On bigger boats, do you ever put a 3rd servo to adjust the relationship between the Jib and Main? I’m thinking of the two strings through a pully on the sail “winch” servo, and to opposite ends of another servo arm.

Not in my Nirvana. It scarcely has space for the two servos it has;)

A jib trim is considered required on most serious racing models. I install them on the Soling 50 which I consider to be a “small” sized model. Some classes do not allow them, but other than that you will find them to be quite common.

Typical installation is a more powerful than your standard servo, I personally prefer one with metal gears… not because of the load the servo has to pull on the jib… that is actually fairly light… but the load the sail puts back onto the servo which is just maintaining position.

It doesn’t take much of an arm, not much travel is needed… the way I install the jib trim is to run a line from the 3rd servo arm up towards the bow and through a single block and back to a point just forward of the jibsheet exit point in the deck. At the end of this line I attach another single block. The actual jib sheet comes off the winch and passes through this block and then exits the deck. As I adust servo #3, I get 2x purchase on the jibsheet and adjust it independently of the main.

The most important thing for me, is the transmitter be correct for this. I refuse to use a mangled or re-worked transmitter, so I either use the Hitech Ranger III or the Hitech Zebra 3-channel either of which has the 3rd channel mounted seperately on top of the transmitter in the form of either a knob or slider. This means that I can sail my model as I would any normal 2 channel boat, and reach up and trim the slot anytime I like without affecting any of the other sticks/gimbals on the transmitter. Otherwise, if I am going for something with more than 3 channels such as a Santa Barbara, I use a 6 channel and setup the landing gear (essentially up/down) for my backstay (tight/loose) and the 5th channel for boomvang.