need to replace the floor
As a footnote: All total, you are probably looking at a $600 to $800.00 do it yourself repair job here. And that's is assuming nothing else needs replacing. (as general, when the floor is gone - the stringers have too - and then you are really into some major work and repair. So, careful thought should be given as to whether your 88 Bayliner is worth the expense and risk of this DIY repair. I mention that, only because, while I have no idea the condition of the rest of your boat or its motor - my 40 plus years of boatbuilding experience tells me - your boat is most likely not worth this repair. Especially since you have never done it before, and have no clue as to what else might be wrong with the floor, sub-floor, hull, or stringers. . .
You have to cut the old floor out. Then repair the supporting wood then lay new plywood down and then seal with epoxy. It's a bit harder to do than most think, and you need to be sure the boat is worth the effort. You can find newer boats at giveaway prices, so why fix bad ones. I an other frequent askers are encouraging askers to choose a best answer. If you like an answer, choose it! Thumbs up are appreciated, but thumbs down need a comment (see button) or explanation, which you can do by posting your own answer. Thumbs down are important if the answer is factually wrong. They are not like Yahoo Comment Post, where it's an opinion poll. Lets all make Boating Answers Better!