Shipwright Dave Sharp shares how steam bending is used to form and install the stern for the Crystal S restoration project.
In the video, we’re steam bending the white oak ribs around the stern to support the vertical red cedar pickets.
These ribs are cut into straight strips in the same dimensions as the hull ribs, from 2” rough sawn, green oak boards (“green” meaning not kiln-dried as with most retail hardwood lumber).
The higher moisture content of the green lumber helps the pieces become more flexible after the steaming process. In fact, we soaked these particular ribs in the river for a couple of days to ensure as high a moisture level as possible prior to steaming.
For steam, we’re using a custom made stainless steel boiler, fired with a propane burner and a smaller wooden steam box that takes much less energy to heat and keep warm than the large original steam box inside Richmond Boat Builders (RBB).
To successfully bend and twist these ribs, we need to steam them for around an hour and a half, but we will always encounter the odd rib that has less than ideal grain which will cause them to break.
This is roughly the same process that has been used for hundreds of years, except that in older times the boiler fuel source might be wood or, in the case of RBB’s original boiler, oil.
For the Crystal S, with these horizontal stern ribs in place, we have completed the stern pickets, finished installing sixteen new hull ribs through the cockpit area and are ready to install the main cockpit bulkhead this week.
