sheathing older plywood boat?

[skiffish]

rebuilding a plywood boat by sheathing with fiberglass?

The senario is an older plywood charter boat, being sheathed with fiberglass. If all moisture is not out of wood when glassed will this cause possible dry-rot later?

Thanks for any input.

Skiffish

[hartley]

skiffish ...re sheathing a plywood boat ,this opens up a real can of worms ..( I dont mean the boat is full of worms) .however you will probably get a dozen different answers from a dozen different posters on this issue .
but my two cents worth ( depending on the boats condition) would be sheathing with dynel cloth and epoxy resin ,i would hesitate to use glass,but then that's just me ......cheers now

[Poida]

Hartley me mate
I have tried fibreglass for sheathing a boat and it's a nightmare to use.

What is dynel cloth and who would normally stock it?

[Ike]

I wouldn't do it. period! I restored a boat that had been sheathed in fiberglass and it was a mess!. No matter how good a bond you think you have between the hull and the glass, water gets in and rots it, and you can't see it or detect it until it's too late.

I have talked to many people since then about this and have heard too many horror stories. It's a lot easier to replace a piece of wood than it is to grind off the old glass, replace the rotted wood, and then reglass it.

[ouwl]

because moisture wood distortion by fiberglass breach water gets in and rots it

[hartley]

Poida maaaate ,dynel cloth should be available at people like "whitworths" or any marine outlet that stocks paint and resins etc .it is much easier to work with than glass cloth ,it even goes around corners ,,,,,to expand a bit about sheathing in general,i remember reading some years ago in a american magazine about a bloke running a business on some lake in usa his business was sheathing the bottoms of plywood speedboats ( these were top quality boats ,as i recall )he used glass and POLYESTER resin ,which in my humble opinion is a definite no no ,he claimed NO failures in quite a few years .I seem to think the mag azine was "wooden boat" so he was probably no fly by night amateur ,by the way dynel has not the strength of glass ..."caveat emptor"
cheers now .

[Poida]

I may need to clear up some misconceptions that I may have about sheathing a boat with fibreglass.

One of the things that has turned me off of building a timber boat is that it needs to be sheathed in fibreglass. I did a canoe once and that was a sticky messy job. To do a boat is something I don't want to do.

Why is a timber boat sheathed in fibreglass anyway? Definately not for strength as timber is used in fibreglass boats for strength as it is stronger than fibreglass.

It doesn't seem to provide a smooth finish. Fibreglass only seems to give a smooth finish if it comes out of a female mould, due to the gelcoat. I would say that paint would provide a smoother finish.

I have been told that wood will rot if it is encapsulated in fibreglass, ie inside and out, by not allowing the wood to breathe.

So do i have to fibreglass a timber boat?
What are the pros and cons?

[tom28571]

Originally Posted by Poida

I may need to clear up some misconceptions that I may have about sheathing a boat with fibreglass.

One of the things that has turned me off of building a timber boat is that it needs to be sheathed in fibreglass. I did a canoe once and that was a sticky messy job. To do a boat is something I don't want to do.

Why is a timber boat sheathed in fibreglass anyway? Definately not for strength as timber is used in fibreglass boats for strength as it is stronger than fibreglass.

It doesn't seem to provide a smooth finish. Fibreglass only seems to give a smooth finish if it comes out of a female mould, due to the gelcoat. I would say that paint would provide a smoother finish.

I have been told that wood will rot if it is encapsulated in fibreglass, ie inside and out, by not allowing the wood to breathe.

So do i have to fibreglass a timber boat?
What are the pros and cons?

Since time began and people started to use wood for various things, it has been coated with all kinds of stuff. Sometimes to make it pretty and sometimes to make it more durable in the elements. Animal fat, pine pitch, varnish,paint and various epoxies and sheathing materials have all been used to protect the wood or make it look nicer. Epoxies and cloth sheaths are just the latest in the line of materials that are used to protect the wood from the elements and physical damage.

