I did something stupid.

It's pretty rare to get those closed-floor hulls anymore.  Dad has a 1968 Glassmaster with the closed hull/bilge setup like yours.  It sure does make for a rigid hull, but yes, water eventually gets in.  In about 1988 we drilled the bilge and installed a brass bung so we could periodically check for water below the floor and never found any.... until we put a drain plug in it. 

Most folks just go back to an open bilge when they re-do it.  Nice to see you're going for the full monty.

You're going to hear people talking about buoyancy foam under the floor.  Don't.  First, if it's in a sealed chamber, it's not buoyancy, it's just weight.  It won't help it float, in fact will will make it sink quicker.  Buoyancy foam only works if it's in contact with water displacement.  Closed-cell urethane foam would be a nice touch for floor rigidity, but eventually (vibes, twists, etc) will make the closed cells no longer closed.  The under-floor foam I had to remove from my Baja was exactly like a huge chunk of apple flesh.  So saturated with water than it squirted when I stuck the shovel into it.

Curtis73 (Forum Supporter) said:

You're going to hear people talking about buoyancy foam under the floor.  Don't.  First, if it's in a sealed chamber, it's not buoyancy, it's just weight.  It won't help it float, in fact will will make it sink quicker.  Buoyancy foam only works if it's in contact with water displacement.  Closed-cell urethane foam would be a nice touch for floor rigidity, but eventually (vibes, twists, etc) will make the closed cells no longer closed.

I had always wondered about that. Nice to have the conformation that most of the DIY "improvements" I've seen were not helping. Makes me feel better about my plan - if I ever get a chance to redo the floor... er... deck ... of mine!

Interesting input on the foam, I took a lot of wet foam out of the old floor for sure. I bought two part m foam but I may reconsider. I think there's advantages in helping to support the floor and dampen and sound though. 
 

I added a few more layers of fiberglass and tweaked certain areas, but today it was time to get the floor in. There was no good way to put in one large piece of wood without taking the boat apart, so I went with a sectioned approach. 
 

The rear of the boat tapers down to 4 feet wide, so one section went there. I had a piece left from the sheets I used for the transom, so that went in first. 

To make sure that the individual sections were well supported, I added 2 x 4 by eights as additional stringers. I trimmed the bottom edge to match the angle of the hull. 

One 4 x 8 sheet of ply was enough to do the rest of the boat, but the center section needed to be 5 feet wide. That meant I need a filler piece to fill in the rest of the 4 foot wide section. 

Next came the front section, which tapers quite a bit. 

it was impossible to get the wood as far out to the edges as I wanted, so to make sure the outer edges were well supported I cut some tapered pieces and secured them with construction adhesive. 

finally the large center section went in. This is where the seats will attach so I wanted one large piece here. 

i'll snap some Chalk lines to add a few more screws, then either add foam or move to more fiberglass. 

In reply to pinchvalve (Forum Supporter) :

That looks really good.   Were you able to run the engine at all before you took everything apart?  If you can get that running well I think you’ll be pleasantly surprised with the performance.   That was one of the best engines OMC ever made, they have a reputation for being nearly bulletproof.    If it has an oil injection system I’d recommend removing that and running 50-1 pre mix in 6 gallon tanks.    Get an in-line fuel filter / water separator and install that in the fuel line between the tanks and the engine.  Clean fuel and the right amount of oil will keep it running a long time.  Good to see more progress.  

The engine turned over, but the gas was so old and stale that I did not want to further contaminate things. It's a risk working on the hull without knowing if I have a good engine, but it's removable right? It looks really clean and there are a few local shops that work wonders on old marine carbs, so I am not too worried.

In reply to pinchvalve (Forum Supporter) :

Marine carbs from that era are dead simple and only have a couple of moving parts. A dunk in an ultrasonic cleaner does wonders. Worst case, a blast with carb cleaner and an air compressor will usually do the trick. 85% of the time, you don't even need a carb kit. The oil in the fuel keeps the gaskets from sticking. 

If it doesn't run after that, I'd put money on it being the fuel pump or the power pack. 

