While I'm not sure, something that popped in my head is that it looks like it could be an early avalanche airbag system. See this history of airbags page for a picture of (one of) the first system made by Josef Hohenester. The hoops you see in the picture you have could be Bowden Cable post expansion.
Unless there is a certain terminology for "backside" plugs, this is a plug (or as I know it: a wobbler. No idea which term is more commonly used around where you live).
I had to bust out my detective hat and pipe to find information on these ones, but I stumbled upon this: an article about this bait
They are(?)/were made by bomber, and ...
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 ...
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 ...
Edit: It is a McKinley. The difference is the padded hip belt vs the frame extending to the side of the hips. The backpack in OPs picture features the padded hip belt.
It is the D2 or McKinley. I can not spot a difference in the picture and description below. I think they revamped the pack ...
Type Cascade (D) 1 from the second half of the 70ies. I bought mine (complete khaki) in 1980. The cascade (D) 2 had larger side pockets and a large square sized leather "badge" with the JS logo sewed on the lower bag. In 1980 I spent approx. 300, - Deutsche Mark in Germany for the Cascade 1 which was quite a lot at that time.
B.t.w. I found the same one as ...
In the absence of any overwhelming evidence to the contrary, I'm obligated to go with the last bit of information I was ab le to glean from the manufacturer:
Thank you for sending the pictures. I've had a couple of people here look at it and they are still saying it is a Cascade. However, the only way we can be 100% sure is if the pack is sent ...
Not sure if this is still important, but those are the Standard Hanwag Trapper GTX, they are out of production, but some shops still have a few sizes in stock. I just ordered some here: https://www.recon-company.com/hanwag-trapper-gtx/3236
Hope that helps...
That is a cog,
A cog is a type of ship that first appeared in the 10th century, and was widely used from around the 12th century on. Cogs were clinker-built, generally of oak, which was an abundant timber in the Baltic region of Prussia. This vessel was fitted with a single mast and a square-rigged single sail.
The name of it was a bomber. Back in the 50s. Very good old lure back then. Or plug. Have used them often in younger years. They were a good fish catcher & have been for years. It seems lures work for a while then quit. As fish get use to seeing them. The fish had not seen that type of lure before plug. That is not a real old one as it uses hook eyes ...