questions regarding old/new fiberglass tabbing for replacing sailboat bulkheads/etc

[sailormanbob]

Hi,

I'm currently prepping the inside of a fiberglass sailboat hull to install new plywood bulkheads, stringers, bunks, et cetera, and I have some questions regarding the prep work. I have grinded all of the paint off, on and around the area, but there is still some of the old fiberglass tabbing from the old pieces on the prepped area that I want to fiberglass the new replacement pieces on to (see middle picture... (old tabbing is green)). I sanded it, and made it somewhat tapered so there are not many abrupt ridges, but the existence of the old tabbing remains and makes the surface not completely flat, but somewhat irregular in places instead.



Questions:

I am wondering, if it is ok to leave the remains of the old tabbing and to fiberglass over them (middle picture (green tabbing), or do I need to grind it all off (top picture))?

Another idea, somewhere in between the two, is to use some epoxy with filler to level out the areas where the old tabbing meets the original hull, so that the new tabbing has a more smooth area to sit on (bottom picture (old tabbing is green, new filler is red)). is this a no no?




Any advice from people who know what they are doing would be appreciated. Thanks!

[Cheechako]

In most cases yes remove the old tabbing. You can probably cut the "upright" portion of the old tabbing off with a sawzall which will allow you to flex the blade a bit. Or the right grinder/cutting wheel will cut it off making a lot more dust. The tabbing on the hull can just be ground enough to remove any paint etc and give a clean glass surface to put the new tabbing over.
For a small non structural bulkhead, I suppose you could try to fit it into the old tabbing , epoxy (or use one of the new super glue products that come in a caulking tube) and clamp the old tabbing glass to the bulkhead.
I suppose that is viable anywhere with the super glues if the old tabbing is really nice and long. A good pic would help.

[sailormanbob]

Thanks for the response. The vertical parts of the old tabbing have all been removed, and only the flat horizontal parts are left. But they still leave the surface a little unlevel. Pictures are a good idea and I am going to go get some and be back to post them in a little. Thanks!

[Cheechako]

With the verticals gone, just grind the other parts aggressively down to fresh glass. Sure the smoother the better, but in reality, it probably wont make a heck of a lot of difference as long as you wet out the tabbing well.

[sailormanbob]

Awesome. I hope it is true. I am also wondering about how much the strength of the tabbing will be reduced if I just fiberglass over this stuff, due to the lack of conformity in the bend of the tabbing of a whole piece, and how it will possibly receive tension in more concentrated spots at the point where it is connected to the hull. Thanks again.

Here are some pictures if this helps anyone.

[Cheechako]

Hard to say but yeah that looks well done. The old tabbing sticks up a bit for sure above the lower surface where the bulkhead sits.... although you have rounded it off well. Why not just fill the low part with fiberglass prior to putting in the bulkheads making it level?
However, it is often said that the bulkhead should not sit firm onto the hull anyway. I think some builder put foam material between the bulkhead and the hull. (this eliminates "hard spots" and hull deformation. Maybe you should do that?

[Frankly]

Get an old wood chisel and try carefully driving it under the remaining old tabbing (don't gouge the original hull laminate). You should find that the inter laminar shear strength is not all that great, the old tabbing won't just peel off but sure beats all that grinding.

Hope you realize that there needs to be some space between the hull and bulkhead and the new tabbing should have some radius on it. If you make a tight joint might get a hard spot and crack in the hull after a hard slug to windward.

I always used a small foam spacer strip and then sanded a smooth fillet. Epoxy will give the best secondary bond.

[jimbunyard]

Originally Posted by sailormanbob

Hi,

I'm currently prepping the inside of a fiberglass sailboat hull to install new plywood bulkheads, stringers, bunks, et cetera, and I have some questions regarding the prep work. I have grinded all of the paint off, on and around the area, but there is still some of the old fiberglass tabbing from the old pieces on the prepped area that I want to fiberglass the new replacement pieces on to (see middle picture... (old tabbing is green)). I sanded it, and made it somewhat tapered so there are not many abrupt ridges, but the existence of the old tabbing remains and makes the surface not completely flat, but somewhat irregular in places instead.



Questions:

I am wondering, if it is ok to leave the remains of the old tabbing and to fiberglass over them (middle picture (green tabbing), or do I need to grind it all off (top picture))?

Another idea, somewhere in between the two, is to use some epoxy with filler to level out the areas where the old tabbing meets the original hull, so that the new tabbing has a more smooth area to sit on (bottom picture (old tabbing is green, new filler is red)). is this a no no?




Any advice from people who know what they are doing would be appreciated. Thanks!

If the old tabbing is well adhered you can grind it relatively smooth and just glass over it. If you can pry it up with a chisel or screwdriver you need to remove it. The glass in the photos looks good, so it is probably well adhered...

