Repairing cracked frames

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KenMcCulloch

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I have several 1" square steamed oak frames (clinker built boat, mahogany planking on oak frames) that deserve to be repaired in due course.

Several options appear possible. Completely removing the existing frames and steaming or laminating new ones is certainly possible but presents many problems, for example fastenings at the gunwale are inaccessible without taking the deck off which is not sensible.

Sistering with new pieces steamed or laminated to fit alongside the damaged ones, extending above and below by as many planks as access allows would be a strong repair and relatively straightforward to do. Several frames have been strengthened in this way at some point in the past. I know some people argue that sistering just sets up problems for the future by introducing new hard spots in the hull, I'm not convinced this would be a major problem. Aesthetically it's not too appealing although most of the work would be in fairly rarely-examined locations.

Another possibility would be to cut out the cracked section and scarf in a new piece extending say 2 planks either side of the point where the cracking happened. The scarfs would be fastened with epoxy and the nails & roves through the planking. This would be a neat solution, as strong as the existing 60 year old frame and if done neatly almost invisible once slathered in bilge paint, but is clearly a good deal more laborious than sistering, making up the new pieces not too difficult but cutting the scarfs in the existing frames accurately would be quite time consuming I think.

What does the panel think?
 
Doubling or "sistering" as the yanks call it is nothing but a bodge, the frame strength is doubled except at the point of the original break and it will break again at the same point.
A prime example of this was an old Blackwater 2 1/2 tonner that had been completely doubled from end to end not just once but twice. Every rib both sides including the doublers was broken in a line along the turn of the bilge. All that was holding the top of the boat to the bottom was the stem and sternpost.
If you dont want to go mad cut a scarf and put a section in, its neat and requires little more work than doubling.
 
Remove the old ribs maybe two at a time spacing them out say leaving two ribs between the ones you are working on.
Cut your new rib into two pieces about three quarters of the full length required steam and fit one to the top and one to the bottom, then mark out and cut a scarf joint say the width of two planks fit them drilling though the original holes with two or three temporary nails to hold them in position, then drill for the nails in the joint, when satisfied the are OK apply a suitable glue to the scarf joint and rivet up.
A slow job and they will look like new and you will have no weak points where the sister ribs end.

I see you mention quote;- for example fastenings at the gunwale are inaccessible without taking the deck off which is not sensible.
The top rib fastenings on my boat go right though the gunwale and are roved on the inside so it may be possible to re fit the fixings all the way though using longer nails.
It would all be a case of can you get in there to rivet them up.
 
Agree with the others - doubling a broken rib is only a temp. fix and will concentrate stresses at the break - creating a fracture there later again.
It has to be replace if you want a proper job done.
 
I did a repair of this kind on a friend's 26ft carvel fishing boat. As in your case,the upper ends of the ribs were obscured by the deck. I used laminae which I cut in increasing lengths up the stack, rather like a leaf-spring in appearance. I then cut the old ribs in steps to match the new laminated section. I started with the ribs which needed least pulling up, at the end of the area of broken ribs, and worked towards the middle, where the knuckle in the planking was worst. It was very satisfying to see the knuckle getting less with each rib that was repaired. The laminae were epoxied to each other, but a sheet of cling-film was placed over the planking to ensure that the ribs were not glued to it. Refastening was by the usual copper rivets, using the existing holes in the planking. After painting it was not easy to pick the repaired section.
Peter.
 
Just scarph in a new section. Works really well. I have done dozens, and no faliures yet! also did about 10 on my clinker dinghy, using polyurethene glue. No fastenings. I did it as an experiment, to save changing the timbers. Still fine 15 years later. The timbers have to be in a condition to glue to though.
 
Thanks for the contributions, it looks as though scarfing in new bits is the way to go. The timbers that require attention seem quite sound apart from the actual fractures so that shouldn't be a problem.
 
Reading with interest as WS has at least one cracked and several strained timbers which I have been trying to ignore, not least because of the dismantling required first.

My question... how do you actually mark and cut the scarf given that it is in the turn of the bilge etc etc?
Presumably the new piece will then have to be pre bent, whether steamed or laminated, so that the position and angle of the cut scarfs can be marked on it? Perhaps a bit of card cut to the inside of the planking or something?

Oh btw, is it alright to use an oak scarf on the CRE timbers?
 
This is all of extreme interest to me as my falmouth Pilot has several cracked frames which I need to tackle. Peterduck's suggestions look the most practical. However I do have a couple of queries here.

You presumably cut away a section of the frame where it has failed. In the case of my boat this is on the sharpest curve of the bilge. As far as I can see this means that the first laminae is a but joint or is it shouldered to give a but/scarf?

I do see the sense in repairing the least critical frames first as there must have been large forces at work to break the frames that have gone. This may have been due to excessive drying out at the boat sat in a barn from 1963 - 1989!
 
[ QUOTE ]

My question... how do you actually mark and cut the scarf given that it is in the turn of the bilge etc etc?
Presumably the new piece will then have to be pre bent, whether steamed or laminated, so that the position and angle of the cut scarfs can be marked on it?

