Design "feature" of R-class

General naval discussions that don't fit within any specific time period or cover several issues.
Byron Angel
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Re: Design "feature" of R-class

Post by Byron Angel »

Just a thought -
Installed power is one factor in determining maximum speed.
But waterline length is another component, in that it defines critical speed hump (the speed at which (hull) wave resistance begins to grow much more dramatically as speed is increased.

Critical Speed threshold (IIRC) as a rule of thumb = sq rt of waterline length -
for a 400 ft ship - 20 knots.
for a 625 ft ship - 25 knots.
for a 900 ft ship - 30 knots.

Driving a ship at speeds beyond its critical speed threshold requires a (relatively speaking) huge increases in power. The extent of this effect can usually be seen in speed versus required horsepower graphs.

Hope I have not just traversed ground already covered here.


Happy Saint Patrick's Day BTW to all our compatriots of Irish heritage.

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marcelo_malara
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Re: Design "feature" of R-class

Post by marcelo_malara »

Byron Angel wrote: Sat Mar 18, 2023 3:43 pm Just a thought -
Installed power is one factor in determining maximum speed.
But waterline length is another component, in that it defines critical speed hump (the speed at which (hull) wave resistance begins to grow much more dramatically as speed is increased.

Critical Speed threshold (IIRC) as a rule of thumb = sq rt of waterline length -
for a 400 ft ship - 20 knots.
for a 625 ft ship - 25 knots.
for a 900 ft ship - 30 knots.

Driving a ship at speeds beyond its critical speed threshold requires a (relatively speaking) huge increases in power. The extent of this effect can usually be seen in speed versus required horsepower graphs.

Hope I have not just traversed ground already covered here.


Happy Saint Patrick's Day BTW to all our compatriots of Irish heritage.

B
HI Byron. I disagree with those numbers. Critical hull speed occurs at a Froude number of 0.4. As the ship travels thru the water it generates a set waves, most important are the bow and stern waves. Wave length augments with the speed, so the bow wave length will be longer at higher speed, till the point that the trough of the bow wave occurs at the stern of the ship. The stern wave starts with a trough, produced by the low pressure area behind the ship. The combination of the trough of the bow and stern waves produces a deeper trough that the ship can not overcome.

As usual I have my excels :D. In this you have waterline length, m and ft, the travelling speed of w wave of that length, and the speeds corrsponding at Froude numbers of 0.3. 0.4 and 0.5. The critical hull speed for a length is the one found in the 0.4 column.



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marcelo_malara
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Re: Design "feature" of R-class

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wmh829386 wrote: Sat Mar 18, 2023 3:05 pm
Thanks, this makes more sense now! However, I think the actual speed from the QE is still quite disappointing. From actually trials, I think the best speed made for QE is barely above 24 kts.

The R-class though, they are just pretty dreadful in WW2 in overweight conditions... They are making 18/19 kts like the pre-dreadnaughts...
Well, sometimes in history you have to look where we come from more than where are we going. I mean, before QE the highest power installed in a RN BB was 29 000 hp for 21 kts, so powering a BB with 56 000 hp and achieving with it 23 kt sounds as a step forward. For sure then came Hood with her 144 000 hp, but that was future by then.
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Re: Design "feature" of R-class

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marcelo_malara wrote: Thu Mar 16, 2023 2:52 pm
Hi Paul. I have always wondered that the RN honored world´s most famous admiral with that....ship. Nelson class was a big compromise, the designers tried to accommodate 9 16" guns and good protection in just the 35000 t allowed by treaties, something needed to suffer and it was propulsion, with just 2000 t allowed to it. Higher power would have needed more machinery space and in turn that would mean more protection weight. Personally I think the Japanese did better with Nagato.
The irony is that a well designed improvement of QE will almost certainly serve RN better with a more balanced design. There are some fairly obvious improvement that can be made.

- Geared steam turbine
- Small tube boilers
- slightly lengthened with more allowed displacement
- rearrange deck armour by focusing on one thick armour deck
- Remove casemate armour
- Turret improvement as in Hood

A 27/28 kt design that is better protected than Nagato with 15" guns just seems to provide more utility. Of course, RN will certainly felt a lost of prestige by not going for 16" gun.

