Anything but wood!

Hi,
I'm rbuilding a 15.5' tri-hull fiberglass boat from the eighties. The deck, stringers, and transom were comepletely shot, so I'm getting ready to replace all of the above. I want to go 100% composite or at least 100% non-wood. This boat is for me and my three sons, and if possible, i would like to use it longer than the lifespan of puny wood. I plan of using Seacast for the transom, and possibly the stringers, but that leaves the rear deck and floor open to suggestion.

 

SeaCast, if what I think, would be a poor selection for load bearing members like beams and stringers. Tri's are rather weight sensitive and making radical changes to the weights, locations of this additional weight, changes to the properties the structures were intended to bear will have a negative impact on the abilities and performance of this little yacht.

The reason wood was used and is still used is the qualities it has as a building material and load bearer. Not many materials compare well to wood. The other materials tend to be heavier, more costly, more toxic, more difficult to shape or machine and in general don't have all the qualities that make wood so hard to get away from.

The deck could be replaced with a glass layup, but it'll cost more and require more work, in a one off effort, then a new plywood (my assuming) deck covered in Dynel and epoxy. Stringers could be made by tabbing foam or tubes to the hull(s), but this is just what was done with the wood (another assumption) in the original construction.

Use SeaCast for the transoms if you'd like, but the fact is, pound for pound the plywood that was used (yet another assumption) is stronger than steel! The fact is, nothing can flex like wood and remain able to return to it's original shape, repeatedly (though we're getting close with some metals) The fact is, in your size range not much can compare to the cost of a one off boat done in wood.

It's likely your little tri is a polyester/glass matrix with wood for stiffeners and supports (man, I'm making a bunch of assumptions here) It is now well known that this stuff doesn't stick worth a damn to wood, the jury wasn't quite in on the subject in the early 80's and folks learn hard for the most part. Epoxy will cure this problem. Encapsulation of the wooden members of the craft will allow the bond to take and polyester can be used elsewhere to save costs (with a strength penalty)

I'll bet you have wood furniture and the like in your house. Why don't you sit on a fiberglass sofa? It would last longer, could live with major neglect for much longer, but the hemorrhoid issue might rear up and bite you in the . . .

 

Thanks for all the wood

Thanks for the ample response.

After conversations with you and a few others, I have been swayed to the side of wood. I am considering pressure-treated 5/8 plywood. I am told that this has a longer lifespan in waterborne applications than "marine grade" plywood. Conversely, I am told that marine grade plywood is completely dry before it reaches the market, whereas pressure treated is still "green" sometimes. The undesireable result I fear with using green wood is encapsulating it in resin/glass with the very water that I need to protect it from.

Anybody got the final word on plywood?

 

There is pressure treated marine plywood. The best of both worlds.

 

BS1088 (British Standard) is the grade most of us see in this country, for marine grade plywood. This standard defines the wood used in the panel as very durable (class 4 or better as set down by BS EN 350 yet another British standard) and generally the veneers used are heartwood, though a small amount of sap wood is allowed. These are separated into two classes, standard and low density. Deterioration resistance, defects, adhesives and panel layup are all closely watched and covered under this grading system.

American made plywood is graded by the American Plywood Association's (APA) voluntary product standard. The marine grade is PS 1-95 with letter grades assigned based on the quality of the face and back. APA panels are made of all Doug fur or all Western larch, with a higher amount of flaws then are seen in BS marked stock.

Medium density overlay (MDO) and high density overlay (HDO) also meet APA's marine standards and have a fiber based sheet bonded to their faces, which takes paint very well.

There are a number of other grading systems, CTBX (France) Japan's JPIC, the Dutch Komo class A and several more.

All of the above marine grades listed will out perform any pressure treated plywood bought at a lumber store like Home Depot. That lumber (pressure treated) is a poor grade of veneers glued to even more poor grades of veneers and treated with bug killer in an attempt to buy off the sure to follow rot and decay. Pressure treated (PT) plywood has little place on a boat, but for maybe the deck of a pontoon boat to be covered with astro turf (and to rot out anyway in 5 years)

The people who are giving you this advise about PT should shut up, or at least speak what they know, or better yet, you should stop paying attention to folks whom don't know their ply from a hole in the ground. PT is junk, but does make a nice porch roof on the back of the house, once covered with tar paper and shingles it'll last quite a while.

In the end you'll get what you pay for. If you want junk wood, by the PT, if you want a boat to last then get the good stuff. In the end the price of the plywood will be a small cost of the project, but a big part of the over all picture.

 

There is marine grade pressure treated lumber.
Par: I am disappointed in your attitude. In the past you showed courtesy and professionalism.

 

Yes, there is a PT marine grade plywood, I was talking about the PT available at the local Lowes/Depot type stores. It's junk. Sorry if I offended, but the wood is real poor quality, minimum number of plys, the panels are poorly assembled and the treatment doesn't work very well in most marine applications, let alone continuous underwater exposure. I think they're using what the companies are calling HemFur, a hybrid of hemlock and fur. Fast growing, wild grain, crazy internal stresses, Junk.

