Update to core rot and removal.

J

Jackie

New member
This is an update on my rotten core and seat box delamination post and a link to another Vimeo video showing my progress. https://vimeo.com/416142754

Today I removed the port side seat box and discovered why (I think) the seat boxes came loose from the floor. On my year CD 16, the foot rests that are part of the seat box are open in the front. Water can easily flow under the foot rest and back against the seat box part if it gets under the v-berth, and there is no outlet for that water. The actual seat box is completely sealed off with fiberglass tabbing on all four sides inside, and around the side with toward the center and the back on the outside. So in front, water can work under the tabbing because it is only toward the interior of the box, and water can run along the side of the box and around to the back via a channel between the tabbing facing inward and that facing outward. And since it has no outlet, it remains and then freezes and thaws and eventually lifts off all the tabbing holding the long, one-piece sidewall and seat box to the floor. It actually lifted off the entire length along the starboard side, and had gone around the port seat box and up to the side wall. I have added photos to my album that show the mud trail from where the water sat.

So, that was a design issue that caused that delamination, and is apparently unrelated to the rot, which I still think was from water intrusion at the v-berth supports, but I have found two really wet areas that make me wonder if water was also getting in from somewhere else. Most rot and wet has been on the port side and I am still excavating around the two wettest areas. One is a narrow area far forward and over toward the outer wall. It is well behind where the screw sat. I would have expected the water to mainly run toward the center and aft, but this path is taking me toward the bow and outside. That seems uphill in two directions. The other is aft midway between the side and centerline. I was starting to think the wood was getting dry when I hit an unexpected rot pocket. I will finish exploring those tomorrow.

Some of the wood looks a nice bright pink, but when I was levering it out water would squish out under pressure. Very few of the exposed areas you can see in my video or photos are actually dry. I will look for a moisture meter tomorrow. Question: I can get fiberglass supplies here in town and know where to order that, but where do I get a replacement for the balsa wood core? As always, any tips or advice is appreciated.
 
Jackie":jpkbe7ek said:
This is an update on my rotten core and seat box delamination post and a link to another Vimeo video showing my progress. https://vimeo.com/416142754

Today I removed the port side seat box and discovered why (I think) the seat boxes came loose from the floor. On my year CD 16, the foot rests that are part of the seat box are open in the front. Water can easily flow under the foot rest and back against the seat box part if it gets under the v-berth, and there is no outlet for that water. The actual seat box is completely sealed off with fiberglass tabbing on all four sides inside, and around the side with toward the center and the back on the outside. So in front, water can work under the tabbing because it is only toward the interior of the box, and water can run along the side of the box and around to the back via a channel between the tabbing facing inward and that facing outward. And since it has no outlet, it remains and then freezes and thaws and eventually lifts off all the tabbing holding the long, one-piece sidewall and seat box to the floor. It actually lifted off the entire length along the starboard side, and had gone around the port seat box and up to the side wall. I have added photos to my album that show the mud trail from where the water sat.

So, that was a design issue that caused that delamination, and is apparently unrelated to the rot, which I still think was from water intrusion at the v-berth supports, but I have found two really wet areas that make me wonder if water was also getting in from somewhere else. Most rot and wet has been on the port side and I am still excavating around the two wettest areas. One is a narrow area far forward and over toward the outer wall. It is well behind where the screw sat. I would have expected the water to mainly run toward the center and aft, but this path is taking me toward the bow and outside. That seems uphill in two directions. The other is aft midway between the side and centerline. I was starting to think the wood was getting dry when I hit an unexpected rot pocket. I will finish exploring those tomorrow.

Some of the wood looks a nice bright pink, but when I was levering it out water would squish out under pressure. Very few of the exposed areas you can see in my video or photos are actually dry. I will look for a moisture meter tomorrow. Question: I can get fiberglass supplies here in town and know where to order that, but where do I get a replacement for the balsa wood core? As always, any tips or advice is appreciated.
Click to expand...

I’m right there with you.
I pulled my lazaret hatch yesterday and for a bunch of rotten core. Good luck and hopefully a speedy turnaround.
 
