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Thread: DC explosion effect on vessel

  1. #11
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    Default Re: DC explosion effect on vessel

    Quote Originally Posted by Resmoroh View Post
    Pavel, Hi,
    This is just intuition, but I suspect that the effects of a nearby significant explosion (at whatever depth) would be different on a wooden hulled vessel, then on a metal hulled vessel. Both would probably lose some incandescent light bulbs, but I would bet some of your money that the metal hull would spring more leaks than the wooden one!!!!!!!!!!
    HTH. Stay safe.
    Peter Davies
    I'm not so sure about that! From my experience with the local commercial fishing fleet in British Columbia, "Popping a plank" in rough seas is common enough, indeed. It depends on how well these vessels are maintained, the condition of the planks and ribs, the nails, and the "Corking" between planks.

    I think it all comes down to the proximity of the charge to the vessel in question and its condition.

    Jim

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    Default Re: DC explosion effect on vessel

    Caulking, JDC, if you'll 'scuse me saying.

    Further, on the B Bomb, from SD 719 Armament Vol I: Ch 2 notes, of the developed and delivered B.2 design, issued to units in 1939 but "no record to show that the bomb was ever used against shipping".

    Should have also noted Ch 3 Anti-submarine bombs - a lot of work was done to make sure that these eg the Mark IV could be set to detonate at shallow depth, 20 feet.

    Likewise on Depth Charges, Ch 4, notes eg the Mark VII mod to provide shallow depth pistols - 20 ft detonation again the goal, likewise the 250lb Type M (intended for surfaced U-boat attack).

    Highly recommended ref, the Armament vols.

    Nothing I can see re effect on smaller surface vessels, timber or otherwise. I don't wish to be aboard any such vessel when any of these weapons go bang nearby at 20ft depth, thank you.

    David: snap!
    Last edited by Don Clark; 10th January 2021 at 22:23.
    Toujours ŕ propos

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    Default Re: DC explosion effect on vessel

    Jim, I think that would be "caulking" between planks, and a word understood by most persons interested in keeping vessels (large and small) in good, watertight condition. I will let the following definition from a rather elderly dictionary speak for itself (Pocket Oxford, as 4th Edition, 1959 reprinting). "Caulk. v.t., Stop up (seam), c. seams of (ship), with oakum & melted pitch (or, in iron ship, by striking plate junctions with blunt chisel)."

    Also worth bearing in mind that submarines were well understood by all naval architects to be "particularly tough nuts to crack", in that they were constructed much more ruggedly than typical surface ships, by virtue of fact that their designers had to ensure that the pressure hull (that which contained the crew, engines, fuel and batteries, and main armament and all living and fuel spaces as well as the cylinders which contained the vital compressed air used for refilling the ballast tanks, the latter being OUTSIDE the pressure hull) was built to resist external sea pressure under the most extreme conditions, and including depth charge attack (when these weapons were invented in WW1). As the pressure hull of WW2 submarines was usually of circular cross-section, and constructed of very strong steel, carefully designed, it was peculiarly well suited to resisting the submarine's second "enemy", the depth charge (first enemy was of course pressure of the surrounding sea water). It was soon learned that the explosive power of a depth charge had to be of a high order to rupture the submarine's pressure hull. The hulls of surface ships, whether civilian or military, were by comparison rather flimsy affairs, although warships tended to have the option of carrying armour plating to varying degrees, including "belt armour" attached to the hull sides (although later it was extended to well below the waterline), the turrets and other smaller gun positions, and often also had armoured decks. Battleships and other large warships also adopted sloped armour below decks, often from the waterline upwards, to give protection to the "vitals" of the ship, including command and communications personnel, the "citadel" (which contained all personnel responsible for spotting, navigation, and aiming the big guns), and engines, and most of the ammunition. With the advent of submarine warfare in WW1 they also had to come up with means to provide protection against underwater torpedoes, both at sea and at anchor, including systems of boom-supported nets around ships at anchor, and very large "blisters" along major length of the hull (were these air or water-filled?) when underway. The armoured decks were primarily installed to provide protection from heavy shells coming in from distant opposing fleets ("plunging fire"), but the advent of real air power in the 1920s and 30s saw to it that such armour was improved to resist bombs from above. It can be seen that, no matter how surface ships were armoured, their ability to resist powerful, nearby underwater explosions was compromised by many other considerations (including ship stability), but for submarines, their incredible vulnerability to the laws of physics when at depth dictated that overall hull strength was an absolute priority, which coincidentally was a huge bonus when depth charges arrived on the scene. Depth charges were much later supplemented by acoustic torpedoes as well as such close-up weapons as "Hedgehogs", which ensured explosions were much closer to the submarine, and aerial rockets were eventually used against submarines fighting back on the surface, the latter rather erratic, but devastating should they hit.

    Didn't mean to write a mini-thesis on why underwater damage to surface ships might be more devastating then some people might imagine, but thought it worthwhile to point out that submarines, designed almost entirely to resist massive underwater forces, might provide an interesting counter-view of how well a surface vessel hull might hang together when exposed to such violence.

    David D
    Last edited by David Duxbury; 10th January 2021 at 22:14.

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    Default Re: DC explosion effect on vessel

    Around where I come from, it’s pronounced “corking”. If you asked someone to caulk a structure on a boat they would think you would be referring to something on deck. One of my better friends in my boat yard is a highly respected shipwright of over 40 years with many thousands of hours doing it.

    It is by the way, a fascinating procedure to watch when it’s done by someone who knows what they are doing.

    Jim

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    Default Re: DC explosion effect on vessel

    By way of return to topic, it seems that Pavel as OP at least has found my post #9 re DC vs Type B bomb etc in SD 719 Armament, of some interest.
    And perhaps PNK & others too, on DC use vs Type B bomb non-use, in my #11 further Armament notes, either now or at some later date.
    Toujours ŕ propos

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    Default Re: DC explosion effect on vessel

    Hedgehogs had to hit to explode, not just to be near. I suspect that they had shaped charge heads not just high explosive. The lack of visible effect if they missed was presumably the reason why they were not initially very popular and thought to be ineffective.

    As far as I'm concerned, caulking is pronounced corking, but what various local dialects and accents may do to this is quite another matter!

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    Default Re: DC explosion effect on vessel

    Hi,
    From what I understand, there would be several factors which could affect the outcome on a submarine, a wooden vessel would not fair any better as depth charges were designed to fracture both inner pressur hull and outer hulls on subs.
    1. Charge weight and filling.
    2. Depth of detonation
    3. Range from target
    British air dropped depth charges MkVII were filled with 290lbs of TNT. MKVIII,MKXI and MKV all had 170lbs of Torpex (50% more powerfull by weight than TNT).
    The link below is to an article on depth charge lethality, the table half way down the page gives the damage distances for different charge weights of TNT.
    https://www.alternatewars.com/BBOW/S..._Lethality.htm
    I expect that a wooden hulled vessel, if straddled by charges would be broken up by the pressure bubbles.
    Hope this is of use,
    Alan.

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    Default Re: DC explosion effect on vessel

    Alan thank you for your reply and really interesting link!

    Pavel
    Czechoslovak Airmen in the RAF 1940-1945
    http://cz-raf.webnode.cz

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