DE Docent: 2010

Thursday, July 29, 2010

07/31/2010 - 3" 50 Cal Lesson Plan

This is an outline of a talk I gave on 7/31 to other Docents (Tour Guides) and Student Interns about the 3" 50 Cal Gun. While the Mark 22 (shown above) was used on most Destroyer Escorts with 3" 50 Cal.; the USS Slater has Mark 26 mounts.

Basics

3" Diameter
50 Caliber: Gun Length = Caliber * Diameter (3*50=150")
Range - 14,600 yards, 29,400 ft Ceiling
Rate of Fire - 15 rounds per minute
Dual Purpose - A/A, Surface
Muzzle Velocity 2,700 fps
Recoil Length - 11-1/2"
# used: WWII Start - 690; WWII End - 14,002
Chrome Plated Barrel, 4,300 rounds

Main Components

Barrel - Gun
Housing - Breech
Slide - Recoil/Counter Recoil Mechanism
Mount (vs. Turret), Stand
Elevation / Train Power Drives
Sight Setter - Sights
Fuse Setter
Ready Service Ammo Boxes
Salvo Latch, Hand Operating Level

Operation - Gun Crew

11 Man Crew
Mount Captain
Pointer
Trainer
Sight Setter
Loader (Plug man)
Hot Shell Man
Fuse Setter (2)
Ammo Passers (2)
Sight Checker
Pointer, Trainer, Sight Setter Duties depended on Mount Mark
Hand Served - Loaded by Hand
Fired Local or Remote
Using Trigger (Electric) or Foot Pedal

Operation - Fire Control - Basics

Influence of Gravity
Wind
Time of Flight, relative to target speed/course
Temperature
Range
Ship Speed and Direction
Roll
Rifling
Vibration (Gun vs. Director Control)
Parallelex (Deviation from Director)
Roller Path Distortion
Ship Distortion - Flex
Gear Distortion - Play
AA - Fuse Setting Lag to load

History - Gun Mount and Fire Control Changes

Mark 20 - Manual
Mark 22 - Director Input (not control)
Mark 26 - Director Control
Later Changes - Mark 27, Twin 3"-50

Maintenance

Routine Maintenance - Grease, Oil, Paint
Effects of Salt Water (31 vs 33)
Chamber and Barrel
After Firing, Cleaning (Soda Ash), Paint Smiley Faces
Sight Alignment - Bore Gage, Tram, Bore Sight

Safety

Hang Fire, Miss Fire
Cook offs
Power Drives - Crushing
Firing Cutouts - Shooting into the ship (none detailed on 3")
Ouches & Burns

Ammunition

Projectile - Approx. 13 lbs
Fixed ammunition, approx. 7 lbs case (Steel/Brass), 4 lb propellant
AA - 30 Second Mechanical Time Fuse (Green)
AA - VT - Variable Time Fuse (Green)
AP - Armour Piecing (Black)
HC - High Capacity, Min. Wall Thickness (Green)
Illumination (Star Shell, Stars and Light Blue)
Smoke / WP (not available in 3")
Short Charge

Overall Effectiveness

Compared to 5" 38 (55 lbs, 18K yards, enclosed mount)
USS Reeves - SS Seakay Experience
AA - Director Control
VT 3 X effective over MTF AA

Who Made What

Naval Gun Factory - Charleston WV
Naval Gun Factory - Washington DC
Miehle Printing Press, Blaw-Knox, Baldwin Locomotive
Arma Corp, Brooklyn NY

References

During the training, I was asked about the rate of fire for the 3" twin Mounts (Marks 27-33). It appears that the rate of fire was approximately 50 rounds per minute. As shown in the photo, these guns were loaded from either side, and the loader was synchronized with the cycle of the gun firing. Because the 3" could fire a VT fuse, many of the 40mm mounts were replaced with this type of gun during the post-war era.

