Early one morning, about 5 1/2 years ago, most of Hawaii's citizens were rudely roused from their sleep by Civil Defense warning sirens. The cause for the alarm was immediately broadcast by radio and television.

A powerful earthquake had been detected in the waters offshore of Japan and it had possibly generated a tsunami, or what was once called a tidal wave.

In a Water Ways column shortly after, I noted that the view of the Ala Wai marina and the ocean beyond, by the time of the tsunami's 10:30 a.m. predicted arrival, was remarkable in two ways.

First, it was remarkable to see such an unusually large number of boats and ships congregating offshore on a weekday morning, and second, it seemed remarkable that over two-thirds of the Ala Wai's boats never left the marina.

Why didn't more boat owners attempt to protect their investment, I wondered. Was it a lack of understanding of the danger of a tsunami, or a lack of knowledge on how to avoid its danger?

Because April is Tsunami Awareness Month, and because experts have recently warned that Hawaii is overdue for a tsunami, it seems appropriate to once again advise boaters to check out the state's informative handbook, Hawaii Boater's Hurricane Safety Manual, which has a special section dealing with tsunamis.

Along with giving a general overview of the causes and effects of tsunamis, it gives a brief history of tsunamis that have struck our islands and presents an evacuation plan for recreational boaters.

All coastal areas of the Hawaiian islands are vulnerable to inundation by tsunamis. Naturally, if your boat is on a trailer in Wahiawa, you're safe. But, if your boat is moored or on a trailer at one of our state's marinas, the DLNR has a ten-point guideline for you to follow:

1. Move any trailered boat out of the evacuation zone (see GTE white pages phone directory for maps).

2. Moored boats should be taken offshore to at least the 200 fathom (1,200-foot) line.

3. Leave the dock with enough food, water and fuel for at least 24 hours.

4. Leave the dock with enough time to arrive at least 2 miles beyond the channel entrance buoy prior to the estimated time of arrival (ETA) of the tsunami.

5. Attempt to reach your moored boat without driving your own vehicle. It may fall victim to the effects of the tsunami.

6. If you are unable to move your boat offshore, remove whatever equipment you can and leave evacuation zone at least one hour before the tsunami's ETA.

7. The same advise should be considered when the Islands are also experiencing hazardous weather conditions, such as high surf or winds.

8. As police and Civil Defence personnel plan to establish road blocks 45 minutes prior to the tsunami's ETA, all actions by boat owners should be completed by that time.

9. Heavy vehicle traffic should be anticipated and extra travel time allowed.

10. Try to have an alternate person designated to carry out your evacuation plans should you be unable to do so.

For more details on these tsunami evacuation guidelines, pick up a copy of the Hurricane Safety Manual at any state small boat harbor office, or call the DLNR on O`ahu at 808- 587-1963.

Remember, the question is not if there will be a tsunami, just when.