I would love to try seagrass but I don't think we have it in New Zealand. Also, foam is expensive to buy. I have noticed that from time to time people throw out old foam mattresses and evidently have no idea what new foam is worth. Consequently I have kept a watch on Trademe (our version of ebay) and managed to acquire three or four of them for next to nothing over the past few years. I have made use of one of them, for my little boat, by sewing up a new cover and presto - a new squab for next to nothing. The others are waiting for when I get around to covering them. If you want extra thick foam, an old foam lounge suite that has foam filled squabs is a good source - when they get scruffy people throw them out, or sell them for next to nothing just to get them taken away. Recycling that sort of thing appeals to me. Foam squabs (as from lounge suites) can be glued together with contact adhesive  to make a full length squab, then re-covered. I hate seeing that sort of thing wasted.

This is fascinating. But I can't tell from the picture, is this actually an algae seaweed (such as Fucus or Chondrus species) or is it a seagrass (Zostera sp.) which is a vascular plant, not an algae, and would be more like hay when dried. Zostera is also become highly protected and might have restrictions on harvesting for mattresses unless it is washed up on a shore already. I'm interested in using this at some stage.  

Jan, please excuse my bad english. By seaweed I meant seagrass (Zostera)! You are absolutely right, it dries to a hay-ish like thing. Zostera is indeed highly protected, because it is endangered, and I would strongly advise to NOT cut it from the seabed! This would be quite unpracticable, anyways...

The usual approach to harvest seagrass is to wait for the next onshore storm, and visit the beaches the next day. There will be plenty of fresh seagrass waiting there on the hard, you just need to collect it (At least in Germany, you are allowed to take anything from the beaches that is washed ashore). Typically, doing this you are doing a favor to the municipalities: they pay a lot of money to clean the beaches from that "rubbish" - to make those beaches bright and shiny again, for tourisme purpose. In Germany, the municipalities even have to depose it as "hazardous waste" on landfills... That's really a shame!

A hundred years ago, it was quite common in northern Europe to make matresses from seagrass. It was also used commonly in coastal areas to insulate houses. I heared stories of old villas from the 19th century being demolished nowadays, where the walls and floors are found totally rotten, but the seagras insulation is still as new, freshly smelling like hay.

What an amazing, underestimated material! And its free, washed upon the shores from time to time.

If you are interested (and willing to use a translator), have a look at:

Strand-Manufaktur

Seegrashandel Lübeck

Hi,

I bought from a company called efoam.co.uk.

In the Saloon I used their 4” Reflex Superior foam (firm) with 1” Memory foam

spray glued on top.

For the Quarter berth where height is restricted I used 4” Reflex Superior (firm) alone.

I used their 5” Reflex Superior (firm) with 3” Memory foam in the V Berth.

I added a layer of Dacron Wrap to the top and sides and then Stockinette to make 

fitting the covers easier.

For the back cushions I used 2” Reflex Superior pink medium firm, again with 

Dacron Wrap and Stockinette.

It wasn’t cheap but I’m really pleased with the results.

paul

Peter,

if you consider taking a rather unusual - but traditional - route: we built our own matresses stuffed with seaweed, and are more than happy with it!

Just sew a simple cover or take one from a foam matress, and stuff it with seaweed to the appropriate hardness. Dried and washed seaweed you can buy, or you collect it yourself and go through the process of washing it (a lot with fresh water) and drying it. It makes for a (admittedly rather hard) good matress, like seamen used 100 years ago. They smell like fresh cut grass, not at all like stinky algae or fish. It is all natural, and cozy. But the main advantage: due to the high salt levels inside the seaweed cells, it cannot burn, will take in a lot of water before being "wet" and it cannot rot at all, even if you treat it badly. We are now sleeping since two months nonstop on those. They are not vented at all, laying on a flat hard cold surface without any possibility of air circulation. We never lifted them during the day to dry them, not even once. No rot, no mould, not feeling wet, not stinking, no nothing. Just warm and cozy. Only disadvantage: you have to restuff them (5 min work) after some weeks with permant usage, because they adopt your body shape just a bit like this form remembering foam developed by NASA. This can get a bit uncomfortable over time, but is easy to fix.

Maybe you give it a try?

I've bought from Foam for Comfort numerous times, for both boat and house projects. They're not inexpensive, but they give good advice and service. For simplicity, you could use a firm domestic grade of foam for a 100mm thick boat mattress, but there are so many ways to go on this - memory foam, latex, soft/medium/firm layers etc - so it's best to enter into a dialogue with them.