Replacing rotten floor on aluminum boat

[baytonemus]

I'm looking for a little guidance regarding replacing the floor on my old Alumacraft (circa 1960).



The floor had been replaced at some point in the last 20 years, I believe, with what appears to be 5/8" treated plywood. The ply was attached with drywall screws to the floor "joists" and covered with indoor/outdoor carpeting that was glued down.



I was actually surprised by how soft and absorbent the floor was. People use this material as sheathing on framed wooden basements and it's supposed to last a lot longer than that.

It's clear that this approach didn't work. I'm wondering about material selection for the new floor, what to treat it with prior to installation, and also whether or not the floor should be vented somehow. I'm planning to put carpet down again but I'm inclined to not attach it so I can pull it up, clean it, and let it dry out from time to time.

I also have concerns about all of the caulking on the seams and rivets shown in the photo above. However, I think I'll address that problem on the thread I have going that deals with how to replace rivets that are leaking or missing.

Thanks!

 

[Woodonglass]

Re: Replacing rotten floor on aluminum boat

Welcome to iBoats!
Nice looking boat! Lots of posts on people doing exactly what you are doing. Most of them have done the following... Use exterior grade plywood. Give it two coats of Polyester or Epoxy resin followed by a layer of 6 to 9 oz fiberglass cloth soaked in resin. The cloth gives it structural strenth. You may or may not put cloth on both sides. Some people put the cloth on the Top side ONLY. Up to you. Some People attach with PL adhesive, other use Stainless screws, others use rivets. Again personal choice. Carpet can be attached by snaps, velcro or glue. Again personal choice. Lots of choices on carpet types. Main thing is to make sure the wood is sealed and that anytime you make any type of intrusion into the wood you always seal it with epoxy to protect it from moisture.

Good luck with your project.

 

[baytonemus]

Re: Replacing rotten floor on aluminum boat

Thanks for your reply, Woodonglass.

Welcome to iBoats!
Nice looking boat! Lots of posts on people doing exactly what you are doing. Most of them have done the following... Use exterior grade plywood. Give it two coats of Polyester or Epoxy resin followed by a layer of 6 to 9 oz fiberglass cloth soaked in resin. The cloth gives it structural strenth. You may or may not put cloth on both sides. Some people put the cloth on the Top side ONLY. Up to you.

I'm not clear about the need to add structural strength to the plywood. From an engineering standpoint, screwing the floor to the framing members (joists?) will add far more structural strength than fiberglass cloth ever could. Maybe there's something I'm missing, though. This is my first boat restoration.

Some People attach with PL adhesive, other use Stainless screws, others use rivets. Again personal choice. Carpet can be attached by snaps, velcro or glue. Again personal choice. Lots of choices on carpet types. Main thing is to make sure the wood is sealed and that anytime you make any type of intrusion into the wood you always seal it with epoxy to protect it from moisture.

Good luck with your project.

I assume that pre-drilling and squirting some epoxy down the hole prior to installing the fastener would be best, plus a coat over the screw head. No way to get at the bottom of the fastener, though.

What about the matter of venting? Would it still be a good idea to leave a gap between the floor and the back/transom of the boat or isn't that necessary?

 

[Woodonglass]

Re: Replacing rotten floor on aluminum boat

The structural strength refers to the resin. Without the glass it is subject to cracking which would then allow water to intrude into the wood. As to venting, is it your intention to Deck the entire boat? If so will you have a bilge area in the stern of the boat? It is always a good idea to have access to the hull of the boat just in case water gets between the deck and the hull. You will need to have a way to get the water out. A bilge allows water to drain from under the deck to the bilge and out a drain hole in the transom. As you know, Vents would work both ways, so.... It will be up to you. I would think you would want the deck to be as watertight as possible. Most of the guys seal their decks as best as possible and some put floatation foam under the deck. Do a search on the forum for decking an aluminum boat and I think you will find a lot of threads with pics and ideas to help you out.

 

[baytonemus]

Re: Replacing rotten floor on aluminum boat

The structural strength refers to the resin. Without the glass it is subject to cracking which would then allow water to intrude into the wood.

OK, that's helpful.

As to venting, is it your intention to Deck the entire boat? If so will you have a bilge area in the stern of the boat? It is always a good idea to have access to the hull of the boat just in case water gets between the deck and the hull. You will need to have a way to get the water out. A bilge allows water to drain from under the deck to the bilge and out a drain hole in the transom.

