Any untradeable ship can be put in the HQ, but still can' t be traded, it's not hard to do. the yellow sailor can be put in the HQ,  but no tradeable.
this is for save some space and make the harbor looks clean.......

another suggestion is "trade password is needed when selling BB6/CV6", and remove the trade password window for selling the ECL1, since they are always can be bought in the list and fully  refunded....