Explosive force

Archived from groups: rec.games.frp.gurps (More info?)

Anyone know of an algorithm converting G.U.R.P.S. dice of damage to pounds
of motive force? Specifically, it was the practice of submarine captains in
mid to late WWII to rig torpedoes to detonate underneath target surface
ships. The magnetically fused warhead would (ideally) detonate just under
the keel, raising the ship out of the water and, hopefully, breaking her
spine. Obviously, one needs to ensure that the amount of explosive charge
is adequate to the job, but Vehicles 2nd is silent on this. I figure having
a conversion ought to be helpful in moving other things via explosives as
well...
17 answers Last reply
More about explosive force
  1. Archived from groups: rec.games.frp.gurps (More info?)

    I never really thought of the ship rising or falling. I thought the
    effect was that the water acted as a tamping to focus more of the
    explosion towards the ship. The explosive force follows the path of
    least resistance (this is how gun barrels work on a simplistic level).
    An explosion on the side allows a lot of the force of the explosion to
    go into the air. Underneath it has nowhere to go but into the ship,
    and at a very critical part (keel) at that.

    This technique is quickly learned by 10 year olds who put fireworks
    under things rather than next to things to do more damage.
  2. Archived from groups: rec.games.frp.gurps (More info?)

    I Googled this after your reply and found various sources stating both
    your reason and mine (vacuum vrs focusing of explosive force) without a
    clear reasoning behind either. All sources were very clear to the
    effect of under keel being a more effective location of torpedo
    detonation, but no scientific backup was given for either argument.

    I don't have a strength in physics, but do have experience with
    explosives and the multiplying effect of tamping your charges. I'll
    have to experiment with this one ("Honey, why are you setting off M-80s
    in the bathtub?").
  3. Archived from groups: rec.games.frp.gurps (More info?)

    "MnTigger" <MnTigger@ether.net> wrote in message
    news:11cn9bg7mlcsube@corp.supernews.com...
    > Anyone know of an algorithm converting G.U.R.P.S. dice of damage to
    pounds
    > of motive force? Specifically, it was the practice of submarine
    captains in
    > mid to late WWII to rig torpedoes to detonate underneath target
    surface
    > ships. The magnetically fused warhead would (ideally) detonate just
    under
    > the keel, raising the ship out of the water and, hopefully, breaking
    her
    > spine.

    For the record, this is technically wrong. The explosion did not raise
    the ship, it displaced the water from underneath it, creating a hole for
    the ship to fall into. If the torpedo could generate enough force to
    actually lift the whole ship into the air, it could generate enough
    force to break the keel on a direct hit, obviating the need to develop
    this tactic in the first place. This is a *very* important distinction
    if you wish to attempt to convert damage to force.

    --
    Rob
  4. Archived from groups: rec.games.frp.gurps (More info?)

    "MnTigger" <MnTigger@ether.net> wrote in message
    news:11cn9bg7mlcsube@corp.supernews.com...
    > Anyone know of an algorithm converting G.U.R.P.S. dice of damage to pounds
    > of motive force? Specifically, it was the practice of submarine captains
    in
    > mid to late WWII to rig torpedoes to detonate underneath target surface
    > ships. The magnetically fused warhead would (ideally) detonate just under
    > the keel, raising the ship out of the water and, hopefully, breaking her
    > spine. Obviously, one needs to ensure that the amount of explosive charge
    > is adequate to the job, but Vehicles 2nd is silent on this. I figure
    having
    > a conversion ought to be helpful in moving other things via explosives as
    > well...

    It seems to me that you wouldn't need to do that conversion. I'd figure it's
    like rolling to hit the vitals (-3 to hit). Then I'd double the weapon's
    damage and compare that number to the ship's hit points. If the weapon
    inflicted more damage than the ship had hit points, the ship is done. Of
    course, you could fiddle with the to-hit penalty and damage multiplier till
    you get values you like.

    Fun as it is to fiddle with Vehicles (I do it, too), I regard it as a
    separate hobby and don't let it get in the way of my RPG fun. Going through
    all these calculations adds nothing to a role-playing game. Also, as a GM,
    I'm going to ask myself: Is it more interesting in terms of future
    developments in the plot to have that ship sink or not? Sometimes, the
    torpedo gets all sixes and that old tanker limps home anyway, because the
    adventure ends prematurely otherwise.
  5. Archived from groups: rec.games.frp.gurps (More info?)

