Building our First Corecell Dinghy
Building our new Corecell Dinghy
Designing the dinghy.
Our old dinghy “THAT Dinghy” was a conversation piece. It worked ok and had a number of nice features, but size wasn’t one of them. Now that we are home and looking forward to a new boat where size wouldn’t be as big an issue. I started scribbling on a piece of paper trying to decide what we wanted on the next dinghy.
Bigger? Definitely, the old one is just too small.
Lighter? Definitely, when we have to carry the old dinghy Bonnie has a hard time with her end of the lift.
Glass bottom? Before we go to the Bahamas YES! But now, not so much. The twin keels on the last one protected the glass bottom really well, but our feet scratched it so the glass should be where we’re not going to stand on it.
Lockers? We definitely loved the locker we had in our dinghy but with the new dinghy we had new opportunities for MORE STUFF!
- Anchor, for a small anchor and rode
- Safety, for a couple of life jackets, bailer, flares, throwing rope … all the usual stuff that everybody has to carry but never has room for was at the bottom of our old dinghy locker, this dinghy has everything in one place that is out of the way.
- A locker for a small gas can, oil for mixing, etc. Maybe.
- A locker that can be locked and can protect stuff from spray, the bigger the better.
- Seats? Definitely! I want to be able to sit down reasonably comfortably and steer looking forward.
What size outboard? Our 2.5 hp seized last year and I freed it up but it’s life is limited. A 9.9 hp would be max.
The other thing was we had to be able to store the oars without being in the way constantly.
All this and Bonnie had to be able to lift her side!
After a few scribbles this is what the design looked like.
Can we do this?
After a few scribbles this is what the design looked like.
Can we do this?
Our design ended up being 12 feet long with a 52 inch beam, that’s a big boat for two people to lift easily.
We saw the first “Spirit of Canada” being build for Derek Hatfield’s race around the world. It was a 40 footer being built by Corecell and the empty hull weighed less than 500 lbs when it was done. It was interesting stuff. We sent an email to the manufactures of Corecell and they put me onto one of their naval architects Molly Schrum. She was extremely helpful and had lots of patience listening to my ramblings. I decided on using Corecell for the new dinghy. I ordered the materials I needed to build the dinghy and thought I could start the dinghy while my step-father was recovering from his hip replacement surgery, in late December of 2006 and early 2007.
We got the material in 2006 but the building didn’t happen. What did get done was the building of a simple half mold that I could use to get the shapes of the panels I would need to build the hull.
After our trip to Texas we came home and did this, that, …, it goes on forever. During the summer a friend said a couple of people were going to get together in their garage this winter and build new dinghies, was I interested? YOU BET!
After we got home from our trip to Exuma Park, I started working at laminating the Corecell and working on getting the panel shapes extracted from the half mold.
The first part was using mylar film to cover the half mold.
The mylar can be spread over the hull and won’t stretch like paper and won’t rip as easy as paper. I tacked it in place with instant glue and then used a knife to trim the excess and after I was done I pulled off the mylar to get the shapes.
If I were doing it again I would have used a much larger scale than 1 inch equals 1 foot. One of the books I have read suggested a scale that would give you a 30 – 40 inch half mold is required for an accurate panel shapes. After doing this I would probably have done a 30 inch model for this dinghy. Hind sight is so much better.
The next step was to get the shapes of the panels into a spreadsheet that I could use for making the real sized panels.
After doing it a couple times I would suggest that you draw the size of your panels onto your graph paper so that you can position your mylar shapes onto the graph paper to optimize your panels.
After getting the panel shapes, we could start drawing the full size shapes on the panels and cutting them out.
The sides were easy to laminate into one long panel 16 feet by 2 before being cut. Here is a picture of the sides being laminated together.
I used 8:1 scarfs for the panels but after sending an email to Molly I switched to using a 1:1 scarf. The table saw set at 45 degrees makes a lovely 1:1 scarf and it’s fast
The transom was easy, the bottom had to be done in three sections. We couldn’t get a 12 by 6 foot panel out of my basement!
Once we got to Jeff’s the first step was to laminate the bottom panel to get the right shape
Note the back end of the bottom. There are two strips of higher density (A800) to support the keels laminated into the bulk of the material(A500) as suggested by the naval architect
Stitching it into place.
