When I bought my cabin, there was a 12' aluminium fishing boat included. I already had a boat, so I gave this one to my son. It did not have boat seats, so I decided to build some. At the time I had a 1986 Chev S-10, extended cab. In this truck in the back are two fold down jump seats. I thought these would work perfect for the boat seats, so off to the auto wrecker and bought two for $10.00. Here is what I did.
2 - Jump seats from Chev or Gmc S-10 extended cab pick up
3 - pieces of scrap 3/4" plywood
4 - 1-1/2" - 3/16" bolts
8 - 1" X 3/16" bolts
2 - 1" X 7/16" bolts
12 - 3/16" T-Nuts
2 - 7/16" T-Nuts
14 - Washers
1 - 6-1/2" metal swivel base
Start by cutting a piece of 3/4" plywood to fit the seat on your boat. Mine was 14-1/4" by 10-3/4". Next cut your sub base from 3/4" plywood. This should be 10" X 10". Now cut your seat base out of 3/4" plywood at 8-1/2" X 7". Once these are all cut it is a good idea to paint them. Once they have dried it is time for the assembly. Place your sub-base on to the base and position the sub-base in the centre of your base and clamp the two together. Now drill the four hole that will attach the two together. Once these are drilled, hammer in the T-nuts to the bottom of the base you will use these to attach the sub-base using the 4 - 1-1/2" bolts. Also in the sub-base drill an access hole so you can fit a socket through to attach the swivel base. With these two cut, put them aside and begin the seat base.
Take the seat base and put the metal swivel base on it. Position the metal swivel base centred on the seat base. Mark and drill the holes for the T-nuts and bolts. Also in the seat base at one end drill out two holes to accept the 2 - 1" X 7/16" bolts. These two bolts will attach the seat base to the jump seats. What I had to do with mine was, un-zip the seat cover and move it out of the way. I then welded the two 7/16" T-nuts to the metal frame of the jump seat, to match the two hold drilled in the seat base. Every thing should now be measured, cut and drilled.
Next you attached the metal swivel base to the wooded seat base using the T-nuts and bolts. Once this is done, attach the seat base to the bottom of the jump seat using the 2 - 7/16" bolts. Use the washers at the head of all the bolts.
Now you attach the sub-base to the seat base using 4 of the 1" X 3/8" bolts. This is where the access hold comes into play as you are attaching the sub-base to the metal swivel base. Once you have this assembled, attach this assembly to the base using the remaining bolts and washers. Make sure everything is attached firmly and you have a inexpensive swivel boat seat. You can bolt the seats to the aluminium seats in the boat or attach them using small c-clamps. Now you can have a little comfort while fishing.
Once again, if you have an questions, please don't hesitate to email me.