Playing with molds

[erikgreen]

I thought this might be of interest to more people if I didn't bury it in my main build thread.

I am in the middle of a complete rebuild of my 1981 Sea Ray 210. I've essentially dumped everything but the lower part of the fiberglass hull and I'm rebuilding her into a sort of center console layout.

As part of this, I need to replace part of the top cap... basically I just intend to extend the sides of the hull up to a sheer line, then except for the first 6 feet in the bow (which is the foredeck area) I will put an approximately 6 inch wide gunwale top on the sides.

I considered (in another thread) several different ways to do this. I ended up deciding to try forming a mold against the side of the hull with MDF, then reinforcing it so it wouldn't move with a wooden skeleton assembled in place with hot glue.

Here's what I did today: First, I trimmed the existing boat side on the starboard bow to a flat top that was coplanar (flat) with the rest of the side down to the first chine. I had already removed the flange from the cap/hull joint because leaving it there would have forced me to have a vertical top panel, which wouldn't work.

Trim line:

After trimming, I fit the MDF to the hull. I had calculated that I wasn't going to add even two full feet to the height, so I cut a sheet of MDF down the middle and got set up to create a 12 foot long mold.

Using my extend-a-clamp(tm) 2x4s, I held the MDF in place while I drilled a hole at one end through the MDF and hull, then put a screw in through a piece of wood on the outside and into a block on the inside to hold it there. Then I leveled the MDF appropriately, moved the clamp to hold it in place, and did it again. I moved down the hull ensuring the MDF followed the curve exactly.

Front 8 feet done... now for the extra 4 feet (I decided to try for about half the side of the hull).

The reason it looks uneven is because I had to angle the front sheet downward to match the curve of the hull. The old bow had one of those dropping noses you see on a lot of modern boats... very hard to stand on, and I didn't like the look. So I placed the sheet to permit me to correct that, which left the back edge going up diagonally. I trimmed the second sheet to fit as closely as I could and attached it the same way as the first.

I started forming the reinforcement with a pair of "stringers".. 1/4" plywood set on edge the long way. I had rough-cut the ply to match the curve of the MDF fairly closely, so I could bridge the gaps this left with small pieces of ply:

I was attaching the ply with hot glue... I bought a new harbor freight $20 glue gun and a pack of the 12 inch "industrial" glue sticks. Let me say, they work VERY well. I assembled the rest of the structure using scrap plywood, off-cuts, basically any small piece I didn't have another use for:

It looks like a pre-teen's first wood shop project, doesn't it?

It's fairly solid, though. After all this work I needed to try to remove it.. I braced it as well as I could with spare boards, removed the screws and....

(next post)

 

[jspano]

Re: Playing with molds

man you've been thinking alot!!!
i try to stay ahead of my restore in my head
i've had times where i wake up from thinking about my restore.

looks good!!!!!

 

[erikgreen]

Re: Playing with molds

Yay! It came off without too many problems... it actually fell a couple feet to the floor before I got it stabilized in my arms. Bit unwieldy, it weighs about 50 lbs or so I think:

As I stood there looking at it on the truck I suddenly remembered... I hadn't marked the level of the existing hull! Without that I couldn't accurately figure out where to mold the edges of the new part or how high to make it... since I was considering adding an edge for the transition to the gunwale tops I needed that. I measured the screw hole to edge distance on the boat, thinking I could match that and come up with a line... but I realized the "right thing" to do was to put the mold back on and mark the line.

That was when the fun began.

Just as I was getting the mold in place I felt it "tear"... like MDF breaking. I hurried a bit and my neighbor stopped by to chat at just the wrong/right moment... not knowing what I was doing he actually did some more damage trying to push the mold in place against the boat side. But then he held it until I got it back in place with the screws on it.

Then I had to repair what had torn... the hot glue is great stuff, and I had used an entire package... but the MDF wasn't as strong, and the skeleton ripped away from the MDF here and there. I did an ok repair though, and got the thing off the boat and back on the truck, this time with the line in place.

