Ventilation caused by through hull?

[simple]

Over the winter I installed a through hull fitting on my 1810. The style of the fitting on the underside of the hull is what I've been calling a "clam shell" It has kind of a scoop to it. It was installed through a fiber glassed plywood section in the bilge. Which I'm certain is factory installed. On it also sits the bilge pump. This brought the clam shell roughly about 2 inches off centerline of the boat.
Last weekend was the first run of the year. On the way in, the sea when beam and I was getting what I believe is called ventilation. Typically the engine will run at a steady RPM. While this was occurring, the RPM's where jumping around (up and then back to where it should be) by as much as 5,000 RPM and I felt a loss of momentum. I also believe I could hear the makings of air being sucked (like when you run a sump pump without enough water).
Has anyone ever heard of this occurring? Solutions?
Thanks a lot.

 

[Outta Here]

You cannot install anything to interfere with the water flow directlly in front of motor. Can also cause motor overheating.

Parker installs thruhulls about a foot off center. You can contact Parker and they will advise as to location. You might salvage the hole by installing a tilted element Airmar (assuming you could use a upgrade transducer). To check, try running a screw thru a fender washer thru hull to a block of wood and nut on back. Run boat and check for cavitation.