I know nothing about boats but am building a Pontoon, where to post trivial question?

Hi all,

Title is the question. I found 2 old 24' pontoon logs in the woods on my in-laws property and decided to take on a pontoon boat project. I sit in front of a computer all day - IT job - but getting my hands dirty on mechanial projects make me happy. That said, I know next to nothing about boats.

My good friend is a boat inspector and has answered a lot of my questions, but I currently text him more than his wife. So for his sake, I'm hoping maybe some of you fine people would be willing to answer my dumb questions.

Here is an example of my latest dumb question: I pressurized the logs and found a small crack in one where the frame joist connects to the log. Can I use alumiweld to fix it?

I'll end up asking a bunch of these as I pull parts from junkyards and put things together. So, am I in the right place? is this the right forum? Is this the appropriate section?

Thank you everyone!

Zach

edit: Wow I can't type. sorry about the title.

 

Alumiweld is an aluminium solder/brazing product, not a welding product.
I think you should pay a professional welder here.
AlanX

 

Yes

Not a very sound decision in my opinion. Why, what's the objective?

Have you considered gardening?

You will learn, perhaps the hard way.

He/she is not a very good friend if you're still moving forward.

You probably shouldn't be texting his wife.

Fire away.

Sure.

Absolutely.

No problem.

Zach, what's the objective?
I can tell you there are better places to put your efforts and money.
But, if you are determined, carry-on.
Post some pictures of these "pontoon logs" and what you plan to do with them.

BB

 

Thank you for the advice. Is it because the Alumiweld won't be strong enough? I've posted a picture of the crack in a post below if that helps.

 

BlueBell, thank you for the detailed response.

I'm dying . Guess my grammar needs some work.

Honestly, I know parts of this - if not all of it - will go terribly. But the "fun" is in the building and learning about new things. Some people blow there money on $500/night Disney vacations; I'd rather make something, even if it ends up a total bust. Why a boat? We happened to have the logs, and I happen to live in Tampa, FL where boating is a year round thing. And I'm already having fun learning about it.

You bet! Here is a photo of the logs.


And a photo of the crack I'm having to patch. Its on the last left back connection.


As for plans - especially when your flying blind - they tend to change. That said, here is the current list of steps I have:

1. Cut and haul the logs out of the woods.
2. Soap down the logs, pressurize, and look for bubbles indicating leaks.
3. Patch the found leak with Alumiweld
4. Use rubber stopper from West Marine on the tube drains. The holes or pretty misshaped, so I may have to grind them off and weld on new drains. (This is part of a future dumb question I'm sure)
5. Test it actually floats without taking on water by slowly dropping it into my in-laws pond.

That should get me floating.

After that I'm planning to:
1. Build out the deck. Get a ~75hp outboard - friend suggests Yamaha 4 stroke - and attach it.
2. Salvage yard or online new to source steering (probably hydraulics, but idk yet) throttle, batteries, and other key components.
3. Setup the steering, throttle, power, etc.
4. On land test
5. In Pond test

That's what I have so far. Appreciate you!

 

Kudos to BB's reply

You have several issues at play here - if you really wish to use this as a 'boat' too.

The crack, you really need to remove the region of the plate and replace it. A simple weld or weld-repair wont be sufficient.
Thus, this is the job for a skilled and experienced aluminium welder. Since you're most likley going to need a patch with a backing bar attached in order to obtain good full pen weld of the old to new plate.

Secondly, to be sued as a boat you need to address the flaws in the construction.



The blue circles show the welds, simple stitch welding. Since these members are main structural members of transverse joints, these will experience flexing and torsional loads.
As such the gaps, shown in black, cannot exist. In other words, these must be fully continuous welding.
Again, seek a professionally qualified aluminium welder for this.

Finally, the reason for the crack, is that - there is no weld and importantly weld return at the highest stressed region, this one:


The little blob of weld at the end is a sign of a cold weld i.e. not must penetration and it is a stress concentration and is subjected to the highest loads, when the member is loaded.
It is not finished i.e. no return..and so the load needs to go 'somewhere'....into the plate and pulls, but how...it pulls on the small blob of weld and starts the crack.

If the region across the flange (in black) was fully welded and around the other side....the load goes into the weld and then into the plate.

This simple fixes for a professional... but may be beyond your ability and budget?

 

Zach,

You passed the litmus test, good on ya.
You'll be fine.

BB

 

Heed Ad Hoc's advice, it doesn't get any better than this!

Search on this Forum for pontoon info (top right search window), this has all been covered before.
Your key issues are weight vs buoyancy.
On that note: what is the diameter of your pontoons, 20"?
EDIT: And, what do the other end of the pontoons look like, tapered as well?
And what the hell is that crazy looking superstructure on top of the pontoons all about?

