Slitherine

quote:

ORIGINAL: wdolson

I know someone who was a sailor on a Gearing class DD in Vietnam. He claims he saw the CVN Enterprise do 70 knots once, but those who know more about hydrodynamics and ship design say that's impossible. I would probably lean towards the impossible, however there have been many times "impossible" things have been done. Somewhere in the 40 knot range might be possible though.

The sailor on the DD said the carrier was putting up a rooster tail as high as the flight deck before it disappeared over the horizon.

Bill

quote:

ORIGINAL: witpqs

quote:

ORIGINAL: wdolson

I know someone who was a sailor on a Gearing class DD in Vietnam. He claims he saw the CVN Enterprise do 70 knots once, but those who know more about hydrodynamics and ship design say that's impossible. I would probably lean towards the impossible, however there have been many times "impossible" things have been done. Somewhere in the 40 knot range might be possible though.

The sailor on the DD said the carrier was putting up a rooster tail as high as the flight deck before it disappeared over the horizon.

Bill

I've read that the USN is quite happy to let the rumors fly about the top speed of the CVNs, but that in reality they are almost certainly nothing like 40 knots. The notion being that if someone is going to be shooting torpedoes at you, why help them know how close they really need to get.

quote:

ORIGINAL: wdolson

I know someone who was a sailor on a Gearing class DD in Vietnam. He claims he saw the CVN Enterprise do 70 knots once, but those who know more about hydrodynamics and ship design say that's impossible. I would probably lean towards the impossible, however there have been many times "impossible" things have been done. Somewhere in the 40 knot range might be possible though.

The sailor on the DD said the carrier was putting up a rooster tail as high as the flight deck before it disappeared over the horizon.

Bill

quote:

ORIGINAL: crsutton

In the 1970s I sailed on a merchant ship that "cruised" at 28 knots. Name another conventional ship with a cruising speed that fast. I can't think of a single one. So fast that on the New York to Bremerhaven and back run we would on sometimes set the clock back (or ahead) two hours in a single night. A normal merchant burned about 30 barrels of fuel an hour. This ship burned 300 barrels. The ship was called a SL-7 and if I recall around eight were built.

They were sold to the Navy and totally rebuilt as rapid deployment support ships.

http://www.msc.navy.mil/factsheet/fss.htm

quote:

ORIGINAL: jcjordan

Isn't there currently a class of Russian subs capable of 40+kts?

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I would probably lean towards the impossible, however there have been many times "impossible" things have been done.

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I never tried to keep a DD at sea long enough to accumulate enough SYS damage to loose 5 knots top. Any idea?

quote:

ORIGINAL: janh

Both hulls, however, have significantly smaller drafts than those of a CVN, so their Cw value will be sizably lower. Assuming it is accurate that Enterprise has four steam turbines with an maximum output of 210 MW total, this power is probably fully covered by the reactors, and transferred with similar efficiacy as QM to the propellers, the question comes down how much the friction goes up with the much deeper draft and larger displacement? The beam is about the same as QM, 41m, the length along waterline also about the same ~317m, but the draft 20% deeper at 12m. There are some approximations for areas of typical hull shapes, some very simple like A = const * sqrt(V * L), but for a really simple estimate both hulls can be treated as the same. So with only a change of the draft, which enters A over the length and width, A is larger by less than 1.2, more like 1.1.
With P(QM) = 88 MW ~= A(QM) * v_max(QM)^3 and v_max(QM) = 30 knots, this gives: P(E) = 210 MW = 2.4 * P(QM) = 1.2 * A(QM) * v_max(E)^3
Putting both together: v_max(E) = (2.4/1.2)^(1/3) * v_max(QM) = 38 knots. Surely someone can do it more accurately, but it sounds reasonable so far. Since there is two other resistance components that grow very fast and important at speeds beyond 20 knots, this is probably an overestimate. Maybe Big E has a slightly better efficiacy, or advantages in hull shape, coating paints or other factors, but that is likely to be more than eaten up by the inreasing additional friction terms at speeds above 30 knots. If the hull area were only larger by "only" 1.1, it would be 39 knots, and 37 for 1.3. If the efficiacy lower or higher, say 180 MW or 250 MW effective output, it would be slightly below 37 or 41 knots. So going over 40 knots, even ignoring additional friciton, might take almost 20% power, that's quite a bit. I guess I will settle with a maximum speed of 38 then.

quote:

ORIGINAL: MineSweeper

Was the Soryu the fastest capital ship ever built?

Nearly made 35 knots on trials in November 1937....CVN Enterprise could only manage 33.7 knots.
The Iowa's could possibly do 35.4 at max power and light weight but it was never attempted.
Pic from Soryu's trials.

quote:

ORIGINAL: tocaff

A friend of mine who served on nuke attack subs was with a CVBG in the Med. I don't remember the time frame, but he said that the sub dove and took off as did the CV. I don't remember the class of the CV, but if memory serves the sub was a Sturgeon class boat. The carrier left all the ships in the dust, so to speak.

quote:

ORIGINAL: janh

Already near 34 knots is quite impressive. Something close to or in the low 40s I would still believe. Someone with a good knowledge of hydrodynamics could probably estimate it based on the power transfer of the propellers or power output of the engines/turbines, if that is known, and the hull shape and displacement of the object. I mean to have read about a civilian liner in the 50k BRT range, maybe one of these new modern Caribbean ships, which was said to make short sprints 40+ knots on steam boilers. So it probably is reasonable also for a CVN as well?