Try defender.com for balsa, if you can't get it in Anchorage. Here's a sample: [ur=https://www.defender.com/product.jsp?id=21788l]Defender balsa[/url].

Remember, the balsa doesn't provide structural rigidity. It's only there to hold the fiberglass apart, making the glass like an I beam.

Boris
 
Jackie,
You are doing a great job both documenting and doing the work.

A couple of comments; The tabbing is put in later after the hull has cured. The surface of the cured fiberglass still has wax on it from the finish layer of laminating resin or gel coat. When the hull fiberglass is laid down wet layer upon wet, or with more modern resin infusion, there is a primary chemical bond, which is fairly strong. But...when the tabbing is put down--maybe weeks later, there maybe surface dust, lack of removing wax, lack of sanding to get surface slightly rough for a better "tooth". Thus there were probably microscopic areas of lack of bonding. The freeze thaw cycle then took over. It eventually popped tabbing which might have been OK for a year or two.

I learned something about your AK winters and water freeze thaw in the Tom Cat 24 which is also being redone. He found water migrating upwards from the freeze thaw cycle. This may be what is happening to your boat also. You might want to compare some notes on sources and issues with John S, who has the Tom Cat 24 in Sterling AK (I realize that is some distance away, but the logistics may be smiler for purchase. He is dealing with core issues also).

The cuts you see in the balsa are the Kerfs which are put in place to allow the core to bend. If these are hot fully filled with resin, then water will easily migrate thru them. The freeze thaw cycle then pushes the water out into the area of the cells of balsa. There is then minor delimitation, and more soaking--a vicious cycle.

As for purchase you will probably want to check with a number of places and get the best price/shipping. Corelite has many thicknesses and types of coating etc., but they are in Miami FL, there may be cheaper alternatives ref shipping and total costs. You probably will want to figure what your total order will be for resin, cloth (Mat, 1708, glass cloth tape etc) and order because of delay time of shipping.

Looking good.
 
Another update. I have removed an enormous amount of the core. I had to take out the v-berth bunk in order to get underneath. Not fun. Drilling to test areas proved unreliable because the kerfs in the balsa core allowed water to run fore to aft and side to side willy-nilly. As I expanded my cuts due to water and rot evidence, I cut out around drill holes that had looked good only to find they were surrounded by rotten wood where water followed the kerf lines. It would flow til it hit a weak spot then leave a big pocket of rotted wood.

I posted a few more pics in my album showing the progress and another shorter video on Vimeo. Here's the link for that: https://vimeo.com/419137107
At this point I have probably 40% of the bottom removed. In the bow, I had a lot of water working its way back high on the port side and I removed that pretty well. On the starboard side the wood looked great but was not at all adhered to the bottom of the boat. I could stick my putty knife up to the handle underneath it, and when I cut those areas out there would be a very thin layer of sludge underneath. I think I have it cut pretty well back to where everything is stuck down firmly in front.

At the rear, I still have one dark soft line to follow back. I’ve been narrowing in my cuts so it is starting to look like a layer cake and wonder if I should just keep it even so I can fill it back more easily? A final note: I bought a cheap pin moisture meter which maxes out at 35%. Every place I cut, even those that look nice and dry, hits the max on the meter. I put lamps on overnight and the moisture came down to a good level, but I imagine that is only surface deep. Thoughts on anything?
I haven't ordered anything yet because I want to get the right amount. I did look up the core material on Defender and a few others. Thanks for the link. It helped once I knew what to call it. 3/4 inch seemed to be the thickest everywhere I looked. I think I need about 1.5 inch thickness. I'll check the corelite.
 
Wow that sucks! Good luck, your making progress!

I just finished gluing my core around the foreword hatch and glassing it today.
I just about cried when I had to cut big sections of the Ceiling out of the V birth. I can’t imagine how your feeling with this project. The reward for me was when I finely finished getting all the rot out.
Good luck and keep us posted.
 
