Transom replacement- need glassing advice (caution - fun inside)

[hanslanda]

Got the second bay cleared. You can see how the stringer that was open to air dried within an hours compared to the still wet other side im still clearing in this picture.

 

[hanslanda]

Question for the masses.

My tabbing is almost rotted in some spots due to the combination of foam and loosely sprayed or layed chopped glass mat.


Would it be okay to cut certain sides of the stringers out in the mid section of the boat? Also i've been thinking about the problem of what to glass to. What if i snag some "Vinyl Foam: Divinycell 3 lb. Density"? It's foam board that should allow me to glass to it. Fiberglast sells it. I could cut sections of the foam board, contact cement them in place. Viola, glass over it, foam fills and still get the compressive strength of the foam expansion.


Is that an acceptable means of construction?

Next question is what should i use to build up to the old thickness? Multiple layers of chopped mat?

 

[Sleeper-6]

I would use the pour in expanding foam. Being a closed cell foam with no void spaces once it expands it will minimise the chance of collecting water in the future.

 

[hanslanda]

I would use the pour in expanding foam. Being a closed cell foam with no void spaces once it expands it will minimise the chance of collecting water in the future.

Oh I’m with you for filling the remaining void. I’m talking about using some 1” foam board to reconstruct the fiberglass walls I’m cutting out. Just as something to glass against and make a new wall. I definitely plan to pour after the new wall is in. I’m just wondering if it’s acceptable to use the foam board as a base for the fiber wall.

 

[JASinIL2006]

Are you talking about trying to reconstruct walls of the fiberglass stringers you're cleaning out? If so, I'd rebuilt the sidewall of the stringer by putting in something temporary (e.g., a section of plastic-wrapped plywood clamped in place) against which you can glass a new fiberglass wall, then remove and foam the whole thing as normal.

Using some sort of foam board, and leaving it in, would give me some concerns about adhesion of poured-in foam to the stringers. I think the more the below-deck structure functions as one piece, the stronger it will be.

 

[AShipShow]

you could use some stretchy cotton t-shirt fabric and stretch it over the tops of the stringers and hold it with spray adhesive... then saturate it with resin... once its cures, it can support the heavier layers that go on top. I would rebuild with 1708... Don't bother with CSM, it uses tons of resin and doesn't add much strength... I think 4 layers of 1708 over the top should be enough.

 

[kcassells]

Pc. of resined cardboard for the walls.

 

[Sleeper-6]

Oh I’m with you for filling the remaining void. I’m talking about using some 1” foam board to reconstruct the fiberglass walls I’m cutting out. Just as something to glass against and make a new wall. I definitely plan to pour after the new wall is in. I’m just wondering if it’s acceptable to use the foam board as a base for the fiber wall.

I was thinking more along the lines of leave the existing side walls in place and just pour the foam in where the old foam was. No need to reconstruct the entire stringer. Just trim the new foam to the height you need minus your planned glass thickness and cap it with new glass wrapped down the sides to bond with the old stringer walls.

 

[kcassells]

If they aren't compartmentalized at this point then you should consider that. SOOOOooooo if 1 gets compromised the rest are independent.
Oh yea once the cardboard is fitted and sets up all you need to do is glass it out to match thickness. Not a brainer.

 

[AShipShow]

I would make an effort to recap the stringers first and then pour in the foam... The edges of the foam form a kind of dense closed-cell skin that is highly resistant to water... Once you cut the skin off the foam, you open the core of the foam and open up cells that can absorb water.

 

[kcassells]

If you cut the foam as noted all you need to do is brush it out with poly or EEEppppoooxxxyyyy. Any way that's what I would do.

 

[hanslanda]

With some nice resin weather on the horizon i'm going to get into fiberglassing tomorrow. Here's a fun progress photo. All foam cleared. Boat is officially completely dry after 1 year of ownership. You'll notice i cut out all the pass-through's. This is due to rotten foam being trapped in with the chopped strand around the pvc tubes. This was present in many areas around the tabbing of the stringers. I will be grinding down some of the tab areas to lay a small fillet of chopped to reseal those areas. Glastron in-fact missed many areas where tabbing wasn't completely sealed. I would argue normal bilge water could have penetrated the stringers.

Up towards the bow, the foam was relatively dry. Only maybe the bottom 1-2" of the foam was saturated. Now towards the aft-end, especially near the transom, the foam was mostly saturated. My fear was the pass-through's were eventually going to pass water back to the foam, or the wet foam near the transom would invariably soak the transom again.

So here we are! 4-5 garbage bags of foam later. Around 100lbs of water/foam weight.

TRICK QUESTION

Did they use 2lb or 4lb. I'd use 2lb for displacement alone and i'd use 4lb for structural... but we have some debate on this yet. I'm leaning that this foam is indeed structural. At least from the aspect of having enough compressive strength to prevent the stringer from buckling in any direction as it absorbs loads.

 

[hanslanda]

Bow section done. This was vinyl. Ya'll sure weren't lying about CSM eating up resin. I built this section to have a .250 thick top and its tabbed in with around .125 all covered in veiling. I went with CSM specifically to replicate the thickness needed here. You can see i glassed in a section of ply where the seat supports sit. I don't know what this would have taken with an experienced person but i used up almost an entire gallon of resin on just that bow section. Granted they are by far the largest pieces. I figure a need for around another gallon for aft sections. They are much smaller but there's more of them.

So far i'm confident i am meeting the original build strength!

Going to work on grinding out and finish prepping the pass-throughs so when the new resin shows up i can begin that fun mess.

 

[sphelps]

I would be adding some 1708 multi layers . Csm doesn’t have hardly any strength..

 

[hanslanda]

I would be adding some 1708 multi layers . Csm doesn’t have hardly any strength..

The original didn't have any cloth as far as i can tell. Looks like clear resin even?

 

[hanslanda]

I would be adding some 1708 multi layers . Csm doesn’t have hardly any strength..

Since the 5 layers of CSM are already cured and done do you think adding 1708 is helping anything here and now? I can add something to the other areas but it didn't even occur to me cloth would be needed here.

Anyone have additional feedback around this one? Time is eating me and i'd love as much input as possible around this topic.

 

[kcassells]

Yup add the 1708, sphelps is correct.

 

[sphelps]

With cloth drying clear sometimes its hard to see the actual print of the cured cloth . It may just look like csm only ..
Csm is really just a binding layer for the cloth when poly is used . That and it is used to build thickness when needed . But not really for structural applications by itself ..

 

[hanslanda]

Roger that. I'll spend the next few days doing prep work since the weather isn't playing nice. Any idea what a layer of 1708 adds in terms of thickness? I have around 9ft of woven roving but that's for the transom, as it was the skin over the transom before i removed it.

I have some 1708 showing up monday.

 

[hanslanda]

Any build technique advice with 1708? It looks like 45/45 cloth with mat on one side. I would think i sand down the existing CSM surface i made... put the 1708 cloth-down mat-up.. maybe two layers of that. Call it a day.

Do you guys generally use 1708 for tabbing as well? Iv'e only planned to use CSM so far. I would love to hear some general purpose layering advice with 1708 specifically around tabbing.