Necessary to Fill Prop Aperture

I have a 1962 Alberg-design Pearson Triton sailboat. Long ago I removed the inboard engine, opting for an outboard hung on the transom. I built a new rudder at the same time, with the leading edge straight (no cut-out for a prop). I have the boat out of the water for some work and was thinking about filling in the cut-out in the hull that formed half of the prop aperture (as many people do who remove their inboards, prop shaft, and propeller). However, if there's no reason to do this, I can spend my time and money on other projects.

So the question is: how much drag/turbulence/etc. is created with this cut-out in the hull (and a rudder with a straight leading edge)? Would I see any improvement in speed or balance with the cut-out filled in?

Thanks in advance for your suggestions/advice/recommendations.

Jay

 

Depends.. how well the cut-out is done originally. Filling one will decrease form drag but increase wetted surface so it's trade ofs. However most boats would benefit of filling. Make a deadwood plug and see it yourself. You can always take it of if not happy...

 

Aperture

I agree with Teddy, put in a removable plug and try it out. It's quite advantageous to fill the aperture and fair the stern post to the rudder. Remember that on most points of sail, but especially hard on the wind, pressure builds on the lee side, moving aft towards the rudder. If it finds a place to scoot to windward in the aperture it creates turbulence and makes the rudder less effective due to less pressure differential. On a fiberglass boat I would probably grind the area, fit a piece of closed cell foam and glass it into place with cloth, mat and epoxy resin, fair and fill, then paint with Interprotect 2000 primer then 3000. A tight rounded fit of rudder to stern post really does help. When I did this to my wooden modified SPRAY to get rid of the 1" gap the difference in light air performance was very noticeable, especially when I put the tiller over trying to tack in a 3 knot breeze. Before she would stall, now she just keeps turning. See the SPRAY thread page 5 for a pic of the boat BERTIE.