retabbing bulkheads on older FRP sail boat....
 

Advice and descriptions appreciated.
Courtney
--
s/v Mutiny
Rhodes Bounty II
lying Oriental, NC
WDB5619

retabbing bulkheads on older FRP sail boat....
 

On Mon, 07 Jun 2004 17:35:46 -0500, Courtney Thomas
wrote:
Advice and descriptions appreciated.
Courtney

============================================

I don't claim any special expertise but have done a few. First thing
of course, is to remove all of the old tabbing. I used sharp
woodworking chisels and a disk sander. Ideally you should insert a
thin layer of structural foam between the bulkhead and the hull if the
builder left a sufficient gap for that purpose (it eliminates a "hard
spot" on the hull which can lead to stress concentration). Next build
up a rounded fillet using expoxy thickened with microbaloons or
fairing compound. The idea is to create a curved surface with about a
1 inch radius which joins the hull and the bulkhead. Small, round
beverage bottles are frequently used to get the desired shape. Allow
fillet to cure and lightly sand. Next step is to apply unthickened
epoxy to the fillet and adjoining surfaces, followed by an application
of 3 inch glass tape, another coat of epoxy, and a second layer of
tape. Apply additional tape if needed for increaded strength.
Repeat all the above on other side of the bulkhead.

Broken tabbing is usually caused by hull panel flex going through
heavy seas, and can indicate that the original designer/builder did
not give enough thought to structural support. Consider adding more
panel support if feasible.

retabbing bulkheads on older FRP sail boat....
 

A couple of alternative suggestions:
Save the effort of sanding the fillet by laying he glass at the same time.
For a perpendicular bulkhead, the circumference of a 1" radius fillet is over
1-1/2", and 3" tape gives very little bearing on the hull or the bulkhead.
For such a fillet i'd suggest at least 6" tabbing glass. 6X the radius.
Miultiple layers should be slightly staggered or varying in width so they
taper out onto the panel. If the original tabbing failed, it didn't spread
far enough on the panel. Go further.
Woven tape will have half of its fibers running along the joint, contributing
nothing to its strength. I recommend 45-45 knitted glass. It has the added
joy of being more conformable to curved joints. For the final layer or small
work, bias-cut glass cloth is OK.
If the final finish matters, cover the last glass with peel ply and squeegee
it smooth. For curved joints, multiple pieces will be needed. THink of a
mason's step flashing.

"Wayne.B" wrote:

On Mon, 07 Jun 2004 17:35:46 -0500, Courtney Thomas
wrote:
Advice and descriptions appreciated.
Courtney

============================================

I don't claim any special expertise but have done a few. First thing
of course, is to remove all of the old tabbing. I used sharp
woodworking chisels and a disk sander. Ideally you should insert a
thin layer of structural foam between the bulkhead and the hull if the
builder left a sufficient gap for that purpose (it eliminates a "hard
spot" on the hull which can lead to stress concentration). Next build
up a rounded fillet using expoxy thickened with microbaloons or
fairing compound. The idea is to create a curved surface with about a
1 inch radius which joins the hull and the bulkhead. Small, round
beverage bottles are frequently used to get the desired shape. Allow
fillet to cure and lightly sand. Next step is to apply unthickened
epoxy to the fillet and adjoining surfaces, followed by an application
of 3 inch glass tape, another coat of epoxy, and a second layer of
tape. Apply additional tape if needed for increaded strength.
Repeat all the above on other side of the bulkhead.

Broken tabbing is usually caused by hull panel flex going through
heavy seas, and can indicate that the original designer/builder did
not give enough thought to structural support. Consider adding more
panel support if feasible.

retabbing bulkheads on older FRP sail boat....
 

Cutting slots in bulkhead would weaken it. Instead, the objective is to get a
ggood bond to the face of the panel.

Peel ply is a nylon or dacron taffeta fabric which is used to impart a better
finish to wet-layup composites. After the resin cures, it is peeled off, hence the
name. Leaves arelatively flat. bond-able surface with no amine blush. It's
available in small quantities from Aircraft Spruce . Tape is a woven selvege-edge
glass cloth. Available 2-6" wide in a variety of weights.

"structural foam" such as core-cell is available in quarter-sheet quantities from
Defender . While a foam cushion/fillet between a bulkhead and a hull is a good
idea for new construction, I don't think i've ever seen someone retrofit same.

What is meant by "panel support" [bulkheads ?] ?


Courtney Thomas wrote:

Thanks to all.

Does anyone have comments on....cutting slots in the bulkhead and
tabbing... from hull... through slot... onto hull again ?

What is "peel ply" ?

By "tape" I'm assuming you mean cloth, to be imbedded.

Source of "structural foam" ?

How might "panel support" [bulkheads ?] be best implemented ?

Most appreciatively,

Courtney

Jim Conlin wrote:

A couple of alternative suggestions:
Save the effort of sanding the fillet by laying he glass at the same time.
For a perpendicular bulkhead, the circumference of a 1" radius fillet is over
1-1/2", and 3" tape gives very little bearing on the hull or the bulkhead.
For such a fillet i'd suggest at least 6" tabbing glass. 6X the radius.
Miultiple layers should be slightly staggered or varying in width so they
taper out onto the panel. If the original tabbing failed, it didn't spread
far enough on the panel. Go further.
Woven tape will have half of its fibers running along the joint, contributing
nothing to its strength. I recommend 45-45 knitted glass. It has the added
joy of being more conformable to curved joints. For the final layer or small
work, bias-cut glass cloth is OK.
If the final finish matters, cover the last glass with peel ply and squeegee
it smooth. For curved joints, multiple pieces will be needed. THink of a
mason's step flashing.