Next step, move it to my high-tech fiberglassing facility:

AKA my garage (detached.. the boat itself is in the attached garage).

I have it here suspended between a pile of tires and an old workbench. The framework is pretty solid, but I still had to reinforce it with some staples... since I have to fair the joint anyway they weren't a big deal.

After the staples were in I glued (with gorilla glue, I was out of hot glue) another piece of MDF behind one side of the joint to make a backing for the filler. Then it was bondo time:

...and that's where it's at now.

Total time to this point is about 7 hours nonstop (ok, about 45 min for lunch).

What I have to do next is sand the bondo, do a last check for holes and bumps, and then I can try to attach other parts in order to get my gunwales into the mold, or I can just go ahead and lay up the panel.. either way I have to figure out first how high it's going to be and mark that, and pre-cut glass to fit.

But... after going through all that, I tried to remember why I was pulling the mold off and moving it to the garage. To save time? To make the layup easier?

If you look back at the pic where I put the first 8 foot mold section on the boat, the MDF is smooth, exactly in place... basically I could have stopped there, waxed it, and laid up the panel in place. Then I could remove the MDF, overlap the joint outside and inside, and repeat 5 more times for the rest of the hull (assuming I did 8 feet at a time, which seems easiest?)

Hmmm.. now I'm wondering if I'm making this much harder than it needs to be... I could take a page from Oops' book and just strap the molds to the boat and lay up the part. No fooling around with hot glue, support skeletons, staples, or filler.

I'm going to have to go back and read my other thread to see if I can figure out why I didn't do that instead. *sigh*

Comments and thoughts very welcome... I'll pick this project up tomorrow again.

Erik

 

[erikgreen]

Re: Playing with molds

Thanks!

I think I've overthought this part about 5x though myself I keep waffling back and forth between ideas and techniques... I think the thing is, I needed to actually try something to see how it worked... the more I think about what I did today the better I feel about abandoning it and trying again the other way...

Erik

 

[jspano]

Re: Playing with molds

i know how you feel, i was trying to find a pc of alum for my transom skin(see my thread) and after find some and going to buy it finding out it was sold. i found a place that works with metal fabing and scored a pc i needed. marked it out and had to make the cuts... my mind was racing a mile a minute trying to see if i missed anything. measure 2x cut once hasn't always worked for me. LOL

 

[erikgreen]

Re: Playing with molds

I took it slower today... then got sidetracked by the need to build an enclosure for my garbage cans (no lie... stupid city ordinance) which absorbed most of my time today. Beautiful weather though.

All I got done was the cutting/sizing of new MDF for the mold... this time I'm going with a 16 foot section (PITA to move around) and I pre spliced it with liquid nails. It's sitting by the boat now, and tomorrow I'll wax it before lifting it into place and attaching it with screws. Then I can start layup of the forward 16 feet on the starboard side of the boat.

I found a good way to do a nice thick layup and save some cash... I remembered I'd bought fiberglass scraps by the pound on ebay a while back, and I still had some. 32 oz biax with 2 oz mat attached builds up thickness very quickly... I'll use that instead of a core. As long as I can come up with cash for the resin, I'm golden. The only problem is with this stuff I have to pre-wet it in a tray before putting it in place... it's too thick to wet easily if I don't do that.

More pics soon.

Erik

 

[jonesg]

Re: Playing with molds

Theres a problem, if you pull a part from that mold it will be backward or inside out. You'll end up with the rough surface out.
The smooth surface will be on the wrong side.

Thats why I said just use the hull as the mold and pull parts right off the hull.

 

[ondarvr]

Re: Playing with molds

You shouldn't need to pre-wet it and then put in place, just use a fuzzy roller, it shouldn't be too hard.

 

[erikgreen]

Re: Playing with molds

Theres a problem, if you pull a part from that mold it will be backward or inside out. You'll end up with the rough surface out.
The smooth surface will be on the wrong side.

