New project 1971 proline flatback. First decision engine bracket.

[Conrad4784]

That sucks.
IMO, to save time and effort, I would take a sawzall and cut the transom skin out instead of trying to repair it. I'd remove the Plascore knees between the transom and the Plascore inner transom (to give you some working room) and then grind everything down to prepare for new glass.
Next I would plan leaning a sheet of melamine against the aft of the boat, clamp it to the hull and then use that as a mold to build your new perfectly flat transom from the inside. You can spray the inside with PVA mold release or wax the inside so the melamine is easy to get off.
3 layers of 1708 is enough overlapped on the sides and bottom at least 3", 6" and 9" (4,8,12 is normal). Then glue/clamp in the new transom core and finally add 3 more layers of 1708 to the inside. Now you'll have a solid transom. You'll have a little fairing to do on the outside along the edges but that will be easy.

Using the melamine sheet is how the previous owner did the transom that s why the outside looked so flat.  I believe the inside is rock solid and it was just the first coosa board that didnt get clamped down good enough to the exterior skin he made.  I'm going to drill out the drain hole to see if there is a gap between the two coosa boards at the bottom.  If there isn't I'm on the fence on ripping it all out.  Either way it will be a lot of work whether its more fairing or more glassing.  Structurally it seem solid as its sitting right now but I'm no glass expert.   

[RickK]

Working the transom core in from the outside and then laminating an outer skin without going around the outsides of the hull, to tie it in is tough work, requiring a lot of fairing.  That is why I suggested the sawzall approach.

[Conrad4784]

Working the transom core in from the outside and then laminating an outer skin without going around the outsides of the hull, to tie it in is tough work, requiring a lot of fairing.  That is why I suggested the sawzall approach.

I hear you, thank you for the info, I will most likely have to go that route.  Hopefully i can sand the glass off the other side of the coosa and reuse it.

[Ulysses485]

On second thought, I’m with Rick. I would remove the core and salvage it if possible, and build it with a MDF mold. Do it once. I think the piece of mind down the road would be worth it alone.

I’m making a complicated mold on my 240 to eliminate any and all fairing that I can. A flat MDF board mold across a transom to build from is the way to go.

[Conrad4784]

So I got back to work on the project and cut the transom back out.  I started sanding the gelcoat on the inside of the transom to see the glass.  On the small part exposed the glass work looks like it bonded well.  Seems the previous owner just didn't get the coosa put in place quick enough and not enough pressure to bond it to the exterior skin.  I plan on grinding down the inside glass on the coosa just enough to verify there is not bubbles or voids, if its okay I'm going to leave the poly on the inside.  The exterior facing part of the coosa I'm going to use some thickened poly to fill a few dips i grinded and make sure its perfectly flat.  I'm going to attach a piece of waxed mdf to the back of the boat and build it back up again like yall suggested.  How do you attach the board to the back of the boat?  Screws and grind them off on the inside?  Also while in the transom is out I'm going to cut some access holes and mount some deck drains to be plumbed to scuppers.  I bought a glass leaning post on facebook and plan on glassing in a livewell/seat where the cooler sits in the pictures.  I will need to move the electrical pvc and console forward 7 inches leaving just enough space in the console to mount two house batteries.  Moving it forward will give me apporx 14inches of space between the console and leaning post.  Yall think this is enough?  behind the leaning post I will have 3 feet behind the livewell.  look at the pictures and tell me what yall think, I'm all ears if yall have anything you might do differently. 

