Cat sailors seem to fall into two camps on the issue of rudder toe-in. Some advocate a small amount of toe-in and others believe parallel is better. I'm a parallel guy simply because nobody has ever been able to explain to me why toe-in is benifital. I'm listening toe-in guys.

With toe-in and a bit of weather helm, the windward rudder runs straight while the leeward one carries load. This was helpful on both of my Nacras (5.O and 5.5u) with their large rudders, but parallel is working better on the Prindle 19.
sail fast

On a 16 with the asymmetric hull, the toe-in allows the leeward rudder to "smooth" the flow coming off the curve of the inside hull. When the windward hull is flying, the windward rudder has little effect.
On symmetric board boats, I believe that a very small amount of toe-in "preloads" the rudders so that they don't flop around as much. Given that almost all rudder systems have some slack; two perfectly parallel rudders would tend to "hunt" slightly, whereas a very slight angle of attack would tend to keep them from moving. I've been told that most new cars run very little toe-in (definitely less than 10 years ago) for less tire scrub, less drag, better mileage. However, IMO, they are a little "twitchier" on the road. From that standpoint, maybe a little rudder toe-in adds some "feel" even if does add drag. 1/8" total toe-in is only 1/16" per rudder; over a 12" chord works out that each rudder is at a 2.4 degree angle of attack. I'll leave it to someone else to figure out the extra drag caused by that angle. Most boats seem to have a little weather helm, anyway; even perfectly straight rudders might see that angle or more upwind.
Chris

When sheeting in the mainsail tight on some cats, I have found the bows tow in, and the sterns tow out.
Perhaps toeing in the rudders compensates for the sterns towing out?
Older boats flex more, so the older the boat, the more rudder 'toe in' required?
Perhaps someone could field measure the delta.

It's unlikely that the sterns actually tow out unless there is play in the beam to hull connection. The back beam is too close to the transom for that. Although pressure from the mainsheet bending the beam up, could possibly pull the transoms closer together slightly.
Is it toe or tow?
If you had a boat that didn't flex at all with a rudder system that had zero play then parallel rudders may work best.
if you can adjust you rudder alignment whilst on the water, just take the boat up in to irons adjust 'em and sail on various points of sail. Go by feel to find the sweet spot.

We put a small amount of toe in on our boats, the reason we do this is that when you are sailing upwind, you will usually have an amount of weatherhelm, and so the rudders are travelling through the water pointing slightly to weather. If you have parallel rudders, and fly a hull, the windward rudder comes out, then when it re-enters the water it is not travelling straight, the result is usually that the rudder stalls, if have have a degree of toe-in this stops this.

regards

john p

>It's unlikely that the sterns actually tow out unless there is play in the beam to hull connection. The back beam is too close to the transom for that.<

Sounds like you never have measured your boat?
It has more to do with class of boat. Every class boat is different, etc.
I have measured '70s vintage Tornados, a '90s H20, a '80s TheMightyHobie18, & '70s H16.
Since the beam is so close to the stern, it is not linear proportional.
Torsion comes into play too, and the beams flex/twist a miniscule, etc.
The toe measurements also vary between the top of the rudder and bottom
due to some twist coming from somewhere as the main is sheeted in.
I never measured each boat to find out why, as the deltas as so small.

Hi John,
You have it right! Boats sail faster to windward with the rudders loaded, carrying some of the side force equal and opposite to the sail side force. The windward rudder in this situation which in moving into and out of the water vertically as the windward hull moves up and down will stall if it has the same angle of attack as the leeward rudder which is totally submerged. Reduce the angle of attack of the windward rudder a couple of degrees, rudder toe-in, and the windward rudder does not stall as it moves in and out of the water vertically and as the boat travels ahead.
Good Sailing,
Bill

Hi, Bill,
Nice to see you over here in "nice country" on the new forum. We all need your expert input over here.

As you say Bill boats work better to windward if the rudder is used as an additional centreboard, this is why the Tornados all changed to very raked rigs during the late 90s, something you used years ago on your boats with the forward placed daggerboards.

regards


john

Ok Bill and John...stalling as a rudder reenters the water is an explanation I can understand. I wonder however if this is more an issue for high performance boats (I sail an H17) and isn't light air performance compromised....Thanks Dan

Dan, the idea is that the windward rudder is running parallel to the direction of travel, so minimum drag, the leeward rudder is pointing high, giving you lift and balancing the weather helm, this will be the same in all wind strengths upwind, where parallel rudders would be a bit quicker is if you are sailing with no weather helm.

john