epoxy alone? or epoxy with fasteners?

[Chub]

Which method do you prefer?
I recently had a visit to my shop from a professional cabinet maker and good friend. When I told him I was bonding the frames of my boat with epoxy only and absolutely no fasteners, he just about flipped. "NO FASTENERS!! Are you crazy?? Your boat will fall apart in a couple of years from stress cracks alone.”
This got me wondering about the longevity of epoxy glued joints. Should I back up the joints with screws or continue to build with epoxy alone?
Any feedback would be greatly appreciated.
Thank You.
tongue.gif

[ 10-04-2005, 12:30 AM: Message edited by: Chub ]

[BRobinson]

Yeah...use screws

[JimD]

What's the boat, Chub?

[Chub]

Originally posted by JimD:
What's the boat, Chub?19" ply on fame planing power dory.

[Bob Smalser]

http://pic3.picturetrail.com/VOL12/1104763/8408305/113106749.jpg

Here's a 40-year-old plywood-epoxy boat....yes, even the most-loved boats will look like this some day.

Every epoxy joint that didn't also have a fastener was either broken completely or cracked. Exceptions were several plank laps that were heavily filleted.

The glue only penetrates the first plywood lamination....when loss of protective coatings deteriorate that lam with time and weather, just the lightest mallet tap breaks the joint cleanly....including the lighter fillets.

I didn't powerwash this one first as usual because I'm certain many of those intact plank lap fillets would break.

[ 10-04-2005, 01:07 AM: Message edited by: Bob Smalser ]

[Keith Wilson]

Screws let you get by with fewer clamps, and give a nice feeling of security. Rationally, they're probably not necessary, but the only drawbacks are a bit of cost and extra work, so why not? There are a lot of glued-lapstrake boats out there with never a fastener in the plank seams, and if your frend were right, there would be a lot of people swimming.

[George Roberts]

Chub ---

Certainly good engineering/building will allow the use of epoxy without screws.

But whether a designer used good engineering or not is open to debate.

[BRobinson]

It's not the epoxy that will fail, it is the wood it is attached to it that will. Epoxy is stronger than wood, it is not like welding metal.

Consider screws as an insurance policy.

[Mike Vogdes]

What do the plans call for?

[Dan McCosh]

The great myth to glued joints is that they fail at the wood, not at the glue, hence are stronger than the original wood. This is misleading. Glues, and epoxies in particular, end up forming a hard line bonded to a layer of fibers. This can be quite strong, but still prone to causing a fatigue failure of the fibers. Such a failure will leave a layer of wood on the glue, but it still failed. A joint can be easily designed for epoxy, but most are questionable. The fastener distributes the load in a different way--deep into the surrounding wood, but more concentrated. With both, you use the best properties of both. Using either by itself generally lets the weak points of glue and fastening emerge.

[Chub]

Originally posted by Mike Vogdes:
What do the plans call for?Plan are my own. smile.gif
http://calderaboatworks1.blogspot.com/ (http://caderaboatworks1.blogspot.com/)

[ 10-04-2005, 03:16 PM: Message edited by: Chub ]

[Chub]

Thank you all for the helpful info.
I will be adding some SS screws to the already glued frames and use them in the rest also.
I think that if they are countersunk deep enough that a good mixing of epoxy and wood flour should hide the visible ones.
Like most of us, I would like my boats to last forever.. ;)

[Bruce Hooke]

As I recall, the Gougeon Brothers (and others) have built plenty of boats with few if any fasteners in many of the wood-to-wood joints and I have not heard any stories about their boats falling to pieces...

[Matt Cohen]

Here's a WEST System guide to Gluing with Fasteners (http://www.jamestowndistributors.com/decoder_westsystem4.jsp)

[Gary E]

Glue or epoxy wich is a glue...alone?.. not if your smart...yes if your lazy...

I have been thinking on this epoxy question for a min or 2 and have decided that epoxy was invented by lazy people. Those lazy people grew up in the 40's and 50's cementing model airplanes together with the help of the straight pins that they stole from their mothers sewing basket. Those kids grew up to become chemical engineers and now have kids and decided that the time building those models would of been a lot shorter if they had a fast setting glue, and that's why we have epoxy. Not that epoxy is a better fastener, but only because it's faster. After all it was a model, not something that people actually got in and flew or paddeled around in on a lake. Then the next generation of inginneers took that formula and tweaked it some to make it better for their use, and now the lazzy people seem to have won and idiots now believe that "epoxy" no matter what it's use is the best'est in the west'est.

Unless your building models, or dont know how to screw, or have hundredes of inginners to help you in what you are doing...as do all the Boeings etc, funk epoxy.