In reply to Toyman01 (Moderately Supportive Dude) :

Thanks for the tips! For the motor, I am doing the obvious stuff like draining and replacing the gear oil in the lower unit, adding new rubber hoses and new spark plugs, cleaning up all electrical connections and cleaning the carbs. With limited space, a 12-gallon tank won't fit, so I am going to use 2 six-gallon tanks and pre-mix the oil. (no oil injection on this one). I will add a filter and oil/water separator as well, thanks for that tip as well

In the end, I decided to go with foam under the floors. That's the way the boat was originally built and I had already bought the foam. While I understand the waterproofing aspect, I took 40 years for the first stuff to be destroyed and I don't plan on keeping this boat that long. 
 

I drilled some holes and pour the foam in sections. It was cold and after 30 minutes the foam hadn't expanded much. I figured I'd get as much coverage as I was going to get and went to bed. The next morning however I found a little surprise. 
 

apparently the foam kept expanding slowly for a few hours and by morning the bilge area was full. And hard. The two drain holes that I hadn't got a chance to cap allow the phone to fill up the bilge. At least that means most of the space under the floor was nicely filled.

after spending an hour cutting out the excess foam, The next step was to replace the fiberglass floor I had removed. 

I begin by sealing any gaps in the wood and adding one more layer of water seal to the wood. I had removed a few large sections of the fiberglass floor which I then glued back down. To make sure things were sealed up as possible, I used fiberglass body filler to fill in any seams or holes in the fiberglass sheets. 

Somehow, I did not save the sheets from the rear of the boat. I think I was cutting this in small sections to get a sense of what was under the floor before I realized it was all coming out. So for the back I built up a new fiberglass floor from several sheets of fabric. I tied this into the bilge to make sure the water went where I wanted it to go. 

The final step was to go over all of the seams with fiberglass tape to make sure everything was sealed. I also sealed the outer edges. I'm fairly certain that this will seal up the floor 100%. I'm not too concerned about appearance as there will be a floor covering going over all of this, I just wanted to be as watertight as possible. 

there were a few cracks in the fiberglass under one of the front benches, so I added some reinforcement there as well. This will be under a bench seat but I wanna make sure there's structure. 

Not sure if any of these methods are the correct way to repair a boat, but I'm sure they will be fine for my purposes.

It has been a while since I have updated, but work has been slowly progressing. The back of the boat is all glassed in now, I had to replace the section of the floor that I removed and discarded, so that took a few sheets. The bilge area may need another touch-up, but its OK. I did add stainless drain plugs to isolate the under-floor area. Why let water into the foam if I don't need to?  I also added two pieces of wood to stop batteries and fuel tanks from sliding out. They will be secured, but its extra precaution.

I also re-did all of the fittings with stainless steel bolts or screws. I added reinforcing plates on the back side to reduce strain on the fiberglass hull.

Next up was to cut out all of the wood I would need to cover for panels and seats. I am using Pontoon Deck bolts where possible to keep things nice and flush, SS screws elsewhere.

New running lights meant that it was time to start on the wiring. I ripped out everything that was there because it was so bad and started from scratch.

First up was to cover the dash with vinyl and reinstall the steering wheel. I added a horn button to the right there, next to the bilge pump switch. I also added a switch panel that will be the central hub for electrical stuff. I have a plug on the battery so that I can easily remove or isolate it. Once plugged in, the panel goes hot.

I then can see my voltage, and I have 2 USB plugs for phones etc. Three switches will be for lighting onboard, and the 4th sends power to the radio, horn and bilge. This is another way to easily kill power just in case. Here is a close up of the horn button...

and the horn...

And amazingly, it all works! (I used the little waterproof connectors with built-in solder and they worked great. All you need is a heat gun.)

You're really trucking along.

I must have missed it... what are you going to put on the floor as a final coating?

I've decided to use EVA Foam because I like the look of it over outdoor or marine carpeting.

This weekend, I got the electrical finished. I added some interior lighting, installed the stereo and speakers, and I got the speedometer and pitot tube hooked up. I also took the time to loom and secure all wires and cables for a clean look and to avoid pulling anything out.

