33 CFR 401.7: Fenders.

(a) Where any structural part of a vessel protrudes so as to endanger Seaway installations, the vessel shall be equipped with only horizontal permanent fenders—

(1) That are made of steel, are of a thickness not exceeding 15 cm, with well tapered ends, and are located along the hull, close to the main deck level; and

(2) On special application, portable fenders, other than rope hawsers, may be allowed for a single transit if the portable fenders are—

(i) Made of a material that will float; and

(ii) Securely fastened and suspended from the vessel in a horizontal position by a steel cable or a fiber rope in such a way that they can be raised or lowered in a manner that does not damage Seaway installations.

(b) Tires shall not be used as fenders.

(c) On special application, vessels of unusual design may be permitted to utilize permanent fenders not greater than 30 cm in thickness.