cedar rotting pattern

[Maranto]

Hello again. Its been awhile since I last posted but I've been busy with all sorts of work on Maranto. Currently, she is up on 'hard deck' undergoing plank replacement in the stern quarter and transom. The shipwright I'm working with (Ian MacKenzie) was as baffled as I was at the way in which the problem planks had rotted. I'm wondering if there is any input out there as to how this might have occurred.

The planks had no visible rot inside the hull and once removed showed no transferring to the frames. We only detected the rot because some had progressed to the point where the rot was caving in the outside face, but not the inside. The strange part was that in all cases, the rot travelled inside the plank like a tunnel. In several sections, there was literally a soft decaying tunnel bounded by good wood on all sides of the plank. Also, there was no corelation between rot tunnel areas and fastenings and in fact all fastenings were in great shape for a 35 year old hull. All the planks were above the waterline. On one particular piece, you could plane all four faces and see good wood, but if you looked at the end of the plank you could easily push a dowel in. The answer is academic at this point but of great interest. The only idea we have come up with is maybe the rot was there from the original load of wood but that was 40 years ago and surely it would have surfaced long before now. So, any ideas out there?

As soon as I figure out how to get photos onto this forum, I'll post some of the progress. Any help in that department would be appreciated.

OK, back to work here.

Cheers all,

Pete.

[RGM]

Are you sure that the planks in question are original? Once they were removed did you see any evidence of a previous set of fastener holes (now plugged) in the frames? The reason that I ask is that the decay/deterioration you describe is what you frequently see happen to kiln dried material. Without knowing/seeing more my initial thoughts were that these are not original planks and perhaps are approx. 3 to 5 years old. Any chance of that? How long have you had the boat?

[Maranto]

I should have mentioned the history of Maranto. She was constructed by my father from 1961 to launch in 1973. He has since passed away so unfortunately cannot contribute to the possible solution. The cedar planking was all purchased green (by account of one involved - dripping wet and heavy as lead) and sticked and air dried in a basement for 3 years before use. All planking as she currently sits is original, never been opened up or modified. The rot has only surfaced and been noticed in the last three years. Prior to that, no concerns were ever raised about the hull planking. I have been involved in the yearly pull-out/inspection/bottom painting for 15 years and can attest to the integrity of the hull planks. The rot problem as it is now is completely baffling.

I only post this as a point of interest. Hopefully, we have arrested the problem and can expect a good many years without further deterioration but it would be nice to have some idea of why this happened.

Cheers,

Pete.

[Mac_Muz]

Would these planks happen to contain heart wood? Mac

[thechemist]

Also, what seems to be the spacing of growth rings on those pieces? I know with cedar it's hard to tell unless you saw cleanly and sand very smooth and look carefully, maybe wet....

Old growth redwood has maybe 30-60 growth rings to the inch and even the summergrowth fibers are small and tight, whereas the commercialized mutants have only 5-12 and are porous as hell and very rot-prone, whereas the old-growth was quite rot-resistant.

It may be that fast-growing cedar is more rot-prone, and maybe in the early years it did grow fast, and the center [which checks more anyway] is more susceptible.

Different woods are different. Alaskan Yellow Cedar has a rot-resistant heartwood and a rot-prone sapwood. Your cedar, I dunno.

Water wicks into wood easily through the end grain, and if the air/water balance is right and the temperature nice, rot goes quickly.

There is also the issue of what sugar level may have been in the wood, since you mention you bought it green. This was brought up in a thread well worth your reading, called, I think, winter-cut; for it or agin' it...lemme try to find it:

http://media5.hypernet.com/ubb/ultimatebb.php?ubb=get_topic;f=1;t=001515

I firmly believe that wood with a high sugar level is more prone to rot than wood with a low sugar level, all other things equal.

[WWheeler]

Sounds like sapwood...

[Hughman]

...sapwood fractured along the growth rings, aka "shakes", caused by a slam into the ground while felling, allowing rot spores to spread longitudinally.

[plimsol]

Was the wood treated with a preservative? The rot would progress until it reached the preservative that had penetrated from the surface. I have seen this effect several times over the years.

[NormMessinger]

Well, actually the fungus mycelia travel along the wood tracheids much more easily than across cell walls. Thus rot will travel along the board rather than across it, mostly. I can't explain how the fungus started in a few of the growth rings but once in there it is clear how they might hollow out an otherwise sound board. It is not good enough just to dig out and replace the rot because the fungus has already spread along the grain far beyond the end of visible rot.

--Norm

[Maranto]

Thanks for all the input. I'm piecing it together as far as the cause goes. It was constructed before I was old enough to take an interest but several of the points raised are good ones.

First, it is old growth as far as I know but it could very well have been damaged in the original instance. Dad was a hoarder of everything (not at all a bad trait) and whilst I was looking through the pile of wood left from the original cutting (yes, some of the trims from the plank cutting done in 1961-1963 are still around in a very dry basement - amazing ) I found several offcuts which look alittle crushed on the edges. Not a load type crush, more like a soft broken edge.

Second, he did use alot of cuprinol at the time and this may account for the rot not breaking out of the inside surface of the plank. His method of choice for the outside was to start with a very diluted enamel as an undercoat. This would have slowed the rot near the outside surface.

We have cut the infected planks well back from the problem areas. Since this is hard to see until it breaks out, we are hoping that we have got it all. Of course, that remains to be seen down the road.

Thanks again,

Regards to all,

Peter.