Real Submarine Technology & History Q&A

[LukeFF]

Originally Posted by DaveyJ576

Diving times were usually measured under the following parameters: boat fully surfaced and running at a standard bell (approx. 15 knots), and time to get to periscope depth. For the Gato/Balao/Tench classes PD was 65 feet. At the start of the war the fleet boats were credited with 50 second dive times. By the end of the war that was down to an average of 40 seconds. With a lot of training some boats were able to dive in 30 seconds. For a boat the size of the fleet boats this was pretty impressive.

Thanks as always, Dave! This info here made me realize how off I was on the dive times for RFB.

[LukeFF]

Dave,

Do you have any data handy on surfaced acceleration rates for fleet subs? I have good data on submerged acceleration rates but none for the other.

[DaveyJ576]

Originally Posted by LukeFF

Dave,

Do you have any data handy on surfaced acceleration rates for fleet subs? I have good data on submerged acceleration rates but none for the other.

I am expecting a package from a friend out in California that will have construction data in it on the Gato class boats. When I get it I will take a look. Other than that, nope. I am sure those data curve charts exist (or existed) somewhere, but I haven't seen them.

[Nit]

Dave, please publish this data at a forum. It would be desirable to know the data of dive time exactly.

[Fishbreath]

Reading patrol logs from www.hnsa.org I see a lot of skippers writing things like "proceeded at three-engine speed".

Now, I assume this means that they have one engine shut off for fuel reasons (?), but how hard are they driving the other three, and about how fast would they be going?

[LukeFF]

Dave,

In other recent conversations here, it's been discussed where the ladder in the Gato/Balao control room was actually located during the war years. Pics such as this one from Wahoo show it to be behind the dive planes:



While this undated picture shows it to be behind the main gyro compass:



So, was it standard during the war to have the ladder behind the dive planes? And if so, was it part of the postwar revision process to move the ladder to the other position? Pampanito shows the ladder to be behind the dive planes. Since it doesn't seem like that particular boat was extensively modified in the postwar years, that would lead me to believe the ladder's correct position should be behind the dive planes.

[DaveyJ576]

Originally Posted by Fishbreath

Reading patrol logs from www.hnsa.org I see a lot of skippers writing things like "proceeded at three-engine speed".

Now, I assume this means that they have one engine shut off for fuel reasons (?), but how hard are they driving the other three, and about how fast would they be going?

A USN fleet submarine has four "normal" ahead speed settings: 1/3, 2/3, standard, and full. A 1/3 bell would have one engine/generator on line and would provide a max of about 6-7 knots (a knot is one nautical mile per hour, a nautical mile is exactly 2000 yards). A 2/3 bell would have two engines on line and would give you about 8-11 knots. Ahead standard would have three engines on line and would provide about 11-15 knots. Finally, ahead full has all four engine/generator sets on line and and will give you about 15-18 knots. In most cases, the engine is set to run at it's most fuel efficient speed. You vary the boat's speed within the ranges that I gave by varying the amount of electricity that is sent to the motors, sending the rest to the batteries as a "running charge".

While charging batteries, you will normally have multiple engines on line, but your speed will be reduced because much of the current is being drawn off for the battery charge. For instance, if your battery is badly depleted, you can have a four engine battery charge running but your speed may only be about 8 knots. As the battery charges up, less and less current is sent to the batteries so the excess is drawn off to propulsion and the boat's speed gradually increases.

Now you are probably wondering about the ahead flank bell. Flank speed is a special condition that is achieved by running all four engines at their maximum rated speed and lining the batteries up in series and pulling extra current out to supplement what is coming from the engine/generators. This condition will push the boat to it's maximum rated speed of 21 knots. This obviously will draw down the battery charge.

When the Barb made her famous raid into Namkwan Harbor, Gene Fluckey had his engine room chief tie down the governors on all four of the GM 16-248's and ran up a 150 percent overload. In this condition, Barb was estimated to have hit about 25 knots while exiting the harbor. This is a very dangerous condition and once clear of the harbor they "slowed" to flank speed to keep the engines from tearing themselves apart and to allow the shaft bearings to cool!

Notice how many times above that I said "about" when refering to speed. The maximum achieveable speed is dependent upon the material and mechanical condition of the propulsion plant and the amount of marine growth on the hull. Thus, it is not uncommon to have a submarine whose max speed is reduced by several knots. A thorough overhaul and hull cleaning would correct this, but you didn't get those very often.

[DaveyJ576]

The location of the conning tower ladder did vary a little bit from one boat to another. However, it never moved very far.

