hi there
if this works - here is a quick scribble of how the jib works.
One servo (we will call it the hook servo) the cable comes from the hook servo drum, over the top pulley and out over to the pulley on the end of the jib. It goes straight down to the end of the hook.
The 2nd servo (we will call it the jib servo) the cable comes up, out off the drum, over the top of a 2nd pulley on the top. Then out over to the jib around the 2nd pulley and back towards the first pulley and is made fast to a securing point.
I do hope that is clear.
Now, a couple of things to consider (which I myself found out). With these types of vessel, we have to be very careful of the weight we lift. Very small weight. We are going into grams. The reason for this is, as we swing the jib out over from the vessel - you will see that the vessel will begin to tilt - and it is alarmingly in some cases. Sometimes even moving the jib of the crane off centre of the vessel will cause the vessel to list - so I strongly advise sticking your model in a bath/test tank and play around with the crane before actually committing the model to open water.
I have an idea, which I may experiment - whereas using a 2nd servo in the vessel with a counter-weight on it. The counter-weight will move in an opposite direction to the crane jib. Thus counteracting the list. As I say, this is in the experimental stage, don't know if it will work or not.