Many of you will now have noticed that Inanda has a frame (Ribs) problem in that she has a lot of cracked frames and a lot of sister-frames have been put in, some of which have cracked as well. I need to get on and sort that out before i do any serious channel-bashing and it isn’t the sort of work that i can start where she is now without committing to a lift-out and lengthy period ashore in either Chichester or Wareham….i really don’t want to have to drive all that way too often.
In ‘Sleepless-Nights’ i talked about how i spend a lot of time thinking about how i am going to do jobs and solve problems, well recently i have started a new practice of thinking/writing about each job in the spare hour that i often have in the department between getting there and starting my first job of the day. In the first session for example i just sat with my notebook and a coffee and worked out a shopping list and therefore costs of doing the boat’s first stage re-rig. Because i now write the initial post several weeks ahead it’s possible that i may have already got the shopping done, had the stick out and re-rigged it by the time this post comes out.
This post though addresses a longer term problem because i don’t know where to start with this one and i do know my way around rigging. Just to re-cap, Inanda is a classically carvel built yacht, larch on oak we think with the bottom few planks also oak. The frames (ribs) are most likley oak and many of them have cracked in the same line at about the point of maximum curvature in the hull. As far as i can see the existing ribs are all ‘one-piece’ and i suspect were originally steamed and bent. Over time a lot of them have cracked and have had sister-frames put in between ribs. Previous owner Pete….all round good-egg that he is says that sistering isn’t a good practice to start with and what should really have been done is for the cracked frames to be repaired and the sisters taken out. What this post is all about then is me learning and thinking out loud everything i have found out about the repair that i need to do and me working out how to do that repair….there seems to be several options. It doesn’t sound viable to try and replace an entire frame without taking the entire deck off and taking the longitudinal stringer out…that would be a total rebuild. My options seem to be either making new partial frames and scarphing the new piece into the old, and then re-fastenning or step-laminating new material into each frame in several layers a bit like a long leaf-spring.
With my ability to work at home now in the almost functional workshop i have also been trying to work out if it would be possible to do some of the work at home, one thought for example is to make very accurate templates of each frame ( i could probably get away with one template over an ‘average’ 3 frames) and make a laminating jig at home and make new frames at home. The fitting job aboard would then be marking the scarph angles onto the existing frame, cutting/shaping that and then glueing the new piece in before re-fastenning the whole frame back to the boat. I was sweating a bit on that idea when i thought that i might have to cut a curved scarph top and bottom but now i’m not convinced that would be necasary. I am going to add in some crude diagrams of what i think the new frame piece should look like and i think that a straight scarph would work depending on how long the scarph has to be.
Problems…..many websites that i have come across talk about the problems of glueing and laminating oak as some say that oak and epoxy aren’t compatible and i have also read somewhere that is only a problem with American white oak and not English oak. I will need a session with the Gougeon brothers book to work on that one. On the material side i think laminating is the way to go and i think i can get structural oak veneer at around 2.5mm thickness which should be reasonably easy to steam bend and lay-up in a jig at home. Glueing up remains the problem i’m unsure about. I have to admit that with my limited knowledge i don’t understand the reason to stay with oak….why not use a mixture of woods or just ash for example which is strong, flexible and shock-resistant and does glue well ?. I may just be demonstrating my profound wooden-boat ignorance here and there could easily be something really simple that i don’t know yet.
A couple of creative solutions have come to mind. I have thought about taking a load of lengths of ‘width-cut’ veneer down to the boat with me and setting up a steaming-rig on the pontoon and bending the thin material directly in place next to each cracked frame and wedging each layer into place with a ‘bridge’ screwed into 2 adjacent frames and either simple wedges underneath or running a bolt through the bridge ‘interference’ fit and tightening that down to keep the veneer layers in their new shape. Left in place for a while to dry and retain their bend i would then glue them up in situ (lots of parcel tape as masking) and hey-presto i should have new frame sections to then scarph and fit.
Stage 2 of the learning process.
My plan in Chichester was to try and find boatbuilder Nick Gates and firstly see if he would be able to take on some of the critical woodworking jobs. I felt that with my lack of skills and the importance of the job it might be better to invest hard cash in the job. I must say that Nick was great, he would take the job on but reckons to be 2 months behind with other work at his shed. A lot of that simply comes down to a very cold and wet spring when his lads just couldn’t work outside. Nick also reckons on a total job time of 4 hours per frame, i suspect that would come down some when there are lots to do but that would still be very expensive boatbuilder time.
Nick was very kind though to talk me through the job of making and fitting new laminated frames and put me right on the glue problem and with the faults in the step laminating approach. Nick’s view about glue is to not use epoxy (which i am familiar with) but rather to use a waterproof polyurethane glue to both laminate and attach the new frame pieces. Also he recommended not step-laminating although it might initially seem easier because the new frame can then start to break-out at any step point. So what he is saying is to make a pattern for a group of frames , 3 with one pattern, make the new frames with 5mm stock strips in a laminating jig and then cut those with a good long and straight scarph. Then transfer the scarph onto the old frame and cut accurately to the mark, then glue and re-fasten. With this method i could make all the patterns on the boat, then make all the new frame pieces at home and have them ready to go for when the boat comes ashore. I might then need some technical help to scarph the new pieces in and at that stage i might need the help of an experienced boatbuilder. Nick even gave me the name of a contact down here for just that. The problem with epoxy is apparently a chemical one in that the gallic acid in oak can weaken the epoxy joint.
At home i am working on making a dedicated bench for a laminating jig which would allow me to have maybe 3 different frames being laminated, glued and clamped all at the same time….essentially go into production mode. If the principle of 3 nearby frames coming off the same pattern works then i would use each separate jig 3 times and that would be 9 frames off the bench in 3 sessions.
Once again here is Nick’s own sailing and boatbuilding film series, and also Pete Thomas’s ‘Transcur’