Nelson & His World

Discussion on the life and times of Admiral Lord Nelson
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 Post subject: Skimming Cannonballs?
PostPosted: Fri Dec 05, 2014 7:46 pm 
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I've seen an article in the Daily Mail today which says that scientists have figured out the perfect way to skim a stone across water. And apparently, the 18th century navy used this as a tactic:

Quote:
Naval gunners as far back as the 18th century bounced cannonballs as a military tactic - removing the launch angle as a variable in sinking enemy ships. To get the best bounce on the surface of the water in this instance, Proffesor Truscott said the angle should be less than seven degrees


Which to me sounds like nonsense. Because given the height of a gun deck on a ship, the only way to get a seven degree angle would be to shoot at the enemy from miles away. By that time, any power from the shot would have been lost, and if the ball DID bounce, it would surely have lost so much power that it wouldn't do more than chip the paint of the enemy ship! Either that or, as one commenter pointed out, they'd have to fill the ship with water to get the guns down low enough. Plus, I've never read about this being used as a tactic.

I don't claim to be an expert on either physics or 18th century naval warfare however, so can anyone shed any light on where the DM have got this idea from?

Here's the article in full: http://www.dailymail.co.uk/sciencetech/article-2862293/The-perfect-way-skim-stone-Throwing-angle-20-degrees-boosts-number-bounces-water-skipping.html

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 Post subject: Re: Skimming Cannonballs?
PostPosted: Fri Dec 05, 2014 11:21 pm 
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Vicki:

I recall an exchange on this subject on our 'mother ship' 'About Nelson'. I tried to copy it here, but I had to tidy it up a bit as all sorts of extraneous things appeared. I've numbered the posts for ease (I hope) of understanding!

I hope I haven't abused copyright.

1.
I recently watched once again the British war film "The Dambusters", made in 1954, which tells the story of Professor Barnes Wallis and his development of the famous bouncing bombs which were used to good effect in 1942 against the greats dams of the Ruhr Valley.

It was intriguing to note something I had not really taken on board previously. Barnes Wallis credits his "invention" to Admiral Nelson who, he claims, began "bouncing" cannon balls during sea battles in order to achieve greater effect against the enemy.

In all the reading I have done about Lord Nelson and his tactics, I cannot recall this brilliant idea having been mentioned and I am intrigued. Is it hearsay, folklore, imagination or - incredible as it may sound - true? Is there any evidence for this?

I have great confidence that an answer will be forthcoming.

2.

Quote:
Recalling the way Admiral Lord Nelson skipped cannon shells across water, Wallis wondered if perhaps he could deliver a bomb by skipping it across the reservoir and into the face of a Nazi dam.


Nelson certainly never 'skipped cannon shells' across water. Explosive shells of that period were fired in high arcs from special mortar vessels.

Ordinary solid round shot, however, would skip if fired on a low trajectory, with the right wave conditions. But this was known to sailors ( and land artillery officers) long before Nelson's time. I cannot think of any reason to credit Nelson for either its 'discovery' or use.

3.

As a footnote to this thread, I was able to contact an expert on Barnes Wallis and his theories, and I asked him whether he was aware of anything in Wallis' papers in this connection. This is his reply:

There is a bit in the film, when Wallis and the Ministry men are returning from the drop site, where a successful drop has finally taken place, and one of the men asks Wallis where he got the idea from. He very modestly says that he got the idea from Nelson.

For a while, I wondered if he either thought the idea up himself (maybe with only subconscious help from history) and found out about the Nelson connection later, or maybe even the film had added this in for a bit of colour. However, I have since seen in the archives Wallis' very earliest written paper on the bouncing bomb, and although Nelson is not mentioned, it does mention that "ricochet gunfire was known as early as the 16th century and was used in naval gunnery in the 17th and 18th century to extend the effective range ..."

