Since the I20 has canted hulls, should the rudders be at the same canting angle? Or, be plumb to the whole platform?

If they should be canted, do you measure alignment, toe-in or toe-out the same way?

The rudders are parallel to each other and are perpendicular to the cross bar, on a stock boat.

I didn't think that the 20 had canted hulls, but I am having the same thoughts with my infusion which certainly has canted hulls.
When you are measuring the difference between the front and back edges of the rudders, it is important to imagine a line across the blades which is parallel to the waterline. Then measure at either end of this line. This is true for all cants of hull.
it always amazed me how good the tiny rudders on the 20 were. I used to run with a little toe in. What setting are you aiming for

Paul

I20 hulls are definitely canted...but I thought the rudders were also in the plane of the hull (i.e. canted). I didn't realize the rudders were plumb....measuring tonight.

My inter 17 has canted hulls. The Rudders are plumb. The plates are in the plane of the hull.

Chris,

I replaced the rubber snubbers in our rudder system this evening, shortened the tiller bar (since only about 3/16" of rubber was exposed between the tiller and the rudder arm), and realigned things. I can tell you that this boat is not modified in the sterns but the rudders are not square with each other and are canted with the hulls.

Alignment was a little frustrating. We tried taking measurements up high (staying as straight back as possible) and then down low. We couldn't get anything to come out right with accuracy better than 1/8". Frustrated, I slid the beach wheels forward of the daggerboards, dropped the boards in (had a friend put some weight on the bow) and sighted the rudders down the hulls using the daggerboards as a reference. We then came back and measured between the rudders just above the lower gudgeon and then back to where the rudder shape tapers down to the trailing edge. It measured perfect there, it looked right, so we set the screws.

Thanks for the help. Two of you have suggested that your sterns are not modified. What modifications are you referring to? How would I be able to tell?

What has caused me to ask this question is that I have one rudder that is in the plane of the hull and one that is plumb. The NACRA owner mannual does not indicate. The boat is relatively fast, so I am being careful about changing anything.

There is a good bit of hum coming from the leeward rudders at certain speeds, which I believe is because the trailing edge was filled to knife like edge instead of the flat. Does plumb-ness or toe-in induce any hum?

Jake, By “rubber snubbers” so I sure of what you mean, you mean the part that connects the tiller cross bar to the tiller arms and provides the flex to allow the system to be steered? Can those rubber snubbers be turned a quarter turn and be redrilled and reused if the current alignment is off? Does an adjustable system like the 6.0 exist? Did you check the alignment with the boat rigged and tensioned? Is this necessary?

Thanks again,

I'm not sure - I assumed he meant that some people would remount their rudders so they would cant with the hull.

I would think the rudders would be more efficient (very slightly) if they were plumb with each other - how did you measure "plumb with the hull"?
Dunno -I have yet to find a reliable solution to silencing the humm

Boat was rigged and tensioned - but I don't think it matters for the rudders. There's very little side stress from rigging pressure on the hulls behind the main beam. I really doubt the rudder area would be affected in any finely measureable amount. As far as an adjustable setup goes, you could probably find a way to retrofit the 6.0 style adjuster somehow...but there's really no need. Once you have set the rubber pivots up correctly, there is no need to adjust them again. Even on the 6.0 if you aligned the rudders (and the adjuster hadn't slipped) you didn't need to do anything else.

I'll measure the amount of rake in the rudders and compare it to the hull tonight - my interest is peaked.

Jake, my rudders have never hummed (although my daggarboards sure did around 16 kts and again at 22 kts GPS)

I opted to take the last 1/16" and file down one side, leaving the other as is. Not knife-edge sharp, but flat edge at the back.

My thinking is that this small fairing now makes the shape slightly asymmetrical, and therefore less likely to produce any harmonic vibration.

I've tried to do the same with the daggars, with limited success (keep getting nicks in the trailing edge from where it rubs the daggar-well when we hit stuff)

Of course, I could just be some kook sailor who is lucky enough to not have his rudders hum..

COULD be?!?!?!?!?

Went out this morning and looked, the rudders are definitely aligned with the hulls and not the crossbar, (I am getting old is my only excuse, I remembered that they were not square looking, just got it backwards as to what they were square to) Jake is the man, go with that.

I don't know about that....obsesive compulsive maybe...