Subject: Re: [harryproa] Bending foam?
From: Rob Denney
Date: 3/27/2009, 9:01 AM
To: harryproa@yahoogroups.com.au
Reply-to:
harryproa@yahoogroups.com.au

On Thu, Mar 26, 2009 at 9:47 PM, Gardner Pomper <gardner@networknow.org> wrote:
> Rob, you should know by now that answering questions just creates more
> questions <grin>. Mine are inline.

Keep them coming, this is the enjoyable part of boat design, for me.

>
> Are you just restating what I said for specs, or do you actually think
> the boat can weigh 410 kgs? I just made up numbers for rig and beams
> and stuff.

Suspect it will be more than this as your laminate is a bit light for
a knock around boat with foam core. Cedar or kiri are much more ding
resistant.
>

> I was thinking to set it up as a "normal" easyrig, then be able to
> raise just the main an extra 10' (guess) when in really light airs.
> Have the jib forestay attached to the non-telescoping part.

The forestay has to be on the telescoping part, as this slides down
over the lower mast. Having the top mast as the internal is "normal"
but much harder to organise.
>
> I don't understand the unarig. On a monohull, a single sail is always
> far forward, like a cat rigged boat. I don't understand how the
> unarig, placed in the center of the boat works. I know it is in the
> design plans for Rapscallion, but I never saw an explanation. Have you
> tried this?

On El and Harriette and on my Easy rigged boats with the jib down. I
think it works because the clr is a long way aft with only one beam
mounted rudder.
>
> Oh, and did I forget to mention that I want to be able to pack the
> boat in a container, so the mast should not be longer than 39'
> collapsed, or it should be able to come apart the way I have shown in
> the camper_mast.pdf file in the Files section.

Should be pretty easy, if the ww hull is less than 8' wide. Joining
masts at the deck is not a good solution as it is the highest stressed
area.
>

>>
>> Assuming the dimensions and calculations are correct (I rough checked
>> a couple and they were), the drawings look good. I assume you have
>> drawn it in the other view and 3d to be sure it all fits. If
>> possible, I would extend the lee hull length to 35', and leave out the
>> kink in the topsides.
>
> I uploaded my 3D rendering to the files area. It looks ok to me.

The bow of the lee hull can be lower, but otherwise fine.
>
> Is there a specific reason to extend the lw hull to 35', or just the
> "longer is better" idea? That hull already has a l/b ratio of 25:1.

Longer is better, faster, safer and more comfortable. Not that much
trickier on the trailer.
>
> Is the "kink" the part that raises up in the middle, like rapscallions
> boat? Are you saying that I should raise the deck the whole way along,
> or just slope it up from bows to the mast? I did it like this to give
> me a convenient place to mount the crossbeams and because it was done
> that way on Rapscallion. I am not disagreeing; I just am not sure I
> follow what you are telling me.

No, the kink is in the section view. The hull sides can be straight
from the bottom radius to the deck.
>
>
> Why timber stringers? Would it be possible for me to just use glass
> covered foam for stringers?
Timber for ease and longitudinal strength. Could be foam/glass with
some uni added.
>

>
> What is a "rebate"? Is it just an overlapping flap of fiberglass?

An area of the panel where the surface is lower than the rest, such as
where the glass over the polystyrene overlaps onto the hull panel.
The overlap sits in the rebate, so fairing is minimal.
>>

>
> The beams can wait. Hopefully I can get these made in China, along
> with the mast and rudders. I am mostly concerned with being able to
> start the other parts of the boat. If I end up with some sort of
> swinging crossbeam system, that might raise the deck, which will
> cascade changes to all parts of the boat, so I probably need to
> decide that before I start building it.

Swinging beams are also fraught.
>
> Do you think that telescoping is the best (simplest, most reliable)
> way to do the reduction in beam? I know there have been alot of ideas
> tossed around on the forum. Also, can you give me a figure for how
> much overlap there needs to be in a telescoping beam? Roughly 10% of
> length? 20%? I know this is someplace where engineering needs to be
> done, but I just want to work out the approimate minimum and maximum
> beams I can do.

I have a single swinging beam system which is easier, but telescoping
is tried and tested so you know what you are getting into.
Overlapping sliding beams (like a horizontal gunter rig) are easier to
build and use, but not very attractive. Overlap should be 10-15% of
the unsupported length, but this always looks too short on beams, so
2' is minimum.
>
>>
>> Anything else, let me know.
>
> I can't believe you are still saying that <grin>
Like I said, this is the enjoyable bit.

regards,

Rob
>
>>
>> regards,
>>
>> Rob
>>
>
> Thanks very, very much!
>
> - Gardner
>
>> On Wed, Mar 25, 2009 at 11:23 PM, Gardner Pomper <gardner@networknow.org>
>> wrote:
>> > 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
>

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