Deck core replacement in bow of CD16

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d&linAK

New member
I'm contemplating a deck core replacement project on my 16 angler and leaning toward a full-deck replacement with 1.5" Canacore. I'm wondering what I will do to lay the core towards the bow below the v-berth - in this section it looks like the core starts to curve much more significantly than the rest of the deck. Is this section even cored? Would I need to just score the Canacore with a circular saw so it could flex enough to follow this curve?

Thanks!
 
What is the condition of the current deck? Is the entire core rotten? Have you drilled test holes from underneath? How do you know that the entire core has to be replaced?

Replacing a bow deck on any boat is not easy! Are you gong to keep the top mold layer and laminate from underneath, turn the boat upside down (I am serious) and then weight the core material as you let the resin set up? (This is the way the deck is constructed, and a common method used for smaller boats) or take the top molding off, and totally reconstruct it--which means a lot of fairing, and then formation of nonskid, with a mold? (We rolled out the nonskid on the cockpit floor on the 25--but that was the way it was done originally. although this could be done on the foredeck, it is more labor intensive.)

If working from inside, consider the issue of fumes when laminating--you will be best off with a positive pressure respiratory system.

I have never worked with Canacore. It is very similar to Nida Core (which I have used for the deck replacement in the cockpit of the C Dory 25)/ For these cores to be most effective they should have a scim of fiberglass mat on the surfaces. I don't see where the canacore has this...but it may?

How thick is the bow deck of your 16? My recollection of the 22's is that it is about 3/4" core--no more than 1" core--balsa. Balsa remains a very good core material. It has many times the shear strength of Canacore.

The thicker the sandwich, the more rigidity it will have. There may be a point of overkill; probably 1.5" Canacore is overkill. There are several ways to put in core material, where there is a curve. One is to kerf the material (as you suggested--(without a scrim, this is going to be very difficult), the other way is to use several thinner layers, with a layer of mat between, and that is generally better. Baltek end grain Balsa has enough flexibility, because of the way the blocks are laid, that it can accommodate moderate curves--and I believe that is what was used in the 16 of your vintage. Balsa has good adherence to fiberglass resin.

No matter what core material, you need to put epoxy around any bolt holes--including the bow railing bolts, anchor roller pulpit, cleats etc. If you are using balsa core, you will get indefinite life, if it is properly done. I cut up some boats which were over 30 years old which had balsa decks, and they were was good as the day they were laminated, when properly sealed. (Part of our core laminate study post Hurricane Ivan; in development of ultrasonic measurement tools for boat laminates.)
 
Thanks for the thorough response! I'm uncertain about the condition of the entire deck but there were old penetrations in the bilge/gas tank area, a number of bad rivets extending from the bilge area to the seats, and loose screws in the v-berth supports with obvious rot under each area. I suppose the next step would be to drill exploratory holes in the open areas of the deck without hardware.

Also, by bow deck I meant the bottom deck below the v-berth that extends behind where the brass keel guard lays, not the area surrounding the window/hatch.

I've been leaning toward the Canacore because of cost savings (seems to be about 1/2 the price of balsa) and durability (of course dependent on my ability to install it correctly). I've spoken with a few local fiberglass professionals who have used the material before and had good things to say about it.
 
I misunderstood, I thought you were replacing the deck. You are really considering replacing the hull core on the bottom of the boat. This is entirely different. (You don't have to turn the boat upside down for one thing!).

Rot in the bottom of the boat especially where there are freeze thaw cycles is fairly common where there are fasteners. A lot depends on how much the time the boat is out in the weather with water in the bottom of the boat vs being in a covered environment.

Many of the C Dorys are solid glass forward of the console--I do't know about the 16. There have been quite a few who have had issues with "pop rivets" and screws into the bottom, and using these fastenings are not a good idea. Far better to either tab "furniture" in using strips of fiberglass, than putting fasteners into the bottom of the hull. I suppose it was faster and cheaper to use these fasteners, than do it correctly...Too bad, because we all can have issues with this.

Most who have repaired the bottom, as you are considering have used balsa again. There are many properties of balsa which make it good for the bottom of the boat. I am not convinced that a honey comb material will do the same, and will have the necessary shear strength. Are those local fiberglass people using the Canacor for hull laminations, or for bulkhead and decks? I think it is better suited for bulkheads and decks, than the bottom of the boat. Some have used foam, of a density similar to the balsa. 3/4" Balsa 2' x 4' sheets are about $47 each from Jamestown. Balsa is stronger in both shear and compression than most foams (except for some synthetics which weigh more). The most important issue is the thickness and adherence of the laminates on each side of the core. That is what gives the strength to the boat.