    Sam Spade wrote:
    > "MnTigger" <MnTigger@ether.net> wrote in message
    > news:11cn9bg7mlcsube@corp.supernews.com...
    >
    >>Anyone know of an algorithm converting G.U.R.P.S. dice of damage to pounds
    >>of motive force? Specifically, it was the practice of submarine captains
    >
    > in
    >
    >>mid to late WWII to rig torpedoes to detonate underneath target surface
    >>ships. The magnetically fused warhead would (ideally) detonate just under
    >>the keel, raising the ship out of the water and, hopefully, breaking her
    >>spine. Obviously, one needs to ensure that the amount of explosive charge
    >>is adequate to the job, but Vehicles 2nd is silent on this. I figure
    >
    > having
    >
    >>a conversion ought to be helpful in moving other things via explosives as
    >>well...
    >
    >
    > It seems to me that you wouldn't need to do that conversion. I'd figure it's
    > like rolling to hit the vitals (-3 to hit). Then I'd double the weapon's
    > damage and compare that number to the ship's hit points. If the weapon
    > inflicted more damage than the ship had hit points, the ship is done. Of
    > course, you could fiddle with the to-hit penalty and damage multiplier till
    > you get values you like.
    >
    > Fun as it is to fiddle with Vehicles (I do it, too), I regard it as a
    > separate hobby and don't let it get in the way of my RPG fun. Going through
    > all these calculations adds nothing to a role-playing game. Also, as a GM,
    > I'm going to ask myself: Is it more interesting in terms of future
    > developments in the plot to have that ship sink or not? Sometimes, the
    > torpedo gets all sixes and that old tanker limps home anyway, because the
    > adventure ends prematurely otherwise.
    >
    >
    Actually, it came up as a vehicle design question. A character was
    needing to design a submarine, and wanted to equip it with torpedoes.
    This raised a design question of how big did those torpedoes need to be,
    which in turn led to "how big do the warheads need to be?" Dredging up
    obscure tidbits about German submarine tactics, I wondered wether it was
    more efficient to try and set off a large explosion underneath the hull,
    or deliver a shaped charge warhead into the hull.
    I made an arbitrary ruling anyway, but thought a formula along the
    lines of 1pt damage = 1 lb. of force might come in useful otherwise.
  6. Archived from groups: rec.games.frp.gurps (More info?)

    On Wed, 6 Jul 2005 04:34:00 -0500, "MnTigger" <MnTigger@ether.net>
    wrote:

    >Anyone know of an algorithm converting G.U.R.P.S. dice of damage to pounds
    >of motive force? Specifically, it was the practice of submarine captains in
    >mid to late WWII to rig torpedoes to detonate underneath target surface
    >ships. The magnetically fused warhead would (ideally) detonate just under
    >the keel, raising the ship out of the water and, hopefully, breaking her
    >spine.

    What an absurd idea. The spine would break long before the ship was
    moved out of the water.
  7. Archived from groups: rec.games.frp.gurps (More info?)

    "mathilda" <smart_aleck72@yahoo.com> wrote in message
    news:1120676813.393469.217550@o13g2000cwo.googlegroups.com...
    > I never really thought of the ship rising or falling. I thought the
    > effect was that the water acted as a tamping to focus more of the
    > explosion towards the ship.

    [snip]

    Interesting, but totally wrong. Newton's laws, Pascal's Law, and all
    that. The most economical way to ensure the greatest magnitude of force
    from an explosion is directed toward the ship is to have the torpedo in
    contact with the ship. Unfortunately (for submariners), if the resources
    are available, it's far easier to build a stronger ship than it is to
    build a more powerful torpedo, thus necessitating a change in tactics.