PT in marine grades will have to meet the marine requirements for content, imperfections, repairs, etc. I think CCA (the bug killer used in PT) isn't all that good (certainly don't want to be enclosed with it in living spaces) and there are better methods of dealing with wood meant for a life on the water.

PT decks used outside down here in Florida don't last long, nor do fences and other products using PT. If the land based products don't survive long in an admittedly harsh Florida climate, then it's life will be shorter on the water.

Gonzo is quite correct, I was overly rude, I'll flog myself for at least a half hour before bed time this evening. I just get burned by people talking about what they don't know as if they did. I'll try to be nice in the morning . . .

 

No problem. We all have bad days. No tar and feathers for you today

 

It's a better day today, I only yelled at one person. Not to high jack a thread, but this guy's driving me nuts.

You see, I sold a set of plans to this fellow who wanted to build his own yacht. This was my first (maybe my last) plan for a backyard builder. He seemed quite talented and knowledgeable, but I did the plans with an extra amount of detail and factored in slightly heavier scantlings, so he could screw up some and still work out okay. I even worked out an easy way to do the framing and planking saving time, money and materials.

It's been since February and he calls every day. Most days I get more then one call. Sure I'm available for help and discussion on how things are working out, but I never intended to hold his hand through the process. What you do with someone's need to be nurse maided? He called again today and on the second call I went off on him a little. I'd just drove a course thread bugle headed screw into my left index finger (had to reverse the drill to get it out) and wasn't in the best frame of mind to hear is voice.

I explained that I did a good job anticipating his needs in the plans and the set is quite complete, more so then I do for anyone else. Then I degraded into the nuisance he's becoming and how bad my finger hurt worked into the voice inflection, etc.

Ever run into this problem anyone? He's pissed, I'd imagine, but he has a plan for a great little pocket cruiser. Maybe it's a little bigger (32') then a pocket cruiser, how about a painter's pants pocket cruiser . . .

Gonzo, I may need the tar and feathers yet.

 

Interestingly enough, my father--who has performed all types of construction and remodeling--and my brother --who is a professional remodeler--both referred to store bought PT plywood as "crap", and urged me to research marine-grade. The owning family of a local marina, however, have blasted marine grade repeatedly, repeating the mantra, "Jess go git it at Lowe's".

Where do I look to buy the BS1088, and how much should I expect to pay?

Thank youa ll for your help, especially Par. Anyone who stand by their expertise that adamantly is either correct, or is twistedly setting you up for a failure.

 

I'll bet the local owner of the marina just doesn't like the price of quality materials and is looking to cut costs (if not corners) as much as he can. He probably uses red oak in place of white on boats too, not knowing the difference (red is all Lowes carries) and shouldn't be on a boat of any kind unless used as inside cabinet trim. If you'd like to find out why cut a piece of red oak into a 1/4" x 1/4" x a few inches log section and stick it in a glass of water. Put you mouth over the end (like a soda straw) and blow hard. You'll see bubbles, not a good quality for boat building lumber to have (if the air can get out, guess what can get in)

You'll find the folks who use the stuff regularly (Lowes/Depot PT) don't think much of it as a quality wood, but much better then non treated wood left natural (except teak, pitch pine and a few others)

As for availablity, it's gotten at specitally wood suppliers (try the phone book in major cities) You will want to pick it up as shipping on plywood isn't cheap. Atlanta should have a few local suppliers. Try a quick search on the web.

Try:

M.L. Condon 914/946-4111
www.boulterplywood.com
www.noahsmarine.com
www.mcclanahanlumber.com

The other half says I'm quite twisted, but I say it just curves to the left a little . . .

 

Also looking for BS1088 in Atlanta

Did you happen to find a supplier in the Atlanta area? I am also looking and have not had any luck.

 

Southern Crown Boats 770 454-8798 carries bs-1088 ply.

 

lightweight strength

Medicine man
There is a product called Betostyrene a concrete additive which replaces the coarser grains of sand, is water impervious and depending on the mix ratio used will float on water also the Plastics industry has developed mesh(tilers use it)and reo bar.Now these materials used together will be much stronger than wood or GRP, float ,not rot and as easy and flexible as concrete to install.You could even use polyurethane sheet as permanent formwork.I have
abstacted this system through my work as a concretor & tiler which is maybe why no one else, to my knowledge uses it.My own dream is to build a vessel from these materials which have been fully engineered and used in civil consruction,all the best.Horrie

 

The arsenic based pressure treated plywood or any wood is on the way out anyhow.
But while it still last, there are three main grades of PT woods.
.40, .80, 1.25. This deals with the % of arsenic salt in the wood.
.40 is for just being in the weather, the .80 is ground contact and the 1.25 is considered water contact. Marine grade PT is suppose to be in the last category. But a lot of the suppose to be Marine grade PT plywood on the market is actually .80 stuff.
I would use okume or maranti anyhow and make sure it is encapsulated well. It is better wood and better on the environment
The price for the okume and maranti is not much more than AC fir So.....
Ben