Fiberglass cloth draped over the bottom before initial trimming.
A layer of fiberglass on the bottom serves two purposes. First, it provides a tough protective layer for rough treatment on a trailer or accidental grounding. Second, it holds a nice, thick epoxy layer that makes the bottom more water proof. Nothing is really water PROOF. But epoxy is pretty close. It takes a long time for water to migrate through unbroken epoxy.
It only takes a few days to add this beneficial protective layer, and now is the time!
We used 6 oz. 0-90 bi-axial woven roving. Let’s break this down. Six ounce means the fiberglass cloth weighs 6 ounces per square yard. 0-90 bi-axial means the threads in the cloth intersect at a 90 degree angle. Woven roving means the fabric has a simple over-and under weave to it. This cloth drapes well and will conform to the shape of our bottom.
Rough-cut fiberglass cloth is wet-out with epoxy.
When you apply fiberglass to anything, it’s held there with some form of resin. In our case, we use epoxy. If you do a good job, the resin fills the weave and displaces the air, making the cloth essentially invisible. It’s really cool how this works.
Trim the edges with a sharp knife while the epoxy is still green.
While the epoxy is still “green” (partially, but not fully, cured), it’s time to trim the edges of the cloth with a sharp knife.
Fiberglass applied.
After the first coat of epoxy cures, we can 2-3 more coats to fill the weave and the cloth will disappear completely.
Famowood putty is used below the paint line. Wood bungs are used above the paint line.
We still have over 1000 screw holes in the bottom that need to be filled somehow. We’ll use two methods, depending on whether the screw hole will eventually be under paint or varnish.
Over 1000 screw holes to fill and sand smooth. Good thing our putty is quick-drying!
I use a wood filler called Famowood for any screw holes that will be under paint. It’s pretty waterproof, dries quickly, sands easily, and won’t shrink. It’s been around for years and is superior to most other wood filler putties you can get at the big box stores.
For those screw holes that will be under varnish, the traditional approach is to fill the hole with a bung cut of the same wood, glued in with varnish or some other fairly un-tenacious glue so that the bung and screw can be removed later if repairs are necessary. Boats do run into things occasionally, and it’s best to be kind to the poor person who may have to replace a plank later on.
Epoxy looks like varnish, but it’s a lot tougher and more waterproof.
After all holes are filled and sanded smooth, we’ll add a coat of clear epoxy as a sealer and to provide something for our fairing filler to adhere to. Then we trowel on the WEST System 410 fairing filler to the low spots. Let it cure and sand it smooth.
Fairing filler is used to fill low spots. It’s unsightly, but it’s going to be under paint.
At the risk of getting ahead of myself in terms of blog entries, we flipped the boat this past Saturday. This entry is a little out of sequence, but I’m too excited to wait and post it in order. I’ll catch up on the other steps for finishing the bottom later.
Once the bottom is finished, barrier coated, and painted, it’s time to flip the boat over and continue with it in the upright position. You can see in the picture above the apparatus we use to flip a boat. It’s a 1-1/2 inch pipe suspended above the boat in a couple of purpose-built bearings. I use 4 inch load straps over the pipe, which turns in the bearings, and allows us to roll the boat.
Click on the link below to see a short video of the flipping of the boat.
You can see where the planks alongside the keel have been ground down smooth with the keel.
Now that all the planks are glued on to the bottom, it’s time to go boating, right? Not quite. There’s still a lot of work to do. We have to “fair” the bottom. That is to say, we need to make it smooth, with no abrupt dips or rises. It needs to be “sea-kindly” so that the surface addresses the water with as little resistance and turbulence as possible. We’ve just glued a set of flat planks onto a curved bottom. It stands to reason there’s going to be some sculpting to get them to follow the curves of the bottom smoothly.
This is best accomplished by the judicious use of a 6″ Festool DA (dual action) rotary sander/grinder with a soft pad. This tool will move some material. So take it slow. Don’t be afraid to stop and feel often. You can see what is fair after you’ve trained you’re eye. But your fingers can feel “fair” with no training at all. Trust them and take it slow.
