I can't stand having spiders on the boat. Or anywhere I am. Luckily, they're fairly easy to control on a boat if you know a couple tricks.
I've been using the Ortho stuff lately, and like it. Check the label and make sure you're getting the water based stuff, so you're not spraying some oily crud on your decks.
There may be hundreds of spiders on and around your boat. Start by controlling the ones that are outside. Every night, every spider comes out from its daytime hiding spot (most of the spiders around your boat are nocturnal) and builds a new web. So, just stay on your boat until after the sun goes down, and all the spiders are on their new webs. Grab your flashlight and go on a spider hunt. Give every last one of them a blast with the Ortho. The ones up in the spreaders will defy you. The rest are easy, because they show up so well in the flashlight.
It will be obvious where they like to build their webs on your boat and your dock, so give a good heavy blast where you know they would have to travel. They get it on their feet, lick it off, and it's lights out.
You will have effectively wiped out the population around your boat. Extend your hunt to the other side of the dock and wipe out as many of your neighbor's spiders as you can. Hopefully, you can point out to your neighbor how your spiders are absent, and show them how to eliminate their's, which will increase your "dead zone".
They like to hide during the day, so if you can find some of their spots, you can spray treat them. On my Catalina, they like to hide out under the hull to deck joint.
Once you've gotten the outside spiders under control, you can blast the indoor spiders. As long as you know when they're out and/or where they like to hide, you can use the Ortho to eliminate them.
We've had the experience of getting our boat and slip very much under control, and then taken a trip to another port that has a lot of spiders. If you stay overnight and don't blast the spiders around the dock, they're going to get on your boat and come home with you.
To be spider free, you have to stay ahead of them, but you're on your boat often enough to do it. If they should get out of control, the good news is, you can get them under control in just one night.