[TimothyB]

Originally posted by Bruce Hooke:
As I recall, the Gougeon Brothers (and others) have built plenty of boats with few if any fasteners in many of the wood-to-wood joints and I have not heard any stories about their boats falling to pieces...This is true, but generally they cover the whole structure with fiberglass and epoxy or molded laminates to provide stiffening and tensile strength to prevent the sort of 'hard spot' failures mentioned in an earlier post. When you have an entire fiberglass skin transversely glued on, and maybe two more on top of that, what you have created is a monocoque structure that follows different rules...tack and tape is different too, since you are essentially creating an epoxy 'weld' with heavily reinforced joints.

On the other hand if all you do is glue up some joints, you may fall prey to this problem.

On the other hand, lots of people have glued up masts/frames/etc with epoxy and haven't had problems. Then again, some have. Generally speaking, though, I would bet the folks who didn't have problems paid strict attention to grain when they made their mast (gluing on the edge and not the side) so that fiber tearout risks were minimized. This is also a good reason to properly orient your strips when gluing up strip plank, and it also underscores why the 'birds mouth' method of mast building is so successful (large glue area and fiber oriented 30 to 45 degrees to the stresses).

From an engineering perspective, it makes sense to 'back up' a glued, non reinforced wooden joint with a mechanical fastener. The glue ends up providing shear strength and the fasteners provide torsional strength, and protection against embrittlement and fiber tear out. For example, if I were laminating in a frame repair using epoxy I would use extra long fasteners to re-attach the planks to the frames, if not go all out and use bolts or rivets.

[Billy Bones]

As well as what the design calls for you might also consider where you are/intend to sail. Where I am there is no metal fastener that will not corrode faster than any wooden joint around it would deteriorate. Hence, leaving little bits of metal in the wood, here, is like leaving a time bomb behind you in your work.

My skiff has no metal in it at all, except for a few bits of hardware and the cb cap which needs got at now and then.

Also worth noting is the fact that some epoxies are harder and more brittle than others, which might come in handy in different applications.

An aside, I always chuckle at people (not unlike your friend, chub) who go into hystrionics over the absence of fasteners in plywood designs: "Whatsamatta, you don't trust glue? then why are you building with plywood?!? Delamination of plies is much the bigger worry than epoxy lap failure. :rolleyes: "

[JimD]

Originally posted by Chub:
</font><blockquote>quote:</font><hr />Originally posted by JimD:
What's the boat, Chub?19" ply on fame planing power dory.</font>[/QUOTE]Sounds like it's likely to take a thrashing. I'd screw. Matter of fact I'd screw anything heavier than a kayak or canoe.

[Popeye]

hence the demise of the lowly trunnel eh?

http://www.shipwrecks.nf.ca/news/images/eileenlake.jpg

In the early shipyards of outport Newfoundland long iron nails were often hard to come by and vessels were trunnelled with wooden nails, similar to a dowel. The trunnel extended completely through the plank, the seal and the timbers, and this technique provided extra strength. However, Eileen Lake was fastened with wooden spikes that reached several inches into the timber. Spikes were quicker to pound into the planks than trunnels and were easier to make. It was a shortcut that probably hastened the demise of a fine ship.

[ 10-04-2005, 02:28 PM: Message edited by: popeye ]

[dmede]

glue and screw, if for no other reason than because the screws will act as clamps to hold your glued up surfaces together, let alone provide extra mechanical fastening.

best thing to do, since these are your own plans, is to see what other professional builders have done in similar sized boats.

[Gary E]

Spikes were quicker to pound into the planks than trunnels and were easier to make. It was a shortcut that probably hastened the demise of a fine ship. Wasnt it STEAM that put those old wind blown things out of biz?

[Popeye]

yup http://www.heritage.nf.ca/environment/images/s_s_kite_600.jpg :D

[ 10-04-2005, 02:35 PM: Message edited by: popeye ]

[pcford]

oops. wrong thread.

[ 10-04-2005, 02:34 PM: Message edited by: pcford ]

[Bob Smalser]

Originally posted by Billy Bones:
Delamination of plies is much the bigger worry than epoxy lap failure. :rolleyes: "http://pic3.picturetrail.com/VOL12/1104763/8408305/113944403.jpg

Failed plywood-epoxy gluejoints in a 40-year-old boat....knees and braces.

I penned a black line where the glue cracked....and you can see that the remainder of the failure was due to delamming at the weather-eroded surface lam as either the boat flexed (darker delams) or I removed them with a light mallet tap (lighter delams that would have eventually failed). Some of these were also fastened.

If I were building with epoxy without benefit of fasteners, I'd limit the practice to small, light boats and make sure I used large fillets reinforced by fabric. Betting kiesters on one pissant lam of plywood less than several inches wide is too risky for me.

