Why doesn’t the US Navy build big?

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GoBig

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Why doesn’t the US Navy build big?

Below is my analysis of why warships should be really big. In reality, they are not. What part of the analysis is wrong or what factors are not considered?

A larger warship has more margin for growth, can operate un-resupplied for longer, can travel farther faster, can supply more electrical power and is more damage tolerant. If the operational requirements are held constant (don’t try and cram more into the bigger ship), the incremental acquisition cost of going large should be relatively small. The operational costs of the bigger ship can actually be less. A larger size allows for simpler / heavier systems such as dual direct drive diesels. It also allows a reduced focus on weight / volume / power minimization to allow less expensive development of similar capabilities.

The proposed Go Big ship - 125,000 tons, 30+ knots, 2 x 65MW two stroke diesels, estimated range of 70,000 NMI at 20 knots with 12,500 ton fuel load - 360m length x 49m beam x 12m draft

In an extreme case, could a 10,000 ton DDG-51 be replaced at a reasonable cost by a 125,000 ton Go Big destroyer?

DDG-51 – 10,000 tons, 30+ knots, 4400 NMI at 20 knots - ~2billion 155mx20mx9.3m

The primary costs of the DDG-51 are acquisition ($2 billion) and operation ($70 million /year). Assuming a 30 year life cycle, that is roughly $4.1billion. A Maersk Triple E is bigger (~200,000 tons loaded) and simpler, but only costs $200M. So, it is not the cost of steel or large assembly that drives costs, but the complex military hardware a DDG-51 carries. Let us have the Go Big destroyer carry exactly the same military hardware, but be built on a much larger frame and use the heavier, but more efficient 2 stroke diesels. As an approximation we will add the cost of the Triple E to the DDG-51 - $2.2billion. It should be less as there is overlap in equipment between the two vessels and the proposed Go Big destroyer has a loaded displacement only 60% of the Triple E.

Operations are the other major cost. The DDG-51 $70 million yearly cost can be broken into 3 major categories – personnel (~300 crew) $40M , fuel - $10M, maintenance/upgrade - $20M/year. The Triple E has a crew of 22, so again size is not the driver, but system complexity. By being bigger, full supplies can be carried on board (fuel, food, water, ordinance, etc.) so fewer specialists are needed for distillation, frequent UNREP, etc. Some automation would be carried over to achieve closer to a DDG-1000 crew size (123 crew). Finally, merchant marines would be part of a mixed crew to support non-combat systems. The total crew size would be 200 ($27M /year).

Fuel is another large cost - $10M/year. The larger ship while 12.5 times as heavy only requires 2.5 times as much force to push through the water at the same speed. Being able to carry more than a full deployment of fuel avoids the cost of navy fuel tankers which accounts for 20% of the DDG-51 fuel cost. The more efficient 2 stroke diesels would use 25% less fuel. Finally, bunker fuel rather than MGO would be used to reduce costs another 50%. All told $10M * 2.5 * 0.8 * 0.75 * 0.5 = $7.5M.

Maintenance is the final category. It again appears to be primarily driven by system complexity. An approximation of the DDG-51 maintenance cost + a larger container ship maintenance cost is used - $23M/year. This is an area that could use further reductions.

Lifecycle costs for the Go Big destroyer would be $2.2B + 57.5M*30 = $3.9B

As long as similar operational requirements are maintained it seems that a much larger ship can fulfill the role of the smaller DDG-51 for a lower total cost while providing significant advantages.

It makes even more sense to Go Big (to 125K tons) for larger ships such as the USS America (LHA-6) – 45,000 tons, 22 knots, estimated range of 20,000 NMI at 20 knots with 4500 tons fuel - 257mx32mx8m

But, warships (other than the biggest aircraft carriers) are not built anywhere near the proposed size. What part of the analysis is wrong or what factors are not considered?
 

Blackshoe

Defense Professional
Verified Defense Pro
Sarcastic Answers:

1) Well, we build the largest warships in the world, they just have flat roofs.
2) If those aren't good enough, we have the 15,000 ton "Destroyer" that costs a cool $3.5 bil per version.

I started really giggling when you talked about using 2 MPDEs for a DDG. Also, why you think a larger hull wouldn't invariably lead to more systems=more complexity=more cost.

I feel like I could give this a really Fisking if I wanted, but I'm not sure I have the energy to do so.

I'll just summarize and say "signature".

