foam core question

I am planing to build a trailerable house boat, about 10m long. Think of a 30foot container that floats. It will be powered by 15 hp motor, clam water only and will be mainly used in freshwater. When it is on the trailer, it will be used like a caravan. Weight is a consideration, but not critical.

I looked at prefabricated panels, but transport to my location is prohibitive.

I was going to use Klegycell 80 (closed cell PVC) 15mm.

A friend says that this is a total overkill for my needs and suggest to use Urethane foam instead. Others say that this core will break down due to vibration. Others say that it will soak up water, and and and.

I spoke to so many people about foam core and am more confused than ever. Any thoughts and suggestions from people with experience in this field are most welcome.

 

I'd be looking at bulking fabrics like Coremat which are easy to use but can bulk out a solid laminate and are a lot more bashable and economical than fragile cores like foam.
Check around different suppliers I think it goes up to 5mm with a woven or stitched fabric either side and suitable panel sizes (bulkhead and stringer placement) it should be fit your purpose.

http://www.ballinafibreglass.com.au/product/coremat-2mm/

 

Some thoughts... I would make it a tad shorter. A 30 foot trailer or boat is alot hard to deal with than say a 26 footer. I would also considered making it out of Aluminum. Since the shape will be simple it should not be to expensive to build. And it will be much lighter and stronger. You can hull premade into 3 separate sections and then you can assemble them by simply bolting them together. You can then build superstructure separately out of regular wood, or fiberglass or aluminum also. Just some thoughts, good luck.

 

Coremat is very heavy since it saturates with resin.

Klegecell will not absorb water into the foam.
Any foam can be damaged, which separates the skin and the foam, significantly reducing the panel strength.
Klegecell is a urethane foam. The "80" foam is pretty high density - better for impact but may not be required for strength.

You could replace the foam with wood - like cedar- and will have greater strength, but more weight.
The Wood sandwich has more impact strength, but you have to make it a sandwich with an inner and outer layer of glass. Use epoxy, polyester doesn't stick well to wood.

Any sandwich needs to be well maintained or it will degrade.

If you use wood, it is extremely necessary to epoxy seal every fastener and fitting that is screwed into the hull.

Foam needs to have a plug removed and wood or glass used wherever there is a fastener or fitting, since it is easy to crush the foam with a bolt.

 

Klegecell is pvc. Yes coremat does use resin about 60% of solid glass, but no need to use epoxy and no "core" to hollow out for fastenings. Way more economical.

 

Thank you all for your input.
Initially, I planned to make the hull skin in aluminium and the stringers and upper structure with foam and glass, as I am pretty skilled with Aluminium. The adhesive between the alu and glass was planned to be Sikaflex. However, I was made aware of the different expansions of the two materials. I thought that the flexibility of the Sikaflex would absorb it, but apparently not. There are so many different views and I appreciate everyone's input.
I still like the aluminium idea, I might dent it, but it would not bruise like fibreglass and therefor would not soak up water. But what about the expansion issue? I understand the issue, but I can not calculate how much of a problem it is.

I have a reply from Sikaflex
Hello Lori,

I would suggest you look at our Sikaflex 252 in conjunction with our cleaners and primers as per the attached data.
It is recommended that you have at least 3-4mm of product left between the Fibreglass and Aluminium.
To acheive the gap I would suggest using double-sided tape in areas to maintain the 3-4mm.

 

If you can work with aluminium you could do the hulls in ally but I would stick with ally for stringers and frames and perhaps fix on a composite top sides with fasteners and methacralite ?

 

Wikipedia say methacralite is used for windscreen repair kits and bone cement.

Why would you suggest this?

 

A build of 100% marine aluminum is nearly indestructible. Use thicker aluminum, it will still be lighter. Weld it together, use stainless steel bolts or all rivets to put parts together. Only problem with AL besides skill and welder needed is insulation. For something like your building give it final coat of 100% silicone, it will be a great temperature insulator. Take a look at all the fancy houseboat designed for lakes. Somerset I believe is one.

 

Because it sticks like **** to a blanket, it gets used for a lot of structural bonding in different industries and you will usually destroy the components before the bond breaks. It's not cheap but it solves bonding problems other methods can't. (like dissimilar materials)
The stuff I've used comes in two part tubes with a mixing nozzle and various jell times.

 

Why do you think it is so important to make the entire substructure in aluminium? Your thoughts and reasons are important to me.

 

Yes, it does stick like **** to a blanket, but it is not flexible. I prefer a polyurethane like Sikaflex as it can handle heat expansion from different materials, just my thoughts.

 

An other idea to protect the foam core sandwich panel below the waterline could be "Rhino coating". It is a spray on product that is used in the automotive industry to protect tray backs. It is very flexible and ultra tough! Has anyone tried this? Perhaps someone knows a generic product that is more affordable. I think a similar product is used for industrial flooring, but have never heard that it was used in the marine industry.

 

Homogeniety, if you can use aluminium I assume you can weld, what advantage can be had by using dissimilar materials, it sounds like complexity for the sake of it ?
Why does the foam need protection if it is in a glass sandwich ?

 

For cost effectiveness, longevity and resale, I would side with an Aluminum construction. There are many companies that can do the job.

If cost is not a primary determinant for design and construction, I would use Coosa with an appropriate lamination schedule.