    --
    Rob
  8. Archived from groups: rec.games.frp.gurps (More info?)

    mathilda wrote:
    > I Googled this after your reply and found various sources stating both
    > your reason and mine (vacuum vrs focusing of explosive force) without a
    > clear reasoning behind either. All sources were very clear to the
    > effect of under keel being a more effective location of torpedo
    > detonation, but no scientific backup was given for either argument.
    >
    > I don't have a strength in physics, but do have experience with
    > explosives and the multiplying effect of tamping your charges. I'll
    > have to experiment with this one ("Honey, why are you setting off M-80s
    > in the bathtub?").
    >

    I think a lot of the reason for the under the keel explosion is that a
    torpedo only has so much explosive power available. If you can move
    enough water out from under the ship you have the entire weight of the
    ship focused on the keel at that point which is a lot more energy than
    you could have produced with your torpedo. And water is much easier to
    move out of the way than steel.
    Also to prevent direct explosions with shaped charges from working a lot
    of warships had double hulls so that the torpedo's explosion was
    "wasted" blowing a hole in the thin outer hull. The bulk of the
    explosive force was then vented into the space between the hulls and lost.
  9. Archived from groups: rec.games.frp.gurps (More info?)

    <raven@westnet.poe.com> wrote in message
    news:WoXye.1900$Q75.307548@newshog.newsread.com...
    > mathilda <smart_aleck72@yahoo.com> wrote:
    > > I Googled this after your reply and found various sources stating
    both
    > > your reason and mine (vacuum vrs focusing of explosive force)
    without a
    > > clear reasoning behind either. All sources were very clear to the
    > > effect of under keel being a more effective location of torpedo
    > > detonation, but no scientific backup was given for either argument.
    >
    > > I don't have a strength in physics, but do have experience with
    > > explosives and the multiplying effect of tamping your charges.
    I'll
    > > have to experiment with this one ("Honey, why are you setting off
    M-80s
    > > in the bathtub?").
    >
    > No, you're correct and you're detractors are wrong: becuase contact or
    not
    > isn't the point: ideally you're topedo would dive down and come up
    > directly from the bottom to strike the keel. But the extra tamping
    effect
    > of not having the explosion come in contact with air sooner is worth
    the
    > slight degredation of having the explosive go off not in contact with
    > ships hull, so long as the depth isn't absurd.

    That ain't what the TMs on my boat taught me. There just plain *isn't* a
    torpedo that could sink a carrier or a battleship with a direct hit
    based on its explosive force alone. If you learned differently on *your*
    boat, I'd love to hear about it.

    disclaimer: I speak strictly of non-nuclear torpedos.

    --
    Rob
  10. Archived from groups: rec.games.frp.gurps (More info?)

    On Wed, 6 Jul 2005 04:34:00 -0500, "MnTigger" <MnTigger@ether.net>
    wrote:

    >Anyone know of an algorithm converting G.U.R.P.S. dice of damage to pounds
    >of motive force? Specifically, it was the practice of submarine captains in
    >mid to late WWII to rig torpedoes to detonate underneath target surface
    >ships. The magnetically fused warhead would (ideally) detonate just under
    >the keel, raising the ship out of the water and, hopefully, breaking her
    >spine. Obviously, one needs to ensure that the amount of explosive charge
    >is adequate to the job, but Vehicles 2nd is silent on this. I figure having
    >a conversion ought to be helpful in moving other things via explosives as
    >well...
    >
    i think the actual mechanic of damaging the ship is that the explosion
    creates a bubble into which the ship "falls" breaking her back in the
    process.
    --
    "Ineffective, unfocused violence leads to more violence. Limp,
    panicky half-measures lead to more violence. However, complete,
    fully-thought-through, professional, well-executed violence
    never leads to more violence because, you see, afterwards, the
    other guys are all dead."
  11. Archived from groups: rec.games.frp.gurps (More info?)

    If this is in regards to WWII torpedos, I don't believe they were
    shaped charged.
  12. Archived from groups: rec.games.frp.gurps (More info?)

    On Wed, 6 Jul 2005 04:34:00 -0500, "MnTigger" <MnTigger@ether.net>
    wrote:

    >Anyone know of an algorithm converting G.U.R.P.S. dice of damage to pounds
    >of motive force?

    You can try to approxximate it with a double conversion.
    In GURPS 4th there's a formula to convert, IIRC, weight of explosive
    (knowing explosive force of the substance) into dice of damage, and
    vice-versa.
    If you know how much motive force is generated by a certain amount of
    TNT, you can do two-step conversions.

