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Help me build a gangplank.
December 18, 2013 5:19 AM   Subscribe

I need to get on and off my boat easily. More to the point my pregnant wife needs to be able to. (Because we both live in the boat). I have recently built a new wooden gangplank which is not too bad. (but heavy) But for reasons I will go into below I think I need a replacement.

Because of the rise and fall of the tide it is already suffering.
The main problem is that I didn't get round to properly securing it to the quayside, or adding wheels on to the bottom on the deck side so as the tide rises and falls it pulls on the uprights (which is how I've temporarily secured it)

So I think by the time I have enough time and light to fix it properly it will already have pretty much degraded. I was thinking of instead of repairing this one, building a new one, taking what I've learned from this one to improve it.

One of my thoughts was to replace the side beams of wood with aluminium channel because it is a very very heavy gangplank. Aluminium would make it much lighter.
This leads me to my question:

If I get a bit of aluminium that is at least 3.6m long, possibly 4m long, what thickness would be needed to support a heavy human standing on it. Is channel best? or should it be box section? etc, etc...
(I was looking at various size options here)

Is there a downside to mixing wood and aluminium construction?
Like for example I was going to stick my treads (cut from wooden decking board) in the channel and then screw in through the aluminium itself.
How easy is it with domestically available tools to cut, drill and generally fabricate with aluminium. I don't have anything specialised and haven't worked with aluminium before.
posted by Just this guy, y'know to Home & Garden (13 answers total)
Instead of trying to fabricate something, have you looked at ready-made aluminum scaffolding planks? They come in various lengths and you can either make your own or get guardrails for the sides. It's also fairly trivial to attach an axle to one end and put wheels on.
posted by RonButNotStupid at 5:35 AM on December 18, 2013

You could also buy aluminum walk ramps, like what you use with moving vans, some of the ramps will hold 1000lbs @ 16ft long.

It'd be a simple modification to put some straight wheels on one end to account for the movement due to tides and waves, and secure the other end.

Obviously it's cheaper to build it yourself, but that assumes you have the knowledge and tools to do it, which most of us don't. And this way you can be confident that the ramp will hold the declared weight and not collapse.
posted by jpeacock at 5:40 AM on December 18, 2013

Aluminium is easy to work with in terms of drilling and screwing - any metal drill bits from Home Depot will work fine with it. It is harder to weld anything (obviously) but drilling and bolting things to it is easy.

That scaffold ramp looks perfect, to me. My first immediate thought was to get to pieces of Ali I-beam and you could put the wood between the two channels. The wood would have better grip (ali is very slippery when wet - use grip tape on it to retain traction if you use it) and just bolt some kind of rail to it. The channel could be 1/8" and it would never bend under the weight of a person. Look at how that scaffold ramp is made for ideas on suitable thickness for 500lb rating.

Also, that scaffold has a tube through the end. You could REALLY easily put an axle through there with two nylon wheels on it to make it roll. No bolting required at all.... Also, you could really easily fix the shore end to the railings with a length of (zinc coated) chain through another of the holes through the plank (say, 2 feet down from the end) and padlocked/hooked in a loop around the railing. Easy peasy and easily removable or adjustable (and securable as Ali is good money at the scrap yard!).

So I suggest you either get that scaffold option and just fabricate a frame (Stick with metal, preferably Ali) for a railing. Or, if you'd rather mix and use wood you can make the two I-beam with wood between option. As I said, 1/8" I-beam is really cheap to buy (for Ali) and super strong.
posted by Brockles at 5:54 AM on December 18, 2013 [2 favorites]

You do realize that they sell these products commercially, yes? I mean, here. They aren't terribly cheap--but buying enough aluminum to make something like this wasn't going to be anyway. Indeed, as you say you've never done something like this before, it is almost certainly going to be cheaper to just buy the damn thing than try to do it yourself. You'll likely wind up with a better product too.

My recommendation? Head down to your local boating supply store, buy whatever it is they have in stock, and have done with it. Problem solved. Probably set you back a grand or two, but hey. That's living on a boat.