I will ask a hypothetical retort: why isn't anyone else, either? The US is building the biggest surface combatants of anyone in the world.
 

ngatimozart

Super Moderator
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Verified Defense Pro
First of all welcome to the forum. Uuum where do I start? Warships, in fact any ship, are specific sizes because of the mission sets that they are required to perform. Big most definitely is not always best, especially at sea. The larger the ship, the greater the level of both on shore and at sea infrastructure required to support it. Just look at the supporting infrastructure required for the USN CVNs. The most expensive part of a warships operation is the cost of crew. The crew on a Gerald R. Ford class CVN is approximately 4,300. The ship itself displaces 100,000 tonnes (full load) and the cost of its construction is approximately US$10 billion dollars. Very roughly calculated that equates to construction costs of approximately US$10,000 per tonne. If you extrapolate that for your suggested destroyer then you are looking at a minimum of US $12.5 billion per ship just in construction costs. Extend that out to its term of life costs and you are looking at US$37.5 billion which is the total annual defence budget of some pretty good sized countries.

Destroyers are a workhorse in a fleet the size of the USN. Currently there are 62 Arhleigh Burke class DDGs in active service with the USN with another 14 contracted to be built. Depending upon which flight they are, there fully laden displacement ranges from 8,300 tonnes (Flight I) to 9,800 tonnes (Flight III). So if working on your concept, the construction costs for 76 of your destroyers would be in the region of US$950 billion which is far more than the current annual US defence budget.

Therefore I would strongly suggest that you reevaluate your idea because it is in all reality very unworkable and extremely expensive.
 

gf0012-aust

Grumpy Old Man
Staff member
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Why doesn’t the US Navy build big?
I'm really not sure where to start as you make some really flawed statements and assumptions about why warships are fitted out, sized and crewed as they are against commercial vessels

can I start with asking what your background is?

that might add some clarity as to why you've made some claims.....
 

GoBig

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Thank you all for taking the time to comment. My background is in autonomous systems (ground vehicles, robotics) and complex software systems. While doing some initial propulsion power budgeting for a small autonomous boat using Michlet I went a bit off tangent and looked at a few commercial and military ships in comparison to the simulated results. I also noticed the trend of going big in commercial ships and wondered how that might apply to military ships.

Blackshoe:

I was looking for a thorough Fisking of the proposal if you felt up for it some time. I came at this from mostly a cost and logistics point of view as there were a lot of interesting papers from the Naval Postgraduate School and other sources on those subjects.

From a speed / reliability / cost / maintainability point of view I couldn’t find the requirements a diesel would not meet on a ship of the proposed size.

Signature – a bigger ship does have a bigger signature (radar, thermal, acoustic, visual, etc.). I also assume that a diesel would put more acoustic energy into the water than a turbine. Propeller cavitation seemed to be the main concern and going with big slow turning propellers was one way to address that. At higher speeds I assumed there would be plenty of acoustic noise no matter what the propulsion system. At lower speeds a shaft generator / motor with a diesel genset would be used. Rather than avoiding the poor BSFC of a turbine at low power as the approach is frequently used it would be done to reduce noise.

My question would have been better phrased as any navy rather than just the USA.

Ngatimozart:

One of the ideas of the large ship was to reduce the logistics. As the ship grows the un-refueled range goes up. A ship of this scale would be capable of traveling to any point in the world, operating for a number of months and returning without refueling or “re-fooding.” It is not quite to the scale of the floating island idea.

I was pushing a bit on the acquisition cost. Large commercial ships can be acquired for $1000 per loaded ton. That is 1% of the $100,000 per loaded ton of a carrier or 0.5% of the $200,000 per loaded ton of a destroyer. I was proposing that the differential was due to the hardware on board rather than simply scaling linearly with size. By keeping the military hardware constant I was proposing to increase the size to gain other advantages (logistics, growth, etc.). The modification of commercial ships for LCAC carriers and other uses is probably from this cost difference per ton.
 

ngatimozart

Super Moderator
Staff member
Verified Defense Pro
Warships and commercial vessels are to different entities and operate in completely different environments for completely different purposes. That is what a lot of non naval and military people don't necessarily understand. All of the people who have answered you are defence professions well versed in their professions and all of us have served in the forces with two of us serving at sea. Big is not always good especially at sea, nor in the air.

I very strongly suggest that you read the rules for this site, because they are enforced especially by the God moderator. All of the moderators on this site are defence professionals so they run the site with a firm hand.

With regard to this particular subject you really need to do some research into matters naval, especially how vessels are utilised, naval combat tactics and naval strategy. Whilst technology is really good and is in many ways essential it is only one part of the equation. It is not the be all to end all.
 
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