After we were done making the panel shapes, I made a quick little template that consisted of two boards to make a shelf with two nails 5/8s of an inch below two nails 2″ apart. This way I could make a consistent set of marks down the side panels. Once they were all marked I drilled them all.
I got a little to excited and stitched the panels to the bottom by myself. I shouldn’t have as I ended up not getting the bottom of the bow as tightly stitched as I should have. Also I’m not sure I would use cable ties to do the stitching again. It is to tempting to zip up the ties too tight and then you can’t back them off without replacing it.
After you have a couple hundred cable ties in place, it is a deterrent to clip them all.
Here is a picture of a few of the cable ties with small fillets in place to tack the boat together so I can clip the cable ties.
One of the suggestions I read in a book was that it is a good idea to make a “landing” pad to prevent hard spots on the dinghy where the bulkheads meet the panels. I had a fair amount of scrap so rather than throw the scrap I just passed it through the table saw a couple times with the blade at a 45 degree angle and made a whack of landing pads.
You can see a couple of the landing pads in the picture.
In the picture above, all the landing pads for the bulkheads are in place, including one mistake. The last landing pad is for the rear seats not one that should go all the way across. I am going to put the landing pads for those seats in place after I have the fillets done on the stern so that transom is as strong as I can make it. I’m also going to beef up the fillets a little around the transom as well.
You can see the small gyproc screws in the first landing pad. These stay in place only until the epoxy is dry and are removed before the bulkheads are put in place.
The clamp around the top of the sides is the same thickness as the landing pads, so I put it on before I started installing the bulkheads. Yes, there was a sale on clamps at Canadian Tire, no there aren’t any left in the Oromocto store.
We had three clamp explosions, the remnants of one is in the picture above. We were talking and all of a sudden there would be a snap and a clamp would fly through the air. Doesn’t pay to buy too cheap a clamp, the exploding ones came from the Dollar Store.
Once the clamp was in place the next step was the bulkheads. The picture above shows the bulkheads in place with screws supporting the bulkheads until the tiny tacking fillets dry.
Note that the cable ties used for stitching have all been removed.
The nose at the bottom had two problems, One was the cable ties were too tight in the bow when I started stitching it together and I didn’t have enough height to hold both ends up high enough to easily tie the bottom of the bow to the bottom at the same time. Shouldn’t have done it by myself.
The nose was within an eighth of an inch and we reefed it pretty hard.
We were breaking cable clamps with tension but the Corecell didn’t give way. Here is a splash of thickened epoxy to fill the gap. The nose didn’t end up being exactly the right shape but it is still pretty good.
Jeff is having work done at his house and needed some room. We moved our boat forward off the tall work tables and onto the shorter setup in the foreground. Bonnie was pressed into service to see if we were still light enough for her to handle the heavy end. It’s still an easy lift for both of us.
One of the things that worked really well with our last dinghy was the fillet system we used. The systems consists of a piece of peel ply (or polyester dress fabric if you are in our area)about 10 inches wide, on top of it is a piece of 6 oz fiberglass 8 inches wide and on top of that is a piece of 6 oz fiberglass 4 inches wide. Each piece is then cut to the length required for a particular place, then rolled up, labeled, and put in it’s approximate position. Labels are important and it is easier if the system for labeling is consistant.
If you pick up a bundle and it says “Port Fwd Seat bulkhead Aft” it is the fillet that will go on the port side of the forward seat on the aft side of the bulkhead.
Here is our little pile of fillets ready to go.
The last time we did all of the fillets at once as suggested in the book. We found it very difficult to get the fillets to work well together when they were all wet. This time we are trying to do all of the vertical fillets one day, all the chines the next day, and then all of the cross pieces the following day.
To make the fillet we would mix filleting filler (2/3 wood flour and 1/3 Cabosil) to a slightly thin peanut butter consistency and then spread it on with a spatula made of a plastic lid cut in a circle of the appropriate radius for the thickness of the material being bonded. Meanwhile Bonnie was unrolling the precut fiberglass bundle. She would lay the peel ply in the bottom of a small wooden tray that we used as a “glassing box”. The largest width of fiberglass went down on top of the peel ply, then epoxy was used to wet out the fiberglass, once the fiberglass was wet, the thinner width was put on top and it was wet out. Once both pieces were wet we would pull it out of the glassing box by the peel ply and carefully press the fillet into position. Once it was in the correct position we would use a fiberglass roller to smooth the fillet and remove as many air bubbles as possible. The fillet system worked well and we were very pleased with the result.
