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backbone

12 October, 2005

dry run of the backbone assembly

I write this as I commence with the final assembly of the backbone. Over the past year I have taken time off to work (building a deck in Garrett Park Maryland, and shorter stints working as a landscaper or with Pat Monihan and his sons as a welder’s assistant). Last winter I laminated up the keel out of 1″ stock and have shaped it in plan and elevation, leaving the fore-aft bevel until planking. The shop of very cold, but that also meant it was dry. I would laminate up several layers of plank and then cover the entire operation in a plastic tent with a small space heater, so the epoxy would be cured by the morning. It was a tremendous amount of work prepping and gluing so much wood. Wendy and Kate came up during Kate’s spring break and we laminated the outer stem. Working on my own I got dead wood, stern feather and post etc. done up.

By the Spring, Alice Hershey had moved out to Philly and worked for several months with me part time, which was a big help. She started out fairing various backbone components. We also built the frame for the transom. It was great having a second pair of hands in the shop. Sadly she finally had to get a real job and started working at a market research firm full time in August.

Keel bolts are fashioned out of 1/2″ and 3/8″ diameter 316 Stainless Steel bar stock and 1/2″ silicon bronze. “Interior” keel bolts (bolts that will be protected by a layer of cloth and lots of epoxy) will be steel while ballast keel bolts (which stand a much greater chance of being exposed to the water) will be bronze. While the catalog claimed that 316 stainless is of “good” machinability, it is actually absolutely terrible. I got out to the machine shop at Swarthmore and Smitty, the machinist, took one look at my bars and just shook his head. I labored for hours using different combinations of dies and lubricants to get the damn bolts threaded.

So that takes us more or less to 12 October. We are way behind schedule, and now plan on planking this spring. I am at home with a messed up back which I don’t want to make any worse given am to be one of Stu Merkel’s groomsmen this weekend. Mary Horstmann and I glued and bolted the outer stem to the keel earlier this week. Waiting for me in the shop are the components of the dead wood and tailfeather (I even have a chain hoist and I-beam trolley ready so I won’t strain anything!) as well as the three marine plywood layers of the transom, all waiting for assembly.


Zach cutting out part of the stem

Having made two trips out to Wisconsin, I have managed to haul all of our white oak back to Philly and have begun constructing the backbone. I was delayed by a contracting job I took in Springfield Township so I haven’t put in as much work as I would have liked in the past month. The last week of July Zach came up from Takoma Park and we cut out the pieces for the inner stem. We first made templates of the stem out of plywood and then transferred them to oak boards. The inner stem is to be constructed using a method described in Dave Gerr’s book Elements of Boat Strength, which he credits to the Covey Island shipyard in Nova Scotia. Using this method, the stem is built like you would a sawn frame, with the plys running longitudinally fore and aft.

After several delays described below, Bob and Zach came up to Philly and assembled the inner stem. It finally consisted of 7 layers of oak with staggered joints, bolted together with 5/8″ diameter 316 stainless steel bolts. It took us four hours of gluing to wet out each piece, apply silica thickened epoxy, and bolt everything together. We use a $30 postal scale to weigh our resin and hardener and then mix it with a drill mounted mixer. Zach and I then headed up to New York to see Jeremy in a play she helped produce. When I returned on Monday, the epoxy had set up nicely. Next chance I get I will fetch our power planner and start shaping the stem to the lofting floor lines. I am currently shaping up the wood that will go into our keel. Our current goal is to have all of the backbone structure laminated up before the weather gets much colder and then spend the winter setting up molds and preparing for a spring planking.

A girder fails...

While stem building commenced, there have been plenty of distractions. I took time off to run a get-out-the-vote effort in my South Philly neighborhood (divisions 2 and 3 of the second ward). We surpassed our turnout goals, handily won the city and state and got beaten in Ohio.  Clearly it was time to get back into the workshop. In the meantime, in late summer the still angry remnants of hurricane Jean tore through the city dumping plenty of rain. One of the storm drains relieving the leaky workshop roof clogged (a baseball knocked “out of the park” by one of the neighborhood kids was the culprit) and one of the rotten old girders holding up our roof threw in the towel. My area of the shop now floods quicker than ever in a serious rain (we have taken to storing our wood in the adjoining offices to keep it dry). Thus on rainy days (such as today) I stay out of the shop so that I don’t get tempted to run 220V machinery standing in 2″ of water.

testing a frame sample

Another project I have been working on in the past couple of months is test of our planned laminated frames. There is still an amazing amount of speculation and disagreement about the long term efficacy of epoxy resin especially when laminating white oak. Larry Pardy is perhaps one of the foremost anti-epoxy champions, although, with the greatest respect for his skill as a craftsman, he seems to come from a school of boatbuilding that frowns on any construction methodology more modern than old Nat Herrshoff was using 100 years ago. Dave Gerr also cautions against using epoxy and white oak, citing the acid in the oak interfering with a good bond. On the other hand, System Three (our expoxy supplier) claims this is not the case and I know that Covey Island has built a 57′ Herreshoff design using laminated white oak frames. In the past we have also used epoxy laminated white oak in other projects with few serious problems. Given all of the chatter, I decided to put my Bachelors of Science to use, and do some testing. I laminated six 1.5″x1.5″ samples. Three of them I boiled for 4 hours in salt water, dried for 8 hours, and then boiled again. All of the samples were then tested at the mechanics lab at Swarthmore College. We ended up satisfied with the results of the tests. For full results, click here.

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