Alternatives to marine ply: Birch? Cedar?

[science abuse]

Hello all.
Mostly what I'm doing at this point is retro fitting things to an exsiting hull. In place of expensive and hard-to-get teaks and marine plywood, I've utilized more common (in the US) rot-resistent woods, birch plywood and cedar strips.

I coat them depending on their planned exposure to water (on a bad day, everything is exposed). Polyurethane for components that only get splashed, and West Systems epoxy for submerged components (ama's, rudders, etc). A layer of fiberglass fabric for reinforcement when needed.

I've only been using the stuff for a couple of years and it seems to have held up perfect, but the submerged stuff has never been submerged for more than 48hr at a time. Does anyone have long-term experience with these materials? How ill-advised would it be to attempt an entire boat this way? What I'd likely build first would be something akin to ocean-crossing row boats.

Thanks
Eric G.

[Autodafe]

Hi Eric,

I'm not an expert, and I've never built using american timbers, but I'll wade in with my impressions:

Boats can and have been built out of non-marine plywood and lasted for decades.
If you chose a rot-resistant timber, make sure it has a marine type glue (phenolic "A" type it get's called here) and carefully check for voids inside the sheet then it is likely to be just as good as "Marine" standard ply.

I have made dinghys(tenders) and prototypes out of exterior and even interior plys.

However I would say that building any significant boat using non-marine ply is ill-advised unless you have a really clear reason for doing so.

Building a boat will take hundreds or thousands of hours of blood, sweat and tears. Saving a few bucks on ply seems like a good idea before you start but will be an eternal gnawing regret after you finish - unless it is intended to be a "disposable" vessel like a tender to be dragged on rocky foreshores.

IMHO - spend up on the hull and basic structure, and then save on the stuff you put in it.

The Marine grade plywood standard here in Australia specifies, among other things:
-The species' of wood that may be used
-minimum strength for the wood
-type of glue
-number and size of "voids" permitted in the wood
-number of "plys" that each thickness should be made from
-range of permissible density

If you can get non-marine plywood that meets the standards on all these points (and it is possible) then it is technically just as good, but finding out can be a lot of work, and you may lose on resale value.

If you do buy Marine grade make sure that each sheet is stamped with the name of the manufacturer and the number of the standard it complies to - in some places a lot of "marine ply" isn't.

Hope some of that helps.

[science abuse]

Thanks for the input Autodafe. This isn't going to be a grand project, just something around 16-17ft. However, the cost savings of using domestic wood rather than marine ply are more than significant, which makes them alluring. Here in the middle of the US, it comes at a hefty price as the trees it's made of aren’t indigenous. It would appear that, at the very least, structural components should be constructed of marine ply.

[science abuse]

For an indication of what cost difference I'm presented with here, I can get "premium" fished birch ply for a bit more than 1/100th the cost of Marine ply (from West Marine). Furthermore, West sells nothing bigger than 4ft square.

Are there better sources?

[Madcat]

Originally Posted by science abuse

For an indication of what cost difference I'm presented with here, I can get "premium" fished birch ply for a bit more than 1/100th the cost of Marine ply (from West Marine). Furthermore, West sells nothing bigger than 4ft square.

Are there better sources?

New member here, I found Marine ply at: Marine ply

I'm trying to decide the same as you. I'm looking at building a 20' mini cabin cruiser and the expense analysis is almost $2000 in just plywood for the hull. From what I understand plywood is rated Exterior/interior with veneer ratings varying from N to C (n is supposedly hard to find and just as pricey as marine ply) AA is typically the best you can find with reliability.

Marine and exterior ply are supposedly both made with waterproof glue. From what I understand the huge difference between the two is internal voids and gaps that you can't see. Having gaps weakens the strength of the board, which isn't a good thing if you have a few thousand pounds of displace water that would love to get in.

I'm considering building my boat with Marine ply at the waterline, and exterior above. Mine will be a trailer sailor, so it won't be sitting in the water for any length. The whole hull will be epoxied and glassed, it's just kind of nutso that the cost of building a hull is 80% plywood.

