Humminbird HDR 600 Depth Sounder
I can''t speak to the 3 year durability but I have the exact model you''re interested in installed in my Helms 25. I sail on a tidal river so it''s a real help. I''m very pleased with it, it seems to work well and is easily visible from the helm day and night. VITmarine.com has them for 75 bucks.