Book Research

[Snarf]

Pg. 408

'Later I was informed that the Mark 28 torpedoes had not been tested in shallow water. Tests showed that ships propellers emitted both a direct sound path and a strong sound path that reflected or bounced off the bottom at lesser depths. Thus, those that we fired headed for the bottom to bury themselves in the mud or sand, or they failed to start.'

[Sailor Steve]

Originally Posted by TorpX

Ok, I don't know why people are assuming my comments about the Mk. 18 are based on ignorance, and that I've never read anything about torpedoes before. I'll just state that that is not the case.

Sorry. I didn't mean to sound condescending. The truth is that I haven't read all that much about torpedoes myself, and sometimes when I come across something that seems obvious to me I tend to forget that it may or may not even be true, much less "obvious" to someone who may know more than I do.

I'm not sure who wanted the wakeless torpedo. Certainly, many liked the idea, but it is not clear to me that there was any pre-existing yearning, much less need, for such.

Upon closer reading of the Wiki article I linked, the "they" who wanted the electric torpedo seems to have been Admiral King, period. He may not have been the only one, which is why I wrote "seems to be".

The problems written about, seemed to come as a rude surprise, and I question whether either the Navy or it's skippers, would have accepted the electric torpedo, if they had known of the disadvantages that came with it.

Probably not. To quote the article:

The first submarines to use Mark 18s (still not perfected) were Eugene Sands' Spearfish and Mush Morton's Wahoo in September 1943. Wahoo disappeared, and Sands "experienced enough torpedo problems to drive an ordinary man berserk": one sank, one broached and ran wild, three fishtailed at launch and hit the outer doors before disappearing, and seven missed astern. His results, as described by his squadron commander, "Gin" Styer, in a masterpiece of understatement, "were disappointing".

I think most of the impetus for the Mk. 18 came from the extraordinary frustration with the Mk. 14, and perhaps, a certain amount of German-envy. (I'm talking about the common, prejudiced idea that any German weapon/technology was superior to the Allied counterpart.) If you have been stuck depending on a defective tool (whatever the reasons), you would naturally be looking around for something else to try.

Of course, that is just my opinion. I'm sure others will disagree.

Others possibly, but not me. That makes as much sense as anything I've heard.

[TorpX]

Quoted by snarf:

'Later I was informed that the Mark 28 torpedoes had not been tested in shallow water. Tests showed that ships propellers emitted both a direct sound path and a strong sound path that reflected or bounced off the bottom at lesser depths. Thus, those that we fired headed for the bottom to bury themselves in the mud or sand, or they failed to start.'

Ok, I guess I had forgotten that, or assumed that they failed to start (like with trying to start your car when it is -30 F ??). In any case, that is a significant design problem as you have the potential for your torpedo exploding underneath your sub in shallow water - not good!

Sorry. I didn't mean to sound condescending. The truth is that I haven't read all that much about torpedoes myself, and sometimes when I come across something that seems obvious to me I tend to forget that it may or may not even be true, much less "obvious" to someone who may know more than I do.

It's ok. I probably annoy twice as many people as you do.



About the electric torps, I'm struck by the notion that the navy had the same pattern repeating. Defective torpedo design - inadequate testing - poor results in the field - redesign work. This book just seems to confirm it. The Germans had the same problem, but handled it much better. BuOrd let the Navy down, I'd say.

[Snarf]

I've just finished reading Wahoo and Clear the Bridge! also. An interesting tidbit with the screw count for knowing the enemy's speed. On Tang, they ended up bringing aboard a metronome. The sound man would match the metronome to the ships screws, and he could instantly tell if the ship was speeding up or slowing down before you would ever be able to tell by ear.

