Buoyancy ?

[Jim Schofield]

Having just seen the recent video about Andy Lane's voyages, posted by Jake Kavanagh, on the Yahoo Group, I'm thinking about buoyancy. Andy mentioned his boat had 1.5 cubic metres of buoyancy and yet it was not enough.
I hope to take part in this years Baltimore Challenge and have begun putting lots of pool noodles into every corner I can. It is a small boat and a cubic metre should be enough, but how can I be sure ?

Any and all responses welcome.

Jim

 

[co256]

Hello Jim,

An object displaces the same weight of water as it weighs

If you calculate in Kg... 1 Kg of water is the same as 1 Ltr volume of water. (Although sea water weighs 1.025 Kg per litre from memory.)

So an object of 100 ltr volume will when totally immersed displace 100 Kg of water. (or 102.5 Kg of sea water.)

When the amount of water displaced = the weight of the object it will be floating and will not go deeper into the water.

So a 50 KG object will displace 50 ltr of water if the volume of that object is 100 Kg it will only be half way into the water.

There are lots of simple boat design/building books that go DEEPER... sorry?!

Good luck!

 

[oldbilbo]

I hope to take part in this years Baltimore Challenge and have begun putting lots of POT ( sick! ) noodles into every corner I can. It is a small boat and a cubic metre should be enough, but how can I be sure ?

I've hunted through Google, DuckDuckGo, and various 'pedias.... and I've yet to find a Conversion app that relates a volume of Pot Noodles to Pasta Shells to Porridge Oats. Perhaps one of the more erudite Jesters might enlighten one....

 

[PabloPicasso]

Etap yachts were designed with built in positive bouyancy and can even continue sailing while swamped. Retro fitting that level of useful bouyancy may be "possible", but must be physically difficult to do with any reliability, and may well be impracticle.

If you want positive bouyancy it may be easier, more reliable, and in the long run cheaper to buy an Etap

 

[Gargleblaster]

If you want positive bouyancy it may be easier, more reliable, and in the long run cheaper to buy an Etap

Or go through Roger Taylors videos on how he fitted additional buoyancy to Mingming II. Of course Roger has not yet managed to sink a boat since 'EndeavourII' so whether his ideas are correct might be questionable. But then has an Etap been in a position where it would have sunk except for its buoyancy?
http://www.thesimplesailor.com/video.html I just looked at September 2012 where he discusses where he will put the foam buoyancy. Perhaps in a later video he may actually show himself doing it.

 

[rptb1]

An object displaces the same weight of water as it weighs

Only if it floats! A submerged object displaces its volume.

So a 50 KG object will displace 50 ltr of water if the volume of that object is 100 Kg it will only be half way into the water.

I think you mean that a 100 litre object that weighs 50kg will displace 50kg of water and float with half its volume submerged.

Sorry to be pedantic, but this is about safety and we need to be careful.

I am planning to install over 1m³ of closed cell foam on Tammy Norie. I am half planning to deliberately swamp her to see what happens.

Also relevant: Every internal locker on Tammy Norie is filled with these excellent airtight containers that cost £1 each https://www.flickr.com/photos/rptb1/18702165529/in/album-72157636041296953/ . Some of them have food in, but I make a point to only half fill them. They will provide extra buoyancy in case of flooding. Many will be displaced by foam in future.

 

[mog]

if you are interested I am currently doing this job in Meteor of Gloucester and have some photos. I am skint and cant afford £35 a sheet for 25mm Roger Ts closed cell foam in bulk. My yacht has an internal grp moulding to form lockers and furniture. I am using a combination of air and watertight lockers filled with polystyrene insulation and sealed with closed cell spray foam. I am also filling and sealing the voids between the hull and interior where they are not needed for stowage. An RT style collision bulkhead with the bow filled with polystyrene is also under construction. Same treatment for the stern now all hull fittings are on.
I know polystyrene boards can absorb moisture over time so all spaces are carefully sealed and she is totally watertight above and below. I have difficulty in calculating the exact volume achieved but it is in excess of 2m3 (the volume of polystyrene swallowed) plus the cans of foam. My yacht weighs in at 1400 kg approx and 6.6m long. I cant fit anymore in so if it aint enough to stop a sinking I will be testing the liferaft that someone else built!!
pm me if you want to see some pix of the dirty work!
Nick

 

[Triassic]

I have various watertight compartments and have just started filling them up with empty 2l pop bottles. They are incredibly light, quite easy to post in and stack in each compartment, and more importantly easily removed if for some future reason I need to get into the compartment at a later date (for example the bow fittings in the prow).