Gardner,
No hard and fast rules, which is why I am having mine professionally designed with FEA
studies, load analysis and such. Too expensive to make big mistakes. So far LW hull has
bulkheads every 5 feet plus double bulkheads for beam sockets, double bulkheads for
mast loads. Each bulkhead uses 12mm marine ply with 2 layers per side 600gsm fiber.
End compresssive strength is an issue with foams and such so better with reinforced ply.
Decking has either 30mm foam and 5 foot bulkheads or less foam and closer bulkheads
plus supplemental stringers.
Al that with specialized CAD design and load modeling software. If you don't check then
may have to overbuild to compensate for the unknown. There is added weight from fillets,
reinforcements for lockers, tanks, hull bottom. Did you add up the wiring weight ?
Hundreds of extra pounds in field materials. I expect the beam mount rudders, bearings
steering hardware to be in the 70 -80 pound range each. Huge loads takes a lot of
reinforcement.
I don't think they weighed the beams alone on Rare Bird. My beams are still in design. I
have Rob's Visionarry planset but can't share details on the forum. Lets just say 12 - 18
layers of 300gsm fiber with an internal 400 x 300 bulkhead every 1,25 foot. See if you
can add that all up plus internal fillets and kiri strip planking all around for your proposed
beams. I surmise they are heavy ! Their design was strong enough to support three
corners of the boat without visible deflection on the fourth unsupported point. My design
will do the same even when loaded.
Devil is in the details..... even paint or gelcoat adds. If you are close to Rare Bird in size
then expect you will ultimately be in the same ballpark for weight. If you want to be less
weight see what you do without in comforts to go faster. I am OK with 2/3 to 3/4
windspeed so I can enjoy the trip. Not a racer nor slug will I be. Call it perky...... or
otherwise a little overweight from Rob's ideal.
Hope you can rationalize where you want be in terms of performance priorities. I still have
to please the "admiral". Tis true in balancing speed, comfort and cost, you can only
optimize two.
Regards,
JT
--- In harryproa@yahoogrou
>
> Hi,
> I am not arguing with anybody. I definitely expect that it will weigh more
> than my calculations. My issue is that I really need to be able to get
> realistic numbers out from my layouts/designs, or I can't determine which is
> the best for what I want. I am trying to locate the errors in what I am
> doing.
>
> The big unknowns seem to be the beam structure, the rudder design/weight and
> internal framing/bulkheads. If I can find out the weight of the beams for
> Rare Bird, that would give me some idea.
>
> What do I need to know about placing bulkheads? My hulls are typically
> between 2 and 2.5 feet wide. The distance between the crossbeams is 25 feet
> (roughly). I should have bulkheads where the crossbeams join, and where the
> masts step. Where else? Every 10 feet? More? Less? Can I assume a bulkhead
> will just be the same 3/4" cored material with 18oz fiberglass as I am using
> elsewhere?
>
> For simplicity, I have assumed 3/4" core material for everything. That is
> way overkill for cabinets and seats, and underspeced for the hardtop which
> is 10'x12' and supported only at the corners. Is there a rule of thumb I can
> use for the stuff that is not subject to sailing stresses? I want to be able
> to walk anywhere on the boat without it flexing. I weigh 300 lbs. What does
> that mean for the stiffness vs distance between supports?
>
> In terms of the collapsable beams, my current goal is to come up with a
> design that can collapse, but probably build the boat with fixed, detachable
> beams and use them until I am in a situation where I need to be in a slip
> for extended periods of time (I have a dock at the moment). Then replace
> the fixed beams with hinged/etc and make the other modifications according
> to the original design. That way I have the option, but can stick with the
> advantages of fixed beams (simplicity, cost, strength) until I need it.
>
> Thanks for all feedback. I am learning a tremendous amount from these
> discussions.
