LHD/LPH/LPD design speeds

[Martes]

Again, probably a silly question, but why almost any LHD/LPD there is now does not exceed 25 knots of speed, and that's on a good day, with most designed for 18-20? Is this economy, or it is somehow connected to their shallow hulls and stern docks?

 

[Yellow Palace]

Speed is always expensive, and hullform needed to accommodate a dock makes it especially so. There's also no need for an amphibious force to make that kind of speed, so the expense would be unnecessary.

A pure helicopter ship could be made a fair bit faster without too much difficulty, and more than a few full-dress aircraft carriers have performed quite adequately in the role. But with a clean sheet design, it's still a better trade to have a smaller ship, or more carrying capacity in the same size.

 

[Martes]

There's also no need for an amphibious force to make that kind of speed, so the expense would be unnecessary.

Move at squadron speed in contested waters, keep with escort and all that? Or the general assumption is that if the waters are contested to this extent, no LPD is going there at all?

 

[Yellow Palace]

Or the general assumption is that if the waters are contested to this extent, no LPD is going there at all?

Pretty much. They have similar cruising speeds (18-20 knots) to faster warships, they just don't need to go any faster than transit speed. When they've finished transit, they'll be going dead slow in the operating area.

Speed with a flooded dock is typically low single digit knots.

Move at squadron speed in contested waters, keep with escort and all that?

This would be counterproductive - the escort needs to be faster than the force it's escorting to be able to manoeuvre, so if you make the amphibious ships faster you need a faster escort.

 

[Martes]

the escort needs to be faster than the force it's escorting to be able to manoeuvre, so if you make the amphibious ships faster you need a faster escort.

There was this requirement for the carriers and their escorts to have similar speeds in order to precisely maneuver together, as a squadron, so I thought it should've been natural for larger amphibious units as well, especially on long and potentially opposed transits - unless there is a very serious reason not to.

But indeed, it's probably either an integrated dock or a fast hull.