Fantasy T31 and Fantasy Fleet Builder [New]

[clinch]

Left of field, but what if the Leander team offered six hulls for the price the Treasury has set? Would the politicians be tempted by the opportunity to say, "Look, we are growing the fleet"?

[NickC]

Negative of A140 for me is;
- Technically: with 4 engines and larger hulls, its maintenance load will be larger, and less fuel efficient.

That's totally incorrect, contradicted by Danish Navy and OMT/Maersk based on their vast experience of designing and operating commercial ships, which should be noted BAES seem have folowed with the Type 26 . The whole design philosophy with the Iver Huitfeldt class (A140) was to minimise through life costs by making ship very easy to maintain and spend by building in large space, weight, cooling and electric power margins. The exact opposite of a small dense ship which makes maintenance expensive and difficult plus possible future upgrades limited. The fuel efficiency of the IH is outstanding with a range of 9,000+ nm at 18 knots.

An exponent of "Steel is cheap and air is free" done correctly.

Detailed exposition in video, which have posted before

[donald_of_tokyo]

Negative of A140 for me is;
- Technically: with 4 engines and larger hulls, its maintenance load will be larger, and less fuel efficient.

That's totally incorrect, contradicted by Danish Navy and OMT/Maersk based on their vast experience of designing and operating commercial ships, which should be noted BAES seem have folowed with the Type 26 . The whole design philosophy with the Iver Huitfeldt class (A140) was to minimise through life costs by making ship very easy to maintain and spend by building in large space, weight, cooling and electric power margins. The exact opposite of a small dense ship which makes maintenance expensive and difficult plus possible future upgrades limited. The fuel efficiency of the IH is outstanding with a range of 9,000+ nm at 18 knots.

An exponent of "Steel is cheap and air is free" done correctly.

Detailed exposition in video, which have posted before ...

I knew this and I do not change my mind.

Leander is 3600t relatively small vessel, narrower than A140, so less fuel needed. This is physics. Leander is also not densely equipped; the same armament to 2600t Khareef, which itself is less armed as a corvette.

A140 being efficient is, compared to Dutch DZV class, T26, Spanish F100, FREMM, or T45. All diesel, surely it is more fuel efficient than GT based escorts. With easier access to cabling, the mid-life upgrade will be cheaper. But, Leander is not densely armed and all diesel propulsion. A140 is good as it is. But not affecting my point.

#Long range and fuel efficiency is not directly related; just a large fuel tank can also do.

<a little related>
Iver Huitfeldt class is less densely armed, has "shock resistant islands" (space and weight consuming), 4 large diesel with big gear box (as well). This means, it uses many weight and space to make them happen. So, although it is 6600t FL, I regard it has similar capacity as 5000-5500t hull. Actually, it is very similar to German Sachsen-class FFG. But, its maintenance and running cost will be cheaper, because its access to machinery is easier, fuel efficient (no GT), and using many COTS equipments. It is a good design, I agree.

But again, not related to my assessment that Leander will need less maintenance/running cost than A140.

[Tempest414]

- 10 units of 30mm gun will be not easy without using T23's. If not, just leave it vacant. Simple 20mm gun or 7.62mm mini-gun can do. Also, 30mm gun is not costy. In a few year, T23 will anyway decommission, and 30mm guns will come out for free.

Or you could take 20 x 50 cal HMGs ( 4 per ship) from MOD stocks and replace 2 with 30mm as type 23 go out of service

[NickC]

Negative of A140 for me is;
- Technically: with 4 engines and larger hulls, its maintenance load will be larger, and less fuel efficient.

That's totally incorrect, contradicted by Danish Navy and OMT/Maersk based on their vast experience of designing and operating commercial ships, which should be noted BAES seem have folowed with the Type 26 . The whole design philosophy with the Iver Huitfeldt class (A140) was to minimise through life costs by making ship very easy to maintain and spend by building in large space, weight, cooling and electric power margins. The exact opposite of a small dense ship which makes maintenance expensive and difficult plus possible future upgrades limited. The fuel efficiency of the IH is outstanding with a range of 9,000+ nm at 18 knots.

An exponent of "Steel is cheap and air is free" done correctly.

Detailed exposition in video, which have posted before ...

