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A twin hull rebuild

Aug 6, 2010

We wanted to lead the voyaging life and we found a catamaran we thought could be our boat. The catamaran had washed ashore at Paihia here in New Zealand’s Bay of Islands. After we bought Mazuran, a 42-foot South African “bullet” design, the first 40+ offshore catamaran designed by Alex Simonis in the mid-1980s. Mazuran had hull damage and we had a boatbuilding challenge to complete. Fortunately my partner Craig Nickalls and I have the same passion and Craig is a professional boatbuilder.

At first glance, the hulls didn’t seem that bad — the frames were pretty much still there, and all that was missing was from the waterline down. It seemed fairly simple. At first the plan was to fix her up and put her back in the water. But then Craig had the idea that we could redesign Mazuran’s hulls. It wasn’t until we cross referenced the waterline back to the original plans that we found that the boat was sitting 13 inches lower in the stern and seven inches in the bow. This fact made up our minds. We seriously needed more buoyancy or we would end up half submerged after loading Mazuran with voyaging supplies!

For more than two weeks Craig studied both plan and boat, set up centerlines, and cross-referenced between the two. Using his old manual boatbuilding apprenticeship techniques, he calculated center of weight (fore and aft), center of payload distributions and many other factors that help determine the performance of a vessel. We found that there were many issues that may have contributed to her sitting lower than on the drawn/designed waterlines. One of the major changes we found was the change from a single central 40-hp outboard to two 27-hp diesel engines, one in each hull — certainly a major weight change that would help lower the stern considerably from the initial design allowances.

Need more clearance
We have often talked to offshore voyagers discussing bridge-deck clearance, recognizing that this was crucial for comfort during ocean passages. If it is too low, the vessel ends up wave slamming and the passage can become very uncomfortable and noisy. Craig worked out that without any load aboard, Mazuran had a clearance of 22 inches. It seemed to us that this wasn’t great tolerance, especially if we were to have two children and a whole lot of gear still to come aboard. We therefore decided to try to get as much buoyancy as possible without rebuilding the entire boat. But we were confronted with a problem: how could we marry it to the existing hulls?

My stepfather, Alan Yardley (another multihull enthusiast) had just found a fantastic boat design program on the internet (www.freeship.org), and after only a few days of self-taught trials, he took on the challenge to help redesign our “new” hulls. We had Mazuran transported to my parents’ place in Kerikeri on the Bay of Islands.

There were endless hours both day and night, learning a new program and doing the redesign. While the design was being calculated, we decided to get an accurate weight of the current boat. We used digital scales and found that she was the respectable weight of 9,500 pounds. On transferring the information back to the original paper plans, we found that the center of weight was too far aft of the center of buoyancy — one of the contributing factors to the transom being very low in the water. Because the weight of the boat was reasonable, we decided to change from our newly built stub keels, to centerboards. We felt this was another benefit to make the boat more performance orientated, being ex-GBE and tornado sailors. We liked the system of retractable foils (rudder and centerboards) for shallow anchorages — all for a better night’s sleep.

A new design brief
So the new hulls needed more buoyancy farther aft, a longer waterline, and an increased bridge-deck clearance. This was our new design brief. We liked that the new hulls were a much more up-to-date design. The end result was a series of frames that we printed out on paper at 1:1 scale, transferred onto MDF in a female form, and cut out to shape. We then set the frames up in the shed under the wing-deck of my parents’ 37-foot Searunner trimaran and we had a beautiful form of a new hull shape after three days. This was a huge milestone in the way we were starting to think about our new home.

The next step was adding three quarters of an inch of foam. This was to match the original boat foam. We used 220-lb foam in the bow sections to make a more impact-resistant shell. The rest of the foam was 176-lbs. Because the foam wouldn’t bend across the profiles without breaking, we strip-planked the foam into the mould, glassed the inner shell first and added additional patching for more strength in higher-stressed places. The boat was originally constructed with vinylester resin, so we decided to use the same, which ended up being more economical.

We were so fortunate to have Craig’s dad, Paul Nickalls, to stay with us and help with the construction of the hulls and some preparation of the interior for new work. This meant work could proceed fast enough to get the hulls ready for completion by December and attached while the weather was still warm. It was a great opportunity for father and son to work on yet another project together.

