Buoyancy- Underseat Tanks or Foam

The Peapod (like some other CLC designs) has foam blocks attached to the underside of the seats to provide buoyancy in cases of swamping/damage.

Has anyone considered the possibility of replacing the foam blocks with tanks constructed out of plywood.  They would provide about the same amount of positive buoyancy and with a suitable hatch give a small amount of dry storage for a mobile phone, spare jumper, sandwiches etc.

Paul


5 replies:

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RE: Buoyancy- Underseat Tanks or Foam

I haven't built a Peapod but I've used that idea in other boats. Things to watch out for are:

1. On a small open boat no place is ever truly dry. Put your electronics in a drybag or other watertight container before putting it into the storage space. Hatch lids (homemade or commercial) are notorious for their propensity to leak.

2. If the hatch will be on the top side of the seat it needs to be strong enough to stand on and flat enought to sit on for extended time periods. The lid also has to remain secure no matter what or you will have a water ballast tank instead of an air flotation one.

3. Air weighs less than foam so it'll give more buoyancy per volume but this advantage is nibbled away by the weight of the plywood and of anything stored inside the tank. Don't overload it.

4. If the tanks are large there needs to be some way to secure any contents inside so that they don't go bouncing around as the boat encounters wakes, waves, etc.

5 Finally, make sure that the tanks don't block access to critical areas. They're a lot harder to remove and replace than foam blocks.

Have fun,

Laszlo

 

RE: Buoyancy- Underseat Tanks or Foam

Paul

On my Peapod I've thought about building a small box or two and installing them into the foam. The boxes would be say 6" x 6" x 6" with a door. Maybe a drawer but that would require a box to slide the drawer into...hum.  I'd carve out a hole and include it in the glassing of the foam and then slide/glue the box in later. 

Let us know which direction you go. I've not reached that point yet and not sure what I will do.

Dean

RE: Buoyancy- Underseat Tanks or Foam

As far a the idea of waterproof storage for things like cell phones which must remain absolutely dry in all circumstances, it has been my experience that a Pelican case is the only thing to which the word "waterproof" might be applied without requiring limiting modifiers like "mostly" or "reasonably".  Even a Pelican case will admit water if immersed deeply enough, but that depth isn't likely to be attained in anything short of a complete sinking, in which case you've got worse problems than the loss of a cell phone.  If you make sure the gasket surfaces are clear of any debris or stray corners of bandanas and such, make sure the latches are properly secured, and make sure the air vent valve is fully closed, it's extremely unlikely that anything inside will get wet, even if the case is immersed as might happen in a capsize.

Don't get me wrong--I have used various dry bags, gasketed plastic storage containers (my current favorites are the Lock'n'Lock, see here) and even Ziploc bags to keep things reasonably dry in wet boating conditions like rain, spray and water sloshing around in the bilges in many different boats over the decades, but my trusty old Pelican case is the only one which has never let me down.  Dry bags are great for clothes, but the seals can admit some water if the tops get immersed for any length of time, as might happen in a capsize.

I have used our PMD's under seat air chambers, both with the circular hatches, to store things, but I have had a bit of water get into one during a capsize (probably because I didn't get the hatch screwed down properly.  Stuff in dry bags small enough to fit through the hatch should stay dry reliably, though, as long as the hatch doesn't fail completely to admit a lot of water.

Sorry if I've wandered off topic a bit....

.....Michael

RE: Buoyancy- Underseat Tanks or Foam

   I had an idea for my skerry where I could build plywood tanks that are removable and could bolt on/off. I think the points brought up are true but this may be a way to keep the good looks of wood with some increased safety/right the boat and a minimal amount of semi-dry storage.

 

RE: Buoyancy- Underseat Tanks or Foam

Thanks for the hints and tips everyone.

I drew up some preliminary designs based on the templates for the foam blocks in the manual.  These suggested that wooden tanks would weigh about the same as the foam, provide about the same amount of buoyancy, and in the UK at least cost about the same.

I even got as far as running up two quick prototypes in MDF, hardboard and cardboard to prove that they will fit (which they will with a bit of trimming).

In the end I decided to stick with the foam blocks: (i) They will be simpler to construct and attach to the seats (ii)  I did not want to have to explain to the insurers that a newbie boat builder is competent to diverge quite so far from what the designer intended and (iii) I understand that solid foam is part of satisfying regulators safety requirements.

Incidentally a friend has successfully carved a storage area (with a water tight hatch) into the foam.  His advice is that it should be perfectly feasible (and possibly easier) to cut a void into the individual blocks before the layers are stuck together.   

With any luck the links below should connect to a couple of photos of one of the prototypes.

https://www.facebook.com/photo?fbid=223289479796852&set=pcb.223295816462885

https://www.facebook.com/photo?fbid=223289433130190&set=pcb.223295816462885

 

Paul

 

 

 

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