August 24, 2016

Why is the 16 SLBM Columbia class SSBN-X larger than a 24 SLBM Ohio?

Question:  Why is the 16 SLBM Columbia Class SSBN-X larger than a 24 SLBM Ohio? (see Table way below. Displacement and Beam is larger).



Cutaway of SSBN-X from page 9 of 2016 Report to Congress.


COMMENTS 


The larger the submarine the smaller the influence of its weapons on displacement and length.

The displacement of the future SSBN-X's 8 fewer SLBMs (16) than the Ohio’s 24 and dimensions for 8 fewer tubes doesn’t mean the SSBN-X is 33% less in displacement/length/beam. 
-  Beam always needs to be the same or greater to accommodate the length of the 
   SLBMs.
-  The Ohio’s 24 SLBMs were a break in the decades old pattern (page 36) of 16 SLBMs.
-  The most pessimistic predictions (of many opposing Russian SSBNs) didn't 
    materialise. (see comparative Table below).
-  The USN must be calculating that threat, stealth and budget means 12 x 16 SLBM 
    SSBNs is adequate for the 2030-2080 SSBN-X era. 
-  But more Common Missile Compartment (CMC) quad-packs and more MIRVs
   per SLBM can always be retrofitted if need be.

The SSBN-X crew (at 155) remains the same because all the requirements needed to maintain the submarine and its SLBM payload involve the same crew specialities, damage control and other fixtures for 16 as they do for 24. There may even be a need for a few more crew in, say 22 years time, to improve stealth.
-  the task of safely operating the reactor requires many crew no matter how many missiles are carried

An inbuilt capacity to absorb improvements and stealth over the 42 year life of SSBN-X involves room to grow into spaces left empty in the hull. Much of this is expanding the computer power by adding more memory and other processing on spare racks in the combat system database. See “must be fitted with the most up-to-date capabilities and stealth to ensure they are survivable throughout their full 40-year life span.”(# below), So more electronics and memory for future active stealth and combat system upgrades may take up much extra space-displacement.

Perhaps more decoys the size of HWT sized UUVs (if the 4 torpedo tubes are retained?).


The tubes for SSBN-X's SLBMs are the same 87-inch diameter as on the Ohio-class, but are a foot longer  -  leaving some margin for a future missile design. This explains the need for a space/displacement increasing Beam of 43 feet compared to the Ohio’s Beam of 42 feet.

The new reactor may be very slightly heavier and larger, with more 90+% HEU for the longer life between refuels (stretched from the Ohio's 19 year mid-life, to being sufficient for the SSBN-X’s whole 42 year service life).

SSBN-X and Ohio class Comparison Table

Measure/Replacement or Ohio
Ohio Replacement, SSBN-X, Columbia class
Ohio class
Number of SLBMs
16***
In Common Missile Compartment (CMC) quad packs #
24*
But just 20 after 2018*
Launch tubes
Same 87 inches SLBM launch tubes ***
Same 87 inches SLBM launch tubes ***
Length
560 feet ***
560 feet ***
Beam
43 feet ***
42 feet ***
Displacement
Larger,  20,815 tons “(as of August 2014)” submerged ***
Smaller, 18,750 tons submerged ***
Crews Blue/Gold
2 x 155 #
2 x 155
Years between HEU refueling
42
(service life) ***
About 19 *
Drive, propulsion
electric-drive propulsion train ***
pump jet, X-plane rudder#
mechanical-drive propulsion train*** bare propeller,
cruciform-H rudder
UK Successor and Vanguard classes
On UK Successor class    8 x Trident IIs, In Common Missile Compartment (CMC) quad packs # UK made warheads **
UK Vanguard class carry 16 x Trident IIs, UK made warheads**

* page 3 Ronald O'Rourke’s Navy Columbia Class (Ohio Replacement) Ballistic Missile Submarine (SSBN[X]) Program: Background and Issues for Congress, of August 18, 2016 CRS 7-5700 www.crs.gov R41129 https://news.usni.org/wp-content/uploads/2016/08/R41129-1.pdf (5 MB PDF)
** page 4 https://news.usni.org/wp-content/uploads/2016/08/R41129-1.pdf

Pete

5 comments:

Ztev Konrad said...