I knew this and I do not change my mind.

Leander is 3600t relatively small vessel, narrower than A140, so less fuel needed. This is physics. Leander is also not densely equipped; the same armament to 2600t Khareef, which itself is less armed as a corvette.

A140 being efficient is, compared to Dutch DZV class, T26, Spanish F100, FREMM, or T45. All diesel, surely it is more fuel efficient than GT based escorts. With easier access to cabling, the mid-life upgrade will be cheaper. But, Leander is not densely armed and all diesel propulsion. A140 is good as it is. But not affecting my point.

#Long range and fuel efficiency is not directly related; just a large fuel tank can also do.

<a little related>
Iver Huitfeldt class is less densely armed, has "shock resistant islands" (space and weight consuming), 4 large diesel with big gear box (as well). This means, it uses many weight and space to make them happen. So, although it is 6600t FL, I regard it has similar capacity as 5000-5500t hull. Actually, it is very similar to German Sachsen-class FFG. But, its maintenance and running cost will be cheaper, because its access to machinery is easier, fuel efficient (no GT), and using many COTS equipments. It is a good design, I agree.

But again, not related to my assessment that Leander will need less maintenance/running cost than A140.

Donald-san, could you expand your thinking and info to support the Leander will need less maintenance/running costs.

Crew would be same in numbers and think fuel consumption would only be marginally higher, do take your point that A140 as a larger ship by 2,000 tons has capability / capacity for larger fuel tanks for extended range at higher speeds. Would point out in relation to A140 the smaller Leander will be more densely equipped, though only two diesels will have all the associated electric motors, transformers etc. and same hardware kit as the A140 making maintenance harder.

Though no naval architect my understanding is the longer LWL by ~ 30 metres A140 will give it a natural advantage over the shorter LWL Leander, reflected in its higher crise speed 19 knots v. 12 to 16 knots e.g. the QE at ~ 70,000 tons ten times the displacement of a Type 26 yet can can achieve ~ max. speed with only 2+ power, physics . The general rule is the maximum speed/efficiency of a displacement hull, approx. hull speed in knots is 1.34 times the square root of the waterline length in feet , 1.34 x √LWL.

With the Type 42 destroyer they chose a short LWL for speed and economy in preference to a longer LWL design. The Batch 1 T42s proved that to be wrong, Batch 2s were lengthened and in the end Batch 3 were stretched to T42s original long design.

[donald_of_tokyo]

Donald-san, could you expand your thinking and info to support the Leander will need less maintenance/running costs.

Crew would be same in numbers and think fuel consumption would only be marginally higher, do take your point that A140 as a larger ship by 2,000 tons has capability / capacity for larger fuel tanks for extended range at higher speeds. Would point out in relation to A140 the smaller Leander will be more densely equipped, though only two diesels will have all the associated electric motors, transformers etc. and same hardware kit as the A140 making maintenance harder.

2 large diesels vs 4 large diesels. 32.8 MW vs 20MW. Clear. A140 needs more maintenance in its engine. If with the same power requirement, CODOE vs CODAD is a good comparison, but it differs by 60%.

Hull is 6600t vs 3700t, which means the internal area, all equipped with fire-fighting sensors and valves, both redundant, is 1.8 times larger in A140 than Leander. Small crew means automation, which further means you need a maintenance of these "kits for automation" at port. Not sure how expensive it is, but I'm sure Leander has less running(including fuel)/maintenance cost. There is a reason why FREMM and T26 is not 10,000t, but 6000-8000t. "Steel is so cheap" that it is the ingredients in these sections, for example damage control standard, which is dominating the cost, I think.

Though no naval architect my understanding is the longer LWL by ~ 30 metres A140 will give it a natural advantage over the shorter LWL Leander, reflected in its higher crise speed 19 knots v. 12 to 16 knots e.g. the QE at ~ 70,000 tons ten times the displacement of a Type 26 yet can can achieve ~ max. speed with only 2+ power, physics . The general rule is the maximum speed/efficiency of a displacement hull, approx. hull speed in knots is 1.34 times the square root of the waterline length in feet , 1.34 x √LWL.

