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$52 HOME MADE HARPOON BUILD
I recently decided to make my own harpoon for commercial tuna fishing after looking into buying one and not wanting to cough up the $250-$350.
This harpoon will be used for "stabbing" commercial fish (73"+) boatside after a rod and reel fight, or throwing very short distances.
I did some research on the internet but only came up with one home made harpoon, I incorporated much of that build into my own build.
Here is what you will need
Materials:
1 6'-8' X 1-1/2" wooden dowel (get a straight one!)
1 22" X 3/8" 304L Stainless steel round solid rod
1 harpoon dart
1 10"-14" X 1-1/4" 304L stainless steel pipe
1 1-1/4" 304L stainless steel pipe end cap
1 (4'-6') length of 1/8" stainless steel cable coated to 3/16"
2 or 4 1/8" copper cable crimps
3 3/4" stainless steel screws
1 set of 2 part epoxy(JB Weld or other)
1 can of wood stain/sealer
1 can of spar-urethane
a couple wooden BBQ skewers and a few toothpicks
Tools:
Drill
12" X 3/8" drill bit for wood
3/8" drill bit for metal
drill bit for metal same diameter as the stainless screws
small woodworking plane
metal files(course and fine)
bench vise
paint brush
dead blow hammer/mallet
Welder and 308 welding rod (if desired)
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What to do:
First, Plane down or sand down the dowel so that the pipe will fit over the dowel. I used a 10" pipe so I planed down about 10", checking the diameter several times with the end of the pipe. Do not plane/sand the dowel down so that the pipe slides easily down the dowel. You want to have a tight, hammered into place fit.
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Now drill a 3/8" hole in the end of your dowel for the dart shaft to be placed. I chose to make the hole 6" deep, this leaves 16" of the 22" shaft exposed(you will lose anoth inch or so later on). You want to center the hole, use a punch if you need to, to stop the drill bit from moving around as you start drilling. Try your best to drill right down the center of the dowel. Take your time and check it several times with the dart shaft. If you have to drill it bigger, dont worry, you will be epoxying it in anyways.
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Now that you have the hole drilled, you are ready to mount the dart shaft permanently inside the dowel. I used JB Weld 2 part epoxy. Rough up the part of the shaft that will be imbedded in the dowel(6") with a course file to better bond the materials.
Try to put some epoxy into the dowel hole and then coat the dart shaft. As you put the dart shaft into the dowel, make sure you have enough epoxy on it. You can always add more as you go. Work the dart shaft in and out a bit as you go.
When the shaft bottoms out, you need to center it. Use a flat surface to roll the dowel on, to see where to put your BBQ skewers or toothpicks.Position skewers/toothpicks where needed to align the dart shaft with the dowel. Once you are happy with the position of the dart shaft, set the harpoon up(dart shaft up) straight for the next 15 hours or as reccomended by the epoxy manufacturer you use. Leave some excess epoxy around the hole and shaft.
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Next is staining, and sealing the dowel. I used a stain/sealer for the first coat. Then followed up with 3 coats of spar-urethane. This will take a few days. You may want to do this last, up to you. I would at least seal the last 12" that will be inside the pipe.
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Now you need to drill 3 offset holes in the pipe for the set screws. Use a drill bit the same thickness as your set screws.
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Now drill an oversized hole in the end cap. The hole should be a bit oversized to make up for any imperfect drilling off center. Otherwise when the cap is screwed on, it will push the dart shaft over if it isnt perfect.
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After the dowel has dried, you can fit the pipe and end cap into place with a deadblow hammer. If using a vice to hold the dowel, you WILL mess up the urethane. As I learned lol.First, rough up another 1" of the dart shaft with a course file. Apply more epoxy to the dowel and inside the pipe. This will help bond them and will also help fill any voids left from uneven planing/sanding. Screw the end cap onto the pipe then put it over the dart shaft (try not to smear epoxy onto the dart shaft) and hammer the pipe down untill it stops. It will go a bit further than the length of the pipe from the end of the dowel because of the space in the end cap. Wipe off any excess epoxy on the handle end. Now you need to set the harpoon upside down. Unscrew the the end cap(keep it near the pipe and still on the dart shaft) and fill it with epoxy. Screw it back on tight. Use a pipe wrench if needed. Turn the harpoon dart shaft up. This should fill the void inside the end cap. Wipe off any excess epoxy. Let the epoxy set.
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Now you can either epoxy around the dart shaft and end cap hole or weld it. I suggest welding it. This will best secure the dart shaft to the pipe, which will be secured again to the dowel in the next step.
Now we need to put some screws into the harpoon to better secure the pipe and dart shaft. Use a smaller bit to drill into the dowel(so the screws will grip and hold the wood) to the desired depth. I chose 3/4", they should go approximately 5/8" into the dowel. Now put a bit of epoxy in the holes and screw them into the dowel. Do not over tighten and strip the wood. The screw heads can also be welded.
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Add a stainless eye bolt to run your mainline through. Place it far enough from the dart so that it will be beyond your dart cable/rope.
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Also, the rope used in the pics is just dockline I had, not what it will be rigged with on the boat! 
