I have a 74 model 43' Nautaline.  My question is on one side about an 6 to 8 foot section of the catwalk is soft and wanting to pull away from the boat.  I know there is some rot going on there, the ac units drain down the side of the boat at this location.  What kind of support system is under the fiberglass shell.  I assume i'll have to remove the rub rail, the hand rail and the screws holding the top of the catwalk down, hoping to try and figure on what to take with me to the lake as to eliminate 50 trips to the lumber company.  Also what would be the best way or best area to drain the ac units.  They currently have a piece of plastic tubing just draped to the side of the boat, which has caused or certainly helped this problem.  Thanks in advance. 

I have just recently sold my Nautuline that I spent 8 yrs re-doing(enjoyed every minute) and I re-did both side catwalks. It took 2 men 6 days to remove them, remove the rotted plywood backing(that was the easy part) and glassing in new plywood. I believe the plywood was 3/8ths and I used exterior grade(do use pressure treated) and you will need a small piece of 2x6 to make the end braces.you will need a jig saw as there are about 12 ribs to be cut out for the repair and you will need plenty of fiberglass resin and cloth. my brother helped(he works with fiberglass daily)and it took 4 days for the repair and 1/2 a day to remove the decks 1 1/2 days to re-install them.(it is easier to remove and install them with a 3rd person) while they are off the boat by some dow rods and coat them with resin and fill in the old screw holes, this will help secure them tighter when re-installing them since the holes are probly ovaled from the screws flexing in the holes.also mark were the trim came off or you will go insain trying to figure were it goes when you are done. The effort is well worth it and the repair is good for another 10 to 15yrs. We did my fathers starboard decks also and are going to do his port this summer.

Good luck and happy boating.