[ 10-04-2005, 04:13 PM: Message edited by: Bob Smalser ]

[Billy Bones]

Fair enough. And about a mile from where I sit there's a lovely old very dead strip-built boat whose gluelines have all split. (Resourcinol, in this case, no edge fastening.)

Still, an unscientific recollection of reported problems on WBF since '99 or so in glued plywood boats seems to indicate at least a couple of plywood delaminations for every epoxy failure. This mirrors my experience too, with the disproportionate weight of joint failures in furniture, anyway, resulting from (inappropriate, IMO) reliance on fasteners.

Also, while it's a fairly narrow point, it deserves mentioning in this context: generally speaking glue doesn't interact well with hard spots (be they bulkheads or fasteners or whathaveyou). Glue seems to survive best when flexure is even across the structure. Thus, as fasteners can create areas of uneven flexure, they can become a liability in another way.

My suggestion might be that if one is going to use fasteners, leave them accessible. Bob's positive analysis of the regluability of epoxy surfaces combined with accessible fasteners seems like a good repairable compromise. This business of edge nailing strip-built boats, encapsulated or not, seems like suicide to me, at least in my climate.

[Gary E]

So just what lasts in your area?...

Dugout canoes??

[Bob Smalser]

Originally posted by Billy Bones:
...And about a mile from where I sit there's a lovely old very dead strip-built boat whose gluelines have all split. (Resorcinol, in this case, no edge fastening.)

... in glued plywood boats seems to indicate at least a couple of plywood delaminations for every epoxy failure. Much as love resorcinol, it's fussy. No way could anyone get the high clamping pressure it requires without either a serious set of Jorgies or fasteners. I suspect the problem was headspace, not glue.

I've always suspected there's a relationship between plywood age and its propensity to delam....even with the best plywoods. Compared to traditional, airdried boat wood, those lams are severely tortured by slicing, steaming and rolling before they ever see glue. Old plywood can go from worn-but-serviceable to garbage in a couple short seasons, if you aren't paying attention:

http://pic3.picturetrail.com/VOL12/1104763/7910361/104473121.jpg

That's one reason I avoid using it wherever I can...including in plywood boat restorations:


http://pic3.picturetrail.com/VOL12/1104763/8408305/113600127.jpg

[ 10-04-2005, 08:47 PM: Message edited by: Bob Smalser ]

[L.W. Baxter]

I have been thinking on this epoxy question for a min or 2 and have decided that epoxy was invented by lazy people. No rush, Gar. Take another minute or two! :D

[hoss]

I don't know.
I made a Bolger dory about 25 years ago and the exact thing described above happened, the plywood delaminated and not the epoxy, (I did only use Exterior ply).
However I just sold a Mirror dingy made in the early 70's by a rank amateur using Mahogany Plywood and Polyester resin, it had taped seems no fillets, and no bottom cloth. It lived it's whole life outside covered by a poly tarp. All of it's seams where strong, and the guy I sold it to is sailing as we speak.

I really think the key is the tape, the epoxy will not fail in it's bond with the wood, and by distributing the load over a large area by using fiberglass tape inside and out the plywood should not delaminate.

Of course I could be wrong and my present rowing skiff could explode into it's component parts 2 miles off shore some cold morning.

[Frank Wentzel]

Built in 1970, the Gougeon brother's trimaran "Adagio" was only glued together - no fasteners. At 35 years old she is still racing. The longevity of Allegro demonstrates that if you understand epoxy bonding you can build enduring structures. I know we have quite a number of traditional boats as old and older, but after 35 years most have had, or need, a considerable amount of rebuilding or even full restoration.

So why do we see examples where boats have suffered massive epoxy-bonded-joint failure. I thing most of the failures are caused by the use of "common sense" when we decide how to bond components together. Just because a joint design works with fasteners it does not follow that it will endure when it is used with epoxy. Just as the wrong joint geometry will fail with fasteners - faulty joint geometry will also fail with bonded joints.

The difficulty we all have is that our previous experience is in fastener-based joinery. To be successful it is necessary to completely change our point of view. The Googe Bros. have used an engineering approach and, from what I have seen, they have been successful with a large variety of applications: from boats to windmill blades and scores of other applications. I’m not sure how to realign my thinking in a new direction: I’m a chemist not an engineer. But the way I see it is: if engineers can glue wings on jet airliners we should be able to figure out how to glue a boat together.

/// Frank ///

Good sense is a thing all need, few have, and none think they lack.
Benjamin Franklin

[RonW]

But the way I see it is: if engineers can glue wings on jet airliners we should be able to figure out how to glue a boat together.

