Choosing Your Boat
(in the 15' to 25' range)
How do you find "the" boat? It's a question that we often get asked and quite frankly, it's not always an easy answer. Most of us are a lot more familiar with automobiles that we are with boats. At least we understand that there are basic differences between a family sedan, a sports car, a minivan or a pickup. When we go car shopping most of us have at least a rough idea of the "type" of vehicle we want, mostly due to familiarity and also because we know some of the questions to ask:
1) What is my primary use for the vehicle? Everyday grocery-getter and kid-hauler? Commuter? Towing a large 5th-wheel or boat? Hauling tree branches, rubbish and yard debris? Enclosed space for construction tools and equipment?
2) What kind of performance is necessary? Is this my week-end rocket ship? Am I after great economy for commuting? Do I have to tow a great deal of weight?
Well, boats have the same kind of differences that vehicles do, it just isn't as obvious if you're not as familiar with boats as you are cars. And, all the same types of questions should be asked...and answered. What is my primary use? What kind of performance is necessary?
I'll use some analogies to different vehicles to try and convey how each type of boat might be viewed. Others may have different opinions and that's fine, hopefully what I have to say will add to you own personal knowledge base and allow you to make an informed decision about which boat is best for you based on your needs and desires.
There is one area of major difference between vehicles and vessels...the influence of speed on design. Unless you're looking at a very high-end sports car, top speed is of little importance (handling and acceleration but usually not top speed). We just sort of assume any new car we choose will cruise at legal highway speeds. So other than tuned suspensions for top-notch handling or slippery shapes for fuel economy "speed" per se doesn't dictate much of the car's design. Not so with boats...speed defines everything about the hull's shape. This is almost the first thing you must do...decide on a speed range that you want your new boat to operate in. Without getting into some very exotic materials and designs (none of which are available at the local boat dealership) all boats operate in a specific "envelope" of performance.
Boats come in three main types...displacement hulls, semi-displacement hulls and planning hulls (I'm oversimplifying this but it covers the basics). A boat with a displacement hull stays down in the water and its speed is limited by the length of the hull (specifically 1.34 times the square root of the waterline length; the number generated from this exercise is called the Speed/Length Ratio); this type of boat is the typical trawler yacht. [It could also be a true displacement working hull but that's not something you'll typically find when shopping for a new boat.]
The semi-displacement boat has a hull shaped to exceed the "speed limit" of the true displacement hull and by applying more power the design of the hull allows the stern to lift in concert with the bow and the boat can accelerate. These are pretty rare boats these days at new boat dealerships. These hulls generally operate in the 1.5 to 2.5 range of Speed/Length ratio (that is, 1.5 to 2.5 times the square root of the waterline length of the hull). To put that in perspective for a 15-footer that's 5.8 knots to 9.6 knots and for a 25-footer 7.5 knots to 12.5 knots.
The planning style hull requires enough horsepower (and the right hull shape) to climb over its bow wave and to "plane" on the surface (generally this is a Speed/Length ratio of 3 or more) and this type boat is fairly light (for it's length) and most often powered by large engines. The two most important types for our discussion are the deep-v hull and the modified-v hull. The deep-v hull was originally developed for racing and heavy weather use (military and rescue primarily) and has been continuously refined for many decades. Unfortunately, it has also been so over-advertised that many folks looking for a new boat think this is the only type of hull available. That's like saying the only car you can buy is a Corvette. Obviously, there are lots of choices and lots of reasons for choosing a particular hull style.
Economy follows speed...the displacement boat has the best and the planing hull the worst. In general it takes 4 times as much horsepower (and fuel) to go 2 times as fast. Another way of saying this is: if you want ultimate economy you have to slow down. Semi-displacement boats usually get better economy than planing hulls but nowhere near a displacement hull. That jump from displacement speed to semi-displacement or planing is an expensive one; both in terms of up front investment and in fuel.
So back to operating speeds...you have to nail this down...it's the one thing that most defines the boat you're about to purchase. There is no right or wrong, only different, and your choice here will set the fundamental hull design no matter what the boat "looks" like aesthetically. Specific boat hulls have specific operating ranges (windows, or envelopes) outside of which they are not happy (and by extension, neither are you). You can only stretch the operating speed range so far so if you read about a boat that's "too good to be true"...it is. With very rare exception boats only operate "best" in the speed range for which the design in optimized, and sometimes "ok" in one other range...almost never in all three ranges (displacement, semi-displacement, and planing); especially not mass-produced boats which are really the subject here.