If "bilge area" in this context means an opening in the deck above the drain hole, then, yes, I will. The drain is in the hull of the boat near the rear, not in the transom. I'm planning to have an access lid there.



It appears as though someone knocked holes in the vertical deck supports at the very back of the boat so that water could get from between those supports down to the main drain hole. Strange that there would have been no allowance for this originally.

As you know, Vents would work both ways, so.... It will be up to you. I would think you would want the deck to be as watertight as possible. Most of the guys seal their decks as best as possible and some put floatation foam under the deck. Do a search on the forum for decking an aluminum boat and I think you will find a lot of threads with pics and ideas to help you out.

I'll definitely check that out. It seems like there would be more chance of mold forming under the floor if it can't breath a little. Plus, if the deck is sealed so tight that water you take on from above can't get down inside the hull where it can be drained, you're kind of asking for trouble there, too, aren't you?

I'm really not meaning to be argumentative. I just want to get the best understanding of the issues that I can and I appreciate your input. Thanks again!

 

[thiker15]

Re: Replacing rotten floor on aluminum boat

Having just finished rebuilding my Lund this is what I did after months of research. Use no other plywood except marine ply. Its a bid more money but well worth it in the long run. I than epoxied all sides using a foam roller, let dry for a couple of days. Next I glued 24oz marine carpeting(not the kind from home centers)using glue for marine applications. Finally I used stainless steel screws to attach the floor to the stringers.
It's ashame that people take short cuts or use products not ment to be in wet areas. Check out my thread to see my project. hope this helps.

 

[gunner1]

Re: Replacing rotten floor on aluminum boat

I'm on my second resto now and I'm starting to remove the deck. Both boats had carpet and both decks had rot. I know carpet looks nice and is nice on bare feet, not to mention quiet but it also as the tendency to hold water. And where water sits, rot can start. I simply used a commercial wood sealer from Home Depot in my first boat. I just saw the underside of the flooring from that boat and it still looked the same as it did when I sealed it two years ago. The topside was more worn obviously but still in good shape- especially considering the fact that the boat didn't have a cover and sat exposed tothe elements from april to september. I think in my current boat, I'll seal the exterior grade plywood with epoxy and cover with a nice marine vinyl. Then all you have to do is hose her out and you're GTG.

 

[baytonemus]

Re: Replacing rotten floor on aluminum boat

Use no other plywood except marine ply. Its a bid more money but well worth it in the long run. I than epoxied all sides using a foam roller, let dry for a couple of days.

So you didn't use a layer of fiberglass cloth and a second or third coat of epoxy? I've seen that recommended in other posts and threads, but it would add a lot of time and expense.

Next I glued 24oz marine carpeting(not the kind from home centers)using glue for marine applications.

I'm inclined not to glue my carpet down. It would be nice to be able to pull it up and let it dry out, at least once in awhile. Plus, it's not that expensive and I'd rather just throw it away and replace it if it starts to get nasty.

Thanks.

 

[baytonemus]

Re: Replacing rotten floor on aluminum boat

I simply used a commercial wood sealer from Home Depot in my first boat. I just saw the underside of the flooring from that boat and it still looked the same as it did when I sealed it two years ago. The topside was more worn obviously but still in good shape- especially considering the fact that the boat didn't have a cover and sat exposed tothe elements from april to september.

That's interesting. I have to admit that I'm a little bit daunted by the potential cost of just replacing the floor if I "do it right."

$150 - 2 sheets of marine-grade plywood ($70/sheet min.)
$165 - high quality epoxy resin & hardener (plus shipping)
$25 - fiberglass cloth
$25-50 - carpeting
$20 - misc brushes, rollers, etc.

$385-410 - TOTAL cost for floor

I'm not sure my boat will be worth much more than that when I'm done.

 

[Isaacm1986]

Re: Replacing rotten floor on aluminum boat

That's interesting. I have to admit that I'm a little bit daunted by the potential cost of just replacing the floor if I "do it right."

$150 - 2 sheets of marine-grade plywood ($70/sheet min.)
$165 - high quality epoxy resin & hardener (plus shipping)
$25 - fiberglass cloth
$25-50 - carpeting
$20 - misc brushes, rollers, etc.

$385-410 - TOTAL cost for floor

I'm not sure my boat will be worth much more than that when I'm done.