Jackie, have you put a ruler by the balsa core to see how thick it is? I had thought that 3/4" was the standard for the C Dory, but it is possible that a thicker core was used in your boat...

I think that there has been water in there a long time--and many freeze thaw cycles...So sorry to see that. But when you repair--it will be a new boat--literally! You are doing a fantastic job! Thanks for the updates.
 
Today I decided to expand the cut toward the stern to chase down the dark mushy line toward the outside. My moisture meter wasn't maxing out, but I knew rot was following the line. I cut back about 4 inches and as soon as I stuck my wonder bar in and gave it a tug, water just oozed up. Everything looked rather nice, but behind it was another water pocket and the balsa is not attached to the bottom in many places. I'm worried I can't trust anything and may wind up removing the whole floor! I'll keep exploring.
Bob, my core is definitely 1.5 inches. And it is a solid piece, not two 3/4 inch mats on top of each other. I looked up the CoreLite site and their balsa product comes in sizes up to 4 inches so I know I can find what I need. I'm still exploring sources as I'm not quite ready to order yet anyway.
Thanks everyone for the encouragement. Here's today's even shorter video if you want to see the water squishing out. Fortunately you can't see it squishing out my eyes!
https://vimeo.com/420155647
 
Well, I have cut all I'm going to and am finally ready to order supplies and get to rebuilding! While I'm waiting though, I know I have a lot of clean up and preparation. The bottom of the boat has pink fiberglass areas interspersed with smooth black (rottenish?) areas that can be a bit sunken, and areas where the mat tore away from the blocks I pried out and is all fuzzy. There are also a lot of places near the bow and the sidewall edge that have pools of thick epoxy and filler with air bubbles and pockets. My main question is how do I prepare all this for the new layer of mat I want to lay before putting in the replacement balsa? I've sanded most of it to remove any left over balsa, but how smooth does it all need to be? What about the fuzzy fiberglass bits? I've added photos to my album showing these. ( I've read how to get the photos right into the post, but I'm a Mac user and it just doesn't seem to transfer :roll: ). I also added another Vimeo video showing the whole area and close ups of my questionable areas. https://vimeo.com/423842526

While I'm waiting, I might as well prepare the v-berth bunk I removed and the area I cut it out of, so I'd appreciate tips on that as well.

I hope that I have found someone to purchase everything I need from. Or at least the balsa. I contacted C-Dory in Bellingham and their balsa distributer referred me to a man in Homer, AK. It is Eric Sloth of Homer Marine, in case anyone in the area (I'm about equally as close to Seattle, but hey, we're a big state!) ever needs anything. He can be found on Instagram and FB under Eric Sloth Boat Builder
 
Hi Jackie, Again, what wonderful videos and explanation of where you are. With the MaC, put the curser over the photo, and hit control. Then scroll down to "Copy image address". Next paste that into the text of your post, after you hit img. After the image address, hit "/img". That will bring your picture to the current post. You can also paste in the image, then highlight the address and click on "img".

The resin used in the boat construction is polyester. I grind the bottom smooth with a right angle flat grinder. I used to have a 1 1/2 HP "Craftsman" we used when building boats (and I was young and healthy)... That was a beast. There are a number of good grinders, I have a Milwaukee which is 4 1/2" disc grinder, cut off wheel and wire brush. Mine is a 6140, which is still being made. Mine is well over 20 years old, and still going string. It is light and fairly easy to handle. I use 36 grit discs, and it only takes a very light touch to get the old polyester cut down o a fairly smooth base. You actually want some roughness and that is why I use the #36 grit. (Don't push it too hard--it is very aggressive".

I would try and level out as much as possible. You are going to put a layer of resin and cabosil down to smooth out the bottom. and set the balsa in this before it kicks off. I use a notched floor mastic spreader trowl to spread it out. and keep it from being to thick,.. When you bed the balsa into it, it will flow and even out.

You are dong a great job.
 
Thank you for the encouragement, Bob. I am definitely acquiring tools doing this job! Not complaining about that; I like tools and will now be adding an angle grinder to my repertoire! I rather figured that is what I needed.