The speedometer is in a weird location, the original was surface mount and I thought the replacement would be too. It's easily visible and this is an a speed boat so I'm not too worried. I also got some work down on the trailer. I added safety chains...which were way too long and needed trimming. I added a missing roller in the center...which was too high so I had to fab custom brackets for it. Re-did the trailer plug...which was a rat's nest of wires and needed a replacement. UGH, all these little delays are why project take longer than you expect. Still hoping for Memorial Day though!

Next up is the cushions for the seats, which Mom is sewing corners for.

Just wanted to say that I love the old school workmate in the photos...and great job on the boat, I mean stupid thing

In reply to russde :

It's funny that you say that, my OG Workmate died on me a few years back and I actually replaced it with a new one. It does so many things well!

I think the goal to have her on the water by Memorial Day might actually happen. I got the floors in:

Got the cushions all constructed. They are not pro-level quality, but it was a combination of me cutting wood and foam, and my mother sewing corners, and then me trying to staple it all together. Came out acceptable for my purposes.

Oddly enough, I invested many hours and dollars into a boat without knowing for sure that the motor ran. But I drained the lower gear oil and replaced it, changed plugs, swapped in fresh rubber hoses, and she fired right up and ran like a champ. The river will be the real test, but seems OK. (famous last boating words right?) I gave the outboard some touch-up paint and new stickers, and painted the whale-tail thingy blue. Why blue? Because I had a can of blue Krylon Fusion and it sticks to weird plastics well.

And of course, she has to have a name. Boaty McBoatface was a working title, but in the end I went a different way. (remind me to remove that old sticker residue when I have a minute)

That looks very good.

Edit: Never mind I found it.

What flooring did you use? I really like the way it turned out. 

This has been very entertaining to follow. 

Crappy weather today, hoping for a Memorial Day to get her wet. 

I had not really followed this thread but I jumped in today.  Wow, it all looks really good.  I really like the faux teak and holly flooring.  The vinyl looks great too at a period correct color. 

For the first outing, make sure you have all the coast guard requirements like current flares and etc.  Don't overload the boats person capacity and have the right float/jacket for each person.  On these early weekends, they love to write citations.  

In reply to pinchvalve (Forum Supporter) :

The floors and overlay came out really great. 

X2 on the life jackets and safety gear suggestions from John.   I’d also suggest a spin on fuel filter / water separator in the fuel line to keep the engine happy as well as a second six gallon fuel tank.   The boat looks amazing, great work restoring it.  I think you’ll be pleased with the performance, I hope you have a great summer with it. 

Finally had decent weather for Memorial Day so we got on the water before it got too crazy and tested her out. Bottom line, its officially a boat.

 It was a little chilly, but the sun was out and the skies were clear.  My son loved having so many places to chillax.

 The motor fired right up and ran well, but I don't think it was 100%. It revved up and topped out at a nice clip, 20mph if the speedo is to be believed. It just seemed like it had more to give, more revs perhaps. I never cleaned the carbs, so I will look at the plugs and give it a good cleaning and see what happens.

Air temp was about 68, water temp was about 50, and this fool wanted to go for a swim. Not me. The other concern on the motor was that we went through 15 gallons of fuel in a day. Maybe that's par for the course, but it seemed excessive. It was enough to get us through a day and almost all the way back to the dock.

Thanks to PGH River Rescue for the 1/8 mile tow to the dock. Man, so close!  Drained two 6 gallon tanks and a 3 gallon tank, so I have to both reduce fuel consumption AND watch the fuel level more closely.

even with the tow, the family had a great time and it was a first outing to remember. Even the dog found his groove and had fun. 
 

Man! That was great until that last photo. 

You did such a great job on this, I hope the tow line was for something minor!

oh man... what a wild swing of emotions on that last post...  But also, fantastic job, it looks so great and period correct.  I'd be curious if you had an approximate 'total' that you spent, including materials and hours?  Curious if I need a project car or boat in my life right now, I'm at a crossroads.