While it's not the best-looking weld, it still just looks like it's been overloaded to me. Welding tempered aluminum will also be significantly weaker in the immediate vicinity of the weld.

Also, I can't tell exactly what's going on from your pictures, but sometimes adding reinforcement to a structure can cause stress concentrations, and end up creating failures that might not have occurred had the part not been stiffened. All depends on how and where the stiffness is added.

Marc Googer in Mt. Pleasant (@Tigweld) could probably get it sorted for you -- he's done one or two things for me in the past and I was always pleased.

 

That's a previously repaired part.

 

I wish but I actually paid to have this cross bar added and it was not originally there.

 

I see two or more rows of welds suggesting it has cracked and been re-welded once before. The proximately of the flange is preventing a full weld around the tube and it at least one of the reasons why it fatigued. It needs a full weld or a gusset. It may be better to remove the old pipe and to weld in a new one. A good welder will now how to make it better.

 

After a few times re-welding cracks and adding reinforcements to my first poling tower (vintage 1988...) I finally realized that I'd be money ahead with a new tower entirely (using the original Maverick fiberglass deck, of course). Over the years since I've been pleased with the results....

The original tower on my skiff had only two legs - bolted to the transom only... the replacement had four legs and was a much, much stronger design...

 

@lemaymiami i agree with you completely, unfortunately I’ve got to try to make this one work for a little longer. Plus the wobble improves core strength and balance! I do notice the movement more when trailering than poling.

I think the problem stems from the legs angling back to each other similar to the old platforms referenced above.

 

Can you post a picture of the whole platform so that we can see where the bar goes?

 

Here is an old picture from before the bar was added, the bar runs under the fiberglass lip on the backside of the platform. I can try to get a better one once I get back to it.

 

Ok this has several things going on.

1. If you want that to be strong in the direction it's failing you need to have the flange removed and have a full circumferential weld around the tube. Or as an alternative, have the welder tie the tube into the flange if your configuration allows for that but make sure it's clean like super clean with a SS wire wheel before it's welded.
2. Looks like Fish eyes(crater crack/holes) at the termination point of the weld in the second pic, comes from several things but usually excessive heat, not feeding enough wire when terminating the weld, contamination (person welding this should using grinders wire wheels dedicated to Stainless/alum/non-ferrous and cleaning between passes. Notice the black soot, some is common and ok (but should always be cleaned between passes to prevent incomplete fusion), too much can cause porosity, if tools are clean then increase the flow rate on your Argon). Fish eyes can be helped by feeding more wire at the end, allowing more time to cool between passes, and running less amperage.
3. When you have if fixed remove all the old weld, it does more harm than good (stress riser, uneven heat dissipation of additional weld bead, increased chances of brittle fracture)
4. Aluminum has a relatively small fatigue limit, once it starts to crack, or you leave a propagation/start point for a crack (like the un-welded area that's receiving stress combined with a fish eye) you will have a crack, and it will grow quickly in most cases where the part is stressed or moved frequently.

There are multiple ways to have weld issues but those are likely the most common for what you're seeing. Hope that helps

 

I gotcha. I think the root of the problem is in the design. I think that even with a very high quality weld, you'll still see failure.

You're trying to restrain that side to side "racking" motion -- originally, the fiberglass top was a structural component. Once you add that bar, the fiberglass lid isn't carrying much load in the range of deformation allowed by the aluminum bar, since the glass is less stiff. So, the bar makes it stiffer, but isn't strong enough to take the entire load on it's own, so it cracks at the joint (which also happens to be the weakest area due to the strength loss from welding).

Anything you can do diagonally will help. I would avoid tying the two sides together unless you do it in a really strong manner -- you'll basically have to imagine that the fiberglass isn't there. Either way, try to add a tube in each corner diagonally to form a triangle when viewed from the front.

 

Is that on a Hewe's?

 

Boat is not a hewes

 

You may want to bite the bullet on that tower if you've got the slightest "wobble" when you're standing on it... I put up with that sort of stuff years ago and it's just plain bad news - and speaks louder than words about imminent failure....

Granted recreational types aren't living on their skiffs the way guides seem to do but putting up with a less than stable platform when poling is a recipe for a trip to the ER.... Too many things can happen under those circumstances - none of them good unless you like to tell funny stories about painful incidents.

 

LowHydrogen covered the bases but here’s my two pennies.
That’s just a terrible welding job and the top looks like it never got welded so it opened up from stress and once it cracks like that it’s got to be pretty much removed or it will just keep cracking. To save money you could have a shop cut all the legs below that point and re-fab a whole new top section and either sleeve it and weld or cut the legs low and make it removeable with knuckles and knobs or just scrap it and have a fresh platform made.