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This article originally appeared in row360 - issue 09
The Science of Drag
Click on the image for the PDF version of the article as it appears in Row360


Proving the Theory: Part 1
The Science of Drag

Most competitive sports, even at the Olympic level, use equipment that is not one-design. This somewhat surprising lenience permits the designer and manufacturer to give the athlete a small but still significant competitive edge. Rowing, in particular, permits unlimited freedom in the length, beam (width) and shape of a shell, with the only limitation being the overall weight. Some people might argue with the term “unlimited freedom”, but even the new FISA rules instituted in 2015 (all eights must be sectional with the longest section 11.9M), permit boats that are over five metres longer than currently built, so there is little restriction there. 

Over the years the development of shapes has been gradual, as one might expect of an evolutionary process, but now that we have towing tanks and computer software that can analyze the resistance of long slender hulls, we can speed up the analysis of many possible hull configurations. 

The designer must, however, ultimately ensure that there is logical thinking applied to the analysis.
All boats, whether canoes, powerboats, sailboats or rowing shells, have their speed limited by two factors — frictional drag and wave-making drag. Frictional drag is just as it sounds; it is the water dragging against the hull surface and creating resistance. Perhaps thinking of the boat pushing though honey, rather than water, provides a better image of the interaction. The wave-making drag has nothing to do with the natural waves on the lake, but the waves created by the boat. In a rowing shell the bow wave is small, but in a sailboat for example, they are large and in fact are the limiting factor to how fast a beamy boat can travel.

In skinny boats like rowing shells the wave-making drag becomes less of a factor since the narrower the boat the less wave-making drag there is. The ultimate narrow boat would be a thin flat plate set vertically in the water and it would be hard to discern any waves. But in the challenge of designing rowing shells to have minimum resistance at racing speed, the amount of each type of resistance becomes critical.

Fig. 1 - The top blue shell has a bias towards reduced frictional drag while the longer orange shell keeps wave-making drag to a minimum.

If frictional drag were the only component of concern, the boats would be very short to keep the surface area touching the water (the wetted surface) to a minimum. If wave-making drag were the only drag, the boats would be very long to keep them narrow and the waves they produce small (see Figure 1). The reality is in between these two, but optimizing the length requires a rather exact knowledge of the value of each type of resistance. A comparison of different manufacturer’s products in your boathouse can show variations of a metre or more in length, all designed for the same class and weight of rower. Different theories and varying experience levels have led to different conclusions.

Fig. 2 - A typical wave plot showing transverse waves behind, and divergent waves emanating from the bow, for a narrow hull.


Speed Range of Interest
Fig. 3 - Upright Resistance versus Speed - Frictional Drag dominates the overall drag in a rowing shell. In this example 4 person shell 88% of the drag is due to wetted surface friction. (Predictions made with Flotilla software)drag to a minimum.

The components of frictional and wave-making resistance for a typical four-person shell are shown in Fig.3. It can be seen that the contribution to overall resistance due to wave-making drag is very small, in the order of 12% of the total at a normal racing speed of 5.5 metres/second. The initial reaction of the designer to optimising this boat might be to concentrate on keeping the wetted surface to a minimum as it is creating most of the drag. That is true but the subtlety of the trade-off of those two factors with length is very important and sometimes surprising.

 The shells that you row have been designed to give minimum drag for a given weight and skill level of crew. A novice crew will row faster in a boat that has greater stability than one designed for an experienced crew. In order to optimize the length of a shell during the design process, the fixed parameters must be set carefully. We must consider not only minimising the drag of the hull, but setting a minimum internal width of the boat to accommodate the crew and setting a minimum permissible stability that we know the targeted crew, experienced or intermediate, can handle. 
The consideration of stability has a marked effect on the outcome of such a study. In my experience, for a given length of hull, a rowing shell can always be made faster by making it narrower (and a bit deeper). However, doing so will take the stability below the acceptable value for the crew. So the minimum resistance is governed by the stability of the boat. In performing a length study, therefore, for each length the minimum resistance will be achieved by the narrowest boat that will still offer the required stability for the crew. 

Hull Width
Fig. 4 - For a given hull length, variations in width and depth are plotted below their total resistance. The left hand hull although it has the lowest resistance, is below the allowable stability and therefore does not qualify to be part of the optimized length study.


Minimum Total Drag
Fig. 5 - Minimum Total Drag versus Length - A plot of Drag versus Length illustrates that there is a penalty in designing too long (too much wetted surface) or too short (too much wave drag).