    Or, if you know:
    1- what the DR of the hull supposed to break is,
    2- what is the percentage of hull actually breaking,

    you can figure out the dice of damage done by the mine/bomb/whatever,
    so that, if you know the explosive relative force of the explosive
    substance, you can use the above mentioned formula to convert in
    weight needed.

    Example: DR 70 has 50% of braking under 20d of damage (since each die
    delivers 3,5 points of damage, on average), and it will be almost sure
    to break under 30d of damage.

    If you need a way to figure out FAST what are the expected damages for
    a certain number of dice (expecially LARGE amounts):
    http://divnull.com/omnihedron/

    Hope this is of help.
    Korin Duval

    --

    "Truth requires a great amount of courage;
    Fiction requires a great amount of maturity."
  13. Archived from groups: rec.games.frp.gurps (More info?)

    On Wed, 06 Jul 2005 12:52:24 GMT, "Robert Bunn" <adalger@twcny.rr.com>
    carved upon a tablet of ether:

    >
    > "MnTigger" <MnTigger@ether.net> wrote in message
    > news:11cn9bg7mlcsube@corp.supernews.com...
    > > Anyone know of an algorithm converting G.U.R.P.S. dice of damage to
    > pounds
    > > of motive force? Specifically, it was the practice of submarine
    > captains in
    > > mid to late WWII to rig torpedoes to detonate underneath target
    > surface
    > > ships. The magnetically fused warhead would (ideally) detonate just
    > under
    > > the keel, raising the ship out of the water and, hopefully, breaking
    > her
    > > spine.
    >
    > For the record, this is technically wrong. The explosion did not raise
    > the ship, it displaced the water from underneath it, creating a hole for
    > the ship to fall into. If the torpedo could generate enough force to
    > actually lift the whole ship into the air, it could generate enough
    > force to break the keel on a direct hit, obviating the need to develop
    > this tactic in the first place. This is a *very* important distinction
    > if you wish to attempt to convert damage to force.

    As I recall it, the damage wasn't from either of these, but from the
    multiple hammering effect of the gas-cloud smashing against the bottom
    of the ship several times successively.

    Also, it was the intended use of magnetic triggers in torpedos right
    from the beginning of the war, but many of the torpedos, or their
    triggers were insufficiently realiable for this to be a viable tactic
    (US torpedos were particularly poor).


    --
    Rupert Boleyn <rboleyn@paradise.net.nz>
    "Just because the truth will set you free doesn't mean the truth itself
    should be free."
  14. Archived from groups: rec.games.frp.gurps (More info?)

    On Wed, 06 Jul 2005 21:02:03 GMT, "Robert Bunn" <adalger@twcny.rr.com>
    carved upon a tablet of ether:

    > That ain't what the TMs on my boat taught me. There just plain *isn't* a
    > torpedo that could sink a carrier or a battleship with a direct hit
    > based on its explosive force alone. If you learned differently on *your*
    > boat, I'd love to hear about it.

    Depends on the exact location of the hit, and various odd effects of
    'lucky' shots. The Iowa and her sisters, for example, had rather
    thinner torpedo protection schemes over their 'A' turret's magazines
    than was really desirable (due to thier very fine bows), and so a side
    hit with a large warhead (and they were designed before the power of
    the Long Lance torpedo was discovered) could well do far more damage
    than anticipated, and if things went badly that could mean a magazine
    explosion - and that's a destroyed ship. Another example - a near miss
    by a propeller can bend the shaft, and if it's not stopped immediately
    that can split the hull wide open, immediately flooding most of the
    engineering spaces.

    Then there's the broken back scenario, which bypasses all the
    anti-torpedo defences aside from simply being very big, and very
    solidly built. I wouldn't place money on any ship being immune to a
    large torpedo that detonated 'just right'.


    --
    Rupert Boleyn <rboleyn@paradise.net.nz>
    "Just because the truth will set you free doesn't mean the truth itself
    should be free."
  15. Archived from groups: rec.games.frp.gurps (More info?)