Thanks, you are right here on L/V ratio. (I'm also not a naval architect )
- But, first of all I understand "1.34 x √LWL" rule is valid for a hull with the same cross-section (or width) (as T42 batch 1/2 and 3).
- Also this estimation means, Leander with 117m is 9% faster than Khareef with 99m, even with the same propulsion (on which the original Leander is based on, I guess). (I couldn't find LWL of those two, so just used overall length). This means, 25 knots x 1.09 = 27+ knots. In other words, Leander will meet the 27+knots requirement for CVTF escort, naturally. (But there is a reason it is rated as 25knots, not clear.)

But, this is on the top speed. On "fuel efficient speed", the surface drag do matter and heavier ships tend to require more fuel. Could not find reference, but as I remember, T42B3 requires more fuel than T42B1/2, although its top speed is higher.

On the cruise speed of 19knot vs 16knots, I see no "cruise speed" argument in both of them. It is just a speed to calculate the range. In RN case, I think it is historically 16knots = the fleet speed. In USN it is 20knots. That's it.

[Lord Jim]

On the positive side the RN does appear to have two viable options for the T-31e and therefore should be able to utilise competitive tendering to decide which one is chosen and therefore gat the best deal, possible getting the baseline designs for less that the £125M per vessel allowing optional extras to be fitted. Who knows.

[Ron5]

@Donald-san
1. What happened to the 250 million price point?
2. What happened to the requirement for minimal equipment reuse?
3. Are used 3" guns available?
4. How can range be unchanged with more powerful (and thirstier) engines?
5. Blue watcher HMS is not good enough, the RN would want something useful.

Thanks
- Engine is not critically expensive. Similar engines was bought "military off the shelf (MOTS)" for Khareef, which was 133M GBP/hull average. Only issue is the electric motor and its diesel gen sets, but recently CODOE is very popular, so I guess it is not cost-driving. Note, I kept the motor power low. If needed, can be much lower, say 1000kW for 10 knots?

- The equipment reuse "from T23" is minimal. I'm proposing to just buy "cheap re-used equipments" off the market.

-- 5 units of old re-used 3inch gun can be bought MOTS. Call Japan, we have many.

-- 10 units of 30mm gun will be not easy without using T23's. If not, just leave it vacant. Simple 20mm gun or 7.62mm mini-gun can do. Also, 30mm gun is not costy. In a few year, T23 will anyway decommission, and 30mm guns will come out for free.

-- Many used triple AS torpedo launcher can be found. Call Japan. Also, it may not be connect to CMS for simplicity (RNZN did not).

-- BlueWatcher HMS is not good enough, and thus it is cheap. It has commonality with Merlin HM2, and easily connectable to CAPTAS-based multi-static ASW software.

--> So, virtually, it is only Artisan and CAMM, and 30mm guns, which could be re-used from T23.

- It is the CMS and its integration, which costs a lot. Therefore, "space for CAPTAS2" could be just a space, i.e. we might need to improve the CMS when we want to connect CAPTAS2. (CAPTAS1 may be OK). If we cannot meet 250M GBP with all these mitigations, I will just propose to omit "Artisan and CAMM" from 2 of the 5 hulls. CMS could be down-graded in these 2.

- range may or may not change. 20V S8000 M91L is a sister of M91, used in Khareef, and the fuel efficiency for 16knots may not change. Anyway the range is still much longer than T31e RFI.

It is quite ugly though.... it basically looks like a .............. well imagine stretching a 3 series into a limo

Agreed, but sorry it MAY be because of my power-point skill

Good answers @Donald-san.

I like your idea of upping both the main & electrical power but I fear that it would not be quite as cheap as you hope. Newer models of any product, like marine diesels, tend to be more expensive. Plus there would be some knock on costs: bigger shafts, bigger bearings, larger screws, larger motor room.

Actual range would suffer. The ship would use the extra power (otherwise why fit it?) and that costs extra fuel.

I don't like your trade-off very much. Whether we like it or not, Artisan and CAMM are higher up the Type 31 priority list than ASW. I think leaving space for a towed array and allowing for a FTR HMS (both of which is already apart of the design) would be the RN choice to keep the price down.

I'd also prefer a 5" gun but that seems to be ruled out on expense. Sad. A 3" seems rather weenie. Wouldn't scare me much either on another ship or land. I don't buy the claims they have a useful AA capability, the Phalanx on the back and CAMM on the front are much more lethal.

