Turn your boat so that vents are lined up with the direction of the prevailing winds. This will improve airflow and help keep fresh air in the cabin and other portions of the boat where mold might attempt to grow. Periodically open doors, cabinets and any storage bins or containers that may be on your boat. If your boat has a sail or any canvas storage solutions, make sure that these are aired out regularly as well.

Lift seat cushions or set them on the deck to prevent condensation from forming under them. If cushions get excessively wet when the boat is in use, remove them and place in full sunlight to allow them to dry thoroughly. Wipe down any upholstery if you have been sitting on it with wet clothes or swimming outfits.

Inspect your boat periodically for places where water is pooling or where condensation collects. Place towels or other absorbent materials in these areas to soak up water before it has a chance to pool. These towels should be changed and laundered whenever they start getting noticeably damp.

Avoid leaving used ponchos, foul-weather gear, life jackets or swimming outfits in the shower or other enclosed spaces. Any wet clothing or gear should be allowed to air dry in full sun (if possible) so as not to add to the overall humidity of the cabin or shower area.

Clean up after yourself when using the shower or kitchen area. Use a towel or chamois to wipe up any residual water so that it can't promote mold growth. Make sure that you place the towel or chamois that you use on the deck to allow it to air out and dry completely before bringing it back into the cabin.

Create a regular cleaning schedule. Wipe down all internal surfaces with an appropriate cleaner, and make note of any new areas where water seems to be collecting so that you can try to prevent the water pooling with towels or other absorbent materials. Perform your cleaning on time whenever the boat is being kept at a dock or otherwise on the water, even if it hasn't seen much use.