Newby replacing aluminum boat's floor

Hello, I'm finally diving in and preparing to replace the soggy floor on my 16' aluminum fishing boat & I have a few questions. Any help would be appreciated immensely!

At this point, I've come up with a few rough questions after wandering around the internet in an attempt to accumulate enough knowledge to ensure a quality replacement.

Marine Plywood vs Exterior PT
Epoxy-over some type of cloth/matrix (a bit confused about that process)- This area of the project is where it seems everyone has a different opinion, I just want to coat the wood enough to at least get 5-10 yrs out of it. What I really am confused about though is how to apply the stuff? Also, i've read about using polyester resin?
Carpet vs Fiberglass (I plan on using carpet but if fiberglass wouldn't be terribly difficult/expenisve I would consider.)
SS screws vs Rivots (I've been drilling out old rivots and have come to the conclusion SS screws would be better choice. I'm wondering, however, if I can simply pre drill holes in the aluminum tabs and expect the same firm attachment? Also, I read that when using ss screws it's wise to coat them with an anti-corrosive such as Tef-gel. Does this mean I simply coat the screws, let it dry, and then screw them in? Do I have to worry about the SS screws reacting with the aluminum tabs?

Basically, I feel after reading through numerous posts I may be making this more difficult than it has to be. All that I will be doing is simply drilling out the old rivots and using the old wood as my templates. What I am confused about is after i've cut out the new plywood, how do I use the epoxy? Do I simply screw the plywood down and expoxy over the wood, or sit the wood on top of the aluminum tabs with pre-drilled holes & then epoxy?
Since I am a college student $ is an issue here but I am willing to spend $200-250 to get this project finished. Lastly, the back third of the floor near my 40 hp Mercury outboard looks and feels as if it has been replaced somewhat recently.. the only question I have there is if I tear off the old carpet can I epoxy over the existing wood the same time i expoxy over the new stuff?
Any insight would be helpful and appreciated, I can also provide pictures if it would be helpful, thanks guys!

 

Well, first of all, welcome aboard the forum!

Yours is a problem that seems to come up a lot. It would appear that not too long ago, a lot of the factories that turned out these aluminum skiffs decided to cheap out and just rivet down some treated plywood for a cockpit sole. Now, they're all rotted out. (Point of terminology- the flat part of the boat on which you walk is the "sole", a "floor" is one of the structural members underneath it which transfers load from the sole to the hull.)

Some of the more puritanical boat restorers on here will no doubt bash me for what I'm about to suggest. But given your constraints:
- New sole to last 5-10 yrs
- Complete project to cost no more than $250

I would suggest good old AC exterior plywood. (AC, by virtue of having one crappy veneer on the outside where you can see it and patch it, often has slightly better core veneers than AB.) Cut it to shape and cut all the holes you'll need to cut.

Then treat it with resin, both sides and all exposed edges- including all the holes you just cut. If you want greatly improved abrasion resistance, stiffness and longevity, use a 10 oz fibreglass cloth on each side as well.

The resin can be polyester, yes- I've done polyester on plywood, and it can work. The trouble is that poly is a royal pain in the arse (sometimes it takes forever to set, sometimes it sets too quick, sometimes it falls off in a week, sometimes it just gets all gooey and makes a mess and you have to scrape it off, and usually it ends up porous and not watertight anyway), especially if you're trying to use it outside of a controlled, fixed-temperature production facility. You pay a premium for epoxy but it is so much easier to use, so much stronger and just better in every way, that it's worth it.

Alternatively, you could use exterior pressure-treated ply. Trouble here is that the chemicals used to kill off rot also have an irritating tendency to attack metal. Especially aluminum.

You can get stainless-steel Tek screws (self-drilling) that are designed for attaching wood to aluminum, or you can use ordinary SS self-tappers, or rivets, etc. All will work, and all will have a risk of corrosion. None will last forever. Thin aluminum tabs don't tend to hold screws that well, though, so rivets might be better if you're dealing with very light gauge metal.