It is important to remember that no two boats came out of the builder's yard exactly the same. There were always numerous minor detail differences from one boat to the next. One of these minor variances could have been the location of this ladder. The general location was fixed by two features that did not vary: the location of the conning tower in relation to the control room, and the location of the conning tower hatch which was always in the forward port corner of the conning tower. Therefore, the ladder leading up to it from the control room was always going to be in the general vicinity of the dive planes and gyroscope.

I think the variation that Luke is seeing is simply a 90 degree rotation aft. Some boats that I have seen has the ladder rungs facing the dive planes. Others have had the ladder rungs perpendicular to the planes. I think what they were doing was rotating the ladder 90 degrees aft along the conning tower hatch rim. This would have gotten it out of the way of the planesmen. This was probably a later mod that was based on operational experience.

One other factor that might be affecting what you are seeing in the photos is the location of the trim and drain manifold in relation to the air manifolds. The fleet boat control room had a "dry" side and a "wet" side. The air manifold for blowing ballast tanks was always on the opposite side of the control room from the trim manifold used to vary the amount of water in the trim tanks. This was usually an Electric Boat vs. Government yard difference; one used a dry port/wet starboard config and the other a wet port/dry starboard config. Which was which is escaping me right now (old age brain fart!!). This difference may have moved the location of the dive planes station a little forward or aft and this may be accounting for some of the differences you are seeing.

[Sailor Steve]

Originally Posted by DaveyJ576

(a knot is one nautical mile per hour, a nautical mile is exactly 2000 yards).

Actually a nautical mile is exactly:

One minute of arc along a meridian of Earth

1852 meters

2,025.372 yards

6,076.1155 feet

As established by the First International Extraordinary Hydrographic Conference, held in Monaco in 1929.

The United States didn't adopt this standard until 1954, but even during the Second World War it wasn't exactly 2000 yards - it was 6080.2 feet, which is 2026.7333 yards.

[DaveyJ576]

Originally Posted by Sailor Steve

Actually a nautical mile is exactly:

One minute of arc along a meridian of Earth

1852 meters

2,025.372 yards

6,076.1155 feet

As established by the First International Extraordinary Hydrographic Conference, held in Monaco in 1929.

The United States didn't adopt this standard until 1954, but even during the Second World War it wasn't exactly 2000 yards - it was 6080.2 feet, which is 2026.7333 yards.

I stand corrected! I always strive for accuracy and this one eluded me completely! During my days as a U.S. Navy Quartermaster, we always used 2000 yards as our baseline for navigational computations and never ran into problems. Interesting.

[LukeFF]

Originally Posted by DaveyJ576

I think what they were doing was rotating the ladder 90 degrees aft along the conning tower hatch rim. This would have gotten it out of the way of the planesmen. This was probably a later mod that was based on operational experience.

That was my guess as well. Based on all the interior photos I've seen, the above-posted photo with the ladder perpendicular to the planes was probably either taken late in the war with, say, a Tench class boat or a photo taken in the immediate postwar era.

[Fishbreath]

Originally Posted by DaveyJ576

<snip informative post>

Thanks a lot. I wasn't entirely clear on the relationship between ordered bell and which engines are doing what, and now it all make sense.

[Platapus]

Originally Posted by DaveyJ576

Flank speed is a special condition that is achieved by running all four engines at their maximum rated speed and lining the batteries up in series and pulling extra current out to supplement what is coming from the engine/generators. This condition will push the boat to it's maximum rated speed of 21 knots. This obviously will draw down the battery charge.

I learn something every time I read this thread. I never knew that flank speed drained the batteries. I just thought flank speed was overreving the motors.

[Nuc]

Originally Posted by LukeFF

That was my guess as well. Based on all the interior photos I've seen, the above-posted photo with the ladder perpendicular to the planes was probably either taken late in the war with, say, a Tench class boat or a photo taken in the immediate postwar era.

These builder's plans for a Balo class show the ladder behind the planes station



Edit: In Looking at the plans and the pictures of the ladder I noticed that in the game the hatch is rotated 90 degrees from where it should be. regardless of the ladder orientation the long axis of the hatch runs fore and aft with the hinge such that the open hatch is up against the port side of the conning tower. In the game it runs the other way (athwart ship) and when opened the hatch would stick up in the middle of the deck.

[LukeFF]

Dave:

In this overhaul picture of the Wahoo, taken in July 1943, I have a couple of questions about some of the objects on the bridge:

http://www.navsource.org/archives/08/0823843.jpg

-The circular item on the far left: is that a voice tube?
-Is the item adjacent to the above item a pelorus?
-The "box" on the far right: is that a loudspeaker?