|
|
|
|
Riveting and Oil Soaked Planking - an excerpt from correspondence with a customer Let’s talk about the fasteners first. The bottom four or five planks on each side of the keel in your boat are heavily oil soaked. They smoke when I drill a countersink hole in them. This is completely normal for a Fay and Bowen of its age. A common way the change the oil in early engines was to pull the drain plug in the oil pan and drain it into the bilge. Then a bilge pump could be used to discharge the oil waste overboard. It was even a widely held belief that saturating the bilge with oil over the winter would prevent dry rot. Almost every pre-WWII motor launch we have ever worked on has had oil soaked planking. It gives you problems in a few different ways. First, oil soaked wood will not absorb water and will not swell. Second, it is very difficult for any type of seam caulk to stick to oil soaked wood. These two issues make for a leaky boat. But the most damaging problem is that oil breaks down the lignin, the compound that glues the wood fibers together, in the planking. This makes the wood spongy. The planking cracks very easily on impact and fasteners can pull right through. When we drive in a fastener; be it a nail, rivet or screw; what helps hold the fastener tight is the wood being compressed and pushing back under the head of the fastener. With oily wood, this compression under the fastener head is quickly lost and the planks loosen causing the fasteners to fall out and the planks to leak. My decision to migrate from rivets to screws was based on discovering that your planking in the area where we were installing sister frames was very spongy. When we rivet, we drive a copper nail into a hole drilled smaller than the shaft of the nail. This greatly helps keep the nail shaft from kinking inside the plank when we peen over the end. When the shaft kinks, it can straighten out under stress causing the rivet to loosen. We set the rivet by driving in the copper nail as described previous, then one worker holds a heavy bucking iron against the head of the copper nail from the outside of the hull. On the inside of the hull, the second worker drives a snugly fitting copper washer over the end of the nail. The copper washer now has a cone shape from being driven over the nail and this is flatten out by driving a tight-fitting heavy tube over the end of the nail down on top of the washer. The nail end is clipped off about 3/32” above the now flat washer. Last, we use a ball peen hammer or special light air impact hammer to flatten and form the end of the nail over the surface of the washer, causing the nail to draw tight on whatever is in between the nail head and washer. How do we know when to stop? When a good head is formed over the washer and the wood members we are fastening are tight. So what happened when the wood is oil soaked? When we form the head, the wood in between the nail head and the washer does not offer much resistance as it compresses. It squishes, the members we are trying to fasten never get very tight and we can accidently pull the head of the nail right through the wood plank. When you rivet, you have less touch feedback than you do with a screwdriver. With screws, you can drive them into the members you are trying to fasten until the members become tight or you drive the head of the screw half way through the plank. Then you stop because you know that is as good as it is going to get. With the rivet, you cannot see the position of the head of the nail. So you can see that setting rivets through oil soaked planking can become very complicated and time-consuming. Other than these issues, I was trying to stay very close to our labor estimates. It is very easy for costs to rise a thousand dollars in a week if I am not careful. It was originally discussed that we would remove as little of the interior as possible when doing the keel and framing work. Some of the outside pieces of flooring go underneath the side ceiling. To remove these pieces of flooring, we have to pull off some of the lower pieces of ceiling to access floorboard screws. With the seats, they are not constructed modularly. They are built in place in the boat. To remove them, they need to be disassembled. This in it self is no big deal, but the screws holding the seats together are all mahogany bunged and finished. So, to pull the screws we have to pop out the mahogany bungs. When the seats are re-assembled, the new mahogany bungs will have to be stained and varnished to blend in with the rest of the seat wood. Without removing the seats and flooring, there are many areas where we are putting sister frames where we cannot swing a hammer or fit the air gun to rivet. And we really don’t want to use the air gun – remember the oil soaked planks. The bottom line is you are our customer and we want to do what makes you happy, as long as professionally we don’t think that you are making an uninformed decision. |
Contact InformationBerkshire Wooden Boat
Send mail to berkwood@verizon.net
with questions or comments about this web site.
|
