How a Dredge Works

Most of the dredges in the Fairbanks Mining District were built by Bethlehem Steel Corporation out of Bethlehem, Pennsylvania and a couple by the Yuba Manufacturing Company out of Yuba, California. The dredges were then shipped by rail to the Port of Seattle to be loaded onto ships bound for Alaska. Unloaded in Anchorage and put back onto rail cars for the trip to the interior gold fields. Upon arrival in Fairbanks, the pieces were loaded onto trucks and taken out to the reassembly site.

The mining company had decided where the dredge would be reconstructed and a deep hole was dug into the ground - large enough to lay in the keel of the dredge. The dredges came in pre-fabbed units - each unit numbered and identified for easy reassembly. Still visible on the walls of Number 2 are section identifications such as: starboard - upper deck - rear side wall. Section by section, each dredge was reassembled, the equipment hauled on board and installed. When reconstruction was complete, water from the Davidson ditch was diverted to the deep hole until the dredge was floating. At the back end of each dredge there was either one or two huge steel pilings called spuds. These were dropped down to anchor the dredge in position during the dredging operation. The engines were then fired up, the forward ladder dropped to ground level and the bucket line put into operation.

The buckets tore into the earth filling with soil and lifting back up to move along the ladder assembly to dump the contents into a hopper as they rolled over the top of the ladder to begin their journey back down to the earth. The hopper dropped the soil into a gigantic rotating drum called a trommel. The trommel had holes in it no larger than a quarter. It is important to understand that the mining companies were after the majority of the gold - which was sized from fine dust up to the size of a quarter.

Water pumps on the lower deck sucked water out of the pond and pumped it to several locations on the dredge. Pipes took water to the trommel where it was sent in a continual stream to wash the soil and rocks as they tumbled in the turning drum. Anything smaller than the size of a quarter fell through the holes to the next process below. Any thing larger than a quarter continued through the down sloping slowly rotating drum to a conveyor belt at the rear of the dredge. The conveyor belt carried the material up the stacker and dumped it out.

The conveyor belt sloped upwards inside a housing called the stacker. There was a narrow wooden walk way on either side of the belt from the base of the trommel all the way up to the end of the stacker. A man walked this path checking the material going out to make sure that no large nuggets were lost. Now keep that thought in mind as we continue on with the operation.

On either side and beneath the trommel were sluices boxes lined with gunny sacking that was held down by wooden slats called riffles. More water was pouring over the material dropping down out of the trommel, washing it as it moved it through the sluice boxes toward the rear of the dredge to the trailing sluices on either side of the ladder. Here it was dropped overboard to return to the bottom of the pond.

On the very top deck was the captain's room with a wide open view overlooking the ladder and buckets. A small side window on the left side gave easy access to the bucket line. Out of the floor 2 banks of levers rose from the decks below. These levers controlled the entire operation of the dredge. Trommel speed, conveyor belt speed, lowering and raising each spud individually, moving the dredge forward or backward, swinging it to left or right and lowering and raising the ladder and the bucket speed.

Bucket speed was dependent upon the type of ground the dredge was working. Bedrock, boulders, frozen or partially frozen ground slowed the operation down - to as low as two to three buckets per minute dropping material into the hopper. Soft, easy, well thawed ground allowed speed to be picked up - maximum dredge speed was 22 buckets per minute.

Now lets go back to the stacker a moment. But before we do let's discuss the size of the buckets. The smallest dredge operated in the Fairbanks area had 4 cubic foot buckets, the largest had 10 cubic foot buckets. No matter how you look at it, there was a lot of dirt being moved. Imagine 22 ten cubic foot buckets dropping material every minute into the trommel. Imagine the large material dropping onto the conveyor belt and moving it quickly upward to drop overboard. Walk along that walkway watching the material for nuggets. "Wait!!! Stop!!! Oh, darn I think that was a big one that just got away!"

Was gold lost in this manner? Most definitely! But the large companies felt that the amount of gold lost was negligible in comparison to what they retained.

When bedrock was reached and no more material could be lifted, the ladder was raised, one of the spuds was lifted and the dredge swung one way or the other pivoting on the spud still anchored. The ladder was lowered and began digging at the bank. When the dredge moved in the manner it was called 'walking' or 'stepping forward'.

Though the dredges operated for approximately 50 years, they never moved more than four or five miles from where they were first built. It was a slow process, back and forth across the valley, eating up the soil, washing it through and depositing it behind in softly undulating stacks of gravel called tailing piles.

Gold was the reason for the dredge operations, but gold was not the only valuable taken from the ground in Alaska's interior. The captain in his pilot house watched the buckets coming up the ladder toward him. If something unusual caught his eye, he slowed the buckets down until that particular bucket was outside of the window on his left. He could then stop the buckets and reach out to retrieve the item that had caught his attention.

Ivory was collected and sold as a sideline product of the gold mining. This was the land of woolly mammoths.