Repairing crack in hull

[Chuckmeister]

G'day Gents,
After some searching I found a 5cm hairline crack in near the weld close to the keel. It's letting in about a bucket full after about 5-6hrs on the water. I want to get it rewelded but have heard that cracks can reappear next to the new weld on a stress area.

Is there anything I should know before setting off to get it fixed? I was tempted to seal it with sikaflex if it was going to be problematic but I'm not sure how good a job it would do.

Thanks in advance.

[snelly1971]

G'day Gents,
After some searching I found a 5cm hairline crack in near the weld close to the keel. It's letting in about a bucket full after about 5-6hrs on the water. I want to get it rewelded but have heard that cracks can reappear next to the new weld on a stress area.

Is there anything I should know before setting off to get it fixed? I was tempted to seal it with sikaflex if it was going to be problematic but I'm not sure how good a job it would do.

Thanks in advance.

Dont put sika anywhere near a crack, The bloody welder will kill you...It will make any future welding in the place where the sika has been spit and spat everywhere.., Just get a good tradesman who knows what he is doing to do the repair, and find why it cracked in the first place.

Mick

[gofishin]

What type of tinny (type, not brand), and where along the keel is the crack? As snelly says, do not use any sika or sealant or any kind. Depending on where it is, a crack along the keel is mostly caused by fatigue due to the bottom sheet flexing (or being allowed to flex). 95% of the time you will find that it is due to a rib not being where it should be, whether by manufacture fault or force - incorrect trailer setup/use over time/abuse). Photos, inside (floor up) & out would be good?

There is only one solution and that is too weld it up, but before you get to this you need to work out why it has cracked, else yes, it may very well come back

[trev1]

badly set up trailers wreck more alloy boats than anything else

[Chuckmeister]

What type of tinny (type, not brand), and where along the keel is the crack? As snelly says, do not use any sika or sealant or any kind. Depending on where it is, a crack along the keel is mostly caused by fatigue due to the bottom sheet flexing (or being allowed to flex). 95% of the time you will find that it is due to a rib not being where it should be, whether by manufacture fault or force - incorrect trailer setup/use over time/abuse). Photos, inside (floor up) & out would be good?

There is only one solution and that is too weld it up, but before you get to this you need to work out why it has cracked, else yes, it may very well come back


Firstly, thanks for the advice. It's a 5.6 bowrider. The crack is about 1m down from bow end of keel and right near a rib. I treat the boat kindly but not sure how it was treated in rough stuff by previous owner. The trailer has skids except for the central rollers. Interestingly though, where the crack is, is near a roller. Could be coincidence. See what I can do about photos.

Thanks

[Bros]

Firstly I would get in touch with the manufacturer as they would almost certainly have a procedure on repairing cracks and if they were a decent manufacturer they would be very interested in failure of one of their products.

It may require more than just welding they might suggest a backing plate.

After that the fun begins to find a good aluminum welder who can weld thin sheet.

[Chuckmeister]

Thanks for the replies.

Here are a couple of pics one each of inside and out.

Cheers

[Bros]

With the oxidization on the inside it makes it extremely important that the preparation is perfect.

[dnej]

chuckmeister,
That looks like it has been welded previously.
Give David a call at Riptide Boats at Springwood. Specialises in aluminium .I think it may need strengthening.
Rollers for the keel,and skids to stop the rocking wobble,of the boat is correct.

Sometimes however,some owners do not just snug up the skids,and there is too much weight on the skids.
David

[Dan5]

Mate the first photo show's some undercut alongside the weld this is where the crack would have most likely started from then travelled along the heat effected zone of the weld.

It's an easy repair as access to it look's reasonable,make sure a small hole is drilled at each end of the crack to help stop it traveling further before welding.

Go and find a good sheety's shop and get it repaired,a couple of hundred dollar's will cover it for sure,then fix the offending roller situation as said before trailer's are usually the culprit in cracked ally boat's.

Dan..

[gofishin]

...and right near a rib. ...where the crack is, is near a roller. Could be coincidence...

1st photo - some more detail (different angle) might shed some more light, but what’s alarming is that the rib does not look like it has been notched around the top of the sheet groove (keel extrusion), and hence the rib is sitting above/clear of the bottom sheet at the keel. Even though the sheet is stitch welded to the keel (they do this to help prevent fatigue cracking), if the rib is not contacting the bottom sheet it will eventually crack even if there is no abuse.

