Rebuilding Wilson (hull 113) blog 2 First blog had so much material it was slow

[bob mitchell]

CONTENTS
PLYWOOD HULL REPAIR AND SOP (SEAT OF PANTS) TESTING
INSIDE PLYWOOD TEST 2

PLYWOOD HULL REPAIR AND SOP (SEAT OF PANTS) TESTING

HOW FLOORS ARE CONNECTED TO KEELSON

CARRIAGE HEAD KEELSON/FLOOR BOLT TORQUE TESTS



THIS IS A TEST.
Let's say your boat is in a great, cheap, slip, and it is not leaking below the waterline, but you are replacing the lower frames that hold the main mast step, and you find a dry rotted area in the plywood hull behind the frame. Small areas of plywood that dry rotted from the inside have got to be a common Newporter problem. If there was an alternative way to stabilize or repair the problem without pulling the boat out of the water and cutting through the fiberglass sheathing it would be a good thing. My impression from Clyde's comment is that boats are sunk trying stuff like this. In this situation, where the dry rot has progressed from the interior of the boat outwards, the best wood will be to the outside of the 3/4" sheathing. So the goal is to remove 1/2" of the bad material from the inside of the boat and replace it with sound material. Kind of tricky, unless you use a router!! First install a wider base to router (first photo). .

to insure that you can move across the rotted area at consistent depth (1/2"). With my small router it took two 1/4" passes. I would definitely use a template to rout the bad area because 1) the cutout from the template might be used as a patch, 2) a good fitting patch with a uniform gap ensures a) no wasted expensive epoxy, and b) no areas where the patch has to be forced into the routed out area (to tight) in a way that there isn't enough epoxy (see failure zone discussion below). Next reset the depth to 1/4" and, using a new template, do a 2" perimeter around the rotted area you just cut out. This will be in sound wood forming a ledge. Make sure that the bad wood area is well dried out. Maybe a heat gun would help, or fan. I am sure you have heard about epoxy that is thinned for maximum penetration to fix rotted areas, but Gougeon brothers (West System) says that the solvents used to thin the epoxy result in decreased strength. They say an alternative method is to heat gun the wood to be penetrated ahead of time and the epoxy will penetrate fine. However, it may set up faster, so be prepared. To make a long story short, cut a 1/4" plywood patch for the Inner area, and a 1/4" plywood patch for the outer area. Wet down the whole area with epoxy and lay in a thin layer of fiberglass mat in the inner area, wet it down good, let it overlap the lip surrounding the inner area. now press the plywood patch on top. Lay another thin layer of mat that covers the outer recess, wetted down well, and then press the outer plywood patch in place, and clamp or weight down somehow. The diagram shows the above discussion in cross section.

So is the above idea workable??? Well as a test on the patch, I went to my local bowling ally, told them what I was doing, and asked if they had any trashed bowling balls. Amazingly, the guy never blinked, went over an pulled out two trashed 10+ pound bowling ballls, and rolled them across the counter. My sophisticated test apparatus was ready to go. I used bowling balls because the way they contact the surface would be consistent and reproduceable by anyone. So I set up the 11 ply chinese cabinet plywood between a couple of supports (patch side down so the impact of the dropped bowling ball would be similar to a log in the water hitting the hull) and started dropping the ball from 5 feet above the plywood. If you wanted to you could calculate the foot-pounds(english system) or Joules (metric system) of Kinetic Energy that the bowling ball strike was delivering from KE=1/2m(v)(v), knowing the distance and being able to calculate the velocity from Vfinal=the squae root of 2 times tthe acceleration times the distance. Just be sure to use consistent units. (or using conservation of energy you could say the Kinetic Energy is equal to the work you did lifting the bowling ball 5 feet up, which is now stored as potenial energy: KE = PE = (mass)(g)(h))
So the next photos, strike side first, patch side second, are the failure of the patch after 7 strikes.

