A. It meant someone was testing their whistle, and/or
B. Someone was saying they were using astern propulsion to stay clear
of, or assist themselves in swinging to the tide.

Peter J Ross wrote:
On Mon, 11 Aug 2003 15:31:08 +0100, a team of surgeons from
alt.sailing.asa removed the following benign growth from Donal:


Yesterday, as we approached a large, anchored, oil tanker, it gave one
short blast. About a minute later it gave three short blasts.


Does anybody know what this meant?


I expect somebody who has some experience of sailing will know. Try
alt.sailing.