OK, we’ve received a myriad of questions about how, once the hull is ready, we go from 4’ x 8’ sheets of Aquatek Marine Plywood to the inner skin of our True 5200 bottoms. John shares his “tricks of the trade” in this clip.
Once John has fabricated all of the pattern pieces for one face of the bottom, tension builds. If we have done our work well and the hull is true stem to stern and port to starboard, once flipped to the other face, the panels will fit perfectly.
Today they fit within 1/16 – 1/8 inch, which is excellent, given that we began with a corkscrewed, hogged hull. Phew!
Once we have fabricated all of the component pieces, which we dry screw in place so we can ensure an absolutely perfect fit, we release them and begin prepping them for installation.
Each sheet will receive 3 heavy coats of Clear Penetrating Epoxy Sealer (CPES). [Yes, as Danenberg prescribes, the second coat is applied immediately following the first coat. We then wait 24-48 hours to apply the third coat and give it 48 hours to cure.
Once they are sealed, the inner surfaces will receive a heavy coat of Sandusky Paint Company Chris-Craft Red Bilge Paint, and we will begin installing the skin, piece by piece, heavily bedded in 3M5200.
Before the plywood begins going down, however, we will ensure that all mating frame surfaces have received one light coat of the same bilge pain – again following Danenberg, By this time next week, plywood should have replaced construction paper.
Bedding the bottom planking in a 1/8” thick layer of 3M5200 without making a huge mess and without creating even more work cleaning it up, is perhaps the most critical component of the last “woodworking” step in fabricating a True 5200 Bottom.
Yes, I know we have covered this topic earlier, but it bears repeating. “Frosting” the plywood inner layer with a full 1/8” thick layer of 5200 is critical, as doing so ensures that there are no voids, and that, when fastened down, the squeeze out will fill the seams between the planks.
Fill the seams, yes, but do so without also filling the fastener countersink, as fairing the surface once the 5200 has cured requires that the countersinks be filled with 3M Premium Marine Filler.
Every, and I mean every spec of 5200 must be removed from the countersinks once the fasteners have been driven home.
Our method results in minimal infiltration of 5200 into those countersinks. You will need multiple cases of 5200 on hand. Use mahogany 5200 for forward planks that run upward through the waterline. White, which is much less expensive, if fine elsewhere. My rule of thumb for estimating cases needed is 40 – 60 percent of Length Overall (LOA). Since beam, and therefore the width between chines grows with LOA, I plan on closer to 60 percent for a 22-foot boat like this U22. (I am planning to use 12 cases for her.) In response to the many questions the community has sent my way, here is the “chronology” followed at Snake Mountain Boatworks: • Dry fit and fasten all of the planks with a dozen or so fasteners each; • Drill every pilot hole/countersink now; • Remove the planks one at a time, starting at the keel; • Using a permanent marker, draw an outline of each plank – one side and the butt – before it is removed; • Use these outlines to guide frosting one plank area at a time with a 1/8” thick layer of 5200; • Have at least four boxes of latex or, better, nitrile exam gloves and have a large garbage can nearby; • Apply the 5200 using a pneumatic caulking gun in a closely spaced squiggle pattern; • Spread the squiggles into a uniform layer using plastic spreaders; • Lay that one plank in place and begin inserting silicon bronze wood screws by hand, sinking just enough of them as you go to hold the plank in place; • Begin at the forward end of the planks terminating at the stem, using the length of that plank as the lever to slowly bend it into the correct shape; • Once there is a screw in every pilot hole, each of which has been screwed about 90 percent of the way home, drive all of the screws home; and, finally • Make a first pass using plastic scrapers along the plank’s open edge, and along its seam with the previously-installed plank, scooping all the squeeze out from the surface; • Using Interlux 333 Special Liquid – sometimes called special thinner, and lots of rags, clean and clean and clean until all squeeze out is gone. Time to install the next plank ….
Our 1946 Chris-Craft Mahogany (Brightside) U22 project enters the bottom planking fabrication stage today.
We will replace all existing planking, which is mostly cedar, with newly fabricated mahogany.
