View Full Version : Spruce mast cracking
08-06-2006, 05:02 AM
I have just discovered the main mast on my (30 year old) 38' ketch has cracked up one side.
The mast is spruce and is approx 22cm x 15cm at the base.
The crack starts at the base and (at this stage) has progressed about 2m up the mast.
I drilled a 15mm hole about 50mm up from the step and water poured out (about 200ml).
My guess is the water is getting in somewhere around the hallyard blocks which is job for next weekend.
It appears the mast has an offset hollow centre where wires used to routed as i found bits of wire in my drill bit.
All the wiring now is external to the mast - so no problem there.
My question is, what should I do now to prevent the wood rotting?
I've drilled another hole about 1.5m up from the lower one in an effort to get some air circulating through the cavity.
08-06-2006, 04:00 PM
Generally, cracks running lengthwise on a solid spar are no problem.
If the mast did originally have a hollow center for wiring, it must also have had an opening at the base where the wiring came out. That would also provide an outlet for any water that did find a way in. I would try to find that and open it up again. I am not sure I would worry much about it otherwise.
Or... you might try this if you are worried: Pour some diesel into the upper opening of the hollow until it starts to come out at the bottom. This may sound strange to you, but an old boatwright I know used to do this as a preservative when making a new solid spar mast.
He would first sink the timber down to about 50-60 meters for a month or two where the pressure forced saltwater into the wood. Then he would rough form the mast right out of the deep. After that he drilled a good sized hole near the top and poured diesel in until he could see it coming out the bottom of the spar. The diesel pushed the water out and preserved the wood at the same time. He claimed that once the process was well started, you could see water running out of the bottom of the mast. He claimed that a mast made in that fashion seldom got the long cracks you see on masts made of dry-cured timber.
A bit smelly for a while, but diesel is pretty effective as a preservative if you use enough. It also easily gets into those hard to reach spots... just like water does ;)
08-06-2006, 05:03 PM
I would strongly suspect there's a lot more going on with your mast than you really want to know. Is the mast as old as the boat? If so, I'd want to take it down and examine it very carefully from top to bottom. That crack might well be a symptom of something more serious.
08-06-2006, 10:07 PM
Any clue as to the rationale behind the salt water impregnation/diesel fuel strategy? How much salt is left in the wood after the diesel fuel has chased all the water out if in fact thats what it does? If the diesel is the preservative, why not soak the timber in diesel fuel to begin with? What keeps the diesel fuel from eventually evaporating out of the wood over time? If in fact the salt is the preservative, why chase out the salt water with diesel fuel? Wouldn't it be best to let the water evaporate out leaving the salt behind? Is the idea to have the salt and diesel fuel acting togther as a preservative? If thats the case, why not let the timber air-dry after being hauled up from the briney deep (so the salt remains behind in the wood), then soak it with diesel fuel (which doesn't dissolve the salt)? Why not just use wood preservative to begin with?
08-06-2006, 10:50 PM
Hollow mast? Crack?
Is the crack along a glue line? Your mast may well be coming unglued. Might be time to disassemble/reglue it.
08-06-2006, 10:58 PM
Spruce rots really easily. I'd be worried.
08-07-2006, 02:04 AM
Beware of using DIESEL FUEL as a rot inibitor. Diesel fuel will support fungus growth and not preserve the wood!! This is a known scientific fact and not a point of argument! Fungicide additive is used in marine diesel fuel tanks to prevent fungus sludge from forming. I have repaird many boats that had rotten sturctural components that were literaly soaked with diesel fuel.
Your mast must not have a drain hole at the heel. If the crack is in a glue seam. You will, most likely, need to spline the seam by either running a skill saw or rounter on a guide for the length of the seam and then inserting a glued spline and clamping same. I would strongly advise you to have a local builder or surveyer check out your problem before attemping any repairs.
08-07-2006, 02:44 PM
I'm not going to post an argument for or against or try to give a chemical analysis... I just posted the opinion of a traditional boatwright. There are probably plenty of other opinions. The boating world is full of expertise. It seems.
Sinking boating timber in salt water is not new. It is commonly used when building traditional craft here - perhaps especially when there is a need to press wide & thin hull planking into shape with out it splitting. I know, for example, that Oselver boards (only 3 planks pr side on hull) are sunk to depth in sea water for long periods before use. I also noticed that the typical use of "saltwater ponds" in USA boatyards is mentioned in another recent mast topic.
My guess is that the pressure and salts does two things to the wood... makes it more resistant to cracks and splitting, makes it more flexible.
As far as diesel goes, yes, it is a natural substance. Just like creosote or tar. Things can live in it. It contains fats and waxes. It mixes with water. (In fact, that makes it rather good as a soap for washing cars - a couple of glugs of diesel in a bucket of water, swish it around and wash. You get not only a clean car but also rust protection. And that beautiful gas station aroma! Yumm.)
I am sure pretty much any boatbuilder has had to replace diesel soaked plank from rot infested bilges. But I'm not sure that is a good mast comparison. And what about planks that HAVEN'T been soaked in diesel? Had to change any of those??? Have the diesel planks held up longer or shorter? From what I remeber of my old Sabb diesel powered boat, the soaked planks were sounder than most other parts of the bilge.
For what it's worth, I've seen masts soaked in diesel. They were long lived and virtually crack-free. Probably the most negative thing was the dark color the diesel gave the wood. Of course, the masts were fully surface treated after the initial diesel treatment. The ones I saw were on a traditional boat and were probably about 1.5 to 2 ft in diameter. I saw no bugs or slime growing on the mast.
On the other hand, I made a Sitka mast a couple of years ago for my own boat. 12 meters long. I didn't use diesel - because I didn't want the dark color. That too seems fine after 2 years of use. I will report back on how it is holding up in 20 years. ;)
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