Turning a deep-draft racer into a shoal-draft cruiser
Issue 116: Sept/Oct 2017
As we approached our retirement, Sandy and I confronted a dilemma. We had owned our Tartan 37, Higher Porpoise, since 1997 and had come to love the boat and her accommodations and performance, but she had a fin keel that drew 6 feet 7 inches. For cruising Southwest Florida, our destination, we needed a more reasonable draft of around 5 feet. We faced a critical choice: buy a boat with shallower draft or reduce the draft of our current boat. We considered both paths, but in the end we chose to keep and upgrade the boat we knew, and to reduce her draft.
The draft-reduction process was the final step in an extensive refit. We researched the available methods and found that, since Higher Porpoise had an external lead keel secured with bolts, we could replace it with an entirely new custom-designed keel.
We also found that we could have the keel cut to reduce the draft, with the lost ballast replaced by a heavier split bulb through-bolted to the remaining keel section. However, the split-bulb option would only work if the design was proper and if the cut line would be below the embedded ends of the existing keel bolts.
We began to gather the information that would tell us whether or not the keel reduction was feasible. We contacted Tartan Yachts and, through conversations and correspondence with Tim Jackett and Art Averell, located someone who had been involved in casting the fin keels all those years ago. We were able to confirm that the cut line for removing the desired 19 inches from the keel would be below the keel-bolt embedment. We also looked at the stability calculations for the boat as designed by Sparkman & Stephens, and it was apparent that additional ballast would be needed if we were to retain the boat’s original righting moment and overall stiffness.
After reading several articles describing such keel-reduction projects, we elected to work with MarsKeel Technology of Burlington, Ontario. The company is a renowned leader in keel technology and we wanted to be certain we were on the right path.
Design and casting
William Souter and the staff at MarsKeel were extremely professional throughout. We provided the information they would need, including the keel-bolt depth, detailed measurements of the existing keel, and the cut-point dimensions. We produced an accurate template of the keel at the proposed cut point and sent it as an AutoCAD file for them to use as a model for casting the bulb halves. They designed the split bulb to weigh approximately 2,300 pounds, replacing and augmenting the 1,800 pounds of ballast lost in removing the bottom 19 inches of the original keel. The cost of the casting was higher than expected, based on what we had read about prior projects. However, that was largely due to a dramatic increase in the price of lead over the last couple of years, something that was beyond MarsKeel’s control.
MarsKeel cast the bulb in two halves and shipped them to Larsen Marine in Waukegan, Illinois, where the modifications to the keel would be carried out. We bought Higher Porpoise at Larsen Marine in 1979, and the yard was highly recommended by fellow Tartan owners. The only missing part preventing the work from getting under way was Higher Porpoise. She was still at Mark Twain Lake, Missouri, where she had gone through the rest of her refit, which included installing a new engine and new standing rigging.
In early July, Higher Porpoise was loaded onto a transport trailer for her ride to Waukegan. As soon as she arrived, she was offloaded and placed in the area where the work would begin. Ian Gates and the Larsen crew went to work immediately, and Ian documented the entire project in photos.
Prep and assembly
The first step was to measure and mark the keel for removal of the bottom 19 inches. Next came the cut, after which the boat was lowered so the keel stub was resting on blocking. The crew then carefully and precisely maneuvered the two halves of the split bulb into position so the holes for the through-bolts could be drilled.
After drilling the holes and testing the fit of the bulb, Ian and his crew removed the bulb halves so they could prepare the keel surfaces. They removed all the old coatings down to the lead and roughened the surface to provide some tooth for the heavy thickened epoxy they would use in the final installation.
After attaching the bulb and tightening the bolts, they removed all of the thickened epoxy that had extruded under pressure, then used the same compound to fill the bolt holes and smooth any gaps between the cut keel and the underside of the bulb. They faired the entire bulb and the mating surfaces to produce a clean smooth surface before final finishing, which consisted of a barrier coat and several coats of new antifouling paint.
While the modifications were under way, Sandy and I were in Portland, Oregon, delivering family heirlooms to our daughter and her family. When we finally returned to Larsen Marine, we were anxious to see the finished project. We walked over to visit Higher Porpoise as she hung in the travel lift slings and were very pleased to note that her new keel looked as if it had come that way from the builder. To our eyes it was beautiful.
How does she sail?
The proof, as they say, is in the pudding. We had a number of questions that could only be answered on the water. On August 2, 2016, Higher Porpoise was launched in her new configuration. A couple of days later, after we’d tuned the rig and moved aboard, we began a 3,000-nautical-mile journey to our new home port at Burnt Store Marina in Punta Gorda, Florida.
Our first question was, “How will she feel?” We wondered what effect the keel modification would have on her overall stiffness. If anything, she seemed to be slightly stiffer than before.
The second question was one of performance. Our Tartan 37 with its deep fin keel had always been an excellent performer when going to weather. The purists wrung their hands and told us we’d be spoiling a good boat and would lose that performance edge. We have sailed to windward enough on our voyage south to say that, if she’s lost anything at all, it isn’t much. She still points quite high and goes fast when properly trimmed. If she does make a bit more leeway when going to weather, we have not noticed it, and in any case our racing days are over. We were also concerned that the modified keel might adversely affect weather helm, but to our delight we found it basically unchanged. She’s still a great performer and that’s good enough for us.
The third question was that of durability. How would the bulb and its attachment hold up to inevitable stresses, including groundings? (Yes, we did find a couple of shallow spots along the way!) Once we were safely home at Burnt Store Marina, we had a professional diver clean and inspect the hull, rudder, and keel. He reported that the keel was in excellent condition, and he was surprised when we told him that it was an attached split-bulb modification.
This was an expensive improvement. Anyone contemplating this modification for their boat and having the work done by professionals must expect the project cost to run from $10,000 to $16,000 depending on the boat’s size and the weight of the split bulb. Replacing the entire keel would likely be even more expensive. Those bold enough may be able to save as much as 60 percent of the cost by doing the cutting and installation work themselves, but should be mindful of the difficulty in working with lead and the potential health risks involved.
To sum up, we are glad we decided to keep our beloved boat and modify her keel. Faced with the same options and armed with our experience, we would make the same choice again.
Tom Wells had a long career as a professional engineer. He and his wife, Sandy, both retired in June 2016, and in August 2016 they set out from Waukegan, Illinois, on a 3,000-nautical-mile voyage south via the Great Lakes, Erie Canal, Hudson River, and the East Coast. They now live aboard Higher Porpoise and are based in Southwest Florida, cruising and enjoying life.
Thank you to Sailrite Enterprises, Inc., for providing free access to back issues of Good Old Boat through intellectual property rights. Sailrite.com
