Subject: Re: [harryproa] Bending foam?
From: Gardner Pomper
Date: 3/25/2009, 10:23 AM
To: harryproa@yahoogroups.com.au
Reply-to:
harryproa@yahoogroups.com.au

Rob,


Ok, you asked for it! <grin>. I haven't moved this to a new thread, but maybe I should.

These questions are all based on the camper files I uploaded to Files->Gardner's Layouts->Camper. Yahoo won't let me get to them at the moment, but hopefully that is a temporary problem.

First, the purpose of the boat is to be a long distance single person cruiser. I want to do the same type of thing that Doug is doing with his, but I probably weigh twice what he does and have a higher minimum comfort level, I expect. Secondary purpose is as a fast, fun daysailor for the family (2 adults, 1 child, total weight 550 lbs). But, I do *NOT* want to capsize. I don't want to fly a hull. I want relaxation at speed, not adrenaline rush.

As I have mentioned in prior posts, we live in an area of light winds. Summers here often have winds light and variable, 5 kts or less. Over 10 kts is uncommon. Over 15 and I don't go daysailing. Because of all this, I want a large sail area that can be easily reduced to cope with higher winds. I also want to be able to sail in 30+ kts, for those times I am cruising and get caught.

The primary building characteristic of the boat must be simplicity. I have no boatbuilding experience and want something forgiving. To this end, my concept for this boat is that it can be built in 3 major sections, lw hull, ww hull and deck. The idea is to build the deck first, as it is simplest and least important to the structure, which will give me some experience before I tackle the hulls.

One last thing; ignore the bicycle pedal idea for now. I may go with a sculling oar and/or a portable electric outboard. That is all undecided and I don't want it to hold up the rest of the boat.

Questions:
1) I figure an empty weight (all up) of  200 lbs per hull, 200 lbs for the deck, 100 lbs for rig (guess), 100 lbs for crossbeams (guess) and maybe 100 lbs misc, for about 900 lbs. Payload about 700 lbs (150 lbs equip + 550 lbs crew for daysailing; 200 lbs equip, 300 lbs crew, 200 lbs stores for cruising). Does all that seem reasonable, given the measurements in the drawing?

2) 3/8" core throughout, except for horizontal deck surfaces wehre I walk. Use 1/2" there. 6oz fiberglass everwhere, except under the waterline, where 18oz for grounding protection. All ok?

3) Build telescoping beams by wrapping carbon fiber around PVC tubing wrapped in plastic sheeting and vacuum bagged. Slide the PVC tubing out after resin sets. What diameter tubing should I use? should I wrap carbon, then wrap foam around, then another layer of carbon, or just 1 thick layer? I seem to be able to get 12 oz carbon fiber twill reasonable cheap ($26/yd in 47" width, so just over $2/sq ft).

4) If I can still get it, there might be a few sheets of 3/8" airex available at about the same price as corecell. If I just use it for the keel sections, I figure I can cut 2'x8' pieces for teh keel and use 4 pieces for the lw hull and 2 pieces for ww hull, so just 3 sheets of it. That should allow me to make the 4" radius bend in the ww hull and 6" radius in the lw hull.

5) When I get to the rig, I want to look at your ideas for a telescoping mast. That sounds appropriate for the light wind days, and I can just keep it down on days with more wind and reef when it gets really windy. I have not done the calcs yet for bruce number, but I would like to get close to a 2 when loaded for sailing.

6) I would like to start building the deck first. Given my idea of just dropping it on top of the ww hull, I am assuming that we can make minor changes in the hull specs without my having to redo the deck. I was not planning on having the hull/deck vertical transition be seamless; I was just going to make the deck rectangular and let the corners stick out, to simplify building. Do you think I can get away with that?

7) What would you change in the design, given my requirements?

Thanks,
- Gardner


On Wed, Mar 25, 2009 at 6:13 AM, Rob Denney <harryproa@gmail.com> wrote:

G'day,

My Elementarry is 3mm foam with carbon each side. 10mm/3/8" will be
heaps for yours. Flat floors on ww hulls hit with a bang after a
capsize. Definitely 18 oz either side. Airex wil do, but it is very
expensive. I'd persevere with the Core cell.

