Steering Cable Question

[SHIMANOFAN]

I need to replace the steering cable in my 1990 renken Classic 2000 Cuddy Cabin. The numbers on the cable indicate a 180 inch cable but my measurement show 168 inches. Did I do something wrong or is a foot of difference to be expected? I measured from center of steering wheel to center of gunwale to rear of boat to center of outdrive. The number on the cable is 300619-180IN. This is the first I-O I've owned so I'm kinda lost here.