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The Hull Truth: SeaVee Z
SeaVee's stepped-hull boats provide sure handling in a variety of sea conditions. For a complete performance report of the 390-Z, look for our test during 2014.
FasTrac, SureTrac, Z-Trak, Z-Plane -- the world of hull design is a hive of buzz phrases. But what they really mean could be a telltale sign of which used boat to buy, or not to buy.
Oooh, the clean sweeps and crisp lines of those boats. Such style! You'll see a lot of that on these pages. But hull design is not just a matter of style. At least it shouldn't be.
A boat hull has all sorts of shapes, bends, fins and grooves -- things you can see most clearly when the boat's on the trailer. Surely, you've wondered: Why the hull do boat makers do that?
Well, they do it because a deep-V hull is seaworthy but slow, and a flat-bottom is fast but flakey. Finding a blend of seaworthiness and speed has become a tantalizing challenge for some builders. Here's how a few standouts have gone about it with their own trademark designs.
Case Study: SeaVee Z Series
SeaVee boats have long been heralded for their great-running conventional deep-V hulls. At the 2013 Fort Lauderdale Boat Show, the Miami boat builder introduced their new “Z” series line of stepped-hull boats.
I sea-trialed SeaVee’s 390-Z and then met with John Caballero of Sea Vee to get the “hull truth” behind these new double-stepped center console boats. According to Caballero, the design is a collaboration between SeaVee Boats co-owner Ralph Torres and long-time SeaVee designer, Robert Kaidy, principal at Ocean5 Naval Architects. It features a pair of small, 2-inch tall steps with large vents at the chines. This feature purportedly prevents the vents from clogging up and allows the more air to be fed to the hull, alleviating the “hitch” or “hesitation” –it's an instantaneous loss of speed, really--that many stepped hulls exhibit due to clogged vents. During my trial of the 390-Z I can say that I did not experience this hesitation. I will also say that I have experienced it aboard other boats. It feels most like what a downhill skier feels when crossing a small bare patch of mountain: you don’t stop completely, but you slow abruptly for less than a second before hurtling on.
The second key feature incorporated into SeaVee’s Z series hulls are the so-called “speed rails.” These are the 90-degree inside corners molded into the chines and strakes, as seen in the above photo. These are on the aft hull panel only—that is, the part of the hull aft of the aft-most step.
Speed rails keep the boat tracking true, particularly in turns. Many stepped hull boats get “squirrely” when turning. But I was able to haul the SeaVee 390-Z through some high-speed, hardover turns with as much confidence as I would when commanding a conventional V-hulled boat.
Finally, the Z series hulls feature a flat keel for most of the length of the underbody. This stays wet and allows installation of through-hulls to be successful, something always problematic aboard stepped-hull boats. But more importantly, the flat keel section provides more lift, easing the transition onto plane. Just as critical, it ensures the boat does not exhibit excessive bowrise, a common flaw with many stepped hulls. Since boating measures bowrise as part of our certified boat tests, I can say that the SeaVee 390-Z does not exhibit excessive inclination (bowrise); the most I measured was 3-degrees.