From what I can see, it looks as if the strut's flange (plate section that gets bolted to the hull) was covered over with fairing putty at some point. A good 3-5mm of it. Along with loads of the stuff troweled onto the hull as well. And that now the putty is cracking & coming adrift, starting in the area around & on top of your strut.
You'll need to scrape & chip the stuff off in the area around, & over the strut's flange so that you can ascertain the health
of the strut as well as it's fasteners. And it's possible that a fair amount of the putty on the hull perhaps has poor bond strength, especially around the strut. As water
will have gotten underneath of it through cracks in the putty around the strut, & migrated as far as entropy allowed it to. Thus worsening some of the putty's bonds to the hull. How much putty is on the hull remains to be determined.
Note that I can't say this with 100% certainty from one image. So you may wish to do a bit of semi-destructive inspection
, & then call in a surveyor
or not based on what you find. But before calling one, sound the hull with a mallet or the butt of a screwdriver to check for loose sections of fairing compound, & possible water
intrusion between the putty & the hull proper.
Now's a good time to get things fully diagnosed. Since if you need to strip off a lot of paint
& putty in order to let things dry, if you do so now, it'll at least be exposed to the air over the winter so that it can air out some. Plus water freezing in between the hull & layers of putty could make things look ugly. Key word, look.
Also, do some reading on here & online about the use of thermal imagers in boat
surveying. As with such tools you'll likely be able to see what's truly going on with the hull & possible water penetration between the hull & the putty. Ditto on the health
of your deck