You may as well replace the whole sole in one shot, rather than trying to salvage the little bit near the engine, unless it is already in very good shape. I would strongly suggest doing all your epoxying outside the boat; the aluminum hull will last for many decades yet, and ensuring that no epoxy gets in the boat will help to make it easier to take the new sole out if you or a future owner need to get into the bilge.

 

I am nearing completion of the decks of my 17' bowrider. I had to replace the stringers, transom plywood and decking plywood. I have done a lot of research on suitable plywood for my project.
The plywood I am using is HDO(High Density Overlay). MDO will also work as well. This type of plywood is used for sign making and for concrete pour forms. It is high quality, and very resistant to the elements. It has few if any voids in its laminates, uses a high grade glue between the laminates, and is sealed on both sides with a coating that is impervious to water. I have had a test piece outside for 5 years in rain and sun, also laying in puddles, and is as good as the day it was cut.
For your bolt or rivet application this material would be perfect. No need for any epoxy, though you may brush some on the cut edges if you wish(my test piece was left bare). 8'x4'x3/8" sheets were $80 per delivered. 1/2" sheet may be a little more. Nothing will stick to the surfaces, not even epoxy. If you wish to paint it, it has to be prepped with an autobody type wax and grease remover, then thoroughly sanded with 180grit paper, then it may be painted with a water based latex primer, and left to thoroughly dry before appling top coat.
This plywood comes in dark or light color surface.
If I were you, I would just cut the HDO and use as is.
Do a bit of web reseach. I think this will suit your needs well. Good luck.

 

This is a common subject on every site, what to do with a sole (floor) in an aluminum boat.

You can go all the way with the best materials and it may last a very long time, but if you only need it to last 5 years or so you can get by at a very low cost.

It's very easy to put a new floor in most aluminum boats, so the down side of a low cost job not holding up long enough and needing to be done again isn't as critical as on a fiber glass boat. Cheap exterior plywood and some kind of deck or porch paint for wood will hold up for several years and just use some sand as a non skid finish. This is the lowest cost method and the paint can easily be touched up when needed. Coat all side and the edges of the wood with paint.

You can up grade the plywood and even use PT, but with PT you need to use something between the aluminum and the wood to prevent corrosion. some boats have a plastic or rubber sheet as a barrier, others use pipe wrap tape (thick tape similar to electrical tape).

The problem with carpet, or any thing else that covers the wood, is that it will hold water and keep the wood wet all the time, this leads to rot. This can happen when the wood is covered with glass also. If you keep the boat covered and let the wood dry out when not in use, it will last a very long time.

My aluminum jet boat has a honeycomb floor and is completely sealed, but the cost is high for these products.

 

ondarvr,
i have the same project myself. i assume you mean a good exterior paint but i was also considering using a waterproofing stain on an AC grade plywood. the stain hold up any better than the paint?

 

Why plywood at all? Why not cedar, fir, or pine boards cleated together? They can be painted with polyurethane porch and deck enamel, assembled, and they will last well if fastened with bronze screws or nails.
No, stains are poor protection and costly. That applies to decks and to boats as well. Two coats of polyurethane paint without primer works nicely.
I don't think plywood is best for fiberglass or aluminum cockpits unless you're willing to put on three good coats of epoxy. Edges too. But then you're sealing moisture in below the ply. That's why boards are better. They can have a slot every 3-5", 1/8" wide. The bilge gets much-needed air. The wood lasts because it can dry out. Plywood can get damp and stay damp.
And carpet? It's how boats built by minimum-wage factory workers can be made to look neat and tidy. It's no way to build a boat----- maybe it should be put on just before you sell the boat. It hides so much.

Alan

 

The reason for plywood is the low cost and speed of construction, this isn't designed to be the best method, just one that can be done for less money and time, plus may last a good many years if cared for. It can be upgraded in any area for possibly better long term results, but most people don't keep the boat long enough for them to pay off and you never get the cost back in the sale price.

Waterproofing stains typically don't do much to protect the wood, but can interfere with painting or glueing. Good paints will normally work better and a non skid can be added to it.

