You have a kayak? Single hull or an Island? I have a Hobie island kayak and I mounted 2 manual downriggers for salmon fishing. I use 12 lb to go down deep all the way to 175. If I'm fishing shallow above 50 ft, I use 8 lbs. Anywhere in between I will put 10 lbs on. My max speed is about 2.5-3mph. Any faster and I would need to drag more weight than what I mentioned above to prevent blow back. What are you fishing for in HB with downriggers? If you have a single hull kayak that would limit the amount of weight you can put on it so you don't flip.