[Ron5]

ooops deleted, I see Donald-san has already commented.

[Lord Jim]

Both the 76mm and 57mm can cripple vessels up to destroyer size at quite long range, obviously ASMs out range them, but there are few if any CIWS that can intercept shells incoming of this size. even the 57mm has guided rounds able to reach out to 20km that were developed for use on the LCS and together with the 3P rounds give this weapon a pretty good anti-surface capability. Also the weight of fire put out by these two weapons far greater than the faithful 5" and time and time again this has been a factor realised once the shooting starts. The bolting on of as many MGs as can be fitted seems to be quite a common practice when going where the bad guys are.

Also why are we all trying to get the T-31e turned into a ASW platform, aren't they supposed to be GP platforms first and foremost? The biggest ASW capability the T-31e should really be bringing to the party is a Merlin. More important should be its anti-ship capability, secondary to its self defence abilities. Future options could be to increase its missile capacity and the types of missile carried to provide additional capacity to a task group, with data links providing targeting data in a co-operative net.

It is going to be interesting to see how the T-31e programme pans out. So many things need to be clarified but the outcome could be quite good for the RN. Can someone remind me of what the programme timetable is?

[Simon82]

Surely a ‘General Purpose’ warship should be capable of ASW, ASuW, local air defence and shore bombardment. If not it isn’t exactly general purpose, it’s just a souped up OPV.
Of course I’m being slightly pedantic here as I’m aware ‘general purpose’ in this context actually means a warship built without any expensive specialist items of equipment for financial reasons and is therefore incapable of doing anything well. However, my point is that with a falling number of surface combatants in the Royal Navy the priority must be more capabilities per hull, not less. The USN are in the enviable position of being able to focus on the ASW mission with the FFG(X) as a supporting Arleigh Burke or carrier air-wing is never going to be far away. Single mission surface combatants are not, however, an option for the now much reduced Royal Navy and similarly neither is a ‘general purpose’ ship that can add little capability besides defending itself against rudimentary threats. True, in times of peace it could function as a naval ‘presence‘ to fly the flag where required by the Foreign Office as well as any other vessel, but in combat it would be a liability, at best unable to contribute anything and at worst being a draw on the already over stretched escort fleet.
The Type 26 is such a large, expensive and (potentially) capable vessel for a reason and is probably the closest the Royal Navy has had to a truly general purpose vessel since the abortive Type 82 programme.

[Ron5]

Surely a ‘General Purpose’ warship should be capable of ASW, ASuW, local air defence and shore bombardment. If not it isn’t exactly general purpose, it’s just a souped up OPV.
Of course I’m being slightly pedantic here as I’m aware ‘general purpose’ in this context actually means a warship built without any expensive specialist items of equipment for financial reasons and is therefore incapable of doing anything well. However, my point is that with a falling number of surface combatants in the Royal Navy the priority must be more capabilities per hull, not less. The USN are in the enviable position of being able to focus on the ASW mission with the FFG(X) as a supporting Arleigh Burke or carrier air-wing is never going to be far away. Single mission surface combatants are not, however, an option for the now much reduced Royal Navy and similarly neither is a ‘general purpose’ ship that can add little capability besides defending itself against rudimentary threats. True, in times of peace it could function as a naval ‘presence‘ to fly the flag where required by the Foreign Office as well as any other vessel, but in combat it would be a liability, at best unable to contribute anything and at worst being a draw on the already over stretched escort fleet.
The Type 26 is such a large, expensive and (potentially) capable vessel for a reason and is probably the closest the Royal Navy has had to a truly general purpose vessel since the abortive Type 82 programme.

Excellent post which makes an excellent point: the fewer ships you have, the more tasks each one has to perform.

Unfortunately the more things a ship can do, the more expensive it becomes. So fewer can be afforded.

It's quite a challenge.

[Ron5]

Both the 76mm and 57mm can cripple vessels up to destroyer size at quite long range, obviously ASMs out range them, but there are few if any CIWS that can intercept shells incoming of this size. even the 57mm has guided rounds able to reach out to 20km that were developed for use on the LCS and together with the 3P rounds give this weapon a pretty good anti-surface capability. Also the weight of fire put out by these two weapons far greater than the faithful 5" and time and time again this has been a factor realised once the shooting starts. The bolting on of as many MGs as can be fitted seems to be quite a common practice when going where the bad guys are.

