Is this terminal (within common sense)

An awl is a sharp pointed tool stuck into a wood handle, like an ice pick.
Replace rotten frames and the hull will come back into usable shape.

On my wood 37 foot Egg Harbor, I replaced many rotten frames, but all bottom planks were ok. I also sealed the surfaces of all bottom parts inside and outside with a layer of polyurethane rubber. I had all the planks off, but did it in quarters or the boat would have disintegrated. I thought about epoxy and fiberglass, but too many horror stories changed my mind. I also used house paints for the topsides, and acrylic latex caulk (Dap Dynaflex 230) for the plank seams above the waterline. Below the waterline, all seams were done with a mix of wood sanding-saw dust and PL premium polyurethane construction adhesive. The polyurethane coating I painted on was Sanitred Permaflex, but I now like Loctite Black PL roof and flashing, it has worked well underwater.

One regret, not being aggressive enough on frame replacement, eve though I was very aggressive, I left some original to 1970 frame sections in the lower bilge under the engines. At the time they were ok. But that was 10 yrs ago and now some of them have rotted near the keel. But the way I rebuilt my hull, in that the planks are glued together, it has not mattered. A future repair is possible by removing the bronze screws, cut the bad section of frame and slamming out and in the new frame by sliding them between plank and floor (joist)

I also cut my own frames from arsenic treated SYP dimensional lumber to forestall any future rotting, and they all have been fine. In my boat, most frames sit sandwiched between outer hull planking and floors ( huge oak joists) that span the beam of the hull.

 

Gotta pay close attention to keel joins.

The keel is really middle board at the bottom running for an aft.

 

I would think you could make minor rot repairs with glass and epoxy. Or even laminate in some wood veneers for smaller stuff.

Laminations might be stronger than original wood if done correctly.

 

The two frames are damaged and have signs that they were repaired in a not very professional manner. What often happens with wood boats is that once one part of the structure fails, other areas fail because they are now trying to do more than they ever were designed to do. For example, once the frame cracked, they stopped properly supporting the stringers, and the angled blocks that were put in just concentrated the loads in local areas of the stringer, and that caused the stringer to crack. One of the biggest failure areas of this type of construction is that the frames are very stiff and the beating of the bottom against the frames eventually beats out the joint where the frames and stringers meet and once that fails the failure spreads. This may be part of the reason for the gap you're seeing between the stringer and frame that you now have.

The first thing you need to do is determine if the frames are pushed up or is the bottom of the hull pulled away and is it misshaped. First look at the bottom from the underside and lay a straight edge on it along those stringers. If the hull has pulled from the frames you will need to pull it back up, if not you are going to have to rework the frames and then fill the gap. There appear to be several cracked stringers. These can be repaired by grinding a small amount of material in the crack, filling it with epoxy and then closing up the crack with clamps. Following this repair I would add a doubler along the sides of those broken stringers under the frame to increase the strength. If it broke once, it will probably break again. The doubler would be the same height as the stringer and would be probably an inch wide. Strip the finish off of the bottom and the stringer and bond in the doubler with a filled epoxy. The doubler would be at least a foot long and past the crack area it should taper down to zero width over four or five inches. This will make the stringers stronger locally and increase their width in the area under each frame.

It may be easier to remake the lower portion of the frames. First I'd remove the plywood patches and see what I had. If the frames are extensively cracked (as I suspect they are) then it will be easier and better to just remove the entire lower piece of the frame and use it as a pattern to make a new frame. The new frame should be at least as thick as the one being replaced. I would then bond one layer of 8 oz glass on each side of the bottom frame and then bond 1/4 inch of plywood on each side. The objective of the glass is to ensure the frame won't crack in the future, by laminating on some glass, the shear stress of the beam is significantly increased, and frames like this crack because they lack shear strength along the grain. Bond the frames in place using plywood end doublers as was done in the original build. Finally, cut some 1" square blocks into triangles. Bond these in place where the stringers meet the frames on both the forward and aft side of the frames. The purpose of these is to increase the area of the frame where it meets the stringer. If you add an additional 2 inches of width to the frame at the stringer joint, you won't beat the stringer to death and it will all last a good long time.