Thats why I said just use the hull as the mold and pull parts right off the hull.

Not sure what you mean... if I used the mold I pulled off the boat, then smooth surface would be outside?? At any rate, I think I'm going to use the in-place molds. I have a plan for getting the whole thing done with two helpers this Sunday.


Ondarvr, you don't think it'll be difficult to wet out properly? That stuff is heavy as heck, and I sure don't want to miss a full wet out in that particular location. I've bought a six pack of short nap fuzzy rollers for this, plus I've got my aluminum rollers ready to take out bubbles.

Erik

 

[ondarvr]

Re: Playing with molds

You should be able to get it wet out with a fuzzy roller, just don't be afraid to really put some resin on it and start by doing a shorter section so you can get the feel for it.

 

[erikgreen]

Re: Playing with molds

Okay, I'll be giving it a try.


I'm all set to glass this on Sunday... I have a full length mold on the starboard side of the boat, all trimmed to height and supported enough to glass. I'm going to pre-cut the glass tonight and roll it onto PVC pipe sections for easy application.

I have two friends coming over to help with this. Hopefully it won't take more than a couple hours.

I'll be waxing the mold with 2 layers of partall #2 and spraying 2 layers of PVA on top of that, probably saturday night.

Layup schedule will be:

2 layers 1.5 oz mat
1 layer DB1200 cloth
1 layer 1.5 oz mat
1 layer DB1200 cloth
1 layer 1.5 oz mat
core layer - 3208 cloth/mat
1 layer 1.5 oz mat
1 layer DB1200

If I see I want more thickness at this point I'll add another layer of mat/cloth if I feel like it. When I have the thickness I want I'll glass in some small glass tabs on the bottom edge to help hold the panel in place when I remove the mold.. I wouldn't want it to crack the joint.

I thought about overspraying with PVA to let it harden (I'm using unwaxed poly resin) , but I don't think I need to do that... it'll have time to harden anyway.

I might roll a layer of peel ply over the last fiberglass to prep it for more reinforcement.

After mold removal I'll glass along the joint inside and outside with tape and epoxy before fairing the outside and installing reinforcing members on the inside.

Watch for pics here,

Erik

 

[erikgreen]

Re: Playing with molds

Phew.

I was too tired to take pics last night, and I didn't remember to do it during the work either - I was short on helpers.

One of my friends and I did the glass layup starting about 1pm Sunday and finishing about 5:30pm. I had hoped for three people, but schedules collided.

I used the mold setup as I described above... I had a mold along the whole starboard side, although I had to cut it off short at the bow a bit because I ran out of room.

I waxed the mold and buffed with a cheap car polisher from harbor freight. Wax was partall #2. Then I sprayed PVA with a cheap HVLP sprayer. Two coats, and I had masked off the top edge of the lower hull to ensure I could stick glass to it (at least a short section.. I'm going to clean/grind and reinforce with epoxy tabs).

Then I rolled on (didn't want to try learning my new gel coat gun then) a layer of duratec surfacing primer. Went on nice and thick.

After that I waited for my help to arrive. I had pre-cut all the glass and rolled it around PVC pipe, and I labeled it with green tape. I had a five gallon pail of poly plus about a half gallon can too, and enough MEKP to catalyze it. I used a syringe to measure.

We started out by coating the duratec after it cured to the touch with a thin layer of poly. That went ok, but the duratec alligatored a bit probably due to an incomplete cure. No worries, that I can fix later.

For tools we used two roller handles and about 2 fuzzy short nap covers each, plus four or so 4 inch chip brushes.

We started after the initial poly coat by ripping off small bits of mat to run along the bottom edge, to ensure the corner had some glass in it. We were going to do our best to butt the new glass against the old edge, but to make sure it was solid there we did this.

We ended up going with two layers of mat, then cloth, then mat. At this point we'd used over two gallons of resin, and we took a break to let the first few layers kick so we didn't have them moving around or putting a lot of heat into the later layers.

