Any mathematicians here?

[Weatherlawyer]

I need someone to explain the relative speeds of ships as determined from their wakes. I have read something about it but need pictures to help me get my head around it.

Thanks in advance.

[Jonathan]

On 12/27/2015 3:00 AM, Weatherlawyer wrote:
> I need someone to explain the relative speeds of ships as determined from their wakes. I have read something about it but need pictures to help me get my head around it.
>
> Thanks in advance.
>

I found this conversation about hull speed
relative to the wakes created by the bow
and stern, see the video at the bottom
showing this effect.



It is my recollection that this hull-speed limitation is
determined by the wavelength of the bow wave - that the distance
between crests of the wave increases with boat speed until there is
a crest at the bow and another at the stern, and the center of the
boat is essentially unsupported. It would thus sink lower in the
water relative to the wave height at bow and stern.


My understanding is that hull speed, assuming monohulls, is a
factor of the relative situation of bow and stern waves along
the hull length at various boat speeds. As the hull moves
forward both a bow and stern wave is created. As the hull
moves progressively faster the stern wave can be seen
cresting farther and farther aft -- all the while the bow
wave remains where you would expect it, at the bow/stem. At
hull speed, the aft wave is cresting at or near the furthest
aft inwater section of the hull, typically near the transom.

"The kicker here is that at hull speed the bow and stern wave
create something like a trough, along the length of the hull,
moving along with the hull in which the hull is, in effect,
trapped. The amount of power, or thrust as you put it
required to blow the hull out of the envelope is enormous
relative to the power required to get the boat to hull speed
(assuming a non-planing hull) so that locked-in condition is
known as hull speed. The longer the hull's waterline, the
higher the theoretical hull speed - this is why you often see
strange looking hull extensions on IOR type boats - typically
transom extensions at the water line."

The formula you gave, stating that hull speed is proportional to
the square root of the waterline length, will follow from the
criterion above if the wavelength is proportional to the square of
the boat speed. Since the bow wave moves along with the bow of the
boat, the wave speed is the same as the boat speed. Is the
wavelength of a water wave proportional to the square of the wave's
velocity? I'm not an expert in water waves, but I located a Web
page that says,

"The speed of a deep water wave is dependent on the
wavelength and/or period. C = gT/2pi or C^2 = gL/2pi.
The greater the period or wavelength, the faster the
wave speed."

Thus the wavelength L is proportional to the square of the speed.
The speed at which the wavelength matches the waterline length LWL
is proportional to the square root of the waterline length. In
fact, using the acceleration of gravity g = 32 feet/sec^2, I can
work out the constant:

1 naut. mile 3600 sec
C = sqrt(32/6.28 ft/sec^2) * sqrt(L ft) * ------------ * --------
6076 feet 1 hour

= 1.337 * sqrt(L ft)

in knots (nautical miles/hour). How about that, it worked! Now all
I have to understand is why the period of a wave is proportional to
its velocity. (Since distance = speed * time, we have L = CT, so
the formula for wavelength follows.)

- Doctor Rick, The Math Forum
http://mathforum.org/dr.math/

http://mathforum.org/library/drmath/view/53491.html



Hull Speed tank run of an AOE 6
video
https://www.youtube.com/watch?v=3lffCqqluYI


s

[Weatherlawyer]

On Sunday, 27 December 2015 08:41:43 UTC, Jonathan wrote:
> On 12/27/2015 3:00 AM, Weatherlawyer wrote:
> > I need someone to explain the relative speeds of ships as determined from their wakes. I have read something about it but need pictures to help me get my head around it.
> >
> > Thanks in advance.
> >
>
>
>
> I found this conversation about hull speed
> relative to the wakes created by the bow
> and stern, see the video at the bottom
> showing this effect.
>
>
>
> It is my recollection that this hull-speed limitation is
> determined by the wavelength of the bow wave - that the distance
> between crests of the wave increases with boat speed until there is
> a crest at the bow and another at the stern, and the center of the
> boat is essentially unsupported. It would thus sink lower in the
> water relative to the wave height at bow and stern.

I believe that idea would give you a polarity where the prow is pushing the water over the surface and the stern is dredging water from below so that the hull overall is balancing the average. Wouldn't this lead to the link to wavelength?

Benjamin Franklin made the first scientific discussion on the subject but failed to pursue it. More research was done on this coming up with the inverse square ratioin the 19th Century. It was in WW2 that Britains Photographic unit came up with the modern military use, propounded to the block-heads at the Admiralty by the USA, just in time to save us from the British upper classes.

