using Tanilised wood for wooden boat building

[Paddingtonbear]

As some of you may be aware I am currently (well for the last 2.5 years!) taking legal action against a seriously negligent surveyor. In the course of a conversation with my solicitor, who knows nothing of boats (but a lot about negligence) he asked me why Tanilised wood was not used to build or repair wooden boats, I had often thought likewise but not wishing to incur the wrath of the clever dicks on here did not post the query. Any clues? My boat is larch(?) on oak.

 

[reeac]

I recently had some 100 mm. pressure treated fence posts rot through after about 12 years so whatever treatment they had [probably copper/chrome/arsenic] had a limited life under permanently damp conditions. Maybe with paint protection, as in a boat, they'd have lasted longer.

 

[chinita]

I think there are some examples of use. I know of one Wylo (steel) which has a centreboard constructed from tanalised wood.

Why not the whole boat? I imagine purely a combination of cost, availability and maintenance. Another answer may be that tanalised wood is softwood and not best suited to boatbuilding. Not even sure if a hardwood may take the tanalisation process!

Could equally ask the question why build in larch or mahogany and not teak I suppose.

 

[John the kiwi]

I work for a supplier of timber preservatives.
"Tanalised" is a brand name belonging to a competitor. It has become a generic term like "hoover" or "aspirin".
Even within the context of the owner of the Tanalised brand, the term does not refer to just one timber treatment process or chemical.

The whole field of timber preservation is poorly understood even (or perhaps especially) by those who are in trades where you would expect good expertise and companies such as ours (and give them their due, our competitors also) spend a lot of energy in trying to educate builders and specifiers so that they use preserved wood in appropriate ways.

We have in our product lists a variety of products each with their pros and cons. Nature on the other hand has a large variety of timber species each with its own characteristics. Nature also has a large arsenal of timber destroying moulds and fungi and insects. - The battle is on!

To help us , we have tables of two characteristics of timber species.
first value is natural durability:
second value is the permeability (which is the ability to penetrate the wood with preservative solutions.)

Durability

1 - Very durable ie. 25 years services life+ (untreated)
2 - Durable ie. 15-25 years
3 - Moderately durable - 10-15 years
4 - Non-durable - 5-10 years
5 - Perishable - less than 5 years service life
NI - No information

Permeability

P - Permeable. Full sapwood penetration and some, if not all heart
MR - Sapwood permeable, heartwood not easily treated
R - Sapwood treatable with some difficulty
VR - Sapwood normally untreatable, heartwood impossible
ER - No penetration of preservative possible

Botanical Name Common Name Durability Permeability
Larix decidua European Larch 3-4 R
Quercus robur Penunculate Oak 4 P

So on the face of it it would appear that both species are not very durable but more or less treatable so why would you not?
One valid technical reason is that some treatments can impair glue bond strength, but this only applies to some combinations of preservatives and glues so I suspect that the real reason is that boat builders generally have little knowledge and less interest in the pros and cons of preserved wood.
Salt water is also a preservative and has been saving boat builders butts for centuries. Its when wood gets wet and stays wet with fresh water that it becomes susceptible to rot fungi and insect attack.


Good Luck

 

[srp]

Tanalith treatments work best on open or coarse grained softwood timbers that will allow a good depth of penetration of the preservative during the vacuum pressure treatment. These timbers are often UK grown, with large growth rings and little in the way of natural preservative especially in the sapwood. You wouldn't really want to use them for boat building but they're fine for gates and sheds.
Most of the boat building timbers are close grained, few or no defects such as knots, and are oily, resinous or contain tannin (all of which help prevent fungal decay and deter wood boring insects). Salt water also acts as a preservative. These include teak, iroko, oak, larch and douglas fir, which are all classed as moderately durable or better. Most of the mahogany species are not as durable, but will last a fairly long time it they are well maintained. Many mahogany substitutes available now (the sort of timber used to make doors in B and Q) are rubbish and won't last 5 minutes on a boat - they might actually benefit from the Tanalith process but why use them when there are better alternatives.

Edit - I've always understood English oak to be moderately durable from all the sources I've read. As for permeability, the sapwood would never be used in any decent joinery work, marine or otherwise, and the heartwood isn't permeable enough to make treatment worthwhile.

 

[jwilson]

Most generally available "treated wood" eg tanalised is rubbish timber to start with, it allows cheap softwood to last adequately on garden sheds, fences etc. Nothing to stop you taking decent timber to a wood treatment plant and getting it pressure treated, but as said by John the Kiwi some may not penetrate well, also affect glue joints if relevant to the construction.

International did use to make a clear wood preservative that once well dried and soaked in did not seem to affect glue strength or colour the wood. About 40-odd years ago I used a lot of it before painting and varnishing dry timber on a couple of boat refurbishments, and having seen one of the boats I used it on many years of neglect later (long after I sold the boat) it seemed to have helped, particularly in preserving mahogany, which is always a bit subject to rot. They still sell something similar, though possibly slightly altered for elfin-safety.

Not likely to use it again, as current preference is sod-pretty-give-me-low-maintenance-plastics.

 

[viago]

i understand from local info that marine projects did indeed use tanalised soft wood for some of the interior, non visible, construction on the moody boats they built. seems like a reasonable thing to do and would likely last as long as untreated hard woods.