Historically, trawlers are commercial fishing boats that pull large purse-shaped nets called “trawls” and, depending on the geographical area where they are built, a distinctive profile, usually one with a prominent pilothouse. These vessels are also known for having hulls with a large submerged volume (displacement) for their length on the waterline. (For the technically minded, a D/L > 400.) Their large displacement equates to carrying capacity for larger loads.
Over the last several decades, the term “trawler yacht” has evolved into common usage. It’s applied to a group of pleasure craft nominally intended for long-distance cruising and extended liveaboard, but with hulls that exhibit less displacement (submersed volume) than true commercial trawlers and are more suited to the needs of recreational sailors.
Although trawler yachts vary from one another in terms of their level of fit and finish and interior accoutrements, as a group, they are distinguished from “luxury motor yachts” by their general emphasis on function over form. The most popular trawler yachts also tend to be small enough to be owner-operated by a couple, without the assistance of a professional captain or crew — a limiting factor that has become easier and easier to meet these days because of the widespread adoption of bow and stern thrusters and electronic controls that include position-keeping functions.
For all reasons and seasons
For sailors making a transition to power yachting, LOA for LOA, a trawler yacht will generally have more and roomier accommodations than a sailing yacht. The trawler yacht also generally encompasses more of what could be termed “shoreside conveniences”, all-electric galleys, full size refrigerators and freezers, king- or queen-sized beds, and spacious heads. Perhaps, most telling, trawler yachts generally have more and larger windows and, therefore, more natural light in their accommodation spaces — a big plus for extended cruising and liveaboard.
Which trawler yachts are the most attractive depends, in most cases, on your background and experience. For instance, most sailing yachtsmen, who are used to maximum speeds of 6 to 8 knots, have little trouble transitioning to a full displacement trawler yacht with similar cruising and top speed. Indeed, yachtsmen moving from a sailing yacht to a trawler yacht usually find the elimination of the rigors of sail handling, plus the pleasures of navigating from an enclosed (climate-controlled and sheltered) helm position more than enough to justify their transition, without making any gains in passagemaking speed.
A trawler yacht is a trawler yacht is a trawler yacht… not!
Trawler yachts are also distinguished from one another according to their hull forms which include full displacement, semi-displacement, and planing types. The last of these categories being generally referred to as “fast trawlers” which exhibit more powerful main propulsion engines (usually twins) and achieve top speeds well into the “planing” range.
There are a lot of myths about which hull form is best for a trawler yacht, but the fact is the correct choice depends on what you want primarily to do with your trawler, what her main waters of operation are likely to be, and how fast you want to go, both most of the time and occasionally.
Full displacement trawler yachts are vessels that move through the water with their weight supported entirely by buoyant forces. As such, their immersed volume (displacement) remains constant underway, and the resistance which they face is generated primarily by the wave system they create as they push water out of their way. In general, a full displacement hull for can achieve a maximum top speed in knots of about 1.4 times the square root of its waterline length — or about 8 knots for a yacht that measures 36’ on her load waterline (LWL).
In contrast, semi-displacement trawler yachts have hull forms that generate a significant measure of hydrodynamic lift underway. This additional lift causes them to rise as they move through the water and thereby reduce the immersed volume of water (displacement) they must push out of their way. With less underwater volume, these semi-displacement hull forms can achieve higher top speeds than full displacement vessels — on the order of 13 to 15 knots for a yacht 36’ LWL.
Finally, there are the fast trawlers which are cruising yachts with trawler-yacht above-water profiles set atop of what are essentially full planing hull forms. Underway, these vessels generate enough hydrodynamic lift for them to rise pretty much onto the surface of the water and run with relatively very little hull volume immersed. And in this way, attain speeds on the order of 15 to 19 knots or higher top speed, depending on the size (HP) of their engines.
To be thorough, I also need to mention what I refer to as hybrid trawler yacht hull forms. For instance, full displacement hull forms that gain a modest boost in practical top speed through the addition of a bulbous bow — an underwater protrusion at the hull’s forefoot that overlays its own wave system on that of the hull proper and, in so doing, smooths out the latter, thereby reducing wave-making resistance.
Searching for the best of all worlds
You might think that having a semi-displacement hull form gives you the best of all worlds, efficient displacement speeds for long-distant cruising plus higher speeds when you want them. And to some extent that’s almost true.
Unfortunately, in the world in general, when you gain some flexibility with a “combo tool”, you almost always give away the top-rate performance of a special-purpose tool designed for a specific, narrow application. And the same is true in the world of yachts.
You might find a semi-displacement trawler yacht that will do an acceptable job running at displacement speeds and a pretty good job running at semi-displacement speeds. But you’re not likely to find one that runs at displacement speeds as efficiently as a well-designed full displacement vessel.
Finding the “sweet spot"
Independent of the speed range in which a particular yacht operates, every hull has its own “sweet spot” for cruising, namely, the point at which nautical miles covered per gallon of fuel consumed is maximized.
This is not just a matter of running slow or slower than you might otherwise want. Since the major contributor to a given hull’s total resistance is wave-making resistance, a given yacht might achieve better economy (nautical miles covered per gallon of fuel burned) and greater range running by faster rather than slower.
For example, suppose a given semi-displacement trawler yacht with a 36’ LWL burns 10 gallons per hour total at 8 knots but only 6 gallons per hour at 6 knots. You might decide it makes sense to operate most of the time at 6 knots which represents only a 25% reduction in speed yet a 40% saving in fuel costs and a 25% increase in range.
Well, you might do well to think more than once about it. The numbers might also indicate that, at 8 knots, the semi-displacement trawler yacht in question is running just below the speed at which she starts to rise significantly, reduce her effective immersed volume (displacement), and run at a reduced rate of increase in resistance. And that, consequently, if you push her to 12 knots, she’ll find her “sweet spot” and burn only 14 gph (which would work out to 0.85 nm per gal).
It’s obvious that 14 gph at 12 knots is a lot higher rate of fuel consumption than 4 gph at 6 knots. What is not so obvious, however, is that running at 12 knots with this particular yacht would achieve almost as good fuel economy as running at 6 knots, when measured in gallons per nautical mile covered (0.85 mpg versus 1.0 mpg).
On the other hand, let’s suppose you don’t care to ever run as fast as 12 knots but are content to run always at 8 knots or less. In that case, you might be better to select a full displacement hull form which will be much more efficient than a semi-displacement form when running at displacement speeds. Indeed, a full displacement trawler yacht of the size we’re talking about could conceivably use as little as 2 gph or 3 mpg running at 6 knots.
The bottom line is that, all other factors equal, you’re better off choosing a trawler yacht hull form that most closely fits your anticipated operational profile. Naturally, the case is rare when, in fact, all other factors are equal. In which case, you need to decide just how operating efficiency (fuel economy, range, etc.) fits into your prioritized list of requirements.
The Seattle Boat Show begins January 28th and will be entirely virtual this year.
Bill Parlatore from Seattle Yachts discusses the options for guns and other weapons while cruising on your boat.
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