No doubt that's why armies the world over are equipped with 2" and 3" artillery (heavy sarcasm).

The Type 31 would carry a 5" to perform NGFS. Relying on guns to sink enemy ships kinda went out of fashion 50 years ago.

Also why are we all trying to get the T-31e turned into a ASW platform, aren't they supposed to be GP platforms first and foremost? The biggest ASW capability the T-31e should really be bringing to the party is a Merlin. More important should be its anti-ship capability, secondary to its self defence abilities. Future options could be to increase its missile capacity and the types of missile carried to provide additional capacity to a task group, with data links providing targeting data in a co-operative net.

The desire is to enable the Type 31 to be able to perform within a carrier task force in a high threat environment. Artisan and CAMM enables close AA escort (goalkeeper). A hull mounted sonar plus anti-sub weapons would enable ASW close escort. Anti ship missiles would not be required.

It is going to be interesting to see how the T-31e programme pans out. So many things need to be clarified but the outcome could be quite good for the RN. Can someone remind me of what the programme timetable is?

Try google, very good for finding all kinds of info.

[Ron5]

There was earlier chatter about warship top speeds that I'd like to add a few observations:

1. 1.34 times sq rt of LWL is a good way to estimate the top speed of a displacement sailing vessel (yacht). The curve of wave resistance of a hull vs speed shows a steepening at this point. Sails are unable to generate enough power to get over the "hump" so in practice that speed becomes the boats top speed. For warships and other high speed displacement hulls, it doesn't have that connotation and is not part of the naval architects lexicon. Enough power can be generated to go faster by putting in more powerful engines.

2. Warships spend very little of their time in peace and war running at max speed. A few percent at the most and dependent on the role being performed: an AA speed profile is very different to ASW. It's kinda like us driving our cars, there's more reasons to go slow than fast. In particular, the unspoken assumption on these boards that a CVF centered taskforce will be running around at 27 knots is farcical. One poster thought it was great that the new oilers would be able to tag along with the gang at top speed and even deliver fuel without anyone slowing down. Hold them horses kemosabe. The major reason aircraft carriers are fast to to generate wind over deck. They also turn out of formation into the wind to make sure the wind blows directly down the deck. The extra speed comes in useful in regaining their station with the fleet. It's not to enable 27 knot task forces. Even in the USN.

3. For frigate/destroyer warships, their hull shapes don't differ that much, so power density (installed KW per ton) gives a rough estimate on top speed. A140 at 5,700 tons driven by 32.8 MW has a power density (PD) of 5.8. Leander is 4.9. In comparison the Types 45 & 26 are 5.4 and 5.2. Donald-san's favorite La Fayette is 4.4. So I think the brochure figures for Leander & A140 of 25knt/28knt to be believable. The A140 might even be a tad conservative. Donald-san's Leander power upgrade to 20MW moves the Leander PD needle to 5.4 so his calculation of 27+ knots appears to be consistent. Once again, like the carrier, an escort has to busy off and do stuff so needs the speed to get back in line quickly so 27 knots might be required for goal keeping duties.

4. Of course all my blather means nothing when the sea gets rough. All ship architects & builders quote still water speeds. In realty, a 27 knot Leander or 28 knot Arrowhead would have a lot of difficulty keeping up with the QE in heavy seas. Which reminds me of the old tale of American sailors in their 35 knot destroyers not being able to keep up with their 30 knot shadowing Russian counterparts when the going got rough. Turned out the Russian ships had better hull forms for the rough water than the American ships which were optimized for high speed in still water (the US builders got incentives for every knot above the requirement, so built them like speedboats). The US changed so Arleigh Burkes etc don't have that problem but it's a cautionary tale. Another would be the 37 knot Type 21's which started to fall apart when the going got rough and couldn't keep up with the RNs older warships until they had a few hundred tons of extra steel strengthening added. Which of course cut their top speed down by 5 knots or so. Anyhow, I am digressing, dog needs a walk.

