Potential answers to two previous generic questions:
First of all, how to carry out the approach. One method (shallow angle) has been described and it is the usual method, especially for two ships of the same class. There is a second method, however, used when dealing with two ships that are affected differently by the winds - and you are manoeuvering on a windy day. It's called "crossing the T". Basically, you use it when towing a ship that goes beam-to the wind when stopped - which is the case of PROTECTEUR - by coming with the towing ship steaming slowly up-wind at 90 degrees to the stopped ship going just off her bow. Lines are passed from amidship, so that hopefully you are already heaving in the heavy messenger by the time the stern of the towing ship lines up with the stopped ship. In the present case if there was non-negligible wind, since the IROs have a lot of sail area, that would have been my choice. In such cases, however - you must make absolutely certain that the stopped ship has NO FORWARD MOMENTUM at all. I think this is what happened here. PRO still had some way on - maybe 1/4 or 1/2 knot and everybody noticed too late to do something about it. Not necessarily a big mistake as it is extremely difficult to note such movement in any kind of sea.
Second one, generic question concerning "stern push": As a generic, it is hard to answer this question because it depends on many factor. When a ship puts its helm over, it pivots around its pivot point. portions of the ship forward of this point cut into the turn, while the portions aft skid out of it. Going forward, the pivot point is roughly 1/3 of the way from the stem. So for example a 300 ft ship that would have a 30 degrees change of direction in a few seconds after putting the helm over would see its stern skid out by sin 30 degrees X 200 feet = 100 feet minus the amount that the pivot point itself has come in to the turn in relation to the original course, say 40 feet, would give you a "skid" of 60 feet. All ships keep tables of their turning data for navigation purposes so these type of things can be calculated if need be.
All this however for very slow speeds, works out for a single screw-single rudder ship or a standard twin screw-twin rudder ship. The IRO's aren't such ship. They have twin variable pitch screws and single central rudder. At very low speeds, such as must have been the case here, their screws are feathered but still turning. As a result they act like parachutes and drag down on the ship. Also as a result, there is little flow over the rudder at these speeds and they provide little help in steering. All this, plus the constantly varying drag of the port and starboard screws when the ships are rolling in any kind of seas, make slow ship handling an IRO at sea a very difficult and demanding task for the handler.
