sealing hatch openings, etc. in cored hulls

My project is a (Woods) catamaran. My material is foam sandwich, VE resin/glass and Divinycell foam. I'm installing hardware and so forth now. Some of my locations do not have non-compressible core, and for those, I will over-drill and fill around bolts. I plan to use backing plates for most hardware.

For hatches and ports, I plan to use barrel nuts. People have told me to remove all the foam from the perimeters of these openings, and fill with thickened resin. The theory is, I guess, that otherwise, water can perhaps penetrate at the openings, freeze, and jack apart the glass/foam connection. Swelling, delamination, generally very bad days. Is this general practice? How deep must the fills be?
I'm confused here because I've been told that Dinvinycell does not absorb water.

Also, I plan to use sheet metal screws to install my rub rails (except at the ends).
These screws will be in the outer laminate and penetrate into the (foam) core. How could I treat these spots to prevent damage to the core?

 

You and me are in the same (proverbial) boat at least Cy.

I am not buying it. If I decore anything, it will be the bottom of window sill areas or areas we step on raw edges.

Anything on decks where we walk directly on a raw edge, I decore and backfill. We use a sharp chisel and pluck it all out, or I have a flycutter and I set it on the panel ahead of time, but usually all the decoring has been by hand. I pull it back about 1/4"-3/8". I figure a deck leak is more likely than a port leak and delam from walking more likely than delam from a window or door edge getting a bit damp.

I have about 18 meters of window perimeters and door perimeters are another 3 meters in the main cabin and then another 3 meters in the hulls and another few meters for 2 ports in each hull. No way am I decoring 25 meters. Not unless someone tells me I am a fool to not. Then my front anchor locker have another say 2-4 meters to decore. Again, not buying it. If I started to decore everything and fill and sand and repair it all, it would probably take a full week. I have 6 6" removable panels in the hulls for things like senders and panel access for putting the boat together.. Those we decored because we will always be walking on those edges.

The most I plan to decore is the bottom of them where water could actually migrate and freeze in.

Sorry if this is rambling. I need to get to the boat today. Monday is my office day and boat work starts when office work ends. Let me know if you have any other questions...

 

I also decore anything that is exposed to the elements. Any doorways covered are not getting decored.

 

Here is a picture. Red is all decored, blue is not.

 

Cores have a few problems with penetrations. Almost all will be crushed by fasteners. Many will rot if exposed to water. Even the ones which won't rot will delaminate when trapped water expands due to a phase change into either ice or vapor.

Any fasteners which tug on one skin only can also start delamination.

Connecting the two skins with either resinated cloth or bog is considered as best practices.

 

I should mention, the door has no core penetrations.

I would bolt most anything not decored as well for the reasons BK mentioned; glass peeling mainly