[Lord Jim]

Both the 76mm and 57mm can cripple vessels up to destroyer size at quite long range, obviously ASMs out range them, but there are few if any CIWS that can intercept shells incoming of this size. even the 57mm has guided rounds able to reach out to 20km that were developed for use on the LCS and together with the 3P rounds give this weapon a pretty good anti-surface capability. Also the weight of fire put out by these two weapons far greater than the faithful 5" and time and time again this has been a factor realised once the shooting starts. The bolting on of as many MGs as can be fitted seems to be quite a common practice when going where the bad guys are.

No doubt that's why armies the world over are equipped with 2" and 3" artillery (heavy sarcasm).

The Type 31 would carry a 5" to perform NGFS. Relying on guns to sink enemy ships kinda went out of fashion 50 years ago.

Also why are we all trying to get the T-31e turned into a ASW platform, aren't they supposed to be GP platforms first and foremost? The biggest ASW capability the T-31e should really be bringing to the party is a Merlin. More important should be its anti-ship capability, secondary to its self defence abilities. Future options could be to increase its missile capacity and the types of missile carried to provide additional capacity to a task group, with data links providing targeting data in a co-operative net.

The desire is to enable the Type 31 to be able to perform within a carrier task force in a high threat environment. Artisan and CAMM enables close AA escort (goalkeeper). A hull mounted sonar plus anti-sub weapons would enable ASW close escort. Anti ship missiles would not be required.

It is going to be interesting to see how the T-31e programme pans out. So many things need to be clarified but the outcome could be quite good for the RN. Can someone remind me of what the programme timetable is?

Try google, very good for finding all kinds of info.

Regarding shooting at ships with guns, I just though as you mentioned that being shot at by a 3" whist on a boat didn't scare you I would offer a differing opinion.

I agree having a hull mounted sonar is a positive, I am more concerned about those who are advocating adding a tail and so on. As for the AShMs, I am a fan if fitting Mk41s to everything and so having 1 or 2 8-cell launchers on a T-31e would allow for more Sea Ceptor, AShMs eventually as well as other useful items like ASROC. All wishful thinking I know but this is the Fantasy thread.

[NickC]

Maximum speed 27kn *1 (modified from BAE brochure), 13 kn with motor (improved from 7kn of Khareef)
Main Engines (2x, 20V S8000 M91L) 20,000 kW total *1 (10% improved from Khareef)

Minor point, understood the rule of thumb is that it takes double the power to increase speed by 4 knots, so a 10% power increase will give an approx. additional max. speed of only 0.4 knots, so will make minimal difference of Leander quoted max. speed of 25 knots.

As an example being the IH (A140), the same hull as the Absalon, IH uses four MTU 8000 M70 8.2 MW each whereas the Absalon only two, IH max. speed ~ 29 knots, Absalon ~ 25 knots.

It also highlights that the larger 6,000+ ton Absalon can achieve 25 knots max. speed with lower power engines than BAE claiming for the the 25 knot 3,700 ton BAE Leander ?

[Ron5]

Maximum speed 27kn *1 (modified from BAE brochure), 13 kn with motor (improved from 7kn of Khareef)
Main Engines (2x, 20V S8000 M91L) 20,000 kW total *1 (10% improved from Khareef)

Minor point, understood the rule of thumb is that it takes double the power to increase speed by 4 knots, so a 10% power increase will give an approx. additional max. speed of only 0.4 knots, so will make minimal difference of Leander quoted max. speed of 25 knots.

As an example being the IH (A140), the same hull as the Absalon, IH uses four MTU 8000 M70 8.2 MW each whereas the Absalon only two, IH max. speed ~ 29 knots, Absalon ~ 25 knots.

It also highlights that the larger 6,000+ ton Absalon can achieve 25 knots max. speed with lower power engines than BAE claiming for the the 25 knot 3,700 ton BAE Leander ?

I don't know where you got your rule of thumb but it's nonsense.

The plot of a given ship's resistance vs speed is a curve that is not at all consistent with your theory. The curve various in steepness, after an initial linear progression (due to resistance being dominated by surface drag), it becomes steeper and steeper due to wave drag becoming the major factor. The steepness at point can approximate to a power of 2, then 3, then 4, etc.. In other words, it depends entirely where you are at on the curve how much extra power is required to increase speed by 4 knots.

