Indeed.
While on DP with divers in the water you are definitely not able to move much, but that MAY involve another rule? (Flag A hoisted)
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Not sure what the debate is here. If due to the nature of your work you are restricted in your ability to maneuver, you are by definition RAM. So if you’re just hanging around off a rig doing essentially nothing but sitting there you wouldn’t be RAM. If you are holding position in a specific location because of the work your vessel is performing, the you’d be RAM.
Being in DP mode or not does not necessarily make a vessel RAM or not.
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It depends upon what is meant here by “actively working”
Are DP vessels considered RAM while they are actively working inside the 500M zone around platforms?
A PSV next a rig in DP getting lifts taking off it (with no simultaneous hose work) is probably only RAM when the crane hook is attached to the lift until the lift is clear of the vessel, in between lifts when they are waiting for the crane to come back and get another lift they’re not RAM.
I hope if you are next to a platform you refrain from using your sound signals, cause they will shut that down real quick.
That doesn’t sound practical to me. You’d wear out the guy hauling the day shapes up and down.
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What guy? Just kidding but in my experience if your not on the back deck involved with cargo, driving the boat or in the fun house you’re asleep .
As for sound signals the rig is doing just fine sounding the Morse code signal as shown on the chart in restricted visibility and any vessel that is working the rig within the 500 metre limits should stay mute and merge. The vessel servicing the rig is within an area prohibited to other vessels for navigation anyway.
I guess we can debate this until the cows come home, and probably rightfully so because there isn’t really a perfectly defined explanation of what “actively working” or “nature of work” is. I’d say if you’re holding a position for a reason beyond killing time, you’re RAM, underway making way.
Rule 27 (d) covers the shapes that should be displayed by the barge while engaged in dredging during the day. At night if the barge is moored to the shore and no other obstruction exists it does not require any lights, but if there is a lot of traffic then a single all round white light would be a CYA measure.
There is some confusion here. If a PSV is working a platform then it is engaged in an underway replenishment and it doesn’t matter where the hook or hose is it is restricted in its ability to manoeuvre.
The rule applies to more than the gray navy.
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The vessel is “Underway, but not making way” while in stationary DP.
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The state of “being in DP” doesn’t make the vessel RAM, it’s the nature of the work that makes it so. Alongside a rig, you are RAM.
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There is theory and reality, in practical sense a PSV next a platform doing supply work will almost never have to do collision avoidance with another vessel, so it never usually actually matters if they’re technically RAM or not.
If a vessel in DP moves at 0.1 knot technically it is making way, it is only underway but not making way when it is a 0.0 knots.
No need to parse this too closely. From the COLREGS restricted is:
ii) a vessel engaged in replenishment or transferring persons, provisions or cargo while underway;
So strictly speaking the lights / shapes maybe could be justified but as a practical matter transferring cargo from a single crane the vessel still can and should move to avoid a collision.
Perhaps in the event of a collision the court could find fault for not showing the RAM lights/shapes but again as a practical matter once it becomes apparent the other vessel is not taking action it’s going to be whatever it takes to get clear.
Technically wouldn’t it be underway and MAKING way? If they were not making way, they would be drifting with the wind/current. By holding the position they are in fact driving into the elements, therefore making way (albeit at 0.1 STW maybe).
If SOG is 0.0, but STW is 0.3, I believe the vessel is making way.
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That would be my understanding and I would definitely move. Back when I was with “grey funnel” we on occasion had to alter course during underway replenishment for someone who didn’t follow the rules.
What is the feeling if the rig told you to take one for the team. 
Here’s another interesting one I came across:
is a DP drilling unit that is connected to the seabed by the marine riser and or drill pipe underway or not? There are differing opinions on this subject based on individual company and regulatory philosophies. It is Diamond Offshore’s belief that a DP drilling unit is “underway but not making way” when in the drilling mode and “underway making way” when changing location.
The colregs were written when offshore vessels and DP didn’t exist, so there are arguments and debates people have now where the colregs are aren’t very clear.
A self propelled barge is a vessel. A barge without self propulsion is a barge. How about a barge self propelled by kedging an anchor. Is it a vessel or a barge? Either way, is it under way or is it at anchor?
Dredges used in sheltered waters that are barges that move by kedging anchors are common in waterways and in harbours. They should display the lights and day shapes proscribed in rule 27 (d). Even though anchors are being used the vessel does not exhibit the lights or shapes of a vessel at anchor. A dredge underway and making way displays the lights of a power driven vessel in addition of the lights required under rule 27.
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