The hardest thing to make a boat do is go through very rough water very quickly. The more the design is optimized for that the less likely it is to be comfortable (or effective) at other speeds. Large jets can't land and take-off at small airports because they can't slow down enough to touch down and get stopped and/or there's not enough length of runway to allow them time to get to the speed necessary to generate enough lift in the wings to fly. Nothing about that seems to surprise people and it makes perfect sense. Yet folks always seem surprised when the 26-foot deep-v boat they bought, powered with a 7.4-liter engine and designed to run at 30 knots plus doesn't seem to do well when the water gets rough and they try to slow down to 15 knots. If it were an airplane it would have just stalled and fallen out of the sky! Similarly the hull (mostly at the very 'v'-ed stern runs out of lift (hydrodynamic support) at slower speeds and settles deep into the water; typically leaving the bow pointing skyward.
This part I'm sure most boat dealers would rather you not read...you need to become an informed consumer. Look, if you head into your local car dealership to buy a nice family sedan and the only salesperson around has a real love of sports cars s/he's not going to get to very excited about the latest comfort features of your mall cruiser. And, of course, that's a generalization and isn't always true but you understand my meaning. The same holds for a boat dealership. If you're looking for a nice economical family boat and you show up at a dealership with the latest high performance deep-v, go-fast boats guess what they're going to want to sell you? You need to decide what you want and what will best your uses. That's what I'm hoping to convey here. So, lets continue...
A boat with a real deep-v hull is a performance boat. Every one of us would agree that a Corvette is a performance car, to call it anything else would be less than fair, same for the deep-v hull. Sure, the Corvette will take you down to the grocery store and back but that isn't what the designers had in mind when they put the car together and most folks would not find it very satisfying to operate it that way. A deep-v hull requires a (relatively) high horsepower engine and (relatively) high speeds to achieve its design goals. Think of it as driving a sports car through the mountains. If you love the thrill of acceleration, the adrenaline rush and the fine art of performance handling you'll love a full-on deep-v hull. But just like most sports cars, I've found over the years that the drivers are usually a lot happier than the passengers! And, just as most of us would find driving a Corvette through town and rush hour everyday a bit of a chore and a "waste" of a good sports car the same holds true for the deep-v hull. It really wants to get out there and perform. At low speed it usually s-turns and a mid-speed it tends to sink into a "hole" created by the deep-v stern which results in a bow high attitude and lousy fuel economy. Up on top at high speed and in moderate waves it's in its element. When the waves get really bad even a deep-v has to slow down and this is where my major complaint about this hull type comes in. When you slow down the bow goes up, the stern goes down and the fuel economy hits the skids.
A boat with a modified-v is a little harder to define...it can be oriented toward being like a special edition sedan...not really a sports car but with a sporting flair...or it can be a oriented toward being like floating minivan, able to do a little bit of everything pretty well. Just like a minivan you can load it up with 6 folks and go across the mountains comfortably and safely...just don't try and keep up with the Corvette that just passed you! So when looking at boats with modified-v hulls you need to really get to know the boat and ask lots of questions to figure out what the best attributes of a particular hull are and whether or not they fit your needs.
There are a couple of boats out there that are the floating equivalent of the old Volkswagen Camper bus; basic comfortable amenities, simple design, good fuel mileage and aimed and pure fun, albeit at a modest pace. They're safe and they'll go darn near any where but they need an owner that is not is a really big hurry, at least not in rougher weather.
In really general terms... a deep-v hull does one thing really well, it goes through rough water with more comfort than other hull types. Unless you're looking for this type of performance, and many are, a modified-v hull is a better choice giving better fuel economy, a wider range of operating speeds, more stability at rest (or when trolling) and less lateral movement when someone moves around the boat while running. In other words, there are more of us looking for minivans than Corvettes. That doesn't make the Corvette any less fun, just maybe not what we need. The interesting thing is that there are more Corvette wannabe's out there then there are minivans. You'll need to keep looking to find just the right boat. Don't let the boat salesperson sell you his/her dream, it might be your nightmare.
Good luck and happy boating,
Les Lampman
E.Q. Harbor Service