[/ QUOTE ]
Well my plan is to make up the new pieces either by steaming or laminating them clamping alongside where the repair will be to get the curve right. So long as the new piece is the same thickness as the original timber then just marking the ends of the scarf on both pieces (original and repair) should allow an accurate joint to be cut. I think I will cut the scarfs in the ends of the existing timber first and then I can adjust the repair piece (rather than vice versa) to get a good fit, simply because it's easier to work on a smaller portable piece than on the ends already attached to the rest of the boat.
 
I'm glad this thread is developing because I need to declare an interest as well. Four or five frames have cracked in various places rather than concentrated in one area - a couple are adjacent showing a bit of stress in a particular point. I googled for some while last night looking for actual details or pictures of a completed scarf but didn't find anything very useful except (maybe) a West Systems book on repairing wooden boats (which I've ordered).
So guys; What sort of slope, across a seam or across a plank, is it OK to mix timbers (I've elm frames, can I scarf in a piece of oak for example), just nails and roves or glue the scarf as well, etc. etc.?????
 
[ QUOTE ]

So guys; What sort of slope, across a seam or across a plank, is it OK to mix timbers (I've elm frames, can I scarf in a piece of oak for example), just nails and roves or glue the scarf as well, etc. etc.?????

[/ QUOTE ]
My plan is to make a scarf a little longer than the width across the lands of one plank, which will be about 4:1 or a little more. That will allow me to rivet a little way in from each end of the scarf when renewing the rivets that have come out to allow the operation to happen. I will also be gluing my joints with epoxy or PU glue, probably the former as that will make the tolerances in the scarf a bit less critical. I don't think just relying on mechanical fastenings is a good idea, glue will give much greater strength and will also keep moisture from penetrating into the joint which would not be a good thing. So far as the compatiblity of different timbers is concerned I couldn't really say but so long as the mechanical properties are similar I can't see it being a huge problem.
 
Broken ribs are almost invariable on the turn of the bilge, as this is where the ribs are most highly stressed. The reason that I went for a stepped scarph is that it is much easier to cut, and hence easier to shape well. The butts at the end of each laminate don't really contribute to the strength of the joint, but the area of overlap of each laminate past the last one makes up for that. We [the boat's owner and I] rivetted the laminae into position immediately, so that the planking was pulled tightly into the new ribs, and the glued faces were held tightly to each other. A smooth scarph [the longer the better, and I would advocate something more like 6:1] is more difficult to get nice and even. I don't think that mixing species would be a problem as long as the new timber is as durable as the old. Don't forget to cut the scarphed piece with the growth rings parallel to the planking.
Peter.
 
WEST do a special epoxy for woods like oak as it has been known to be difficult to glue. Might be worth getting some advice from whichever epoxy co. you choose.
A
 
Hi there, just interested, is she the one that was sold in Marine Auctions in Poole about 1989, I recall looking at her, she had a huge Lister air cooled engine and no joinery she was sold and fitted out in Newhaven I think, Name then was Goblin, Bought new from FBC as a bare hull,and never fitted out for some reason.
Regards


John Lilley
 
Ken, You don't say how many of your timbers are fractured and whether all are located in the same area of the hull. My understanding is little of the hull's strength in clinker construction is derived from the timbers themselves and even then the over-engineering is generally large. Several timbers are fractured in Pied Piper but whilst their neighbours remain intact and there is no visible hull distortion or damage to the planking, I am tempted to leave well alone. Apparently many timbers in the tight tuck at the stern of the Stellas were fractured before the boats made it into the boat builder's dock.
There is no way I could repair these (50 year-old) faults without removing the engine. It's not top of my priority list. The top half of the boat is attached to the bottom half by stem post, transom and a several thousand copper nails.
 
[ QUOTE ]
Ken, You don't say how many of your timbers are fractured and whether all are located in the same area of the hull. ........ I am tempted to leave well alone...

[/ QUOTE ]
In all there are about 6 or 7 in various areas of the boat including nice symmetrical partial cracks in 2 of the frames either side under the cockpit where as you say Folkboats and their derivatives have a tight turn. I'm not in any rush to do this work because as you say it's not a major structural issue. It's more about gradual improvement and making ready for the eventual repairs to some of the planking that I think will be called for in the fullness of time, whether by me or some future custodian.
 
I remember that one well and coveting it, but I already had my 1963 Eventide and taking on another boat was not allowed! Seem to remember it going for about £2k.
 
Peter,
I'm not convinced that a stepped scarf is easier to cut accurately. I think using a thin Japanese pull saw I can cut the existing frames to an approximate shape and then a bit of plane and chisel work to get the face as flat and smooth as possible. Cutting the scarf on the repair piece will be straightforward because I can climb out of the boat and plane away on my portable bench! I just need to source some suitable bits of oak now.
 
Dont 'sister' - it's an invitation to rot - a bodge.

Laminating is fine, cut the four or five laminates back far enough to be sufficient distance from a major turn in the bilge. Dry out and epoxy your laminates; then nail. Don't do too many timbers in a row like this.

Steaming a whole timber is good. The places where the old nails have been removed tend to generate more cosmetic work on the outside tidying up afterwards.

Bon chance. OF
 
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