Wednesday, July 21, 2010

07/11/2010 - Ships Laundry

I was asked today about who/how laundry was done? In the 60s (aboard both my cans) each compartment had two laundry bags, one for whites and one for colored (basically dungarees). Everyone's clothing was stenciled. A few times a week the person cleaning the compartment (always a junior seaman) would take the bags to the ships laundry. Next day he would pick it up, and then throw the clean laundry on everyone's rack (their bunk) so they could fold and stow. This process always occurred after inspection.

I discussed this topic with one of our WWII volunteers and it was fairly similar. Instead of laundry bags they used a sheet, and they didn't sort the clothing into white/color piles. This process was probably done in the ship's laundry.

The USS Slater has a virtual tour of the ship, and they have fairly good description of the laundry room, which is on the 1st platform, starboard side, aft (right side, near the end).

The description notes that the ships laundry equipment was manufactured by two companies: the Hoffman Machinery Company, and the American Laundry Machine Company. There are interesting on-line references to each company. The American Laundry Machine Company is a defunct set of buildings in Rochester, NY. The Hoffman Machine Company was the centerpiece for a holding company in the 1950s.

Sunday, July 18, 2010

07/18/2010 - Convoys, Armed Guard

This Sunday I gave two tours. One group was comprised of family members of WWII Destroyer Escort Weapons officer. It was a great tour. The DE Sailor was over 90, so the tour took time. We opened the flying bridge (which was the duty station for the Weapons Officer). It took a while for the to climb the steep ladder. It was a great accomplishment. I'm glad we had a special tour.

Prior to service on a Destroyer Escort, the vet told me that he served as an Armed Guard Officer. He noted that he sailed on convoys near Iceland. I was happy that I had an opportunity to serve as the guide for this visit. However, I really wished that they visited on Friday, when Bob Bull was on duty on the USS Slater. Bob was a WWII DE sailor who also served as an armed guard.

Here are a few links relative to Armed Guard Service in WWII:

A very detailed history of the armed guard service is on-line: Administrative History of the Naval Armed Guard Afloat in WWII (OP-414). One chapter summarizes their mission: "....The Armed Guards had only one main mission -- to defend merchant ships and transports from enemy air, surface, and submarine attacks. Their primary duties, therefore, were watch standing and manning guns and maintenance of guns and defensive equipments. They had nothing to do with running the merchant ships although they greatly assisted at times in fighting fires, and in salvage operations, especially when the merchant seamen became panicky or abandoned ship. ...."
The picture above details an attack on an arctic convoy to Russia in 1942 (PQ-18). A detailed listing of all convoys is available at Arnold Hague Database on Convoy Web. PQ Series convoys typically departed from Iceland. Here is the Arnold Hague entry for PQ-18.
The period from 1939 to 1943 was a tough time for Merchant Ships, During this period 5,758 ships were lost from all causes. The combined tonnage was 22,161 (thousand), in modern terms these losses would equate to the loss of over a 1/2 million tractor trailer trucks (using a 40 ton base for a tractor trailer).
Another blogger (Bud, from Ft. Wayne) has written a detailed story about the Armed Guard which is a good read.
There is a detailed web site dedicated to the Armed Guard (Armed-Guard.com): "....The U.S. Navy Armed Guard was a service branch of the United States Navy that was responsible for defending U.S. and Allied merchant ships from attack by enemy aircraft, submarines and surface ships during World War II. The men of the Armed Guard served primarily as gunners, signal men and radio operators on cargo ships, tankers, troop ships and other merchant vessels. Disbanded following the end of the war, the Armed Guard is today little known or remembered by the general public, or even within the Navy. ...."
Naval History Center has an interesting oral history account about an Armed Guard Sailor, Seaman Basil Izzi, "....an Armed Guard crew member on the Dutch merchant ship SS Zaandam which was torpedoed by German submarine U-174 off the coast of Brazil. He was rescued after 83 days adrift on a raft, 2 Nov 1942 - 24 Jan 1943. ..."

Monday, July 5, 2010

07/05/2010 (Monday) - More on 3"

There seemed to be plenty of guides on 4th, so I worked on Monday 5th instead. Seemed pretty slow, I gave one tour and went home early.