However, the triple 16"/45 gun turret is not a good design. Due to the three fixed shell-bogies in the working chamber, the three guns have to be loaded together, causing lower rate of fire and use of full salvos instead of the usual half-salvos. In practice, the output of Nelson is lower than Nagato and Colorado.
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marcelo_malara
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Re: Design "feature" of R-class

Post by marcelo_malara »

Byron Angel wrote: Sat Mar 18, 2023 3:43 pm
Critical Speed threshold (IIRC) as a rule of thumb = sq rt of waterline length -
I made some algebra, to know exactly what that rule of thumb formula calculates. And it is the Froude number 0.3 speed for a determined length. But bear in mind that FN 0.3 is actually a hollow in the speed/power curve, at which you can sail with little resistance. True that passed it resistance increases, but the hull limit of speed is actually much higher. For example a destroyer 400 ft/120 m long had a FN 0.3 speed of 20 kt, a FN 0.4 speed of 27 kt, but even that theoretically unpassable limit is trespassed by any destroyer that can be called that.
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Re: Design "feature" of R-class

Post by Byron Angel »

Hi Marcelo,
I think we are speaking, more or less, about the same thing, only your presentation is far more technical than my 'street corner" description.

Go here - https://www.vedantu.com/physics/froude-number

Byron
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Re: Design "feature" of R-class

Post by dunmunro »

wmh829386 wrote: Sat Mar 18, 2023 5:36 pm
marcelo_malara wrote: Thu Mar 16, 2023 2:52 pm
Hi Paul. I have always wondered that the RN honored world´s most famous admiral with that....ship. Nelson class was a big compromise, the designers tried to accommodate 9 16" guns and good protection in just the 35000 t allowed by treaties, something needed to suffer and it was propulsion, with just 2000 t allowed to it. Higher power would have needed more machinery space and in turn that would mean more protection weight. Personally I think the Japanese did better with Nagato.
The irony is that a well designed improvement of QE will almost certainly serve RN better with a more balanced design. There are some fairly obvious improvement that can be made.

- Geared steam turbine
- Small tube boilers
- slightly lengthened with more allowed displacement
- rearrange deck armour by focusing on one thick armour deck
- Remove casemate armour
- Turret improvement as in Hood

A 27/28 kt design that is better protected than Nagato with 15" guns just seems to provide more utility. Of course, RN will certainly felt a lost of prestige by not going for 16" gun.

However, the triple 16"/45 gun turret is not a good design. Due to the three fixed shell-bogies in the working chamber, the three guns have to be loaded together, causing lower rate of fire and use of full salvos instead of the usual half-salvos. In practice, the output of Nelson is lower than Nagato and Colorado.
Rodney and Nelson used 1/2 salvos during WW2. See:

http://www.kbismarck.com/rodney-gunnery-report.html
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marcelo_malara
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Re: Design "feature" of R-class

Post by marcelo_malara »

Byron Angel wrote: Sat Mar 18, 2023 8:32 pm Hi Marcelo,
I think we are speaking, more or less, about the same thing, only your presentation is far more technical than my 'street corner" description.

Go here - https://www.vedantu.com/physics/froude-number

Byron
To be fair I have to say that there me be a point in paying attention to FN 0.3. Look at this set of data of Hood speed trials. For a WL of 260 m, the correspondings FN are:

FN 0.3 @ 29.48 kt
FN 0.4 @ 39.31 kt

In the data the most important calculated value is the last one, it is the exponent with which varies the power between two consecutive speed values:

variation in speed = (speed2 / speed1

variation in power = (hp at speed02 / hp at speed1)

variation in speed ^ value in last column = variation in power

This is the value that as a rule of thumb in our amateur engineering we take as 3 (the power varies with the cube of the variation in speed). But actual data shows that the variation is actually with an exponent a little higher than 3. But interestingly coming close to the 29.48 kt of the FN 0.3, at 27.77 and 28.37 kt, the exponent rises to a value between 4 and 5, returning to lower values passed that speed.





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wmh829386
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Re: Design "feature" of R-class

Post by wmh829386 »

dunmunro wrote: Sat Mar 18, 2023 9:06 pm Rodney and Nelson used 1/2 salvos during WW2. See:

http://www.kbismarck.com/rodney-gunnery-report.html
Double salvos are not the usual half salvos...