> My understanding is that hull speed, assuming monohulls, is a
> factor of the relative situation of bow and stern waves along
> the hull length at various boat speeds. As the hull moves
> forward both a bow and stern wave is created. As the hull
> moves progressively faster the stern wave can be seen
> cresting farther and farther aft -- all the while the bow
> wave remains where you would expect it, at the bow/stem. At
> hull speed, the aft wave is cresting at or near the furthest
> aft inwater section of the hull, typically near the transom.

As the Bow wave is bearing down the relative height isn't going to change much whereas the relative depth it affects will but won't be visible as a soliton.

> "The kicker here is that at hull speed the bow and stern wave
> create something like a trough, along the length of the hull,
> moving along with the hull in which the hull is, in effect,
> trapped.

It is this trough that changes with wavelength that becomes the spectrum observed militarily.

>T he amount of power, or thrust as you put it required to blow the hull out

> of the envelope is enormous relative to the power required to get the boat

> to hull speed.

That would be the logarithm of the fuel consumption I imagine.

> Assuming a non-planing hull, that locked-in condition is known as hull speed.
> The longer waterline, the higher the theoretical hull speed - this is why

> you often see strange looking hull extensions on IOR type boats - typically
> transom extensions at the water line."

Apparently one solution in prehistoric time was to adze pits in the hull. Economically viable on river boats.

> The formula you gave, stating that hull speed is proportional to
> the square root of the waterline length, will follow from the
> criterion above if the wavelength is proportional to the square of
> the boat speed.

Not me I assure you I am not smart enough, all I did was add some logic to make it look like I can keep up with you.

I cribbed from "Spies in the sky" by Taylor Downing. 2011.
Abacus: ISBN 978-0-349-12340-0
A Section: Shipping pages 112 to 116 of chapter 6.

"At whatever speed it travels, a ship's wake has precisely the same angle. Using research from Reading University's archives Westwood was able to work out the spacing of the waves within the pattern created in a ship's wake would increase in the ratio of the square of any increase in speed.
From aerial photography it was possible to calculate its speed by taking the square root of spacing of the waves."

That would be their wavelength wouldn't it?
I still can't quite grasp it though.

> Since the bow wave moves along with the bow of the
> boat, the wave speed is the same as the boat speed.

Yes but that wouldn't give you the rate of knots.

> Is the wavelength of a water wave proportional to the square of the wave's
> velocity? I'm not an expert in water waves, but I located a Web

> page that says:,

>
> "The speed of a deep water wave is dependent on the
> wavelength and/or period. C = gT/2pi or C^2 = gL/2pi.
> The greater the period or wavelength, the faster the
> wave speed."

The impression I get is that the speed of the bow or stern wave would be the same as the vessel but you can't tell the speed of the bow wave by the height (Maybe by the length of the trail or that would be related to its displacement too?)

> Thus the wavelength L is proportional to the square of the speed.
>
> The speed at which the wavelength matches the waterline length LWL
> is proportional to the square root of the waterline length. In
> fact, using the acceleration of gravity g = 32 feet/sec^2, I can
> work out the constant:
>
> 1 naut. mile 3600 sec
> C = sqrt(32/6.28 ft/sec^2) * sqrt(L ft) * ------------ * --------
> 6076 feet 1 hour
>
> = 1.337 * sqrt(L ft)
>
> in knots (nautical miles/hour). How about that, it worked! Now all
> I have to understand is why the period of a wave is proportional to
> its velocity. (Since distance = speed * time, we have L = CT, so
> the formula for wavelength follows.)

I can't follow your maths I am afraid but I found something that might help someone understand diurnal tides. Too off the wall and off topic for this thread I will put it on a thread in my blog later.

> - Doctor Rick, The Math Forum
> http://mathforum.org/dr.math/

I have got a problem with the frequencies of earthquakes you might be interested in. Long file though.

What it is: Taking 5.5 M. as an arbitrary datum (because it fit) there is a lull in the USGS lists of 5.5 or larger quakes of several hour prior to the inception of a tropical storm. The time lapse increases according to the energy of the storm. starting at above gale strength some time around 15 hours between earthquake of 5.5 or larger the time increases logarithmically every three hours to 1 step in Beaufort scale.

Far fetched I know but after a time lapse of several days the conception goes backwards as the gestation period increases and the energy level concerned, rises.

> http://mathforum.org/library/drmath/view/53491.html

Is this the link?

