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Brown bear mating pair "kissing"
Alaska 2013
  • Territory: Washington State, British Columbia, Alaska
  • Time: May - August, 4300 miles traveled
  • Vessel: "Teacup", Nordic Tug 37
  • Primary Activity: Wait for the rain to let up.

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Aground Once Again
Figure 1 : Hull breach, into a holding tank
Figure 2: The damage extends upward into the keel
Figure 3: Repairs nearly complete
Figure 4: Location of collision (red dot),
North entrance to Pond Bay, Duke Island
(54° 59.707' N, 131°, 17.956' W)

I have been sailing and boating for almost 30 years. I can remember each and every time I've grounded a boat or hit something in the water hard enough to jeopardize a boat's watertight integrity.

This season, I went aground hard, hard enough to shred the keel of my boat, while entering an anchorage using a route I had taken before, in a passage with a charted depth of seven fathoms.

If I'm entering an anchorage for the first time, I'm very careful and I move dead slow. After a few visits, I choose an efficient route consistent with safety and water depth, and I might go faster than one or two knots. In this case, only my second entrance to this bay and at low tide, I was probably moving at a speed of two knots, along a route I had taken before, when without any warning, my boat came to a grinding halt in a distance of about 50 feet.

I was able to back off right away, which is generally a sign of minimal damage. A severe collision may pin a boat to the ground in a way that the engine can't develop enough power to dislodge it, until the tide rises and lifts the boat. So I thought damage might have been minimal.

Over the next few days I realized I was wrong — the damage was substantial. First, I remembered that the keel on my boat isn't solid — it encloses a holding tank, and I noticed the holding tank was quickly filling with salt water, as fast as I could pump it out. Bad sign. Second, there was a new vibration while underway, a sign of prop damage.

After thinking about the situation, I realized that, although the bottom of the keel was smashed and the holding tank was compromised, it couldn't sink the boat (the holding tank was plumbed in a way that prevented it from filling the bilge with water). And I could live with the prop being unbalanced. So I carried on.

After my cruise, I had the boat hauled out and got a chance to look at the damage. The bottom of the keel was ripped apart in a number of locations along its length and required substantial fiberglass repair (Figures 1 and 2). The prop needed to be reshaped and rebalanced.

This was a surprising amount of damage, and it forced me to realize I've been harboring unrealistic expectations about modern power boats based on my experience with two Pacific Seacraft ocean boats — one that I sailed around the world for four years, another that I bought after my return (pictures here). The ocean boat had a hull thickness of three inches of fiberglass below the waterline, and a solid keel filled with lead. In retrospect I'm glad I was so conservative in my choice of boat for ocean sailing, and until now I've been assuming that my present boat was similarly robust. I don't think that any more.

The grounding took place along a route into Pond Bay on Duke Island south of Ketchikan, at location 54° 59.707' N, 131°, 17.956' W (see Figure 4). Based on the time of day and the tidal height at the time of the collision (which I acquired from my program JTides), I estimate the water depth at that spot to be one fathom, not the charted seven fathoms.

And I don't have any doubt about the location of the reef. If a sailor sees an uncharted rock and wants to maximize the accuracy of his position report, he can approach from one side, take a GPS position, sail around to the opposite side, take another position, then average the two positions — very accurate, very professional. But in this case, I didn't need to do that, because ... how shall I put this ... I was on top of the rock I needed to report. No need to take an average.

Not surprisingly, I spent much time thinking about this collision after the fact. It occurred to me that I went aground because of the particular depth of the reef on which I grounded, at that moment in time:

About this collision, the moment of truth came when I noticed an abrupt decrease in the depth sounder reading. Instead of performing an emergency stop, I said, "No way — there's seven fathoms of water here." Crunch.

Kinetic Energy

A word about speed. Many people think the potential for damage in a car or boat collision is proportional to speed, but it's worse than that — the energy in a moving mass, energy available to do damage, increases as the square of speed. Here's the physics equation for kinetic energy, which applies to any moving mass:

(1) $ \displaystyle e_{k} = \frac{1}{2} m v^2$
Where:

In a moving car, the evidence for kinetic energy is easily seen by the length of braking skid marks, which increase proportional to the square of the car's speed. I often wonder how many people don't know this about cars and stopping distances (more on this topic here).

But I digress. When my boat (with a mass of 16398 kilos) is moving at 8½ knots (my normal cruising speed, 4.37 meters/second), it has a kinetic energy of (½ * 16398 * 4.372) 156575 joules, or enough energy to light a 60 watt bulb for about 45 minutes.

Imagine that — in an idealized physics experiment, my boat's momentum could be used to light a 60-watt bulb for 45 minutes as the expended energy gradually brought the boat to a stop.

If I slow down to two knots, as I did as I entered Pond Bay, my boat's kinetic energy is just 1/18th of its energy at 8½ knots, enough energy to light the bulb for only 2½ minutes. But that low energy level was more than enough to shred the bottom of my boat.

Incident Reporting

I reported the collision on the responsible agency's reporting page (NOAA's Discrepancy Reporting System), which replied in a somewhat boilerplate way:

Thank you for alerting us about the uncharted feature. Your information will be forwarded to our cartographers for potential inclusion on our nautical chart products.

NOAA's Marine Chart Division

Tough Boat Story

My all-time favorite boat grounding story was one I witnessed in Suva, Fiji, during my around-the-world sail. One night a very tired French sailor approached the Suva harbor breakwater in the wee hours. Apparently fatigue got the best of him and he fell asleep before making it into the harbor. Because he was asleep, his boat was free to sail wherever it pleased, so it crashed into the breakwater's rocks.

During the night the boat got firmly stuck on the rocks, pounded by the open ocean swells breaking against the rocks and the boat. But this wasn't an ordinary boat — it had a steel hull. The boat withstood the pounding surf until daylight and the next high tide, at which point the boat could be floated off the rocks.

The sailor brought his boat into the harbor, dropped anchor, grabbed a ball peen hammer, went down into the bilge, and pounded out the dents. An hour's work, boat repaired. Steel hull. They have to be painted constantly to avoid rust, but they're very strong.

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