(Answered) UMUs, PSRs and Battlemech high-diving

[Feign]

This really ought to be a very simple and straightforward question, but it's causing debate...  If a Mech that mounts UMUs enters Depth 2+ water directly (via an external jump pack, drop parachute, pushed right off a cliff, etc.) does it sink to the bottom and make a PSR for entering water, or does it stay near the surface thanks to its UMU equipment, simply ending its movement?

The TacOps rules stated for the UMU itself (p295) seem to indicate that a PSR is required for entering Depth 1 water because walking movement was used and UMU MP expressly can't be used in Depth 1, but these rules never mention entering right into Depth 2+ water by other means.

In the rules for fighting aboard ships (p157 being the first page mentioning Mech UMUs) it mentions that UMU-equipped Mechs that fall off a large naval vessel are placed at Depth 2 (I think?  The wording there is a bit fuzzy) and they take no falling damage and no additional PSRs.

The latter part indicates (well, former part, by page number) that stopping at Depth 2 is an automatic function of the UMU and doesn't require UMU MP to be spent, but that's never explicitly stated to be the case when non-UMU MP are deliberately spent to get there.

[Feign]

Since it's been a while I'm going ahead and updating with what we house ruled at the time.  Since the ballasts of the UMUs would have to be empty when the mech hits the water, it would be forced to remain on the surface until it can spend UMU MPs to sink.

Later on, it came up that a player had a mech with both a Mechanical Jump Booster and UMUs, and it was house ruled that he couldn't use the MJB unless he was at the lowest elevation of the water hex, and that he couldn't land in anything but the lowest elevation, as emptying the ballasts would require UMU MP.

I don't know if we got any of that right, but if so it might need a bit of errata.

[Feign]

one-and-a-half month bump.  Saw a wave of other questions answered, and this one remains.

I guess I really do ask the tough stuff. #P

[Feign]

Well, I noticed a different UMU question answered, so it's likely a subject you're researching at the moment.  Seeing as how this is about to fall off the first page without an answer, I figure this might deserve a bump after six months.

[Xotl]

Thanks for your patience on this one.

Specialized Attacks (p. 157)
First paragraph on the page

If the ’Mech has UMU MP, however, it does not take falling damage but is simply placed in the adjacent hex at a depth equal to the deck of the unit off of which it fell.
Change to:
If the ’Mech has UMU MP, however, it does not take automatically falling damage but is simply placed in the water hex at a depth equal to the deck of the unit off of which it fell, without a Piloting Skill Roll being required for entering water. If the water is insufficiently deep, place the ’Mech at the bottom of the hex and assign falling damage for striking the bottom of a water hex as normal.