> Hull Speed tank run of an AOE 6
> video
> https://www.youtube.com/watch?v=3lffCqqluYI

Ah!
Thanks.
Have one of mine:
http://earthquake.usgs.gov/earthquakes/search/

[Jonathan]

On 12/27/2015 6:47 AM, Weatherlawyer wrote:
> On Sunday, 27 December 2015 08:41:43 UTC, Jonathan wrote:
>> On 12/27/2015 3:00 AM, Weatherlawyer wrote:
>>> I need someone to explain the relative speeds of ships as determined from their wakes. I have read something about it but need pictures to help me get my head around it.
>>>
>>> Thanks in advance.
>>>
>>
>>
>>
>> I found this conversation about hull speed
>> relative to the wakes created by the bow
>> and stern, see the video at the bottom
>> showing this effect.
>>
>>
>>
>> It is my recollection that this hull-speed limitation is
>> determined by the wavelength of the bow wave - that the distance
>> between crests of the wave increases with boat speed until there is
>> a crest at the bow and another at the stern, and the center of the
>> boat is essentially unsupported. It would thus sink lower in the
>> water relative to the wave height at bow and stern.
>
> I believe that idea would give you a polarity where the prow is pushing the water over the surface and the stern is dredging water from below so that the hull overall is balancing the average. Wouldn't this lead to the link to wavelength?
>
> Benjamin Franklin made the first scientific discussion on the subject but failed to pursue it. More research was done on this coming up with the inverse square ratioin the 19th Century. It was in WW2 that Britains Photographic unit came up with the modern military use, propounded to the block-heads at the Admiralty by the USA, just in time to save us from the British upper classes.
>

I think you're asking if a wake can be used to determine the
speed of the ship, but from what I've read only it's position
and direction can be determined from the wake, as the wake
travels at the same speed and generates the same angle
regardless of the speed of the ship. Provided it's not
exceeding the hull speed or is planing.

Just as the speed of sound is constant for a given
altitude and density.

Wake
https://en.wikipedia.org/wiki/Wake


This site is interesting, it has a wave wake predictor.
Apparently certain patterns in the wake can show the
speed, but it starts getting pretty complicated to
go that route.

Feed in all the data of the ship and it spits out wake
height etc.
https://www.amc.edu.au/maritime-engineering/wave-wake-predictor



But I guess wake height might change with speed.
This pdf probably has more than you could ever
want to know about that...more than I want to
know that's for sure!

Predicting Boat-Generated Wave Heights: A Quantitative
Analysis through Video Observations of Vessel Wakes
http://www.dtic.mil/dtic/tr/fulltext/u2/a571742.pdf



s

[Weatherlawyer]

No That bod from the backroom in WW2 realised that you can measure the velocity from wave patterns think doppler radar:

"The physicists tested their idea with satellite images of boats and ships from the website Google Earth, measuring the wake angle and length of the boat from the pictures and inferring the boat's speed from details of the wake. Sure enough, the wake angle remained constant up to a certain speed--actually a certain "Froude number," which is a combination of boat's speed and length--and then falls as predicted, the researchers report in a paper in press at Physical Review Letters. Simulations show the same effect."

I think the journalist also missed the point as did the British Admiraltyway back when it counted:
http://news.sciencemag.org/2013/05/lord-kelvin-wipes-out-speed-boat-wakes

If you look at the patterns the speedboat can break the barrier because it is not a conventional hull they tend to have stepped hulls. (As is the prehistoric row-boat found in the Thames a few decades back.)

We'll have to get which angle is being discussed sorted out before we can look at moiré patterning but I think it is the intricate fractalisation that does the job.

Beach-masters in ancient cultures use it to navigate. They take their shoes off and stand on the main timber in the hull and read the wave currents to find out how to get ashore. Indonesia I think (Not sure.)

That stuff about Beaufort Scales was Froud Numbers; I always forget them. It was in that link, thanks.

Just going out for a couple of hours. I am feeling like a volcano is going off.

[george152]

Overcomplicated
If you can see the bow wave and the wake then you can see the ship.
Much easier to track and determine speed.
Even with the old Predictors

[Weatherlawyer]

The initial idea was based on the early era of photographic operations. The RAF took over Medmenham House and set up something similar to the Bletchley Park outfit.
A genius working on stills from the previous hours worked out what would tell him the speeds of new boats which of course were in enemy occupied territory.
Somehow he found out that a lifetime earlier Lord Kelvin worked out from the wake patterns etc., etc..
The Admiralty didn't want to know then the Japanese told the Americans to wake the fuck up.
So they did.

Do you think that you can tell me from a wake pattern in a B&W still what the latest engines in the latests German Destroyers were capable of?
How?

Initially being a Phot Ops crewman was a 100% death sentence for British and French aircrew. Syd Cotton took over on behalf of the Admiralty until the bloke who ran off with Auchinkleck's wife sacked him.
When I first got interested in Geo-Physics there was a TV series called Open University, one of the first free to air colleges.
I was fascinated by the physics stuff -not good at it but interested.
One programme was dealing with cosmic waves and the presenter had come up with an idea that fitted analogue systems together more efficiently than the digital stuff that was just taking over in those days.