The vertical bulkhead fillets are dry and smooth, we did a quick pass with a wet cloth to clean up any blush that may have formed. I doubt it did because the garage is very warm and very dry. The polyester dress fabric becomes like and extremely stiff wax paper when the epoxy dries and it will often rip as we peel it off but once it is off it does a great job. We don’t need to sand these fillets at all. In the future, We replaced the peel ply with 6mil construction plastic and other than making it harder to get the air out it worked better and was much cheaper. Any folds in the construction plastic were impossible to remove and showed in the epoxy
When we were doing the nose the two chine fillets intersect. So rather than to try to get the two layers of peel ply to weave together we used the peel ply to smooth the fillet and then removed the peel ply and then applied the peel ply on the Port side.
It was interesting to see the difference between the two sides. The Starboard showed the weave of the fabric. The port side was smoother.
The bottom fillets were done last and this shows the vertical and chine fillets.
Corecell doesn’t change color like wood when it is covered with epoxy so it is hard to tell that the sides are actually covered with glass. The excess is shown overflowing at the top. Once the sides are completely dry I’ll trim it all off.
The bow sides are both done, once dried the excess will be trimmed off. Looks like I may have some sanding to do. It is an anchor locker so as long as there is reasonably smooth to make it easier cleaning I’m not going to go for too fine a finish.
After a couple of false alarms, the workman are going to be arriving tomorrow! So we really had to get room for them. Here are the other two dinghy’s being built in Jeff’s garage.
In the picture above on the starboard side you can see a plastic pipe running from the bow locker to the hold. This is a electrical conduit. I will eventually have nav lights and I’d love to have a cheap depth sounder for scoping out anchorages.
The conduit was put in place before fiberglassing the sides. It is covered by the fiberglass.
Landing pads and shelf supports for rear seats in place. There are two layers of glass on the floor and transom.
That was a mistake there were supposed to be four on the transom. So I got to sand those off and add two more layers of glass to the transom. I get excited.
Once I got the bulkheads all done and I had a bit of epoxy left I wondered what I could do to move it along and thought about the rear seats. Bottom was done so I did the next bit and never thought about the transom.
Corecell does sand away easier than wood. On the last dingy I epoxied the two side clamps on at the same time and in the same orientation. One had to be reversed so I ended up turning a 2x3x4ft pine board to sawdust using a grinder.
The forward seat is also a locker. Here is a picture of the bottom of the two sides being glassed.
The next day I took my router over and made a nice rounded edge on the top side. I decided that rather than try to make it look nice and flush to make it rounded and more obvious that there is a locker under the seat There is going to be a latch with a lock anyway so it will be obvious no matter what.
After glassing the tops and letting them dry I mixed up thickened epoxy and spread it over the supports for the seats and then pushed the tops into position using the lid of the locker to make sure the spacing for the pads is correct. There are still lots of things to do for the locker,
- Put a smoother fillet with a little glass around the edge of the seat sides
- Rig a hinge for the opening part of the locker
- attach the locking latch which I don’t have yet
In the picture above, the transom with four coats of glass, with the bulkheads for the seats are in place and the vertical fillets are drying.
I just had to do a quick test, with Jeff’s gas tank to make sure things fitted the way I wanted them to
Fits just great!
The seat tops were the next thing to do but it was going to take several days of small jobs so we decided to flip it over and do the bottom and work on the seats as a between jobs thing.
Once we flipped the dinghy we realized we had a lot of stuff to do before we could glass it. All the tiny holes we made to tack bulkheads in place, the holes from stitching and scarfing all had to be filled and then sanded. We also touched up any scarf joints that were not level and cleaned up the bow joint a bit. We also did two layers of glass on the transom before we put the two final layers of glass over the entire bottom giving four layers of glass on both sides of the transom.
The picture above is just before we started to lay out the glass for the first skin.
The first skin when right down the center from the top of the transom to the tip of the bow. The 60 inch width of the glass meant that we had to cover the remainder of the sides with two arch shaped side panels.
I actually took this picture to see if it made much difference to let the fiberglass “settle” for a few hours. This was taken about 3 in the afternoon. We came back later the same night to do the glass work.
