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Second Design Concept for Kayak-towable Thermal Fishing Bob

by kgrevera | May 13, 2015 13:30 13 May 13:30 | #11810 | #11810

Second Design Concept for Kayak-towable Thermal Fishing Bob


This concept has arisen from the same project as the pool floatie thermal fishing bob. In that project, Sara Wylie from Northeastern University and I are working to further develop the thermal fishing bob. In preliminary testing last summer the fishing bobs were having issues with submerging and taking water damage. So, we are working on a design for a rig that would hold the fishing bobs above the water with only the thermistor submerged. Ideally we would like to tow this rig behind a kayak. Our hope is that by having the fishing bobs floating outside of the water, this should help reduce water damage and improve visibility.

Research Questions

  • What is the best way to keep the fishing bob from submerging?
  • What objects can be used as the base of the floating rig?
  • How do I get the thermistor far enough into the water to take a reading without compromising the structural integrity of the floating rig?

Child's Boat Prototype

  • How should I attach the thermal fishing bob to the boat?
  • How do I prevent water damage from the site where the thermistor needs to enter the water?
  • How do I keep the thermistor still enough to take readings?


The first concept we came up with was to set the fishing bob into a child's toy boat. The boat would be designed to cut through the water without flipping over and would already be waterproof. The boat we purchased has a ring and cord already attached to the front so a child can pull it. This will be utilized to tether the toy boat to the kayak. A ring of foam will be set down into the base of the boat and held in place with rubber cement. The fishing bob will be slipped into this ring like a coffee cup into a coffee cup holder, but not permanently affixed in place so that it can be easily removed. Initially we intended to drill a hole through the hull to dangle the thermistor through, but we became concerned that this would compromise the ship's structural integrity and lead to leaking and water damage. So, our next idea is to affix a plastic or glass straw to the side of the boat with rubber cement and feed the thermistor through it, weighing the thermistor down with nuts on the bottom. This will allow the thermistor to hang into the water, but hold it relatively still.


First Sketch


Next Steps

Test out ideas.

Sled Prototype

  • How can I best attach multiple fishing bobs with different length thermistors to a rig in order to get multiple temperature readings at different depths?
  • Where on the sled should I place the fishing bobs so the whole rig doesn't flip over?
  • How should I attach the fishing bobs to the rig?


For this towable rig, we will be using a foam sled as the base. Originally we were going to carve recesses into the sled's surface and duct tape the fishing bobs into those recesses, but later decided this was unnecessary. Now we are going to use the coffee cup method from above and nestle the fishing bobs into foam rings that are rubber cemented to the sled's surface. The thermistors will be fed through a glass or plastic straw and either poke through the bottom of the sled or be affixed to the side with rubber cement. Two holes will be drilled in the front of the sled so it can be tethered to the kayak. In addition, we were originally going to tow three fishing bobs this way, one at the front, and two at the back, but have since decided to tow only two positioned side by side at the middle of the sled to improve the rig's balance. So the first sketch of the sled rig will depict the original configuration. A new sketch with the new design will be uploaded later.


  • 2 thermal fishing bobs
  • foam sled or boogie board
  • foam
  • duct tape
  • scissors
  • rubber cement
  • glass or plastic straw

First Sketch



Second Sketch



Next Steps

New drawing, and then test it out!


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