Alpha-rhamnosidase involved in ulvan degradation (PubMed:31285597). Ulvan is the main polysaccharide component of the Ulvales (green seaweed) cell wall. It is composed of disaccharide building blocks comprising 3-sulfated rhamnose (Rha3S) linked to D-glucuronic acid (GlcA), L-iduronic acid (IduA), or D-xylose (Xyl) (Probable). Endo-acting alpha-1,4-L-rhamnosidase cleaves rhamnose sections interspersed between xylose residues within the polymer, degrading larger oligomers with consecutive Xyl-Rha3S units that are resistant to the ulvan lyases and producing dimers Xyl-Rha3S and Xyl2S-Rha3S as the smallest products (PubMed:31285597). By ulvan and rhamnose. Belongs to the glycosyl hydrolase 39 family.