So the effect was known, and it may have been through knowledge of Nelson using it (though he didn't invent it) that it came to Wallis' attention. Or Nelson may not have used it at all, and it use of the effect in some other naval engagement that brought it to his attention.

Cannons usually being mounted quite low, it would have been relatively easy to get the effect to work, though I presume it was found out accidentally the first time!

I hope this is useful.

So, a bit of colour added to the film, then!


For anyone wanting to know more about bouncing cannon balls should read:

Gen. Sir Howard Douglas, A Treatise on Naval Gunnery 1855, (London, 1855). pp.645, (soft back with pictures of the great guns).

A reprint can be purchased from http://www.naval-military-press.com

The book goes back to the Napoleonic period, describing all aspects of gunnery. It describes ricochet practice firing in some detail.
Not a book for the casual reader, it is very in depth.

4.

As an aircraft engineer who spent some time many years ago trying to make anti-ship missiles do as they are told, I was interested to read this discussion on bouncing balls. The fact that spherical objects can skip like the "duck stones" of our childhood was indeed known by RN cannoneers, but the relatively poor roll stability of the gun-deck made predictable results almost impossible to achieve. I don't think that Barnes Wallis actually attributed the idea to Nelson, but it was probably permissible in the circumstances.

For those who like to play at being a Nelsonian gunner there is an amusing interactive display in the Trafalgar museum at Portsmouth. It is important that the projectile leaves the muzzle at the right point in the ship's roll. If you fire after the top of the roll (i.e. on the way down) then you will fall short. Firing at the the right point on the way up maximises range. To achieve bounce requires a pretty flat trajectory (as the interactive Dam Buster simulation in the link to the initial question illustrates) and a good forward velocity.

When you think about it, during an engagement the ship was manoevering constantly, and a broadside could itself modify the roll characteristic, so they did pretty well to hit at all at max range. The RN's big advantage was the ability to sustain a rapid rate of fire, which enhances the gunner's chances of applying range correction, and this was directly attributable to Nelson, who made sure his gun crews practised at every opportunity. Victory's gunners could fire a 37 pounder at a rate of 60 to 90 seconds per round. I did a basic RA gunnery
course at Larkhill and we had trouble beating that with a 25 pound howitzer!

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 Post subject: Re: Skimming Cannonballs?
PostPosted: Sat Dec 06, 2014 3:25 pm 
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Thank you so much for digging that out, Anna :)

So really, it was a thing that could happen, and was known about, but wasn't actually a 'tactic', as such. As far as my own knowledge on Nelson's tactics goes, he was always one for going as close to the enemy as possible, far from 'extending the effective range' of a shot.

Also I've just realised the quote contradicts itself anyway... First saying that skimming cannonballs would "remove the launch angle as a variable in sinking enemy ships", but then saying it would require a 7 degree angle. So actually, if you were aiming for that to be a tactic, the launch angle would be absolutely crucial?

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 Post subject: Re: Skimming Cannonballs?
PostPosted: Wed Dec 10, 2014 10:45 am 
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I think the truth of the matter has now shone through! Whatever physics says, the time honoured battle tactic of the Nelsonian Navy was to get as close to the enemy line as possible, resist the temptation to fire prematurely, and then deliver a devastating broadside which destroyed the fighting capacity of the enemy. You don't do this by playing ducks and drakes at a distance.
Of course there must have been instances where this tactic could not be applied. Ships at the front of an advancing line could afford to follow it, but those at the end (whose arrival at the decisive point would obviously be delayed) would be sorely tempted to throw a few shots at the enemy as soon as they came within theoretical range - even though the inaccuracy of long range fire meant that they were liable to hit their own side.
Likewise the enemy might not be so obliging as to wait. A frigate (or a line of battle ship for that matter) chasing a fleeing enemy might well gamble on using the bouncing technique to lengthen their effective range. The most scientific exponent os 'scientific' gunnery was of course Captain Philip Broke of the 'Shannon'. Does anyone know if his writings/standing orders contained reference to the use of this technique?
Brian


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