No need for any money at this stage. Ask questions, I'll answer. I
am away for 2 weeks from next week, so ask before Sunday, please.

regards,

Rob



On Wed, Mar 25, 2009 at 12:14 PM, Gardner Pomper <gardner@networknow.org> wrote:
> The pipe idea is a good one. I may try that on a small piece.
>
> This is all for my sidecar for fat people version. I was thinking of using 6
> oz everywhere, except under the waterline, where I was going to use a layer
> of 18oz. Since that is where the bend is, I guess I need to do more testing
> with the 18oz.
> Another possiblity I have considered, and is getting more attractive, is to
> get some Airex foam for just the highly curved sections. I was thinking of
> the ww hull with a 12" flat floor, and a 6" radius curve up the sides. If I
> use corecell for the flat section, glued to 12" strips of airex, then glue
> more corecell up the sides, then I should be able to bend it. I had a lead
> on some 3/8" airex a month or so ago that I didn't follow up on, so I don't
> know if it is still available.
> I think it is about time that we talk about how I hire you for some design
> work on this. I don't want to buy 3/8" airex, if I need 1/2". I just need
> something preliminary. Or, I can just wait until I have the topsides built,
> but airex is harder to come by than diamonds nowadays.
> - Gardner
>
> On Tue, Mar 24, 2009 at 10:20 PM, Rob Denney <harryproa@gmail.com> wrote:
>>
>> Sound good to me. I would do some more little panels first. If they
>> will bend, then the big one should not be a problem. Could also use a
>> 6" radius pipe to bend it over. Is 6 oz the laminate you will be
>> using on the boat? If not, use whatever you will be using.
>>
>> regards,
>> rob
>>
>> On Wed, Mar 25, 2009 at 10:17 AM, Gardner Pomper <gardner@networknow.org>
>> wrote:
>> > I tried bending it by hand and it bent unevenly, almost like a crease.
>> > If I
>> > was bending it over a mold, then maybe I could use tiedown straps or
>> > something and just tighten it once an hour or something. This was a
>> > small
>> > (3"x12") sample piece I was just bending in my hands. I didn't really
>> > want
>> > to waste a whole panel trying something bigger. If I do a 4'x8' panel,
>> > should I just hang it with straps from the ceiling and pour in sand or
>> > something to weight it down? Add more sand once and hour or something?
>> >
>> > - Gardner
>> >
>> > On Tue, Mar 24, 2009 at 8:46 PM, Rob Denney <harryproa@gmail.com> wrote:
>> >>
>> >> G'day,
>> >>
>> >> Surprised you needed to cut it for a 6" radius. Slow, steady and even
>> >> pressure which evenly crushes the foam on the compression face should
>> >> have done the trick.
>> >>
>> >> The depth of the cuts is trial and error, dependant mainly on the
>> >> radius of the curve and the foam thickness. Deep enough so it bends,
>> >> shallow enough so it doesn't show on the outside.
>> >>
>> >> More, shallower and thinner are best, but time consuming. You should
>> >> also make sure all cuts are filled with bog before folding otherwise,
>> >> if water gets in (usually through a skin fitting) it travels along the
>> >> cuts and eventually gets a bit smelly and messy.
>> >>
>> >> regards,
>> >>
>> >> rob
>> >>
>> >> On Mon, Mar 23, 2009 at 12:58 PM, Gardner Pomper
>> >> <gardner@networknow.org>
>> >> wrote:
>> >> > Hi,
>> >> >
>> >> > I am experimenting with vacuum bagging and resin infusion for the
>> >> > first
>> >> > time. I am trying to figure out how to bend the foam. I have tried 2
>> >> > pieces
>> >> > of corecell, one 1/2" and one 3/8", both with 6 oz fiberglass on one
>> >> > side. I
>> >> > tried using the circular saw, and cut 8 grooves 1" apart, 3/16" deep.
>> >> > This
>> >> > allowed me to bend the pieces into 6" semi-circle, but the foam
>> >> > creases
>> >> > and
>> >> > you can see the fold lines on the outside of the fiberglass; it isn't
>> >> > a
>> >> > smooth curve.
>> >> > Is there some information on how to do this with corecell? I have a
>> >> > older
>> >> > booklet that talks about airex, but it is bendable.
>> >> > Should I be cutting thinner grooves than a circular saw blade? Closer
>> >> > together? Deeper? Shallower?
>> >> > Thanks!
>> >> > - Gardner Pomper
>> >> >
>> >
>> >
>
>


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