>
> - Gardner
>
>
> On Thu, Jan 8, 2009 at 11:44 AM, jjtctaylor <jtaylor412@
>
> > Robert is right.... as you go up in size, your structure mass rises
> > as well. Found a buckling issue on my lee hull, thus needed more
> > stringers and bulkheads. The rigidity of expando beams may become an
> > problem and might have to beef up to avoid excessive flex. You will
> > also find as the surface area of anything grows so does the
> > underlying support. Orrr you can take your risks.
> >
> > Mine will be similar size to Rare Bird so have a reasonable
> > baseline. But as you add the weight of tankage and systems those too
> > will bring structural issues. Rare Bird is light on creature
> > comforts and there is a penalty to pay for niceties. With one-off
> > design not much opportunity to improve upon existing except to
> > design/fab under the best known engineering practices.
> >
> > JT
> >
> >
> > --- In harryproa@yahoogrou
> > "Robert" <cateran1949@
> > >
> > > There are a suprising amount of panels needed for interior
> > separation,
> > > such as bulkheads, storage areas, bouyancy compartments, cupboards,
> > > shelving. Rare Bird was strip planked so would have to include a bit
> > > of bog. Rare Bird also has a dinghy ramp. The crossbeams and rudders
> > > need to be pretty substantial as do the reinforcing to transfer the
> > > loads between them and the rig There is also the weight of hatches.
> > > Rare Bird weight should be pretty close if you can keep the bogging
> > > down to a minimum.Blind date is a fair bit lighter.
> > > Your calculations of area seem just a little more than an extended
> > > Harry 15m/9m that I have been trying to design so we are making
> > > similar mistakes -- In
harryproa@yahoogrou
> > "Gardner
> > Pomper"
> > > <gardner@> wrote:
> > > >
> > > > Hi,
> > > > I have been spending way too much time researching materials
> > online,
> > > but the
> > > > end result is that I am again confused on how to estimate the
> > weight
> > > of a 50
> > > > ft cruising harryproa. I have gone through and added up the hull,
> > > bulkheads,
> > > > furniture, hardtop, cockpit, bunks, etc, etc and come up with 2100
> > > sq ft.
> > > > This does not include the rig, crossbeams or rudders, since I
> > don't
> > > know how
> > > > to calc that.
> > > >
> > > > Anyway, I then research the core material (pretty much all of
> > them are
> > > > 80Kg/m3), which translates to 0.3 lbs/sq ft for 2/4" (20mm) core.
> > > Add in 2
> > > > layers of 18 oz/yd2 fiberglass (1 top and 1 bottom) and an equal
> > > weight of
> > > > resin and I get 0.8 lbs/sq ft total. Add 20% for fillets, bog,
> > etc,
> > > and it
> > > > comes out pretty much exactly 1 lb/sq ft.
> > > >
> > > > I add in my batteries, outboard engines, refrigeration, water and
> > fuel
> > > > tanks, instrumentation, ground tackle, etc and get another 1500
> > lbs.
> > > >
> > > > With schooner rig, I would estimate each mast/sail/boom combo at
> > > about 500
> > > > lbs, so that is 1000 for the rig.
> > > >
> > > > I am now up to 2100 lbs for structure + 1500 lbs equipment + 1000
> > > lbs rig =
> > > > 4600 pounds.. supposedly only missing the crossbeams and rudders.
> > > >
> > > > I am happy with that. But then the urge to do a reality check
> > comes
> > > in and I
> > > > look at Rare Bird at 6,720 lbs, and it doesn't have a 10' x 12'
> > > bridgedeck.
> > > >
> > > > So, what am I doing wrong? At about 5000 lbs and 1000 sq ft of
> > sail,
> > > this
> > > > should be a screamer, but if it is 10,000 lbs with the same sail
> > > area, that
> > > > is a totally different boat!
> > > >
> > > > I would probably be safe by just taking Rare Bird and adding a
> > couple
> > > > thousand pounds, but I actually want to be able to do this stuff.
> > Help!
> > > >
> > > > Thanks,
> > > >
> > > > - Gardner Pomper
> > > > York, PA
> > > >
> > >
> >
> >
> >
>
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