As a sailors who are also organic gardeners, we prize our wonderful spiders who are very beneficial in the garden...however, in the boat is another matter. Most likely the spray will do more harm to you than the spiders, especially in an enclosed cabin.First, figure out what kind of spiders they are - because they are not living on air alone - they must be eating something, like other bugs. Are they biting the crew? Then consult with some people who know spiders...local university, garden stores, etc. maybe they just want cover for the winter, or got in and can't figure how to get out with all that surrounding water. You can catch them in an 'intruder extruder' and put them ashore...and, hopefully, you won't have to smash the little darlings to death, because spiders are really great to have around! [They kill the 2 most deadly insects known - flies & mosquitoes, which carry deadly diseases.]