A new blade is still under wraps in the Croker factory and there is no media announcement to date. Word on the street is that the latest from Croker will be launched at the Head of the Charles 2024, but there have already been a few sightings and some whispers around the pontoon. Rowing Illustrated have reported that the Sinkovic brothers, who only use Croker, are currently testing the new design. So, let’s explore what the new Croker Bolt is all about.
The Croker Bolt
Fundamentally, the Bolt is Croker’s answer to the Comp from Concept2, as it employs similar design principles. You can see from the image above that the new blade has a distinct hooked curve on the outside edge and you would imagine it could help to grab the water like the cupped hand of a swimmer.
The design concept that Croker are chasing is what Concept2 introduced in the early 2000’s with the Vortex Strip (see image below). The Vortex Strip forces the water to stick to the blade giving more grip and reducing the amount of slip in the water. Conversely, Croker have permanently moulded it into the blade itself, and simplified the design, thus creating the Bolt.
The Concept2 Vortex Strip
Both blades are designed to affect the horizontal flow of water as it cuts out away from the boat in an attempt to get the blade to follow the perfect geometrical form of the Tractrix.
The above image shows in red the actual path of a blade through the water and the blue shows the ideal path if the blade had 100% hold on the water without any slip.
The ideal path and the actual path of the rowing blade in the diagram shows a performance void and what oar designers have been attempting to close. We have calculated that an oar slips close to 9-degrees with a stroke between 90-110-degrees, which means that blade slip is close to 10% of the total stroke. The positional loss due to slip is staggering!
“When I think about what we know about blade design, my key takeaway is that all current blades on the market are so staggeringly inefficient.”
Oar designers are seeking to create a blade that has zero slip and delivers that 100% of your effort is transferred into propelling the boat. This is why the power meters record catch slip and finish wash as these aspects represent a massive loss of potential motion. You will notice that there is increasing and diminishing ratios of boat travel to oar movement. Understanding this helps to show that the most effective leverage is at the catch and the finish, provided that there is no slip. Therefore, it is in blade design where we can most effectively achieve performance gains in our sport.
The Vortex Strip has a long history of proponents and detractors with many clubs and colleagues keeping them on for blade protection. Titans Oxford Brookes always row with the Vortex Strip, but others say the strip gives the sensation of slowing the blade down and making the boat feel heavy. You might be interested to read more on the development of the Comp here on JRN.
The Vortex Strip was added to the Comp to save it from a design failure, as early-stage testing showed it was too light through the water and had a problem of excessive slip. The appropriation of the Concept2’s Vortex Strip by Croker makes sense, as it has been shown through independent scientific trials that the concept works. Concept2 have some extensive data on blade design that it looks like Croker have decided to capitalise on.
At the blade, there is an incredible amount of energy lost from the rower. The current numbers are almost unbelievable. According to a 2010 study published in the Journal of Sports Sciences, which investigated the total energy loss during the rowing stroke, only 55% of a rower’s energy output is transferred through the blade.
“It is in blade design where we can most effectively achieve performance gains in our sport.”
With so much potential for performance gains, it is about time that both manufactures focused more on delivering these possibilities. Now that both leading oar manufacturers Concept2 and from Croker accept that redesigning the edge of the blade is where performance increases to our sport, I argue that they have only scratched the surface.
When I met with Daren Croker in 2018 to show him a prototype of the Randall foil, we discussed the fact that the application of a foil to the top edge of the blade is most effective at reducing slip and increasing energy transfer the very thing we have been chasing. So much so that the University of Porto has recently published research showing that Randall foils outperform Concept2 oars.
When I think about what we know about blade design, my key takeaway is that all current blades on the market are so staggeringly inefficient. As such, the next generation of blade designs need to take the current research to the next level, but it is also up to our clubs, coaches, and rowers to want to adopt available innovations and start going faster.
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