Hull material for arctic cruising

[Ad Hoc]

Mike,
sorry for delay, been away.

There is no minimum CVN (Charpy V-notch) test for grade A steel. The only guidance from IACS is that steel exposed to low service temperatures will have a longitudinal CVN of 27J at +10C.

Grade A steel less than 50mm thickness DOES NOT have to demonstrate a minimum CVN. So, this is why i would recommend EH grade and not A grade, when exposed to icy conditions.

 

[sailor2]

Anybody thought about condensation of metal hulls in cold temps ?
If insulated then what about corrosion, insulation prevents getting all the water out and can prevent inspection as well. In a cat there is a lot of surface area to condensate, or was the idea to put all the accommodation on centre/bridgedeck cabin ?

 

[Ad Hoc]

Not just the arctic!

Same thing happened on some cats my colleague and I designed running in Lisbon. Hot summer heat, inside the hull, humid. The voids were full of condensation, dripping!

 

[MikeJohns]

Mike,
..................this is why i would recommend EH grade and not A grade, when exposed to icy conditions.

From our steel suppliers they will guarantee this (-15 deg C ) as a standard spec.

 

[Autodafe]

Sailor2 - for this project all accommodation is in a central pod, partly to avoid condensation and noise, and partly because cruising solo or as a couple accommodation split between two hulls is inconvenient. Condensation is still a corrosion and storage problem though.

My knowledge isn't reliable on sea surface temperatures but I heard somewhere that seawater below -12C is very rarely still liquid, so -15C testing sounds more than adequate.

Although Alloy looks to be the best for light and tough, I'm actually back to using wood/epoxy with a fibreglass skin, because I know how to design and build for the material.
Metal may be better at resisting impact, but in this design, due to light weight and many watertight bulkheads, a hole in the hull is unfortunate rather than catastrophic.

Thanks for all the info and offers of help so far chaps!

 

[kach22i]

What do aircraft use?

Don't they operate in very cold conditions?

Just a random thought, very little time spent thinking about this topic.

I'll go now, discuss.

 

[TeddyDiver]

What do aircraft use?

Don't they operate in very cold conditions?

Dry air and low water content drinks to mumyfie paying passangers

 

[ImaginaryNumber]

any progress?

Autodafe,

It's been awhile since you've posted anything on this thread. I'm wondering if you're still working on this design, and if so, where you are at?

Best wishes,
John

 

[Autodafe]

Hi John,

Thanks for the interest.

I'm still working on the design, but I've spent more time building a shed to build boats in than actual boat work lately.

It's taking me a while to get my head around load paths - my field is electrical more than structural.

I'll start a fresh thread to post some drawings and pictures when I have something worth looking at.

 

[rugludallur]

Avoiding condensation with metal hulls

In my humble opinion the best and only guaranteed way to prevent condensation on the insides of a metallic hull is to insulate it with spray/pour in polyurethane foam on top of a complete epoxy/urethane paint system, this is also the best commercially viable insulation for a given thickness*. The downside is that if the system breaks down and corrosion starts you won't know until it's a big problem. Older foam insulation used to give off cyanide gasses as it burned so it's important to use a modern system which is fire retardant and does not give off poisonous gasses when it burns.

I think most aircraft still use fiberglass insulation but they don't have to deal with condensation since their air conditioning systems tightly control the cabin pressure/humidity and they usually fly above weather systems (ever notice how dry your mouth gets while in the air and how much fluid you have to drink?). Now what really makes them worry is mercury inside the cabin, it's near impossible to clean up and reacts with aluminum to form aluminum amalgam eating at the aluminum.

* Aerogel is the best insulator but would be a tad bit costly

Jarl
http://dallur.com

 

[apex1]

Though I fully concur in your second section Jarl, I would like to contradict your first statements.
Spray on PU is NOT the best material for such application. In fact it is a very poor choice.
You mentioned the downsides already.
The reason, that you find it still in use by the industry is simple: it is cheap to get and to apply.

Armaflex is by far the better choice! Assuming the same primer and coating system (epoxy based), you have a more reliable insulation which cannot break down.

Aerogel was a nice hint yes! And it sucks water like a sponge.

Vacuum panels btw. are the best insulators. But it is not sensible to insulate a hull with them.

Regards
Richard

 

[rugludallur]

Absolutely correct, vacuum is the best insulator but as you say it's not very practical and then you also need to worry about infrared radiation so you need to to have mirror polished stainless to deal with that.

What I like about PU is that using a closed cell foam and pouring/spraying it and restricting it with plastic it will actually form a hard watertight skin, this means that I can make water drain directly into the bilge without having it seeping between the insulation and frames/stringers.

I think cutting the urethane after it hardens is asking for trouble even with closed cell it can still enable some water ingress.

It might be possible to do the same with material from a roll but it would need to be glued to the hull skin and the sides bedded with a sealant very carefully to make sure there are no watertraps.

Apex, I would be interested in hearing your thoughts regarding this, it's not every day one gets into an intelligent discussion like this

Jarl
http://dallur.com

 

[Ad Hoc]

Rug..r
"..Apex, I would be interested in hearing your thoughts regarding this, it's not every day one gets into an intelligent discussion like this.."

Agreed, sadly becoming more rare, as most posts are taken over by amateurs wanting to sprout numbers from their programs (look how clever I am I can press buttons), rather than real facts, like Richard is giving.

 

[apex1]

I´ll give it a look, thanks Jarl!


And fully concur on the cutting urethane topic, a nono.
With Armaflex it is common practice (a costly practice), to glue the "tiles" overlapped and to form two layers of material. When proper done it lasts and provides superior insulation. But of course, it is about five times the effort than spraying some foam.

Regards
Richard

 

[apex1]

Interesting website / project Jarl! I remember I did visit the site once in the past.
When do you expect the launch? And what will YOU use for insulation?

Regards
Richard