How Designers Balance Speed and Comfort
How Designers Balance Speed and Comfort
The designer of your typical new racer/cruisers starts with a design brief—sometimes complex, sometimes not. Once the importance of speed versus other considerations has been established, designers begin to focus on such issues as hull shape, weight, cabin dimensions, sheeting angles, structure, and layout, not to mention cost. The design brief acts as a priority list from which a spiral of design decisions evolves. Each decision impacts the next, as the designer tries to strike a balance between speed and comfort.
Our first priority with the J/109, says designer Al Johnstone, was to establish its performance goals relative to other boats. Based on this decision, the shape of the boat was more important than the interior and helped define the length, beam, and wetted surface. Most other designers presented with specifications for a new boat go through a similar process. Bill Tripp, the designer of the Turner 56, says, It usually takes about 10 days to establish hull form, rig, ballast, and interior, in that order. Then we look at the performance range. The details often take the better part of a year.
Hull: Fast Shapes vs. Weight-Carrying Capacity
The designer must consider total weight when evaluating hull forms. The interior specifications are all up front, says Jim Andersen of Carroll Marine, builder of the Farr 395. Our weight studies are part of the preliminary design. The internal weight study considers materials, which affect cost and ultimately how fast the boat will go.
Hull form starts with length, which is the greatest attribute in a monohull for creating speed and interior volume. We all like to draw bigger boats because it helps internal volume on a racer/cruiser, says Tripp. But when you have a long waterline you have to be careful that the boat doesnt get too flat on the bottom. Its all about speed, control, and seaworthiness.
Computer technology facilitates the drawing of hull lines. Tim Jackett, principal designer for Fairport Yachts, which builds Tartans and C&Cs, says, On the new C&C 99 I was able to try about 100 different hull forms in a two-week time span. In the old days, it would take two weeks to draw one plan. Now I can test one out in two hours. Jackett can refine his design by importing data between the hull form software and a two-dimensional drafting program for the interior.
As designers use the computer to adjust the hull form to meet performance and weight-carrying goals, two dimensions that can be changed on a racer/cruiser hull are the entry and beam. A faster, narrower hull form can actually make for a more comfortable boat in a seaway but the boat will have far less volume for the interior. On race boats, you often see the bow knuckle out of the water, says Bruce Marek, designer of the new Cape Fear 38. But on a racer/cruiser you might have the knuckle sunk 9 inches for buoyancy to accommodate chain lockers and such.
Cabins: Soles vs. Headroom, Style vs. Function
After hull form, the next design priority is often the placement of the cabin sole. Cabin sole height affects how much interior volume the boat has, as well as headroom. Designing an interior for a racer/cruiser under 40 feet is tricky because the first issue is headroom, says Marek. Im only 54 but most customers expect 62 headroom on a dual-purpose boat. From a styling perspective, having freeboard and a cabin house that dont look like the World Trade Center is tough to do. On a 40-footer, the cabin sole will often be 9 inches below the waterline, but on a boat 5 feet longer, the sole can be 12 inches below waterline. Up forward, with the slope of the deck, headroom and sight lines become even more difficult on a 40-footer. Headroom is one of the reasons Marek put the head aft by the companionway on his Cape Fear 38 instead of placing it forward of the bulkhead.
Although designers told us that one owner-accepted change in design over the years is the extended height of freeboard and cabin houses, none of them liked the change. High cabins raise the center of gravity and in general, designers try to add volume below the waterline to counter this. High sides arent pleasing to the eye and are a central issue for any designer. With computers its easy to make dimensions work, says Jackett. But I find it important to manipulate the tool to fit my eye. I print out the design and tack it on the wall right in front of me so I have to look at it every day and live with it before it becomes physical.
Once headroom is established, the interior layout has to accommodate the live-aboard aspect of the racer/cruiser. Theres a tendency to miniaturize things, but the human body doesnt shrink—so you have to have a commitment to size, says Johnstone. Weve produced more than 30 designs, and know from experience about absolute minimum sizes: length of a berth should be 64, settee berths should be angled slightly, and a nav table has to be 24 inches wide—bigger is even better. Rodger Martin, designer of the new Aerodyne 43, relies on experience as well, but uses cad men in his scaled drawings to make sure the boat is functionally the right size. He also will sometimes mock up a layout with cardboard.