The next photos show the failure Zone. I have to admit, when I was mixing up the epoxy and filler for the edge joint, I put to much filler in, and pumped in more resin and hardener without mixing them first. To the right of the "weak zone" you can see part of the joint where the wood failed instead of the joint, which is how epoxy joint failures are supposed to ocurr. OR the patch was forced into a routed area with too tight a fit at a location and not adequately wetted, i.e. not enough epoxy. Definitely I would use a template for rout out to insure a gap that left room for epoxy - BASED ON MY EXPERIENCE FROM THIS TEST I WOULD SAY A GOOD FIT IS MORE THAN JUST COSMETICS, IT CAN BE STRUCTURAL WHEN DEALING WITH EPOXY. I do not know what the ideal gap should be, but maybe the outer edges should be a scarf done with a camphor bit instead of a vertical bit, although that is becoming a little more involved. A third possibilty is that "burnished" router cuts along the edge prevented proper epoxy penetration (West System Users Manuel, page 6, Product Guide 002-950). I was not using a sharp carbide tipped router bit, and burnished areas are definitely visable on the failure line. Burnishing the surface seals the pores to some degree, and prevents proper secondary bonding. I should have roughed up the burnished surface with 80 grit sandpaper. The inner patch edge is also visible in some of these shots. Will run second test today. One thing I will definitely do in my next test is try to eliminate the corners and straight edges by doing a more circular patch

Next is a photo of me trying HARD to tear out the patch, with No success. Anywhere there was matting the patch was rock solid. The Failure Zone CHANGED DIRECTIONS AT THE PATCH AND WENT AROUND THE PATCH!!! If you were unsure you could always add another layer of epoxied plywood, again from the inside of the hull, knowing there was no bad wood underneath.

The final photo is another piece of the same plywood with no patch, which failed under similar conditions with 10 five foot drops, just for some idea of control test.

How Chinese plywood relates to marine grade Doulas Fir I can not say at this point, but I am fairly sure that this method of interior repair can be perfected. It is of course relevant that there was no frame backing up the patch!! (I meant to do that test first) Once again, don't take my word - do your own testing to see if you are comfortable with the situation. This is only a first try which surely can and will be improved upon in the next test. It is all about gaining experience and insight into how material systems operate. One thing I am pretty sure about at this point is that if you want a strong piece of plywood two quarter inch sheets with thin matt epoxied in between would probably do it - more testing to come.

INSIDE PLYWOOD TEST 2

Working off the ideas from "PLYWOOD HULL REPAIR MADE FROM INSIDE" I continued the seat of the pants (SOP) testing to develop reliable methods of Newporter repair from the inside. My impression from Clyde's comment is that boats are sunk by people working below the waterline when the boat is in the water! This particular test involves removing and replacing areas of dry rot in the plywood hull sheathing that developed from the inside out because of leaky deck hardware.

The above photo shows the 1/4 " inner patch and the scrap it was cut out of - which now serves as a template for the router that makes cutting the patch shape a piece of cake. Note the V groove router bit with the guide bearing at the top. There is 1/2" of cutting bit to the bottom of that bearing, which is exactly what I need. So set the router depth at 3/4, tack down the template, ease the Vgrove bit in, and circle the template. The V groove gives a bevel to the outside (baby scarf) instead of vertical (butt joint). Now switch to regular bit and, being careful not to take out the edge bevel (you do take inside of Vgroove) clean out the "rot". Now repeat the template and patch scenario for the upper patch. Because the template is out of 1/4 inch material, I had to shim it 1/4" higher to make the bit cut the correct depth. The picture below shows the lower area cleaned out, and the Vgroove now cut in the upper area, with the material in the upper 1/4" depth area ready to be cleaned out.

The next photo is the inner patch laying in the rot area - and the other patch bottom up, showing bevel on patch edge. I thought I would just adjust my router table and crank it out, but that does not work for curved surfaces so I moved the guide back and freehanded it (on the router table). Good light helps to keep eye on Vgroove point at edge of patch as you are routing. It just was not that hard. You may notice the patches are two different plywoods. That's because the patch is asymmetrical, and the asymmetry devil snuck up on me AGAIN. I beveled the wrong side of the first patch and had to run to home depot and grab 1/4" B-C sanded on one side for $17.88. And while we are talking plywood the next piece in my scrap pile was B-C 3/4"exterior 7 ply, so I used that instead of the chinese stuff for the "hull sheathing". It seems much stronger. Also, I used West System epoxy in all tests. The 206 hardner took hours to cure. Don't forget to add fiberglass between patch layers (basically follow first test method).

To make a long story short, I screwed a 1 1/2 " by 2" mildly beetle infested picece of oak to serve as a rib across the patch, turned it over and dropped a ten pound bowling ball from 5 feet, which did not phase anything. Then I dropped a 55 pound rock from 3 feet, and the edge of the patch (located exactly where the epoxy had not filled the gap - I noticed the sawdust accumulating there when I was sanding patch smooth) showed a crack, then I dropped a 60 pound rock from 4 feet and the rib broke, but the patch is still intact with the cracked edge. A mass achieves a velocity of 16 ft/sec when dropped from 4 feet (on earth). This would be like running into a 60 pound floating log cruising at 11 miles/hour! (actually because of the hull angle the log in the water would be a glancing blow, not dead on like the rock drop) The photo of the cumulative total damage is below. Not bad, and no external hull breach yet!