Yes, we abhor being unable to save the original planking, but most of it is just too oil-soaked, split and broken. Not replacing these planks means a bottom that is not well adhered to the 3M5200, and cannot hold paint from amidships aft.
John and I are dry fitting the original planks in place, and will scribe them on the plywood skin. Given the structural work this hull has received, especially removing the twist and hog from it, means that some of these planks, and especially those running to the stem, must be sanded in to fit.
Once we are confident we have a perfect set of pattern planks, we will scribe them to new mahogany.
The new planks’ faces and edges will be thoroughly sealed with CPES before we begin laying them down.
Following a final application of CPES to all exterior surfaces, we will begin applying the first of five coats of Interlux 2000E barrier coat, followed by three coats of period-correct blue antifouling paint.
Let the True 5200 Bottom assembly begin! It has been a long winter, but, finally, all of the structural work is behind us. Today begins the final steps in giving this 1946 Chris-Craft Brightside U22 a True 5200 Bottom.
We begin at the transom and work forward, which allows us to make huge strides right away. Once we’ve installed the first two sheets of Aquatek Marine plywood, we are at least 80 percent of the way to the bow.
Using our pneumatic caulking guns. Ribbons of mahogany 5200 are applied to the frames and bottom landing on the keel. Then, using 7/8” strips of plastic caulking spreaders, we carefully “frost” the surfaces with enough material so that there will be a bead of squeeze-out visible along the frame-plywood seams in the bilge. (ACBS judges have been known to penalize boats sporting no leak bottoms that have no visible squeeze-out. Why? The absence of squeeze-out signals the possibility of an incomplete seal between the frame faces and the plywood.)
We have learned not to apply a ribbon of 5200 to the chine frame face. Rather, there is always surplus material available as we smooth the 5200 along the frames. The chine frames offer a perfect depository for this surplus, which also greatly reduces waste. (The other reason involves the risk of T-shirt bottoms draping and dragging in 5200, which will NOT come out in the wash.) Once all of the surfaces have been frosted, we carefully lay the sheet in place, being sure to pound it flat. You will notice that the fasteners sunk into the frames are one 8” to 12” centers. Our goal here is securing the sheet until the 5200 cures. We will be sinking screws through the external planks on about 2” centers when they are installed.
Finally, and most unpleasant, is the task of cleaning, cleaning, cleaning the excess 5200 that squeezes out around the edges of the sheet. Our go-to solvent here is Interlux Brushing Liquid 333, which liquefies the 5200 and allows us to wipe it away. (Yes, we ruin lots of old shop towels in the process.)
Then, since the 333 tends to retard curing, we make a final pass along all of the beads of 5200 with a rag soaked in Acetone. The Acetone both removes the 333 residue and contributes to accelerated curing.
I have had several requests for a video showing our crew installing the bottom planks into a bed of 3M5200.
Here it is. Using the 1959 17’ Chris-Craft Sportsman as our “lab rat,” John and RJ share some of the tricks we have learned that help us ensure a complete seal between the planking and the plywood outer skin, and, what in some ways is critical, that the 3M5200 ends up where we want it without suffering hours of misery cleaning the 5200 off places it does not belong – in countersinks, oozing between the planks, and – horror of horrors, dripping down the topsides.
First and foremost, as Danenberg urges to all who will listen, scrimping on the 5200 translates into a shortcut 5200 bottom that will not last. Lay it on … thickly. We lay down at least 1/8” to 3/16” of the goo. Yes, that translates into a huge number of very expensive tubes of 5200, probably at least 60 for the layer between the inner plywood skin and the bottom planks in this case of this 17’ hull. And, yes, you will end up removing lots and lots of the stuff where it squeezes out through the seams. But, as is so trite, but also so true, price and cost diverge quickly here. A proper 5200 bottom means investing in mountains of 5200. Do it right, however, and you have a bottom that will last many decades. Take the shortcut route and, well, you might well experience the pain and suffering of removing a failed cheap alternative.
And, not Life Caulk, which is fantastic when used for its intended applications, cannot be substituted to save money. It’s cheaper now for sure, but oh so much more expensive in the long run.
