Real Submarine Technology & History Q&A

[LukeFF]

Dave,

The WWII patrol reports mention the use of what is called a "bubble sextant" for navigation. Many commanders also mention how it was sometimes difficult to use this device. How did this new type of sextant differ from the "old" style sextant, and what made it so more difficult to use?

[Platapus]

Ok, now I am going to ask the stupidest submarine question.

Good thing I am a landlubber so I can have some excuse.

Given all the technology we have these days, why are not modern submarines constructed without sails?

Everything could be in a very streamlined "whale" shape. Now that Periscopes do not need a direct optical path as they are more sensors than a periscope, why is there still a need for a sail on a submarine?

What is the use of the sail on a modern nuclear submarine that spends 99% of its time underwater tryin to be sneaky?

[DaveyJ576]

Originally Posted by Platapus

Given all the technology we have these days, why are not modern submarines constructed without sails?

This is not a dumb question at all. In fact, several leading naval architects have asked the same question. They really wanted to eliminate the sail as it is a major source of hydrodynamic drag.

The main purpose of the sail was to provide a streamlined housing for the masts. These masts have to be a certain length in order to be able to penetrate the surface while at the same time keeping the boat at a deep enough depth to maintain control. This made for a fairly long mast. In order to house the mast completely when retracted, the hull of the boat would have had to be huge in cross section. This is impractical so the compromise is the sail.

The other important feature of the sail is the bridge. A partially sheltered, raised bridge is vital to safe navigation once the boat is on the surface entering or leaving port. It has to be some distance above the hull in order for the OOD and lookouts to be able to see anything.

On two separate occasions in the 1950's and 1960's the proposal to eliminate the sail was seriously put forth. However, each time the designers ran afoul of the problems that I described above. They tried one more time in 1968 during the CONFORM project, which was the first attempt at designing a follow on to the Permit and Sturgeon class SSN's. A scale model of the proposed design was built that had no sail at all. The masts and periscopes folded flush with the hull, similar to the way the snorkel mast folded on the late war German U-boats. The CONFORM design even featured a small folding bridge structure. This project would have produced a radically new and different submarine if it had been built. However, Admiral Rickover was adamantly opposed to these radical changes and championed the more "conservative" SSN-688 design. Rickover's forceful protestations eventually won out. CONFORM died and his design eventually became the Los Angeles class.

Realistically, we are only just now coming into a technology level that will permit the removal of the sail structure. CONFORM would have stretched the state of the art to its limits, and ultimately may not have been practical. Our newest submarines of the Virginia (SSN-774) class have non penetrating masts (i.e. they don't retract into or penetrate the pressure hull). This would allow a serious reduction in sail size. See this link for an artists impression of a proposed sail design for later Virginia class boats:

http://www.navsource.org/archives/08/0877413.jpg

[DaveyJ576]

Originally Posted by LukeFF

The WWII patrol reports mention the use of what is called a "bubble sextant" for navigation. Many commanders also mention how it was sometimes difficult to use this device. How did this new type of sextant differ from the "old" style sextant, and what made it so more difficult to use?

When using a standard sextant, the angle to a celestial object is determined by sighting it, then bringing the reflected image of the object down to horizon level by moving the index arm along the semi-circular arc scale at the bottom of the sextant. Obviously, in order to do this, you have to be able to see the horizon. See the following link:

http://www.tpub.com/content/administ.../14220_230.htm

If for some reason you are unable to see the horizon, you would need to find a substitute. In a bubble sextant, the visual horizon is replaced by a regular alcohol bubble level. The reflected image of the celestial object would be brought down to the artificial horizon created by the bubble and the angle read off of the arc scale as normal. See this link:

http://www.users.bigpond.com/bgroble...t/sextant.html

Not being able to see the horizon was usually a problem for aviators flying at night. A shipboard navigator usually takes his sights at morning twilight, when it is still dark enough to see the stars, but when it is light enough to drown out the minor stars, making the major navigational stars easier to distinguish and the horizon visible. Aviators flying night missions may not always have this luxury of choosing the time of their sightings. At night and at altitude it would be very difficult, if not virtually impossible to see the horizon.

I have never used a bubble sextant and therefore can not directly comment on its ease of use. However, it is probably quite difficult to keep the bubble level enough to take an accurate sight on the pitching and rolling bridge of a fleet boat. Why didn't they just use a normal sextant? Well, it would give them the advantage of getting a fix at any time during the night, not just at morning twilight. The more fixes you get, the better your navigational situation will be.