I'm also trying to find a 20-25' hull to retrofit & customize a bit, if I can get one in good shape fairly cheap it's definitely cheaper.

[science abuse]

Originally Posted by Madcat

I'm also trying to find a 20-25' hull to retrofit & customize a bit, if I can get one in good shape fairly cheap it's definitely cheaper.

That is precisely what I'm doing now, albeit a smaller 16ft hull. It is that of a Bayou 160 plastic canoe. Once the gunwales and plastic "decking" are removed, I'll essentially have a HDPE hull "skin" that I can fill with ribs and a structure of my own design.

Though I'll be doing my best to keep water out, some will inevitabley get in and I'll have a small bilge pump to deal with it. The keelson and ribs in the bilge will have more prolonged exposure to moisture than the deck will.

For the start-from-scratch project, I'd be looking to have it on the water for a week at a time, rather than spending a whole season in a slip.

[Madcat]

Originally Posted by science abuse

That is precisely what I'm doing now, albeit a smaller 16ft hull. It is that of a Bayou 160 plastic canoe. Once the gunwales and plastic "decking" are removed, I'll essentially have a HDPE hull "skin" that I can fill with ribs and a structure of my own design.

Though I'll be doing my best to keep water out, some will inevitabley get in and I'll have a small bilge pump to deal with it. The keelson and ribs in the bilge will have more prolonged exposure to moisture than the deck will.

For the start-from-scratch project, I'd be looking to have it on the water for a week at a time, rather than spending a whole season in a slip.

I personally have found that the best way to maintain your bilge is to try to glass it a bit and paint it white and sand it smooth. The white makes it easy to see any mildew, where water sits for any length of time and debris shows up very well against a white background. I will admit, I am very anal. I tend to keep everything bright and clean, up to and including scrubbing almost the entire boat bow to stern and keel to bridge almost every trip.

[science abuse]

Originally Posted by Madcat

I will admit, I am very anal...

As a captain should be! This is great advice. I was planning on using just the epoxy to seal the wood, but I've got plenty of fiberglass fabric, I'd be a fool not to add some for reinforcement.

[Wayne Grabow]

If you are looking at marine plywood sources, there are quite a few you haven't mentioned. Use the internet. I got mine sent from Noah's in Toronto. Most sources are in the NE or NW USA, but some are also located in SoCal and Florida. When you get through building a boat, the cost of marine ply will be only a small portion.

[ecflyer]

If you really know your plywoods and grading you do not need to use marine ply. Here in the US you can go to any local lumber yard/Home depot and request underlayment grade plywood. Most is made of exterior glue and has no inner ply voids. A secret in the wood industry is that underlayment grade cannot allow interior voids because it is used under vynil flooring of new homes. Big ladies with spiked high heels can exert 1000's of PSI with their tiny heels. This would likely puncture the flooring if there existed a ply void underneath. This ply is also mfg'ed with water proof glue because it is often used in bathrooms where toilets have a habit of leaking and kids splashing out of tubs. You can confirm that the ply is assembled with water proof glue by studying the glue line between the plys. If the glue line is dark brown to black it is water proof. You could also ask the lumber yard to show you the specs of the ply they are selling. In using such ply building a boat, one must be careful to coat the entire sheet w/epoxy especially the edges. The edges will wick up water/moisture quicker than the surface of the sheet. So one coat on the sheet and 2 coats on the edges should suffice. Good boat building !
Have a Spiffy G'Day
Earl

[PAR]

Ecflyer, your advise shows you don't know the difference between a quality marine sheet and construction grade. Construction grades use inferior interior species and they are full of repairs and defects, not to mention questionable species selections. The veneer count is minimum and the outer veneers tend to be very thin. This material doesn't have to be strong, nor is it expected to bend uniformly, like would be necessary in a boat.

You can use these cheap panels on disposable craft, those destined to have a short life, but if you want a product to preform uniformly and have considerably more strength, rot resistance and durability under dynamic loading, then selecting a suitable marine grade is only good sense.

