I have especially seen Jerry 5 gallon yellow cans of Diesel and blue containers of water.secured on the side decks in cruising boats particularly sailboats. We carried either one or two motor bikes on the deck forward of the main mast on our 62 footer, there was a windsurfer lashed on one side, and the boarding "Passerelle" on the other side. We carried our HD Achilles 13' dinghy also rolled up and in a sunbrella cover forward of the mast. I made specific hold downs for these items bolted to the deck, and made "double" sunbelt covers. The "pants" part were pulled up from the bottom, up to the fuel tanks and seats etc. The second cover "Shirt" went over the top, and secured under the bikes and to the hold downs--even though there were cables with turnbuckles securing the motor bike in place. That way, it would be very difficult for salt water to get on the bikes. We also sprayed them liberally with LPS #3, sort of like Cosmoline, as a rust preventive.
We have avoided items on the foredeck, in the C Dory, because it tends to lessen our visibility forward.