Plywood

I know it is a good Idea to use marine grade plywood on all exposed areas of a boat but for the area's that are not exposed to the water or the eliminates couldn't you use a regular plywood. I know it has gaps but I don't see a problem when using it for parts not touching the water.

What is your opinion on this?

 

Four questions...

1. Are you keeping the craft in the water or pulling it out after use?
2. Are you considering this for a structural application like part of the hull? Or are you talking about something like the exterior sides or top of a non (or minimally)-structural cabin section?
3. How long do you want it to last?
4. How easy will it be to repair?

 

My current boat is built with AC exterior ply and fibreglass skin.... she lives on her trailer of course, but I haven't had any wet-wood problems nor have many others with similar boats.
AC is preferred to AB, since with AB the crappy C grade layers are in the core while with AC the core is a good layer and the C grade is exposed where you can easily repair it.
Whether it's suitable for you depends on your application.

 

Marine vs. exterior ply.

It is quite obvious that if Marine and Exterior ply were both the same price, all boatbuilders would chose the former. The glue used in each possibly doesnt differ much, but the veneer quality does, A LOT.
Building your own boat from new materials, even the cheapest that are reasonable for marine use, is a more expensive exercise than buying a second hand craft from the many people out there, who are desperate to quit their boat.
Therefore it is not a reasonable argument to say that I really want a boat, but am so poor that I have to build one, and also have to cut corners with materials, compromising the longevity of the final product.
The activity of boatbuilding is for the passion, and the enormous satisfaction seeing your creation grow. It is not an exercise in sticking to a very low budget. There are thousands of cheaper hobbies, by the way!

 

You would probably have no problem whatsoever using 'good' regular exterior plywood. I'm not so sure boat mfrgs. even use marine ply very much. Ask at a cabinet shop where they get their ply for countertops and other hidden places where they don't use the hardwood faced stuff. I guess make sure it's 'exterior', but I don't know if they actually even make anything with an 'interior' glue anymore. I stay away from A-C as it is usually sort of a scam, with the A side veneer real thin with 4 fat plys of something else in a 3/4" sheet. You get a good idea of how many and how big the voids are when you can look at a whole stack of sheets. Quality will vary from company to company and also I think from batch to batch within a company, depending on the quality of the logs they are using that day, the quality of the labor and how hung over they happen to be, etc. Use stuff with an odd number of plys and an even thickness of plys. I have a sheet of 3/4" 7 ply B-C pine that layed on the ground for about a year until the bottom was 'one' with the soil and bugs, while the sun and rain beat the other side. It never warped. I pried it up, brought it home, hosed off the dirt and set it on it's end and it is still flat like a table. $35 a sheet at the real 'local' lumberyard. I can't imagine marine grade doing much better than that. There is also some stuff called MDO, medium density overlay, that sign makers use and that Hiway Depts use for their signs, which some boatbuilders highly recommend over marine, even for hulls. Sam

 

The quality of "marine plywood" can vary greatly from one supplier to the next. Do some research on marine ply, maybe pick up an issue of Wooden Boat magazine & look at the suppliers listed within.

I would build out of all top quality marine ply that I have determined was the best practically obtainable & that I have personally inspected before purchase. Make all structural parts of your hull, deck, & cabin structure able to live through a sinking & refloating. Built to this standard a boat should have a long happy life if generally seeing normal (whatever that is) service.

TGoz

 

Noticing (belatedly) your location I realize you will probably have somewhat of a trip involved to personally inspect your plywwod prior to purchase.

Good excuse to get out to the ocean if your situation permits.
Take care.

TGoz

 

OK I will first reply to the person that mentioned building because you can’t afford a boat. I own a boat at present. Thank you for all the good information. I see this subject is one that is debated among boat builders. I will make a couple of small vessels and try both materials. I am thinking about building a PDRacer for my first couple of boats. They are very ugly but that is what I like about them.

 

You have got to be very aware that a professional boatbuilder has pressures in costs of materials that are very different to an amateur. If reputation or longevity of the business is not a major issue, then cost saving using inferior material is par for the course, is it not?
Look at the example of resins for instance. Polyester (cheap and less water resistant) versus epoxy, (expensive and highly water resistant).
What are most commercial boats made of? This is not to say that a boat made from exterior ply or polyester resin is no good; it is just less good!

 

To me a boat trancends the material, and in it's own way, lives upon the waves.

If one is expecting a child, they hope for it to be as healthy, intelligent, & perfect as possible in every way. A good mother does all she can while the baby is "building" in the womb to insure the above, with the hope that the child, after birth, will have a long and fruitful life.

I feel much the same towards boats.

One must also remember that your life may very well depend upon the integrity of your chosen craft, sometimes much more than others.

The above is not to say that good and functional boats cannot be built from exterior ply and other less expensive materials, but lets not fool ourselves by thinking that the same design built out of top shelf materials and with the same skill level would not be a somewhat better boat.

Just my humble opinion & not meant to offend.

TGoz

 

All of the professional boat builders I know use marine grade ply for all the underwater parts of the boats, some even use the marine grade for any part of the boat, to quote one "If I know there is better stuff out there and I don’t use it then I am liable but if I use the industry standard then I am covered"
For a small skiff or something like that I guess AC would be ok for a couple of years, a bigger boat NO WAY its your safety your playing with.
Just my opinion
Ben

 

I don't think it's enough money to save by using lower quality plywood.
The price is maybe half of what you pay for BS1088.
And the plywood is a very small part of the total cost.

 

This is a new age. It's not our Granpa's materials anymore. There are scads of glues & coverings that more than compensate for the differances of a few gaps or loss of a couple plys.. A small boat won't be subject to anything that will reveal a weakness. A big boat can be built stromger with extra ribs, stringers, etc..
For a ameture builder the cost & availability AND amount is critacle Buying payday to payday, storing and the ability to reach "stages" of construction to maintain enthusiasm are primary events to Ol' Backyard Joe.
Looking at why boats sink and it's clear that stupidity is the main reason and not structural failure of a slightly less stromg material.
Give me a well crafted, well designed boat made from exterior plywood over a careless Cap'n & crew anytime.
And poor people like to be on the water too.
While we all share the same sky, we each have a different horizen.

 

Previouly this summer I chimed in that using pressure treated screwed to 2X4 framing with stailess and encapsulated completely was a bad idea because the stainless will experience crevice corrosion. This application was/is for a fishing platform on an aluminum craft. Well, there was a verbal tirade quoting the space shuttle construction, etc.
Here I will vote for the exterior ply being acceptable for the application described by desertgoldhound.
I would double-up on the sealing of the grain and then probably seal it again and by then I could have purchased and shipped the marine grade ply.

 

FYI:
Better than plywood............................or so everyone tells me so.

http://www.coosacomposites.com/