That's it, I am done.
There will be no airline tickets in my future.
It will be 1 if by land and 2 if by sea, but there will be no # 3.

[Adamant]

I tend to fasten joints as if there were no epoxy in the joint. I do mostly repair and restoration work and this is very different than new consteuction. if new construction is engineered properly it may be possible to build without fasteners and examples of this are out there. I think youre doing the right thing adding SS fasteners but would try to encapsulate them in epoxy.

[Leon Steyns]

Originally posted by Bob Smalser:

I've always suspected there's a relationship between plywood age and its propensity to delam....even with the best plywoods. Compared to traditional, airdried boat wood, those lams are severely tortured by slicing, steaming and rolling before they ever see glue. Old plywood can go from worn-but-serviceable to garbage in a couple short seasons, if you aren't paying attention:
Bob,

I'm sorry I must disagree with you on this one. If a suitable marine plywood was used in your example, there's no way you'll see delamination in a lot of seasons. An example of 'suitable marine plywood' would be Bruynzeel Suprahecht. It comes with a 20-year warranty for a reason... ;)

Greets, Leon Steyns.

[Leon Steyns]

Originally posted by Gary E:
Glue or epoxy wich is a glue...alone?.. not if your smart...yes if your lazy...
Gary,

Sometimes it would be a good idea to read back what you wrote before hitting the "add reply" button. What you write is nonsense. Some construction methods require fasteners, some don't. You'd be surprised how much is glued together around you... :rolleyes:

Greets, Leon Steyns.

[Popeye]

Originally posted by RonW:
But the way I see it is: if engineers can glue wings on jet airliners we should be able to figure out how to glue a boat together.

That's it, I am done.
There will be no airline tickets in my future.
It will be 1 if by land and 2 if by sea, but there will be no # 3.The Boeing 747 aircraft has 62% of its surface area constructed with adhesive bonding, while the Lockheed C-5A aircraft has 3250 m2 of bonded structure.

[Billy Bones]

Morning everybody. This bears repeating:


Originally posted by Frank Wentzel:


The difficulty we all have is that our previous experience is in fastener-based joinery. To be successful it is necessary to completely change our point of view. Boat hulls and holes being an historically bad combination, what else but stodgy thinking could induce us to drill any holes, let alone lots of them, in our boats, after all, when we have the easy and readily available means to avoid doing so? Just food for thought.

[Gary E]

Originally posted by Leon Steyns:
</font><blockquote>quote:</font><hr />Originally posted by Gary E:
Glue or epoxy wich is a glue...alone?.. not if your smart...yes if your lazy...
Gary,

Sometimes it would be a good idea to read back what you wrote before hitting the "add reply" button. What you write is nonsense. Some construction methods require fasteners, some don't. You'd be surprised how much is glued together around you... :rolleyes:

Greets, Leon Steyns.</font>[/QUOTE]I stand by exactly what I said..

Epoxy was invented by chemists that were building model airplanes as kids and were to lazzy to use fasteners. So the impatient now inguinneers invented a faster setting glue so their kids didnt have to wait so long.

As for using it on Mass Transit aircraft,,yeah they do... and it's supervised by lots of ingineers.. how many you got looking over your shoulder watching what you do?

[Gary E]

Originally posted by Billy Bones:
Morning everybody. Boat hulls and holes being an historically bad combination, what else but stodgy thinking could induce us to drill any holes, let alone lots of them, in our boats, after all, when we have the easy and readily available means to avoid doing so? Just food for thought.So the Dugout canoe is your style? :D

[Tom Lathrop]

Originally posted by Gary E:
Glue or epoxy wich is a glue...alone?.. not if your smart...yes if your lazy...

I have been thinking on this epoxy question for a min or 2 and have decided that epoxy was invented by lazy people. Perhaps, but so is making a snap judgement on a complex issue. Many, if not most, great inovations come about by someone thinking about an easier way to do things.

Sloppy work or bad design or engineering always result in boats that fail or don't last.

Why is it that when epoxy work fails, some are so quick to say that the material is at fault rather than the workman. All boatbuilding materials must be properly used or the boat will fail. Plywood and plywood/composite construction have a proven record and are here to stay and some should just get over it.

Any glued part of the boat subjected to high stress (like humidity movement) or point loads should be backed up in some way. Rub rails are a good example that need some mechanical fastening and are generally better off if a flexible adhesive is used instead of epoxy. On main hull joints like chine and keel, the standard epoxy/filet/glass construction is almost foolproof if done right and no fasteners needed.

This is not an either/or proposition but rather doing the right thing for the specific task at hand. Traditional plank on frame construction calls for using the right material, good design and proper skills to build a boat that lasts. Epoxy or composite construction may be viewed as easier (lazier?) but it still needs similar attention to get good results.