I would drill exploratory holes, or begin stripping back the top glass layer, If you have decided to replace it, then you have to pull the top where it is rotten. Where it is not (and that becomes obvious very quickly) is fine, and can be left. It is very possible that there are only limited areas--or extensive--sounding and using a moisture meter will give you some very rough idea before you start pulling up everything. If it is limited areas, a few 2 x 4 sections of Balsa, will be adequate, You only replace what is damaged, and you can then re-glass over all of these, sand the entire bottom, and put in a layer of mat and glass, and then properly tab in the furniture.
 
I did confirm that the fiberglass guy I mentioned has built skiffs with Canacore hulls, typically 3/4" or 1" at the thickest, bedding them with either a product called Core Bond or 2oz matt. Apparently he's seen boats constructed this way put through the wringer (collisions, running aground etc) and was confident about it's durability/strength.
 
I would be reluctant to mix core types in the bottom of the hull. For a deck--it is OK. In fact often done often in decks for places where cleats and points of stress are located. There are small areas of increased density materials used in the hull around thru hulls in cored boats, You may want to increase the thickness of the inner laminate if you use different core materials. This may be the reason they use 2 oz chopped strand mat, rather than the usual 3/4oz CSM. Mat is often used as a filler or bonder, to give better adherence between woven cloth or mat (which gives the strength in the hull). Even though the 2 oz will give a thicker laminate, it will not be as strong as a similar laminate made of roving or triaxial cloth.

Core Bonding Compound? It an be used for differential properties in the bottoms of boats, but I question use in patchwork--but it may well work.

Let us know what you find in the exploration of the bottom core! Photos are helpful for others who may have similar issues.
 
I think if I went this route it would be a full replacement as opposed to a patchwork of balsa and Canacore. I will definitely post updates! Might not be anytime soon though as I'm still in the research phase.
 
I ended up diving into this project recently and completely stripped the core up to about a foot in front of the consul. It was a mess - enough rot around the v-berth supports and seats to where I could remove handfuls of rotten core mush that had zero adherence to the glass. Around the middle of the deck the core was in the best shape - still looked like wood and still had a good bond to the glass but it was wet (I could squeeze it and water would come out). Everything was Heavy, I probably removed about 150lbs of material. I could easily scrape out the most rotten material with a drywall scrapper but I had to use a flat bar and hammer to remove the core material that still had a good bond. Before I did this I took a circular saw and cut the upper fiberglass skin into ~6" squares. This method of prying out the core caused a little damage to the glass below, tearing out some strands of the glass mat below. I plan on sanding the bottom surface clean and potentially making small patches to fill any little divots that were created.
 
Materials update:

I was so close to ordering some nidacore for my deck core replacement but I spoke with a local fiberglass guru and he tipped the balance - after handling the nidacore and hearing his thoughts on the shear strength/avenues for failure in my specific application (as was also outlined to me by Bob/Thataway in the past) and also finding a good source of balsa at a comparable price, I'm going with balsa.

I'll be ordering 1.5", resin coated, contourable balsa core from a company called Composites One. I think I'll also be ordering some poly Core-Bond for the layup of the core material - it sounds like this might be the best bet for creating a good consistent bond, especially as used by a novice like myself.

Top to bottom I think my layup will look like this:
Gelcoat
3/4oz CSM
18oz roving
3/4oz CSM
1.5"balsa core
Core-Bond
18oz roving
3/4oz CSM
Old fiberglass outer skin

I think I'll also try to use Iso Resin (apparently the elasticity is better than other types or resin?).

Any thoughts? Advice?
 
I agree with your use of Balsa vs Nida-core (I have used Nida-core for bulkheads and actual decks, but not for hull structure laminates.

Your laminate schedule is OK--it will probably be stronger and heavier than the original--I don't know what the laminate schedule for the 16 was originally. If I were doing the project, I probably would put 1 1/2 oz mat on the bottom then the core, a layer of 1 1/2 oz mat, then 18 oz roving, 3/4 oz mat, another layer of roving and 3/4 oz mat. Reasoning, is that there may be more irregularity in the bottom layer of laminate of the hull, and that the 1.5 oz will give a little more "cushion" to even out and prevent any voids under the core. I have not used "Core-bond"--it does give you the same effect as a thicker layer of mat.

