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Thread: Does too much heat weaken you hull?

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    Default Does too much heat weaken you hull?

    Many people ask what's better stitch welds or solid welds in the construction of the hull. I've read and heard that excess heat reduces the strength of aluminum and stitch welding is preferred since it reduces the amount of heat on the hull plate. Obviously there's no way around heating the bottom plate during the manufacturing of the boat but using techniques that minimize the effects of excess heat are required in most government contracts and the technique is used by many boat builders. I decided to do a test and the video link below should show why proper construction techniques that reduce excess heat during the build process is extremely important. I really wasn't expecting to see such a big difference. Watch for yourself and try it at home if the video doesn't convince you.

    http://www.youtube.com/watch?v=JblHmPFbtNY

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    Member Yukoner's Avatar
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    Are you more concerned with warping during construction or heat affecting the strength of the alloy?
    Big difference between the two issues.
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  3. #3

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    Quote Originally Posted by Yukoner View Post
    Are you more concerned with warping during construction or heat affecting the strength of the alloy?
    Big difference between the two issues.
    My concern is the strength. I wanted some way of quantifying what I've heard and read on the internet concerning how heat effects the strength of 50 series plate aluminum such as 5052 or 5086 with 5052 being the softest of the two commonly used in boat manufacturing.

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    Member cormit's Avatar
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    There are a lot of things to consider and even fret about when welding and fabricating aluminum. Weakening plate from heat generated by welding is probably not one of them. Distortion and warping from too much heat concentrated in one spot is the biggest concern.

    All good welding has to be done "hot" .... even if it is just stitches. Cold welds with poor penetration are not adequate for any project. The reason for stitch welding is to prevent concentrated heat from causing distortion and warping ..... it is not to prevent weakening of the plate being welded.

    In boat building ...... keeping control over warping is one of the biggest challenges. When builders use stitch welds to attach hull stiffeners, framing members or lift strakes, for example ....... the stitch welds are chosen to limit distortion and to save time .... not because they are stronger than a continuous weld.


    Quote Originally Posted by Halibutgrove View Post
    My concern is the strength. I wanted some way of quantifying what I've heard and read on the internet concerning how heat effects the strength of 50 series plate aluminum such as 5052 or 5086 with 5052 being the softest of the two commonly used in boat manufacturing.

  5. #5

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    Quote Originally Posted by cormit View Post
    There are a lot of things to consider and even fret about when welding and fabricating aluminum. Weakening plate from heat generated by welding is probably not one of them. Distortion and warping from too much heat concentrated in one spot is the biggest concern.

    All good welding has to be done "hot" .... even if it is just stitches. Cold welds with poor penetration are not adequate for any project. The reason for stitch welding is to prevent concentrated heat from causing distortion and warping ..... it is not to prevent weakening of the plate being welded.

    In boat building ...... keeping control over warping is one of the biggest challenges. When builders use stitch welds to attach hull stiffeners, framing members or lift strakes, for example ....... the stitch welds are chosen to limit distortion and to save time .... not because they are stronger than a continuous weld.
    What he said is spot on!

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    Supporting Member HMS Erne's Avatar
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    Quote Originally Posted by Halibutgrove View Post
    My concern is the strength. I wanted some way of quantifying what I've heard and read on the internet concerning how heat effects the strength of 50 series plate aluminum such as 5052 or 5086 with 5052 being the softest of the two commonly used in boat manufacturing.

    Do an impact or drill test of some kind. Bending is one thing but punctures and dents are a whole different set of events


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    I also agree with cormt +10

  8. #8

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    Quote Originally Posted by cormit View Post
    There are a lot of things to consider and even fret about when welding and fabricating aluminum. Weakening plate from heat generated by welding is probably not one of them. Distortion and warping from too much heat concentrated in one spot is the biggest concern.

