Stress cracks!?

B

bncwaite

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C Dory Year
2006
C Dory Model
16 Cruiser
Vessel Name
Roe Boat
Well after a good clean up Saturday I noticed quite a few stress cracks along both sides of my gunnels. I contacted C-Dory and am waiting for a response but my question is this. My boat seems to be riveted along the gunnel where all the cracks are appearing. I searched thru the all the albums of 16's and I can't find anyone else who has these rivets like mine.

I'm trying to figure out why these rivets are there. Here's a pic of the problem area outlined in RED:
http://img122.imageshack.us/img122/7868 ... 002gz6.jpg

Any ideas?

Brandon
 
I don't have any in the area you outlined but if you go to the forward end of yours and up over the curve onto the gunnel below the start of the window I definitely have one. I think they are pretty common in areas that get stress, like corners. But yours are another matter entirely, can't imagine what could be causing them in that location.
 
lloyds,

So you do you have the rivets in those areas too? I'm trying to figure out if these rivets came from the factory or the dealership.
 
I'll have to check this afternoon after work and let you know. I don't recall seing any. I will get back to you. Inside the cabin, where the screws and washers are holding the liner against the hull, I had three of those pull out immediately after I bought the boat. The factory sent me some longer replacements so I replaced them and added some extras, but I don't have confidence it will be enough in the long run.
 
It might help if you had a real close up of the cracks and a rivet. It may be that the gel coat was not relieved before the screw hole was drilled. Some people use a counter sink, turning backward--or even just a little counter sink before drilling a full size hole. This tends to relieve any stresses in the gel coat and prevent stress cracks or chipping of the gel coat.
 
I do have rivets, and surprisingly I also have some gel coat crazing. Port side forward rivet has cracks radiating around the top of the rivet about the size of a baseball, and a couple other places as well. I don't think it is anything serious, but a little unsightly. I am surprised the gunnels took that kind of stress.
 
I see two types of stress cracks--the ones nearest the pop rivet which radiates out from the hole, and the flexion cracks on the upper part.

I would see how much this area flexes--if it flexes a lot, I probably would back up this material.
 
Backing it up would seem to be one heck of a project. There are a few folks that know real well what is behind there, like Dave, but it is beyond anything I want to try. I am guessing the flexing is vertical, maybe caused by someone like me who is a little larger than average stepping down onto the gunnels hard. You would have to brace the gunnels vertically to prevent that. I am just going to live with it. I wonder if you could shoot those with gelcoat and get them to fill? Probably just show up again though. The big one I have at the corner where gunnel joins cabin top has been there since the first rough water a couple years ago and hasn't changed.
 
Well I just got off the phone with Bret from the factory and he told me just to take it to my dealership and the gel coat will be repaired. :thup Gotta love these C-dory's. 8)

I know there isn't anything structurally to worry about. Its all cosmetics but it sure is an eyesore to me now that I know they're there.

Thanks for the help lloyds/Bob. :wink:
 
Bob... whatever the reason for the rivets' installation, by their very nature, they concentrate forces in a small area. Fiberglass's strength is in great part due to it's spreading of forces over a broad area. When these transient forces meet a rivet, it creates concentrated force "turbulence", like a windstorm of forces inside the glass and that's where your stress cracks are coming from.

John
 
I don't think I will even bother. My dealer was les on whidbey island. That is about a five hour drive one way. And I have to believe that they will repair them and they will just come back. Seems like you would have to take the rivets out and do a structural bond, without rivets, to make it work. That is a lot of work for gelcoat crazing.
 
John,
Your are absolutely correct. Beefing up this would most likely mean removing the rivets, laying more layers of glass and epoxy between the pan and gunnel, maybe stiffening up under the gunnel, either with glass or a core material--if is actually the gunnel which is flexing, rather than the attatchement of the liner. One could not tell without looking at the area under load--putting at least a couple of big guys on the gunnel, then on the floor, seeing if by leverage you can move the area which is stressed.

As for "repair" of stress cracks--if they are just surface cracks, due to too thick gel coat--which I doubt in this case--but not having inspected it I cannot be sure.--each crack needs to be "V" ground out with a dremmel tool, or all of the gel coat ground down and the entire area re gel coated.
This is not a simple spray on some more gel coat--if you do this, the stress cracks will recurr.

Getting back to Dr John's comment--If I found that there was flexion, I would put wet glass/epoxy between the liner and down turned lip of the gunnel and then clamp the joint until the epoxy hardened--then the load is evenly distributed. Pop rivets are only for very light loads--although I realize that some builders actaully put the hull to deck together that way, it is most likely to fail--and there had many examples of this type of failure.

In fact to take John's thoughts a bit further, one reallly does not want to use rivets where there are heavy loads--if you are tying two non load bearing fiberglass extrusions, that is a possiable use--like a cover over a pannel.
 
thataway":2fe9bhv1 said:
This is not a simple spray on some more gel coat--if you do this, the stress cracks will recurr.

Getting back to Dr John's comment--If I found that there was flexion, I would put wet glass/epoxy between the liner and down turned lip of the gunnel and then clamp the joint until the epoxy hardened--then the load is evenly distributed.
Click to expand...

I have an appointment for the 11th of April for service and will see what their gelcoat repair guy says. I simply don't want the area re-sprayed. I'm going to suggest the wet glass/epoxy method that you suggested and see what they say.
 
Before you go to the dealer for the repair--get a couple of good sized people to stand on the gunnel and then step down on the floor/liner--try and move the area which has the stress cracks. This will give you a lot more information for the dealer. If it is flexing--then he needs to know that---and take appropiate actions.
 
I did send off an e-mail to EQMarine Services, just to document the concern. I am going to wait and see if anything changes before I take it up there, or anywhere else. If the rest of you find out something which pins down the problem, and there really is a good fix, I may go to the next step. In the meantime I will keep enjoying the boat.
 
Brandon - I believe Lloyd is right about the gel coat crazing. it will probably come back.

I do not have the rivets or screws securing my side panels to the gunnel's. There is Styrofoam flotation between the panels and the hull that hold the panels in place, this way they are allowed to float. When they are riveted together, something has to give.

My theory is the glazing happens when there is a lot of weight exerted on the gunnel's like someone stepping down on them from a dock or a heavy person setting down hard on the gunnel's. It could also be from pounding in the waves.

I think the only way to solve the problem would be to remove the rivets then repair the glazing and not replace the rivets, let it float free as in the older boats..

The following photos show the area on my 16.

As you can see in the 1st photo the panel does not have any fasteners at the top, it is floating free and held against the gunnel's by the Styrofoam between the panel and hull.

P1210043.sized.jpg

The next photo shows the area in a cutaway cross section photo with the Styrofoam and panel removed

P1250018.sized.jpg

________
Dave dlt.gif
 
My boat has rivets but no crazing.
 
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