Force Outboard Zincs & Anodes

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Force Anodes How-To's

What anodes to use on my boat

What Anode Do I Need for My Outboard...

Anodes are a very big deal in any case. It is on any boat, but your metal boats are obviously more prone to corrosion than fiberglass boats. The last thing you want is your ... read more outboard engine corroding. That's money down the drain. Save some money and invest in a some force outboard anodes. How do you know which one you need? This is where we will provide some of those answers. The surface area of the sacrificial anode determines how much protection you will get for your force outboard. The weight of the anode helps you know how long it will last. The capacity of the anode is measured in Amp Hours per Pound. You need to get the correct surface area and weight to last the required time and do the job effectively for your outboard.

Determining the correct anode for an outboard can seem a little difficult, but protecting the life of your boat, it is worth the investment of time. So the important thing to remember is the SNAME Formula. The acronym stands for Society of Naval Architects and Marine Engineers' formula. This group created a formula in order to identify which anode is best for your boat. The formula is as follows:

Area x Current Density x Seawater Immersion

  • Amp hrs/lb x 1000mA/Amp


  • Area is simply the wetted surface area. Currently, density is given in mA/sq ft. Seawater immersion is the factor times hours per year you think you will use your boat. Amp hours per pound of anode material: 1108 for aluminum, 368 for zinc, and 500 for magnesium. These math classes from school are starting to pay off now huh? Well, here's some more math for you. To determine wetted areas, you calculate based on these:

  • 1.0 x LWL x (beam + draft) – motor yachts full bodied sailing vessels
  • .75 x LWL x (beam + draft) medium displacement
  • .5 x LWL x (beam + draft) light displacement


  • So do your math and if you need extra assistance it is best to contact your boat manufacturer and/or local dealer. Fiberglass hulls don't need this kind of math because they are protecting metals of props, shafts, etc. However, anodes still play an important role in maintaining the performance of your boat. Those are matched up typically by the engine. So that's how you find out what anodes you need, and it is a process, but remember your boat and outboard engine life depends on finding the right anode so it is worth your time.

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    A warning about Zinc

    A Warning about Zinc

    Zinc is in all types of metals, but do not use a zinc anode in the water and only use it as an alloy with other metals. Zinc is released ... read more into water life and has very harmful effects as it can impair reproduction of aquatic life. The EPA has set water quality criteria in regards to zinc concentrations at 120 and 81g/L. Zinc acts as a great anode and will protect your boat from corrosion, but it can have harmful effects. So use aluminum anodes, for example, which only contain about 5% zinc to help reduce zinc pollution. You're ready for the water and ready to store your boat in the water as you now have all the know-how you need to identify the correct anode to protect the other metals and your outboard engine on your boat. read less
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