If it is at all possible to class a legend sailor as BO, you might find that he makes quite a splendid one. Do your calculations with BO potential, numbers of vets and experts and guideline length (Adalbert's guide).
I'm actually using an elite repair (with potential +9) as my Kaiser BO, even late-classed at lvl 103 in order to reduce potential in comparison with repair. With 140 vets, his guidelines are exactly at the guns' range. I don't need to take off rookies to reduce guideline length. That means I can keep all his repair ability.