In another post, you had recommended that I lay a layer of mat (1708?) to reinforce the hull before I put down the core material. I do think that is a good idea. Where the core had just completely liquified the underlying glass is really black and depressed - like it was dissolving away. I think it could use another layer.

I've also been rereading all of Limpet's (Marco?) photo album posts and thinking of other things to do as long as I'm out of the water, dry in a garage and waiting for supplies. I am so envious of his configuration, that he was able to remove the rivets and just pull the side panel and seat box completely out so easily. That would have saved me a lot of ugly cutting on the seat boxes, as well as the bunk. I had to cut off the flanges on either side of the porta potty cut out in order to get the v-berth bunk out. Ugh. But while it is out I thought I might be able to find a permanent gas tank that I could install under there. I don't want to hang it, but wouldn't mind building some sort of cradle for it to fit in. I've been looking to see if there is one that is short enough to fit more forward than Marco's did while still leaving enough head room for the fittings. My dream had been side tanks, but I can't get my side panels off so that is out.

The other advantage of his seat boxes is that they were closed in the front. I am going to close mine up before reinstalling them. They had absolutely been designed to let water run under them and I am going to put a stop to that!
 
Jackie,
Just wanted to update you on what I ended up ordering for balsa.
I looked at Barry’s link he sent me http://www.fiberglasssupply.com/
I ended up ordering 4 sheets of 3/4 that measure 24x48 inches (8 sq ft) For a total of $211.00 and they even gave me a military discount, shipping was very reasonable at $28 for 4 sheets via Fed Ex in 3-4 days.
Hope that helps.
 
Thanks, Teufelshunde! That is good info. Because it is such a sharp bend to conform to the bow, which leaves a really wide kerf opening, I was thinking of getting two sheets of the 3/4 inch and layering them up there to reduce the bend. But I don't want to do the whole job in 3/4 inch since that is essentially doubling my workload, so I'm going to get 3 sheets of the 1.5 inch stuff to do the rest. The gentleman in Homer is going to get the thicker stuff for me, but I will look into your spot for the 3/4 and maybe all the mat, etc I will need. There is a 4 week wait for the thick material, but that gives me plenty of time to prep all the surfaces and to allow for extra drying of the remaining core.

I'm excited and apprehensive to get started! My son's boat needs some FG work done and I figure I'll be a pro (ha, ha) by the time I'm done. Just gotta figure out what to charge him.
 
Jackie,

My seat boxes are not fully closed in front. The foot platform is open such that water can (and did) run under them. On the original build, the seat boxes had rivets and caulking. The caulking didn't seem to serve any purpose other than to slow the draining of water out from underneath. I'm not sure what that was all about.

As in my photos, I epoxy filled the over-drilled holes and used SS screws to re-attach the boxes. No caulking. Water can now just run out from under the boxes. Two construction methods: 1) make sure water never gets in 2) make sure water can drain and do no damage. For boats, I always go for method 2. If you have tabs on your seat boxes, I would recommend epoxy fill and drill.

My gas tank suspended from the underside of the berth was in part because of my "get it off of the floor" goal. Holding anything to the floor on the 16 means that there will be core penetrations. Those can be addressed with epoxy fill and drill, but I even wanted to avoid as much of that as possible. Plus, hanging the tank meant that I still had room for a boat hook, net, and paddle under the berth with no chance of tangling with the gas gauge wire.

Sourcing a tank to fit took some searching. I ended up with a "belly tank" for a newer production boat (set crosswise in my install). I measured more than twice for that one. 23 gallons can go pretty fast for a multiple night cruise. I don't know how people live with two 6 gallon tanks. Of course, I can still fit my two portable tanks in the splash well for a total of 35 gallons. No smoking, please.

Mark
 
n another post, you had recommended that I lay a layer of mat (1708?) to reinforce the hull before I put down the core material. I do think that is a good idea. Where the core had just completely liquified the underlying glass is really black and depressed - like it was dissolving away. I think it could use another layer.
Click to expand...

