Boat enthusiasts have long accepted 316 stainless steel as the standard by which all nautical propeller shafting systems should be judged, but Aqualoy has performed better in both corrosion resistance and strength (measured in annealed yield strength psi).
Aqualoy is currently available in four types: Aqualoy 17, Aqualoy 19, Aqualoy 22, and Aqualoy 22 High Strength. All of these are excellent choices for a broad range of vessels, including pleasure boats that spend a lot of time docked and fishing vessels that require premium performance.
The primary difference between these marine grade alloys and standard steel is their chemical composition. For example, Aqualoy 19 has more nitrogen, chromium, and manganese than otherwise comparable stainless steel 304. Nitrogen is responsible for determining an alloy's strength, so having more of it (plus chromium and manganese, which improve nitrogen's solubility) allows Aqualoy 19 to significantly outperform its non-marine grade cousin (30,000 psi vs. 50,000 psi). Larger amounts of Aqualoy 19 also get stronger, with psi readings of 105,000 possible on the largest systems.
Likewise, Aqualoy 19 is also more resistant to corrosion. The most common types of corrosion in a marine environment are pitting and crevice corrosion. Metals that resist one tend to resist the other as well, allowing a metric called PREN to calculate how corrosion-resistant one metal is compared to another.
Aqualoy 19 offers a calculated PREN rating of 22.7, significantly better than 304's rating of 19.14. Clearly, Aqualoy 19 is better than steel 304 if you're looking to maximize the lifespan of your boat.
The same comparisons demonstrate the superiority of Aqualoy 22 over stainless steel 316. Once again, the marine grade alloy has more nitrogen, chromium, and magnesium than its more traditional counterpart. Once again, this translates into a significant strength advantage (30,000 psi vs. 55,000 psi)
Aqualoy 22 also offers a superior calculated PREN rating of 34.06 vs. stainless steel 316's 24.07. Quite simply, Aqualoy 22 is the best alloy for marine use on the market today.
Scientific research supports this superiority. For instance, one recent study pitted Aqualoy 22 against stainless steel 316 in a corrosion resistance contest. Both materials were submerged in seawater for nine months, after which the Aqualoy 22 had no visible signs of pitting while the stainless steel had obviously corroded. Similar results were achieved in a study substituting the seawater for 50 hours in an acidic ferric chloride solution.
If you want even more strength to complement Aqualoy 22's corrosion resistance, Aqualoy 22 High Strength offers the strength of Aqualoy 17 with the corrosion-resistance of Aqualoy 22. It makes an ideal choice for boating applications demanding top of the line strength and corrosion protection.
The specific requirements for any boat depend on the variables that boat contends with, including salinity of its environment and the vessel's overall size. Chances are, an Aqualoy material is available to cover whatever your specific needs may be.
Propeller Depot is considered as experts when it comes to inboard prop stainless steel shafting. Reach out to the professionals at Propeller Depot for all of your inboard stainless steel shaft needs.