Some think that wood needs to breathe. Silly notion. The wood is dead, that's DEAD and dead wood has no need to breathe.

There is no such thing as "dry rot". Rot spores are everywhere waiting on a suitable place to breed (you are probably breathing some now). In order to live and breed, the rot spores need oxygen, moisture and food (wood). Deny either of these and there will be no rot. Epoxy is now the best thing around to seal wood from both rot requirements. Any moisture vapor that makes its way through the skin will still need a source of oxygen to reproduce. Xynole make the skin very tough and able to take bumps against stuff and not have the protective skin breached. Dynel has been shown in my tests to be inferior to Xynole in toughness. Paint or epoxy without the cloth is less durable.

If the toughness provided by a cloth sheath is not needed, why bother to put it on? If the boat is to be drug over rocks and shells or scraped against pilings and docks, Xynole in epoxy is well worth the extra trouble and expense. Putting on a cloth sheath is no more work than many other tasks in boatbuilding. It all take paitience and the commitment to do a decent job.

[ouwl]

Since time began and people started to use wood for various things, it has been coated with all kinds of stuff. Sometimes to make it pretty and sometimes to make it more durable in the elements. Animal fat, pine pitch, varnish,paint and various epoxies and sheathing materials have all been used to protect the wood or make it look nicer. Epoxies and cloth sheaths are just the latest in the line of materials that are used to protect the wood from the elements and physical damage.

Some think that wood needs to breathe. Silly notion. The wood is dead, that's DEAD and dead wood has no need to breathe.

There is no such thing as "dry rot". Rot spores are everywhere waiting on a suitable place to breed (you are probably breathing some now). In order to live and breed, the rot spores need oxygen, moisture and food (wood). Deny either of these and there will be no rot. Epoxy is now the best thing around to seal wood from both rot requirements. Any moisture vapor that makes its way through the skin will still need a source of oxygen to reproduce. Xynole make the skin very tough and able to take bumps against stuff and not have the protective skin breached. Dynel has been shown in my tests to be inferior to Xynole in toughness. Paint or epoxy without the cloth is less durable.

If the toughness provided by a cloth sheath is not needed, why bother to put it on? If the boat is to be drug over rocks and shells or scraped against pilings and docks, Xynole in epoxy is well worth the extra trouble and expense. Putting on a cloth sheath is no more work than many other tasks in boatbuilding. It all take paitience and the commitment to do a decent job.

seal wood is good way .it's insure unable Rot wood
the plan be defeated bring on rot wood

[Ike]

First off, you do not need to sheath wood in fiberglass, epoxy or anything else. Since the first prehistoric man floated across a stream on a log, boats have been built out of wood. At some point in history someone discovered that if you paint wood it seems to last longer. Probably the ultimate extension of this is the WEST System (Wood Exposy Saturation Technique) where wood is soaked and, hopefully, saturated with resin such that it is something more than wood.

Bare woods react differently to fresh or salt water. Obviously the wood soaks up water and swells. When the wood dries it shrinks. Even moisture in the air causes wood to swell and shrink. That's why you see ads touting the diferences between air dried and kiln dried wood. What else happens depends on the kind of wood, whether it is end grain, cross, grain, plywood or what. Oak has different charactistics than fir or cedar, or the multitude of other woods used in boatbuilding. Old growth white oak gets so hard from aging than it's even hard to cut it with a power saw. It's also almost impossible to get unless you can tear down an old barn or house that was built 100 years ago when it was very common. Not so softer woods.

Of course "dry rot" is not caused by the wood being dry. It's called that because for hundreds of years the rot was discovered when the wood dried out after the boat was careened on dry land and allowed to dry out.

Anyway. There is no absolute necessity to sheath wood in glass and it can actually cause as many problems as not painting or coating the wood. It all depends on the boat you are building, the construction method (strip plank, cold molded, lapstrake, clinker, Plywood, etc, the list goes on) and what you are going to use the boat for.