Blackstone Canal Locks

For a Stone Lock on the Blackstone Canal

By Holmes Hutchinson


(The following specification for a Blackstone Canal Lock was hand written by the engineer, Holmes Hutchinson, and furnished to us by the American Antiquarian Society.  Any failure to correctly read every handwritten word is the editor’s.)

Head                             5 ft.
Upper gate                    7
Between Gates            82
Below gates                12

                                106 ft
wings in curve             22   or 20 ft on a straight line

                                  128 ft

Walls to 106 ft long 5 feet thick at bottom and built plumb on both sides and to have a Buttress projecting 2 ft from the wall 6 ft wide and to be carried within 1 ft of the top of the lock – according to plan -   There is to be 2 recesses for the gates on each side of the lock – seven ft long.  For the Breast a wall is required 3 ½ ft thick near the head of the lock extending across and to connect the two walls and to be as many ft. high as the lift of the lock  - also a wall 2 ft thick as high as required (about 2 ft) to support a timber under the upper miter sill –

Wings to be 22 ft long 5 ft thick at the end of the lock and 3 feet at the end of the wings and seven feet high.

From the end of the lock the wings are to descent by steps of the height of the courses by treads of 20 inch in front and wide in the scope to the 15 inch courses & proportioned for other thickness of courses to the 7 ft. from floor – to have a buttress on the inside of the curve of the wings 4 by 2 and 2 ½ ft high.

And the lock – wings and breast to be capped (?) with good stone not less than 3 ft square and 12 inches thick

The face of stone to be laid and backed up with cement and the back wall of 2 ft thick level and the center grouted with good Dexter lime – and all the walls water tight.

A groove to be cut from the top of the coping to the breast 4 inches wide and deep to receive stop plank at the head of the lock.  And a similar groove cut 8 feet below the lower gate from the bottom 6 ft up – for the same purpose with proper preparation.

The hollow quoin made in the best manner, properly true to receive the heel post of the gate.

All iron fastenings to be put in.

35 casks water lime         }
111 do Dexter Rock do  }  11 foot Lock

$ 3.05 perch for a Lock - $ 2 bg / foot lift

Lock drawing marked as per the above description.

Notes on the above

1) The lock is specified as 106 feet long. The 82 feet between gates includes the 7 foot length of the lower gate pockets. Thus the difference between pockets is 75 feet. Thus 75 feet is about the maximum length of a boat.

2) "For the Breast a wall is required 3 ½ ft thick near the head of the lock extending across and to connect the two walls and to be as many ft. high as the lift of the lock." The breast wall is upstream of the upper gates and 3-1/2 feet thick in the long axis of the lock. It is as high as the lift of the lock. Because the breast wall is upstream of the gates, the upper gates are the same height as the lower gates.

3) "also a wall 2 ft thick as high as required (about 2 ft) to support a timber under the upper miter sill". This wall would have been at the bottom of the lock under the upper miter sill. It would serve to stop water from flowing under the miter sill when the lock was empty and the upper gates closed

4) One item not discussed here is the gates. From the layout, it is apparent that the upper and lower gates were the same height. This is different from other canals such as the Ohio & Erie or the modern New York canals where the upper gates are upstream of the breast wall and shorter than the lower gates. This would have allowed valves to be installed in the lower part of the gates to fill or empty the lock without flooding a boat in the lock. Usual US practice was for these valves to be of the butterfly type and to be opened and closed by a vertical rod  running to the top of the lock gate. The valve would be rotated 90 degrees to open or close.

5) From the description, we know that the gate pockets were 7 feet long in the long axis of the lock, but the depth is not specified. At Millville Lock, the gate pockets measure 12" deep. The gate itself would have to be slightly shorter, say 6'10", so it would fit into the pocket. The gate thickness would have been equal to the depth of the pocket or maybe a slight bit less. The top of the gate heel post would have been held in place by an adjustable strap bolted to the cap stones. The grooves for these are visible at Millville Lock. The gate would have been operated by a "balance beam" that ran from the miter post (the outboard end of the gate across the heel post and beyond to provide leverage to move the gate. When closed, the gate was forced by water pressure against the quoin, the miter with it's companion gate and the miter sill on the floor of the lock. These three lines of contact sealed the gate.