Another issue that affects interior volume is the cabin house width, which is a function of sailplan and rig choice. Sheeting angle width affects performance, so you want chain plates 12.5 to 13 degrees off centerline, says Marek. Ill draw the jib tracks and then draw the cabintop inside them.
Weight: Reduce, Eliminate, or Position for Performance
Adding a comfortable interior to any boat adds weight, the bane of any racer. So there are a number of ways a designer can eliminate or position weight, but always with tradeoffs. A few years ago a racer/cruiser with a sail-area-to-displacement ratio of 20 was the standard. Today the target for a base boat might be 23 or 24. Loaded with such modern conveniences as microwaves and laptop stations—like those found on the Turner 56—the weight has to be reduced somewhere else—but where and how?
A designers first rule of thumb is to reduce weight in the ends of a boat by centralizing the heaviest things like batteries and tankage. This is the primary reason the head on the J/109 is amidships instead of forward by the V-berth. The second rule is to make the interior structural as well as functional. Learning to make things like seat backs and seat bottoms join at the hull so they become part of the longitudinal structure is still the best way to save weight, says Martin. The least possible elements make for good design.
The engineering aspect of the design includes refining laminate thickness and checking the center of gravity to make sure things match up. Designers also taper laminates and modify the thickness of the core where they can to keep weight in check and costs down. At J Boats, the final design element is the keel. While the keel position is usually fixed at this point, Johnstone and his team can adjust the center of gravity through the keel design.
To save more weight costs money. After centralizing weight and making interior structure functional, the next consideration in weight control is materials, both material control and material selection. How does materials control affect design? Something as simple as how much bonding putty is used for installing headliners concerns designers and creates process- control issues for builders. Most designers expect exacting tolerances from builders. The best builders are weight conscious.
Tim Jackett not only decides which boats C&C builds, he designs them. Because he works for the builder, he works hard at improving quality controls in the production process that can give him an advantage on the design end. For instance, replacing chopped glass construction, typically found in cruising boats, with a vacuum-bagged laminate structure can drastically reduce weight. We went from using 900 pounds of resin to 300 pounds in the latest boat, says Jackett. Its lighter, stiffer, and stronger, but it costs more to produce. Selecting such lightweight materials as Kevlar or carbon fiber can have fantastic performance benefits, too. We used carbon cloth to strengthen the keel sump on the 99, says Jackett, but because of the higher cost, we didnt use the material elsewhere in the boat.
For designers trying to balance weight against cost, one of the final issues is choice of interior detailing. Twenty years ago most cabins had teak trim that a builder could simply oil before going to a boatshow so it would look nice, says Marek. If an owner wanted it varnished hed do it as a winter project. For a builder a varnish job might add another $7,000 to the price of a boat. Because money matters to most buyers, builders offer a choice of finish options such as the mahogany, cherry, or teak choices offered on Mareks Cape Fear 38.
Martin, on the other hand, has styled the interior of the Aerodyne 43 without what he calls gratuitous slabs of wood. Wood can be a nice accent but I want it to be functional as well, says Martin. On the 43 we use it for fiddles and a frame that rings the cabin but doubles as a bookcase. He also says that because the wood accents are structural they allowed him to reduce laminate schedules used in the hull. Structurally, wood works well for curved arches over doors and as terminals for doors and lockers. You cant really separate aesthetics and engineering, says Martin.
Designers dont get involved in finish and fabric choice that often. Those are usually customer decisions. I do get asked my advice on materials though, says Martin. I laugh when people question the sanity of putting leather in a boat. I usually tell them, Well, it was waterproof when it was on the cow and then we treat it.
For designers who have a number of racer/cruisers to their credit and whove stayed abreast of the latest technology, it can still be difficult to bring something different and innovative to a layout that always calls for bunks, head, galley, and nav station. As you peruse the new racer/cruisers at boatshows this fall, keep in mind the designers try to strike a balance to create comfortable boats that go fast, too.