How do I get rid of the goldish stain on the bow of our boat?

Some people would call that the Intercoastal Waterway mustache. Also stains from anchors and chains and some deck hardware can bleed out these same types of rust stains.

I have found that liquid Lysol toilet bowl cleaner works best on these and other type stains.  It is reasonably safe to use. You can apply it with a sponge, a sponge mop or if it isn't windy, I like to use an empty spray bottle which can be purchased at any dollar store for about a buck. If you use a bottle that you have on hand make sure you rinse it out thoroughly with fresh water and do not mix chemicals.

Apply the solution on the stain leaving it for approximately 15 minutes and then rinsing thoroughly with fresh water.  The process may be repeated if necessary. Be sure to protect any brass, aluminum or chrome items as it can stain these metals permanently.

Toilet bowl cleaners, Naval Jelly, LimeAway and lime juice will work quite well.  Some of these products contain Oxalic acids.  Oxalic acid can be purchased in powder form from your local hardware store.  Another product called On Off, which can be purchased at a local marine supply store such as West Marine, is very good at removing rust stains, calcium deposits and even crustaceans and barnacles. Oxalic acid and On Off work best but should only be used by professionals.  These acids can ruin your clothing, burn your skin and are extremely harmful if you get it in your eyes.  So read the product labels for whichever product you chose.  All of these products are hazardous if not stored and used properly. Mixing these chemicals can have violent reactions.  Do not mix these chemicals with household chemicals such as bleach, hand soap, dish soap, shampoo or any type of peroxide which can create highly toxic fumes.

As always, be sure to wear protective eye wear and gloves to protect yourself from injury.