Jackie you cannot go wrong with the suggestions your are getting.

I may have missed it: What resin are you going to use?

1708 is 17 oz with 3/4 oz mat: "n another post, you had recommended that I lay a layer of mat (1708?) to reinforce the hull before I put down the core material. I do think that is a good idea. Where the core had just completely liquified the underlying glass is really black and depressed - like it was dissolving away. I think it could use another layer. " stolen from Jamestown catalog".

I would put 3/4 oz mat down if you want another layer. 2 layers of 1708, and at least a layer of 3/4 oz mat for the inner layer. 1708 is epoxy and polyester comparable. If you use epoxy, be sure any mat has s sizing which is epoxy computable. Many are not.

Unless you have to grind out a lot of the glass (not built up resin) you should OK with the thickened resin, then the mat side down balsa. On top, mat side of 1708 resin down, , then mat side down of second layer, finally a layer of mat.

Depending on the strength required, you can use mat and cloth or mat and 1708 for tabbing.

Go with what Mark recommends, or what you feel is best for the seat box.
 
I would put 3/4 oz mat down if you want another layer. 2 layers of 1708, and at least a layer of 3/4 oz mat for the inner layer. 1708 is epoxy and polyester comparable. If you use epoxy, be sure any mat has s sizing which is epoxy computable. Many are not.

Unless you have to grind out a lot of the glass (not built up resin) you should OK with the thickened resin, then the mat side down balsa. On top, mat side of 1708 resin down, , then mat side down of second layer, finally a layer of mat.
Click to expand...

Bob, I haven't ordered anything except the thicker balsa. I've been pouring over other posts on the forums looking for what others have done and trying to educate my self a bit about fiberglass. (I'm not doing so well!). I'm a bit confused about the differences between mat, cloth, 1708 and when to use which. I think cloth refers to pure fiberglass strands that are woven, and mat is a non-woven fiberglass with some sort of binder on one side holding it together? And that binder is designed to dissolve in a particular type of resin - either epoxy or vinylester or polyester? Is 1708 a sort of cloth mat combo?

I think your recommendation above is for 2 layers of 1708 and one of mat. Since you specified 3/4 oz mat, is that all I really need to know when I order, except to make sure it is compatible with the resin? On the top I also need two layers of 1708 and another of the 3/4 oz mat?

The boatbuilder that is getting the balsa for me suggested using Core-Bond as the bedding for the balsa. That is compatible with the esters. It sounds good because I don't have to mix anything, but I've only found it in 5 gallon buckets so far. That's quite a bit more than I'd need.

I guess I'm a bit lost right now, but I haven't hit YouTube yet. That's my kids goto for info. I checked out all the books on fiberglass from the library but so far I need a chemistry degree to understand most of them!

It has dawned on me that the fact that I can't remove my sidewall may cause problems when I reinstall the core. I cut right up to about an inch from the edge. The original top skin, of course, married in smoothly to the outside wall of the boat, and the inner sidewall was tabbed down to it. Since I can't get the sidewall out, when I re-skin my repair will I just tab it to the inner wall? I won't be able to join up with the top of the remaining core next to the edge. I don't have a good pic of this right now so I hope I'm making sense.

Anyway, I haven't made much more progress. Just getting things ready for when I (magically? suddenly?) do know what I'm doing!
 
I’d suggest watching total boat works on YouTube. I just finished my first ever core replacement and fiberglass job ever. I leaned a lot just from watching that channel and a few others. At least you’ll know kind of what to expect.
 
Hi Jackie,

When I re-read my last post, I realized I had left out a quote on 1708. IT is laid bundles of fiber, it is laid at 45*. it is stitched together. It is not woven as usual roving is. We used to use woven roving alternate with mat. The 1708 is lighter and as strong. It does not have the "print thru pattern" that the heavy bundles do. The cloth is smaller twisted "threads" of fiberglass woven, and the mat as is you described, with a sizing compound.

