What brand and type of varnish did he use?
The good news is rigging a fan has a pretty good chance of drying the varnish, but you'll probably have to wash the cushions and carpet to get rid of the residual odor.
Don't even think about moving aboard if there is still a strong odor. Solvent fumes can make you VERY sick or even kill you in high enough concentrations. Long term exposure will definitely cause long term problems.
You're right, I think the ventilation idea is working a bit. The fumes aren't as strong now.
Here's what he used:
Antique Oil Finish - Specialty Products
I hope the "oil" in this stuff is linseed oil and not some sort of petroleum distillate.
Mind, I'm beginning to second guess whether it is varnish that I'm smelling. I've been sniffing the wood and while there is a general smell of linseed oil wafting through the boat, the wood itself only smells very slightly of linseed. I found this baffling.
However, today I was taking off the upholstery fabric covers and washing them. I sniffed them and immediately recognized the "fume" smell which has been driving me crazy - it's the plastic-like bottom of all the covers. Vinyl? Pleather?
I think I should start smoking so as to dull my olfactory senses.