Gary, you could make your point or opinion known without such a strong attack on the opinions of those with differing experience or opinions.

[ 10-05-2005, 09:27 AM: Message edited by: Tom Lathrop ]

[Bob Smalser]

Originally posted by Frank Wentzel:

The difficulty we all have is that our previous experience is in fastener-based joinery. To be successful it is necessary to completely change our point of view. You're talking to the wrong guy.

I'm a builder. Architects and designers make those decisions. I'll gladly build with epoxy only to an approved and tested design.

But no way am I gonna break any new ground in major structural decisions without the total package being engineered by somebody qualified.

Stodgy? You bet. But you can bet your life on my work.

[Billy Bones]

Oooops, Sorry Bob, "stodgy thinking" was not addressed to you or anyone else specifically, but to all of us as a group, myself most distinctly included.

Your point about the role of designer v builder is a good one.

I'm just throwing out ideas for thought--the fastener-free boat of my imagination is just hypothetical. One needs keelbolts and through-hulls, for example, to be practical.

And stodgy thinking isn't always bad...it tends to keep us from flying into the newest fad without circumspection. Them whizbang fellers that thunk up the newfangled Titanic prolly could have benefitted from some stodgy thinking.

[Bob Smalser]

Originally posted by Billy Bones:

Them whizbang fellers that thunk up the newfangled Titanic prolly could have benefitted from some stodgy thinking.Soldered sheetmetal air tanks for flotation in boats had been around for a century or more before the Titanic was designed.

I always wondered why "watertight bulkheads" was something not understood.

[TimothyB]

Why does everyone always make this so complicated? :)

Epoxy is GREAT for what it is intended to be used for. If you sheathe an epoxy glued boat with glass and epoxy you will have a very long lived boat.

The issue is simply in relying on glue to hold together point loaded or thinly laminated surfaces under stresses induced by expansion/contraction , movement and etc.

You also have to take into account how wood works when you glue something up.

"No Fastener" strip plank boats or plywood boats succeed because of very specific details in their construction.. fabric sheathing in the former, and built up/taped glass connections in the latter. There is a REASON that many hard chine boats use gussets for frame connections.

If you build a stripper with no cloth you WILL have troubles with cracking down the road.. fasteners or no. Unless, of course, you use excellent joinery and excellent quality wood, and orient the grain correctly. In which case, you'll still get cracking, but it will take a lot longer.

If you sheathe a stripper with cloth/epoxy it will last a lot longer, and stand up to a lot more abuse because you have created a load transfer member and moisture barrier that covers the whole skin of the boat.

If you have a join that cannot be sheathed, nor can the gluing surface be large, or if you need to glue plywood w/out sheathing or reinforcement points, or glue up wood-wood joins with the grain in the wrong direction, you would probably be best served by using both fasteners AND epoxy.

A drop of quick setting epoxy is actually really nice as a clamp though, especially when you need to put together a complex piece with fasteners but can't get it all clamped mechanically at the same time.

[Nick C]

So you guys all believe that stainless steel screws are a good backup idea? For some quirky reason stainless likes air or some part of it, oxygen, I think. This is what makes stainless rustproof. When you stick it in an airless environment all you have is metal with the properties of average iron.

Use galvanized screws or silicon-brass screws, expecially if you are going to paint or encapsulate the boat. Silicon-brass screws are better, but they are costly.

[Rick Tyler]

Originally posted by Nick C:
Silicon-brass screws are better, but they are costly.Silicon-bronze, not brass. Easy mistake...

- Rick

[TimothyB]

Totally correct about SS and corrosion.. a great piece on this in 'Planking & Fastening'.

Honestly, I don't see the trouble with using galvanized ring nails in strip construction when you encapsulate with epoxy. Even if you use bronze and lead on the rest of the boat. Electrolytic problems likely won't happen, and even if there was a small leakage, it would probably be limited to a few nails, the mass of which will be relatively small.

But then, you wouldn't be able to say "Structural strip plank construction with bronze ring shank nails and epoxy" in the advert. :)

[Chris Stewart]

Originally posted by Leon Steyns:
Bob,

I'm sorry I must disagree with you on this one. If a suitable marine plywood was used in your example, there's no way you'll see delamination in a lot of seasons. An example of 'suitable marine plywood' would be Bruynzeel Suprahecht. It comes with a 20-year warranty for a reason... ;)

Greets, Leon Steyns.The 20 year warranty is nice, but it was a 40 year old pram, and the runabout looks to be well over 20 years old as well. Potential for delamination is still an issue if you think your grandkids might want to use your boat.