It appears that everyone is stumped with the power button setting (fast/slow ) for the 3" Mark 31 Elevation Power Drive (Follow-up on my June Entry). Tim sent out e-mails to different experts throughout the historical fleet. During the inquiry we were sent this neat photo of a 3" gun being fired. The photo caught the 3" empty case being ejected. You can see the loader ready to ram another round, while the hot shell man (with his protective glove) tries to catch the hot empty. Since some of the sailors are in whites (probably trainees) and others are in dungarees (probably trainers) we think that the photo is from a training exercise perhaps on the USS Wyoming (BB-32). One of our volunteers, Master Chief Floyd (since retired) served on the Wyoming in 1943.

".... The extent of her operations can be seen from a random sampling of figures; in November, Wyoming trained 133 officers and 1,329 men in antiaircraft gunnery. During that month, she fired 3,033 5 in (130 mm) shells, 849 3 in (76 mm); 10,076 40 mm; 32,231 20 mm; 66,270 .30 in (7.62 mm); and 360 1.1 in (27 mm) ammunition. She claimed the distinction of firing off more ammunition that any other ship in the fleet, training an estimated 35,000 gunners on some seven different types of guns. ..."

The Mark 31 power drive was the 1st attempt to link 3" 50 cal to director control. This upgrade resulted changed the Mark # to 26. This was not a major mark and it's very hard to find documentation about the upgrade. The best document to date is an Ordnance Bulletin 1-1946. The bulletin notes that the upgrades started after August 1945, after the USS Slater deployed to the Pacific. Our theory is that the upgrade may have occurred when the USS Slater was transferred to the Greek Navy. The bulletin does not mention the dual setting of the elevation power button. However, there is no doubt the USS Slater is equipped with Mark 26 Mounts.

Expect more on this issue in subsequent posts.

Wednesday, June 30, 2010

06/20/2010 - What is that switch for?

Over the last two weeks we had a steady flow of visitors. I understand that attendance has been very very good. One weekend we were a little pressed for guides. Typically smaller cohesive groups are the best. When you have few guides and heavy attendance you are forced to have larger tour groups. This takes a little longer and makes it a little difficult to get the groups into all the compartments. It seemed to me that the groups were always of reasonable size.

What is that switch for?

On 1st glance it is simple - It is that the power switch for the elevation power drive. Next question - Why does to have a Fast and Slow Button? That's very difficult to answer. I didn't know the answer two weeks ago when I was asked, and I don't know today (after spending many hours of research). I asked Tin Rizzuto (the Ship's Superintendent) and Eric Collin (Restoration Coordinator) and they didn't have an answer either. The initial consensus was that we just used a non-standard button during the restoration. During subsequent investigation I found that this wasn't true. I checked other 3" mounts on the Slater that still had the original buttons. I also pulled the design prints (The Slater has a complete set of prints for the 3" mounts). They both indicate a three button configuration.

What I currently BELIEVE: the switch is a quick fix to a problem with the Arma Elevation Power Drive (Mark 31 Mod 0). I believe in the fast setting the elevation drive would respond quicker under director control but it would loose accuracy. With the slower setting the elevation drive would be more accurate, but it's response would be slower. The Trainer position (moving the gun from right to left) does not have this setting. This leads me to believe that in certain situations, perhaps when the ship was rolling heavily, the normal setting of the drive failed to keep the gun on target. When a gun is under director control, it moves quite a bit to compensate for the roll of the ship. Most of the movement is in elevation. When they tried to speed up the drive the accuracy suffered. Rather than scrap the program, someone though of the dual setting as a quick fix.

Unfortunately, I have no documentation to support this theory. I do have a great deal of circumstantial evidence.

I reviewed the 3" Gun Manuals (ORDNANCE PAMPHLET NO. 811, December 22, 1943 which is available on line; and NAVORD OP811, 2nd revision, January 1, 1968, which is available in the Slater's Library). According to the 1943 manual, the 3" guns do not have a power drive. The later manual appears to reference Elevation Indicators - Mark 21. The description of these Indicators seems to be different that the configuration on the Slater.