[Conrad4784]

couple more pictures

[RickK]

What kind of space do you have behind that bulkhead? You'll need about 18" of working space and be able to grind to raw glass along the sides and bottom in prep for new glass. I would gently cut out the bulkhead (so you can re-use) so you gain the working space you need. lay a 1x2 or 2x4 across the top of the hull sides and secure with screws/wood blocks to keep the hull shape - do this about 2 ft from the rear of the hull. Usually, you use an overlap of cloth in a 4,8,12" or 3,6,9" overlap to tie into the sides and bottom. You should do the same once the core is in and to tie it into the sides and bottom.
To attach the melamine you can glue blocks of wood to the outside of the hull and screw through the melamine and into the wood blocks to secure the melamine tightly against the opening. You'll use the melamine to form a dam to create the new 3 layers of 1708 skin. Then when you're done you can chip the wood off and grind/sand the contact points fair.
If you are going to try to salvage the Coosa core I would feel better grinding the glass off totally, then you know the condition and can laminate to it in confidence. A cheap harbor freight 7" grinder with 24 or 36 grit wheel will make quick work of removing the glass and gelcoat/paint.

[Conrad4784]

I can grind fine from the outside laying glass from the inside with the bulkhead there would be a pain.  I have 11 inches at the bottom and around 18 up top.  I do have a question once I lay the glass for the exterior skin are people laying an additional couple of layer in between the cutout on the back of the boat so when you put the coosa there wont be a gap.  If that makes sense.  I have 2 inches of the original exterior skin that is probably a little less that 1/4 inch.  The coosa runs the full length of the transom seems like there would be an gap unless when you sandwich you put a ton of thickened poly.  Or do you cut down the coosa to fit inside the perimeter of the original exterior skin I left?  I've tried to find some videos of someone doing a transom this way with no luck. 

[RickK]

The normal lay up is mix some thickened resin (chopped strand, cabosil or wood flour to a peanut butter consistency) and use a rounded tool, like a wooden spoon or you can make your own from a stir stick, etc. Use the tool to load the corners all around so there is a rounded corner (hull sides and hull bottom where the melamine meets the hull.
Before you start the "fillets" you want to have 3 layers of 1708 already prepped - lay a 1x2 across the top of the transom and drape the 1st layer of 1708 and then trim it so that you have the overlaps that you need 3,6,9 or 4,8,12 - your choice and your choice if you lay the smallest or the largest overlap first. Then spring clamp the 3 layers of cloth to the 1x2 and flip them out of the boat.
Now run the fillets and let them just start to kick, not harden. Mix the resin while you're waiting. As soon as the fillets start setting up, wet down the melamine with resin, flip the first layer of glass into the boat, wet it in with a short nap roller and hard roll it to squeeze the resin through, Repeat for the other 2 layers of cloth. You are doing this "wet on wet". When the glass hardens lightly scruff the top layer of the glass to get it ready to install the core.
Make sure you dry fit the core material where it will fit to see if you need to round off the rear most corners so they will fit and snuggle into a fillet you'll apply in the next step. To set the core for the transom 1) add a fillet of thickened resin and 2) usually you use a 1/4" notch trowel and trowel on thickened resin onto the new transom skin and then clamp the core in. I would also fill in any gaps around the core and hull bottom and hull sides and let everything harden. Next you'll be scruffing up the front of the core, prepping 3 more layers of cloth and repeat the same process you did to laminate the new outer skin.
So lets say you use the 3,6,9 overlap method, then add a 2" core and repeat the 3 layers with 3,6,9 overlap you are now out into the hull about 20+" with the glass work. You'll have a rock solid transom but it takes some room in the prep.

[Tampa Bay Mike]

I can grind fine from the outside laying glass from the inside with the bulkhead there would be a pain.  I have 11 inches at the bottom and around 18 up top.  I do have a question once I lay the glass for the exterior skin are people laying an additional couple of layer in between the cutout on the back of the boat so when you put the coosa there wont be a gap.  If that makes sense.  I have 2 inches of the original exterior skin that is probably a little less that 1/4 inch.  The coosa runs the full length of the transom seems like there would be an gap unless when you sandwich you put a ton of thickened poly.  Or do you cut down the coosa to fit inside the perimeter of the original exterior skin I left?  I've tried to find some videos of someone doing a transom this way with no luck.