[Chub]

Originally posted by Nick C:
So you guys all believe that stainless steel screws are a good backup idea? For some quirky reason stainless likes air or some part of it, oxygen, I think. This is what makes stainless rustproof. When you stick it in an airless environment all you have is metal with the properties of average iron.
HUH?
Where did yo get your info?

UPDATE:
I did a little research and it seems your are correct about stainless and oxygen.
:confused: WTF?

[ 10-05-2005, 05:52 PM: Message edited by: Chub ]

[Bob Smalser]

Originally posted by Chris Stewart:
</font><blockquote>quote:</font><hr />Originally posted by Leon Steyns:
Bob,

I'm sorry I must disagree with you on this one. If a suitable marine plywood was used in your example, there's no way you'll see delamination in a lot of seasons. An example of 'suitable marine plywood' would be Bruynzeel Suprahecht. It comes with a 20-year warranty for a reason... ;)

Greets, Leon Steyns.The 20 year warranty is nice, but it was a 40 year old pram, and the runabout looks to be well over 20 years old as well. Potential for delamination is still an issue if you think your grandkids might want to use your boat.</font>[/QUOTE]I don't care who makes the plywood....it is all made the same....and it will all delaminate with neglect.

If you believe Bruynzeel manufactures their plywood any different than Simpson just down the road from me, you are mistaken. Go to a plant sometime and watch the process.

The logs after ponding are selected for straightness, debarked, and steamed at 212 degrees in the log. Then they go to the rotary knife lathe and are peeled into lams, whereby the lams are sometimes steamed again and rolled, graded, sorted, and assembled in a press under more high heat with phenol resorcinol on between.

The difference between marine grade and the lowest grades is merely high-grade heartwood lams as opposed to sapwood full of patches.

Compared to solid heartwood of the same species, from my experience the wood in those plywood lams won't last near as long under the conditions of neglect shown in my example boats. Compared to gently airdried stock still full of healthy lignin holding that cellulose together, it has been thoroughly tortured, damaging that lignin and will deteriorate much faster when exposed to the elements.

Keep your plywood boats well protected with coatings and beddings.

The runabout project above is a 1955 Bryant made from top-quality H. Mahog plywood. No rot to speak of....just delamming.

And I can't get too excited about galvanic corrosion in thin, SS finish nails used to place strips in a fully-encapsulated strip boat, although I'd probably spring for bronze myself. I wouldn't use SS screws to fasten plywood planks in a lapstrake boat, however, especially below the waterline.

[ 10-05-2005, 04:00 PM: Message edited by: Bob Smalser ]

[Nicholas Carey]

Originally posted by Chub:
</font><blockquote>quote:</font><hr />Originally posted by Nick C:
So you guys all believe that stainless steel screws are a good backup idea? For some quirky reason stainless likes air or some part of it, oxygen, I think. This is what makes stainless rustproof. When you stick it in an airless environment all you have is metal with the properties of average iron.
HUH?
Where did yo get your info?</font>[/QUOTE]This is called crevice corrosion. The "stainless" quality of stainless steel depends on the presence of a constantly refreshed, microscopically thin layer of oxides that is impervious to both oxygen and water.

If stainless is deprived of free oxygen, this protective layer of corrosion cannot re-form when it is abraded or removed and "crevice corrosion" is the result.

Here's a much more detailed article on the phenomon: http://en.wikipedia.org/wiki/Stainless_steel

Here's a picture of 5 year old bronze and stainless steel bolts from the rudder shoe of an Alberg 30, installed on the same vessel at the same time:

Yikes!
http://www.alberg30.org/maintenance/Steering/CreviceCorrosion/RudderShoeBolts.jpg (http://www.alberg30.org/maintenance/Steering/CreviceCorrosion/)

FWIW, aluminum is subject to crevice corrosion as well, since it, like stainless steel, forms a protective oxide coating on its surface.

Here's another good article, this time on crevice/stress corrosion in stainless rigging components: http://www.dixielandmarine.com/yachts/DLrigprob.html

[ 10-05-2005, 04:08 PM: Message edited by: Nicholas Carey ]

[Leon Steyns]

Originally posted by Bob Smalser:
...and it will all delaminate with neglect.
Oh, that's a good one... :rolleyes:
With neglect, anything goes eventually! Including your gently airdried stock... tongue.gif

No offence intended, but this kind of argument is rather cheap, imho. :D ;)

Greets, Leon Steyns.

