Help fixing an "unfix-able" pontoon boat.

[SCwetbike2]

I need help fixing the design of this pontoon boat it keeps pulling the brackets out of the pontoons. I need to add some frame work to it but I don't want to build it to death. I tig aluminum all day every day so the welding aspect will be a piece of cake its only the design aspect that's got me a little stumped. Any suggestions?

[Fnord5]

Wrap straps around the pontoon to tie into the brackets?
It's not like they're the most efficient watercraft anyway.

[12V71]

Looks like the pontoon is flexing beyond the end of the flatbar. You could possibly cut out the old weld and slip a large circular patch under the end of the flat bar to spread the load out, say 8-10 inch diameter and .250 thick. The flat bar will need to be relieved with a sawzall or something to allow the patch to slide under it. Welding the patch under the flatbar will be challenging, but a "mouse hole" in the flat would get you in there.

[OPUS FERRO]

SCwetbike2

The was destined to fail from inception. Take a good look at
the 'frame rail to tank interfaces' on a gasoline tanker truck.

The intermediary components are called doublers - note the
thickness and overall size. This is how you distribute 'point
load' to a thin skin . . .

hth


Opus

[12V71]

SCwetbike2

The was destined to fail from inception. Take a good look at
the 'frame rail to tank interfaces' on a gasoline tanker truck.

The intermediary components are called doublers - note the
thickness and overall size. This is how you distribute 'point
load' to a thin skin . . .

hth


Opus

That was exactly where my post came from. Tankers.

[thegary]

To really fix it so it will not happen again you need to cut the pontoons loose from the bracket. Go buy some 6000 series sheet aluminum about 3/16 thick and have it rolled to the outside diameter of the pontoons. weld the sheet to the pontoons and the brackets to the sheet so the point load is dispersed more.

Now that I said all that forget about it and clean up the cracks and weld them up. Air test the pontoons after repair with no more than 3-4 pounds of pressure using a soap solution to check for leaks . go enjoy the pontoon and inspect it every season for cracks. Its not worth doing anything more.

[SCwetbike2]

go enjoy the pontoon and inspect it every season for cracks. Its not worth doing anything more.

That would be my plan if it was my pontoon but it's not for now at least so I'm looking for a repair that will hold. Putting a rounded patch under it was my initial thought but there cumming loose all the way down the length of a 24ft pontoon that is going to be time consuming to cut them all loose and patch them all. I was hoping to be able to add a frame across the middle to keep it from flexing so it doesn't pull the brackets out.

[SCwetbike2]

Wrap straps around the pontoon to tie into the brackets?
It's not like they're the most efficient watercraft anyway.

That's actually a good idea.

[Zimm]

Good advice, but with any luck Zapster will chime in. He is the resident pontoon boat expert.

[Rondo]

Gussets?

[455dan]

Wow- haven't seen a Pontoon boat built that way, where are the stringers running the axis of the tubes?

Would it be possible to do 1 side at a time ,


cut off the crap the original builder used and use long rectangular or inverted L Aluminum welded to the tubes. The pontoons I have seen all are built with long stringers attached to the tubes

https://www.harrisboats.com/images/p...acing-side.png

https://www.harrisboats.com/images/p...ion.png?041715

Lot of Labor involved but it would be strong.

[Chad86tsi]

that metal is all fatigued now. Need to end that load surface on fresh healthy metal. Also it is a stress riser by design because it's kind of a dead stop load wise at the end of that flat.

What I'd try:

fix the crack, then weld an extension of the flat to end well past that weakened metal. Roll the tip of that extension by 90* so the termination of the weld is perpendicular to the load, not parallel to it like it is now. Imagine a ski tip shape piece welded where the current flat ends, end that weld 5-6" away and perpendicular to where it currently ends. this nealry eliminates the stress riser, and extends the loading well past that weak metal. Should be fairly easy to implement too. I'd also add a piece that is lapped over the weld seam of the new extension, that seam will have a lot of stress on it.