The manual in the Slater Library (rev 2) refers to Ordalt 2227A (Ordnance Alteration) - "...To provide installation of power drive equipment with automatic control, firing stop mechanism, and hydraulic buffer stops on manually driven mounts MK 22 Mods 0, 4, 17 and 20 converting them to mounts MK 26Mods 0 and 1. ..."

The name plate on the drive has the following details:

Elevation Power Drive, Mark 31 Mod 0
Arma Corp, Brooklyn NY
Serial #177
SK 93744

I ran across this this note on upgrading 3" 50cal with Arma Drive units in the Guide to United States Naval Administrative Histories of World War II. The following excerpt is from the Ordnance Section, Chapter VII: "... The design of 3"/50 power drives was completed in the spring of 1944 by the Arma Corporation, at that time, the bureau of Ordnance was authorized by a directive summary to procure 2,000 power drives for installation on U. S. ships having a battery of three or more 3"/50 guns.[9] However, in the fall of 1944, when the program reached a directive stage for authorization of actual procurement it was decided that 1,000 drives would be sufficient to start the program and the contract for this number was placed with the Arma Corporation. Initial deliveries of power drives were expected during this first quarter of 1945 but due to the difficulty of obtaining a satisfactory design of certain components and to procurement difficulties with subcontractors, the initial supply of 3"/50 power drive equipment was not available until August 1945. Following VJ Day, procurement of drives was reduced to 600; of these, 500 were to be used on 3"/50 caliber mounts Mark 22 scheduled for ships of the post war fleet In which 3" 50 caliber guns are a part of the ultimate approved armament. The remaining 100 units were reserved for the 3M/50 single rapid fire development. ..."

I believe that the USS Slater was one of the 1st ships to be equipped with this Drive, and the difficulties with the program related to the power drives. Those problems led to the power button with the fast/slow setting.

Tuesday, June 8, 2010

06/06/2010 - DE 5K Walk

On the 6th of June I had planned a 5K walk in downtown Albany. I arranged discounted USS Slater tour coupons for everyone who participated. Unfortunately the 6th of June was a washout, and the DE Docent had to walk alone.

Albany is a great place to walk. I outlined two 5K walks with the USS Slater as a starting point. The 1st is a walk was along the the Corning Preserve. (about 1-1/2 miles). It includes a quick loop to the State Capital. The 2nd walk goes along Broadway, toward the visitor center and the AquaDuck Tour (also finishing with a loop around the capital).

This week was very hectic. During the week I came to the Slater several times and gave three tours to School Groups. While the groups were rather large, everything went well. The chaperons were great, and the groups were well behaved.

On Sunday despite the rain, I managed to give two tours to very small groups. The 1st group was just two people, who had recently completed a week long bicycle trip along the Erie Canal (basically the length of NY State). The 2nd group was largely comprised of a group of visiting engineers who were in Albany for a training program (of course this led to quite a few technical questions).

What is the range of Sonar? - This is not an easy question to answer because of the impact of environmental factors. Norman Feidman's book on Destroyers in WWII cites 2,000 yards (page 196). U-boat Net has an excellent article on the topic and cites and average of 1,350 meters. These ranges are for active sonar. In contrast ranges for passive sonar can be a high as 100 kilometers for a very noisy sound source like a convoy.

Some other interesting links:

Tuesday, June 1, 2010

5/31/2010 - Memorial Day

It was a beautiful Memorial Day, and Tim and Admiral Paul did a fine job. Immediately after the ceremony I took off for about an hour to do a quick walk. There seemed to be plenty of guides (perhaps 10), which seemed like a sufficient number to handle the crowd. When I got back I learned that they were barely enough. I was a little sorry I didn't stick around. But as soon as I got back I was able to start giving tours.

The 1st group was small, only two visitors. They remembered seeing the USS Slater at the USS Intrepid. The Slater was there from 1993, when it returned to the US from Greece. In 1997 the Slater was relocated to Albany. This video on Navy TV shows the Slater's condition in 1993. I expedited the tour so they could catch a ride on the Dutch Apple. I'm glad to see it cruising again.

