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Re: Polystyrene as boatbuilding foam?
By:Dick Lemke
Date: 9/18/2001, 8:16 pm
In Response To: Polystyrene as boatbuilding foam? (Dan St. Gean)

I have used foam extensively for R/C multihull construction. While the boats are only 48 inches long x 48 inches wide, I have kept the foam thickness to approximately 3/32. Where some curves and shaping is required, I have gone to 1/4 inch which allows sanding and shaping. The hulls are unbelieveably light in weight.

In one of my electronic newsletters about building R/C foam core composite boats, the original idea and article was from someone who had completed a 21 foot power boat and it was successful. He built using "female" moulds which allows cloth to be added to interior to give some strength. Then the hull is removed from the mould, the "raw" side is sanded and shaped and faired, and the the exterior is glassed.

Some thoughts:

1. You will need to skin both inside and outside with glass cloth. The foam will handle most loading situations with exception of drops from waterfalls.

2. Make the stations (bulkheads) from 3/4 foam and leave in place if worried about strength. Add glass cloth to each side if you are concerned about strength. This will put bulkheads/support at about 2 foot intervals along the length of the boat.

3. Add plywood at feet and butt bulkheads for additional strength and so you can brace yourself.

4. At worst, if the boat blows up when under a wave or standing on end - you have invested less than $30.00 for the foam. Of course cloth and epoxy is probably double the cost of the foam ( or more)

5. Use solid blocks glued up (epoxy) and carve for any areas that are difficult to shape - or for bow and stern stems. You can also glue in wood backing for any hardware mounting.

6. Regular old acrylic spackling compound can be used to fill voids between strips. You have to use something that sands/shapes as easily as the foam or you will sand hollows trying to sand down the joint seams. I have used a variety of different fillers (even WEST Ultralight) but all are harder and sand harder than foam. Spackling compound sands very easily - as does joint (wall board) compound. Don't worry about the water proof issues, as you will be covering with epoxy/glass which will be the moisture barrier. Also, the white filler against the pink or blue foam isn't a problem, as the boat will require a paint job. One thing - a clear finished foam strip composite boat is UGLY !!! Please - paint it. If you want looks - then stay with wood.

Finally, you can save money and cure time by gluing the strips with common wood glue. Since it will be encapsulated eventually, all you need to do is keep strips in place. Epoxy will work, but is more expensive and takes longer to cure. For my "little" boats, I just put a dab of hot glue to hold in place on template stations. When done, I can "pop" the entire hull half off the building templates and just fill the little nick with filler. Don't try to glue the strips together with hot glue, as it too sands harder than the foam and will leave hollows on each side of the seam. Hot glue tends to get sticky when warm from sanding - gumming up your sandpaper.

You can build as you would a regular strip built boat - or you can build in halves (either vertial or horizontal seam) and simply glue both halves together when done.

Will see if I can find the original article that led me down this path. E-mail me if interested in getting the article. It will be in Adobe Acrobat PDF format. If you don't have the Acrobat reader, it is a free download from Adobe web site.

Cheers !

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Messages In This Thread

Polystyrene as boatbuilding foam?
Dan St. Gean -- 9/17/2001, 12:05 pm
Re: Polystyrene as boatbuilding foam?
Dick Lemke -- 9/18/2001, 8:16 pm
Check out these Foam building links. Lots of them.
John Monfoe -- 9/20/2001, 5:52 am
Working with Blue Polystyrene link.
John Monfoe -- 9/20/2001, 6:34 am
Last minute blue thoughts.
John Monfoe -- 9/22/2001, 7:29 am
Re: Polystyrene as boatbuilding foam?
Dick Lemke -- 9/18/2001, 8:34 pm
Re: Polystyrene as boatbuilding foam?
Dan St. Gean -- 9/19/2001, 1:59 pm
Re: Polystyrene as boatbuilding foam?
Dick Lemke -- 9/20/2001, 10:57 pm
Re: Polystyrene as boatbuilding foam?
Dan St. Gean -- 9/21/2001, 9:20 am
Gecko Boat link
Dan Ruff -- 9/18/2001, 12:20 pm
Re: Polystyrene & sailboards experience
Craig Bumgarner -- 9/18/2001, 9:11 am
This is how I would build a solid foam boat.
John Monfoe -- 9/19/2001, 8:05 am
Re: Polystyrene & sailboards experience
Dan St. Gean -- 9/18/2001, 9:37 am
Re: A couple thoughts
Craig Bumgarner -- 9/18/2001, 10:19 am
Re: Polystyrene as boatbuilding foam?
John Monfoe -- 9/18/2001, 7:45 am
Re: Polystyrene as boatbuilding foam?
Dan St. Gean -- 9/18/2001, 9:20 am
Re: Polystyrene as boatbuilding foam?
John Monfoe -- 9/18/2001, 7:12 am