ADA Gangway Slope Calculator: 1:12, the 80-ft rule, and the length you actually need
Enter the rise at lowest water and your gangway length: slope as 1:N, grade and degrees, the length full 1:12 compliance needs, and which ADA gangway exception applies.
How the ADA gangway slope rules actually work
Gangways on accessible routes follow the ramp slope limit: 1:12, one foot of gangway for every inch of rise... which, in feet, is length ≥ 12 × rise. A 3-ft tide range needs 36 ft of gangway; 5 ft needs 60. The check belongs at the lowest design water level, where the float sits lowest and the slope is worst. A gangway that passes at mean tide can fail at low tide, and bid packages are written by people who know that.
Gangways are not ramps, though, and the 2010 ADA Standards (§1003.2, recreational boating facilities) modify the ramp rules three ways worth knowing in a bid: there is no maximum rise for a gangway; a gangway (or series of gangways) at least 80 ft long is not required to meet 1:12 at all; and in facilities with fewer than 25 boat slips, a gangway at least 30 ft long is not required to meet 1:12. Those exceptions are the difference between a 36-ft and an 80-ft gangway on the same tide range, which is real money on an aluminum structure.
The calculator applies the exceptions in order and tells you which path your configuration takes. As always: this summarizes the published standard for early sizing; the standard's full text, the local authority, and your access consultant govern the sealed design.
The gangway length is one requirement. The package hides fifty more.
Mavlon's AI reads the whole marine bid package, extracts every requirement with a page citation, finds the spec-vs-drawing conflicts, and drafts the quote in your own pricing logic. Built by the team whose AI reads entire bid packages.
Book a Demo15 minutes · We run a real marine package live