The first type is characterized by the Dreissigacker/Williams device (referenced above). With this type the flywheel and footrests are fixed to a stationary frame, and the seat is free to slide fore and aft on a rail or rails integral to the stationary frame. Therefore, during use, the seat moves relative to the footrests and also relative to ground, while the flywheel and footrests remain stationary relative to ground. This type is sometimes referred to as a "stationary" or "fixed head" rowing ergometer.
The Challenge AR has the capability to allow the rower to control and adjust the resistance from “Feather light” to “Olympic sprint” delivering a silky smooth resistance to the user’s effort and instantaneous response to input with no “flat sport”.  With water resistance being the most accurate manner in which to simulate actual outdoor rowing, the Challenge AR provides a smooth and consistent sensation throughout the range of motion of the exercise experience.  
At the international level, women's rowing traditionally has been dominated by Eastern European countries, such as Romania, Russia, and Bulgaria, although other countries such as Germany, Canada, the Netherlands, Great Britain and New Zealand often field competitive teams.[55][57] The United States also has had very competitive crews, and in recent years these crews have become even more competitive given the surge in women's collegiate rowing.[58]
It’s time for a revolution — a rowing revolution. For too long, the rowing machine has been the default loner in the corner of the gym that seems to always be available. The desperation needs to end. Rowing machines work three major power groups of muscles — arms, core and legs — and are some of the most efficient power tools. With this one machine, you can target your quadriceps, hamstrings, glutes, shoulders, upper back, arms and core. While there may not be an uptick in gym users, there’s undoubtedly an upswing in fitness studios opting to mix in a rowing component or focus on rowing as a critical fixture.

The Verified Sustainable Hardwoods used for the WaterRower are sourced from the Appalachian Mountain region of the eastern United States, where planting rates exceed harvest rates by an average multiple of 2.29. The Appalachian Hardwood Timber resource includes more than 65.4 million acres in the eastern United States and provides the world with a bounty of the finest hardwood species.

In the 1970s, the Gjessing-Nilson ergometer from Norway used a friction brake mechanism with industrial strapping applied over the broad rim of the flywheel. Weights hanging from the strap ensured that an adjustable and predictable friction could be calculated. The cord from the handle mechanism ran over a helical pulley with varying radius, thereby adjusting the gearing and speed of the handle in a similar way to the changing mechanical gearing of the oar through the stroke, derived from changes in oar angle and other factors. This machine was for many years the internationally accepted standard for measurement.
Rowing is one of the few non-weight bearing sports that exercises all the major muscle groups, including quads, biceps, triceps, lats, glutes and abdominal muscles. The sport also improves cardiovascular endurance and muscular strength. High-performance rowers tend to be tall and muscular: although extra weight does increase the drag on the boat, the larger athletes' increased power tends to be more significant. The increased power is achieved through increased length of leverage on the oar through longer limbs of the athlete. In multi-person boats (2,4, or 8), the lightest person typically rows in the bow seat at the front of the boat.
On a rowing machine, you don’t want to be wearing clothes that are too baggy as the fabric can get caught between the seat and the beam it slides on.  It’s not a disaster if that happens, but it can get annoying if your shorts keep getting caught there while you’re trying to get a serious workout.   It’s better to wear shorter, tighter-fitting shorts (nothing ridiculous), but just enough to ensure it doesn’t the material doesn’t hang down.
If you are anything like me, you read the negative reviews to see what some of the complaints could potentially be...I have found none that match with my machine or experience so far. The boxes it came in were a little bunged-up but everything on the inside was perfect. Only took about 15-20 minutes to build (first time building a row machine) and another 5-10 to fill with water. We used it for a little while before we added the danish oil. 

With the smaller boats, specialist versions of the shells for sculling can be made lighter. The riggers in sculling apply the forces symmetrically to each side of the boat, whereas in sweep oared racing these forces are staggered alternately along the boat. The sweep oared boat has to be stiffer to handle these unmatched forces, so consequently requires more bracing and is usually heavier – a pair (2-) is usually a more robust boat than a double scull (2x) for example, and being heavier is also slower when used as a double scull. In theory this could also apply to the 4x and 8x, but most rowing clubs cannot afford to have a dedicated large hull which might be rarely used and instead generally opt for versatility in their fleet by using stronger shells which can be rigged for either sweep rowing or sculling. The symmetrical forces also make sculling more efficient than rowing: the double scull is faster than the coxless pair, and the quadruple scull is faster than the coxless four.
The dense resistance of water creates substantial drag, but on the WaterRower models, this is perfectly tempered by a whippy cord. It coils and recoils with such steady speed that one tester noted how the Classic “eats the rope back up on recovery.” This smooth agility helps balance out the impact of encountering slow water at the start of every stroke.
In the patent record, means are disclosed whereby the chain/cable take-up and handle return are accomplished without the use of a spring or elastic cord, thereby avoiding the stated disadvantages and defects of this broadly used method. One example is the Gjessing-Nilson device described above. Partially discernable in the thumbnail photo, it utilizes a cable wrapped around a helical pulley on the flywheel shaft, the ends of this cable being connected to opposite ends of a long pole to which a handle is fixed. The obvious disadvantage of this system is the forward space requirement to accommodate the extension of the handle pole at the "catch" portion of the stroke. The advantage is that, except for small transmission losses, all of the user's energy output is imparted to the flywheel, where it can be accurately measured, not split between the flywheel and an elastic cord of variable, unmeasured resistance. If a similar system were installed on all rowing ergometers used in indoor rowing competitions, consistency between machines would be guaranteed because the variability factor of elastic cord resistance would be eliminated, and this would therefore ensure that the monitor displayed actual user energy input.