How to Replace a Floor in a Boat

I used a circular saw to cut the old floor out. The stringers and bulkheads were rotten too, so I fiberglassed in new ones. Every thing was made of outdoor grade 3/4" BC plywood. The new decking was fiberglassed on the bottom and edges before they were installed. Fiberglass matting was put down and wrap up all around the edges providing a strong waterproof floor. Paint and non-skid compound make the deck safe from UV rays and keep feet from slipping in heavy seas.

Difficulty: Challenging

Instructions

Things You'll Need:

• Circular saw, sabre saw, carpenter's square, elecric drill, tape measure, 4" grinder, Dremel tool, belt sander, disk sander, rubber gloves, acetone, fiberglass resin & cloth.

1. First I had to remove screws holding the center console and the helm seat to the deck. The throttle and shift cables had to be removed from shift control box. The steering cable and all electrical wires were disconnected before the center console could be lifted out of the boat.

2. 
    
   Floor cut out and removed.

   Set circular saw blade depth so it barely cuts thru the deck. Stay 3" from sides, front and back of boat. This 3" ledge is where new decking will rest.

3. 
    
   Old stringers need to be ground flush with hull.

   After the floor was up, I noticed that the stringers were rotten also. I dug out the foam. I ground down, and sanded the old fiberglass from the stringers so new stringers could be laid down and fiberglassed to the freshly sanded inner hull.

4. 
    
   New, stronger, stringer will be placed between two old stringers.

   Another view of correctly sanded hull.

5. 
    
   List of stringer measurements.

   To measure dimensions for new stringers, lay a straight edge on top of 3" edge. Use a carpenters square and measure up to bottom of straight edge every foot and create a list of measurements to be used to create new stringers. Take separate measurements for both stringers as each side can be slightly different.

6. 
    
   Carpenters square laying in line where new stringer will lay.

   View a square measuring up to bottom of straight edge.

7. 
    
   stringers

   Transcribe measurements onto 3/4" outdoor grade BC plywood. Top edge of stringer will be even with top of 3" edge of old floor, so ends will have to be notched to fit under old flooring.

8. 
    
   A clamp at the top will hold the stringer straight while f/g sets.

   Dry fit and make sure when new decking is laid on 3" edge that it will lie flush on top of stringers. If one 8' piece isn't long enough, use two pieces that will be butt jointed and held upright with fiberglass.

9. 
    
   Cross braces, cut notched and coated with f/g resin.

   Cross braces in front of and in back of gas tank are notched to fit into stringers. Use 3" x 3/4" notches in top of stringer and bottom of cross braces.

10. 
     
    Everything in place.

    Set stringers and cross members into place. Brace into place with clamps and/or temporary blocks of wood. Then use 3" f/g tape to f/g everything to floor.

11. 
     

    F/g edges of stringers and cross members to each other.

12. 
     

    Another view of stringers and cross members.

13. 
     
    Circular saw set at half the distance of the thickness of the wood.

    The 3/4" decking must be cut so there is 1/2 to 3/4" from edge. Chamfer edges of the sides so f/g cloth won't have to make sharp bends, and will make a smooth transition from floor to sides. The front and back edges, I used a 3/8" deep notch, 1" long so each deck piece can be glued and screwed together where they meet. A circular saw is used to make these notches.

14. 
     

    A Dremel tool with a sanding drum is used to clean notch.

15. 
     
    Front pc.

    Front deck piece, cut, and f/g'ed on edges and bottom.

16. 
     
    Second pc.

    Second to the front deck pc.

17. 
     
    3rd from the front pc.

    Third pc.

18. 
     
    Back pc.

    Back pc., notched for motor mounting bolts, scuppers, and cable pull thru.

19. 
     
    Front pc installed, using 2 part epoxy and weather proof deck scews.

    Use 2-part epoxy and screws on all points where deck will meet, 3" edge, stringers, and cross members. Space screws every 6 to 9".

20. 
     
    2nd pc.

    Add second pc, sealed, glued and screwed.

21. 
     
    Deck in place.

    Aft pc is added before 3rd pc. is laid on top. It is notched accordingly, glued and screwed into place.

22. 
     
    Deck f/g'ed with first coat of resin and matting

    The edges of the sides and joints are filled and smoothed, with resin mixed with cabosil (or similar filler), so when the f/g matting is laid down there will be no sharp bends where air bubbles might develop. The edges of matting, that wrap up 3" on the sides, are cut with scissors so no air bubbles are created when resin is applied. Lay matting in place and mix one quart of resin at a time, and spread with a disposable roller or wide paint brush. Work out ALL air bubbles. Wet matting thoroughly, but don't let resin puddle. I use a syringe to accurately measure hardener to get a consistent mix. Use a respirator with carbon filter when applying resin or using acetone for clean up. A fan helps dissipate the toxic fumes of the fiberglass resin.

23. After first coat has been dried, rough sand deck and edges. Vacuum up dust and wipe deck with rag soaked in acetone. Don't forget to wear a respirator!

24. After applying paint with a non-skid compound in it, reinstall center console and helm seat. Use silicone on all screws going into the deck to prevent any more wood rot from developing. Seal all holes cut in deck with f/g resin.

Tips & Warnings

• For mixing f/g resin see a book on fiberglass repair.
• Wear a respirator! Fiberglass resin fumes are toxic. Rubber gloves make clean up easier.