Rudder flaps

[monocerosin]

1979 Hunter 37c.
There were broken remnants of rudder flaps when we hauled out that we threw away. Since then I have filled the holes and i am reconsidering if I want to try to fabricate flaps or just leave the holes filled and not mess with it.
I have read about cavitation and I tried to find a thread here talking about it with no luck.
Am I fine to leave them off?
Thanks!

 

[Johnb]

The sky will not fall if you don't replace the flaps, but if you want to preserve the original design this is what they look like. I still have them.

 

[shemandr]

Looks like a nice smooth bottom.
For sailboat speeds I would be surprised if cavitation in front or on top of the rudder is a significant increase in drag.

 

[monocerosin]

Looks like a nice smooth bottom.
For sailboat speeds I would be surprised if cavitation in front or on top of the rudder is a significant increase in drag.

I just don't like the idea of more holes in awkward places that will eventually leak. Thanks for the 'props'!

 

[Jim Legere]

On my old H37C, the glass was thick where the flaps attached - at least 1/2". I redid the screw holes, using a 10-24 bottoming tap and just used short SS machine screws (with a dab of silicone as 'Loctite') to hold the flaps on. I never had any issues and never worried about leaks because the holes didn't penetrate through the glass. I suspect the flaps are worthwhile, otherwise John Cherubini wouldn't have specified them in the design. It would have cost Hunter some money to incorporate the recess for the flaps in the molds and to make and install the flaps, so they must have thought it worthwhile too

 

[gockleyd]

What are the flaps made from? Mine never had them and I always wondered what that was for

 

[Marmalade]

Different boat, but same application.
On a Chaser 33, I used 0.010" mylar sheet, with a 1" wide stainless strip at the fasteners. Worked great, was thin, and the water kept it tight against the rudder, even when turning.
Would get 2-3years on a set, but after that, the yard would hit them hard with the power-washer and 1 would eventually crack.

I made them longer than the rubber version probably would have been, but I felt this allowed the water flow to hold them on a more fair-shape.

YMMV

first pic, rudder straight

Second pic, rudder turned full-stop

 

[sandpiper10471]

I made my flaps from a couple of layers of fiberglass wetted out with polyester. Thin and flexible. Did that thirteen years ago and still going.