Floating pontoon

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Johnny5

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I'm looking to build a floating pontoon and connecting walkway
This will be on a tidal river so the walkway will span from the river bank to the pontoon and will be approximately 5m long
The plan is to build a pontoon 4m long x 1.2m wide from treated timber and decking using a total of 8 blue plastic barrels arranged in two lines
This will then float up and down with the tide and provide mooring for my 7m boat
Looking at the height of the water at low tide to bridge the muddy bank the walkway will need to be around 4 -5m long and be hinged at the top so it can pivot up and down with the pontoon
Has anyone had any expireance with this type of thing and offer me any advice ?
 
Planning permission from local council, riparian owner, Environment Agency, Crown Estate, etc. ?


How are you going to secure the pontoon and boat against the flow of the river ? What speeds are expected from ebb tide and or wind forces ? Any risk of debris such as trees coming down and lodging against the pontoon ? What method of anti-fouling are you proposing ? Security access ? How will you secure the boat to the pontoon - forces on cleats will be substantial. what about a non-slip surface to the decking (some treated woods become very slippery when damp.) ?


I use pontoon maintained by a mooring association. Though we only launch dinghies from it, it is more substantial than your outline spec.
 
Johnny5 said:
I'm looking to build a floating pontoon and connecting walkway
This will be on a tidal river so the walkway will span from the river bank to the pontoon and will be approximately 5m long
The plan is to build a pontoon 4m long x 1.2m wide from treated timber and decking using a total of 8 blue plastic barrels arranged in two lines
This will then float up and down with the tide and provide mooring for my 7m boat
Looking at the height of the water at low tide to bridge the muddy bank the walkway will need to be around 4 -5m long and be hinged at the top so it can pivot up and down with the pontoon
Has anyone had any expireance with this type of thing and offer me any advice ?
Click to expand...

As has already been said, your design does not mention how you will locate the pontoon against the forces of boat, current, etc. However, my biggest concern will be the risk of the pontoom capsizing. It is very narrow at 1.2m and with the barrels not giving much buoyancy along the edges. At Bridgemarsh marina on the crouch they are currently making their own tried and tested design pontoons from plastc barrels, a steel frame and timber decking. Go have a look. They are at least 2m wide.

Www.solocoastalsailing.co.uk
 
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Tranona said:
Suspect that is anchored to the river bed at both ends
Click to expand...

Yes - you can see a pair of chains at the near end.

Doesn’t look like the river that one’s on goes up and down very much though. Would the OP be able to do his with simple crossed chains, or is he going to need piles? If he’s got a short walkway to the bank then the pontoon needs to not move about very much.

Pete
 
prv said:
Doesn’t look like the river that one’s on goes up and down very much though.
Click to expand...

I suspect not, Pete. The "tamula" in the filename is a lake in central Estonia. The image belongs to an company which describes it as a "swimming pontoon", which no doubt accounts for the absence of cleats.

As said, anything on a tidal river must take very substantial loads...far beyond those capable of being carried by a fixed walkway to shore, let alone an articulating one.
 
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It's all possible, these (if it works are just up from our club).

https://www.google.co.uk/maps/place...x495c163a920de244!8m2!3d51.584151!4d-2.997664

Our club pontoons have a metal gangway that fixes from the bank (big concrete pad) onto the pontoon, it's anchored to the bank by lines, the whole thing pivots to be stored against the bank in winter. It's on the Usk so has a good tidal range and flow. I can take a few pics next time I'm down if it helps but I recon it would be quite a big undertaking.

https://www.google.co.uk/maps/place...x495c163a920de244!8m2!3d51.584151!4d-2.997664

As you can see it's pretty long and a fair old size.
 
The compact way to anchor against current is diagonal wire ties from an upstream strong point on the bank to the opposite corner of the pontoon and vice versa. This depends on two vertically pivoting struts from the bank (one can be the access walkway) holding it in a fixed position, you can use the same strong points. In plan you have a rectangle with two diagonals, the sides are the bank and the pontoon, the ends are the rigid struts in compression and the diagonals are the wires in tension. Stainless wire is better than chain (recycled shrouds, any rigger and many boat owners will have plenty complete with bottle screws) as it is easier to adjust accurately and does not exert so much pressure on the fixings.
I agree with increasing the width for stability it will not take up any more space, will shorten the gangway and add little to the cost.
 
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I have made many rafts with 200lt barrels, the biggest was a medieval Cog 33ft long and 12 ft high in the castles, which had scaffold towers in. Extend the beam for stability, even though moored up. Alloy ladders make an excellent framework and maintain the stability of the barrel's attachment. I would have a rudimentary bow on each hull to fend off debris, and moor the whole thing a long way fore and aft. Youngman board would be good for the gangway. Wire netting stapled down for grip on the decking.

PS. Do you need all that buoyancy, 1.6 tons when sunk? Four barrels, in the corners, might be enough.
 
Thinking again: do you want space to walk around the pontoon deck? If not, then just make one hull with three or four barrels, bolt the gangway to it, hinge the landward end.
 
Found a pic, here is the 'Aprille' in full battle order (Wan that Aprille withe shoures soot...Chaucer)

sn2lgk.jpg


Incidentally, only eight barrels for the whole thing, ten crew, outboard motor and all the ammo.
 
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Thanks fisherman for your comments
I like the idea of using ladders to make the pontoon sides from I will look into that
Looking at the other pontoons along the river most are held off the bank with scaffolding tubes attached to a tow hitch and ropes or chains at each end secured to the bank
I was thinking about driving timber piles in at each end as there will be a large digger on site that may be able to assist with this ?
Also the use of chicken wire over the decking I have seen before so I think that's the way to go
Do you think 8 barrels is to much ? I intend to increase the beam to 2m so it will be
4m x 2m will this be stable enough ?
Many thanks for all your comments
 
Johnny5 said:
Also the use of chicken wire over the decking I have seen before so I think that's the way to go
Click to expand...

Chicken wire is quite good but tends not to last very long. Think about missing out the wire and just using reasonably heavy staples instead, leaving them a little proud of the deck.
 
four should be ample, one each corner. I don’t know what sort of current and rise and fall you have. If you had a monohull, one row of, say four barrels, 16ft long, 2ft wide, less resistance to flow. With the gangway bolted to it to make it stable, but if you need to walk around on it 4x2 metres will be fine.
 
I have just had a quick look at the tides in my area it looks to be around a 2.7m range
So at low tide to bridge the muddy bank the walkway will need to be around 5m long ?
I'm still in the planning stage at the moment so any advice is much appreciated
 
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