Retro fitting athrough hull marine toilet to an Etap 21i

[Anybetterwouldbe]

Just about to take ownership of an Etap21i and was considering fitting a marine toilet. Any advice on do's ans don'ts
given the double skinned hull construction would be appreciated?

Many thanks

 

[john_morris_uk]

If it’s double skinned below the waterline it gets a bit complicated. I’d be tempted to use a hole saw to remove the inner skin and epoxy in a pad of marine ply, Then glass over with woven mat and epoxy and then cut through the middle with a hole saw of the correct size for the skin fitting and use a backing pad bedded on thickened epoxy when you finally fit the skin fitting.
The last thing you need is water getting between the outer and inner skins of the hull. By building a solid bit of hull you reduce the risk considerably.
Double skins below the waterline stopped being built some time ago IIRC?

 

[Anybetterwouldbe]

If it’s double skinned below the waterline it gets a bit complicated. I’d be tempted to use a hole saw to remove the inner skin and epoxy in a pad of marine ply, Then glass over with woven mat and epoxy and then cut through the middle with a hole saw of the correct size for the skin fitting and use a backing pad bedded on thickened epoxy when you finally fit the skin fitting.
The last thing you need is water getting between the outer and inner skins of the hull. By building a solid bit of hull you reduce the risk considerably.
Double skins below the waterline stopped being built some time ago IIRC?

Many thanks John for the detailed response. Much appreciated George