I recently acquired a sailboat and noticed a small protrusion under the starboard side of the hull in front of the keel. Does anyone know what this is?

The boat is a 1976 hunter 25. I have not put it in the water yet. The head is about directly above in the cabin. The toilet was replaced prior to me acquiring the boat so there is a porta toilet there now, no plumbing.

The hull is fiberglass. The top part looks as if it's wood, and the bottom I can't really tell. There is only one of those protrusions.

Here are some pictures:

Port side view with protruding feature and keel in behind it: Port side view with protruding feature and Keel in behind it

Side view of hull with protruding feature: side view of hull with protruding feature

View from bottom of hull with protruding feature: view from bottom of hull with protruding feature


2 Answers 2


Depth sounder transducer

This is the transducer for your depth sounder. You should be able to find a cable running from that transducer inside the vessel to the depth sounder display (assuming it's operational).

Given that this is installed directly below the head it would appear that a through-hull that had probably formerly been an intake for the head was repurposed. I would estimate that the installer used that wooden block to position the transducer to point straight down in order to get an accurate depth reading.

Here's a picture of a similar piece of equipment:Cruz-Pro D60 transducer and cable

  • 1
    thats it. Its a transducer with wooden fairing block. I looked form the inside and saw the transducer and wiring. Thanks for your help!
    – mvt3641
    Commented Nov 8, 2018 at 1:02

It used to be the direct discharge for the head into the water. Here is a blog about a boat similar to yours, asking if it is illegal

It was not unusual in the era of your boats manufacture to discharge raw sewage into the water.

Legality varies, but currently it is NOT a popular choice.

Adding a holding tank to old boats is difficult, a common solution is to swap in a porta toilet (toilet and holding tank combined).

If you are doing significant repairs, you may want to remove 'protrusion' and re-fiberglass to make that area smooth.

  • Given the position, this was more likely an intake than discharge, but sewage discharge regulations aren't really relevant to the question at hand.
    – Tuorg
    Commented Nov 6, 2018 at 15:53
  • @Tuorg I removed the regulations from my answer. I like your answer. Commented Nov 6, 2018 at 18:30
  • thanks. Don't get me started on overboard discharge regulations! ;)
    – Tuorg
    Commented Nov 7, 2018 at 0:06

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