After a half hour we went back to find the old layers hard to the touch.. basically to the "leather hard" stage. We were working in low 70s F temps, so I'm wondering if we should have cut back on MEKP some.

We spread a new thin layer of poly on, then applied the "core" layer - this was made from scraps 2-3 feet long of 3210 biax fabric I bought in bulk. Thick, thick stuff. It took a ton of resin to wet out, but it went on ok.

After that because we had to get adhesion to the cloth side of the core, we put a mat layer on, losing the sequence I'd prepared. Then we did another cloth layer, and another partial mat layer in the widest part of the hull, and called it quits. At this point I'd noticed that we were matching the thickness of the hull in the center of the panel, and also that we were down to about a gallon of resin. I could have cut more mat and finished all the layers off, but I'm going to reinforce all this with 1-2 layers of cloth and epoxy anyway, so we stopped. Final layup:

Mat-mat-cloth-mat-core-mat-cloth with another partial mat layer.

Total thickness is about 3/8 inch for the most part.

We tried to butt all the layers against the edge of the old hull for adhesion, but some had little gaps and some had overlap. After a two or so day cure I'm going to go back and clean up the inner edge with a grinder, then apply some tabbing between old hull and new panel with epoxy before I remove the mold. After that I'll remove the mold, de-wax and de-PVA, clean the outside up with a sander and overlap a couple cloth layers there.

The joint and new panel will need some fairing work, but not too much hopefully.

I'll be doing the port side panel hopefully this weekend.. the next few weekends after this are booked, so I'm short on the big chunks of time I need to do things like this.

I will need to mold or produce a top surface for these side panels with a step on it, so maybe a 6-8 inch wide strip. I might mold that or I might build it in place with panels, I'll see. That's after I finish the sides, bow, and aft corners.

I'll take pics during the port side work so you can see all the mistakes I make.

I'm going to get two five gallon buckets for the port side for insurance, and I also have some things to mold, like the corners where the transom meets the sides and the stem where the side panels meet the bow.

All in all, it was a lot of work but so far it looks like it went well. The removal of the mold will let me see.

Erik

 

[erikgreen]

Re: Playing with molds

Okay... so, here's some pictures that go with the above mass of wordy text

Edit: Fixed rotated pic

First, here's a pic of me putting the mold on the boat. It's basically secured with screws on the bottom third, the part that overlaps the existing hull. The screws go through a washer, a piece of 1x2 that forms a stiffener for the mold, and then go through the hull via a pre-drilled hole and into a piece of 2x4. When tightened up the mold echos the existing hull curve.

Note the rope to help pull the panel into place for the first screw. At this point (in the pic) the panel is attached partly at the bow of the boat.

Skipping ahead in time, here's what the mold looked like after glassing. You can see we overlapped the top edge some, so trimming will be needed. The shape of the sheer line is basically horizontal from the level of the transom forward about half way, then a quick increase to about 6 inches higher and a gradual increase all the way to the bow.

The reason the width looks uneven is that we're compensating for the varying height of the lower hull edge... remember the original hull had the "droop" in the bow.

The bow area I ran out of space to go all the way to full height, so we had to stop a bit early. I'll have to mold the rest of the bow at another time, which is ok since I'd have had work to do there anyway to join the two side panels.

The bulkhead there is the back of the foredeck area.. it drops down to the height of the mid-deck over the fuel tank, so I'll be installing some stair steps there. I should have thought through installing it too.. it was a pain to work around it for the panels.

De-molding went very well... the mold came off easily once the screws and supports were removed. The duratec surface is as smooth as the MDF was, and looks lined up exactly with the original hull:

Very little resin leaked through between the hull and mold.

The varying gray and black areas on the duratec are places I haven't cleaned off the PVA parting film yet.

Next step for this panel is to clean off the PVA and grind and clean the inside surface of the joint some, then I'll be reinforcing the joint with some layers of DB1200 and epoxy. It's strong as heck already, even though it's a butt joint with poly, but I don't want to take chances.

