Floating duck house

I came across this thread and have similar questions.

My duck house, with platform, will weigh in the region of 35-40kg. Would I need 40litres, in empty soda bottles to keep it afloat?

 

Bairly.
Each liter bottle will float slightly less than 1 KG (subtract the weight of the bottle)

Add the weight oh the ducks and nests to the duck house weight to get total weight needed to be floated.

Decide how far above water the deck has to be.

Measure what percentage of bottle will be above water line, and what percentage will be submerged. Only the submerged portion of the bottle supplies buoyancy. The dry portion is reserve buoyancy (in case a goose visits the ducks or a bottle starts to leak [ replace bottles regularly ]) If 75% of a 1L bottle is submerged then it has .75kg of remaining buoyancy. 50%=.75kg. 38%=.38kg

Divide total weight by the reduced buoyancy to get the number of liter bottles needed.

I suspect it will be around 100.

 

Wouldn't 2 liter bottles be the magic?

 

I'm not sure of beverage container qualities in the UK.
But yes here in the US two liter bottles are far more robust than the one liter water bottles. My personal choice would be 5 gal paint buckets. Screw the lids to the bottom of the platform. Snap the bucket in and good to go. Very robust.