You can and should level the surface where the bulkhead seats. Most people will tell you to use colloidal silica (cabosil) or milled fibers or some combination of the two, I just use glass bubbles mixed with whatever resin I'm using. As noted above, epoxy will give the best secondary bond, but good quality polyester is acceptable and adequate. The ratio should be such that the putty has the consistency similar to peanut butter.

The bulkhead should be seated into a bed of this putty, and a filet or radius should then be made in the putty between the hull and the vertical bulkhead to ease the joint and allow the fiberglass to conform to the bend more easily.



Here's a video showing some good practices;

https://www.youtube.com/watch?v=Drc6zdlLGY0

A picture showing a couple of variations of filets for different applications, on some stringers rather than bulkheads, but the principle is the same...

[Terra Nova]

Originally Posted by jimbunyard

...people will tell you to use colloidal silica (cabosil) or milled fibers or some combination of the two, I just use glass bubbles mixed with whatever resin I'm using....

Very poor tech. Microballoons have extremely poor strength and should only be used for final fairing before primer application, NEVER under structural fiberglass.

[sailortype]

and again, as mentioned above, the bulkhead (or hard filler underneath it) should not be in direct contact with the hull. It creates hard spots and the constant flexing over the hard spot will eventually fatigue the structure of the fiberglass. A 1/4" foam insert with 45 degree angles cut into it makes a good filet to smooth out the bend of the tabbing cloth.
On my previous boat, this was not done and when it was hauled you could clearly see the hard ribs all along the hull

[Cheechako]

Originally Posted by sailortype

and again, as mentioned above, the bulkhead (or hard filler underneath it) should not be in direct contact with the hull. It creates hard spots and the constant flexing over the hard spot will eventually fatigue the structure of the fiberglass. A 1/4" foam insert with 45 degree angles cut into it makes a good filet to smooth out the bend of the tabbing cloth.
On my previous boat, this was not done and when it was hauled you could clearly see the hard ribs all along the hull

Yep, that's the OP's easy solution too.... doesnt need to level out those areas, just put the foam in and go.
It's easy to find boats done in the marina prior to this technique being used. There's an old Cat 34 right at the base of the dock ramp by me with a obvious hard spot on the side imaging the bulkhead placement.

[sailortype]

yup that should work.
As an aside, I am amazed at how tough this stuff is... everywhere you read, it tells you how tough epoxy is and how polyester does not adhere well to plywood, poor secondary bond etc. I have recently taken a couple of old boats apart and am installing new bulkheads in my own Ericson... I defy anyone to get the 40 year old tabbing off the plywood quickly or easily. It will hang on like grim death and you need a jack hammer to remove it. The damage is water from above via the chainplates, not delamination. I have always been an epoxy kind of guy but I am definitely starting to wonder.

[Cadence]

Originally Posted by sailormanbob

Hi,

I'm currently prepping the inside of a fiberglass sailboat hull to install new plywood bulkheads, stringers, bunks, et cetera, and I have some questions regarding the prep work. I have grinded all of the paint off, on and around the area, but there is still some of the old fiberglass tabbing from the old pieces on the prepped area that I want to fiberglass the new replacement pieces on to (see middle picture... (old tabbing is green)). I sanded it, and made it somewhat tapered so there are not many abrupt ridges, but the existence of the old tabbing remains and makes the surface not completely flat, but somewhat irregular in places instead.



Questions:

I am wondering, if it is ok to leave the remains of the old tabbing and to fiberglass over them (middle picture (green tabbing), or do I need to grind it all off (top picture))?

Another idea, somewhere in between the two, is to use some epoxy with filler to level out the areas where the old tabbing meets the original hull, so that the new tabbing has a more smooth area to sit on (bottom picture (old tabbing is green, new filler is red)). is this a no no?




Any advice from people who know what they are doing would be appreciated. Thanks!

If you feathered out the old tabs don't worry about it. However feather all edges.

[NevisDog]

I see some poor advice has been offered here, including that Sail video.
1. Best practice is never place the ply bulkhead in contact with the hull, always place it on top of a foam section to avoid hard spots on hull.
2. Best practice is drill holes or slots along edge of ply and feed glass tape thru to mechanically anchor bulkhead.
Before commencing rebuild work, I recommend you read the chapter in 'This Old Boat' by Don Casey. Better to get it right first time.

[ramblinrod]

Originally Posted by NevisDog

I see some poor advice has been offered here, including that Sail video.
1. Best practice is never place the ply bulkhead in contact with the hull, always place it on top of a foam section to avoid hard spots on hull.
2. Best practice is drill holes or slots along edge of ply and feed glass tape thru to mechanically anchor bulkhead.
Before commencing rebuild work, I recommend you read the chapter in 'This Old Boat' by Don Casey. Better to get it right first time.

Actually, I disagree with the foam between bulkhead and hull. Instead, I recommend solid FRP between bulkhead and hull, but with substantial fillet and
Radius to the tabbing.

The more are the load is distributed over the better, and load is not ditiributed by foam.

Sorry about typos, trying
To
Do
This with POS iPhone.