Fiberglass spider cracks

[Byrnerc]

All,
Researching the repair of crazing, a.k.a. spider cracks in gelcoat in this forum yields the same results as other on-line sources; fill and paint or buff. Few address the underlying problem that the fiberglass is flexing. I've seen on my boat the return of cracks and a long-time marina owner confirmed my observation that the cracks usually do return. My common engineering sense tells me that the only reasonable way to fix the problem would be to fill with a flexible filler and paint with a flexible paint. Of course, the flexible paint will not have the durability of a hard epoxy paint. Also, there is the challenge of applying a filler to the cracks that are so thin that the task of grinding them wider is necessary.
I'm thinking of using a flexible epoxy thinned down to water consistency, if a product can be found, with a one-part paint over top.
Any comments, suggestions?
R/
Ross

[cram]

Where are the cracks? Are they indicative or an issue that needs to be fixed? ( Incorrect rigging tension, previous collision not properly repaired, ...?)

Gel coat is somewhat flexible and easy to repair.... Not sure why you'd change to paint or epoxy.

I'd the cracks came back, there's probably something to fix that is causing the flexing.

[GordMay]

The most common method for thinning epoxy is using solvents, such as acetone, MEK, or denatured alcohol. However, for every 5% of thinner you add, your epoxy might lose up to 35% of its strength.
You can heat most epoxies, to make then thinner, but heat will also dramatically reduce pot life, so be ready, your 30 minute epoxy, once warmed up, may only give you 5 minutes.
Or, you could use a [so-called] “penetrating” epoxy, like "Captain Tolley's Creeping Crack Cure".

[Hudson Force]

I've used West System G Flex Epoxy for applications such as this. I had good results; however, I don't have direct experience comparing different applications.

[Byrnerc]

Thank you, all, very helpful comments.
Cram, the cracks are all over the deck and cabin top but more in the areas of stress such as the winches, main trolley, mast, and gunnels. The boat is a 35 year old Cape Dory, well built but aging. They are not indicative of one problem area but the whole deck getting tired. So, you feel that opening cracks and filling with gelcoat is the best?

Doesn't sound like thinning epoxy will work but I'll look into G Flex. I like the idea of flexing since I'm not going to solve the root problem.

[cram]

Pictures ? ? ?

[MicHughV]

When I see cracks appear, I throw the boat away and get a new one.

I get picky like that

[Byrnerc]

Photos coming in a day or two.

The bank disapproved of MicHughV's method.

[Byrnerc]

PHOTOS:

[deblen]

https://captaintolley.com/


https://www.amazon.com/Captain-Tolle.../dp/B003T6EJ9A


https://www.boat-renovation.com/capt...e-full-review/




CAPT. tolleys creeping crack cure

[Sun and Moon]

Is there a wood core in the underlying deck? If so, I'd check to see if it is rotten and that's what is causing the flex. Fiberglass itself doesn't just "age-out".

[Byrnerc]

Thanks Deblen, Capt.Tolleys is what I am looking for, low viscosity, high flex. It's ordered.
I hope it's not wood under, doesn't feel like rotten wood but you got me thinking!
R

[Hudson Force]

When looking at your photos, I don't see what I am accustomed to seeing as "spider cracks". I've always associated spider cracks as relatively small areas radiating out from a center stress or impact point. These areas usually have the small cracks radiating out to end points that can be drilled to a shallow point in the gel coat to prevent further spread. The cracks can then be slightly opened with a small file of crease of sand paper before filling and adding a cosmetic finish.
The long parallel cracks covering large areas are not familiar to me. I would be wary of something more of a problem than spider cracks.

[GordMay]

From a much earlier [2004] discussion:
“GELCOAT CRAZING and HAIRLINE STRESS CRACKS”

The mechanisms causing gelcoat crazing are always STRESS and MOVEMENT. Movement in one form or another can have a number of causes. Many times the cause of the movement can be determined from the pattern of cracking.

There are a number of types of cracks that are evidenced in gelcoat, and each type may signify a particular problem, or set of problems. Various crack configurations may indicate the underlying causes, and are vital in troubleshooting the problem. In some cases, the root problem has nothing to do with the gelcoat, and is a manifestation of a structural problem, or unanticipated movement of the substrate.

