Recesssed from the inside or outside? Outside is to reduce drag, but not all that critical unless racing long distance. I suspect you mean inside and the recess is where they cut through the liner pan to reach the hull. Once removed, you could build the hull higher with G10. Good idea to replace original Bene thru hulls.

 

Recessed inside. But it’s in to the hull, not liner. Just not sure why they would do that - or how to get them out. I suspect I’ll need to cut them out…. Getting the new ones torqued back in there will be a problem though so might not have any option but to build the hull back up flush. 🤷‍♂️

And yes - they were definitely due to be changed. I broke one clean off just testing the seacock. 😬

 

From the two photos, looks like they sawed a circle through the sole, bolted the thruhull in, and glassed over. Is it correct that the first image shows one you have removed the fiberglass (or epoxy, or whatever) covering?

To remove these, you'll have to remove any covering material and remove the connection, like in the first photo. You'll need a large (size?) socket that fits that nut, an impact driver, and probably an extension that fits the socket to the impact driver.

 

No covering was on either of them. Perhaps originally there was? I couldn't say.
I was considering just cutting them out but I still need a way to reinstall which would require the sockets anyway. Or I fill in / build up the recess ....

 

I'd probably go with a 12 inch reciprocating, metal cutting, saw blade, insert and cut it out.

 

why do you suggest that over socketing it out? Curious.

 

I think you're looking at the parking lot. That's the one he got out. But I could be Wrong..

 

If you decide on the socket approach I think you'll want a step wrench on the other side to keep the thruhull from turning.

However, cutting it out is the best way to go here.

100% agree that the flanged seacock shown by @Minnewaska is the right way to go for the replacement. Of course you'll need that step wrench again to screw in the thruhull from the outside.

Also you absolutely want backing plates for the seacocks. You can make them yourself:
Seacock Backing Plates - Marine How To

Or buy them, Groco backing plates come with threaded inserts for their flanged seacocks

I'm sure they are fine, but the Groco backing plates feel a bit flimsy. After holding them I decided to use g10, threaded for the bolts on the flange.

I used Groco silicon bronze flanged seacocks for all of my thruhulls when I did my refit. However I'd strongly consider Marelon if I were doing it again.

 

If you decide on the socket approach I think you'll want a step wrench on the other side

Painfully, the thru hulls on my old Jeanneau did not have the nub inside to allow the step wrench to work. I did not realize how cheap they really were, until I got into it. In theory, one could use an internal cam pipe wrench, but either method will require two people.

The OP should read this excellent article. Based on the photo in post #5, it looks like mismatched threads to me (just as in my old Jeanneau)

Seacock & Thru-Hull Primer - Marine How To

These are called Thru-Hulls This item is called a thru-hull or sometimes a mushroom-head or even a skin fitting. They are straight threaded (NPS thread) so they can be cut to the correct length, for your hulls thickness, and then be

marinehowto.com

 

I replaced a through hull that was inaccessible by grinding the mushroom flange off from the outside. I believe I used a 4.5" grinder with coarse sand paper.

 

I replaced 13 through hulls this summer, all bronze. In my case, it was ultimately likely unnecessary, which is a testimony to the longevity of bronze.

We had a thick hull to contend with, but what worked was a stepped wrench and a large pipe wrench outside, and a second pipe wrench inside. It wasn’t exactly easy, but it worked for all of them but one, which we cut with an angle grinder (echoing jimlindaevans).

Strongly recommend Groco IBVF replacements - through hull, flange, and valve are three separate pieces, and compatible with their own backing plates as mentioned above. We used those for some of the replacements, but in other cases we had to grind away old plywood bases (epoxy covered, but still wet), and in their place used 3/4” starboard to make new bases that we sealed to the interior of the hull with Sika291. The slight give to the starboard, much like Groco’s bases, was helpful. Dead flat hull sections would definitely be better with G10, but plywood was enough to last >25 years previously, so I figure starboard is a reasonable equivalent. Especially with the separate flanges used in the IBVF application!