Polystyrene Buoyancy

S

SteveIOW

Well-Known Member
Joined
3 Oct 2008
Messages
158
Location
Isle of Wight
Visit site
I need to add some buoyancy to my GRP tender so that it doesn't sink at its pontoon berth when it fills with rainwater. I have a good quantity of 2 inch thick polystyrene doing nothing useful in the garage so intend to use this. Cutting to the required shapes is no problem but am looking for a simple/effect means of holding the 3 or 4 layers of 2 inch thick polystyrene together (each section of buoyancy will be 6 or 8 inches thick). Also need to provide a bit of protection to the outer surface so that small pieces don't break off each time it gets knocked. Have thought of using some form of shrink wrap but have no real knowledge of / experience with shrink wrap.

Any ideas welcome please. I don't want to permanently glass in the buoyancy to the GRP hull.
 
Personally I'd glass it in - how else are you planning to fasten it to the hull? But if you don't want to, then I guess simply wrapping it in gaffer tape will hold it together and provide some protection.

Pete
 
Many solvents, including the styrene in polyester layup resin, dissolve polystyrene very effectively, which rules out a lot of adhesives. Perhaps the best that doesn't is epoxy. I am guessing that it would stick the polystyrene together and you could lay up some glass on the outer edges to protect it.

As said already, how will you attach the polystyrene to the boat? The same problem is addressed in grp canoes by laying up U-section pieces that can be placed around the polystyrene and glassed to the boat. Maybe you could do the same but bolt the U-sections to the thwart?
 
SteveIOW said:
The polystyrene will be under each thwart so no need to secure to hull. (Thank you Pete for prompt reply).
Click to expand...

In which case, in a scruffy tender I reckon I would just wrap lots of black nasty around both foam and thwart. But maybe yours isn't a scruffy one :)

Pete
 
I'm repairing a large tender at the moment and its getting 20 litre drums jammed under the seats and tied in. You could always make up a container of any sort and throw 2 pot pu foam in, £10 for 50 litres.
 
Don't forget the fixings of the buoyancy pretty much need to lift the full weight of the boat.
With the weight of the bloke who gets in to bail it.
Will the thwarts do that?

One method is to get some stout cloth such as acrylic canvas, and lace it down to multiple fittings screwed to the floor. It will keep the sun off and stop the UV trashing the polystyrene.
Or you could just put a few straps over like dinghies do with buoyancy bags.


If you do decide to glass it in, a few coats of vinyl emulsion paint will stop the resin dissolving the polystyrene. Test on a scrap first!
Or you can wrap the polystyrene in polythene first.
 
I was advised several years ago that polystyrene would eventually absorb water and so sealed the shaped blocks in plastic sheeting before ramming them into the compartment that I feared might not remain watertight.
 
SteveIOW said:
Would it be possible to skrink wrap the polystyrene (HOW DO I DO THIS?) to seal and protect?
Click to expand...

My thoughts, too.
Why not go to a "packaging business" or one which uses hot-air guns to shrink-wrap HEAVY duty polythene (like they wrap stuff onto pallets).
If UV degradation is a problem wrap your polystyrene in black plastic first.
I'd put a bit of protection, like gaffer tape, onto the finished slabs to guard against wear and tear e.g. boots, gear etc.
 
Just because I happened to have some I wouldn't use it, having removed what was left in several boats. I think PU is better, but it all needs protection.
I'll use cans because its simple and effective, removable, repairable. I've had too many boats with (badly) built in buoyancy, no one seems to do it properly.
 
Parcel tape. The trouble I have removing the stuff makes me think it would easily last a season. Why worry about eventual seepage? Just replace the buoyancy when it has degraded. A good reason not to install it permanently.
 
Lakesailor said:
Parcel tape. The trouble I have removing the stuff makes me think it would easily last a season. Why worry about eventual seepage? Just replace the buoyancy when it has degraded. A good reason not to install it permanently.
Click to expand...

Yes, if you want to do a permanent job, better to glass in a bulkhead with an inspection hatch. Temporary buoyancy is much better than none!
 
You must log in or register to reply here.

Share this page

Top