[Platapus]

How long would it take for an average navigator to take the sightings he or she needs using a sextant?

[DaveyJ576]

Originally Posted by Platapus

How long would it take for an average navigator to take the sightings he or she needs using a sextant?

The actual taking of the sights doesn't take long at all, maybe 3-5 minutes depending on conditions. It is the prep and post sighting work that eats all your time. From start of work to plotting the posit on the chart, probably an hour for the average navigator, a little less for a really good one.

[Platapus]

As always, thanks for the clear answers.

[DaveyJ576]

There is currently a debate going on in the Submarine Trivia thread concerning the reliability of author Norman Friedman's book U.S. Submarines Through 1945: An Illustratred Design History. This book, while I consider it to be a authoritative reference work, has to be read and absorbed with a certain degree of caution. I can not emphasize this enough: this is not a book for a novice, or even average, reader. He wrote it for an experienced reader with a naval history or engineering background.

Mr. Friedman's writing style is not the best in the world. It is very academic in nature, with a choppy and broken paragraph structure. He will frequently drop interesting morsels like "The Electric Boat S-boats had to be rebuilt", then utterly fail to explain or expand on that statement. He also frequently refers to an extensive notes section, often leaving very important and illuminating information to a section in the back of the book, forcing the reader to constantly flip from the page you are reading to the notes section. This serves to break up your line of thought and makes his material hard to understand, and very easy to take out of context. I have also occasionally found some minor typos. Whoever his editor was did a poor job of keeping him on task and writing a well formulated and readable book.

I have a feeling that when he took on this project he didn't realize what a massive and detail loaded work it would become. A well intentioned attempt to cram as much detail as he could into the book backfired and the result was a sometimes confusing mass of data.

That is not to say that he is unreliable. Rarely have I found an out-and-out error in his works and in general he gets it right. He primarily works from original sources, i.e. Department of the Navy planning and construction documents, construction plans, materiel vendor documents, etc. Therefore, I consider him to be an authoritative and reliable author. But this also puts him at the mercy of the very material he uses. Planning documents will sometimes contradict the construction orders. Construction orders and plans are sometimes changed on the fly as needed to get the job done. These changes were sometimes not properly documented and this leads to contradictions from one document to the other. As the years have passed, some of the original documents have been lost and some destroyed, leaving gaps in the knowledge base and this leads to further confusion and contradictions.

My background has given me the experience necessary to "read between the lines" so to speak and interpret what Mr. Friedman writes. Even still, I have to read his works very carefully in order to understand what he intended.

For the average or novice reader, Mr. Friedman's book should only be used as a backup resource. The book that I can highly recommend is John D. Alden's The Fleet Submarine in the U.S. Navy. In this book, Mr. Alden hit solid gold. He has a well formulated and very readable writing style. It flows well and he makes this sometimes arcane subject easy to understand. I have never caught Mr. Alden in a mistake and his material has always checked out as accurate against other sources. I have refered to my copy of this book (which I have had for about 27 years) so many times it has become a little dog eared and worn. I consider it a true treasure and it is my prime source of info on the fleet boats. Unfortunately, I believe that this book is out of print so it may be a little difficult to find.

[Lt.Fillipidis]

DaveyJ576
I have a question here that has to do with the hull toughness on a VII or IX.
Ill just repost the question i posted on the SH3 forum.

A week ago i've got my hands on "The Curious Case of Benjamin Button" film.
At some point of this ridiculously long film, a tug boat rams a german u-boat which looked like an IX to me. The tug boat collides with the boat and pierces the bow armor, causes the torpedoes to explode and the uboat sinks.
As far as im concerned, the mere tug boat is too light and its bow not pointy enough to do such damage but i would like a second opinion on that...

Thanks!

[Sailor Steve]

Originally Posted by DaveyJ576

Mr. Friedman's writing style is not the best in the world. It is very academic in nature, with a choppy and broken paragraph structure.

I was reading his book on the history of U.S. destroyers, and was pleasantly surprised to find out that naval history came to him as a sideline. His original professionwas teaching physics at the Naval War College. That explained a lot to me I didn't understand about his writing.

Of course even he didn't give me the one piece of information I was looking for, which was the hull plate thickness of the 1890s torpedo boat destroyers.