It’s hard to see in this picture but I think letting the glass settle did help the fit. Hard to say for sure. Bonnie came to do the mixing while Jeff and I were doing the wetting out. She could just keep ahead of us. It was really nice to finally be able to open the garage door and work in the fresh air.
You can see the seats leaned up against the work bench on the right hand side. One is ready to go, but I need to get webbing to make a hinge before the other can be finished
The second skin is ready to get epoxied. The 60 inch width this time goes from the top of the bulkhead on the starboard side as far around the bottom as it will reach and then another piece covers the remainder. This should give completely different seams for the two layers. Again the glass runs from the top of the transom to the top of the bow in one run.
We are going to let the glass “settle” for an overnight just to see if it works better.
We heard that you could use cheap shower curtains as peel ply for fillets etc. It did work great with fillets, with small surfaces it worked great although it took a little more work to get the air out from underneath. The fillets when done were smooth and fine.
With the success of the fillets, we tried to do a peel ply for the large surface of the bottom and sides. It was a disaster. The small folds that wouldn’t lay flat left a mess when it was pulled off. Won’t do that again.
The two seats are placed. The port seat will lift and allow our oars to be set in place and the seat will eventually be lockable, locking the oars into the boat.
The webbing works great as a hinge, won’t rust, shouldn’t poke you, works great after a few dozen flexes to loosen the fabric epoxy bond.
(Addendum to the webbing as hinge. After several different methods of trying the webbing as hinges on the boat, the one that works best is using a light coating of epoxy thickened slightly with cabosil and put on one side of the hinge and then put in place with a very light pressure to allow the epoxy to bond. Put a shower curtain between the hinge and weight to make sure if any bleeds through it doesn’t bond your weight.)
The anchor locker is in, the cutout in the front is spaced so that the U bolt in the bow fits in without a hitch.
We finally moved the boat to our garage after the flood. There was no problem with Jeff’s place but we did want to bring the dinghy home so there was less traveling to work on it. Gas is a bit pricey these days.
Bonnie called this stage the camouflaged stage. I sanded it and did a skim coat with epoxy and a lightweight fairing compound that is almost a chocolate color when mixed. After the skim coat dried I sanded it again and this is the result.
It was a really hard to see what was in need of surface work. The clear epoxy made it look like I had a really ugly place to fix but if you closed your eyes and felt it with your fingers you couldn’t find the problem. So it was time to give it a quick coat of paint to hide the underlying “texture” and bring up the really finish issues. I still have to attach the keels so I can’t paint the bottom.
A sanding of the white paint showed the worst of our problems after that I gave the whole boat a clear coat of epoxy with a little thickener just to reduce the sags and let it dry.
The sanding brought up a reasonable finish, it will never be perfect but as long as it isn’t too bad It should be fine.
The twin keels had to be added before any painting could be done at the rear of the hull. I had a fairly large piece of A1200 Corecell left from the transom so I figured I would try using it as the keels instead of oak as I was planning. I mounted the keels and covered them with three coats of fiberglass and epoxy to help with chafe.
As the keels were going on I started to do the fine fairing of the hull and started painting the bottom.
The hull needs another coat of paint but it is just about done. There is still a little bit of fine fairing that needs to be done around the keels but one more coat and that should be it. I keep debating if I should put antifouling on the bottom. Probably not now but I might later.
After doing a little work with the finishing and interior of the anchor locker. Mainly getting a place for the 4 lb danforth to set so that it will a stay in place. We put a PB fillet of filleting blend and put it on the areas where we want to secure the deck on the bow. We then lined up the bow and weighted it heavily.
After letting it dry we drew the area for the bow locker opening and then covered it with glass and weighted it to try to get a better fit to the round curve. The interior bulkheads have the first layer of white paint to bring up my surface deficiencies.
The floors aren’t painted yet and I haven’t decided if I will. I plan on painting them with Deckolay. The same paint used on Millennium Odyssey’s decks as non-skid
We ran another conduit down the starboard side from the hold to the rear starboard corner. There is a knee there which is more of a hand hold for lifting than a real knee. Below the knee is were the wires emerge for the stern nav light and the wires for the depth sounder. We have decided to put the bilge pump in the starboard locker with a sufficiently large limber hole to allow lots of access for water. We will put a corner under the knee to hide and protect the wires. We still have to do the real knees for the transom.
