Foam - which type?

[Hudds Lad]

thinking of making some porthole bungs, and am bewildered by the vast array of foam types (and price thereof) available.

 

is there any particular type i should be aiming for, or avoiding?

[Jen-in-Wellies]

Are you meaning a self supporting insulation to make the bung out of, or a soft foam to go over, say a ply base? If the former, I would use extruded, not expanded insulation board. Kingspan, or similar. Available in 25, 50 and upwards mm thicknesses. Very stiff and fire retardant. Susceptible to damage if the edges are knocked, so cover with cloth to protect them and make them look nicer and provide a handle to get them out the porthole frame.

 

I keep meaning to make a set, but still have the unpainted plywood bungs from when I first fitted out the boat. ?

 

 

Jen

[Hudds Lad]

a self-supporting piece of foam, to be wrapped in fabric that matches other stuff on the boat.

 

pic shows the sort of choices i mean

 

[Jen-in-Wellies]

Since you are unlikely to sit on them on a regular basis, then I'd pick the hardest one. The foams main requirements when used as a porthole bung are thermal and sound insulation, lightness, rigidity and resistance to moisture uptake, so a closed cell rigid foam is going to be the one to pick.  The one you highlighted in the screen dump is an open cell and although the pores are large, will still take up a bit of moisture.

 

Personally I'd cover a rigid building foam, like this, rather than use a foam designed for sitting on. They are super rigid, very light, good insulation, fire resistant and won't suck up moisture.

 

Jen

[Sea Dog]

We've got some of these, covered with fabric which matched the curtains our boat came with.  I'm always undecided about their merits.  They fit neatly inside the porthole liner and effectively block light and provide insulation between the glass and the boat interior. However, I see no need for them when we're aboard as the curtains or blinds do the job required. The time I have used them is for periods in winter when we're away from the boat.  In this case though, unless the humidity in the boat is already very dry (unlikely when leaving the boat in winter) I worry they'll trap condensation. I'd be interested to hear what has prompted the OP to want them and listen to other views of their merits.

[Hudds Lad]

13 minutes ago, Sea Dog said:

 I'd be interested to hear what has prompted the OP to want them

it was just an idea to try and keep a bit more warmth down by the bed, and a bit less condensation on the portholes come morning. and with an initial outlay of around £15-£20 for three portholes it seemed worth a punt.

 

our first week this year is mid Feb and as we had similar last year and it was a tad parky i was just looking at a cheap way of saving some heat. the bungs would only be onboard when we were (some of the other shareholders are resistant to change).

 

i’m only toying with the idea to be honest, i’ve no real clue if there’s even a benefit, just any solution needs to be temporary as we’re a shared boat.

[Detling]

We have bungs good in winter, but in summer they not only keep out the light they also effectively close the window so the bedroom gets a bit stuffy and airless particularly in hot weather.

[Machpoint005]

I don't think there is any need to use insulation at all. A well-fitting circular piece of ply, lined inside and out with fabric, will not have significantly less effect on heat loss. Portholes are tiny compared with the area of cabin sides and roof. 

[Jen-in-Wellies]

Prefer sleeping in a very dark room, so porthole bungs are ideal. Mine are currently 6mm plywood with rubber draught proof seal around the edges. These are relatively heavy, so I use a removable wood dowel rod across cup hooks each side to hold them in. Have been toying with the idea of fabric covered insulation foam as the light weight and compliance should keep them in without the dowels.

 

Jen