If I'd thought it through farther I could have skipped the duratec since I'm going to glass over part of it, but oh, well... it was a good test of the stuff.

We're going to do the other side this weekend, so I'll be spending saturday getting the boat moved over and leveled, getting molds on and in position, and prepping.

Looking good so far.

Erik

 

[jonesg]

Re: Playing with molds

ok it makes sense now.
I thought you were going to make a mold with those sheets of brown stuff then pull the mold off and then lay up on the brown stuff, but you did actually do the layup directly on the hull.

Because the curve is so slight it looks like you could just do a flat layup without using the hull.

 

[erikgreen]

Re: Playing with molds

Yeah, I thought about both of those. But removing the mold was just too much work, and I wasn't sure I could do a flat layup with the thickness I wanted and the curve the hull has.

I also wanted to include a core until recently, which made the flat layup idea impractical.

Anyway, I did lots of waffling back and forth, but now I'm more confident about molding larger parts. I think I'm going to do some seat boxes the same way, plus I need to mold a bow section and some corners for the transom.

Erik

 

[jonesg]

Re: Playing with molds

What you'll find is pin holes because theres no gelcoat, I think its the resin venting gas .

Pre-painting works if you can find a paint that doesn't curdle or orange peel.

I used 2 part epoxy paint to spray a mold then glass and poly resin, it worked out decent.
Poly doesn't stick to epoxy but the epoxy stuck to the poly because it wasn't fully cured when I started adding cloth and poly resin.

One way you can core your molding is to omit the wood backer sheet, lay the glass up onto the hull and add the core ( whatever you decide to use) then a couple more layers of mat and cloth over it, it will be rigid when you pop it off. With the core you'd be able to use less glass overall.

 

[ondarvr]

Re: Playing with molds

You don't need to worry about using epoxy to glass the two sections together, the polyester will work fine.

Had you overlapped the hull on the inside when you glassed the new section you would be done now, well at least with that part. You can still do it on the other side though.

 

[erikgreen]

Re: Playing with molds

Heh.. I don't know that I trust poly to grab onto the old glass that hard... I'm sure it would work, I'm just not sure I'd get that warm fuzzy that an epoxy joint gives me - Call me dogmatic.

No pinholes on the first side, I used duratec to surface it so it came out nice and smooth. Kind of a waste though because I'm going to apply a couple layers of glass over it to join the gunwale to the side to the lower hull once it's all put together. I also need to install some C-beam type boxes to stiffen the sides.. I'll mold those out of poly too.

I broke my camera friday, so no pics for a while - I have to figure out how to pay for a new one.

But we did get the second side of the boat done on Sunday, so that's good. Similar thickness of layup but I used 1708 this time to save some effort. One layer mat, then 1708, then a layer of super-thick 3210, then two more layers of 1708. That matches the hull thickness where it's thinner amidships.

I still need to mold the bow once I get the whole thing outside... no room in the garage for that. Right now there's a two foot wide gap right at the bow where the sides don't reach.

Next up I'll be molding the transom corners, joining the transom to the new sides, and finishing the deck inside. With the new hull panels the thing looks biiiiig.

I still have a ways to go... finish the transom, finish the deck, build seats, build the gunwales and foredeck, mechanicals install, console... but it's coming along.

Pics when I can,
Erik

 

[ondarvr]

Re: Playing with molds

Modifications like this are done frequently in custom or semi custom shops, only the ones that need very high performance and a low weight tend to use epoxy for it. Even very large boats (Yachts) are extended using just the standard products, so if you get in a bind and need to use polyester, you don't need to be worried about it.

 

[erikgreen]

Re: Playing with molds

Must....hold on... to... epoxy....dogma......eep!



Actually, I'll probably mix poly and epoxy (not literally) within projects in the future... the poly does quite well for almost everything. So I can save the epoxy for working with carbon fiber, or for making a really light structural part or something...

Erik