So, Carrying on with the same abused test patch, I took the oak rib off, and added two 2x4's, separated by 16", with the patch unsupported in the middle. NOW I'LL HAVE MY WAY WITH THIS - whatever. Dropped the bowling ball from 3 feet with no change, THEN I dropped the 55 pound rock from 5 feet, and by gosh cracked the plywood, but still no external hull breach. The next photos show the total cummulative damage from all tests, with the 55 pound rock just in case you are trying to visualize. I did NOT drop the rock on this side, but on the other side, which represents the outside of the hull, shown in the next photo, with no visible breach!

Looking at the 2nd to last photo might even suggest that the strength of the composite patch stopped the plywood from fracturing across the middle. So all in all I am pretty confident I can take care of some patches of dry rot from the inside of my boat while it is in the water if I am real careful (knock on wood). And now, after a glass of Cabernet Savignon, the coup de grace, the 55 pounder hurled downward and corner of rock contact. ahhhhhhh eeeee! I still had to physically tear the patch into two pieces. The arrow points to the outer patch boundry, where when magnified one can see no epoxy, just lonely glass fibers. Final picture, taken before I tore it into pieces for analysis, the hull is breached, there will be no warm fire tonight.

HOW "FLOORS" ARE CONNECTED TO KEELSON

As I was attempting to remove my mast step, unscrewing the first very rusty square nut, the whole bolt started spinning in place. I didn't really have much idea of what I was doing, which is a good time to add a disclaimer. I in no way claim to be an authority on boatwork. What I do claim is to be exploring, let's say sensitizing myself, to the nature of Newporter 40 construction, and sharing my exploratory finds. Hey, maybe all this stuff is obvious to everyone but me! So with the bolt spinning in place I decided to put a pry bar under the nut and washer, and with a significant effort made 3" of extraction progress, but no more. Once again, to make a long story short, I chiseled a "visibility window" at the bottom of the floor where it rests on the keelson, and there I could see a carriage bolt head!
And then the obvious (or in my case the oblivious) hit me.........ALL the floors (and the mast step) are connected with carriage bolts that were put into the keelson FROM THE BOTTOM before the sheathing was applied.

But before I go any further let me define what I am calling what. The keelson is the 12" wide stack of 3/4" plywood that runs down the center of the bilge. The very large bolts on the keelson surface are the ballast keel bolts that go through the Douglas Fir deadwood that is below the keelson, and attach the ballast keel of lead (east coast) or iron (west coast) to the boat. The "floors" are the horizontal cross members of the frames that are attached to the top of the keelson. The lower frame members, the ones the sheathing is nailed and glued to, are fastened to the "floors". Completed frames before they are attached to the keelson are shown in the photo below.

The next photo shows the backbone of a Newporter - deadwood and keelson, before the ballest keel has been attached.

PUT THESE TWO PICTURES TOGETHER AND YOU REALIZE THAT THE CARRIAGE BOLTS THAT COME UP THROUGH THE KEELSON INTO THE FLOORS HOLD THE BOAT TOGETHER. (along with help from the plywood sheathing fastened to the keelson) FURTHERMORE, THE HOLDING POWER OF THESE CARRIAGE BOLTS DEPENDS IN A LARGE PART ON THE CONDITION OF THE KEELSON. I started going back over Dennis Gaffney's critical photos and found one that gave me a perfect view of this reality.

Notice what I think is (could be wrong) a carriage bolt head to the left of the thru hull fitting, and the floor timber directly above. Magnify and study that picture a little. That might also be one to the right of the fitting the way it was originally applied. And my conclusion is that before you go cranking away on the floor bolts realize that there is only a limited amount of torque that can be applied to them. Do everything you can to loosen the nut ahead of time before you crank on the nut.
My current plan is to do a few torque tests to see how much it takes to crush a washer into the wood for various species, and then fill the hole in the keelson that I pulled the mast step bolt out of with a plug and epoxy, let it set up, and see what kind of torque I can apply before it strips. I am in the process of testing torques now, and will let you know how that system works out. I left the other five mast step bolts lightly tapped on with plenty of WD 40, but will apply heat before I attempt to loosen them.
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CARRIAGE HEAD BOLT TORQUE TESTS IN NEW MARINE PLYWOOD KEELSON:
SURPRISINGLY LOW, VERY CONSISTANT, and hahaha - IRRELEVANT for FROZEN NUTS

