I often carried some visqueen when I did deliveries so I could line the area around my bunk and keep at least that one area dry from deck leaks, which were pretty common on wooden boats or any boat with teak decks. Older fiberglass boats often leak around deck fittings like cleats, chain plates and lifeline stanchions, especially if some previous owner used 5200 or silicon as the bedding compound.
Quite often water flows into a boat from an unsealed spurling pipe for the chain and down into the bilge. But none of these leaks are irreparable. They may take money and/or work and time to repair, and none has yet caused me to refuse a delivery or make a boat unsuitable for offshore sailing, just uncomfortable and bothersome.
Deck leaks and leaks around ports or hatches can do an incredible amount of damage very quickly if the water coming in is fresh. It will cause dry rot to any interior wood it comes in contact with. This could definitely compromise a vessel's seaworthiness if structural members are involved.
These leaks are almost impossible to hide, as the water leaves a telltale path on interior wood.
I've not had the experience the OP's friend had with water coming into the boat through the decks in enough quantity to need an inordinate amount of pumping, but several times I have had water flowing into wooden boats that have sat unused for long periods, through open seams in the planking above the waterline, which did require 24 hour pumping, but they usually swelled up in 12 hours to a couple of days. On one 73 foot shrimper, on a voyage from Marco Island to the Dry Tortugas on a very blustery night, we had water several feet over the engine room floorboards (maybe 7 feet of water total). Fortunately, the seams began to swell just about the same time I thought we were going to lose her. Sometimes you just get lucky.