[ 10-05-2005, 05:54 PM: Message edited by: Leon Steyns ]

[RodB]

Per my designers recommendations I did the following in my stitch and glue, encapsulated 18 foot skiff. The deck beams were reinforced (where they attached to the underside of the sheer decks) with stainless 1 1/2" screws and epoxied... and also the rubrail (walnut) was attached and epoxied thru the topsides ply into the sheer decks ( honduras mahogany strips)...also with SS screws. Now since this boat is a total encapsulation stitch and glue boat...and all screws are buried in honduras mahogany, Doug Fir (deck beams), or Okoume Plywood...and all surfaces are either coated with two coats of epoxy or glassed with 6 oz cloth and epoxy... primed and painted... I would be interested to see these "buried screws" in 10- 15 years. I expect very little moisture to reach them but the comments on crevice corrosion are interesting.

Also it was recommended to use galvanized 4 penny nails for the 12 inch wide strip planked sheer decks...with galvanize nails installed on 4 inch centers.

Anyone with direct experience with buried stainless in quality materials over time please speak up.

I'm not at all concerned about the galvanized nails in the sheer decks but I do wonder about the buried stainless #10 screws.

RB

[ 10-05-2005, 08:42 PM: Message edited by: RodB ]

[Chris31415]

Surely if a plywood panel is screwed to a wood stringer using bronze screws then there will be a series of neatly spaced stress risers all the way along the stringers, especially if the screws are not epoxy bonded to the wood so that moisture can enter the joint through the screw holes.
If one uses the method recomended by the Gougeon Brothers (filleting the joints) then the stress will be spread much more evenly.
Screws are a sensible backup but in an epoxy encapsulated boat they must form part of the encapsulating system.
If the recomended method of fully encapsulating the wood is followed then the wood will have a stable moisture content and expansion and shrinkage (which is the main destructive force other than rot in wooden boats)will be minimal.
If the glued and encapsulated boat is then protected by proper painting and fibreglass sheathing then a very durable result could be expected.
To have a wooden boat, which has many engineering variables, to continuous service and exposure to the elements without expecting major maintenance is just plain unrealistic.

[RodB]

Good points. If my boat was meant to be sitting in the water most of the time I would definitely have considered bronze fasteners ( I used very few fasteners in the big picture anyway).

A trailered boat will most likely do great as described above. Also, my stitch and glue skiff is a "monocoque structure"...which makes a lot of difference over time.

RB

[Stiletto]

Rod B, when I replaced part of the deck of my trimaran I used SS screws in strategic places to hold the ply down and then nailed it with bronze ring shanked nails. As the whole lot was buried in epoxy I'm not too worried about the SS holding up in that situation., but have seen problems with SS in the wet areas of several boats. I've also seen boats with SS rudder shafts that seem to have stood the test of time, that's not to say that failure in these isnt imminent. :confused:

[RonW]

I see Mike has once again come to the rescue of stainless, and rightfully so.
All these crevice corrosion stainless bolts,never seem to identify the grade of stainless.
I would bet it is 18-8 and in saltwater.

If stainless has to be surrounded by air, so as not to corrode, then it is totally useless as a fastener and is fit for not much more then a cleat.

Most common and readily available stainless is
18-8 and is a poor choice for saltwater, or confined areas.

316 stainless is food grade and surgical stainless, as well as deemed saltwater safe.
But it also costs 4 times as much as 18-8.
I have seen 316 that is 15 and 20 years old under the most severe conditions, and is still like new.

Doesn't anyone remember the threads on bronze, how much is being imported from the far east, and is pure krapt.

http://www.manasquanfasteners.com/

[Leon Steyns]

I like this article on stainless steel (please scroll down to the Wikipedia-part):
http://www.answers.com/topic/stain less-steel?method=5&linktext=stainless%20steel (http://www.answers.com/topic/stainless-steel?method=5&linktext=stainless%20steel)

If you have any more questions on stainless steel, check this page at the SSINA-website (Specialty Steel Industry of North America):
http://www.ssina.com/publications/design.html
On the same site, a nice explanation of galvanic corrosion: http://www.ssina.com/corrosion/galvanic.html .
And a special PDF-document on fasteners: http://www.ssina.com/publications/fasten.html on this page.

More than you ever wanted to know about stainless steel. Don't ya just loooove the Net? :D

Greets, Leon Steyns.

[Jagermeister]

My understanding of crevice corosion is that stainless steel requires oxygen to form its protective oxide coating. There is more than enough free oxygen in water, salt or fresh, for that to occur. So stainless is good in much more than air. I've seen 30 year old stainless bolts that look good as new at the local treatment plant outflow, where they are pounded by ocean waves. However, when used as a bunged fastener totally encapsulated in wood, there is no water circulation (hence no oxygen replenishment) to reform the coating if the coating is disolved by salts (I think) in the wood. At that point, without the coating, the fastener is just steel, so you have the equivalent of standard steel fastener in your hull. From my limited understanding, this is NOT galvanic corrosion. If encapsulation were good enough to protect fasteners then you should be able to get away with using bare steel screws and nails, which are stronger than bronze or stainless, but everything I've read says at least use galvanized or something.