If you can take another shot from inside down close to the bottom sheet, looking along/forward to the rib (where the crack is) – i.e. showing the contact/gap under the rib. Also take the same for the opposite bottom sheet/other rib.


...where the crack is, is near a roller. Could be coincidence...

Possibly, however at this stage I put my money on sheet flexure being the major cause. Get under your trailer and try and twist all the keel rollers. If any are loose or tight (which this one may be) adjust as necessary so they all have even contact (preventing you from being able to twist any rollers by hand).


chuckmeister,
That looks like it has been welded previously.

Possibly, however it looks to me more like where the tigger has gone over and smoothed the weld where an original 50-75mm tack weld was. When the continuous hull weld runs over these tack welds, it can get a bit bulky and ugly. You should find similar tig weld ‘smooths’ every 500-800 along the keel & chine extrusions if you look closely.

Otherwise, what David has said about the skids having too much weight is 100% true, and can be bad for pressed ally hulls if the skids are carrying too much load.
cheers

[SunnyCoastMark]

Mate the first photo show's some undercut alongside the weld this is where the crack would have most likely started from then travelled along the heat effected zone of the weld.

It's an easy repair as access to it look's reasonable,make sure a small hole is drilled at each end of the crack to help stop it traveling further before welding.

Go and find a good sheety's shop and get it repaired,a couple of hundred dollar's will cover it for sure,then fix the offending roller situation as said before trailer's are usually the culprit in cracked ally boat's.

Dan..


Good advice Dan except maybe for he last paragraph. I would use the sheetys shop as a last choice - try to find a local ally boat builder first. - Apart from the obvious experience and ability to point out the cause (which a "sheety may not be able to do) they are already set up to TIG weld Ally which is what this job needs. A sheetmetal work shop may not always be set up for ally welding, which leads me to my next point:-

A couple hundred dollars is probably a bit much. There is about half to 3/4hr job there. Shouldn't be anymore than $100 for a competent tradesman.

Mark

[skipalong]

yeah when it is welded the stress will cause more cracks around that area

[Chuckmeister]

[quote=gofishin;800818]

You should find similar tig weld ‘smooths’ every 500-800 along the keel & chine extrusions if you look closely.


Good call. That's what it's like.

With the skid setup, I'm sus there may be too much weight on them and not balanced correctly on each side.

This is great advice. I'm always keen to admit when I don't know about something open to learning how to do things properly. This way I hopefully won't screw things up.

Thanks

[Chuckmeister]

Good advice Dan except maybe for he last paragraph. I would use the sheetys shop as a last choice - try to find a local ally boat builder first. - Apart from the obvious experience and ability to point out the cause (which a "sheety may not be able to do) they are already set up to TIG weld Ally which is what this job needs. A sheetmetal work shop may not always be set up for ally welding, which leads me to my next point:-

A couple hundred dollars is probably a bit much. There is about half to 3/4hr job there. Shouldn't be anymore than $100 for a competent tradesman.

Mark

Again good advice. I eventually got hold of my brother-in-law who's an ex-boilermaker. He said pretty everything you pointed out including the cost.

Now to do the job and hopefully no cracks will reappear.

Cheers

[Dan5]

Good advice Dan except maybe for he last paragraph. I would use the sheetys shop as a last choice - try to find a local ally boat builder first. - Apart from the obvious experience and ability to point out the cause (which a "sheety may not be able to do) they are already set up to TIG weld Ally which is what this job needs. A sheetmetal work shop may not always be set up for ally welding, which leads me to my next point:-

A couple hundred dollars is probably a bit much. There is about half to 3/4hr job there. Shouldn't be anymore than $100 for a competent tradesman.

Mark

Yeah maybe some sheety's don't have the experiance,myself being a boily i have a few mate's that are sheety's and are more than competent tradesmen to do a simple repair like this one.I guess some guy's don't get a wide and varied work load like other's.

I myself have worked in sheetmetal shop's from time to time and all of them were setup to do ally.3/4 of an hour is a little understated in time in my opinion by the time you dissconect the battery,drill,grind ,clean,prep set the welder up get in position weld both side's clean spatter packup machine/tool's,re-connect battery etc but $200 would and should be max $$.

Dan.