In addition to grinding down some of the sharp edges, we can also fill low spots with epoxy fairing filler. We’ll apply the filler a little later, but it helps to bear in mind that filling is an option, in addition to grinding down. I use WEST System 410 fairing filler for this job. It’s easy to apply to the low spots, and it sands easily once it has cured.
The outer chine is glued on just a little bit proud of the bottom so it can be trimmed flush later.
Then, it’s a pretty straightforward job to glue the outer chine on. We’ve already defined our line and fit the outer chine, so it’s time to put it in place permanently. Just make sure there’s plenty of glue so you get good squeeze-out. This is definitely a place where you don’t want voids that can trap water and promote rot.
Plenty of glue ensures we won’t have voids that can trap water in the joint.
Trimming the outer chine flush to the bottom with a low-angle block plane
Then we have to trim the top of the outer chine (actually the bottom, but since we’re upside down, I’ll call it the top) flush with the bottom planking. This is easily accomplished with a low angle block plane held to the face of the bottom planking.
Glueing on the bottom planks can be a messy business
Now comes the messy part. You’ve got all 16 planks fit. You’ve glued in all your intermediate frames to provide additional screwing locations between frames. You’ve glued in all the butt blocks to make the splice joints at the ends of two planks in the same strake. It’s time to glue the bottom planks down permanently.
If you don’t think coating the entire side of a 16 foot plank with glue, and then placing it in a puddle of glue of matching size and shape on the boat is messy, try it sometime. And if that’s not messy enough for you, get a year and a half old dog involved in the process!
3M 5200 adhesive (mahogany colored) was used for its greater elongation on the garboard-keel joint.
We used 3M 5200 adhesive to glue the garboard to the keel because of its greater elongation than epoxy. This joint tends to work a bit more than the others because of the size of the solid lumber members, so an adhesive with a bit more “give” is called for. But spreading 5200 is about like spreading bubble-gum. So the remainder of the bottom planks are fastened with epoxy (and a lot of screws).
Screws are in place and ready to be driven home on plank 5P.
The messiness aside, it’s a pretty straightforward, though time-consuming process. I used a 1/8″ notched trowel to spread an even coating of glue on both the plank and the inner ply layer of the boat. Then carefully placed the plank on the boat, using the locator screws from the fitting process to get the plank exactly in position.
Look for good “squeeze-out” along the seams when you tighten the screws indicating a lack of voids that could hold water.
Once the locator screws were tight, I just drilled a lot more screw holes and put the screws in. Each screw was dipped in 5200 before being driven to provide a lubricant, and to seal the screw hole.
Nice curves result from painstaking attention to fairing the frames.
I’m pleased with the shape of the hull. It’s eye-sweet and sea-kindly–the result of a lot of quality time spent with a batten getting the frames fair a long time back.
Garboard planks fit and temporarily screwed down with locator screws
Once the inner layer was fitted and glued, it was time to start fitting the outer layer. These are 1/2″ thick mahogany planks that average about 5-1/2″ wide, though they are considerably wider forward. This is the cool stuff. We rough-cut the blanks and steamed them to the curve of the hull awhile back. See New Bottom Planks and Using the Boat as a Form. Now it’s time to fine-tune these pieces and trim them to their final shape–a process called “fitting”. That process–getting a tight, leak proof seam between two planks that run the length of the boat–involves about 3 parts science, 1 part skill and 6 parts patience. I use the “Router Method” that I described here in Replacing Topsides Planks. It’s a little more cumbersome on the bottom because the clamping devices you have to use cannot be positioned so that you can simply glide right past them with your router. You have to start and stop, then connect the line later on the workbench. But it works tolerably well.
Trimming to the line on the bench
The first plank to be fit is the Garboard. This is the plank next to the keel. On our boat, the garboard is a single plank, without a splice, that runs the length of the boat. I simply clamped it in place next to the keel rabbet, and scribed a line along it that matched the keel rabbet, then cut it to fit. Once satisfied with the fit of the edge in the keel rabbet, I used a batten to mark a fair line on the other edge that the next plank will be fit to. Then I trimmed to the line, making the first cut with my trusy jigsaw, and trimmed to the line with a bench plane. I then marked out where all the screws would be placed on the plank, clamped it back in place on the boat and drilled holes for a few locator screws to hold the plank in its exact position so that the next plank could be fit against it’s edge. These locator screws also serve as indispensable guides when you’re glueing the plank on to get the plank back in exactly the same place you had it when you fit it.
