[QUOTE=ombugge;181682]There are the full amount of power available for straight towing. If you put ALL available power on the propeller you get X BP, if you divert some to the thrusers and winch you get Y BP. The larger the thrusters and the smaller the available total power the larger % is lost to the propellers, thus the BP.
The less pull you have available to maintain tension in the wire the less control you have to maintain relative position, or keeping the wire/chain off the seabed in this case. You can maintain heading but still be push off sideways from you intended track.
My experience is not from the boats, but from the rig/barge side as Towmaster/Rigmover. I have sometimes had to hook up a second boat on the bow of the AHT to get the right trajectory. (Or use a J-hook in the middle of the chain, as was done in the BD case)
In case somebody wonder, I have anchored rigs in up to 2200 m. WD and Drillships rated for 600 ft. in up to 1800 ft., using insert wires.[/QUOTE]
Vessels with shaft generators are always variable pitch wheels, with constant RPM shafts (of course needed for a shaft generator to work). If there is limiting, it will be in terms of pitch reduction, or pitch limiting function on main wheels (as you mentioned). In most cases, under normal conditions you will not see it. On the bigger vessels,32,000HP class, you can have your thrusters near 100%, and picking up +350 tons on the winch while pulling near 300 tons of bollard pull without any issue, heat will be an issue in summer time before anything. Most vessels are not near as capable, but that does not mean you experience any type of bollard pull capability loss every time using thrusters & winches while pulling. The curve is exponential, so it will be in the higher pitch range +80% if you see any pitch limitation, but normally by then, you are in a position where the winch is not needed, bow thrust still required - but nothing in the stern. You are basically on a dead pull and rudder power is pretty high at that point, and since you are high in the exponential curve, 5% means a lot, so 5% extra on one main versus the other can essentially act like a bow thruster to a certain extent.