Against the wind - The making of Wind Horse

Author:
Publish date:

When it comes to long-distance cruising we admit that we’re spoiled. Our last boat, the 78-foot ketch Beowulf, allowed the two of us to make anchor-to-anchor passages of 300 miles per day in the trade winds — without crew. And while this did involve a certain amount of effort on our part (not to mention the odd burst of adrenaline), we traveled many thousands of miles in extreme comfort.

So when it came time to consider switching to power, not wanting to go backward in terms of comfort or performance, we had a difficult set of standards to achieve. Among them: a minimum 5,000-nautical-mile range under power, the ability to average 11 to 12 knots on long passages, comparable heavy-weather abilities to our sailing designs, substantially less work at sea, and being able to put the boat into mothballs for extended periods of storage in less than a day.

Although heavy weather is rare, our practice has always been to design for the worst. With our sailing designs, good heavy-weather characteristics yield boats that are also very comfortable on long ocean passages. These design factors include good steering control upwind and downwind so the autopilot is always able to handle the boat, the ability to run off in big seas without undue worry about broaching, and the capability of recovering from a wave-induced capsize. A hull shape, power package, and structure that allows the boat to be pushed hard in adverse weather substantially reduces the risk of being caught out in the first place.

Read accompanying story: Against the wind

So how did we go about achieving these goals with the FPB 83 Wind Horse? The initial design process involved 3,000 hours of creative time (7,000 hours total engineering time) and literally thousands of configurations. In addition to our real-world database, we made extensive use of computational fluid dynamic (CFD) modeling and tank testing. The final configuration was a hull shape with moderate beam at the deck and a narrow waterline beam, combined with a relatively low center of gravity (for a motor vessel) and substantially oversized active stabilizers.

The narrow waterline beam gives us excellent steering capabilities (in most situations our WH autopilot is turned to the lowest setting), as well as being easily driven. A pair of John Deere 4045TFM diesels, producing 150 hp each, pushes us at 12 knots in most combinations of head winds and seas. The ends of the hull are finer than you might normally see, which makes it easy to penetrate head seas with little motion.

An important part of optimizing comfort is the distribution of weights around the hull. The resulting “polar moments” affect how the boat responds to the waves. This is one of the areas where using CFD modeling is so helpful, allowing us to test varying weight arrangements with a relatively high degree of precision about the impact of different configurations.

The other factor affecting comfort is where we live at sea, relative to the motion center of the boat. We know from experience and from the CFD work that there is a region within the interior where the motion we feel is moderated compared to what it is outside this area. The interior is laid out so we can stand watch, lounge, cook and sleep always within this zone of comfort.

There are a variety of engineering standards to which most yachts are built. For this project we worked with the Lloyds Special Service rule, All Oceans classification. The Lloyds Special Service rule dictates the requirements for every piece of the structure, based on what the designer inputs for boat speed. The rule then offers up a worst-case wave scenario and predicts impact loads throughout the hull. Even though this is a very conservative rule, we felt the result wasn’t as tough as we’d like. So framing and plating specifications were substantially enhanced to double the required stiffness.

On our passage from New Zealand to Fiji, we timed the departure to coincide with a frontal passage to test Wind Horse in confused waves and gale-force winds gusting into the low 40-knot range, with significant wave heights above 20 feet. We were pleasantly surprised to find Wind Horse significantly more comfortable than would have been the case with one of our sailing designs. Another surprise was the noise level. Compared to a modern sailboat with Spectra sail cloth and high-modulus running rigging, the interior of the new boat is quieter even in the lighter wind ranges.

Between Fiji and Los Angeles (a little more than 5,800 miles on the log) we averaged 10.5 knots over the bottom, burning 7.4 gallons of diesel per hour for all requirements. Most of these passages were in head winds averaging 15 to 25 knots, with normal trade wind seas in the 6- to 12-foot range.

Another surprise with the new boat is operating costs. Including an allowance for maintenance and eventual replacement of engines and transmissions, these costs average somewhat less than two-thirds of those we experienced with Beowulf. If we were to slow down to 9.75 knots from 11, cost per mile would drop to around half of what we experienced under sail.

Less work, more comfort, comparable or better security in heavy weather, lower operating cost — what’s not to like? We’ve been sailors for a long time and it is hard to admit we’ve switched sides.

For more information on the FPB 83 and the Dashews’ publishing house, Beowulf Publishing, as well as a host of cruising materials and information, call (704) 365-1486 or visit www.setsail.com .