Plywood vs foamcore-how do they compare?

Eric, I haven't looked at either of the designs, but I can state that the reason they call a first class yacht.... "pro built "... is because the finished boat is delivered to the customer displacing exactly what the designer spec'd.

If its designed at 1000 kg fully found, then the fully commisioned pro build will displace 1000kg ...... even if its pre preg carbon over nomex , cured in a NASA oven..


Obviously a pro builder endeavours to save weight on all aspect of boat construction.

Foam core ? ...good question. Foam is expensive and will require a different laminate schedule and engineering details .

Is this worthwhile for a home build ? No......... the weight you will save with foam in a home build hull is a small fraction of the finished weight.


Best to Follow the designers build instructions for hull and structure exactly, achieving weight saving by concentrating on your craftsmanship skills while using the materials and techniques the designer spec'd .

Craftsmanship skills mean.. careful attention when setting up the hull to produce a fair hull with a minimum of fairing compound , proper glass to resin ratios and top class materials.

After completing the hull and structure to design, you may save weight by using foam core...or other lightweight core materials and exotics for interior furniture. This is the area were you will get the best bang for your buck.

As you know....Weight is critical to good performance. .

In the perfect world you could deliver the finished 1000 kg boat at 800 kg. The missing 200 kg would be added as ballast. Ballast being a bigger battery bank.. four stroke powerplant instead of two...more capacity in your fuel tanks.... additional features. ... but the end result will displace exactly 1000kg... what the designer called for.

My experience has been that foam core and exotics are best used for furniture and non structural weight that is carried up high , like decks, consoles.... and anything that is located in the ends of the boat.

Keep the ends light for good performance. . ..

 

If you go to the extreme of using the proper foam, before you begin you should at least know a bit more about what it takes to achieve the correct cosmetics for a first class boat. Unlike plywood and glass hulls, your glass is normally entirely different and the surface of the glass will require some additional work than most plywood hulls that already has a surface close to smoothe for the two boats you are talking about.

If you don't then if you wish to have the high end shine and finish work your additional materials to fair, prime and paint the boat will add nothing more than just dead weight to the hull. Value? good luck with that one. Competition for like sized boats includes literally thousands of other production hulls which can also sell for fifty cents on the dollar for what you will probably get for your hull after you are done to the average Joe on the street corner. Don't get your hopes up that you will make double your money back if you add a decent price to your labor either if you are not experienced in foam core construction .

 

Rigid Polyurathane Foam

My family & I have been building an extension to our house. Building Regs. require insulation, both under the cement screed and between the joists of the monopitch roof. Being a zealous chap, I plumbed for the thickest available Low Density Rigid Polyisocyanurate Foam (PIR) Insulation Boards within the budget & purchased 29 sheets of 8' x 4' x 5.5" (1220 mm x 2440 mm x 140 mm) from a "seconds" supplier in South Wales for £800 including VAT & delivery. That's 928 sq ft or 86 sq m.

We covered the oversite concrete with the Low Density Rigid Polyisocyanurate Foam (PIR) Insulation Boards and started wheel barrowing the screed. We were astonished to discover absolutely no grooves or footprints on the surface of the foam, even when jumping from a ladder, so we tried jumping onto a sheet of 50 mm thickness. Same result, no impact marks, but it does bend quite well, unlike the thicker sheets.

So, stitch & glue time, both hull & superstructure, we are talking less than £9-30 per sq m & that's not inexpensive, that's cheap, for a hull bottom up to 5.5" thick. Obviously, that might be too thick, but you never know.

The Tolman Jumbo consists of bottom, sides & transom, 5 component parts plus superstructure. Now I wonder? I've got the book!!

http://www.fishyfish.com/billjones/index.html

OTOH, a Low Density Rigid Polyisocyanurate Foam (PIR) Insulation Board superstructure on this Colvic 20 might be fun.

http://www.worldseafishing.com/forums/showthread.php?t=381120

Especially using a Lake Union Dreamboat as inspiration.

http://www.planetyacht.com/broker_detail.php?id=2244

P

 

Hey Perecles,
You cap in a hull with enough thickness like what you are saying and you are gonna have STRONG no doubt. Add to that forgiving to and maybe add unsinkable to the list of attributes, if you want to go that far with it. And just plain easy to deal with. Maybe even fun to work with.

Being that the stuff is so cheap, using it sacrificially by removing it incrementally (after you skin the exterior), you can make connecting 'ribs' network to support the inner and outer layer. Fiberglass tape is all you need. Then you leave all kinds of options on the table. You have a two layer hull with layers supported by a network of verticle 'cell supports'. Adding cells will address the delamination that can occur with this technique. Plus you can re-fill these 'cells with whatever you want. Below the waterline you could do epoxy and 'rock dust' for example. Up high replace the voids with expanding foam if you like. Or just trim the same foam you cut out and refit it. Need lightweight? Make the laminates a little thicker and go without foam. Do a good job on the 'cells' and air pressure could be added as a possibility.

