First set up the rudders so they are solid in the rudder boxes and are held down firmly with the tip about 15mm ahead of the line of the pintles. See if you can pull the tip of the rudder back (it should be very hard to move).
Get a piece of aluminium right-angle extrusion from your hardware store - they are about 2.1 m long I think and only 10mm x 10mm cross-section is all you need (that's not rust - it's mud from the floodwaters).
![[Linked Image]](http://www.catsailor.com/bb_files/114277-rudder_check.jpg)
File a notch near one end. Prop up the back of your boat so you can put the rudders down. Fit the notch over the front of one rudder level with the bottom of the hull. Mark where it touches the other rudder and file another notch in that spot. Keep checking while you file to make sure that when you are finished the notches fit perfectly over the leading edges of the rudders.
Now put the rod on the rear edges of the rudders - again level with the bottom of the hull. If the notches don't fit you need to adjust the tiller bar. Adjust it till the notches fit. I would say "perfectly parallel" is the only setting to go for.
It's important to check front and back of the rudders at the SAME height otherwise any slight error in the vertical alignment will give you a wrong reading.
I should mention that canted rudders are illegal on Mosquitos. They should line up with the centreboards. It's just that very few rudders are perfectly vertical.
Before doing all this it's a good idea to check your hulls are parallel because if you have to fix that, you will have to do the rudders again. It's best to check the hulls with rig tension on - especially if you are using a sloop bridle on an older boat.