With the garboard in position, the next blank, for plank 2PF (that’s Second plank from the keel, Port side, Forward) is clamped about 5/16″ away from the edge of the garboard, and using the edge of the garboard as a guide, the router cuts an exact fit for the edge, reproducing the bevel angle as well. Then using a batten, you mark a fair line on the other edge of the plank, cut it with your jigsaw, tune it with the hand plane, fasten it in place and move on to the next one. Wash, rinse, repeat.
Plank 5S clamped and ready for locator screw-holes to be drilled.
There are five strakes to the side, 2 planks (forward and aft) to each strake except the garboard and strake no. 5, each of which consist of a single plank. That’s 16 planks total. It’s a great day when you fit that final plank. It’s an even greater day when you have them all glued down, but that’s a story for another day.
The pile of savings from fitting all the bottom planks.
The bottom of the boat is made up of two plies or layers. The inner was originally 3/32″ thick by 6 to 8-inch strips, followed by a layer of canvas impregnated with boatyard bedding compound, followed by 1/2″ longitudinal mahogany planks. This ended up being a 5/8″ thick bottom that did not need to soak up water and swell to a tight, leak-proof fit, like traditional wooden boats do.
We’re replacing the inner ply with 1/8″ marine plywood, then bedding the 1/2″ mahogany planks in epoxy, thereby eliminating the need for the canvas layer which would dry out in about 3-5 years anyway and start leaking. Our new bottom should have a life of about 30 years or longer if properly cared-for.
Starting at the aft end with a full 8 ft. piece
So the first step in that process is to fit the plywood to the bottom frame. Starting at the aft end, we lay an 8 foot piece up and cut it to the outside of the framework. As we get further forward, we’ll start laying in 6″ wide strips at a 45° angle to the keel to fit the curve of the forward bottom.
The edges of the forward strips are held adjacent to each other with the help of the intermediate frames.
The edges of the forward strips are held adjacent to each other with the aid of the intermediate frames which we steam-bent to conform to the curve of the hull some time ago in Using the Boat as a Form.
The forward strips are screwed to the intermediate frames temporarily while the glue sets.
After fitting, take it all off, seal the inner face and edges with CPES (Clear Penetrating Epoxy Sealer), and glue it in place with epoxy. I use 5200 instead of epoxy along the keel for its better elongation properties. All of this is held in place with monel (look it up–it’s a very corrosion-resistant metal) staples.
First topsides strake clamped in place after fitting
I wanted to replace the first topsides plank on this boat for a couple of reasons. The boat was wrecked by a previous owner, resulting in partial replacement of the 1st topsides plank on the port side. I had to take this first plank off the boat to replace the chine anyway. So it was a good opportunity to go back with new wood. I didn’t want to replace one side and not the other. While I was at it, I had long enough planks to do it without a splice–one long beautiful plank instead of a fore and aft with a butt splice–how nice!
The method I use for fitting planks employs the use of a router with a guide riding along the plank edge I’m fitting to. It was first published in WoodenBoat magazine years ago. I didn’t invent it. But it’s a great time-saver and with this method it’s always easier to replace old planks than it is to try to save them. Plus, you’ve got new wood!
Hood end after fitting to the stem rabbet
The first step is to fit the forward or “hood” end of the plank to the stem rabbet. You do this by clamping it in place as close to the final position as possible, and scribe your line on it from the stem rabbet. Then cut to the line with your saw and shave to a tight fit with your block plane.
Once that is done, I clamp the blank back on the boat with a 5/16″ gap between the plank edge I’m fitting to, and the new plank. Then route this new edge, following the existing plank edge with your router. This cuts a perfect match with the correct bevel. It’s not quite as simple as these two sentences imply, but it’s much quicker than the old spile-cut-plane to the line-on and off the boat-technique. Although if you’re inclined to slip with the router, this method is not very forgiving. One wrong move and zip! You’ve ruined a plank.
That’s a nice fit! Seriously–you should zoom in on that line!