As to planks falling off bronze fastened boats, are there any details WHY the planks fell off? Was it determined to be fastener failure, wood rot, poor construction, or what? I'm mighty anxious to avoid THAT problem!

[RodB]

I would assume a standard steel fastener buried in an encapsulated hull, sheer deck, et al... within good materials... would do fine due to lack of oxygen and minimal moisture??? ...especially if the boat was to be trailered.

I just remembered my 18 foot skiff hull had a 1/4" layer of Merranti cold molded to the bottom using stainless staples. The staples were left in. The interior of the hull (3/8 Okoume) was glassed with 6 oz fiberglass cloth, the exterior ( 1/4" Merranti) glassed with Xynol cloth plus two coats of epoxy mixed with graphite (total hull thickness 5/8" plus sheathing). I guess those staples will be sealed up pretty well???

RB

[ 10-06-2005, 09:49 PM: Message edited by: RodB ]

[Wes Kisting]

FWIW, my two cents...

When the original post referred to "epoxy only," I assume we're talking exactly that, epoxy only--no tape. A tape and epoxy seam will dramatically outlast an epoxy-only seam--period. Even if the epoxy in both cases were to degrade at the same rate, the tape distributes the bond over a larger surface and itself provides some additional reinforcement, so it's a dramatically superior bond more on a par with the sort of joint obtained with epoxy and fastners.

In short, then, epoxy and fastners provide (with proper preventative maintenance concerning water intrusion in and around the fastners, of course) a far more permanent and durable joint than epoxy alone, and roughly an equivalent bond to that obtained via epoxy and tape. As someone rightly pointed out, an epoxy joint is notably stronger than the surrounding wood, but since the epoxy may only penetrate a few millimeters deep into the wood, it may eventually "tear out" the wood if not reinforced by fastners or tape.

As for plywood: No plywood, no matter how good, is impervious to delamination, though "high quality marine plywood" will certainly RESIST delamination much longer than, say, standard fare ACX exterior ply. But all glues, even the ultra-waterproof glues used to bond marine ply and able to stand up to a "boil test", will eventually degrade and begin to let go. Maybe it will be 20 years or so, but sooner or later, it's inevitable.

Stainless fastners are said to rust if oxygen is not present to help the stainless build up its corrosion resistant skin, so as a few posters noted, they're not an ideal fastner. Having said that, if they're encapsulated in epoxy, they should be fine. They don't actively rust in a non-oxygenated environment; they're just less resistant to corrosion.

The major problem uses of stainless steel are, for example, as a core material for vinyl-coated safety lines on a sailboat... The vinyl coating starves the stainless of oxygen, but (generally, whether at the cut ends, or anywhere the vinyl gets nicked) still allow exposure to moisture that becomes trapped inside the vinyl sheathe... this is a recipe for disaster, which is why stainless lifelines need regular replacement or they become surprisingly brittle and snap.

My father is a steel fabricator, so I have used stainless in a LOT of crazy applications, including boat stuff. I never have trouble with corrosion if the stainless is either kept encased(epoxy encapsulated) OR allowed to breathe. It's the in-between that's trouble.

[Wes Kisting]

Forgot to mention... someone suggested above that epoxy is not stronger than the surrounding wood, but this is untrue.

A good epoxy bond will always be stronger than the surrounding wood; however, in cases where the epoxy (not the wood) fails, it is almost always due to exposure to UV, which degrades epoxy quite thoroughly. (Hence the need to cover ANY epoxied surface--no matter how small--with high-quality varnish, PU, or paint to block UV). In the few exceptions I've ever heard of (where UV does not appear to be the culprit), epoxy failures tend to occur from chemical incompatibilities or builder error (a paint that was not compatible with the epoxy, an additive to the epoxy that weakened its bond, or a poorly prepped surface prior to the bond).

[Kim Whitmyre]

There is a topside deck stringer that runs along the center of both of my catamaran's hulls. I added an aluminum beam aft, which required me to chop out about 6" of this stringer on each hull, in order to set in a teak mount for the aluminum beam. This stringer is both epoxied and ss screwed to the deck. I came across one screw in each 6" section: it was disintegrating furiously without any environmental exposure. These stringers are white oak, and in my experience, white oak eats ss for lunch. The boat was built in 1996. Here it would appear that the white oak and lack of oxygen came together to do in these screws. What are others experiences with ss and white oak?

Kim