Advice please - GRP cracking. Any experts out there?

[thefatlady]

GRP cracking

Boat: Sunseeker Camargue 47. This is an exceptionally nice specimen with a couple of concerns for me, of which this is one.

History: The current owner was not aware of the cracks when he bought it. The gelcoat has been ground out and re-done by the first owner - I don’t know why. It looks to me like a very poor job, but I am more concerned with what may lie beneath. The deck feels solid underfoot (with both myself and SWMBO loading it) and does not feel as if it has a structural problem. The present owner has been told that if it is re-done, the cracks will return. I am trying to find out the deck construction.

The cracking looks consistent with flexing of the deck – lines of cracks perpendicular to the direction of maximum tensile strain at the outside. The centre should be under compressive strain and less likely to crack. Makes me wonder whether there are glassed in transverse stiffeners which are coming away at the ends.

However, there is another odd characteristic, perhaps just indicative of crap gelcoat. The cracks are not continuous and are associated with lines of discolouration in the gelcoat. Apologies for all the photos, but I hope they show the problem.

I am speculating that the deck surface was damaged, perhaps by dropping something heavy on it, and then badly repaired. I may make efforts to find the first owner and ask.

I would really appreciate any comments from anyone with knowledge of such things.

Piccies:

Piccy 1: The foredeck centre section has cracks (outlined) on both sides running along the edge and radiating in towards the centre. The blob at the bottom by the date is my toe.

Piccies 2 and 3 show close-ups of each side.

Piccy 4 shows a detail of the transverse cracks. Note the discolouration lines. The cracks appear to run alongside the discolouration lines and where they cross, there is a discontinuity in the crack. In some places, there is discolouration beyond the end of the crack and where there is no crack, suggesting that the discolouration may be a precursor to the cracking.

Piccy 5 shows another detail of the edge. Note the short broken cracks. They stop at the edge of the textured area. Looks like shrinkage cracking, but then, why not all over?

 

[bigwow]

It looks like stress cracking to me, are you sure the horizontal part between the two verticals is supported enough., does it flex when walked on?

 

[PCUK]

Classic stress cracks. If the floor is beefed up underneath and the gelcoat repaired properly it shouldn't happen again. It is not a serious structural problem, just poor design.

 

[Dipper]

I have no technical experience of boat building or boat repairs other than those I have carried out on my own boat so please treat my comments accordingly!

I think the answer to your problem lies under the damaged section of the deck. From the symmetrical positioning of the two crazed areas directly opposite each other it looks like there is a similar problem either side or that the problem extends horizontally across the deck at right angles.

As has been mentioned, perhaps the deck is not properly supported below allowing it to flex excessively although you can’t seem to make this happen under your own weight.

Another alternative (and I could be totally wrong) is that there is a bulkhead (or other support) under that point which is putting pressure on the deck. It might be that in a slamming sea, the bulkhead is pushed up into the deck. If the deck is poorly fitted, not bonded properly or otherwise under strain then these forces could be transmitted upwards resulting in the crazing. This may explain why you can’t make the deck flex under your weight.

Whatever the cause, the answer lies under the deck.

 

[thefatlady]

Thanks for comments so far. Answering all:

The deck does not appear to flex at all with two people walking on it.

There does not appear to be a design fault, but it may be a quality control problem. I have owned one of these boats before and I have looked at seven this time around. This is the newest one. No other one has had this problem.

Interesting point about the bulkhead, but there is no wall or other support that I can find underneath to support the deck at that point. That point is over the ceiling of the forward cabin.

I agree that the problem appears to be in the deck itself and I do realise that it is not structural to the boat. I have already asked for manufacturer's drawings showing the construction and I have a number at Sunseeker to ring on Monday. I suspect that the deck is balsa cored grp, but the positioning of the cracks suggests that there is some internal stiffening at that point.

The discolouration and the intermittent nature of the cracks may be a red herring, but it is peculiar. Anyone seen it before?

 

[tcm]

i think the bulkhead for back of the anchor locker may be directly underneath? So the other bits can flex, not than bit, and standing either fwd or aft causes the cracks. Not super-serious really imho. The gelcoat is quite hard and brittle.

 

[powerskipper]

you need to try and have a look at the other side of this area, look for any movement of bulkheads or cracking of joined areas, check the anchor locker and under the bed, see if you can access the hull as well, take a good look and see if there is any cracking there, if worried get a surveyor to take a look.

 

[Deleted User YDKXO]

Agree with the others. The cracking is too symettrical to be the result of something being dropped on the deck IMHO. If there is no bulkhead underneath as you say, I wonder if it has occured as a result of the bow being stuffed heavily into a wave which would might tend to cause stress forces in the deck?

 

[[2068]]

It looks as if something is trying to push upwards and burst thru the deck (alien style). Somehow, you need to get a good look at what's underneath.

Also consider water intrusion: in a cored deck (most are) bizarre things can happen if water gets inside and goes round the freeze/thaw cycle a few times.

More history would help. Did this appear overnight? Over what period of time? What happened in between? Bouncy Weather or temperature variations? Summer or Winter?

dv.

 

[thefatlady]

The back of the anchor locker is well forward of the cracks.

I don't know how the boat has been used, but I had my previous one for four years and many thousands of miles and it took some very heavy weather and severe banging without any problems. This one appears to be generally extraordinarily well cared for.

I also have no idea how or when the cracking manifested itself - simply that it is there and has been cosmetically repaired once before.

I wonder whether water has got into the balsa core and is wicking up through earlier cracks to discolour the "new" gelcoat from underneath. The "new" gelcoat is then, not surprisingly, cracking in the same places.

 

[tcm]

did the repair use gel coat - it's on nonslip?

 

[thefatlady]

Looks like it to me. The new gelcoat also covers some smooth deck at the edges, but that has almost no cracking. They have very nearly matched the original texture, but, inspecting closely, there is enough difference to see that the whole centre section of the deck has been re-gelcoated.