 

well i thank you for the advice. by cleated boards i assume you mean 1 x 4 ran horizontally rather than lengthwise. but i see that the paint is better and that seems to be a theme. i never have done anything with fiberglass and feel that even tho it is the better route i know that it would probably end up an expensive disaster. i will be sure to update and thanks again

 

I meant running fore and aft. Cleats run athwartship underneath and aren't seen. The cleats can be 1 x 4, and care must be taken to prevent debris accumulating between the boards. A wider (1/4") slot may be better for rougher use. The faying surfaces of the already painted boards and cleats should be bedded in a good marine caulk. Nails can be bent over on the underside to lock all together.
I doubt plywood would be cheaper. Any plywood that was as strong as boards 3/4" thick would be the same thickness and the cost would be about $1.50 per square foot. The boards would appear more expensive until you consider the waste involved in cutting perhaps 1/3 of the plywood into scrap when fitting into curved areas.
Plywood has amazing diagonal strength. Exactly the kind of strength you don't need in an aluminum boat (and most fiberglass boats) in the sole.
As a hull material, diagonal strength is a real requirement. So while ply has real use when bonded or structurally screwed in, it's only advantage (against so many disadvantages) in small manufactured runabout or fishing boats is speed of installation---exactly why it was installed by the factory, and exactly why a home rebuilder should consider solid wood.
If you read a lot of these threads, you will note that plywood cockpit soles (often incorrectly called "floors") almost always cause rot problems. Now that's real labor, fixing all that rot.
It's amazing to me that one would create the same problem all over again by using plywood, or spend hundreds for epoxy and glass or whatever to protect plywood when boards would have ventilated moisture without the need for any epoxy.
What I often see is a design that uses under "floor" spaces for storage and the plywood keeps the spaces "dry". Handy, but unsailorly, as sealing in moisture invites mold and consequent rot. A rain-proof lid need only be located over the storage space. Not elsewhere.

Alan

 

You'll get no argument from me on there being better methods and materials for this repair and I didn't do mine this way, but it normally lasts at least 5 years even if it's not cared for.

The plywood in most aluminum boats is 1/2", some even 3/8", it just depends on how it's supported. One problem with boards is the gap between them, if you fish, everything you drop slips down into the bilge and needs to be dug out later. Like you said, most plywood rots away too soon, this is mostly because it gets cover with carpet, vinyl, fiber glass or a combination of these. When it gets wet it never gets the opportunity dry out when covered, but when it's just painted it tends to dry faster, so it's less likely to rot.

I also took into account the that he only had a couple of hundred bucks to do the job and I wanted make sure it was well under that amount. Three sheets of exterior plywood, some paint and a few SS screws should come to around $100.00. This should take one day with plywood and can be done again in the future (5 to 10 years) if needed for the same low cost.

 

All good points. I neglected to mention that those cleated together sections should be removable. Lift them out and wash the bilge out. For years, all open boats used boards for a sole, and better setups had removable sole sections.
I approach construction with an eye to longevity and practicality. Maybe if plywood is easily removed, or if it is not holding moisture in that affects other parts like frames---- or if the expensive route is taken and everything is sealed in epoxy, plywood can be practical.
I am about to redo a Mirrocraft that has no seats or floorboards. I will be building the sole from cleated together sections that will be stored in a shed off season. The seats will be wood and not padded vinyl. Everything will be removable for maintainence. That hull will outlast us all, and hopefully the interior wood parts will last a long time too.

 

I'm replacing a plywood hard deck on my cat with polycore and GRP (been told to use 600g top 400g bottom). The polycore sheets are about $90 AUS plus the glass. It will probably end up costing about 50% more than ply and GRP but its heaps lighter, very stong and will not rot.

2c worth

PS. I think its a similar product to Nidaplast that's available in the US.

Edit: Sorry, forgot the budget limit... exterior grade plywood and Evidure (saturating epoxy) prolly the better choice for the $$$

 

well this has been extremely helpful in alot more ways than i had expected. i thank all of you for that. this is a 14' 1973 crestliner. i like the idea of removable panels with the cleated floor but i dont think its as przctical for this small of an application. i am building seats as well and plan to recover in the vynl only because it will match the capt. chairs in the front row. if ive learned one thing its to keep my options open because i see value in all of the ideas that have been brought up.