[Chad86tsi]

This failed for the same reason jets no longer have square windows, similar to what caused the failures of the de Havilland Comet.

[Sprockmonster]

What if you cut a round/ski tip pad with a slot through it the width of the upright material? That way you’d just need to grind out existing weld, slide the new piece around the upright, and weld it all together.

[TimmyTIG]

Put some duct tape on it.

[cwby]

What if you cut a round/ski tip pad with a slot through it the width of the upright material? That way you’d just need to grind out existing weld, slide the new piece around the upright, and weld it all together.

What he said - slot an angle to fit over the vertical strap, form the flat leg of the angle to fit the curvature of the pontoon, vertical weld on the strap, all around on the pontoon (3 sides). Should distribute the stresses over a larger area.

[spooled05]

I cut the brackets loose and bend fit and weld a pad to the pontoon than bracket to the pad piece , helps distribute the load .

[WeldCrazyDude]

I deal almost exclusively with A36 steel, not aluminum, but I think the best suggestions have been to bend fit panels to distribute the load. However, if you don't want to do all of that work, I wonder if you'd be able to find some aluminum angle iron that you could weld in an upside down "V" between and to the brackets. That might be the "poor mans" way of trying to distribute the load along the pontoon and between the brackets. It's all about increasing surface area so I'd give that a shot if you want something quick and dirty (over the likely better option of time consuming shaped patch).

[BluCllrPlt]

If you go the patch route, here’s some good information on constructing tank trucks

3.2.2 Attachments
A tank will have concentrated loads imposed where connections are made to the chassis. Stresses due to other loadings, such as the weight of water present for hydrostatic testing, or vertical, lateral and longitudinal loadings caused by acceleration or deceleration of the vehicle, must be accounted for. The details of supports should conform to good structural practice. An important reference is Appendix G of Section VIII, Division 1 of the ASME Boiler and Pressure Vessel
13
(BPV) Code.
The following considerations should be emphasized.
(a) All connections between the tank and its supports must be designed to prevent excessive localized stresses due to mechanical loads as cited above, due to temperature changes in the CT, or due to internal pressure or the hydrostatic pressure from fluid contents.
(b) Round, oval, or rectangular reinforcing plates with rounded corners must be used between a support or the chassis and the tank. They should be welded all around and should be provided with a weep-hole at the bottom of the reinforcing plate. The reinforcing plates should have dimensions and thickness selected to minimize flexing of the plate under forces normal to the surface of the CT.
CTs may also be supported by means of saddles. The contact surface of the saddles shall extend over at least one-third of the circumference of the shell. Supports should be as few in number as possible, preferably two over the length of the CT. The CT may be reinforced by stiffening rings at intermediate sections, or by longitudinal stringers, typically at the top of the tank

[jay gill]

So I having worked for a pontoon dealer for 10 years and owned my own pontoon boats those pictures didn’t seem “right”.
I went out and took some pics of my boat, produced by Godfrey Marine. Looks like there are “foot pads” under the vertical member and the welds are at edges of the pad. Unfortunately it looks like the piece is an extrusion. You could try welding pads under the existing brackets, but there would still be a weld at the point of the load, but at least any repair would be bracket to thicker pad, not the toon itself.
Pics taken stern to bow.






The other path, being spring and when you can get all the money, sell the boat and find a better one

[idacal]

those last pictures look like an incredible step forward from the older pontoon boats. that looks like it could actually handle some horsepower I have an old Party Barge, 20' deck and it is built more along the lines of the OPs boat, not having the cracking yet though. but it is only rated for 115 horsepower and the biggest its ever had was a 90. I wonder if the OPs was over horsepowered and caused some racking at the front of the pontoons maybe cut all the brackets loose at the front there and let everything relieve then reweld. after redecking mine, I had to cut the front nose cone brackets to relieve some of the years accumulation of stress and use, otherwise it was trying to bend a tube

[midwaleswelder]

For some reason I cannot get photos which is annoying