On our continuing series about definitions in the Racing Rules of Sailing, today some thoughts about Obstruction;
Obstruction An object that a boat could not pass without changing course substantially, if she were sailing directly towards it and one of her hull lengths from it. An object that can be safely passed on only one side and an area so designated by the sailing instructions are also obstructions. However, a boat racing is not an obstruction to other boats unless they are required to keep clear of her, give her room or, if rule 21 applies, avoid her.
The used wording clearly avoids a fixed dimension in defining an obstruction. Something can be an obstruction for a smaller boat and at the same time, not be an obstruction for a bigger one. The definition is a hypothetical test from a distance of one boat length. Something doesn't cease to be an obstruction, when you are not pointing at it. Also, the course change must be substantial, a few degrees is not enough. This part is clear enough. It gets tricky when another boat becomes an obstruction. This happens more often than most sailors think.
Each time a keep clear boat meets a r-o-w boat the latter is also an obstruction according to the definition. Same for a boat that has to give room, or encounters a boat aground, capsized or helping another. It never becomes an issue, whether the other boat is or isn't an obstruction, because the right of way rules in part two, sections A & B (and D), will govern the outcome of the encounter, without Section C (rule 18 or 19), ever coming into it.
But this changes when there's a three (or more) boat encounter. Rule 18 and 19 may come into play, between two boats, which both have to keep clear from a third r-o-w boat. There are several calls and cases about this.
Sometimes boats can even become a continuing obstruction. This is something I personally always found very strange. Nevertheless, once you understand the reasoning it is at least consistent.
For instance: two boats close hauled with eased sheets waiting to start, are continuing obstructions to a third boat coming from clear astern. If there's room between them, the boat from clear astern can fill the gab and sail between them, but if there isn't enough space, the boat can't force her way in, by establishing an overlap and then claiming the windward boat has to give room and keep clear.
If you compare this situation to the classical shore situation it would be like: the leeward front boat is the shore (unforgiving, cannot go there, have to keep clear) and the windward front boat is the boat you want to pass. (If there's room, can go there, thereafter she has to give me room)
The SI can also define certain areas as obstructions. In my home lake we have a standard sentence defining the - with buoys marked - navigation channel, as an obstruction. Nothing physical prevents boats to go there, but because of safety issues we want them to stay out of the channel. We enforce this too, by protesting boats that are in the channel; otherwise it becomes an empty addition.
Most protests where an obstruction plays a part are related to the shore and rule 19. Because of the uneven shore, it is sometimes hard to get the necessary evidence that there's room to pass at the moment of first overlap. And because of the many different classes sailing together in a given regatta and the related depth issues, the smaller ones have the advantage in that the bigger ones have to stay well away from shore.
Together with hailing protest, rule 19 is the only time mentioned in the RRS a sailor is obliged to communicate verbally with another boat. Approaching an obstruction close hauled or above she may hail for room to tack. She must give the other boat time to respond and shall not hail unless safety requires her to make a substantial course change to avoid the obstruction. I've noticed that sailors think this also is applicable at any other angle approaching an obstruction, for instance on a reach and then wanting to gybe when approaching a shore. This is not so. But because the hailed boat doesn't know what the rules say either, it does succeed half the time .....