We use blue painter’s tape to keep the 5200 away from adjoining planks and also the surface of the plank being installed. You will see how in the clip.
We learned the hard way what a disaster we and you will have on your hands if the 5200 pushes up through empty pre-drilled fastener holes. The silicon bronze fasteners, the drill bit, the disposable gloves, and the plank’s surface end up hopelessly befouled by 5200. Yes, it can be cleaned using Interlux Brushing Liquid 333, but why put this horror show on you when a technique John and RJ developed absolutely ensures no fountains of 5200 rising through fastener holes?
As with so many super creative and completely intuitive solutions, this one is trivially simple. Sink a fastener in each hole, but stop just short of driving it home. The fastener head will have seated in its countersink just enough to act as a seal. No 5200 can squeeze by.
Once all of the fasteners have been sunk in this manner, a crew member begins at each end of the plank, driving them home. As is illustrated in the video, yes, there is squeeze out, and lots of it, but the escaping 5200 lands on the blue tape, not the wood, or the screws or the gloves, well, not so much on the gloves.
Once every screw has been driven home, the squeeze-out is scooped off the tape using a combination of a plastic scraper and a simple wood paint stirring stick. Having removed all of it, we simply pull the tape, leaving an almost clean surface.
Using Interlux Brushing Liquid 333, we then scrub everything absolutely clean. However, the 333 actually retards 5200 curing, so the final step involves wiping everything down with Acetone.
One more milestone is disappearing in the rear view mirror. My ’53 22’ Shepherd’s port-side bottom is fully planked. Beginning this afternoon, I will be filling its countersinks with 3M Premium Marine filler.
Removing the hog in the keel, combined with natural shrinking of the planks translated into the original keel planks being slightly – about 5/8” – too narrow on both port and starboard, so the original planks could not be saved. Two new planks were fabricated for the port side once the first five courses had been installed. (The starboard side will require new keel planks as well.)
Here you watch RJ apply two full tubes of 3M 5200 on 40% of the final plank. He ended up using five, with another one used to seal the seam between these two planks and the keel. The beads will be spread into what looks all the world like frosting using a putty knife.
Notice just how much 5200 squeezes out along the edges and through the pre-drilled screw holes.
Not seeing ample squeeze out tells you that yours is a shortcut, not a true 5200 bottom. By my count we exhausted 48 tubes, with the 49th tube ending up about half empty.
Cleaning, especially the countersink holes, is the critical final step here. Remove enough 5200 from the seams so that the surface is concave and not proud of the planks. Otherwise you will play hell trying to sand the bottom prior to applying five coats of Interlux InterProtect 2000E Epoxy Primer. The starboard planks are next… Please stand by.
Our goal, fabricating a true 5200 bottom on Shirley’s and my 1953 22’ Shepherd Sportsman, obliterated another milestone today, or I should say, John obliterated it.
When I arrived here way too early this morning, John was already well into patterning, and once again quietly demonstrating his never-ending resourcefulness and creativity, but let’s allow John to speak for himself on the clip. Enjoy!
favorite finishing tools, a monster Makita belt sander and our 48” horizontal belt sander. By lunch the starboard side was behind him and I was hard at applying multiple coats of CPES to the edges and both sides of all four panels.
I notice that John seemed uncharacteristically tense as he dragged his patterns to the port side of the bottom. If the boat is straight and true, he should be able to flop them down and enjoy watching them fall into place, fitting perfectly. His smile told the story. They did and do fit perfectly on either side. Our painstaking, and oft-times incredibly tedious work, first on the keel and then the frames, doing all we could to regain a true hull, something that was lost to her years of hanging from her lifting eyes with water up to her chines all summer, every summer.
By the end of the day, all eight panels have been liberally CPES’d.
Tomorrow we will begin scribing lines needed to locate each rib, and begin also installing the between-rib battens – think of a Chris-Craft hull – Shepherd expert, Phil Jones of Lynchburg, VA, urged that we do. These battens, together with the thicker ribs will render the bottom as stiff as she can be, and fully prepared for anything the dual-quad-four Hemi 331 delivers.