Problem with wooden mast....

PaulJ

PaulJ

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Last Winter I had a new wooden mast built for my Norfolk Smuggler and when we de-rigged it last Autumn we found signs of delamination of the two halves in the section above the mast band where the lower shrouds attach. The builder has agreed to "fix" it and wanted to run a saw down the joint and fill it with epoxy. I am not happy with that as I don't like thick glue lines! I would prefer to rout it out to a width of perhaps 6mm and a depth of 25mm - 30mm and fill with a well fitting piece of doulas fir...... Does anybody have any comments or better ideas please?

Paul
 
The repair suggested is not a particularly tidy or overly successful method . The best repair is to set up a router using a jig of sorts to enable the router to be stable on the mast with a good fence or guide to keep the cut straight and use a parallel cutter, maybe 6,8 or 10mm and rout a channel right over the failed glue line. Depth is up to the operator. Machine a really accurate spline of the correct width but much deeper than the proposed cut, round off the ends to match the router bit and glue in. Once cured, plane back and if the right choice of timber , possibly spruce or Douglas fir, the the repair should be almost invisible. The advantage of this is that new wood is exposed allowing reliable gluing. When the spline is forced in, any excess glue is further forced into the opening below the spline as it is unusual to rout full thickness of the mast.
It is important to make sure the router does not wander so make sure the direction of travel helps the router make the best use of the guide or fence and not fight it. Make sure a smaller cutter is used to remove most of the material first then use the correct size cutter to open the channel with just one run. Each subsequent run opens the channel very slightly making the spline loose.
John Lilley
 
John, many thanks for your advice. It all makes good sense and I will insist that it is done as you suggest.

Paul
 
Paul, just to relate; I have a Cornish Crabber Mk1, 1978 vintage. The mast appeared to be in excellent condition, but it was picked up on the purchase survey there were opening up joints, near the upper mast band and towards the base. I opened up the joints, filled with thickened epoxy, clamped together etc. Two years later I wanted to add an extra cable and so had the yard open the mast to find quite a lot of internal rot near the base of the mast. Up to then the mast had looked in pretty much perfect condition, and it could be my epoxy had been overdone and had blocked any water coming down and trying to escape at the base, but my conclusion was if you have a hollow mast it's not a bad idea to have opened up for internal examination.
 
So the mast was built last winter and is now delaminating at one year old? To be honest running a saw down it or even routing out a section is only going to be a bodge.
My first question would be what glue was used in the first place for it to start failing so quickly!
Whats to stop it failing elsewhere?
In the old days built up masts were often glued with Casein glue (today obsolete) & this would often fail with age plus lack of maintenance, even so it often lasted 25 years or more, i have rebuilt many such spars & it was a case of taking all fittings off sticking a sharp blade in one end & walking it along to separate the two halves, then clean up with sanding board & reglue with aerolite.
I am not a fan of epoxy on spars due to its poor UV resistance, As for PU foaming glues they are not regarded as long lived structural glues & shouldnt be used on spars.
 
Gentlemen, thanks for your responses. Yes, the mast was only built last year out of Douglas Fir. It is 5" square at the bottom so it is laminated from two peices 2 1/2" x 5". Before the mast was built I asked a question on this forum about type of glue and the balance of opinion was that epoxy would be best, the chap that built the mast also favoured epoxy so that is what was used. There is approx 3/4" hole down the middle for wiring. There is a galvanised band maybe 2mtrs from the top where the lower shrouds are attached and the delamination, approx 18" long, is both front and rear immediately above this mast band. The mast is painted white above the mast band so I don't think UV should be the problem and since the mast is new, I don't think rot will be the problem..... yet! The rest of the mast looks fine so the reason for the failure is a bit of a mystery....... possibly the Cap Shrouds were not as tight as they should have been causing it to flex? Of course it still should not have failed but we are where we are and now we have to decide the best way to deal with it..........

Paul
 
At one year old the glue should not have failed, even epoxy should have been a strong bond & the timber should fail before the glue bond fails. One possibility is that the timber had not fully dried prior to construction. This causes stresses in the timber as it dries out that can cause glue failure as well as , in the case of epoxy, a faulty bond as epoxy requires perfectly dry timber. Presumably the glue contact area at the top of the mast is substantial, although I did have occasion to inspect one Shrimper mast that had failed at the top because the builders had excavated the wiring channel far too close to the outer face with subsequently hardly any contact area for strength of bond. I think what had happened in that case was the they had shaped the mast and planed off too much on one side coming too close to the channel,

John Lilley
 
It is generally accepted that around 12% moisture content is optimal for epoxy bonding. This means that both sections of timber should be the same as stresses can occur if one section continues to dry (or absorb moisture) once glued. Temperature at the time of bonding also affects the epoxy bond if it is too low or the mix is not precise. Quite a lot a variables that can cause subsequent problems occasionally.
John Lilley
 
I've always liked resorcinol for spars over epoxy.

One possibility is that there was an error with the glue mix for that section. Get the mix ratios wrong with epoxy and the bond isn't very good at all.
 
I have mentioned this before here. The guys in the SOF that built a really big mast for a classic, used a commercial urea formaldahyde (sp) glue. All 150 odd ft of it. Aerolite is still a good option in the same area.
In the OP's mast. obviously there was a problem with the bond. The builders need to fix it properly, either by cutting it completely in half, planing the joint surfaces and re-gluing it, or building a new spar.
 
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