Holes in rudder?

I've just constructed a new rudder for my 18' Fenwick Williams catboat and am considering adding some toe-holes to use for re-boarding should I ever fall overboard. Now, these catboat rudders are hardly a high-tech foil shape and Chinese junks have had holes in rudders for thousands of years and seem to steer just fine. The holes will be 4" wide and 2" high, two below the waterline and one above. Rudder is approximately 3'x3'.
I'd like to hear some input on this.

 

I would try to shape the front side of each hole to an edge and round the back side of each hole.
I think they've built some of these boats at http://www.landingschool.edu/, so they're a possible source of advice.

 

Thanks Stephen, I had planned on doing just that as well as reducing the radius on the trailing edge of the rudder. I'm thinking a sharper edge may add a bit of response.

 

there are a lot of factors that affect rudder performance, but in general you will likely increase the drag of the rudder and reduce its effectiveness.

If the rudder operates in a bad and disrupted flow field behind the hull, it may not make much difference.

It seems to me costly (in terms of drag) to put holes in rudder just in case you might need them. how about one hole above the water line, and a trailing edge step (instead of the TE making a sweep up the back, put a short section of horizontal TE that you can use as a step).

with the combo of the two you will still be able to use the rudder to get back in the boat and not affect the rudder performance much.

 

Holes in rudders are usually there for a reason,--to get the shaft out without removing the rudder. There is little else reason

 

It makes no sense to make holes in the rudder if climbing aboard in emergencies is the goal. Better to fashion a rope ladder and have it stowed where you can reach it. In rough conditions, a rudder is usually swinging out of control------ not the best thing to be hanging onto when you need to be climbing into the boat.

 

I second this.
Besides, it's a shallow barn-door rudder with surely not an outstanding performance and putting holes on it might further reduce it's steering authority. Think of a 25-30 degree heel situation.
Cheers

 

You could put a step at the bottom that may even enhance its performance and just to even it up one more at the top wich may or may not enhance performance but will not make it worse.

You could put steps on the trailing edge all the way up.

Holes --no

As said if this is to climb out of the water a ladder is traditional.

 

Guys, thanks for the input but my question is not about man overboard technique but about fenestration and its effect on steering. As Stephen mentioned above, little things like keeping the forward edge of the hole square while rounding the aft will help with the additional drag, but will the holes actually improve steering as the Chinese thought? Should the holes be rectangular, round, oval, teardrop shaped? These barndoor rudders cannot be compared to modern shapes. Although my rudder is tapered I don't think it really makes much difference and doubt surface tension (correct term?) plays into it either. Considering the leading edge already has a large aperture for the 3 bladed prop I personally don't think these little holes will make the least bit of difference with all the turbulence these rudders are already operating in.

 

I don't think fenestration will cause bad steering. I do however believe you should think twice before fenestrating while steering and especially in public, which may be illegal. I won't even mention blindness.

 

It will cause a fair amount of turbulence and make steering poorer. A better system would be to cut notches in the trailing edge.

 

I think that's an interesting research project for someone, but after reading the other responses I'm with the skeptics until the fluid dynamic details can be fully explored. I also want to make clear that, for any trailing edge, whether it be deadwood in front of a prop, the trailing edge of a keel, or the front of the apertures under discussion, my advice is to taper it to as narrow an edge as can be made strong (not vulnerable to damage). The notion that the deadwood in front of a prop aperture can be left wide & square is a myth. Tapering it to an edge (angular, not rounded) will always improve efficiency.

There may be literature on slotted foils applicable to your interest in this subject. You might also poke around images and literature on NACA ducts. But for all the reasons stated by others I'm not loving the idea of doing this to your catboat.

 

Was it not in a Marchai book a future sail boat was illustrated with perforated sails?
dive bombers had flaps perforated, chinese had diamond holes in the rudder etc
without starting pc, grabbing book or checking previous theads I recall it had to do with
opposite side boundery layer control, than again, why dont we all have holes
takes reading up but watching a movie too, only saying there is more to it

 

gonzo, while I agree with your idea that notches in the trailing edge would be a better hydrodynamic solution (but not ergonomic). I'm not buying your first sentence - based on what? Have you ever sailed a traditional catboat? Got any facts to back it up - that's what I would like to see- not trying to be confrontational- just interested

 

Thanks, yipster- that's where I wanted to go with this! Now I would like to hear from some old catboat sailors as well as someone who has possibly studied this sort of hydrodynamic interaction