Q.Do COLREGS rule 18 apply in tss?

Yes it applies as per rule 10a this rule doesnt relieve any vessel of her obligation under any other rule except sailing vessel and fishing vessel whhic has to comply with 10i and 10j. For example if svsl is crossing pd vsl from stbd side and if she becomes aware of approach of pdvsl and when they are not in sight of one another then as per rule 10j she shall not impede the passage of pdvsl and as per rule 8fi shall take early action to allow sufficient sea room for pdvsl but if both vsls are in sight of one another and roc exist then only rule 18 applies in both tss and narrow channel.

Yes rule 18 apply in tss

Yes