There is comment at Breaking Defence that by designing the reactor core for the full 40+ year life of the submarine ( the current Virginia's reactor is designed for the 30 year life) that means that 12 submarines can do the work of the current 14 without the long overhaul for refueling the reactor
http://breakingdefense.com/2015/01/new-reactor-cores-key-to-ohio-replacement-subs/

The other main new technology is using turbo-electric drive instead of the existing geared turbines. They tried two previous 'electric boats' with USS Tulibee in 1960 and USS Glenard Lipscombe ( similar in displacement to Shortfin Barracuda!) in 1974 but the results werent satisfactory. Diesel boats are of course electric drive to run off batteries.
USS Narwhal had a unique reactor-direct drive setup which wasnt repeated either ( the turbine was a large diameter slow turning)en.wikipedia.org/wiki/S5G_reactor

The construction cost per boat is supposed to be withing a cap set by Congress of around US $5 bill. But that doesnt include new technology development , especially the reactor and detailed design and first of class costs.
www.wired.com/2013/01/secret-sub-design/

This report gives an outline of how the CMC or quad pack common missile compartment will be built integrally with the hull around it.
"The tubes are the same 87-inch diameter vessels as the current Trident II D5 launchers on the Ohio-class, but are a foot longer — leaving some margin for a future missile design."
warisboring.com/americas-next-missile-submarine-will-be-silent-huge-and-live-longer-than-you-edd02eb8c7a2#

"“If you look at the overall length of the ship, the length of the missile compartment is smaller,” Lennon said. “But it’s distributed pretty much equally — the increase — forward and aft. Very little of that has to do with electric drive. It’s really to do with the other capabilities we’ve had to put into the ship in order to meet the mission needs.”
The new reactor and electric drive dont seem to be the main reason for the increase in size.

Ztev Konrad said...

Some of the detail in the table could have different numbers

"The U.S. Navy today operates 18 Ohio-class submarines -- 14 of which carry the Trident nuclear missile, and four of which have been modified to carry conventionally armed long-range

"The CMC design includes an increased diameter of the launch tubes from 2.21m (current) to 3.04m"
while others say
"The tubes are the same 87-inch diameter vessels as the current Trident II D5 launchers on the Ohio-class, but are a foot longer — leaving some margin for a future missile design."
http://ukarmedforcescommentary.blogspot.co.nz/p/successor-submarine-trident.html
warisboring.com/americas-next-missile-submarine-will-be-silent-huge-and-live-longer-than-you-edd02eb8c7a2#

Its difficult to confirm more official sources for the CMC dimensions

Peter Coates said...

Hi Ztec

Thanks for those extra details. Because of the proliferation of secondary sources, which frequently use old and contradictory info, I've intentionally combed through (and used) the most official, most recent report I know of: Ronald O'Rourke Specialist in Naval Affairs,
Navy Ohio Replacement (SSBN[X]) Ballistic Missile Submarine Program: Background and Issues for Congress, May 27, 2016 https://www.fas.org/sgp/crs/weapons/R41129.pdf (5 MB PDF)

Then the Table cites source for piece of info.

Using that Page 8 "The SSBN(X) is to be equipped with an electric-drive propulsion train, as
opposed to the mechanical-drive propulsion train used on other Navy
submarines. The electric-drive system is expected to be quieter (i.e., stealthier)
than a mechanical-drive system.20"

Thanks for ""The tubes are the same 87-inch diameter vessels as the current Trident II D5 launchers on the Ohio-class, but are a foot longer — leaving some margin for a future missile design."
http://ukarmedforcescommentary.blogspot.co.nz/p/successor-submarine-trident.html"

This helps explain why SSBN-X's Beam will be 43 feet instead of Ohio's 42 feet. (Page 8, https://www.fas.org/sgp/crs/weapons/R41129.pdf )

Yes I think more electronics and memory for future active stealth and combat system upgrades may take up much extra space-displacement.

Regards

Pete

Peter Coates said...

Hi again Ztev

Thanks. I've added to the text:

The tubes for SSBN-X's SLBMs are the same 87-inch diameter as on the Ohio-class, but are a foot longer [ https://warisboring.com/americas-next-missile-submarine-will-be-silent-huge-and-live-longer-than-you-edd02eb8c7a2#.j7gqn4au2 ] — leaving some margin for a future missile design. This explains the need for a space/displacement increasing Beam of 43 feet compared to the Ohio’s Beam of 42 feet.

Regards

Pete

Peter Coates said...

Relevant to the SHORTFIN is http://nationalinterest.org/blog/the-buzz/the-us-navy-getting-ready-build-the-most-stealth-submarine-17549 where it says:
"The “X”-shaped stern [rudder] will restore maneuverability to submarines; as submarine designs progressed from using a propeller to using a propulsor [pump jet] to improve quieting, submarines lost some surface maneuverability, Navy officials explained. "

The Electric Drive to be fitted on the Ohio Replacement, Columbia class, SSBN(X) is just one of the new generational nuclear powered subs moving in the direction of the quietness of conventional subs (SSKs) See http://nationalinterest.org/blog/the-buzz/the-us-navy-getting-ready-build-the-most-stealth-submarine-17549 . Unclear whether the Columbia class will:

1. feature an X-rudder alone or

2. an X-rudder and a pump jet?

The Barracuda SSN also reputely has Electric Drive for the same quietness reason.

Pete