O'Kane had a bit of frustration with the Mk 18 torpedoes too (a bit of an understatement since one sunk Tang). Before the war torpedoes were made at one place and they were handcrafted, even though they had exploder and depth keeping problems, the rest of the torpedo functioned quite well. During the war, they had many contractors who bid bottom dollar to make the Mk 18's so the build quality really left a lot to be desired. O'Kane talks about this in Clear the Bridge!, after their problems getting hits with the Mk 18's he had his torpedomen take apart and test everything and fine tune the torpedos, and then he started getting hits with them. His last patrol, the whole lot were Mk 18's taken aboard from Tambor (as they were experiencing shortages at the time). Once again he had his men make sure the torpedoes were functioning in top shape, and they scored hits with nearly all of their torpedoes, save the last fateful circular run.

Regarding speed again, O'Kane said they were doing 22 knots when they were picking up downed aviators off Truk. I wonder now on the performance difference between the F-M and the GM Vinton engines, as Tang had F-M engines and Barb had GM Vinton's. From what I've read, Barb seems to have the speed record.

Another interesting thing, O'Kane mentioned using the turbos (the air compressors for the ballast tanks) to blow air out the bottom of the ballast tanks to keep the sub as high out of the water as possible with the added effect of creating a layer of air bubbles under the sub which reduced drag, and it made a difference of a knot or two.

[Sniper297]

One common misunderstanding is the difference between U-boats and US fleet subs. The U-boats all had direct drive - a clutch on the back of each diesel connected directly to the propeller shaft. The rotor for the motor/generator was wrapped around the propeller shaft, and was used as either a motor powered by batteries or a generator to charge the batteries.

A US fleet boat had no connection to the propellers at all - each engine was connected to a big generator, and nothing else. The traction motors propelled the sub both on the surface and underwater, there was no other means for turning the shafts.

If you think about the difference between reciprocating engines (especially diesels) and electric motors, the reciprocating engine has a lot of back and forth up and down movement of pistons and valves - over rev a piston engine enough and it will shake itself apart and/or explode before it overheats.

An electric motor is very simple in comparison and has only one moving part, the rotor. Traction motors back then normally used between 500 and 750 volts volts DC, but if you had a way to feed 3000 volts into one you could wind it up like a berserk alarm clock for quite a long time before the insulation would start to melt. Obviously you would need to short around the fuses and clamp down the contactors, but a traction motor would spin happily at 10,000 rpm for an hour or two if there was a way to feed enough power into it. You'd need to overhaul it after that type of abuse, but it would be unlikely to fail.

The real limitation would have been how much power the diesel generators could pump out, and of course the increased drag of the hull moving through the water. The trick with using the low pressure blower and leaving the Kingston valves open to make a stream of bubbles under the hull sounds viable, dunno how much it would decrease drag but it would decrease it.

[Leandros]

Originally Posted by Sailor Steve

Back to ships. The power needed to overcome hydrodynamic drag increases as the cube of the speed. By the time you reach the indicated top speed you would have to double the available horsepower just to get that extra two knots, and that is simply not possible.

http://www.psychosnail.com/boatspeedcalculator.aspx

Fred

[Sailor Steve]

Yep, I've had that information for decades. One of the problems encountered by engineers is that the speed/length formula, while helpful, is also simplistic. Other factors affecting top speed are the fineness ratio (length vs beam) and total wetted area. A very fine ship, such as a destroyer, is going to be a lot faster than a broad-beamed merchant. The more hull that is underwater the more drag it creates. As the ship moves through the water it creates its own waves, which increase drag. Also even a displacement hull will tend to "climb" its own waves, meaning that as speed increases the ship is trying to move uphill over the waves it creates.

All those things are factors in how fast a ship can move and how much power it takes to do so.

[TorpX]

Interesting site. I hadn't seen it before.

[merc4ulfate]

If you prefer to read the actual ships logs you can go here and check out the boat you wish to read.

No book forms just microfiche of the actual logs. I hadn't realized the Barb had did service in the Atlantic before she went to the pacific.

Some logs are shorter than others but I find reading them is fascinating. Random failures, shielding being swept off the boat by heavy seas and at other times not being able to maintain depth even at 120 feet due to high seas. I thought water over the periscope was bad in SH4 until I read about the the fogging issue on the periscope that limited visual time to ten second intervals. That would be hell.

Read them all here:

http://www.hnsa.org/doc/subreports.htm