Sheathed Ply - How to tell if (when?!) it IS covering problems??

[thailand69]

I have been boatless for a while..........so at the moment I do not have a problem!!

Just that I was thinking of buying a boat dating from the late 60's / early 70's which was Professionaly built from plywood and sheathed in Fibreglass from new (I presume they used just FG back then?). Not a well known boat model or manufacturer and who I beleive is long since gone - so the name etc won't mean a great deal.

My understanding is that their is nothing fundamentally wrong with this method of construction (if done well!) - just that it requires more care than FG, albeit less than a planked wooden boat.............but after 35 / 40 years I am expecting, and am happy with, a boat that will require lots of TLC.

She is of course attractively cheap!..........and for reasons I can understand (Old age / unusual construction / no longer fashionable / not the max amount of living space / needs lots of "TLC", including mechanically) ...........but all in all from what I have briefly seen she might keep me (happily) busy for a couple of years.

So my questions are - how easy is it to tell if their is rot and / or delamination going on behind the sheathing in specific areas and any tips / tricks to think about when dealing with this method of construction?.

I am assuming that unlike Ferro it IS possible to get a good idea of what is going on "behind the scenes" - but I stand to be corrected!

I am taking some comfort at the moment that she was sheathed from new, rather than this being an attempt to cover up sins!.......I wouldn't automatically say no to a bit of cutting out and replacement.............I just don't want one that turns into Triggers Brush ("It's the same Brush I've had for 40 years - only had 8 new heads and 4 new handles" /forums/images/graemlins/cool.gif)...........due to it not being possible to identify problems without stripping all the sheathing /forums/images/graemlins/frown.gif

Of course I would throw a Surveyor at her before parting with cash, but I want to be able to save any unneccesary costs by "giving her a good seeing to myself" . /forums/images/graemlins/smile.gif /forums/images/graemlins/smile.gif /forums/images/graemlins/smile.gif

 

[oldharry]

Quite a difficult one this, without more clearly identifying what kind of sheathing was used. If it really was ordinary fibreglass with polyester resin, then walk away from it. Polyester resin does not stick well to wood, and when it breaks away (note: not 'if', but 'when') water gets in and crreates ideal conditions for rot to take hold.

An early and very succesful type of sheathing was 'Cascover' sheathing. Cascover is a resin glue that adheres well to timber, and has proved a very viable means of preserving a plywood hull. My own 25 year old ply boat has cascover sheathing, and is good as new. The problem is that if the sheath is damaged, water that gets in to the timber cannot get out creating ideal...etc etc. It needs great care to get a watertight joint if it needs repairing, and it is not easy to get new glue to stick to the original cascamite resin.

Newer sheathing systems, such as the West system, are epoxy based, and much more durable, but again rely on enacapsulating the wood to preserve it.

How to tell the difference? Thats the problem. Cascover sheathing used a woven glass cloth, similar in texture to a modern Fire blanket but thinner, whereas most GRP sheathing was done with several layers of glass mat. West systems too use an epoxy impreganted glass cloth, and tend to have a better finish the Cascover because the resin is much thinner, and can be smoothed much more easily.

Fortunately both the viable sheathing systems used quite a thin sheath, unlike GRP which can be quite thick. Checking out basically involves going over the hull with a hammer 'sounding' the timber. You will soon learn to detect the solid ring of a sound area, against the much duller 'thud' of a delaminated or rotten bit. Dont be deceived though by areas where the skin is supported internally which give a different sound again somewhere between the two! In severe delamination you can actually hear the layers clicking together when you tap them with your hammer!

Internal examination too will give you an idea of the condition of the timber, particularly in corners where water can lie. Sounding, and a little judicious spiking with a suitable pointed instrument will soon reveal areas of suspect timber.

Finally, check very carefull the top of the hull, particularly the hull to deck join if it is exposed. One of the commonest areas of rot is where the plywood comes up to the gunnel, and under any capping or rubbing bands. Rainwater can gather here very easily, and rapidly causes problems.

Bear in mind that an elderly plywood boat can be a lot of fun to restore, but can also break your heart and your bank account! The dividing line is very narrow. The difficulty is that unless you have a clear idea of the extent of the work before you start, then multiply that by at least 50% for the parts you can not yet see and will only surface later, you may find that the reasonably straightforward 'bit of TLC' is rapidly turning from a dream to a nightmare as you go deeper in. You soon get to the point where you have already invested so much time, money and effort that you simply cannot turn back, yet can see no end to the problems being revealed!

Good luck, and lets hope the dream remains a dream!

 

[Poignard]

I once had a boat that had been built like that [Cascover] and she was fine except for a very small bit of delamination on the inside where rainwater collected. I suppose what you could do before investing in a survey is to make athorough internal examination of the plywood skin, looking for paint coming off or bubbling and places where water has collected, also use your nose - does the inside smell damp and musty? On the outside you are looking for loose paint and blisters and places that sound hollow when tapped. Does the boat seem as if it has been well maintained?

