|Left side view|
|Right side view|
|Right side view of rigging ( closer)|
|Right side view of rigging (even closer)|
|Left side view of rigging|
|Left side view of rigging (closer)|
|The Skagit GT-4 requires some disassembly for convenient transport. The boom lays on a 40 foot flatbed and the gantry folds on top of it. To reassemble the boom is pinned on the front of the machine as in the gantry. A line from one of the main drums is fed through a block on the 'spacer braces' in the gantry and dead ended to a guywire drum. Pulling on the main drum first stands up the spacer brace in the gantry unfolding it, and then the gantry is partially lifted. the boom hoist line is then connected to the boom hoist drum and the slack taken out of the boom hoist. Finally, the gantry is winched over center while slacking the boom hoist which then restrains the gantry from 'flopping down' Once Vertical, the rear legs of the gantry are pinned and the boom can be lifted with the 6 part gantry line into operating position.|
|Boom and Gantryl|
|Smaller Thunderbird can be moved assembled|
|Note folded Gantry on lying on boom|
|Unfold the Gantry|
|Lift part way and snug the boom hoist|
|Six of the drums in the drumset|
This is a Skagit GT-4, one of the 8 or so extra large swing yarders made by Skagit before they went out of business in the Early 1980's. Weighing in at around 60 tons less the boom, gantry and wire, this is a serious machine. It has 3 main drums, as well as a haywire drum, a gantry drum and two guywire drums.
It is entire mechanical with air controls. It has no hydraulic system on it. The drumset is shown in a photo well down the list of photos on the left. The 3 small drums are the 2 guywire drums and the boom hoist. When powered they are turned through an 'aways set' band brake and secured by an air set dog. As is customary the yarding winches are on the front of the drumset. They can be locked together or pulled individually. This will operate a mechanical slack pulling carriage or open/close a grapple. The full width drum is the haulback drum. It needs to be much larger than the yarding drums because it needs enough wire on it to go to the back of the job and reach back to the yarder to pull the rigging out so it needs at least twice as much wire a the yarding drums.
One of the things that makes a yarder like these very special is that it has an interlock option between the yarding drums and the haulback. When you set the interlock, The haulback will go out under power as the yarding drum comes under power. This allows for full suspension logging and provides a good alternative to the 'Wichita 'Brake' solution of olden times. For the record, the Wichita brake is simply a high capacity (usually a disk) brake that is usually water cooled, and the operator simply drags a brake on the out bound drum to provide the necessary suspension or backlash avoidance.
Though made by a different manufacturer, this is the modernized version of the Washtington TL-6. While the Washington TL-6 was billed as a combination yarder-loader because it could be configured for either if you look at it from a yarder perspective, it is the crudest of yarders and was not really capable of fully off the ground skyline logging which is usually defined as being able to fly the logs fully off the ground some distance. Issue here is not so much the lack of a 3rd drum as the lack of an interlock. The third drum allows you to use a grapple or a mechanical slack pulling carriage but neither are needed for full suspension logging. With an interlock between the two main drums, you can hold the brake, and pull the other line until you have achieved suspension, then set the interlock and reel in the logs like a clothes line with one line coming in under power and the other fed out under power. The closest you can get to that with the Washington TL6 is to add a 'Wichita brake' (a high capacity water cooled brake) and slip the brake as you wind in on the other line. While you can suspend logs this way, it's hard on brakes. You can pull slack for side yarding with a 2 drum machine by adding a motorized carriage.
If you look at the rigging closeups you can see how a mechanical slack pulling carriage is rigged. the top line serves as a running skyline-haulback. It just passes to the block to help support the carriage, and goes out to the tail tree and comes back to be dead ended on the carriage. One of the yarding lines splits into to lines at a shackel so you can see 3 lines going in the carriage. Two of them are simply the two yarding lines that go into the carriage and wrap a cats head and exits as the other line. Thus by pulling one and slacking the other you can turn the cat's head. As you might guess, the butt rigging is on the 3rd line. When you want to let out some slack for side yarding you take up the line that is 'single' and let out the doubled line which you can do with the interlocking drums even while holding the carriage in the air. Turning cat's head inside the carriage turns mechanicals inside the carriage that feeds the 3rd line out of the bottom of the carriage. Ultimately, you lower the carriage close to the ground so the rigging slinger has not only the length of the choker but the amount of line that you extended out of the bottom of the carriage to reach the logs. When you go ahead on it, the butt rigging is pulled up to the carriage and the carriage can be raised lifting the logs free of the ground. The interlocking system makes this possible 'without dragging a brake' on some drum.