The Core Bond is basically thickened polyester resin--and applied with a trowel as I described. You can either use something like "Poly-Fair" which comes in one gallon cans, (talk it over with the supplier--you would waste most of a 5 gallon container). and is also made by ATC. I just mix up my own. using Cabosil and low density filler. I am not sure what makes the ATC Corebond "elastic"--But that can be a feature which is not essential with the C Dory.

Another way to go is 945 Vinylester Bonding at $50 a gallon. It seems to be as good as the CareBond, and comes in gallon containers--stronger resin bond. I have not used it, and I would do the initial hull laters with the vinyl ester then polyester on the top of the balsa, and between the layers of the two 3/4" layers of balsa.

You want something which will adhere well to the bottom inner side of the hull, and to the balsa, filling the voids between the hull (you want to weight the balsa to give best adherence) and voids in the kerfs of the balsa. It is cheaper, and in this iapplication probably sensible to use polyester resin. The issue between the resins is the secondary bond. Initially when the boat is newly built, there should be a primary bond--that is all of the hull and core is laid up wet, before the layer below is fully cured. The reason that vacuum infusion is superior, is that it assures that all is laid up at once (as well as saving weight and resin). Hand layup may mean that the hull got partly laid up on Friday and then finished on Monday--Thus giving an inferior secondary bond, rather than a primary chemical bond. This happens occasionally--and may lead to hull failure. There was a new very expensive spot fisher where this appeared to be the cause of total hull failure.

Epoxy resin gives a considerably stronger secondary bond, but is also far more expensive. (we are fortunate to have a wholesale supplier of all of these items only abut 8 miles from my home). There is a huge markup to by places like West Marine. Vinyl ester resin is about half way between in strength between epoxy and polyester. See above about using the 945 Vinylester Bonding.

Yes,you will tab in the sides--basically filling any voids where you cannot get the balsa, with a thickened polyester or vinyl ester compound. It can be thicker than the bonding material used for the core to the hull. You will dry fit the balsa. Then see how much filling you will have to do along the sides. I probably would put that in just before you put in the balsa. Leaved this highly thickened resin slightly concave, and us the bonding agent between the balsa edge and the filler along the sides.

I would probably sweep on layer of 1708 up the side, and then fair and sand smooth as you do the finish work. Tabbing can be done with cloth tape and mat or the 1708 and mat. How much fairing and sanding at the end, depends on your aesthetic sense...not a crime to leave a line of tabbing. But I have the impression that you do very nice work and would want it to look as near to perfect as possible.
 
Thank you, Bob, that is very helpful and leads to a couple of questions. I wanted to lay in the layers of mat and 1708 against the hull maybe several days before putting in the core. I don't know how much cure time there is between layers, but I assume there is some and that it is okay to get that part all ready to receive the core? I would be using just a vinyl ester resin for that with no thickeners or anything, wouldn't I? Then the 954 vinyl ester bonding compound would a new layer that beds the core to the hull I just laid?

At this point I had thought to do the bow with the two layers of 3/4 inch, and then later go back and finish the rest with the 1.5 inch. Will that be a problem? If it needs to be all done at the same time I could put in one layer of the 3/4 inch along with the rest of the floor, and then go back with the final 3/4 inch. I'm assuming they need to cure in between, or do I just lay both 3/4 inches at once? One of the reasons I was interested in the pre-mixed bedding resins is that I read the open times are longer. I have a big area and, since I've never done this, may not be the fastest worker. But I've laid a lot of tile so I'm fairly fast with a trowel.

I'm pretty sure (from walking through the one place in town with any fiberglass supplies) that I'm going to have to order out. I planned to enter a few of the items in the online order forms of the various company names that have been suggested here just to see how the shipping shakes out. That's kinda how I decide when I have to order, and once I do I can call the store and I'm sure they will be able to guide me in the right direction. I just wanted a rough idea of what I'll be needing in advance.

Thanks for all your help. I tend to be look with a more critical eye at work I pay for, but can be tolerant of my own errors :roll: For the boat though, I do want it to look good, and it needs to be sound, so I'm trying not to let any laziness take over! I blame it on being a Gemini!
 
Back
Top