Speed Computations for the Cape Cod Canal

I will try to simplify the speed limits as best I can, but to begin with:

Cape Cod Canal Definitions



Maximum Passage Times Allowed

We will start with the maximum passage time allowed to transit the Land Cut section of the Cape Cod Canal since it is the simplest to explain. You can think of maximum passage time as being the minimum speed that you are allowed during transit.

The Rule

"Vessels of any kind unable to make a transit through the Land Cut portion of the canal against a head current of 6.0 knots within a maximum time limit of 2 hours 30 minutes shall be required to obtain the assistance of a helper tug at the vessel owner’s expense or await favorable tide [sic] conditions. . ." Note: there is no maximum passage time defined for the Hog Island Channel portion of the canal, only the Land Cut.

Simply put, your vessel must be able to travel the 5.9 NM Land Cut section of the Cape Cod Canal in 2½ hours against a 6 knot opposing current.

The Penalty

What happens if you can’t maintain the required speed while transiting the canal?

"In the event vessels within the confines of the canal fail to perform and are unable to make sufficient headway against the currents, the marine traffic controller may activate a helper tug to assist."   I will let you take a guess on who pays for that!

Alright Already. . . So How Fast?

With the Land Cut only being 5.9 NM, this normally would only require a speed of approximately 2.4 knots through the water in a no current situation. The problem is the “6 knot foul current requirement.” When you factor that in, then:

Your vessel needs to be able to make a minimum of 8.4 knots through the water

In order to meet the maximum time requirement. This effectively restricts the passage of most sailboats and many trawlers to times of more favorable current conditions.

Minimum Passage Times Allowed

(This can be interpreted as the maximum speed allowed for any vessel.)

Minimum Passage Time Discussion

To begin, it is best to think of the "Minimum Passage Time" as the maximum speed authorized when transiting the Cape Cod Canal.

Because current velocities are constantly changing with time and location, the chances of a single answer would be correct for the entire passage are pretty slim. A series of continuous calculations and speed adjustments would generally be required to hit the exact minimum transit time allowed as you pass through the canal.

The most common sense approach is to solve the maximum speed problem based on the average maximum currents that can be expected to be encountered. To further simplify the solution we will consider this average over the entire length of each section of the canal. So, while our answer will be close it will not be exact.

Computing the Average Maximum Current Velocity

From the NOAA Tidal Current Tables we can identify and extract the average maximum current velocities for the (7) current stations located in the canal and its approaches:

Current Station
Avg. Maximum
Flood Velocity
Avg. Maximum
Ebb Velocity
Abiels Ledge (Hog Island Channel) 1.3 knots 1.8 knots
Hog Neck (Hog Island Channel) 3.4 knots 3.0 knots
CCC Railroad Bridge (Land Cut) 4.0 knots 4.5 knots
Bourne Highway Bridge (Land Cut) 3.3 knots 4.0 knots
Bournedale (Land Cut) 3.2 knots 3.7 knots
Sagamore Bridge (Land Cut) 3.6 knots 3.7 knots
CCC East End (Land Cut) 3.4 knots 3.3 knots

From this we can calculate the average maximum current velocities for the entire length of Hog Island Channel and also the entire length of the Land Cut portion of the Cape Cod Canal as shown in blue below.

Current Station
Avg. Maximum
Flood Velocity
Avg. Maximum
Ebb Velocity
Land Cut Max. Velocity Averages 3.50 knots 3.84 knots
Hog Island Channel Max. Velocity Averages 2.40 knots 2.40 knots
What We Know

We now have all the information we need to do the Time, Distance, & Speed calculations (T = D/S) to determine the maximum speed that we are allowed when transiting the canal.


Hog Island Channel

 
Cape Cod Canal
East Bound
Cape Cod Canal
West Bound
Current
Min. Transit Time
Distance
Required
SOG
Current Required
Boat
Speed
Required
SOG
Current Required
Boat
Speed
Fair Current 23 Minutes 4.7 NM 12.3 Knots 2.4 Knots 9.9 knots 12.3 Knots 2.4 Knots 9.9 Knots
Slack Water 35 Minutes 4.7 NM 8.1 Knots 0.0 Knots 8.1 Knots 8.1 Knots 0.0 Knots 8.1 Knots
Foul Current 46 Minutes 4.7 NM 6.1 Knots 2.4 Knots 8.5 Knots 6.1 Knots 2.4 Knots 8.5 Knots

The Land Cut

 
Cape Cod Canal
East Bound
Cape Cod Canal
West Bound
Current
Min. Transit Time
Distance
Required
SOG
Current Required
Boat
Speed
Required
SOG
Current Required
Boat
Speed
Fair Current 30 Minutes 5.9 NM 8.2 Knots 3.5 Knots 4.7 knots 8.2 Knots 3.8 Knots 4.4 Knots
Slack Water 45 Minutes 5.9 NM 7.9 Knots 0.0 Knots 7.9 Knots 7.9 Knots 0.0 Knots 7.9 Knots
Foul Current 60 Minutes 5.9 NM 5.9 Knots 3.8 Knots 9.7 Knots 5.9 Knots 3.5 Knots 9.4 Knots

As shown in the table above in red, you now have a close idea of the maximum "average" speeds authorized to transit the canal.

In a couple of "unofficial" conversations with canal control, transiting the CCC at higher speeds was discussed, the consensus seemed to be that regardless of the current, as long as you are not carrying a large sea behind you, rarely is anything said if you were to keep your speed reasonable for the existing conditions. Just remember, that it is the "USACE" that gets to decide what is reasonable; not you.

Timing Your Passage

Obviously, timing the currents is pretty much mandatory for low powered vessels and would benefit even faster vessels with fuel savings. So when is the best time to make the CCC passage?

When Eastbound

The key here is to be looking for Slack Water Flood Begins (SWF.) Due to the fact that the Flood starts from the eastern end of the canal, if you time your passage for the exact time of SWF there is a possibility that you could out run the fair current. This is especially true for higher speed vessels, but could happen to even low powered vessels during times of higher than normal current velocities.

To provide your best opportunity for a fair current eastbound passage the window would begin about 20 minutes after SWF for low powered vessels and 1 hour after SWF for vessels capable of higher speeds.

To truly maximize the fair current you may want to consider timing your passage for 3½ hours after SWF.

When Westbound

Here you will be looking for Slack Water Ebb Begins (SWE.) Like the flood, the ebb begins on the eastern end of the canal and builds to the west although over a much smaller time period. In fact there is only a 12 minute difference between either end of the Land Cut section of the canal.

Entering the canal westbound about 5 minutes after SWE for low powered vessels and 20 minutes for faster vessels will give you the best odds for a fair current passage.

Entering westbound between 2½ and 2¾ hours after SWE should result in taking advantage of the maximum fair current velocities.


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