Roaches can be very difficult to remove so it's extremely important to do everything you can to prevent bringing them aboard. And that means no cardboard or anything the roaches can lay eggs in. Roaches can fly so it's important to keep the screens in at night (and most of the other times as well). One of the big reasons for being on the hook is that roaches can't fly that far but if you're at the dock
they can get on board a number of ways.
Bug bombs are explosive and more than one sailboat's gone "boom".
Whether you use boric acid, roach motels, or bug bombs, you've got to get access to where the roaches live. I highly recommend removing drawers, cleaning
every surface you can, checking every locker for any trace or roach or food they may be eating, and being ruthless. It's also important to know the difference between roach eggs and roach guano.
Borax is a wonderful insecticide, but insects avoid large piles of dust. It is best applied in a thin, almost invisible layer; try using a plastic condiment dispenser. Apply in affected areas, like under appliances
and furniture, squirt in cracks and crevices, (particularly around cabinetry in the galley
and head(s)), and dust the plumbing
. Avoid moisture because it will cause clumping and minimize the effectiveness of the borax.
Most species of pest roaches love the glue on many brands of masking tape- I'm sure the more adventurous among you can find use for that tidbit of information.
Roach discs containing hydramethylnon can be broken into and made into lots of little pea sized baits and strategically placed. This is an expensive, though extremely effective option if you don't have access to other formulations of this
Once you've got the drawers out, hatches and compartment covers off, and as much food and fabric
you can get off the boat, you can set off a few bombs. Try placing the bombs in different locations and if you can get the poison in every nook and cranny you can. Plan ahead for your return. Bug killer is not good to breathe. It can take several hours to get the fumes out of the boat.
Check the boat carefully. There should be dead roaches if things went well. Make note of where they were found. Leaving the bomb residue in the lockers, sprinkle your favorite recipe of boric acid and ? and put it in corners and along edges. Insert some roach traps, put the boat back together and check the traps and areas for dead bodies.
If you were lucky, the number of roaches will be reduced but the eggs have a long life and are fairly resistant to poisons so you may have to do this a few times (or but a bunch of geckos, open the drawers and lockers, and go to a nice motel for the weekend.
You may have to do this eradication several times to get the infestation removed. Then make sure to never bring cardboard aboard again. If you use canvas shopping
bags, I'd check the contents of the bag after emptying the contents; you never know. Several long term cruisers repackage everything into plastic bags at the dock
and take the cardboard to the trash bin, to minimize the chances of a roach jumping aboard.