I laid three additional layers of 1708 in the cutout area when I raised mine from a notched 25" transom to a full height to bring it flush with the existing skin. Then I did three full layers overlapping the bottom and sides - coosa - and three final layers on the inside. It's the same principle with yours except that your "notched area" is pretty much the entire back of the boat since it was all cut out. I would think that if you don't want to go that route then you could taper in a few layers to a foot or two to make it a smoother transition. Or maybe a combination of a taper plus one or two layers.

I can't imagine you'll want to do this a third time so the investment in the extra work and glass now may be worthwhile.

[Conrad4784]

I can grind fine from the outside laying glass from the inside with the bulkhead there would be a pain.  I have 11 inches at the bottom and around 18 up top.  I do have a question once I lay the glass for the exterior skin are people laying an additional couple of layer in between the cutout on the back of the boat so when you put the coosa there wont be a gap.  If that makes sense.  I have 2 inches of the original exterior skin that is probably a little less that 1/4 inch.  The coosa runs the full length of the transom seems like there would be an gap unless when you sandwich you put a ton of thickened poly.  Or do you cut down the coosa to fit inside the perimeter of the original exterior skin I left?  I've tried to find some videos of someone doing a transom this way with no luck.

I laid three additional layers of 1708 in the cutout area when I raised mine from a notched 25" transom to a full height to bring it flush with the existing skin. Then I did three full layers overlapping the bottom and sides - coosa - and three final layers on the inside. It's the same principle with yours except that your "notched area" is pretty much the entire back of the boat since it was all cut out. I would think that if you don't want to go that route then you could taper in a few layers to a foot or two to make it a smoother transition. Or maybe a combination of a taper plus one or two layers.

I can't imagine you'll want to do this a third time so the investment in the extra work and glass now may be worthwhile.

I Definitely don't want to do it again.  I was thinking about doing the same thing adding a few extra layers. thank you

[RickK]

Three layers is usually enough, especially if you use epoxy. 3 layers with poly is ok too. Then core, then 3 more layers.

[Conrad4784]

I am to the point were I have everything ground down with 36 grit, blocks are glued, and melamine is ready to mount.  I want to check the factory specs for the width of the transom at the top but I cant find the info.  Seems like it might be a little narrow at the top after the coosa was cut out but I dont have any Specs to compare.  If anyone has this boat will you measure the top width of you transom please and let me know the dimensions. thank you

[Conrad4784]

I went ahead and started glassing the transom.  It was hard to tell if the back shape was perfect with the small waves going down the boat because the cap is off the boat id assume.  Having kids and not knowing how long I will get to work on the boat I bought laminating resin that is supposed to stay tacky where you can just start glassing the next layer with out sanding.  I laid one layer on the melamine and sandwiched to the the back of the boat using thickened poly with fibers.  Well I just checked and the glasswork i did is hard as a rock and not sticky at all. Damn I thought I was done sanding for at least a day.  Ive been thinking about it for hours and the only thing I can think is the wax I used on the melamine hardened the laminating resin.  Have any of yall had this happen?  I'm going to test a small amount tomorrow and see if it stay tacky or hardens.  Im going to try to lay all the other glass in one go. I have three full layers 4,8,12 and two more to go between the cut out, to build it some, to get a flatter surface for the coosa to bond to. But you never know with kids, weather, and life in general if I can do it in one go hence the laminating resin.

[Ulysses485]

Although it might be laminating resin, that doesn’t necessarily mean it doesn’t have wax. The boatyard polyester resin from FGCI is considered a laminating resin (up to 1/8”) but typically contains wax and will cure tack free (their literature call it a non spec resin that may or may not contain wax). However, it’s hard to read the bottle you have but from what I find online it looks to be made without wax.

Regarding the layup, your best adhesion especially when going with poly is going to be wet on wet so you have a chemical bond and mechanical bond. It’s hard to tell from your precious post but did you layup a layer flat on a table of melamine and then bring that to the boat to bond to transom corners? Most I’ve seen set the melamine against transom and layup till the outer skin is done. Then bond the core into a bed of thickened resin to eliminate any voids or hard spots while also filling to create fillets so it’s close to ready for layup of structural tabbing to inner hullside/bottom.

Just my thoughts..