I'll use google to see if I can find such a curve on the internet. Please remember there is no such thing as a curve that fits all ships. Even today, hull resistance cannot be entirely predicted using math, tanks tests are required then using Froude's rules are extrapolated to full size ships. In practice, naval architects look for an pre-existing ship whose hull is close to their new design and use the pre-existing hull resistance as a baseline before following up with tank testing. The CVF designers, for example, used a library of hull shapes including cruise liners to help them.

[Ron5]

This is the first one that came up on google. It's not ideal because the ship being tested must be a lot smaller than the Type 31's that we are discussing but it does get over my points (I hope). You can see the amount of power required to go from 10 knots to 14 is approximately 100 hp to 500 hp. A lot more than double.

[Ron5]

A plea to everyone, including moderators:

I am getting really frustrated with Type 31 discussion being spread over two threads and discussions about the actual Type 31 program being mixed in with fantasy stuff.

Can we please have at least these threads:

1. Discussion of future fleet beyond the Type 31 program (including rfa, escorts, minehunters or whatever)

2. Discussion of T26 program

3. Discussion of T31 program

4. Fantasy fleets

Keeping the T26 news & T31 news threads as is.

[Lord Jim]

Agreed, in fact across many topics a restructuring would be helpful along those line, namely, what is, what will be and what could be.

[NickC]

Maximum speed 27kn *1 (modified from BAE brochure), 13 kn with motor (improved from 7kn of Khareef)
Main Engines (2x, 20V S8000 M91L) 20,000 kW total *1 (10% improved from Khareef)

Minor point, understood the rule of thumb is that it takes double the power to increase speed by 4 knots, so a 10% power increase will give an approx. additional max. speed of only 0.4 knots, so will make minimal difference of Leander quoted max. speed of 25 knots.

As an example being the IH (A140), the same hull as the Absalon, IH uses four MTU 8000 M70 8.2 MW each whereas the Absalon only two, IH max. speed ~ 29 knots, Absalon ~ 25 knots.

It also highlights that the larger 6,000+ ton Absalon can achieve 25 knots max. speed with lower power engines than BAE claiming for the the 25 knot 3,700 ton BAE Leander ?

I don't know where you got your rule of thumb but it's nonsense.

The plot of a given ship's resistance vs speed is a curve that is not at all consistent with your theory. The curve various in steepness, after an initial linear progression (due to resistance being dominated by surface drag), it becomes steeper and steeper due to wave drag becoming the major factor. The steepness at point can approximate to a power of 2, then 3, then 4, etc.. In other words, it depends entirely where you are at on the curve how much extra power is required to increase speed by 4 knots.

I'll use google to see if I can find such a curve on the internet. Please remember there is no such thing as a curve that fits all ships. Even today, hull resistance cannot be entirely predicted using math, tanks tests are required then using Froude's rules are extrapolated to full size ships. In practice, naval architects look for an pre-existing ship whose hull is close to their new design and use the pre-existing hull resistance as a baseline before following up with tank testing. The CVF designers, for example, used a library of hull shapes including cruise liners to help them.

Re: Fantasy T31 and Fantasy Fleet Builder [New]
Postby Ron5 » 06 Jul 2018, 18:31

This is the first one that came up on google. It's not ideal because the ship being tested must be a lot smaller than the Type 31's that we are discussing but it does get over my points (I hope). You can see the amount of power required to go from 10 knots to 14 is approximately 100 hp to 500 hp. A lot more than double.

Will need a better example than a yard patrol craft to claim the rule of thumb that you need double the power for an increase speed of four knots is nonsense, would be interested if you can come up with a power curve for a warship - frigate or destroyer to confirm your claim.

Its a rule of thumb and is simplistic and so has to be treated with caution, but found gives good ball park figures, as working with ship figures that are 'grey'.

To back up the rule of thumb works gave a near perfect real world example with the Absalon / Iver Huitfeldt. The IH has the same hull, though different internally, has four MTU 8000 M70's instead of the two installed in Absalon and IH max. speed increases by four knots.