Out of pure curiosity, I'll give it a quick try. It's grown lengthier than I thought at the beginning, though. And not quite quick. QM, for example, is given with a top speed of ~30 knots using ~4x22 MW power, QE II with 34 knots on 2x44MW, the difference being due to the hulls, bows, propellers/engines specifics . I suspect it is mainly the 30% larger beam of QM that cost her those 4 knots since the propulsion details are probably less critical as long as the power transferred is effectively the same.
The beam enters one of the three friction parameters that can be used to estimate the ships "Cw" friction value, and that is proportional to the power requirement P to reach a given speed (ignoring a tiny few other factors...). More exactly what enters is the wetted area of the hull, but for simple forms that's still approximately right. Another thing to keep in mind, and every biker or speed-skater would know this too well, is that the friction Cw typically also goes up non-linearly with the speed v since one usually is in turbulent conditions, so it rises more like v^2 (so Cw ~ A * v^2, where a depends largely on the object yet also the medium it is in). So 1 knot more at 30 will require much much less power than 1 more at 35.
With P = Cw * v ~= A * v^3 where A(QM) = 1.3 A(QE) you actually get quite close to the relative P requirements for 30 and 34 knots. So that works roughly. Quite surprising, though, as frictional resistance is augmented by other contributions that become equally important at high speeds.

Both hulls, however, have significantly smaller drafts than those of a CVN, so their Cw value will be sizably lower. Assuming it is accurate that Enterprise has four steam turbines with an maximum output of 210 MW total, this power is probably fully covered by the reactors, and transferred with similar efficiacy as QM to the propellers, the question comes down how much the friction goes up with the much deeper draft and larger displacement? The beam is about the same as QM, 41m, the length along waterline also about the same ~317m, but the draft 20% deeper at 12m. There are some approximations for areas of typical hull shapes, some very simple like A = const * sqrt(V * L), but for a really simple estimate both hulls can be treated as the same. So with only a change of the draft, which enters A over the length and width, A is larger by less than 1.2, more like 1.1.
With P(QM) = 88 MW ~= A(QM) * v_max(QM)^3 and v_max(QM) = 30 knots, this gives: P(E) = 210 MW = 2.4 * P(QM) = 1.2 * A(QM) * v_max(E)^3
Putting both together: v_max(E) = (2.4/1.2)^(1/3) * v_max(QM) = 38 knots. Surely someone can do it more accurately, but it sounds reasonable so far. Since there is two other resistance components that grow very fast and important at speeds beyond 20 knots, this is probably an overestimate. Maybe Big E has a slightly better efficiacy, or advantages in hull shape, coating paints or other factors, but that is likely to be more than eaten up by the inreasing additional friction terms at speeds above 30 knots. If the hull area were only larger by "only" 1.1, it would be 39 knots, and 37 for 1.3. If the efficiacy lower or higher, say 180 MW or 250 MW effective output, it would be slightly below 37 or 41 knots. So going over 40 knots, even ignoring additional friciton, might take almost 20% power, that's quite a bit. I guess I will settle with a maximum speed of 38 then.

BTW: Searching for some info on this, I found this "old" (1952) but very interesting publication from the US Naval Institute. https://darchive.mblwhoilibrary.org/bitstream/handle/1912/191/chapter%202.pdf?sequence=9
Check out how sizable the speed loss/increase of propulsion/shaft power need is depending on sea time since the last dock visit. Even after "only" 300 days, a DD would typically loose 5 knots on its top speed, and the capital ship Tennessee also some 20% after 12 months. Quite large these problems. Probably a reason why they spent so much time in yards. I never tried to keep a DD at sea long enough to accumulate enough SYS damage to loose 5 knots top. Any idea?

quote:

ORIGINAL: wdolson

I know someone who was a sailor on a Gearing class DD in Vietnam. He claims he saw the CVN Enterprise do 70 knots once, but those who know more about hydrodynamics and ship design say that's impossible. I would probably lean towards the impossible, however there have been many times "impossible" things have been done. Somewhere in the 40 knot range might be possible though.

The sailor on the DD said the carrier was putting up a rooster tail as high as the flight deck before it disappeared over the horizon.

Bill

Mike

"Good times will set you free" - Jimmy Buffett

"They need more rum punch" - Me


Artwork by The Amazing Dixie

quote:

ORIGINAL: LoBaron

quote:

ORIGINAL: jcjordan

Isn't there currently a class of Russian subs capable of 40+kts?

Alfa class, but the could not do much else than run. Was built in the 70´s IIRC.

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ORIGINAL: JSG

quote:

ORIGINAL: LoBaron

quote:

ORIGINAL: jcjordan

Isn't there currently a class of Russian subs capable of 40+kts?

Alfa class, but the could not do much else than run. Was built in the 70´s IIRC.

Actually, they were also known for diving real deep.

They were too expensive, had teething problems, were too loud and hadn't the electronics to match the Los Angeles Class later, though.

quote:

ORIGINAL: mike scholl 1

quote:

ORIGINAL: MineSweeper

Was the Soryu the fastest capital ship ever built?

Nearly made 35 knots on trials in November 1937....CVN Enterprise could only manage 33.7 knots.
The Iowa's could possibly do 35.4 at max power and light weight but it was never attempted.
Pic from Soryu's trials.

You really need to know under what conditions/specs the "trials" were run. A lot of ships built before WW II racked up impressive trials speeds (the Italians were notorious for it), but then proved totally incapable of reaching them under wr service conditions.

quote:

ORIGINAL: Apollo11

Hi all,




Leo "Apollo11"

Check out my AAR - Avoiding the Turkeyshoot! (Marianas Scenario, as Japan):
http://www.matrixgames.com/forums/tm.asp?m=3867657