The 2nd group was larger, mostly younger visitors. The tours went fine, and except for the heat everyone had a good time. I was asked a lot about how much things weighed, especially the guns. I have two excellent sources that help with the answers (both from the Historic Naval Ship Association): Gun Mount and Turret Catalog; and Boats of the United States Navy. The USS Slater E-Tour is also an excellent source.

How much does the 3" Gun weigh? Answer: 6,700 - 7,510 lbs.
How much does the Motor Whale Boat Weigh? Answer: 5,550 - 8,850 lbs.
How much does the 50 Cal. Gun weigh? Answer: 83.78 lbs.
How much does the 20mm Gun weigh? Answer: approx. 1,400 lbs.
How much does the 40,, Gun weigh? Answer: approx. 14,700 - 14,900 lbs.

Good questions - Hope I answered all of them.

Thursday, May 20, 2010

5/16/2010 - Spring Returns

Nice day, started with my morning (5K) walk around Albany. Around noon the visitors started arriving. I gave two tours, both groups were of nice size (10-12 people). The 2nd group had was a little tough. It included a mix of visitors who wanted to quiz the docent, and a number of over anxious kids. This is a tough combination. It's hard to give justice to difficult questions without losing control. Unfortunately one parent decided to cut the tour short because of behavioral issues.

One question I was asked was "How far does the 3 inch gun recoil?" I held up my hands and said about this far (roughly a foot). Fortunately, the Historic Naval Ship Association, has digitized the 3" Gun Manual so it's pretty easy to check, on page 25 of Ordnance Pamphlet No. 811 (12/22/1943) there is a table and the precise answer is 11 - 1/2".

The second question occurred on the signal bridge. Time permitting, when visitors are at the Slater's Search Light, I usually tell the story of the USS Cecil J. Doyle and the rescue of the crew of the USS Indianapolis.

I also noted that before it was sunk the USS Indianapolis delivered the A-Bomb dropped on Hiroshima. That seemed to be a point of contention. I was told by one of the visitors that the bomb delivered by the Indianapolis was a ruse. He heard this from someone stationed on Tinian.

Since then I have checked multiple sources and this appears to be untrue. The Nuclear Weapon Website had a very detailed (and well documented) article on Little Boy (including transport) - The first U-235 projectile component was completed at Los Alamos on June 15, 1945. Casting of the U-235 projectile for Little Boy was completed on July 3. On July 14 Little Boy bomb units, accompanied by the U-235 projectile, were shipped out of San Francisco. They were picked up by the USS Indianapolis (CA-35) at the U.S. Navy's Hunter's Point shipyard at San Francisco on July 16, bound for Tinian Island in the Mariana Islands. On July 24 the last component for Little Boy, the U-235 target insert, was completed and was tested the next day. The Indianapolis delivered Little Boy bomb units, and the U-235 projectile to Tinian on July 26. On the same day the target assembly, divided into three parts flew out of Kirtland Air Force Base, Albuquerque on three C-54 transport planes, which arrived July 28 at Tinian.

However, I can see how this rumor can arise. While the Indianapolis delivered the majority of the weapon, several components were delivered by plane several days later. The air delivered components were the U-235 Target Assembly, which I believe is item 13 on the drawing. It appears to me that the separation of the Target Assembly was driven by the unstable nature of the bomb, and perhaps for security reasons. It's relatively easy to see how the scuttlebutt associated with these deliveries by plane, could lead to the speculation that the Indianapolis delivered a fake bomb.

Tuesday, May 18, 2010

5/9/2010 - Tulip Festival or bust!

