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Old 28-04-2017, 01:18   #1
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Best way of insulating a GRP hull during a minor refit?

I hope this is the right place to post this question, if not please move it to the appropriate forum. I'm in the middle of purchasing a 9.5m/31' yacht with a GRP hull and a glass over ply superstructure. It currently has zero insulation. I am looking to do a little rearranging of the cabin layout and thought it would be the perfect opportunity to add some insulation while there will be some better access to some of the hull. I'm looking for advice on the best way to do this to add more comfort for extended cruising/liveaboard use throughout the year in New Zealand. Ventilation seems to be fairly good but it can get cold hence the desire for some insulation. I'll also be adding a heater, probably diesel.

My initial thought is to use EVA foam sheet cut to size and glued in place with taped joints as it is flexible, fairly durable, easy to work with and can be wiped down easily. Does this seem reasonable and is there any benefit to adding a layer of reflective foil? I thought the fact that the EVA foam is soft would also be a good lining in the quarter berth for providing a secure place to sleep with less chance of getting bruised on long single-handed passages in rough weather. I was also thinking about laying sealed cork on the cabin sole as it is fairly hard-wearing and easy to clean. Are there better solutions I should consider? I'd rather do it once and do it right so what do I need to be aware of?.

An issue I have thought of is that if the boat becomes fairly well insulated, the weak point will become the windows which may still be prone to condensation at times although good ventilation and heating should minimize this. As they are mounted on the inside of the cabin, would it be worth doing a little DIY double glazing and adding another layer of window material to the outside of the cabin or would it be more hassle than it's worth?
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Old 28-04-2017, 03:16   #2
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Re: Best way of insulating a GRP hull during a minor refit?


This issue of hull insulation was recently discussed in minute detail; someone with more geek skills will no doubt post a link to it shortly. But the EVA will make fine insulation. Why not just EVA the sole as well? Perhaps cork is more attractice...
There's no need to double-glaze windows--the heater will dry your air enough to keep from excessive condensation. Someone mentioned that reflective foil transfers heat if in contact with the hull--something to look into closely before committing to it.
But do check out that other thread.
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Old 28-04-2017, 03:39   #3
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Re: Best way of insulating a GRP hull during a minor refit?

Greetings and welcome aboard the CF, cj.
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Old 28-04-2017, 07:59   #4
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Re: Best way of insulating a GRP hull during a minor refit?

Take a look at Armacell or Armaflex.
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Old 28-04-2017, 14:44   #5
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Re: Best way of insulating a GRP hull during a minor refit?

Thanks all, I have sent off an email to the Australian Armaflex Distributors to see where I can source it in rolls or sheet form in New Zealand. I've managed to find a couple of threads relating to insulating steel hulls which had some useful info.

Yes, I thought the cork would make a more attractive and durable finish for the cabin sole than using the foam there. I could put foam on the underside of the sole.

I have done a little searching and found some references to using foil, air gaps, and conductivity. Just wondering about installing the foam first to the cabin ceiling, then a layer of foil and then the headlining. Although the foil wouldn't have an air gap as such, having the layer of foam in between should resolve the conductivity issue and still allow for the foil to act as a heat reflector or are my thoughts off base here?

Now thinking I will use anti condensation paint for the repainting while I'm at it. The other thing I'm going to look at is some type of vent or range hood arrangement for the galley to help deal with the steam from cooking.

Still thinking about the windows as weak points, hatches too.
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Old 28-04-2017, 16:19   #6
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Re: Best way of insulating a GRP hull during a minor refit?

Windows and hatches can be improved with temporary double glazing using twin wall polycarbonate sheeting, thin plastic sheeting or eva foam pushed into the frame from inside.

Saying that with a diesel heater running on a small reasonably well insulated boat even set on low the boat is likely to end up too warm in anything the moderate NZ winters can throw at you.

Even when I sailed to Antarctica we didn't have any doubleglazing on the windows and survived just fine. We carried the supplies to fit a crude double glazing if needed on my first trip to east antarctica but didn't use it.

Condensation drips off metal windowframes and deck hardware bolt heads are a bigger issue. I have heard of glued felt helping, but I think decent ventilation is the biggest factor. You just can't close the boat up completely or moisture builds up inside quickly.

Thats the real benefit of a heater. You can leave a hatch half open and increase airflow, while staying warm.

Armaflex looks good. Freinds used it on their boat. It was pretty expensive as I recall. Id ve interested to hear from you what sort of price they are currently asking.

Consider the issues of mold growing in the air spaces between the lining and the insulation.

Cork makes a great warm flooring material.
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Old 28-04-2017, 17:15   #7
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Re: Best way of insulating a GRP hull during a minor refit?


Welcome to CF. Insulation is one of my favourite topics. We have a GRP hull which the original owner lined with one inch thick cork tiles from the waterline to deck. The deck is balsa cored so good insulation. The boat was sailed in mainly tropical waters. However, when we cruised Alaska the condensation issues became extreme as there was no insulation below the waterline and I became allergic to the mold.

We wanted a quick solution so did not search other than what was available in Port Townsend (Washington USA) but found houses in the area were insulated with a bubble-wrap material which had foil on one side. We glued 3 layers of this to the hull and covered lockers used for food storage with a canvas outer covering so tins did not puncture the bubble-wrap. (Warning have plenty of ventilation as sniffing glue is not to be recommended). This was a cheap and readily available material and it solved our immediate problem.

PS: 7 years later it is still working well. Some of the original cork lining is beginning to crumble in lockers that get heavy use but after 33 years it can be expected.

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