Rowing Geometry

The Basics of a Sliding Seat Rowing System

 

Below we outline the basics for correct geometry of a sliding seat sculling rowing system. For information about installing a fixed seat rowing system please visit our Fixed Seat Rowing Geometry page.

This information is useful for those creating their own rowing rigs, installing third-party hardware,or custom installing our Angus sliding seat systems in craft such as canoes or wherries.

These measurements below are derived from the sport of competitive rowing and have evolved over decades for maximum performance. This layout works well for recreational rowing, although sometimes minor tweaks are required for personal preference. For example, increasing the height between your feet and your seat (stretcher height) provides greater comfort and is easier on your back for long distance rowing. We have incorporated this adjustment in our recreational sliding rigger system.

 

Position of Rower/Sliding frame Relative to Craft

Generally, the center of gravity for a rowboat should be just aft of center. The center of gravity is determined by the mass of the boat and everything in it – rower(s), gear, passengers, etc. The rower should be positioned so the collective weight is just aft of center. Since equipment and passenger loads can be variable, often the most practical way to balance the boat is to position the rowing station just aft of center (so it is ideally balanced when rowing solo with no cargo) and then adjust the position of passengers and cargo as required.

As a rough guide, position the rowing station so its (and the rower’s) center of gravity is back about one foot from the center of the boat. The center of buoyancy for most boats is situated a little back from the geometric center, but for simplicity use the linear center. Since the rower slides back and forth, take his/her average position (the position of the seat half way through a stroke) as the location of their center of gravity. Place the sliding seat frame so that this seat position is centered two feet back from the boat center. Keep in mind this is only an approximate guide, and ideal positioning can vary depending on the boat shape and design. Trial this position with the boat in the water and make adjustments for ideal trim.


Rigger Position

Once the position of the sliding frame has been determined, the riggers/oarlocks can be positioned. The riggers are positioned relative to the sliding seat and there are two factors to consider – perpendicular and horizontal positioning relative to the sliding seat and footplate. The perpendicular positioning of the rigger is called the swivel height and horizontal positioning is called the stretcher position.


Swivel Height

The swivel height is the distance from the lowest part of the seat (where your hip bones rest) to the inside of the oarlock where the oar rests. The easiest way to measure this is to set a straight edge through both oarlocks and to measure up from the seat. Be sure that the straight edge does not bow, and press it firmly towards the pin since most oarlocks slope downwards (you want to measure up to the highest point where the oar sits). The swivel height should be 14-18 cm. Spacers are used to lift the riggers to the ideal height.


Stretcher Position

This is the horizontal distance from the location where the tips of your toes are located to the location of an imaginary line drawn between rowing pins. The line should run from the center of the stainless steel pins supporting the oarlocks. Simply wrap a string around the oarlock pins and draw tight as a reference to measure to. Stretcher position should be 50-65 cm. For our systems we find 50-55 cm works best. This measurement will reveal the location of where the riggers should be mounted to the boat.


Stretcher Angle

This is the angle of the footplate/brace and is ideally angled at about 40 degrees.


Oarlock Span or Spread

This is the distance between oarlocks measured from the center of the pins. Ideal spread is 157 – 161 cm. Like a gearing system, a larger spread will be a little easier, although the oars will move slightly slower. For a larger recreational boat, a more generous spread (towards 161) is ideal.

Stretcher Height (Heel Depth)

This is the vertical distance from your heels to the lowest point on top of your seat. This distance should be 15-20 cm.

 

Oars

The two basic blade shapes for sculling oars are Macon and Hatchet. Macons are the more traditionally shaped symmetrical blades and hatchets are asymmetrical. While hatchets are reputed to be fractionally faster (almost immeasurably), Macons offer two distinct advantages for recreational rowing. Being symmetrical, the oars can be used on either side of the boat – particularly beneficial for a spare oar. More importantly, if you decide not to feather due to injury or inexperience Macons are much better at being used without feathering. Hatchets extend further down and are more prone to catching the water.


Oar Measurements

For ideal performance the oar handles should cross over one another. This may feel awkward at first, but you will soon get used to it. Composite oar dimensions we recommend for our recreational craft are:


Macons Handle: Adjustable Grip 5 cm range
Oar length: 294-299 cm
Shaft: Medium Flex
Pitch: 0 degrees
Inboard 79-91 cm

For information on everything you need to know about oars for a sliding seat system, please visit our Oar Page.