    All good welding has to be done "hot" .... even if it is just stitches. Cold welds with poor penetration are not adequate for any project. The reason for stitch welding is to prevent concentrated heat from causing distortion and warping ..... it is not to prevent weakening of the plate being welded.

    In boat building ...... keeping control over warping is one of the biggest challenges. When builders use stitch welds to attach hull stiffeners, framing members or lift strakes, for example ....... the stitch welds are chosen to limit distortion and to save time .... not because they are stronger than a continuous weld.
    Cormit, I agree as well, all welds must be done "hot" with adequate penetration and preventing warping/distortion with concentrated heat is another huge factor. Even where a full length weld is required Stitch welds are used to along the full length and then followed up by filling in the gaps to prevent warping. Some builders actually measure the distance of each stitch to ensure they are laid out evenly along the full length of the weld. This is probably mostly cosmetic but its definitely a sign of attention to detail. Doing so is actually more time consuming then laying out a full length weld. The point of the demonstration was to show how heat effects the strength of aluminum base plate tensile strength. From what I concluded was that it greatly impacts the base metals ability to resist distortion when a force is applied, as in hitting a rock. Given ALL factors equal in the construction design which hull would be stronger? One that was stitch welded to reduce heat or one that was fully welded to look stronger. The base plate that's had less heat applied would be more resistant to bending based on what I saw in doing this test.

  9. #9

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    Quote Originally Posted by HMS Erne View Post
    Do an impact or drill test of some kind. Bending is one thing but punctures and dents are a whole different set of events

    I'm not sure how I could do a drill test. Any suggestions? An impact test is probably more doable. What do you have in mind? Impact on the base plate with a punch or a section of plate that has stiffener thats been stitch welded and one with a full length weld?

  10. #10

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    I agree with Comit. Both have their purpose. I would also include the skill level of the welder and the quality of their equipment and gas used. Along with well planned welding procedures will produce quality welds. Then its up to us to put them to the test in the water.

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    Quote Originally Posted by Halibutgrove View Post
    Cormit, I agree as well, all welds must be done "hot" with adequate penetration and preventing warping/distortion with concentrated heat is another huge factor. Even where a full length weld is required Stitch welds are used to along the full length and then followed up by filling in the gaps to prevent warping. Some builders actually measure the distance of each stitch to ensure they are laid out evenly along the full length of the weld. This is probably mostly cosmetic but its definitely a sign of attention to detail. Doing so is actually more time consuming then laying out a full length weld. The point of the demonstration was to show how heat effects the strength of aluminum base plate tensile strength. From what I concluded was that it greatly impacts the base metals ability to resist distortion when a force is applied, as in hitting a rock. Given ALL factors equal in the construction design which hull would be stronger? One that was stitch welded to reduce heat or one that was fully welded to look stronger. The base plate that's had less heat applied would be more resistant to bending based on what I saw in doing this test.
    Continuous welding is not done to look stronger ..... it is stronger. Carefully laying out a pre-marked welding pattern for consistent length and spaced welds/stitches looks clean and is easier for most welders to achieve. A hull stiffener welded to a hull side for example ...... might have a succession of 3" welds. These are fairly easy to do with a uniform consistent look. Lots of welders can master 3" welds. The same hull stiffener welded continuous from one end to the other ...... not so easy. Because the welder is forced to skip around to keep the heat spread out ..... eventually these skip welds need to connect to each other. When you look at a long continuous weld .... and have a hard time spotting where the starts and stops are located .... rest assured, the welder that can do that knows what he's doing.

    While a metallurgical argument can probably be made that the parent metal adjacent to a weld zone may be 'technically" weakened by the welding process ..... you are probably wasting brain cells here .... as you can't prevent it.

    You could likely crash rocks all day with a 1/4" 5052 or 5086 boat bottom ....... and suffer numerous dents and gouges ...... but I don't think you're ever going to find cracking or fracturing resulting from a boat bottom made brittle because there was too much heat from welding.