In Fig.5 you can see the total drag of a series of shells with the same crew weight, but with varying lengths. The width, out of necessity, must increase as the length reduces in order to keep the volume and therefore the load capacity the same. The plot of total drag versus length shows there is an optimum length for this particular weight class of shell.

At this point we need to be cautious about final decisions for the parameters of a new boat. It is important to know the theory behind, and limitations of, the particular software being used. Since the trade-off between frictional and wave-making drag affects our choice of a longer or shorter boat, the software’s assessment of those factors is important. We have done careful validation of the computer code that we use and each manufacturer will have done the same. One must understand when to accept the predictions at face value and when to use other tools to assess the performance.

This optimal length analysis is unique for a given crew weight and that leads to most manufacturers having several weight categories and lengths for each type of rowing shell. With careful use of software and some way to validate the drag that it predicts, the designer can create a rowing shell of minimum resistance, giving the rowers a small advantage to take into every race.  


A Study to Help Understand the Effect of Crew Weight on Stability

If your crew were to row the same boat that my crew had just vacated, the stability would not only feel different, it would actually be different. Perhaps it seems illogical, but the same hull will have a different stability depending on the weight of the crew rowing it. As the rowing shell is loaded more heavily and sinks lower in the water the stability is reduced. This is counter to the experience of sailboat owners who may add ballast to their boats to make them more stable. The difference here is that the weight we are adding is the crew, a moveable weight well above the centre of rotation of the hull.

When a lightweight eight is taken for spin by the mid-weight men, they may have trouble setting it up. Shells are designed for a given weight class and typically if you are lighter than the intended weight class for the boat you will find it easier to balance. If you are heavier than the weight class the boat is designed for and are an experienced rower, you may be able to set up the boat and row well or the shell may now be too unstable to row efficiently. Being aware of the stability change with varying crew weights may help you and your coach better understand how a boat feels on the water.


Steve Killing is a yacht designer and avid rower based in Midland, Ontario, Canada, who designs for HUDSON. You can see the racing sailboats (multiple C-Class Catamarans and America’s Cup), canoes, kayaks, and classic mahogany runabouts that he has designed at


Use the Forces

Any competitive rower is familiar with the close relationship that the sport has with objective data. Whether it is based on physiological or technical proficiency, there is no shortage of devices that can quantify athletic capabilities. A consistently growing area of study is the role that biomechanics plays in the boat-athlete system. The relationship between forces applied and shell performance is so closely linked, that a change in potential force input can alter the hull shape necessary to perform at the highest possible level.  Therefore, a great deal of time is spent understanding force inputs and their effects on component and hull design. 
Whether the end goal is a better understanding of correlating variables for the purpose of equipment improvement or, simply an individual desire for athletic improvements, knowledge of biomechanical interactions is a critical undertaking.  
The purpose of collecting biomechanical data with respect to HUDSON is twofold:

1.    To gain a better understanding of the relationships that exist between kinematics and kinetics as it applies to rowing performance.
2.    Delivery of key feedback to coaches and athletes to promote knowledge translation.

As data is collected, and relationships are investigated, advancements as a result of our increased knowledge are continually developed. It is critical that the new found information is passed on to the coach and athlete in order to elicit a performance gain. Knowledge transfer as it relates to biomechanical analysis can ensure a proper fit, optimized rigging and quantification of boat-rower performance, helping to ensure best possible results.

Dan Bechard Ph. D. (Biomechanics) serves as a Research Associate at HUDSON, and coaches at Western in London ON.

SOLIDWORKS® gives HUDSON Boat Works competitive edge in the shop and on water

This article originally appeared on

By Karen Majerly

HUDSON Boat used at Pan Am Games

HUDSON boat used at the Pan Am Games

Javelin Technologies customer HUDSON Boat Works continues to impress with its commitment to creative 3D design and its winning ways on a world stage.

HUDSON, based in London, Ontario, is a manufacturer of Olympic class rowing shells and a leader in developing racing hull shapes, carbon composite construction, and original components to advance the sport.

Since 1984, HUDSON boats have won more than 80 medals at the Olympics and World Rowing Championships; this summer, Pan Am athletes, most of them Canadian, won 11 medals in HUDSON boats. Canadian men and women competing in events from singles to eights won seven gold medals and two bronze medals. U.S.A. and Chile each took a bronze in a HUDSON shell.

Craig McAllister is Commercial Manager for HUDSON. He says 39% of the boats raced during the games were HUDSON and that half of the gold medals were won in a HUDSON.

“Success at international events like the Pan Am Games is rewarding and inspiring when you think about the thousands of hours invested behind the scenes by our highly skilled engineering and manufacturing teams. It validates that we have become an industry leader. We do that by embracing innovation and supporting transformational ideas.”

