Collecting freshwater plankton by towing a net using a radio-controlled boat
by Robert Hilton, Fort Wayne, Indiana, USA
I really enjoyed reading Howard Webb's series of articles on Daphnia Collecting. I especially enjoyed the section about collecting at the edge of a pond, I have had my share of boots fill with muddy water. I really enjoyed where he enticed his sons to paddle a paddle wheel boat around a lake while towing a dragnet behind the boat.
His method would not work for me since I have no children around to paddle a boat or anywhere to get a boat. But then an idea came to me, why not use a radio control (RC) model boat to tow a dragnet around a lake? I have always been interested in radio control, especially with aircraft. However I did not have the room or the desire to repair my poor landings. And I did not care for RC cars and all that you can do with RC boats is go around in circles. This never appealed to me either.
But then I read Howard's neat articles and I thought now here is my excuse to play with RC model boats and collect plankton from ponds too. Yep, this sounds neat!
I am retired and on a very fixed budget so the price of radio control boats is a very important factor.
FIRST OF ALL I NEED A BOAT
First of all I need a boat, it has to be able to tow a homemade dragnet while being easy to transport and it might be expedient to purchase a second boat just in case the tow vessel is not able to make it back to shore. So now we are considering two boats.
We can purchase either boats with engines (you know the ones that burn a fuel for propulsion) or electric boats (it is much easier to replace a few AA Nicad or hydride rechargeable batteries). So the choice is smelly, dangerous fuel or a dozen or so replaceable, rechargeable batteries. I chose the latter.
I checked the amateur boat builders' stores that they did not have what I wanted, namely a small, inexpensive, easily transported, battery powered RC model boat. OK, next I checked the Internet. I found two brands of these boats that really stuck out. These were NKOK and NIKKO. I found out that the low priced boats on-line were the micro boats, three or so inches in length, would these do the trick? I do not know, I have one on order, I'll let you know.
The next category was moderately priced boats that were about 17 inches (432mm) long. Carrying two of these would take a fair size case. This size would be my second choice in case the micro boats could not tow a dragnet that well. One feature that I liked about these boats was that they were tugboats, trawlers and coastguard style models and not speedboat styles.
And then I checked a catalog of a store that had local outlets (K Merchandise in the US) and they had NIKKO RC model boats for $22 US. Now this I could afford! However the boats were racing boats, at least in style. But for that price they were too tempting. So I now have a pair of them here in my den. And all for about forty four bucks ($ US). And a Christmas present to me.
OK, now I have the boats that I need and they are 13.5"L X 4.4"W and weigh about 19 ounces fully loaded with six AA batteries. Hey, I have started test the boats in the bathtub, next an open pond that is easy to get to.
Next I need to consider the DNR or Deploy and Recovery methods, the first that come to mind is the leaf skimmer, you know, those things that I would be using to clean leaves out of the boat testing tank if I had a back yard big enough for one.
Remember, the boat weighs 1 pound and 3 ounces. So the DNR should be relatively sturdy. Also it should be small enough to fit inside a vehicle.
The first modification that you should make is install a prop guard, the nasty weeds love to get tangled up in a rotation prop.
I am still considering this prospect. Any ideas?
AND NOW THE EXCUSE THAT I HAVE ALWAYS NEEDED.....THE DRAGNET
My idea of a floating dragnet is to use a twin pontoon style or a twin catamaran style floating device. And have the dragnet suspended below the float so that the top would be above the water line and the bottom of the net would extend a few inches below the water line.
NOTE: I have no way of sketching my ideas so that they can be presented online. I have tried to use the graphics supplied with the Windows XP program, but I am a better sketcher on paper than I am on a computer so I will try to describe my ideas as much as possible with the written word.
Next it is possible to design and build a sub-surface dragnet and here is my idea of this. First of all the dragnet, as above, should be composed of a filter net and a hoop to keep the front of the net open. This hoop should have a small flotation device on top just big enough to allow the dragnet to float below the surface and not to sink to the bottom of the pond.
OK, we now need some way of allowing the dragnet to sink to a controllable depth. Just think of the bow planes on a submarine. A frame could be attached to the bottom of the dragnet which would hold the bowplanes which could be set at a predetermined angle to make the dragnet go down to a certain depth at a certain speed.
Sounds workable doesn't it?
The horizontal pitch of the submersed dragnet could be controlled by some aft planes and/or repositioning the dragline in front of the dragnet.
DRAGNET TOWING VESSEL / DTV
DRAGNET RECOVERY VESSEL / DRV
So far we have only considered the DTV and dragnet but what if the DTV stops running beyond reach from the shore. Then it is time to deploy the DRV. OK, what I envision the DRV doing is snagging the floating tow line on its bow, This should allow both the DTV and the dragnet to move together as the DRV pulls on the center of the tow line. Theoretically the DRV just tows both the RTV and the Dragnet back to shore where they can be retrieved with the DNR net.
But what if the DRV's bow goes up over the floating towline? Then the logical solution would be to fasten a spur that protrudes out from the bow of the DRV. This should be below the water line on the bow, this can be determined by measuring the height of the top of the bow above the water line and, of course, adding perhaps a half inch (12.5 mm) approximately.
AND NOW TO THE DRAWING BOARD
First of all I want to thank Howard Webb for the wonderful series of articles that gave me insight into a better way of specimen collecting, and also for giving me an excuse to get involved in radio control model boats and what they can do to help me collect aquatic plankton.
Next I would like to encourage everyone who is interested in this concept to feel free in using my ideas but mostly I want others to help improve upon these ideas. Now is the time to get your own navy, mine is in use.
Finally, I would like to hear from other with similar ideas or pond tested concepts. Feel free to contact me either via the Micscape Editor or directly via e-mail.
Comments to the author, Robert Hilton, are welcomed.
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Micscape is the on-line monthly magazine of the Microscopy UK web site at Microscopy-UK.