 

I haven't used Grasshopper, only Rhino, so can't help.

 

Pericles,

What would you use for the outer and inner coverings? Needs to withstand concentrated impact loads.

why don't you build some test panels and then test: bending, torsion, shear, point load, peel, etc. Doesn't have to be sophisticated but should be systematic. If you don't have a background in how structures behave you might want to find someone who does to help design the tests. And you might do some thermal testing also with a heat gun to see what happens if it gets hot.

 

Fill one of the cells with super clear epoxy and you have built in TV.

As long as you don't mind Sponge Bob.


AHAHAHA

 

Thanks for the input

Thanks for all your comments. Several points are well taken, and I plan to follow them.
1 - go with the planned design and material. If there is little to be gained in the way of performance, cost, build time, there is no reason to take a chance changing a proven design.
2 - Getting some experience and saving weight by using foam and glass for furniture and interior non structural items makes a lot of sense.
3 - Using low cost foam for interior work is worth investigating. I'm building the boat to use, rather than trying to sell for profit, so cutting costs and customizing with out compromising safety works for me.

If anyone can recommend a good book on foam core construction, I'd appreciate getting the name.
Thanks again.

 

What folks haven't told you about foam cored construction is that it's 90% sanding and working with goo. If you don't mind working with stuff that'll make you itch and protecting yourself from the harms of goo, plus sanding until your elbows go on strike, then you're in for a grand 'ol time.

The foam part of this equation is a minor role in the process. Other then having the proper type of foam for the tasks you'll ask of it (compressive and shear strength attributes, in a closed cell type) and fitting it as required, then the rest of the job is applying sufficient laminate all around the foam, to provide the strength and stiffness desired. How much laminate you ask? Well this is the *** kicker and something the green horns can't respond to, in spite of their offered advise.

Lets say you have a tabletop, you'd like to save some weight and employ a foam cored technique. You figure the table should support a person, just in case you want to have some weird sex with the other half someday, or maybe to use it as a step, to climb out of the hatch above it, so lets call it 200 pounds, dead weight (static load) on the center of the table, with a 2:1 safety margin (pretty skimpy), so now it's a 400 pound static load. How thick should the foam be? For the thickness of foam you've selected, how thick should the laminate be? What type of laminate? We'll assume epoxy as the resin system.

Like I said, even something as simple as a table top requires a fair bit of understanding and engineering. You can use some "rules of thumb" or general guidelines, but these usually just make the sandwich structure heavier then necessary, which translates to additional labor and cost during the build.

Lastly, fairing 'glass is about as enjoyable as scratching hemorrhoids with a stick. It's tedious, time consuming, messy, toxic, itchy and difficult. Most folks don't have the tools to do it properly, nor the skills to get it done in a reasonable amount of time. You will literally spend 90% of the time on sanding, filling, sanding, filling and blocking out.

I'm not trying to talk you out of sandwich construction techniques, but just offering a reality check as to what this technique requires.

 

PIR is an improvement on polyurethane. It is not affected by epoxy resins and is more fire resistant.

http://en.wikipedia.org/wiki/Polyisocyanurate

Try & purchase "seconds".

http://www.bmdinsulation.com/

Use TESA tape to secure panels together.

http://www.trade1st.co.uk/productdetail/Builders-Tape/701.aspx

By using & reusing this thick PET-G film to smooth the epoxy before it cures, hard sanding is almost eliminated.

http://duckworksmagazine.com/03/r/articles/glass/bottom.htm

More photos.

http://www.johnblazydesigns.com/default2.asp?active_page_id=119

Useful data.

http://www.boatdesign.net/articles/foam-core/index.htm

 

The idea of the PET-G film is sweet.

I have been wanting to try shrink wrap (like you use to insulate windows) to achieve the same result. The idea being that you can use a hair dryer to pull out all the creases over a large area quickly. Plus will give a small amount of 'vac' pressure.

PET-G approach might be as simple or better in most apps. Sweet and simple.

 

The film used to shrink wrap boats for winter storage or for securing building materials on pallets would be favourite, but the shrinking might be uneven . It'll take an ex peri ment.

Regards,

Perry

 

I have maybe 50 sq ft of leftovers of that stuff somewhere around here. Wally World special stuff for insulating windows. I will do a test as soon as I find it. I have high hopes that it will be good in the corners and areas where creases are hard to avoid.

If it actually works that stuff is worth $20 a sq ft.!...easily