6) If we say that the gates are 6'10" long, and 12" thick, then the closed gate forms a miter with its mate that is two triangles 6' on the base, 6'10" on the long side, and 3'3" on the third side.

7) The upper stop plank grooves run from the top of the coping stones to the top of the breast wall. These grooves allow stop planks to be inserted to dewater the lock.

8) The lower stop plank grooves are located 8 feet below the lower gate pockets and extend up to six feet above the lock floor. With the canal being 4-1/2 feet deep above the miter sill, this would leave maybe a foot above water for insertion of the stop planks. But, no such groove is visible at Church Street, Goat Hill or Millville Locks. That is probably because all three locks are back flooded to a greater depth than their operating heights by dams or silt downstream. The lower groove is visible at Skull Rock Lock where the water level below the lock has been lowered by the removal of the dam at Millville.

9) The wall buttresses are described above, but not visible at either Goat Hill or Millville as they are buried by the backfill on either side.

10) The wall buttresses at the ends of the wings are also described. But, these are not visible at either Goat Hill or Millville as they are submerged. Such buttresses are visible at some locks on the Chenengo Canal.

11) The description does not include a lock width. On the Blackstone Canal, this was 10 feet. This dimension is critical as it sets the width of the boats and cannot vary from lock to lock.

12) One item not mentioned in the description is that the top row of stones on each wall of the lock (the "cap" stones) are wider in the across the lock dimension than the stones of the courses below. Some of these cap stones are visible at Skull Rock Lock and Lower Taft Lock.

The first paragraph above describes the "breast" as 3-1/2' wide and the "stop plank groove" as "A groove to be cut from the top of the coping to the breast 4 inches wide and deep to receive stop plank at the head of the lock." These are both seen in the 11/8/11 view of Millville Lock. The "breast" is 3'9" wide, the stop plank groove is 4" wide and 14" back from the gate pocket. The stop plank groove goes from the top of the cap stone down 5'11 to the top of the breast.

This is an 11/8/11 view of the lower end of the berm wall of Millville Lock with the gate pocket on the right. No lower stop gate groove is visible. It is supposed to be 6' high from the lock floor and located 8' below the gate pocket. The obvious conclusion is that the water is more than 6' deep here.

On the other hand notice this 1/19/12 view of the lower end of Skull Rock Lock. This lock is an outlet lock to the river pool that extended downstream to the Millville Dam at Central Street. Since the dam is now gone, the river level is lower than during the operating period. In the view above, the stop plank groove is visible about 8 feet to the left of the quoin, which agrees with the specification.

This photo shows the grooves in the cap stone for the gate irons at the lower towpath side gate of Millville Lock. Note that the right (upstream) iron has two bolt holes while the left has three.

These are the gate irons for the upper berm gate of Millville Lock on 11/8/11. Again, there are two bolts on the upper (left) iron and three on the right.

To better illustrate the gate pivot hardware that would have been on the locks, the above photo is from Lock 11 of the Illinois & Michigan Canal taken 7/24/10. The pivot post of the gate would have extended through the collar on the left.

At the gate pockets on the Millville Lock, there are grooves to receive iron connectors between the cap stones on several adjacent stones at each gate pocket, but not elsewhere.

This is a 2012 photo of Lock 2 East on the Morris Canal in New Jersey showing the masonry walls, the wooden floor, and the miter sill. The lower gate pockets are just beyond the worker with the yellow vest on the left and the two ladders on the right. This lock was filled in early in the twentieth century and is now being restored. It well illustrates currently invisible features of Blackstone Canal Locks 

Close up of the Morris Canal, Lock 2 East miter sill looking the other way.

Gates from the Morris Canal Lock 2E

Close up of the butterfly valve in the gates above 

These are the cap stones of Morris Canal Lock 2 East removed from the chamber. They are about the size of the cap stones on Blackstone Canal locks.

This is a 3/18/12 photo of the lower, river side end of Skull Rock Lock showing a cap stone, the gate quoin, and the lower stop plank groove.

This is a 4/15/12 view of Ohio & Erie Canal Lock 37 North with most of the lower gates rotted away, but showing the valves and operating rod and a few other details.