There is no need to use marine plywood. Yes it is a great product, but very expensive. Just get some exterior grade plywood. Epoxy is the best for sealing the wood, however I have heard of people using deck stain, oil based paints, linseed oil, spar varnish, and a variety of other things with pretty good results.

$25 a sheet for exterior grade plywood (x2)
$30 gallon of quality wood sealer
$20 random brushes/rollers
$50 for carpet
=$150 +/- for a deck that will last 5+ years.

It really just comes down to how long you want the deck to last vs cost. for $150 ($30 a year), I would not mind replacing the deck every 5 years. That is a lot of days/hours on the water having fun fishing and with family.

I am in the middle of a starcraft restore, and soon i will be laying down a new deck in mine. I have not decided yet what route I am going to take. It is a tough call.

Good luck on the decision making.

 

[baytonemus]

Re: Replacing rotten floor on aluminum boat

Thanks for your input, Isaacm1986.

Another thing I've been debating is what thickness of plywood to use. What I removed looks like about 5/8" but it wasn't original. Replacing it with 1/2" would be nice from the weight standpoint. On the other hand, one thing that's different from 1960 when this boat was made is that not as many people back then were...how can I put this delicately...as "full-figured" as is often the case today. Half inch flooring seems a bit light for a couple of my relatives.

 

[geedubcpa]

Re: Replacing rotten floor on aluminum boat

My experience is that the indoor outdoor carpet holds water and lets it soak in the wood. Marine carpet will shed water and has rubber backing that keeps the water from getting to the wood.

If the wood gets wet and stays wet over winter, then the wood freezes and the freezing action destroys the wood by expanding the layers.

Thats probably what happened, basing this on my own personal experience.

 

[arks]

Re: Replacing rotten floor on aluminum boat

That's interesting. I have to admit that I'm a little bit daunted by the potential cost of just replacing the floor if I "do it right."

$150 - 2 sheets of marine-grade plywood ($70/sheet min.)
$165 - high quality epoxy resin & hardener (plus shipping)
$25 - fiberglass cloth
$25-50 - carpeting
$20 - misc brushes, rollers, etc.

$385-410 - TOTAL cost for floor

I'm not sure my boat will be worth much more than that when I'm done.

Maybe you should consider just ripping all the wood out of the hull.
Seriously.
I have a 'bare' 14' Lowe and find it very liberating to have a boat that can't rot.

 

[baytonemus]

Re: Replacing rotten floor on aluminum boat

Maybe you should consider just ripping all the wood out of the hull.
Seriously.
I have a 'bare' 14' Lowe and find it very liberating to have a boat that can't rot.

Well, this is actually a nice little speedboat with upholstered seat cushions and backs, etc. It will be used for pleasure boating, not for fishing. Also, the supports for the deck are basically aluminum studs that are riveted directly to the hull. It's just not what I'm after.

Thanks, though.

 

[Isaacm1986]

Re: Replacing rotten floor on aluminum boat

On mine, I probably will be using 3/4". I would rather add a little weight to the boat and have a solid deck, than to try and save a few pounds and have a deck that flexes.

 

[ezmobee]

Re: Replacing rotten floor on aluminum boat

Yeah you won't be happy with a 1/2" floor. 5/8" minimum.

 

[gunner1]

Re: Replacing rotten floor on aluminum boat

Vote #3 for NOT using 1/2" plywood. I used 3/4" in my first and will probably use it again in my next peoject. It's a little more expensive and a little heavier than 5/8", but the structural strength is well worth it. Either way, just shop around and get the plywood with the most plies for the same thickness- i.e. 7 ply vs. 5 ply 3/4".

 

[Woodonglass]

Re: Replacing rotten floor on aluminum boat

5/8" minimum thickness on your ply. As far as Marine Grade and Ext. Grade the main difference based on the manufacturers specs is in the plys. The glue is basically the same. Marine grade has no voids in the plys where as the exterior has some because the wood plys used are not as good of quality. When you coat with resin and cloth you will get bascially the same servicability with a LOT less costs. Water under the deck IS a problem, that is why you want to insure that you can do everything possible to AVOID it but at the same time make sure that if it does occur that you can route it to the bilge. That is why the PO but those holes to try and route the water back to the bilge. When you tilt the boat to the stern any water should be able to flow into the bilge and then out of the drain hole.

 

[Jordeez98]

Re: Replacing rotten floor on aluminum boat

Great thread!...just reading thru this and it has helped answer many of my questions! thx guys! I'll be replacing my deck on my crestliner