My point is if you're building a uncle John's skiff and just want several fishing seasons out of it, then stop by the local big box store and buy some lauan. On the other hand, if you'd like to pass your handy work down to a son or grand child, then you should strongly consider a marine grade.

I have a stock pile of 6566 meranti here, 1/4", 5 veneer and about 23 pounds a sheet. I can bend this stuff around a 28" radius without worry it'll explode an internal defect or other wise self destruct. Now go out and grab a sheet of the best 1/4" underlayment you can find and try it. It'll pop, crack and show you precisely where all the internal defects are, before you've got it bent around a 36" radius. The two glue lines in the construction grade sheet can't take this level of torment, as it's not intended too. It's intended to lie flat and not move, which is about the most opposite thing you can expect from employment in a boat.

The only thing these grades are really good for is as minor partitions, interior furniture, etc. I recently finished a raw hull for a client. It was an 18' daysailor, complete with air chambers, lockers, decking, the whole shot. The plywood bill was $1,500 to do the whole boat, all Okoume and some meranti on the seat boxes and bulkheads. I charged $12,450, so the cost of the plywood for this project was 12% of the project. Considering the plywood is what keeps your socks dry, a small investment in the overall big picture of this particular boat.

[missinginaction]

Compared to PAR I'm a rank amateur. That said I've worked with Okoume 1088 standard (currently $135 for 1/2" sheet at Boulter in Boston), Douglas Fir ($85) and a product called Araucoply. I buy Araucoply at a local Lowes for about $30 a sheet for 15/32.

I'm not a professional. If I were, I'd probably just use Okoume and be done with it as for me Okoume is clearly the best ply I've ever had the pleasure of working with. I really didn't like douglas fir because of the wild grain patterns, but sheathed with epoxy and fiberglass cloth it's OK.

The Araucoply is dollar for dollar my favorite. I've never used it in areas that would be submerged but for interior woodworking, cabin sole, bulkheads (non load bearing), cabinets and more it's my wood of choice. People have said that it's inferior to Okoume. Of course it is! Look at the price. But, properly sealed I've had no problems at all with it. 15/32 sheets are 5 ply, sanded and weigh in at 45 lbs., reasonably light.

I'm going to build my new flybridge if the weather ever warms up here in NY and I'll use Araucoply for that project along with Phillipine Mahogany for the cleats and reinforcements. The panels get a seal coat or two, then a layer of 4 oz. fiberglass cloth, two coats of Interlux Epoxy Primecoat and two coats of Interlux Perfection.

Having said all this though, I'd agree with PAR that Okoume or Meranti are the preferred products. In spite of what others might tell you, you do get what you pay for. I also cannot speak to the bending properties of Araucoply as, well, I just don't bend it!

Might be worth a look.

Regards,

MIA

[PAR]

Hay, MIA, we need more photos of your project. Araucoply is a composite material, made from wood. It's exterior veneers are Radiata pine. The inside veneers are alike a OSB, so it's cheap, but I wouldn't want to trust it on planking. It's heavy, but the faces finish up nice and of course the glue is WBP, just in case you anchor above active volcanoes.

[missinginaction]

Hi PAR,

What a winter. We've been spoiled the past few years, but not this time. I was just down at the boat today. It's still too cold to do anything under the cover yet, but soon enough it should be warm enough.

Spent the winter skiing and spending money on all the things I need to finish this old girl up this year. My own personal economic stimulus package. FUnny, everytime I think I have everything covered I think of something else I need. I'm getting close though.....I think.

Decided to build my own flybridge rather than use the old preformed fiberglass one that came with the boat. More work, but I'll have much better ergonomics.

The name of the game now is patience. I have to make sure that I think everything through and not rush to finish this project.

[science abuse]

Many thanks for all of the input! Looks as though There's more to do on paper before i move forward with anything. I've also been playing with foamecore/sandwich and fiberglass, and have produced some very strong peices. We'll see what sort of trouble I get myself into this fall. Until then, it's boat-using season.