    Aluminum is not tolerant of flexing or much movement. If boat bottoms suffer cracking ...... it is usually because of inadequate framing ...... which allows too much repeated movement. If properly framed and supported ...... aluminum hulls are practically indestructible.

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    Moderator Paul H's Avatar
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    The issue with welding aluminum is you anneal the metal in the heat affected zone of the weld. I'm not positive if I got the exact annealed condition numbers but here is what some googling yielded:

    Alloy 5052 Annealed H32 H34
    Yield 13kpsi 23kpsi 26kpsi
    Tensile 28kpsi 31kpsi 34kpsi

    So 5052 sheet that is sufficiently heated to anneal it will loose approximately 1/2 it's yield strength over the heat treated condition, but the tensile strength isn't diminished as greatly. This is typical for heat treated aluminum alloys and some of them such as 6061 T6 and 7075 T6 have much greater strength loss in the annealed vs. heat treated condition.

    As it is not feasible to heat treat an entire hull after welding to get the entire weldment to the appropriate heat treat strength, designers compensate by choosing a weld geometry or add stiffeners and other supports at the weld.
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  13. #13

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    Quote Originally Posted by cormit View Post
    Continuous welding is not done to look stronger ..... it is stronger.
    Correct me if I'm wrong, but the more heat anneals (softens) the aluminum and making it softer rather then brittle. The 5052 used in the test just bent easier it didn't crack. So how is a longitudinal stiffer welded the full length of the hull make the hull stronger then a stuffers skip welded the entire length to reduce annealing from weld heat applied to the hull and stiffener. Since less heat is applied to each your retaining the original characteristic of the base metal.

    You could likely crash rocks all day with a 1/4" 5052 or 5086 boat bottom ....... and suffer numerous dents and gouges ...... but I don't think you're ever going to find cracking or fracturing resulting from a boat bottom made brittle because there was too much heat from welding.
    Just based on the test I agree it wouldn't probably crack but would be more susceptible to denting rather then possible bouncing off the rock. In the test we used 1/8" 5052 which is what most boats with preformed strakes are made with since 5086 can't be rolled and is a much harder aluminum. 5086 is much slicker on the rocks as well since objects have less tendency to gouge or scratch the 5086.

  14. #14

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    Quote Originally Posted by Paul H View Post
    So 5052 sheet that is sufficiently heated to anneal it will loose approximately 1/2 it's yield strength over the heat treated condition, but the tensile strength isn't diminished as greatly. This is typical for heat treated aluminum alloys and some of them such as 6061 T6 and 7075 T6 have much greater strength loss in the annealed vs. heat treated condition.
    I'd say it was about half based on what I saw on the scale. I really wasn't expecting to see such a big difference.

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    Many new (especially custom welded) boats come with hull stiffeners skip welded to the hull sides. A variety of stiffeners or lift strakes of some type get welded to the bottom plate as well ..... also common to see these skip welded. These parts are structural ...... as they help keep the bottom and side plates from flexing. Flexing over time almost always results in cracks. Aluminum hulls that zip along at 20 to 30 mph take a lot of cumulative abuse ..... choppy water ..... occasional big wave slams ... trailering, it all adds up. Structural hull components (stiffeners, strakes, bulk heads and general framing parts) ..... that are skip welded ....... are where the failures happen first. Once a single skip weld fails ..... it doesn't take long and the next one fails too. This opens the door for major hull failure. When those same hull parts are continuously welded (especially those on the exterior of the hull) ..... that hull is going to be pretty hard to break apart.

    Not many boats over 16' to 18' long use 1/8" bottoms ... especially welded boats. Some of the early Kenai River sleds were 1/8' bottoms ..... but you don't see them anymore ....... as they simply didn't hold up.

    5086 aluminum plate can be rolled, broke or formed pretty much the same as 5052. In heavier plate ..... like 1/4" a more radiused nose bar is sometimes used for a 90˚ bend to lessen the chance of cracking. 5086 is harder and takes a more force to form and bend than 5052 ..... but we bend it and roll it all the time.


