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Thread: Cracked Welds

  1. #16

    Re: Cracked Welds

    To Tunaticer who disagrees with my post..

    Please feel free to comment..

    I have had 4 pressed tinnies of differing brands during my time and all have cracked and been repaired (by different repair places), the 4.3m clark that I have has done a lot of offshore work off the Sunny coast/Moreton and was probably the one I thought was constructed the strongest of them and was repaired by more than one reputable alloy welding place.

    It was bought in 1996 and is still going, I just have stopped welding it and no longer take it to offshore..

    From my experience they continue to crack, you weld them up and sooner or later another stress crack will form either in or around that weld which I guess makes sense as it is effectively weaker in that area..

    As stated above they have a shelf life unfortunately, plate alloy is another kettle of fish but pressed boats I am happy to stick by my word..

  2. #17

    Re: Cracked Welds

    Some light reading

    http://www.almet-marine.com/images/c...vironments.pdf

    For starters, I'm neither a qualified welder or metallurgist but I've spent my fair share of time around aluminium in a marine environment. Talk to a few welders and most will tell you the same story. Aluminium that has been in salt water for a reasonable period is an absolute bugger to weld and will, in all likelihood, either still leak or will crack again. Even plate boats can be a problem child if they are old enough - the aluminium courtesy of one of the corrosion types in the PDF literally delaminates as you try to weld it. Then there is the issues around the thermal shocking of the metal as it cools. Any welder will tell you aluminium must be clean to weld properly. At a guess, it's a combination of corrosion at a granular level and thermal shocking that causes this tendency to re crack. I have one mate - not trade qualified but extremely competent, with a long list of boat builds behind him who simply refuses to weld up tinnies more than a few years old because of this.

    Bit late now unfortunately (missed this one earlier) but my last tinnie that was run offshore for a period of 20 years, did so for the last 12 or so with a blind pop rivet sikaflexed into the hull. I think in that time replaced it out of precaution once. I never cracked the outer skin of that hull - more to do with the vessels set up, horsepower and my driving style than anything I suspect than the quality of the hull - a Savage. I spend a fair bit of time getting my boats to plane slowly as I thoroughly detest getting flogged. For a tinnie especially, a foil or similar planing aids are imperative for offshore use IMO.

  3. #18

    Re: Cracked Welds

    So fibreglass...polycraft maybe?

    Sent from my SM-G960F using Tapatalk

  4. #19

    Re: Cracked Welds

    Quote Originally Posted by TheRealPoMo View Post
    So fibreglass...polycraft maybe?

    Sent from my SM-G960F using Tapatalk
    They all have their design deficiencies relative to the individual owner. Just have to live with whatever suits your usage best and be mindful of the short comings.

  5. #20

    Re: Cracked Welds

    I dunno, a streamlined wheelie bin with a 40 HP sounds hard to beat for a "tinnie"

    Sent from my SM-G960F using Tapatalk

  6. #21

    Re: Cracked Welds

    Quote Originally Posted by Watto79 View Post
    To Tunaticer who disagrees with my post..

    Please feel free to comment..

    I have had 4 pressed tinnies of differing brands during my time and all have cracked and been repaired (by different repair places), the 4.3m clark that I have has done a lot of offshore work off the Sunny coast/Moreton and was probably the one I thought was constructed the strongest of them and was repaired by more than one reputable alloy welding place.

    It was bought in 1996 and is still going, I just have stopped welding it and no longer take it to offshore..

    From my experience they continue to crack, you weld them up and sooner or later another stress crack will form either in or around that weld which I guess makes sense as it is effectively weaker in that area..

    As stated above they have a shelf life unfortunately, plate alloy is another kettle of fish but pressed boats I am happy to stick by my word..
    The use of silicones and sikaflex is bad practice.
    If you use that then decide on a proper repair it will make the welding far more difficult with a high silicon content IN the metal.....yes it is absorbed into the metal a bit, cleaning back to bare metal is not enough.

    The cracks occur from stress, far better to rectify the cause then implement the repair.
    I have rekeeled my boat to solve the problem, cost about $400 from memory.
    Jack.

  7. #22

    Re: Cracked Welds

    You say in the first post the cracks are in the keel and from that information I will assume that the cracks are in the welds where the aluminium bottom plates fit into the keel bar. So the issue with welding there is the plate slips into this keel section and only the outside is welded and inside is left for water, sand and mud to get into the section over time and fills the void with crap. What can happen when trying to repair a crack in this area is being unable to clean the crap out. This is why you can start with a small crack and end up with having to weld a much larger section due to having to get to a section where the weld is not blowing back at you.

    When someone came into the shop with a keel repair I would alway run them through the issue that may occur once we start the repair so there was no surprises when a hour job turns into 6 hours.

    I have repaired many over the years and some will be fine to weld and anothers can be a nightmare. Age of boat and how it has been looked after is important. If a tinny arrived at the shop grubby and not loved you could make a good guess you will have trouble. Over the years more and more tinny's have decks installed and you can't get in to hose the keel area out and the crap builds up much quicker then having a open boat.

    If you decide to go down the road of using anything but weld metal to repair and decide down the track to get it welded remember the welder is going to have to remove whatever you used.

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