    "Rupert Boleyn" <rboleyn@paradise.net.nz> wrote in message
    news:0qroc15fh1c5tbnljn4cbmfhqdpka5d17v@4ax.com...
    > On Wed, 06 Jul 2005 21:02:03 GMT, "Robert Bunn" <adalger@twcny.rr.com>
    > carved upon a tablet of ether:
    >
    > > That ain't what the TMs on my boat taught me. There just plain
    *isn't* a
    > > torpedo that could sink a carrier or a battleship with a direct hit
    > > based on its explosive force alone. If you learned differently on
    *your*
    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

    > > boat, I'd love to hear about it.
    >
    > Depends on the exact location of the hit, and various odd effects of
    > 'lucky' shots. The Iowa and her sisters, for example, had rather
    > thinner torpedo protection schemes over their 'A' turret's magazines
    > than was really desirable (due to thier very fine bows), and so a side
    > hit with a large warhead (and they were designed before the power of
    > the Long Lance torpedo was discovered) could well do far more damage
    > than anticipated, and if things went badly that could mean a magazine
    ^^^^^^^^^^^^^^^^^^^^^

    > explosion - and that's a destroyed ship. Another example - a near miss
    ^^^^^^^^^

    > by a propeller can bend the shaft, and if it's not stopped immediately
    ^^^^^^^^^^^^^^^^^^^^^^

    > that can split the hull wide open, immediately flooding most of the
    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^

    > engineering spaces.
    >
    > Then there's the broken back scenario, which bypasses all the
    ^^^^^^^^^^^^^^^^^^^^

    > anti-torpedo defences aside from simply being very big, and very
    > solidly built. I wouldn't place money on any ship being immune to a
    > large torpedo that detonated 'just right'.

    The rest of my counterargument is left as an exercise to the reader.

    --
    Rob
  16. Archived from groups: rec.games.frp.gurps (More info?)

    On Thu, 07 Jul 2005 02:11:15 GMT, "Robert Bunn" <adalger@twcny.rr.com>
    carved upon a tablet of ether:

    > The rest of my counterargument is left as an exercise to the reader.

    By the logic this seems to imply no ship big enough it's not simply
    blown apart (ie more than about 100') can be sunk by a torpedo.
    Afterall the water rushing in isn't from 'it's explosive force alone'.
    This is what you meant to say, right?


    --
    Rupert Boleyn <rboleyn@paradise.net.nz>
    "Just because the truth will set you free doesn't mean the truth itself
    should be free."
  17. Archived from groups: rec.games.frp.gurps (More info?)

    "Rupert Boleyn" <rboleyn@paradise.net.nz> wrote in message
    news:612qc1dkjqbclfpeek4hg6tlm0t2jmogl4@4ax.com...
    > On Thu, 07 Jul 2005 02:11:15 GMT, "Robert Bunn" <adalger@twcny.rr.com>
    > carved upon a tablet of ether:
    >
    > > The rest of my counterargument is left as an exercise to the reader.
    >
    > By the logic this seems to imply no ship big enough it's not simply
    > blown apart (ie more than about 100') can be sunk by a torpedo.
    > Afterall the water rushing in isn't from 'it's explosive force alone'.
    > This is what you meant to say, right?
    >

    Almost but not exactly. More precisely, no "ship of the line"-equivalent
    of today can be sunk by a torpedo *without creating some magnifying
    effect*. Examples include the ones you mentioned. Current naval doctrine
    is that blowing the water out from under the ship is to be preferred.
    For one, it allows much looser accuracy and detonation-timing
    requirements than other methods; for another, it does not rely upon
    suboptimal action by the enemy ship's crew (such as failure to stop the
    shaft immediately).

    To emphasize, I was *not* asserting your examples were incredible or
    fantastic in any way. They simply didn't address the point: firing
    torpedos with the intention of poking holes in the hull of a battleship
    and thus sinking it is inefficient and wildly optimistic. Building a
    sudden portable hole underneath it is efficient and effective with
    reasonable probability.

    Side note: "water rushing in" isn't what does the damage in the
    backbreaker scenario. What does the damage is the ship actually falling
    into the hole, or more precisely the fact that when it lands, all the
    upward force is concentrated at the ends (due to the bowl-like shape of
    the concavity) while the downward force is more heavily concentrated
    closer to the middle.

    --
    Rob
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