    Quote Originally Posted by Halibutgrove View Post
    Correct me if I'm wrong, but the more heat anneals (softens) the aluminum and making it softer rather then brittle. The 5052 used in the test just bent easier it didn't crack. So how is a longitudinal stiffer welded the full length of the hull make the hull stronger then a stuffers skip welded the entire length to reduce annealing from weld heat applied to the hull and stiffener. Since less heat is applied to each your retaining the original characteristic of the base metal.



    Just based on the test I agree it wouldn't probably crack but would be more susceptible to denting rather then possible bouncing off the rock. In the test we used 1/8" 5052 which is what most boats with preformed strakes are made with since 5086 can't be rolled and is a much harder aluminum. 5086 is much slicker on the rocks as well since objects have less tendency to gouge or scratch the 5086.

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    Supporting Member HMS Erne's Avatar
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    Quote Originally Posted by Halibutgrove View Post
    I'm not sure how I could do a drill test. Any suggestions? An impact test is probably more doable. What do you have in mind? Impact on the base plate with a punch or a section of plate that has stiffener thats been stitch welded and one with a full length weld?
    I didn't have any skill set to perform testing, just experiance hitting rocks (green horn). I've bent the metal; but I think most boats(for the most part) have solid bottoms. One whole piece of metal and the (internal) framing has the stitch or full length welds. So I don't think the stitch or full length welds are the problem, since a break in the weld will be internal, unless you hit hard enough to cause the weld area to crack.

    I agree with stitch welding since I'm told it can flex and take the hits. A hull leak rather than a dent may be the bigger problem.

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    Please forgive me if it seems like like i'm looking for an argument here ..... trust me i'm not. But the claim in the video implying that a boat bottom is stronger if it is skip welded than if continuous welded offers readers of this forum advice that is misleading, unqualified, and not true and therefor should not go unchallenged. Someone might make a purchasing decision based on this claim .... or ask a builder to follow this advice ..... so lets be responsible about this.

    The heating prior to bending experiment in this video is not a test for tensile strength and shouldn't be claimed as such. A test for tensile strength pulls a test piece apart to the point of failure. This is a common test for structural as well as pipe welders and is performed with hydraulic testing equipment. Sometimes pipe welders take a welding test by welding two sections of pipe together. Strips are then cut (called cupons) at right angles to the weld and folded into a "u" to examine for failure especially in a blind root weld.

    Buying a new boat these days is not only expensive ..... but complicated. There are is a lot to choose from and the criterion is endless. People these days often look to forums like this one for help in making those decisions ...... so be careful with advice you give.

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    Moderator Paul H's Avatar
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    It's important when discussing what is "stronger" to clarify exactly what is being addressed. I tried to cut and paste from Alcoa's website but the formatting got messed up. When strength is discussed the type of failure also needs to be discussed. Are we talking yield strength, i.e. the hull deforming most likely from an impact to a rock or something else, are we talking tensile strength, the point at which the material fails and the hull is breached, or are we talking fatigue strength, the point at which repeated stress cycles to the hull cause the material to crack.

    Aluminum alloys are an interesting material to use for building structures, they have high strength to weight, are fairly corrosion resistant depending on the alloy and generally can be readily formed via various techniques. However aluminum alloys are susceptible to fatigue failure and as I recall (it's been over 20 years since I took strength and materials) there is no lower fatigue limit for aluminum. Which means if you cycle it enough, it will crack. That is why aircraft frames have a life cycle.

    How does this relate to welded aluminum boats and stich welding vs full length welding for reinforcements? In the case of a brand spanking new boat that is stich welded and hence has less of the plate annealed being driven into a rock, you'll find for that single overloading of the hull the stich welded hull is stronger. However, those stich welds are stress risers and over the length of owning the boat there is a risk that those welds will start failing due to cyclical loading.