Nine of the 14 nations competing in Pan Am rowing had at least one entry in a Hudson, including Canada, U.S.A., Cuba, Brazil, Chile, Paraguay, Venezuela, Guatemala, and El Salvador.

It’s a big deal

Men's 4x at Pan Am Games

The Toronto Pan Am games marked just one of the highlights of 2015 for the HUDSON crew. The year began with a promise to build 77 rowing shells for Community Rowing Inc., based in Boston. It’s a not-for-profit program that makes rowing more accessible to people from all demographic backgrounds, especially the inner city youth of Boston. As the single largest boat order in the history of the industry, it infused a lot of energy and dollars into the business and provided a serious boost in HUDSON’s profile and status in the United States.

“When we delivered all the boats by the due dates, the U.S. market saw that as a stamp of approval,” Craig says. “Several new orders have referenced the CRI deal. Our ability to follow through on that contract validated our credibility.”

Graham Cartwright, HUDSON’s engineering manager, reports that not only did HUDSON have to deliver a lot of boats on a strict delivery schedule, the team had to quickly design, analyze, test, and produce custom components created specifically for CRI. That’s because CRI boats are used by a diverse group of athletes – in age, size, and experience level. Greater-than-usual adjustability was needed to correctly rig the boats for different users.

“We designed the components in SOLIDWORKS, analyzed them structurally using the Finite Element Analysis tools, and incorporated them into our assembly models to ensure accurate fit.”

How to stand out in the industry

There’s no sitting around basking in success over at HUDSON. Half a dozen people are dedicated full time to improving designs and systems, pushing limits, and bringing ideas to life.

One such project is a partnership with Fanshawe College, also in London. What started as a student project is close to being a physical reality; it’s the first boat test stand in the world that can test stiffness both longitudinally and torsionally, allowing boat-to-boat comparisons. Rowers will be able to understand how their boat compares to norms, whether it’s a new or used (and potentially fatigued) shell.


HUDSON Boat Works design in SOLIDWORKS

The entire stand assembly was designed in SolidWorks. Graham says that because Fanshawe also uses SolidWorks as a design tool, collaboration on this project was easy. “We could transfer models back and forth, so communication regarding design status and changes was effortless.”

Once the mechanical design was completed, an assembly model including all major devices (actuators, load cells, interfaces, panels, etc.) was easily created.

“That allowed us to import various boat models and test for interfaces between our product and the proposed test stand and its range of motion,” Graham explains. “We were also able to position the assembly in a building envelope model to ensure machine clearances and user access. All of this gave us the confidence we needed prior to even starting anything physical.”

With laser focus

The boat test stand gives HUDSON an edge on competitors, as does a new laser projection system designed and produced in house.

W1x at Pan Am Games

Pan Am Rower

Graham tells us that laser projection systems are available, especially in the composites industry, but that they are costly and have a number of features not necessary in HUDSON’s shop.

“SOLIDWORKS has allowed us to design our own simple laser system that works with our current production processes,” he says. “In a nut shell, we have a number of pre-cured composites components that need to be positioned and bonded accurately and consistently within the boat hull. With a 40-foot long cockpit, this requires large, cumbersome tools and fixtures which are difficult to work with and take up valuable shop space.”

The laser system consists of a main structural I-beam and moving carriages that are controlled by touch screen. Once a boat is positioned under the laser system, it can be “homed” so that laser lines mounted to these carriages project down at key positions where components need to be installed.

“SOLIDWORKS has allowed us to take an idea we had and bring it to reality,” Graham says. “We designed and assembled this idea with all its critical components ahead of time so we could be confident it would function as intended once the investment was made to build it.”

Next up – the road to Rio

M8+ at Pan Am Games

One of Canada’s Rowing Teams

In rowing, where milliseconds and millimetres matter, HUDSON will never stop analyzing and improving the hull shape. Right now they are working with a naval architect who can study the hydrodynamics of how a shell moves through water, including unsteady flow, more useful in a rowing environment than steady state testing, which is better for sail boats.

And, of course, there is the road to Rio – the 2016 summer Olympics in Brazil. With only the world’s powerhouse teams making it into the Olympic races, HUDSON will primarily support the Canadian team.

“We’re in the process of redeveloping the whole series of heavyweight men’s models, from singles to eights, trying new shapes.” Craig says. “Our job is to make sure the Canadian team has our latest and best technological advances in their boats.”

Stay tuned for updates on Hudson’s Road to Rio!

Photo Credit: Katie Steenman