This is a nice retrofit for early boats which used a plastic through hull fitting and a piece of rubber flap over the port. The rubber flaps have long ago disappeared. This leaves the engine exposed to water intrusion into the cylinders in a following sea.

Boats that had 1-5/8" diameter exhaust hose and fittings with the rubber flap configuration:
• Catalina 25
• Catalina 27 (see installation tips under "Warnings & Notes")
• Catalina 30
• Catalina 34 (early)
• Catalina 36 (early)
• Catalina 38

1) Will only work properly on a boat with a vertical transom. Will not work on a boat where the exhaust exits through the hull where the surface cannot be vertical.

2) If you own a Catalina 27, you know how difficult it is to gain access to the transom where the exhaust hose is connected to the exhaust outlet. We recommend you install the inspection port found under "May we also suggest" below. Install it in the horizontal surface at the bottom of the lazarette, just above the exhaust outlet. It will provide easy access to the exhaust through hull, hose clamps, and the ability to check for leaks in the future.

3) These are hand made with a welded spot to prevent the flap from over rotating and inadvertently getting stuck in the up position. When the engine is running the exhaust has has enough force to open the flap as is required and the feature prevents any water from entering the system from a rogue wave or a following sea.