Piloting Part 6, Rowing in the Wind

“While not pleasant, rain has little adverse effect on rowers. Heat stress can be a problem for athletes, but the major impact is wind speed and direction.”

BBC July 28, 2012 in discussion about rowing events at London Olympics 

“Sailing would be great if it wasn’t for the calms…
Rowing would be great if it wasn’t for the winds.”
                                                                          T. Clarke 2016

 

Impact of Wind on Rowing

Klaus Filter of the DDR (Deutsche Demokratische Republik), in 1970s, using a wind tunnel, measured the impact of wind (strength and direction) on rowing racing shells of 1-, 2-, 4- and 8-person crews. It is summarized below, extrapolated from his data posted in the Rowing Biomechanics Newsletter.
I combined the data for the four different racing shells since the differences among the 4 were all less than 5%, in most cases only 1% or 2%. Wind direction is relative to course… 0° is a head wind and 180° is wind directly from the stern. Wind speed is given in meters/second and miles per hour. The tabular data is the percent impact on speed.

Per Cent Impact on Speed as a Function of Wind Speed and Direction

The key ‘takeaway’ from this chart, for me, is not so much the percent cost, or benefit, from the wind, but rather it is how the course relative to the wind direction impacts speed… rowing against the wind costs a lot more than the benefit of rowing with a wind of the same speed.
And rowing at an angle to a headwind (tacking, in effect) eases the drag (slightly), but increases the distance to be rowed. See Small Boats Monthly article on Tacking for Rowing.
For the oar cruiser, the percent impact would be greater than in the table above, since the oar cruiser has much more aero drag than the racing shell. How do we calculate the aero drag of an oar cruiser?
The formula for determining aero drag is:

Aero drag (pounds) = .0034 x S x C x V x V where:

.0034 is a constant

 S is the square feet of frontal area exposed to the wind

C is the “drag coefficient”… for simplicity we’ll use “1”

V is the velocity of the wind over the boat.

What is the square feet of frontal area exposed to the wind for a typical oar cruiser?

It’s the frontal area of the boat itself (let’s assume 4’ wide and 18” high for 6 sq. ft.) plus the exposed portion of the rower (assume 2’ wide by 2.5’ above the gunnel for 5 sq. ft.) for a total frontal area of 11 sq. ft.
“V”, velocity of the wind is the wind speed in miles per hour plus the speed of the boat (if a headwind… minus boat speed if heading downwind). Let’s assume a 10 mph head wind and a boat speed of 3 mph for a V of 13.
Plugging these numbers into the formula, we get:

Boat aero drag = .0034 x 11 x 1 x 13 x 13 = 6.3 lbs of aero drag from a 10 mph head wind.

There is another aero drag component that Klaus Filter mentions in his article. And it is a component that we can control… to feather the oars or not.
Lets assume I’m using a set of oars 94.5 inches (a little less than 8 feet [2.4m]) long, with a gear ratio of 2.5 (end of blade to oar lock [67.5 inches] divided by oar lock to end of handle [27 inches]). Let’s further assume the blade is 5” by 24”, which is .83 sq. ft.

When I’m rowing, the handles will move through an arc let’s say 2 feet long. This means the blades will be moving through an arc 2.5 times as long… 5 feet. If I’m rowing at 3 mph at a stroke rate of 20/minute, the blades are moving 5’ under water (no windage), but during recovery they are moving 5 feet in 1.5 seconds (2.3 mph) added to the boat speed of 3 mph for a total of 5.3 mph. If the wind is blowing at 10 mph, then V (velocity of wind over the oars) is 15.3 mph. Plugging these numbers into the formula, we get…

Oars aero drag = .0034 x 1.66 x 1 x 15.32 = 1.32 pounds. 

But since the oars are moving against the wind only half the time, the actual aero drag from this set of oars under the given conditions is 0.66 pounds.
To put this into the context of the real world, we need to add yet another drag component… let’s call it ‘water drag’, which is made up of skin resistance, form resistance and wave resistance.  A complex calculation, but Jim Michalak comes to the rescue.
Jim used his Roar2, which is 14’LOA and 42” wide, as his ‘test boat’. He found that the water drag was (slightly less than) 5 pounds at 3 knots. This figure came from a Hullform derived analysis of Roar2 which he then confirmed by measuring the force on the oars in his own Roar2.
Putting all this information together, we can come up with the following summary:

• Rowing a 14’ nicely shaped row boat at 3 knots in calm conditions (no wind, no waves) requires 5 pounds of force by the rower (to overcome the 5 pounds of water drag).
    
• Rowing a 14’ nicely shaped row boat at 3 knots against a 10 mph headwind requires 5 + 6.3 (=11.3) foot pounds of force by the rower, if the oars are feathered during recovery.
    
• Rowing a 14’ nicely shaped row boat at 3 knots against a 10 mph headwind requires 5 + 6.3 + 0.66 (=12) pounds of force by the rower, if the oars are NOT feathered during recovery.
  

Rowing in the Wind

As we calculated above, rowing against a 10 knot wind takes more than twice the energy than rowing in a calm. But what if it’s blowing 20 knots?
With a 20 knot headwind, rowing at 3 mph requires 24.8 pounds of force on the (feathered) oars, five (5) times the energy required for rowing in a calm…not a pretty picture.
See the post on Rough Water Rowing for tips on how to row when the wind picks up and waves are high. The key points:

• Row with shorter strokes and a quick recovery to maintain boat momentum,
   
• Loosen the grip on the oars… there is a tendency to grip stronger when rowing in difficult conditions, which tightens all muscles unnecessarily,
   
• Feather the oars and make the recovery higher to avoid hitting waves.

Rowing in a beam wind (90° to the wind direction) presents its own set of problems. In my Lillistone Flint, a beam wind causes the boat to turn into the wind…this, in spite of more windage from the bow vs. stern.
Rob Fisher and his son rowed a Welsford Mollyhawk in the 2016 Texas 200. He relates that at one point, when rowing in a beam wind of 20+ knots, they rowed for miles using only the starboard oars in order to maintain course. He felt that a rudder would have helped.
My own thinking is that the ends of the boat should be low (with fore and aft decks added) in order to reduce windage in beam winds. For me, rowing into a headwind is just ‘grunt’ work. But rowing with a strong beam wind is more difficult because the impact on rowing varies and I’m always pulling harder with one oar or the other to keep on course.

The Fine Print...

I’m not a professional pilot. I try to be accurate and I check my information, but I’m not perfect. This post is for information purposes and is intended to be only a starting point for learning the skills of piloting. As with any activity with a small boat, there is always the opportunity for ugly surprises. Practice the skills under ideal circumstances and you’ll increase the probability of being able to use the skills during an ugly surprise to keep you and your boat safe.