He posed an answer that fit the sheer number of observed frequencies through plasma clouds to absorption in the ice and sea. It was something of a moire effect. I don't recall much of it these decades later. I wonder if it can go on to explain standing waves that have so much effect on earth's systems when they reach landfall.

We knew so little about the atmosphere in the days NASA was still setting its satellites to reject data about Glowballs. Now, of course, serious scientific research can only exist in a climate of US xenophobia that is poetically Simpsonesque:
https://www.youtube.com/watch?v=ybcBhg8rw6w

I wonder how much further we could push meteorology if it was being run by the Russians rather than the Americans. I can't really say much about stuff like that since we managed to draw a world war despite all the English traitors running it.

[Weatherlawyer]

Sorry if I frightened you big, strong boys off, ladies:
http://weatherlawyer.altervista.org/moire-moire-curious/

[Dr. Vincent Quin, Ph.D.]

Fred J. McCall wrote:

> So if I send you a still picture you can tell me how fast the ship is
> going?

yeah...0 kph.

...ha ha ha...get it fwed?...a "still" photo...ha ha ha...
;-)

[Weatherlawyer]

That is extremely funny and true. It show the depth of your ability to entertain you.
Someone just tells you the most amazing things you ever heard and that is it?
It is what I'd say too, so you are at least in excellent company.
What does fwed mean?

[Kerryn Offord]

On 12/28/2015 12:55 AM, Fred J. McCall wrote:
> george152 <gbl...@hnpl.net> wrote:
>
>>

> So if I send you a still picture you can tell me how fast the ship is
> going?
>
>

https://en.wikipedia.org/wiki/Wake

Suggests that if you have information on the ship (length and beam at
least).. then maybe you can estimate the speed it is going.. (other
information, such as location and direction may also help)

Looking at the image at the top of that page, one wonders if the speed
of the vessel has anything to do with the rate and separation of the
wake lines

[Weatherlawyer]

It seems to be a dichotomy between what was a military secret until we told the Americans and the British can be funny about stuff like that and stuff the French have been looking at recently.

It is a pity I put Jonathan off with my beliefs but it couldn't be helped. When you are swimming out at sea and you notice straw for the first time in years you go and take a look.

My problem now is that everything I read on the subject is woolly journalism because I have no access to scientific papers, not that I would understand higher mathematics if I tried.

I gather that:

1. The shape of the wake is independent of the shape of the boat but depends entirely on the length of the object, be it ship, boat, canoe, sunken log or promontory, cape, island or continent and the viscidity of the liquid involved (the Froude Number.)

2. In a near perfect liquid the fluid progresses outwards indefinitely at an angle of 81-2 degrees (or so) for water) varying with its physical and chemical properties.)

3. Chains of waves interact with each other passing over and under one another without interfering with each other except to produce temporarily higher and lower waves as they pass through one another and produce moire' effect.

4. It was this moire' pattern that the first adepts were using, despite the ignorance of the figureheads barring the full use that wartime conditions might have looked at more closely had the selection process of fools not been laden with politics.

5. My beliefs about the ability of humans to resolve what amounts to pretty simple earth science problems has put scientists off the idea that one can readily forecast line-storms and earthquakes from the idea. But why would one expect scientists to behave differently from civil servants generally?

6. I may be wrong but what else is new?
Besides what else do you expect from world leaders?

Speaking about dichotomies; a paradigm occurs to me about General Groves and the cadre of experts he was in charge of, at that time. He was an engineer working in a different field; as well as in charge of military secrets. It was his job to provide the logistics for and keep the secret about atom bomb inventions and manufacture.

He had just been censured about the money he had spent on the pentagon by making it a war cabinet that could stand up to a 400 ton guided missile (without appreciating the destructive capacity of or/the future missiles that would be used on it.)

Of all the experts involved in the project, he was by far the finest. He was the real "father of the bomb". Although stories of his pettiness abound, he never flinched from according all the money required as and when. The Oakridge laboratory for eexample was designed and built fully furbished, to make atom bombs with redundant processes some of which were never used built in according to need.

In fact the production cost a mint quite literally.

Compare the British version of events: Lackadaisical idiocies ensured that we would go to world war two unarmed because of the way the Spitfire was developed and then ensured we would lose it (and the Empire) by appointing a war criminal to oversee it.

The only difference between Groves and Churchill was that whilst both men were fat and liked a drink, Groves made sure he found experts while Churchill seemed to go out of his way to appoint treacherous imbeciles.

The scripture about god causing his opposer's eyeballs to rot in their sockets comes to mind but I am too busy at the moment to look it up. help yourself:

https://duckduckgo.com/?q=Bible+eyballs+to+rot+in+sockets+&t=ffsb