You can wait until the bottom is installed to drill the shaft hole and the rudder-post hole in the keel and line everything up. But why not do it now, before the keel is permanently installed? It is so much easier when you can bolt everything on to fit it without having to hop in and out of the boat 50 times. OK, 50 times might be a bit of an exaggeration even for klutz like me, but it does take a few tries to make sure everything fits properly. So I do it with the keel sitting off the boat so I can reach around all the pieces while I’m standing there.
You’ll recall we discussed Mounting the Strut a while back. With that job done, you install the strut temporarily and use it as a guide to drill the shaft hole. This is made easier by asking your shaft fabricator to make you a nice temporary bushing that will fit inside the cutlass bearing in the strut and guide your drill bit at the proper angle. I use a drill bit extension and a 1-1/4″ forstner bit since the shaft has a 1″ diameter.
Blocks clamped on ensure clean entry and exit holes
Since this hole is at such a shallow angle to the keel (19°) I clamp a block at the point where the bit enters and exits the keel to make sure a clean entry and exit hole. Then it’s just a matter of taking it slow and clearing the hole of sawdust often. Don’t push too hard as you might cause the bit to drift off-line. You might as well go slow and enjoy it since it took so long to set this up!
Inboard side of the keel with pocket for shaft log
Then flip it over and bore another, larger partial hole to create the pocket for the shaft log.
Mount everything up and check for proper clearances.
And then mount everything to make sure it lines up. You’ll want to mount the rudder, strut, shaft, and the shaft log. Of course there will be the inevitable cleanup with a wood rasp and round file, chisel, gouge–whatever your tool of choice is.
Once you’re satisfied, seal this hole well with 2-3 coats of epoxy. This would be a great place for water to migrate into your keel and allow the growth of rot spore.
No, those aren’t porcupine quills in the transom framing.
No, the transom framing isn’t growing porcupine quills. Look closer–they’re toothpicks. Bear with me. There’s a method to my madness.
If it seems like I’m procrastinating on planking the bottom, let me explain myself. There’s really a lot to do before you cover up those frames that you need to clamp to. And all those places that are so easy to get to when you can reach through the bottom will take a lot longer to deal with when that ready access is denied by a new bullet-proof bottom. So get those frames and the underside of the deck painted while it’s easy!
Working with the transom is one of those things that’s easier done when you can reach through the bottom of the boat, so that’s what I’m working on now. Of course the bottom plank of the transom was removed long ago so we could replace the lower transom bow. I didn’t want to remover the other two planks until it was time to replace them because they help to hold the shape of the boat. With the new bottom frames coated and now permanently glued in place, the boat is a whole lot stiffer and less likely to be pulled out of shape. So let’s get cracking!
So what’s that hole for? It’s not the fuel tank vent. I don’t really know….
First, why replace the transom planks at all? Well, there’s a hole in the top plank that I can’t explain and can’t think of a good use for. And the fact that the middle plank has been patched. Add to that the prospect of matching stain on one new plank to two old ones, and it becomes easier to just replace all three planks.
So, removal begins with taking all the bungs out to access the screw heads and hoping most of the screws don’t break when I try to take them out. In this case, I was pretty lucky (whew–not too much wailing and gnashing of teeth!).
I fill all the old screw holes with epoxy and toothpicks.
Did you know that when a wood screw is removed from its hole, it loses 85% of its holding power. The screw threads cut into the wood fibers when you put it in the first time. You simply can’t put it back in an old screw hole and expect it to hold nearly as well as it did the first time. So I fill all the screw holes in the framework pieces that won’t be replaced. I do this with epoxy and toothpicks, cutting them off flush after the epoxy cures. Now I don’t have to worry about lining up or missing old screw holes, and it holds together much better.
Old framework. I’ll replace the two plank battens, but the cheeks and the stakes will stay.
Next step is to coat the framework with Smith’s CPES–that’s Clear Penetrating Epoxy Sealant. It’s epoxy that’s been thinned to almost the consistency of water so it will soak in to the wood. Really good stuff! So good, in fact, that you have to wear a respirator with charcoal filters when you’re using it. It’s best to plan this for the end of your day and just leave the shop afterwards. This stuff is really strong-smelling.
Then time to cut out the new planks and steam bend them to the curve of the transom. But we’ll save that for another day.