You could also buy a good quality moisture meter such as the Tramex, as used by surveyors [amazingly, it just so happens I have one to sell!] and measure the moisture content of the wood in various places.

If/when you employ a surveyor you want one that knows about wooden boats, there used to be one on the East Coast called Winter, who I believe has written a book about buying a wooden boat.

 

[johnlilley]

Hi there
the best method to try searching for delamination/rot is to use a small hammer, about a pound, and lightly tap all over, you will soon identify the different soundings of good & bad ply.

If further checking is required, a small spike like a sharpened electical screwdriver but with the point just flattened probing the area, the down side is that this will cause limited damage to sheathing & paint, so be careful.
Check around all piercings where windows, rigging plate fastenings and deck edges where exposed end grain is.
The most likely places are above the waterline where fresh water may have entered the structure.
PM me if you would like a free survey template for this type of construction, you may find it useful prior to any survey.
John Lilley

 

[graham]

Seasons Greetings Bob. having owned/repaired a few old ply boats my experience has been that the hull tends to have less problems than the decks and supersrtructure.(You still need to thoroughly look at every bit of the hull as well.)

Someone allready mentioned that the end grain of the ply hull where it meets the deck at the gunwhale is a potential problem area also all edges of the deck itself can be worth close inspection.

Check the ends of the deckbeams from underneath where they are joined to the gunwhale.If the deck beams are rotten the whole deck usually needs to come off.

The join where the sides of the cabin meets the deck is also a potential dodgy area.

The cockpit area is worth a thorough inspection as rain can collect in the corners.

Prod around all deck fittings where water may have got in to the ply via the bolt /screw holes.

i would spend almost all day poking around a plywood boat before making an offer and then make it subject to a proffesionall survey. even if the surveyor gives it a good report your money wont be wasted as you can use the report to get insurance cover.

Plywood boats are hard to sell so make a really low offer and be firm about it.

At least you havent got Osmosis worries. /forums/images/graemlins/smile.gif

i hope it all goes well for you.

 

[tugboat]

Having restored a sheathed ply boat myself I'd agree with pretty much all the advice given above. A point worth repeating is that it's fresh water that rots wooden boats usually from the inside out. Especially look for places where condensation can lie, such as on top of chine logs (timber that follows the chine inside and that the two panels are fastened to) The tops should ideally have a slope on the top so as to shed any water. Look and prod around usually inaccessible areas and those where ventilation is poor, i.e. extreme bow and stern, inside lockers and under side decks. Prod the beam shelf. I know to my cost that if you find the smallest bit of rot, it will have tavelled into unseen places and you could end up having to strip sound Cascover just to access the problem. Have a good sniff as dry rot can also be a problem- once smelt you'll never forget it. If the deck is sheathed, pay attention to areas round the mast step/tabernacle where sealant may have been disturbed so water can get in. Definitely don't buy without a survey by someone with indemnity insurance, cos I bet you a pound to a pinch of poo that whatever faults are discovered in the survey there will be a surprise or two later. If you're lucky they are small surprises! Good luck.

 

[William_H]

There is lots of good advice here however..... I can't let this thread go without saying the obvious that a solid fibreglass boat will last forever or at least seem to. The low cost of the boat you are considering is testament to the fact that wood is for wood lovers not ones who want a boat to sail.
Yes I know these are wild statements and not true in every case but.......
There are very few sail boats around here less than 25 years old at that point all the maunufacturers saturated the market (went out of business) and the boats they built lasted forever. cos they are polyester resin. There will be p[lenty of superficial restoration needed in a F/g boat but down deep it will be ok. olewill

 

[alienzdive]

20-30 years ago covering ply in sheathing was a fantastic idea and long lasting way of preserving teh timber.

10-15 years ago this was found to be totally wrong. From the plyboats I have seen, and also in discussion with qualified boat builders, they sheahed boats usually rot much faster.

 

[thailand69]

Whoa!!

Quite a response! - thanks folks.

My first thoughts are that folk are pretty much on the same page as me...........buy a bad 'un and regret it at leisure!

Decks and Joins more likely to have than problems than the hull?, makes sense........But quite a bit to think over - ab event scheduled for later today slumped in front of the TV /forums/images/graemlins/grin.gif

Anyway, thanks again and MERRY XMAS to one and all /forums/images/graemlins/smile.gif /forums/images/graemlins/smile.gif /forums/images/graemlins/smile.gif

 

[thailand69]

Re: Sheathed Ply - CONCLUSION!!

As I find it kinda frustrtaing not knowing "the end of the story".......I thought I would post a finale......


The long story short..........in the end it was fortunately quite an easy decision to make myself - as "slightly" more work than I had hoped for / am prepared to get involved in. /forums/images/graemlins/frown.gif,............ but thanks a lot for the feedback folks - really appreciated, and I even learnt a bit! /forums/images/graemlins/cool.gif

The good news is that I have spotted something else that is of interest and for somewhat different reasons - but this time in 100% good old fashioned........plastic /forums/images/graemlins/laugh.gif