Repair one frame completely and then repair the other.

Then inspect each joint at all of the other frames. If any of those have loosened up you will need to cut out any rot or damage, fill with epoxy and then add the same half blocks to that frame. Always make sure you strip to bare wood any place you're going to epoxy and use wood filler with the epoxy. For each joint, first brush on epoxy with no filler to wet the wood, and then put on goop with filler and bond the pieces. Properly done you won't need many or any screws at all to put this all together.

 

Thank you for this. It is possibly the most helpful answer ever as it gives me a pathway to consider looking at repair.

I have since bought a "duplicate" boat as a freshly painted project boat and am currently transferring all my running gear and deck fittings to it. It is the same model but appears to be a couple of years newer which is interesting once under the floorboards as this one holds a heck of a lot more bracing and rigidity timber with no rib separation.

The older boat is an emotional attachment so i'm now happy i can spend the summer about to start on the water whilst bringing my other "much more loved" boat back to water condition. The above commentary makes perfect sense to me and is incredibly helpful, so thank-you.

Given i (now) have time and budget, do you think it would pay to completely replace the cracked frames and "build up" support around them as suggested? rather than doing a part replacement? And am i right in assuming the ribs should in fact only epoxied to the frames?

Thanks again
Brian

 

The first thing I would do is to remove the plywood and doublers and angle blocks that are on the second frame and examine the frame carefully. In looking at the photos there's a lot of old clear stuff that looks pretty much like old polyester resin that was used to waterproof the bilge area a long time ago. This stuff is all over the frames and the inside the bottom. If it is indeed polyester it is easy to get off. Use a heat gun and a putty knife and hit it with some heat and you will be able to scrape the stuff off. You can then hit it with a sander and get to fresh wood that you can bond to. It's peeling up anyway so it needs to go.

After you get the frame cleaned up you determine if it's worth keeping. If it had one or two cracks in it then it could be repaired, but the last frame I did that looked like that was pretty much toast and I had to replace the bottom half of the frame. If the uprights of the frame are good there is no reason to yank them out, you will do more damage and more work to get them out. The lower half of the frame is already separated from the stringers and if you want to get it out that will be relatively easy if it is cracked, it can be cut up and taken out in pieces. You will have to remove the plywood corner braces and remake them, but that's a relatively easy job since you can measure them and make patterns for replacements even before you take the old ones out. Same thing with the lower half of the frame. I would make templates out of poster board by taping it to the frames and then trimming it to shape. That will allow you to make new pieces without a lot of measuring.

If the frames are bad remove them and then inspect and repair the stringers as I noted in the earlier post after you've stripped to bare wood. You can't see it now, but there could be damage to the stringers where they ran under the frames. That is also very common. If there is any damage under the frames you will need to repair that first. That is most certainly the case for the keel stringer where the angled block was used to try to reattach the stringer to the frame that is obviously cracked.

Then you can install the new frame or repair the old one.

When the boat was originally built it is likely that screws were used to attach the stringers to the frames. You may have to cut these to get the frames out. What usually happens is that the screws get loose and during the pounding they end up leaking water into the wood and you get rot locally in the stringer and if it's bad even up into the frame. The head of that screw is covered up by the plywood bottom, so you really can't get to it unless you mess up the bottom. Once the screws get loose they aren't doing anything anyway. In this case the only thing you can do is bond in the frame to the stringers, but this is why you add the half blocks to the frame/stringer joint. If you add a 1 inch half block to each side of the frame you get 2 inches more contact area to that joint. If the frame was made from 1 inch thick material, and the stringer is 2 inches wide, then you go from a contact area of 2 square inches to 6 square inches. The strength of joint goes up by a factor of 3. Since these joints are damaged mostly by pounding (compressive overload) tripling the contact area on the stringer triples the joint strength. Epoxy with wood filler is stronger than wood, and the joint I've described is going to stronger than it ever was when new, even if you don't have a screw in it. The problem with these joints is that the wood gets pounded down and the screw gets loose anyway.