Since we published the news item with the photographs of an indoor rowing tank being installed, we have had quite a lot of interest.
Here are some questions from a prospective tank customer which may be of interest to more people. And the answers we received from Durham Boat are below.
I was wondering how the tank is designed.
I noted the V shape on the bottom of the tank. I assume this is to assist the two opposite waterflows to be separated from each other?
I was wondering how the problem of sculling vs sweep rowing is solved in this tank. Since sculls of course are much shorter than sweeps, the place of the blade in the tank is different. I read on the Durham Boat website that special tank-oars and sculls are used.
I was also wondering whether the proportions of the tank are the same as rowing in a boat (thus about 30 cm of 'overlap' of the oar for sweep rowing) and the same angles of catch and finish as in the boat.
And whether it is possible to also use bigblade-shaped oars, since these have a very different catch (next to their overall behaviour in the water).
Durham Boat's answers
In answer to your questions about the tank design: The tank has a peak that directs the water flow, but allows spill over from one side to the other to keep the depth equalized. The design is based upon minimizing the volume of water to be pushed around the tank and having as little friction as possible with the smooth surface and rounded corners.
One of the keys to keeping the water volume down was done by scaling the sweep oars down in size. Many historical tanks use a full-sized sweep oar and have a much deeper tank. As a consequence, it takes so much energy and the load is too heavy. What happens is that blades are cut down or made with a wire outline. As the blade area is reduced the resistance is less, but less energy is imparted into the tank to move the water.
Because we are attempting to move as much water as we can, Durham Boat tanks have a sweep oar that is made with a scull shaft and full sized scull blade with a special sweep handle that will fit into a scull shaft.
In tank rigging to get the lightest load, you have to get the blade tip as close the outside wall to get into the fastest water. This is counter-intuitive to most of our coaches. They are used to shortening the oar length to lighten the load. Another way some of our customers adjust load is with water height and by rowing all 8-sweeps on one side from time to time. The tank has great versatility.
Most of our customers find it too much trouble to change the spread (span) when going from sweep to sculling and will optimize their rig on one or the other. To get the most out of the tank, the proper method is to move the pins wider for sculling. When customers are interested in doing this we have provided a plate with two holes to allow spread/span adjustment.
Our customers are supplied with Macon shaped blades for both sweep and sculling (the sculling blades are cut-down). I think that a narrower blade works best with our design constraint to keep water depth and total water volume at a minimum. We could do a hatchet blade and would have to cut down the inner part of blade and use our narrowest hatchet (Little Big Blade). Also we would have to increase the shaft length.
There are differences in tank rowing, just as there are differences in erg rowing. However our customers find that it is the best off season teaching tool for improving blade skills and blade work, which is the limiting factor in getting one up to speed on the water.