This Sunday, instead of serving as a tour guide, I volunteered to stand my watch at the USS Slater's booth at the Tulip Festival. On Sunday morning I arrived a little early. I parked at the Slater's lot and I planned on walking to the site of the Tulip Festival, Washington Park. The round trip distance was a little less than 5 miles. Since last year, I have been on a walking program for exercise. Basically I try to walk 5K meters every day (approx. 3.1 Miles). On the way to the park I ran into Joe, one of our younger guides, walking across the Hudson River Way. I am real proud about my 5K a day walks. I asked Joe where he was coming from and how far a walk it was. He told me he was coming from Colonie, a round trip distance 16 miles. I was truly humbled!

The walk to Washington Park, was bright and Sunny, but Cold. The wind was gusting to 40 knots. I felt like I was standing on the forecastle of a Destroyer on plane guard duty. When I arrived at the park, I met Admiral Paul who told me that the Slater's Display was a casualty of the high winds, so we packed up, and I walked back to the Slater.

I had obtained special permission from the Chief (of my household) to attend the Tulip Festival Watch (5/9 was Mother's Day). I called home and received permission to do one tour. It was OK, as long as I returned home by 3:00 (Dinner Plans).

For my single tour, I had a very large group. But everything went very well. I finished on time, and I was home at my appointed time (3:00). During the tour I was asked two very good questions.

One of these, was a puzzle for quite some time - Where were the 3" Guns Manufactured? I asked around, and didn't get an answer so one week later I went to Mount 3-1 and exposed the manufacturing marks on the breech - GMOC NOPSC 3" Gun Mk22 Mod 2. No 22765, 1944.

The next step took a great deal of investigation. NOPSC was the key. This stood for Naval Ordnance Production Facility, South Charleston. It referred to a factory in Charleston, West Virginia. The most complete history of this facility was documented by Justin Salisbury for the West Virginia Historical Society in 2006. The facility was built during WWI, but the Washington Naval Treaty forced it's closure in 1922. Then, in response to the ever looming threats from Japan and Germany - ".....On November 5th 1938 Franklin D. Roosevelt announced that the military would be surveying all federally owned lands and plants capable of use in National Defense. In the same speech, he stated that he had already decided the South Charleston naval plant would be reopened...."

Justin's article, gives a very detailed account of the facility. The GMOC portion of the stamp on the 3" breech refers to General Machinery Ordnance Corp. Justin notes that "....Unlike the contracts for the armor plant, General Machinery Ordnance Corporation was given a ‘blank check’ so to speak. They were told to get the north unit in condition to make guns, and the government would reimburse their costs. The amount of money spent by G.M.O.C. for the rehabilitation of the north unit and some parts of the south unit came to $6,267,380.37 ....".

During WWII G.M.O.C. manufactured a wide variety of weapons under three contacts worth millions of dollars - "...The General Machinery Ordnance Corporation signed three contracts to produce weapons. These contracts were N0rd-144, N0rd217, and N0rd-635. The first contract N04d-144 was signed on July 16th 1941. This contract was for the production of quantities of three inch, five inch and 6 inch gun barrels. The N0rd-217 contract was signed on December 18th 1941 and was for the production of quantities of 1.1”, twenty-millimeter, and forty-millimeter gun barrels. The final contract N0rd-635 was for the production of the 11.75” rocket and for separate components of this rocket. ..." . It is very possible that this facility manufactured all the guns on the USS Slater (but I haven't verified this).

After WWII the facility was eventually closed in 1961.

During this investigation I ran across several interesting linksn:

The 2nd Great Question was - How was a Large Naval Gun loaded? Naval guns 8" and larger were loaded differently than the 3" Guns on the USS Slater. These Guns were referred to as Bag Guns, and the biggest in the US Navy was the 16"- 50 Caliber, Mark 7 (Japanese had bigger guns, 18.1").

Here is a training video on a 16" gun

Saturday, May 8, 2010

4/30/2010 & 5/2/2010 - Open Season

On Friday we had a very large group from a Performing Arts High School in Massachusetts. Things went like clock work. Nice way to start the new year.

On Sunday I gave two tours. Right after lunch on Sunday we get a large influx of visitors. I had a very large group. It was a little tough in the smaller compartments. Right behind me was a smaller group that was moving very fast. It would have been great if I could have shifted some of the members of my group to that smaller group. In any case things seemed to work out fine.