While the hulls were being built inside the shed, the original hulls had to be opened up to accommodate the new shape. As soon as the cut was started, there was no turning back, we were now fully committed.

Preventing hull collapse
Temporary frames were cut and fitted inside the shell of the new hull to keep the structural strength while we transported it around, to prevent the hulls from collapsing. We faired the foam, fiberglassed the outer skin, and did lots of fairing and sanding for an undercoat finish while still upside down. We felt this was a great idea, to achieve as much as possible while it was at a reasonable working height. Each new hull weighed approximately 529 lbs. Craig, Paul and Alan managed to man handle these hulls — rolling them on the grass outside, and with the help of a temporary trolley made of planks, maneuver them into place.

That same night we decided to glue the hulls onto the original boat; the forecast was for rain the next few days. After already working for 10 hours, we went home and had dinner, then went back to work, set up floodlights (and coffee), and glued until midnight. This was a relief to know all was glued on, and we could now leave Kerikeri and head to Auckland to await the birth of our second child.

On our return to Kerikeri, we had a new crewmember, Blake, who was a healthy wee boy. We knew it was going to be a pretty hard next few months with a new baby, but with things going to plan, we would be able to keep to the same working schedule.

Once we were back working on the boat, we came up with another decision to change. We did research on extending waterlines and noticed that all the new modern catamarans had plumb bows. This would both extend the waterline, and depending on the construction method, would help with buoyancy in the bows. Craig thought it would be easier to laminate foam leftovers which would also help as a crash barrier in case there is ever a bow-on collision. With this being completely separate from the original bows, it still allowed the hull to be waterproof if there is ever a collision. It would act like a bumper to a car. While the bows were being formed we added “loops” from carbon fiber. These were to provide enough strength to carry a genneka or screecher.

We decided to change the tramp tracks from stainless steel saddles, to a bolt rope system. We decided this would be a major improvement from through-hull fittings, eliminating any potential leaking of the fittings in the future.

Transom makeover
The transom area was the next area to get a makeover. One of the problems we saw in the original stern was the accommodation of the steps — they seemed to disappear into the water. This seemed to be quite a problem especially when trying to transfer luggage to and from the boat via dinghy, or just wanting to dangle feet in the water. The boat was a 20-year-old design, and fashions have changed somewhat since then, but I knew I certainly wanted a transom that would be user friendly. Our GBE definitely did not have easy access over the transom, and I was often found trying to hoist myself while levering my feet against the side of the rudder boxes. This was something that I would like to avoid if I could in this boat. We decided that a mock-up with customwood would give us a good indication on her new extensions.

The addition of a boarding platform also allowed for an extension of the waterline. This would help the vessel’s performance, as the curvature of the hull would bring the transom out of the water.

Craig removed what he thought was only going to be one set of steps, but after their removal, he found there was another set underneath! Obviously the transom was definitely a part of the original design that needed attention. With the removal of all the little alterations we could apply our addition which would hopefully be the last.

One of the issues we noticed with our mock-up steps was the need for an additional step in order to get into the cockpit area. The new step shape had to consider the extension of the drum rudder on removal, and the restriction of access to the stern platform. A smaller, curved step took form, and once it was fixed into place, consideration to replace the original stainless steel was discussed. Obviously the change to a lashing backstay wasn’t in our original design brief, but after removing the plates, we found that there was slight corrosion. We didn’t want to have to replace these plates anytime soon, so we decided on their new lashing replacement. Creating a new carbon fiber plate meant no need for stainless steel fixings. The backstays would be lashed to the new plates — something that always appealed to us with our previous boats, so it was great to apply those changes to Mazuran.

Working on the exterior of Mazuran has been exciting, as we have felt the need to change original ideas for more modern practical solutions, thus possibly creating a better performing vessel. The changes we have made will improve buoyancy and comfort.

I have trusted Craig in all the suggestions for changes to Mazuran. He has been so creative and is constantly thinking of better solutions. The exterior has taken longer than anticipated, but we are building a better boat, and are making sure everything is “just right,” so there is much attention to detail. This is the way that Craig builds boats. I am very excited that the boat is progressing into more than what I ever expected.

Karen Taylor and Craig Nickalls are New Zealand multihull enthusiasts who plan to cruise aboard Mazuran.

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