Your hull bottom should not have sustained any damage--if it has, then another story entirely. You are trying to create an "I" beam with the strength on the top and bottom of the core. The shear strength and adherence of the balsa will be better than any hollow cored material. Also better compression strength. I like to tell the story of a certain well know small trawler which uses low density in the hull sides--and when they come up hard against a piling, it leaves a dent, because there is not enough glass on the outside. This is not an issue with your C Dory.

As to the resin. If I was building a new bottom from the outside in, I would be using vinyl ester resin as the first few layers. It is a better water barrier than any of the polyester resins. I have only used ortho for hull lamination. The Isopthalic Polyester has some great properties. It looks as if currently it is about $10 a gallon more than the orthophthalic polyester. (In the late 1970's I was buying a 30 gallon drum for what 5 gallons costs now!) I am not sure it offers that much more for your application, since the rest of the hull will be ortho.

The new repair should last a life time since you will not be making any hull penetrations. I assume that anything you put back on the "deck" will be tabbed in with fiberglass and resin. If you were putting a thru hull fitting in the bottom, I would lay it up solid glass at this point.

Please keep us posted with more photos--the ones you have on the album are great! Good going!
 
Just finished the last layer of gelcoat and I'm pretty pleased with the end result of this project!

After the demolition stage I tarped off the boat to keep out the rain and put a heater and a fan in the v-berth area, keeping the inside temperature of the boat roughly above 65F for the entirety of the glassing/gelcoat stage of the project.

Ended up using ortho-laminating resin and going with a layer of CSM and 1708 on top of the balsa core and was very happy with how things laid down - after laying the CSM over the balsa I laid a 4" strip of 1708 all along the perimeter of the deck overlapping with the walls for a little added strength at the corners and to make the layup of the main panels of 1708 simpler (not having to conform to curves while wetting-out larger areas). I did not tear out the bilge/sump area so to tie that in to the new glass I simply overlapped a few inches into the depressed sump-area.

I finished with two layers of gel coat (Guard Astoria Grey), using gelcoat with wax for the top layer. It took roughly 800ml of gelcoat for each layer, covering around 10square ft of surface area. For my non-skid I used silica sand that my local marine supply store stocks (the same stuff that is used for sandblasting) - while the bottom layer of gelcoat was still wet I scattered an even layer of sand down on the areas that I wanted non-skid and then once the gelcoat set up went over that with the top layer of gelcoat. I was happy with how this turned out (it's quite grippy) but we'll see how it wears over time.

For the installation of the fiberglass seats/side panel pieces I will be drilling oversized holes in the deck, wetting out with resin and filling with thickened resin, then drilling pilot holes for stainless screws. For the attachment of the side panel to the gunnel I will be gluing wood backing blocks to the backside of the panel that I can then get a screw into.

While the side panels were out I took the opportunity to do some rub rail repair - the starboard side rail caught on something a while back, ripping out about 8 of the rivets and bending the rail out slightly. Without completely removing all of the rivets securing the seat/side panels the backside of the rub rail is completely inaccessible so it's just been ignored until now. I ended up using 1" #10 stainless machine-head bolts with fender washers and nylocks to secure the rail. This assembly fit perfectly as the holes in the rub rail were already countersunk. Removing the rubber insert was easily achieved with a pair of needlenose pliers, re-insertion was just a matter of placing the lower lip of the rubber insert in the metal channel and using a flat-head screwdriver to press the upper edge into the channel.

I should be posting more photos soon.
 
Sounds good, and the photos look good. My story about silica sand. A boat I was racing Los Angeles to Hawaii in the TransPac, had just had the decks redone with Silica sand, as you did. I wore a hole in a brand new pair of Gortex foul weather pants in about 24 hours! ($300 back then)...! Great non skid however. I have found that with time, the silica will pop out, and leave pits. Because of that, I put another thing coat of paint over the sand, to help seal it in (That was with Micro spheres, which are less aggressive than silica sand, and using 2 part LP paint.

Another non skid "Trick" which C Dory used in some boats, was to roll on gel coat thickened with cabosil. That would give a fairly good aggressive random and cosmetically pleasing nonskid on the inner surface of the hull.

You are doing a great job. I look forward to final photos.
 
Most forms of "grit" chew up garments, elbows, and deck shoe soles, way too fast for me. I switched to polycarbonate grit a while back, and am very happy with it. Plenty durable and plenty of friction.

Sprinkle onto a wet coat of deck paint, allow the paint to dry, and hit it with a little hand driven block sanding, 100 grit or 200 grit, just enough to knock down the sharp edges. Complete with another coat of deck paint to seal it on. The sanding allows you to adjust the degree of non skid effect. System Three sells it: https://www.systemthree.com/products/non-skid
 
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