Cutting a limber hole through a hull stringer

[Ric]

My boat is built with the hull stiffened with glassed-over wooden and foam stringers. I need to cut an additional limber hole in one. Do I need to reseal the foam or wood that will be exposed when I cut the hole? My bilges are pretty dry, but suffer occasionally from the usual boaty mishaps.

 

[Fendant]

If it is a quality closed cell foam like Airex or Divynicell you don't need to seal the surface. If you are unsure about this or your stringers are wood cored or out of some inferior PU foam quality you need to seal it.
Best solution is a PVC pipe which is perfectly sealed in with Sika.
Why don't you keep the sealed compartments ( other than routing some cabling ) ? I prefer that my the results of my mishaps are rather contained in a defined space than moving around all around the bilge.

 

[Avocet]

Yes, best to seal it if it is likely to get wet. I've done a few like that on Avocet. The odd bit of rainwater leaking in (or small mishaps) result in half a cupful of water sitting for ages in various inaccessible crannies and I like to have them all drain down into the sump at the bottom of the keel where the bilge pump can pick it up. I just put a holesaw through the lowest corner of the stringer concerned and then ground the surrounding fibreglass back, glassed up the hole and flowcoated the lot to match the original. Obviously, it's hard to say what effect that might have on the boat structurally, so each needs to be treated on its own merits. I'd be less happy about doing this in stringers around (say) where the keel joins the hull. Mine were at the corners of cockpit lockers.

 

[DanTribe]

I always feel a bit nervous about cutting holes in structural members, you never know when you might need the full strength. If you really must, then certainly seal the exposed edges. I would prefer to let some epoxy resin soak into the edges of the hole then bond in short length of pipe.
Pedantry mode.
I think of stringers as being longitudinal [fore and aft] members, and floors being the transverse [crossways] stiffeners below the cabin sole. Are we talking about the same bits?

 

[bbg]

I think of stringers as being fore and aft, and ribs as being crossways. Not heard of "floors" in the context you mention it.

I'd be tempted to do both - let some epoxy soak in, then seal with a pipe.

 

[DanTribe]

I think of stringers as being fore and aft, and ribs as being crossways. Not heard of "floors" in the context you mention it.

I'd be tempted to do both - let some epoxy soak in, then seal with a pipe.

Perhaps I've been mi-using the term, I probably picked it up from picking the brains of old shipwrights while trying to keep my old wooden boats floating.
Also from Hiscock's book " The frames and /or timbers [ribs?] are let into & bolted to the keel but such joints cannot be strong enough to withstand the leverage of a ballast keel......... so are bound to the opposite members by floors"
Dated terminology now and probably irrelevant to modern yacht construction, but I still think of the triangular gusset between the hull and ballast keel as a floor.
Too old to change now.

 

[JimBrown]

. . . Dated terminology now and probably irrelevant to modern yacht construction, but I still think of the triangular gusset between the hull and ballast keel as a floor.
Too old to change now.

No need to change, your terminology is quite right.

 

[NickRobinson]

An alternative to making drain holes for draining small quantities in nooks and crannies is to lay something absorbent like natural fibre rope or (bit ugly) rag to use capillary action to drain over the rib/stringer and on to the pump. Its the way you can water plants when you go on holiday.
Works beautifully on a little pocket I have on Rivendell.

 

[Andrew41]

Yes, most definitely seal the walls of the holes. My boat has a deep grid of 2" wide x 10" high stiffeners on the hull bottom around the keel/saloon area with no limber holes but 2" holes for the plumbing of 4 large coffin water tanks fitted inside this grid. The stainless tanks had started to leak and a lot of water sloshed around the grid areas undiscovered as the boards and furniture were screwed down. The holes were not sealed and when I opened the area up I found the stiffener cores, which were wood, had turned to a soggy mush extending about a metre either side of each hole. Screws and bolts fastened in these areas just pulled out and I had to get the yard to cut the tops off all the sections, scoop out the mush, dry out then fill with epoxy filler and relaminate. It was a very messy and expensive job so yes seal those holes, as the core, which some may say is just a former and not particularly structural, acts like a sponge and you could have a wet boat and high hull moisture readings in that area. As the holes were large I glassed them then applied copious amounts of gelcoat using my finger and artist's brushes. Well sealed conduit pipe sounds good for smaller holes. This Summer we decided to explore the Ardmore islands off Islay and SWMBO took this a bit too literally and as a result the stuctural integrity of the new keel grid was soundly tested and, upon close inspection, passed with flying colours.

 

[Billjratt]

Why drill limber holes? I know they are part of wooden boat architecture as they drain 'rot pockets' but in GRP they are not needed for that and in fact the little coffer dams created by ribs, floors and stringers are great for diagnosing the source of trickles.
If your boat is new and you think the designer had missed something -then go back to the shop and get it fixed. If it's 40 years old and still afloat, the designer probably got it right.