On Sunday I noticed a printout of the ammunition load of the USS Slater published on the wall in the gift shop. I thought it would be a great thing to document on the blog:

3"50: 816 total, 272 rounds per gun
40mm: 3,200 round - 800 clips
20mm: 45,720 rounds, when clipped 762 magazines
Hedgehog: 288 projectiles - 12 patterns
Depth Charge: 143 MK 9 Charges
Depth Charge: 124 MK6 CHarges
Small Arms: 30 Cal. 1,500 Rounds
Small Arms: 45 Cal. 8,000 Rounds
Small Arms 12 Gauge Shotgun, 100 rounds

Wednesday, April 28, 2010

2010/04/23 - 1st Tour of the 2010 Season

From DE Docent 5K Walk

I gave my 1st tour of the season. The tour was on the East shore of the river. The construction crew was putting the finishing touches on the new mooring, so the ship was delayed in moving from their winter berth (on the Rensselaer side of the Hudson River).

The group was a composed of Engineering Students, so I had an opportunity to discuss the mathematics of Naval Fire Control. It appeared that they had trouble with transportation earlier. When the bus appeared they were anxious to get aboard before the first group. I rushed the final three stops and got them on the bus. Jack Madden's group lost the race (I don't think they realized there was one), but Eric gave them they got a tour of the Motor Room and Engine Room while they waited for the shuttle bus to return.

Regarding math and Naval Fire Control here is a good example of the mathematics involved: ".... A differential equation is necessary to solve the problem of predicting the location of two maneuvering ships because of the changes of course they can make; only in an ideal situation will both of them be moving in a straight line.

Consider the following example. A firing ship is steaming course 000 (North) at 12 knots. Its target is steaming course 315 (Northwest) at 12 knots. Initially, the relative bearing to the target ship is 090 (East) and the range 10,000 yards, just shy of 5 nautical miles (4.937 nautical miles, to be more exact).

If neither ship turns, then their relative positions five minutes later may be calculated with trigonometry. The firing ship will have moved 1 nautical mile along course 000 and the target will have moved 1 nautical mile along course 315. We know that it has therefore moved 0.707 (sin(45) = 0.707) nautical miles along course 270 (West) and 0.707 (cos(45) = 0.707) nautical miles along course 000. Therefore, the distance between the firing ship’s track and the target ship has decreased to 4.230 nautical miles and it has fallen behind by 0.293 nautical miles. These distances form the two sides of a right triangle, with the hypotenuse being the linear distance between the two ships.

Trigonometry and the Pythagorean theorem again allow us to determine the length of this hypotenuse and the angle of bearing of the target ship This distance is 4.240 nautical miles ((0.293)2 + (4.230)2 = (4.240)2), and the angle is 86 degrees (arctan (4.230/0.293) = 86). As this is the angle between the firing ship’s track and the target, which is now slightly astern, the relative bearing becomes 094. The distance converts to 8,588 yards.

This simplest of examples illustrates the basic principles involved in plotting the movement of two ships. A significantly greater magnitude of complexity would be introduced if the target ship were turning to come onto a parallel course to the firing ship An accurate calculation would then require a differential equation. Effectively an infinite series of trigonometric calculations like the example above would have to be calculated as the target ship traced through the arc of its turn. ...."

A few more relevant links:

Monday, April 12, 2010

04/12/2010 - DE Docent 5K Walk

Getting ready for a new season. During the winter I started a very active walking program. The other day I decided to map out a 5K walk with the USS Slater as the starting / end point. This walk goes north into the Corning Preserve, then crosses the pedestrian bridge to Albany. It then goes up hill and loops around the NY State Capital and returns to the USS Slater. It's a great walk. Idea for scout groups to finish off a shipboard camping experience.

The following is a slightly different route. Instead of going North to the Corning Preserve, it goes up Broadway to the Visitors Center, the Aqua Ducks, and several Dining Establishments near Quackenbush Square.

A few DE Docent 5K related links that may be of interest:

DE Docent