Lets look at the new Hunter and compare it to an Arleigh Burke Flt IIA which is slightly longer though with slightly narrower beam and appox. 400 tons heavier
Hunter 8,800 tons, 149.9 m x 20.8 m, 1 x MT30 = 36MW
Burke 9,200 tons, 154 m x 20 m, 4 x LM2500 = 78.3 MW
Hunter max speed quoted as 27+ knots and Burke with 2.2 times the power ~ 32 knots
As said figures are grey as expect Hunter FLD is EOL and do not know at what displacement Burke able to achieve its ~ 32 knots.

In reference to Leander lets compare to a FFG7 with its 'older' design philosophy of higher length to beam ratio.
Leander 3,700 tons, 117 m x 14.6 m, 2 x 9.1MW = 18.2MW
FFG ~ 4,000 tons, 136 m x 14 m, 2 x LM2500 = 32 MW (earlier generation and lower powered LM2500s installed than in Burke)
Leander max. Speed quoted at 25 knots and FFG7 with 1.8 times the power ~29 knots.

That's why very sceptical that a minimal 10% increase in Leanders power could increase speed from 25 to 27 knots.

[donald_of_tokyo]

This is the first one that came up on google. It's not ideal because the ship being tested must be a lot smaller than the Type 31's that we are discussing but it does get over my points (I hope). You can see the amount of power required to go from 10 knots to 14 is approximately 100 hp to 500 hp. A lot more than double.

Power vs Speed of old WW2 battleships.
https://www.tapatalk.com/groups/warship ... 31444.html

imageproxy.php.jpeg

[donald_of_tokyo]

That's why very sceptical that a minimal 10% increase in Leanders power could increase speed from 25 to 27 knots.

Might not question to me, but my point on improved Leander is
- with 10% more power, 1knot more speed (just power of 3, assumed)
- with longer length with the same cross-section, 1knot more. (In case of T42, it was 2 knots more with 10-15m elongation?)
Simple.

By the way, the plot in my last post clearly tells us, the power-vs-speed curve rises quickly at higher speed. Also, it depends on the ship. As we do not know the curve for Khareef/Leander, all my point is just a guess. And similarly, NickC-san's argument is also guess. Because my assumption is based on two independent "engineering", and anyway the addition is very small,


PS found interesting list on Type-42's wiki.
Speed:
30 kn (56 km/h; 35 mph) (2 x Olympus)
24 kn (44 km/h; 28 mph) (1 Olympus and 1 Tyne per shaft)
20 kn (37 km/h; 23 mph) (1 x Olympus)
18 kn (33 km/h; 21 mph) (2 x Tyne)
13.8 kn (25.6 km/h; 15.9 mph) (1 x Tyne)

Olympus is 37MW, Tyne was 4MW. The 20knot/1 Olympus look a bit quire, but if we plot it.
Although it is clearly un-reliable, it will look as follows:

スクリーンショット 2018-07-07 18.10.12.png

[NickC]

This is the first one that came up on google. It's not ideal because the ship being tested must be a lot smaller than the Type 31's that we are discussing but it does get over my points (I hope). You can see the amount of power required to go from 10 knots to 14 is approximately 100 hp to 500 hp. A lot more than double.

Power vs Speed of old WW2 battleships.
https://www.tapatalk.com/groups/warship ... 31444.html

imageproxy.php.jpeg

Thanks Donald-san, great find.

FWIW making big assumptions that I'm interpreting graph correctly and that New Jersey fuel trials 1943 roku are the accurate and not an outlier they seem a near perfect fit for the rule of thumb that you need to double the power to increase speed by four knots


Speed in knots Thou. SHP Thou. SHP increase

15 to 19 15 to 30 15
19 to 23 30 to 60 30
23 to 27 60 to 112 58
27 to 31 112 to 220 108

[NickC]

Update to previous post editing didn't format as preview.

Thanks Donald-san, great find.

Making big assumptions that I'm interpreting graph correctly and that New Jersey fuel trials 1943 roku are the accurate and not an outlier they seem a near perfect fit for the rule of thumb that you need to double the power to increase speed by four knots.


Speed in knots / Th. SHP / Th. SHP increase reqired

15 to 19 / 15 to 30 / 15
19 to 23 / 30 to 60 / 30
23 to 27 / 60 to 112 / 58
27 to 31 / 112 to 220 / 108