Oh, and wood is probably not an awesome idea, for two reasons. First, it's going to be beastly heavy, especially when compared to aluminum. A pressure-treated 12 foot 2" x 6" weighs almost 40 pounds. You'll probably need six of 'em. Now we're up to 240 pounds, just for the deck. And it does need to be pressure treated, because of the second reason, i.e., anything wood that isn't pressure treated that spends all of its time by a dock is going to rot. Fast. So pressure treated it is. If you can make a reasonably sturdy gangway in under 400 pounds, I'd be surprised. Go with aluminum, and just buy one off the shelf.

Oh, and something else: if you make one of these yourself and it somehow breaks and someone gets hurt, that's totally on you. So there's an added incentive to buy a commercial product, in that you'll be more sure that it's not going to break--and have someone else to point to in the unlikely event that it does.
posted by valkyryn at 6:33 AM on December 18, 2013 [3 favorites]

Something that came up while I was pondering the idea of a ladder with a board on it is Youngmans Boards:

They seem like they'd work pretty well, too.
posted by Brockles at 6:45 AM on December 18, 2013

Once one side is moving with the tides, and probably wet too, the aluminum will be slippery. Be sure to add something rough to the walking surface.
posted by Houstonian at 7:57 AM on December 18, 2013

I think you're creating a lot of work for yourself.

Yes, you can use wood. Posh gangways and passerelles use teak. But I suspect your best bet is composite decking designed with marine use in mind.

The issue is not so much the construction of the deck bit, but the handrails. You really want these welded on and, for weight, to be aluminium. In short, you probably want to take this to a fabrication shop, give them the decking and the spec and get them to build you your gangway.

But before you do that, compare against new and used prices for access ramps/gangways - the companies that specialise in these things have the specs already and can churn them out quickly if your job involves customisation only on set units of size. Once you've bought your decking, sourced your aluminium, discussed the spec with a fabrication shop and paid for fabrication you might find that what is basically a commodity item will be cheaper.
posted by MuffinMan at 8:06 AM on December 18, 2013

I'm really more interested in building something than buying something, even taking on board the answers so far, because then I'd know how to.

I'm well aware of how heavy a wood gangplank is (see picture attached, it's that heavy)

however I like the idea of using composite decking to reduce the weight and improve the durability.
Also good to know that 1/8" thick aluminium will take the weight.

I've costed a basic design up and it comes to something like £400 with some rather natty hand rails and all. So that's not bad. I might build a kitchen first.
posted by Just this guy, y'know at 3:49 PM on December 18, 2013

To clarify, two 1/8 I-beams (I'm imagining it being maybe 3" high x 2.5") would be strong enough, of the top of my head. Anything less than that might mean actually having to sketch up some proofs.

Either way, even if you want to make something, get thee to a scaffold rental place and ask to measure up the composite planks they have at the very least. That will give you all the thickness/section info you may need and you may even be able to get some ideas and/or some cheap second hand stuff.
posted by Brockles at 4:20 PM on December 18, 2013 [1 favorite]

Oh, and I'd love to see more of the boat, especially if it's liveable. Just saying...
posted by Brockles at 4:21 PM on December 18, 2013

Well, I live in it. But it's liveability is currently a little questionable.
But, since you asked:
Here and Here are a couple of external shots.
Here is my favourite photo of inside looking out. (Which doesn't show much of the boat, but does show how high up the portlights are)

A lot of the internal ones are just too chaotic to be sharing.
I need to take some more. It was a floating bar not too long ago, so we've had to do a lot of work inside to even approach habitable.
I am currently far behind on insulating it. So I am cold.

I will go and check out the scaffold rental places.
I also have two fairly major building sites which I have to walk through to get to the riverside, both with fairly sociable foremen. I might go chat to them.
posted by Just this guy, y'know at 2:49 AM on December 19, 2013 [1 favorite]

Here are some pictures of the final product.

(please excuse the mess)
posted by Just this guy, y'know at 10:00 AM on April 30

So where did you get that shiny gangplank from in the end?
posted by Brockles at 10:08 AM on April 30

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