Will I need an extra mounting tube for Y&B

Sven, I'm getting ready to order a Y&B. Think I may be on the edge of needing an extra mounting tube. Top of transom to water at rest is about 30". Transom type 3 with approximately 16 degree angle, so it's about 8" from vertical at top of transom. What's your thoughts?

For the transom described in the question the single tube that is included with Y&B standard should be enough.
The Y&B vane base is about 200mm/8" long so the pendulum rudder will well behind the rear of the transom.

As long as the rudder does not stick out behind the transom, that distance should suffice.
If you like to examine these kinds of questions before contacting us, there is a drawing with dimensions in the download section of the website.