Double salvos are fired with both groups of guns loaded. The two groups of guns are fired within a short interval and typically used for initial salvos with a small range or deflection difference between the two groups to create a ladder.

http://dreadnoughtproject.org/tfs/index ... ting_Rules

The practical impact is a bit nuance before straddling is established, but it will drag down the ROF as the control officer will wait for all guns to be loaded.
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Re: Design "feature" of R-class

Post by dunmunro »

wmh829386 wrote: Sun Mar 19, 2023 4:28 pm
dunmunro wrote: Sat Mar 18, 2023 9:06 pm Rodney and Nelson used 1/2 salvos during WW2. See:

http://www.kbismarck.com/rodney-gunnery-report.html
Double salvos are not the usual half salvos...

Double salvos are fired with both groups of guns loaded. The two groups of guns are fired within a short interval and typically used for initial salvos with a small range or deflection difference between the two groups to create a ladder.

http://dreadnoughtproject.org/tfs/index ... ting_Rules

The practical impact is a bit nuance before straddling is established, but it will drag down the ROF as the control officer will wait for all guns to be loaded.
PoW was firing double salvos as well - see her GAR. Double salvos are simply salvos fired so that both salvos are in the air simultaneously, with a minimal time interval between salvos, sufficient to prevent the salvos from being confused with one another.

You have a misunderstanding regarding the loading cycle of the 16in triple turret. The shell bogies feed shells upward to a shell scuttle which held 4 x 16in shells per gun. The individual guns could load from the scuttles at their own pace, depending on the salvo cycle, completely independent from the other guns in that turret. It was only when the RoF exceeded the ability of the shell bogies to replenish the shell scuttles that the RoF would slow.

During normal salvo fire, this arrangement provided for the same RoF as the 14in and 15in turrets but during periods of rapid salvo fire, or during the prolonged use of broadside fire the RoF would fall. However, in rough sea conditions, where extra time was needed for Fire Control, there was extra time for loading anyways.
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Re: Design "feature" of R-class

Post by wmh829386 »

dunmunro wrote: Sun Mar 19, 2023 6:40 pm
You have a misunderstanding regarding the loading cycle of the 16in triple turret. The shell bogies feed shells upward to a shell scuttle which held 4 x 16in shells per gun. The individual guns could load from the scuttles at their own pace, depending on the salvo cycle, completely independent from the other guns in that turret. It was only when the RoF exceeded the ability of the shell bogies to replenish the shell scuttles that the RoF would slow.
Thanks, I didn't realise there are 4 shells per gun waiting in the lower hoist. And that's pretty interesting. It's also fun checking the following site.
http://www.navweaps.com/index_tech/tech-059.php

During normal salvo fire, this arrangement provided for the same RoF as the 14in and 15in turrets but during periods of rapid salvo fire, or during the prolonged use of broadside fire the RoF would fall. However, in rough sea conditions, where extra time was needed for Fire Control, there was extra time for loading anyways.
The problem is apparently serious enough such that the arrangement is not repeated in later design.
Byron Angel
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Re: Design "feature" of R-class

Post by Byron Angel »

The following was written by a Canadian friend, a wonderful WW1 naval researcher who sadly passed away far too young about twenty years ago.
Go here - http://www.hmshood.org.uk/ship/fire_control.htm

Might be the same as what is available on Tone's website, but it comes with several good photos of FC table components. FWIW.

- - -

Chatfield's original 1916 version of the Spotting Rules used to be freely available via Google search, but I was not able to locate it in a search today. I have a copy if anyone is interested; just PM me.


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Re: Design "feature" of R-class

Post by dunmunro »

wmh829386 wrote: Mon Mar 20, 2023 9:35 pm
dunmunro wrote: Sun Mar 19, 2023 6:40 pm
You have a misunderstanding regarding the loading cycle of the 16in triple turret. The shell bogies feed shells upward to a shell scuttle which held 4 x 16in shells per gun. The individual guns could load from the scuttles at their own pace, depending on the salvo cycle, completely independent from the other guns in that turret. It was only when the RoF exceeded the ability of the shell bogies to replenish the shell scuttles that the RoF would slow.
Thanks, I didn't realise there are 4 shells per gun waiting in the lower hoist. And that's pretty interesting. It's also fun checking the following site.
http://www.navweaps.com/index_tech/tech-059.php

During normal salvo fire, this arrangement provided for the same RoF as the 14in and 15in turrets but during periods of rapid salvo fire, or during the prolonged use of broadside fire the RoF would fall. However, in rough sea conditions, where extra time was needed for Fire Control, there was extra time for loading anyways.
The problem is apparently serious enough such that the arrangement is not repeated in later design.
Much of that Navweaps article is a verbatim quote from the book, The Big Gun.
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