    I'd say if the boat designer or engineer takes into account the effect of the material due to annealing and stress risers from skip welding, either technique can result in a hull that will be strong and have a long life. However if the designer or engineer doesn't fully grasp the affects of both annealing from welding and stress risers from skip welding, you could end up with some issues.
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    Stitch welds, Intermentant welds, Back step welding are are all ways to get the job done and getting the job done cost money hence more weld equals more money or cost and that cost is passed onto the customer.
    The type of welding that needs to be done is not a guess, it is engineered and then executed by a competent tradesman [the welder]

    Stitch welds are usually used to just add something in or on the structure like a bump rail or the like.
    Intermittent welds or staggered Intermittent welds would be for something like a Stringer where you weld some on both sides of the piece to the parent metal.
    Back step welds can be Intermittent or continuous , the continuous would be like for seal welding a deck. The reason for back step welding is that method of welding helps pull the two parent metals together and you don't have the parent metal continuing to get hotter if you kept welding non stop in one direction, not to mention it is easier on the welder to reach forward and weld back to the start of the last weld one to two feet at a time.
    Welding can be learned in a short time but learning what to do with it can take years of practice.

    Cormit, you Sir have some good answers, keep it up.

  20. #20

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    Quote Originally Posted by cormit View Post
    Many new (especially custom welded) boats come with hull stiffeners skip welded to the hull sides. A variety of stiffeners or lift strakes of some type get welded to the bottom plate as well ..... also common to see these skip welded. These parts are structural ...... as they help keep the bottom and side plates from flexing. Flexing over time almost always results in cracks. Aluminum hulls that zip along at 20 to 30 mph take a lot of cumulative abuse ..... choppy water ..... occasional big wave slams ... trailering, it all adds up. Structural hull components (stiffeners, strakes, bulk heads and general framing parts) ..... that are skip welded ....... are where the failures happen first. Once a single skip weld fails ..... it doesn't take long and the next one fails too. This opens the door for major hull failure. When those same hull parts are continuously welded (especially those on the exterior of the hull) ..... that hull is going to be pretty hard to break apart.
    Cormit, you appear to be a proponent for using full length welds. The reason the first place you may see a failure in the weld is because the weld in aluminum construction is the weakest part of design. Unlike steal, an aluminum weld is weaker then the parent metal. Here's a reference from Lincoln http://www.lincolnelectric.com/en-us...qs-detail.aspx

    I would think based on the effects of annealing as a result of welding, the overall strength of the parent metal is going to me much stronger when skip welds are used putting less stress on the welds overall. The problem we've seen on full length welds is the crack continues along the weld until repaired, they are after all weaker then the parent metal. Structural skip welds when cracked typically stop when the stress is relieved on the effected weld.

    There are numerous reasons to fully weld an external hull strake, but I don't believe adding strength is a reason. In a boat used in saltwater a full length welded chine extrusion prevents entrapment of water which can lead to corrosion, it's trade off for the annealing that will occur.

    Not many boats over 16' to 18' long use 1/8" bottoms ... especially welded boats. Some of the early Kenai River sleds were 1/8' bottoms ..... but you don't see them anymore ....... as they simply didn't hold up.
    There's a number of 1/8 bottom welded boats over 18' still produced today and some claim their full length welded internal stringers make for a stronger hull structure. A a result of the annealing encountered I believe this weakens the hull not strengthens it.

    5086 aluminum plate can be rolled, broke or formed pretty much the same as 5052. In heavier plate ..... like 1/4" a more radiused nose bar is sometimes used for a 90˚ bend to lessen the chance of cracking. 5086 is harder and takes a more force to form and bend than 5052 ..... but we bend it and roll it all the time.[

    Let me correct myself, 5086 is typically not rolled to form strakes in hull plate since it's too hard and expensive to roll. With a large enough radius sheet can be bent. We've had 3/16 bent at 90 degrees for projects and still experienced stress cracks and found it's easier to cut and weld.

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