 

Ad Hoc. Thank you! Googling the terms in your post taught me about welding in ways I was previously unaware, and I'm sure your post will help many other people who see it. I'll see if I can price something out for an aluminum welder.

Could you clarify what you meant by this?

For some more context on the structure and crack. Each weld area from front to back of the boat has the same 3 joint weld. Here is a middle section:


As for the crack, It is highly likely I put the crack in the pontoon when I pulled it out of the woods. You can see in the next photo the back most bracket is bent and snapped. That is where I hooked up the chain to pull. I assume it caused the crack in the back weld joint. (Posting this for anyone in the future. The logs were in a bamboo forest. Bamboo is weak by itself, but when there are a ton of stalks they are incredibly strong. We had to cut out each stalk growing up through the middle of the logs. Then dragging it out was easy)

 

BlueBell,

The back is capped with a dome. The diameter is ~20"- maybe a little lower. Here is a pic:



and thank you. I'll do some searching.

That is a frame for a bimini.

 

Zach,

Great photos, keep 'em coming!

Looks more like 18" diameter but it's hard to tell from the photo.
The 9" mark looks to be in the centre, no?
Make a pair of calipers out of scrap wood and get a more accurate measure.
As I mentioned, buoyancy is super important with pontoon boats.
In designing an amature pontoon boat, you don't want to load beyond 33% especially with a narrow beam like yours.

Assuming 18" dia and 21.5' of full-dia length (5' taper?)
Yields 76 cubic feet (cf) total displacement (completely submerged).
1/3 loading is ~25 cf capacity.
You live in Florida so salt water use, no?
~64 pounds x ~25 cf = ~1600 pounds
That includes the pontoons and their superstructure, floor, seats, engine, fuel, steering, battery, cables, bimini, docklines, cooler, provisions, flares, fire extinguisher, dogs, people, running lights, snow... you get the idea, everything!

That should give you enough to chew on for a while.
(Don't trust my math, work the numbers yourself please.)

BB

 

Sure, as the pontoon/boat will be in water..and when under sail, there will be a multitude of forces acting on the structure, a simplified example below:



With small stitch welds, these may be "sufficient" under a simple static load, but boats are rarely static...they move and structure flexes. So you need to account for a varying load and forces acting in 2 or 3 direction at the same location at once. As well as the flexing = fatigue.

So, the ends of the welds (red) are now subjected to higher stress - which may be within their limits, but once is ok, twice fair enough... but over weeks/months etc... is not good, especially if poorly maintained etc..
The time it takes to mark out the stitch length for each member is almost as quick as just doing a simple continuous weld, with no stop-starts, also another source of cracking when done poorly.
A continuous weld is far better..and gives you peace of mind that the loads and forces your pontoon is subjected too...has sufficient 'load paths'...which means it has structural redundancy!

So if we also look at the wider picture of the structure:


When looking transversely, the situation is no better.
Crack sites shown in red circles.
Because how does the load that is running transversely in the beam get into the tube?...it does it by the small attachments of those short long.t members, so the load needs to get through small 'area' of weld...again not ideal.

Ideally you would have traverse bkts for good shear area, as shown in red.
And... ideally the corner joints would have mouse holes, like so:



So the long.t weld does not cross the transverse weld.
It will also act as a drain for any water too.

And that's the point.. if a simple lift with no real load (other than the bare bones structure) can cause that crack... how do you think it will be when it has a deckhouse outfitting etc...and waves passing by on it?!

 

It's a pontoon boat, you'll do fine.

This forum is somewhat populated by two groups of folks, one is very down the rabbit hole of fastidious. The other shows up with a budget of 10$ and a dream to sail the world in an atrocious design of their own held together on noting more than hopes and dreams. The clash between the two groups is 75% of the content and the debate reinforces each perspective.


Your wanting to essentially make a modern huck finn/tom sawyer raft out of some pontoons. Unless your planning to take it 75 miles into the gulf for snapper, I'd say your expectations of putting around a lake or just fine. It's just as easy to over think a boat as it is to under think it.

That's some thin aluminum, guessing the crack formed by whatever deposited it in the woods or some other accident. Probably going to need to do a doubler Plat over the crack and maybe even on the drain plugs. Find someone who can tig or who has a modern pulse mig that can manage heat well. Welding old thin aluminum is a pita. I wouldn't change the weld arraignment, chances you don't introduce new leaks or stress points in old thin alloy is low. Fix what needs fixing, don't introduce more complication.

As long as you manage expectations and don't mind spending some money you aren't likely to recoup in it'd entirety, enjoy the process and go for it.

 

Most of our words falling on deaf ears as the OP hasn't been around now for weeks.
Disposable information.
Gotta love forums, eh!

 

Yup...easy come easy go....