"Wayne.B" wrote:


On Mon, 07 Jun 2004 17:35:46 -0500, Courtney Thomas
wrote:

Advice and descriptions appreciated.
Courtney

============================================

I don't claim any special expertise but have done a few. First thing
of course, is to remove all of the old tabbing. I used sharp
woodworking chisels and a disk sander. Ideally you should insert a
thin layer of structural foam between the bulkhead and the hull if the
builder left a sufficient gap for that purpose (it eliminates a "hard
spot" on the hull which can lead to stress concentration). Next build
up a rounded fillet using expoxy thickened with microbaloons or
fairing compound. The idea is to create a curved surface with about a
1 inch radius which joins the hull and the bulkhead. Small, round
beverage bottles are frequently used to get the desired shape. Allow
fillet to cure and lightly sand. Next step is to apply unthickened
epoxy to the fillet and adjoining surfaces, followed by an application
of 3 inch glass tape, another coat of epoxy, and a second layer of
tape. Apply additional tape if needed for increaded strength.
Repeat all the above on other side of the bulkhead.

Broken tabbing is usually caused by hull panel flex going through
heavy seas, and can indicate that the original designer/builder did
not give enough thought to structural support. Consider adding more
panel support if feasible.



--
s/v Mutiny
Rhodes Bounty II
lying Oriental, NC
WDB5619

retabbing bulkheads on older FRP sail boat....
 

On Tue, 08 Jun 2004 14:50:12 GMT, Jim Conlin
wrote:

What is meant by "panel support" [bulkheads ?] ?
==========================================

Anything to provide additional hull stiffness and support; could be a
long shelf, additional framing under the V bearths, etc.

I once stiffened a flexible hull area by laminating vertical strips of
structural foam to the inside with epoxy and glass cloth. The whole
thing got covered by thin horizontal wood strips and looked quite
respectable.

retabbing bulkheads on older FRP sail boat....
 

Thanks to all.

Does anyone have comments on....cutting slots in the bulkhead and
tabbing... from hull... through slot... onto hull again ?

What is "peel ply" ?

By "tape" I'm assuming you mean cloth, to be imbedded.

Source of "structural foam" ?

How might "panel support" [bulkheads ?] be best implemented ?

Most appreciatively,

Courtney




Jim Conlin wrote:

A couple of alternative suggestions:
Save the effort of sanding the fillet by laying he glass at the same time.
For a perpendicular bulkhead, the circumference of a 1" radius fillet is over
1-1/2", and 3" tape gives very little bearing on the hull or the bulkhead.
For such a fillet i'd suggest at least 6" tabbing glass. 6X the radius.
Miultiple layers should be slightly staggered or varying in width so they
taper out onto the panel. If the original tabbing failed, it didn't spread
far enough on the panel. Go further.
Woven tape will have half of its fibers running along the joint, contributing
nothing to its strength. I recommend 45-45 knitted glass. It has the added
joy of being more conformable to curved joints. For the final layer or small
work, bias-cut glass cloth is OK.
If the final finish matters, cover the last glass with peel ply and squeegee
it smooth. For curved joints, multiple pieces will be needed. THink of a
mason's step flashing.

"Wayne.B" wrote:


On Mon, 07 Jun 2004 17:35:46 -0500, Courtney Thomas
wrote:

Advice and descriptions appreciated.
Courtney

============================================

I don't claim any special expertise but have done a few. First thing
of course, is to remove all of the old tabbing. I used sharp
woodworking chisels and a disk sander. Ideally you should insert a
thin layer of structural foam between the bulkhead and the hull if the
builder left a sufficient gap for that purpose (it eliminates a "hard
spot" on the hull which can lead to stress concentration). Next build
up a rounded fillet using expoxy thickened with microbaloons or
fairing compound. The idea is to create a curved surface with about a
1 inch radius which joins the hull and the bulkhead. Small, round
beverage bottles are frequently used to get the desired shape. Allow
fillet to cure and lightly sand. Next step is to apply unthickened
epoxy to the fillet and adjoining surfaces, followed by an application
of 3 inch glass tape, another coat of epoxy, and a second layer of
tape. Apply additional tape if needed for increaded strength.
Repeat all the above on other side of the bulkhead.

Broken tabbing is usually caused by hull panel flex going through
heavy seas, and can indicate that the original designer/builder did
not give enough thought to structural support. Consider adding more
panel support if feasible.




--
s/v Mutiny
Rhodes Bounty II
lying Oriental, NC
WDB5619

retabbing bulkheads on older FRP sail boat....
 

For quick and dirty where the tape is intact, only delaminating from the
wood and tape/hull join was still good Don Casey described the following:

- separate the tape from the wood fully with a flexible putty knife
- vacuum the slot clean
- apply 5200 into the slot; keep the slot open with a wedge ahead and
force the glue down with a thin "pusher" behind
- apply short sheet metal screws every 4" or so to pull joint closed;
optionally install screws over a batten
- remove screws when glue is dry

As I recall, he said the boat was still good 2-3 years later.

Rufus


Wayne.B wrote:
On Tue, 08 Jun 2004 14:50:12 GMT, Jim Conlin
wrote:


What is meant by "panel support" [bulkheads ?] ?

==========================================

Anything to provide additional hull stiffness and support; could be a
long shelf, additional framing under the V bearths, etc.

I once stiffened a flexible hull area by laminating vertical strips of
structural foam to the inside with epoxy and glass cloth. The whole
thing got covered by thin horizontal wood strips and looked quite
respectable.

retabbing bulkheads on older FRP sail boat....
 

All good advice but I would use biaxial tape. With woven tape, you
waste 50% of the fiber.
Biaxial is also easier to use: it takes the radius much better.

Get biaxial tape at BoatBuilderCentral.com.

Jacques from bateau.com