & posse do a superb job at combinedfleet.com, and Toppan's Haze Grey and Underway is also very well done. An exciting discovery for me was Fumio Nagasawa's amazing website. There is so little about Marus in English. Google translator produces an awkward, but understandable, Japanese translation.

Jace -- excellent finds. Thanks! I'll edit in your corrections. And, I definitely agree with Taihosan CG, she's a bit wobbly

[Jace11]

Well I made a fix based on these numbers from nematode. Tested it briefly. Ships are faster when zig-zagging - that is certain. Fewer stragglers etc. It exposed the leader problem for all to see. There still appear to be some AI station keeping problems though...

What are the observations of you guys..

[ATR-42]

Best write up I've ever seen! fantastic work, so well written, researched and articulated.

Thank you for spending the time to write this up with so much care to detail and making such well thought out posts.

you did a tremendous job!

truly amazing.

I will look into this tomorrow!

[tater]

I'll have to find a copy of that book for my library. Anything by NIP is a winner, IMO.

totally awesome work -

It will be a bitch to update them all with Sh4Tweeker, but its a work worth doing.