I row most of the time solo - therefore I set a boat up to optimize solo rowing. The additional gear in the boat
can be shifted around as ballast as required by conditions. The placement of the primary thwart is important to balance, stability,
and rowing mechanics. Balance meaning the impact of ballast distribution - remember we are nothing more than ballast
and power - on the wetted shape of the hull and subsequent performance. Stability meaning the effect we have on righting
moment and both initial and critical stability. Rowing mechanics meaning the the way our power is applied in rowing
from the standpoint of both comfort and efficiency. Lets look at each element individually.
BALANCE
A hull is balanced and performs as designed when it sits at or near the design waterline. The actual waterline
and subsequent waterplane (Shape and area of the waterline as viewed from above or below) often differs from the design waterline
because the boat is over or under the expected weight of displacement. If the boat is trimmed either bow down or stern
down relative to the design waterline then performance will also differ (though it may not suffer depending upon conditions).
Think about placing a heavy weight item or a passenger in the stern seat of a small dinghy. Dragging of the stern occurs
and power is lost and performance suffers. We of course assume that efforts are made to keep weight evenly distributed along
the centerline to prevent inducing heel to the hull. Heeling will cause a change in steering - the boat will not glide
straight. Placement of the aft edge of the primary rowing thwart over the longitudinal center of bouyancy (LCB) or over the
longitudinal center of the lateral plane seems to ensure that the rowers weight is placed above the "Rowing center" of the
boat.
STABILITY
The primary way that the placement of the thwart effects stability is the vertical height of the thwart above the waterline.
The higher in the boat the rower sits, the higher the combined center of gravity and the less stable the boat will feel. The
boat feels "Top heavy" and has an increased tendency to heel. Righting moment is affected. The boat feels less
stable and in fact is less stable. So we should place the thwart as low in the boat as possible. There are several
other considerations regarding the height of the thwart. Primary among them is rowing mechanics.
ROWING MECHANICS
As a reminder, what we are talking about here is both comfort and efficiency. As an example, go take a look at
the rowing skiff on the past designs and projects page. It was 21 feet long, very narrow, and you sat right on the bottom
of the hull on a standard boat cushion. Here is where comfort and efficiency are related. For a short row (under
five miles) the boat was amazing. As the miles glided by beyond that it became increasingly uncomfortable. Around
12 miles it was getting purely uncomfortable and focus on rowing began to suffer. I did 22 miles in that boat - once.
Is it possible to design in both comfort and efficiency? Absolutely. The key is to not design to the extremes.
For instance - sitting on the bottom of the hull does wonders for stability and allows a narrower boat, which in turn allows
for a longer boat of the same displacement and often one that tracks better. Yet it is brutally uncomfortable on the legs,
knees, and lower back and allows for little to no adjustment to the way you fit into the boat. I find that once you figure
out how high off the water the oarlocks must be (partly a factor of oarlock spread) and you know the depth of the boat then
you can place the thwart somewhere between the bottom of the hull and the inwhale. Where depends on you and the boat.
If you want to row sitting on a cushion - place the thwart lower in the boat. I find that 6 inches below the top surface
of the oarlock is necessary to properly recover the oars to the starting position of the stroke (especially in rough weather).
I also like to have the seat 6 inches above the bottom to the boat to make rowing more comfortable on the knees and legs.
Of course the foot stretcher or brace for your feet is a factor in this as well. The only way to successfully set the
boat up is by trial and error. Try mocking up a couple seat heights with wooden boxes (either on a trailer or in the
water). When it "Feels" right it probably is. Just make sure you can row without hitting your thighs on the recovery.