Carriage bolts coming up through the keelson are what anchor the floors (horizontal members of frames) to the keelson (see "How floors are anchored to Keelson")
The nuts on these critical 1/2" fasteners may on ocassion need to be removed, like to replace a floor, mast step, or scarf in a lower frame member. However the nut of the carriage bolt, which generally is on top of the "floor", may be rusted or in some other way bound to the carriage bolt. The head of the carriage bolt is at the bottom of the keelson, essentially inaccessible unless you pull the boat out of the water and cut through and remove some sheathing. The critical point here is that if you take a wrench and crank on a stuck nut the most likely outcome is to spin the carriage bolt head, making it impossible to tighten or loosen by conventional means. And it could have been an acceptable fastening if it had not been overtorqued in attempt to loosen a stuck nut that had little to do with the holding power of the fastener. All means available should be used to loosen the nut before cranking on it "hard with a wrench".
So what is "cranking hard with a wrench"? When we talk about TORQUE we are talking about applying a force to a lever arm that causes a rotation - i.e. for a given force the longer the wrench handle (lever arm) the greater the torque. The torque put on a nut or bolt can be measured with a torque wrench in foot pounds. As the above paragraph suggests, if you exceed a certain level of torque (crank to hard on the wrench) you can rotate, in this case the carrige bolt, in place and make it useless. (please excuse me if you know all about torque, but I don't want to take a chance on losing non-mechanical types). So since I had callously already stripped one carriage bolt, and HAD NO CLUE as to what an appropriate torque for a carriage bolt might be, AND I had a lot of carriage bolts anchoring the floors to the keelson to deal with, I stacked some new 3/4" plywood together for a keelson and torque tested some 1/2" carriage bolts to get some idea of how they behaved.

I was suprised that I could, just by grabbing the socket with my hand and turning (essentially no torque) I could set the intial shoulder taper, and then adding the wrench could set the whole shoulder with under 10 ft-lbs of torque, at which point the torque would increase to 20 ft-lbs of torque as the head "firmed up". At 45-50 ft-lbs of torque the washer on the nut would spin and the wood had a clear impression (T2 and T3), and continuied torque at 60 ft-lbs started crushing the wood in ernest (T4). All tests used new washers and nuts, and were extremely consistent. So now we have some idea of what torque range to expect of a 1/2" carriage bolt in new marine plywood. They never did spin. AND NOW THE REAL PROBLEM HITS ME - I DID NOT HAVE THE CORRECT MODEL OF CARRIAGE BOLT BEHAVIOR!!! - and that's why I do these tests - it's all about the insight! A correctly functioning carriage bolt does not behave like I described our stuck nut bolt.
These correctly functioning test carriage bolts, unlike our frozen nut bolts, never did strip out of the wood, never did spin, because as the torque increased the nut turned, and the head crushed further into the wood increasing the holding power. BUT THE CARRIAGE BOLT WITH THE STUCK NUT CANNOT PULL TIGHTER, IT CAN ONLY ROTATE AND STRIP THE WOOD AROUND IT, - YOU CANNOT LOOSEN IT OR TIGHTEN IT, AS LONG AS THE NUT IS FROZEN, WITHOUT STRIPPING THE WOOD. So the first thing that has to happen is the nut must be unfrozen. THEN and only then would a torque test be relevant and helpful in determining the quality of wood (i.e. holding power) of the wood surrounding the bolt, or establishing the maximum torque that can be exerted without destroying the wood. What I am saying there is that in a correctly functioning carriage bolt you probably need to worry more about crushing the wood, as opposed to spinning in the wood with a stuck nut carriage bolt. Hopefully there will be enough bolt above the stuck nut that can be held to loosen the nut - maybe a couple of jamed nuts.. Of course, if you are going to replace the floor anyway, you can expose some of the bolt below the nut, and grab hold of it there. Or if you are going to keep the floor maybe a channel locks depth notch at the top, or bottom, - anything to get hold of the bolt shaft so you can unfreeze the nut without spinning the head. I have included a Dennis Gaffney photo one more time - let's call it Tale of Two Floor bolts.

The one on the right might be an adequate fastener as long as someone doesn't "spin a stuck nut". The one on the left has crushed a fair amount of wood, and as long as it is accessible why not drive it out, plug the hole with a, say 1 3/4" plug epoxied in, and install a new carriage bolt.