The next step was to install the rub rails and deck pieces for the hold. They were joined and shaped before putting them on the hull to make it easier and a better fit
I finished glassing up the top. All of the excess wire int the hold belongs to the depth sounder.
The vertical surfaces are done with Krylon high gloss white, and the horizontal surfaces are done with “Snow White” Decolay. Both paints are high on the VOCs, but also are nice in that by the time I was all the way around once I could practically go around again doing a second coat.
I didn’t do a “Filling” layer of clear epoxy on the decks and it left me with a linen texture. After several coats of Decolay with a high gloss foam roller the linen texture was still there and I think it will be a wonderful nonskid, SOB to clean though.
Bonnie did a good job with “Simple Green” and cleaned up Millennium Odyssey’s decks this spring
The knees are in. They are set wide enough that a five gallon tank should fit nicely between them and with a bungy cord between the knees they should lock it in place. The inside of the lockers aren’t painted yet as you can see from the pass-thru for the oars. Should do that locker. Epoxy doesn’t like the UV.
Our last dinghy was named “THAT” because as soon as we arrived a boat for a visit the person you say “You’ve got THAT dinghy!” It was a conversation piece, custom built to exact specs. It was a oddity.
The new dinghy was built to be carried on the stern of the “new” boat (not yet built or fully designed yet.) We’ve been working on it most of the winter and it is almost done. I was hoping to get the new one done before launch but it didn’t make it, so THAT dinghy was pressed into service for another year.
This weekend we planned on moving the boat from the river to Douglas Harbour. We had a lot of stuff to take with us so we figured the best thing was to dinghy out to Millennium Odyssey and bring her to the dock and then load the stuff on. Well, it didn’t quite work that way. We got ourselves into the dinghy and motored out to the boat and pulled along side. The motor was stopped, Bonnie had stood up and had a hold of Millennium Odyssey, I stood up and my foot went through the Lexan window in the bottom of the dinghy. Needless to say the dinghy was sinking fast! Bonnie was near the gate and I was near the shrouds for the mizzen. I went vertical and was on deck before my knees got wet! The dinghy sunk out from under Bonnie leaving her with one hand on a shroud and one on a stanchion post.
I pulled her aboard and she was soaked to the waist but other than a sore rib, nothing seriously wrong. We started the engine and went after the dinghy which was barely afloat. The air trapped in the top of the locker kept it afloat long enough for us to grab the tow rope and bring it along side. We towed it, mostly underwater, to the dock where a bunch of friends were there to give us a hand.
We did get the dinghy towed ashore and up on land. The motor was still attached and we were able to get it restarted after a little work. “That” dinghy got loaded on the back of the truck. We borrowed a dinghy and proceeded on down to the lake. The rest of the trip was uneventful, except we had to drain the water out of the carb again on the little motor.
We arrived home with “That” dinghy in the back of the truck. We backed up to the garage and got out. Bonnie took a forlorn look at “That” dinghy and at the new dinghy sitting in the middle of the garage. She walked up to it and pointed to it so that the new dinghy would know she was talking to it “You’re UP!”
Sounds like a great name to me!
After flipping it upside down we started to work on the support for the rub rail. I was thinking of using the 1 inch nylon rode we use for moorings as the rub rail but decided to try the 5/8 yellow poly we use for mooring bridles instead. The set backs and the support should work for both if we decide to change it. After using the dinghy this weekend I might change it over to the nylon.
The set back for the first piece is about 1/4 inch. The second piece has a half round cut out and the half round joins at the base of the curve and arches outbound to come back to the same level as the deck.
She is all done but the tweeking. The oars needed to be adjusted for the new dinghy and it put the collars in exactly the hole in the locker so it has to be enlarged a bit. The depth sounder needs to be attached to it’s support a little better.
All in all I’m pleased.
She rows surprisingly well.
A 2.5 hp motor will almost make it plane with one person on board.
It is heavier than we wanted but it is 150 lbs for a 12.5 ft tender.
Bonnie and I can sit looking forward comfortably as we explore and having a depth sounder is a great tool on the dinghy.
We can put more stuff in it than we ever should.
It is a dry dinghy.
IT is TOO BIG but it is comfortable.
The bow took enough pounding that the anchor support had given way and the danforth scraped up the locker a bit. I covered the locker with kevlar and did a better job with the support.
It has worked well since June 2008