Radial Cracks:
Usually associated with impact, radial cracks are a good indicator of the direction of the impact. The classic "spider" crack is a result of a reverse impact or sharp, localized stress riser. A frontal impact is indicated by a concentric circle pattern, with the diameter of the inner circle having a relationship to the size of the impacting object.

Linear Cracks:
There are two groups of linear cracks: stress field patterns, and parallel stress cracks. The primary cause of these cracks is flexural strain. However, in the case of stress field cracking, either structural elements, or local stress risers, modify the parallel pattern, into a more complex structure.

Parallel stress cracks indicate flexural movement, perpendicular to the direction of the cracks. Parallel curvillinear cracks often indicate a distribution of stress over a supported panel surface. If the surface is restrained in two 90-degree planes, the flexural strain will "fan out," creating a "palm leaf" effect.

Parallel stress cracks radiate from a localized nucleation. The main effect is the deflection of the laminate inward, toward the restraining member. The parallel stress crack is interrupted by a stress concentration around a point.

Convergent stress field cracks may result, when flexural strain is interrupted by a structural member.

Divergent stress fields occur, when the laminate is deflected away from the supporting member, and the crack propagation is consolidated through a localized lack of movement.

Thermal fatigue Cracks:
Thermal fatigue cracks are a result of repetitious expansion and contraction of the gelcoat film. Whether in a parallel pattern, or an isotropic (nondirectional) configuration, thermally induced cracks are characterized by short discontinuous sections, and are usually grouped in forming in a dominate stress field.

Isotropic thermal cracks are a result of the surface expanding, and exerting a tensile strain within the gelcoat film, in a unidirectional fashion.

Parallel thermal fatigue cracks usually are propagated by expansion of the surface, in conjunction with localized flexural stress.

Form stress risers:
This type of crack is a result of an intervening shape, usually a cutout, in the surface of a panel. The form or shape serves to concentrate strain, into a localized area.

In the case of a hard point riser, a low-level strain may result in cracking, due to high-level stress concentration, in a very small area. A square shape with sharp corners is a prime candidate for creation of a hard point riser.

A radial riser may have a different origin. In this case, often a bolt or hardware fitting, exerts a tensile force in the area, around a hole. The edge of the hole distends, causing a tensile failure of the gelcoat in the surrounding area.

[cram]

Originally Posted by Hudson Force

When looking at your photos, I don't see what I am accustomed to seeing as "spider cracks". I've always associated spider cracks as relatively small areas radiating out from a center stress or impact point. These areas usually have the small cracks radiating out to end points that can be drilled to a shallow point in the gel coat to prevent further spread. The cracks can then be slightly opened with a small file of crease of sand paper before filling and adding a cosmetic finish.
The long parallel cracks covering large areas are not familiar to me. I would be wary of something more of a problem than spider cracks.

Concur..... took me a while to consider how to reply after seeing the OP's photos. These are not what we would consider spider cracks.

Cracks occur naturally in small areas due to aging, point stresses (impact, insufficient backing plates) or mixing/application errors. These are usually quite local.

I've attached an example.

The long cracks you have are indicative of either a complete failure of the gel coat application (possible, but rare), hoisting the vessel incorrectly, or stresses beyond what the hull was designed for. These can be caused by rigging problems, water intrusion in deck/hull, etc....

I'd suggest paying a shipright to assess to help determin cause and possible remedies. This could be more than a cosmetic problem and simply repairing the gelcoat or painting could cause the cracks to come back immediately.

Wooden core above the waterline is very common. Is there any flex or soft spots in the cabin top or deck? Is there any brown stains anywhere inside the cabin?

At a minimum, I suspect this would require removing all the deck hardware, removing the gel coat and starting over with gelcoat or paint. Or just live with it, it's an old boat.

However you choose to proceed, a paint or gelcoat repair will require removal of all the deck hardware, not a small task. This often leads to finding loose fasteners, minor water intrusion, etc.... which need to be dealt with prior to fixing the top layer.

What is the boat's market value and what is it worth to you?