[Rhodes22-list] adding keel weight

[Roger Pihlaja]

Rob,

You're welcome.  Sometimes, it takes an engineer to appreciate another
engineer's explanations.

Roger
S/V Dynamic Equilibrium

----- Original Message -----
From: "Rob Lowe" <rlowe at vt.edu>
To: "The Rhodes 22 mail list" <rhodes22-list at rhodes22.org>
Sent: Friday, October 17, 2003 10:56 AM
Subject: Re: [Rhodes22-list] adding keel weight


> As an engineer, I just lover Roger's explanation of things.  Thanks Roger!
>
> Rob Lowe
> S/V Getaway
>
>
> ----- Original Message -----
> From: "Roger Pihlaja" <cen09402 at centurytel.net>
> To: "The Rhodes 22 mail list" <rhodes22-list at rhodes22.org>
> Sent: Friday, October 17, 2003 10:22 AM
> Subject: Re: [Rhodes22-list] adding keel weight
>
>
> > Peter,
> >
> > All Rhodes 22's have a shoal draft keel with centerboard.  All Rhodes
22's
> > have their ballast in the shoal draft keel.  The GBI factory literature
> > lists the ballast weight at 700 lbs.  It is my understanding that this
> > ballast is in the form of lead shot encapsulated in concrete.  This
> ballast
> > is absolutely essential to giving the boat a sufficiently large righting
> > moment to enable it to stay upright under full sail in a 12-15 knot
> breeeze
> > while beating to windward.  The GBI factory claims it has test data to
> show
> > the Rhodes 22 will float with the decks awash with a hole drilled thru
the
> > bottom with the standard amount of ballast and overall hull weight.
> >
> > Given the above data, I don't understand your question.  Do you think
your
> > Rhodes 22 has an extra 500 lbs of ballast?  I doubt there is sufficient
> > volume in the keel cavity for an extra 500 lbs of ballast.  Or, did you
> > think your Rhodes 22 was originally designed as an unballasted sailing
> dingy
> > like a Laser or Sunfish?  This would require the crew to always be
hiking
> > out to keep the boat upright while under sail, which is completely
> > unrealistic for a cruising boat.
> >
> > As long as the concrete has no visible flaws, like cracks or porosity &
is
> > not pulled away from the sides of the keel cavity, there is very little
> > chance that water is seeping down into the bottom of the keel cavity.
> > Portland cement has the unusual characteristic of actually incorporating
> > water into its microstructure & slightly expanding when exposed to
water.
> > Thus, any incidental water that found its way into the cement would
> actually
> > be taken up into the microstructure.  This would cause the
microstructure
> to
> > slightly expand.  The rigid sides of the FRP keel cavity and the lead
shot
> > oppose this expansion, which puts the cement into compression, which
> > actually makes the cement less permeable to further water intrusion.
This
> > material property makes Portland cement an almost ideal material for
this
> > application.  Pretty cool, eh?
> >
> > Installing a keel cavity sump would short circuit this process by
> > introducing a direct path for water to get to the bottom of the keel
> cavity.
> > The void space introduced by the sump cavity would subtract from the OEM
> > ballast weight.  Not only would this ballast reduction make the boat
more
> > tender; but, depending upon where in the ballast you bored the keel
> cavity,
> > you could also affect the fore/aft trim of the boat as well.  Bottom
> line -
> > BAD IDEA!!!
> >
> > The one scenario wherein there might be water in the bottom of the keel
> > cavity is if the exterior FRP skin of the keel has been damaged in a
> > collision.  If the FRP skin has been compromised; then, water might seep
> > into the keel cavity from the outside while the boat is in the water.
All
> > interior ballasted boats are subject to this problem.  Water intrusion
> into
> > an internal ballast cavity can be very serious from an osmotic
blistering
> > point of view and especially if there are freeze/thaw temperature
cycles.
> > There are nondestructive test methods to determine the water content of
> the
> > FRP composite.  If such a test, run by a boatyard or boat surveyer,
showed
> a
> > greater water content in the FRP composite near the bottom of the keel
vs.
> > higher up; then, you might have water intrusion.  The solution would be
to
> > drill a series of small holes in the bottom of the keel cavity, let the
> > water drain out, thoughly dry out the FRP composite, repair the damage
> that
> > allowed the water intrusion, apply a moisture barrier coat on the
outside
> of
> > the FRP skin, and finally apply a couple of coats of bottom paint to UV
> > protect the moisture barrier coating.
> >
> > Hope this answers your original question.
> >
> > Roger Pihlaja
> > S/V Dynamic Equilibrium
> >
> >
> > ---- Original Message -----
> > From: "Peter Thorn" <pthorn at nc.rr.com>
> > To: "Rhodes 22 List Members" <rhodes22-list at rhodes22.org>
> > Sent: Thursday, October 16, 2003 5:27 PM
> > Subject: [Rhodes22-list] adding keel weight
> >
> >
> > > Hello Rhodies,
> > >
> > > My 84 R22 has it's keel cavity filled with about 500 pounds of
concrete
> > and lead.  At first, this seemed OK --seems likely to make her a bit
> > stiffer.  But after some worry and pondering, I have a few concerns:
> > >
> > > -  Is this boat still "unsinkable"?  Does anyone know the amount of
> > flotation built into the R22  in excess of the hull weight?  In other
> words,
> > can she still float swamped with the extra 500#?
> > >
> > > -  Is osmotic blistering of the structural fiberglass in the keel at
> > increased risk?  Now that there's concrete in the way, it's impossible
to
> > completely dry out the lowest parts of the bilge.  I was considering
core
> > drilling a cavity to the lowest point to obtain access for pumped
> drainage.
> > Is this a good idea?
> > >
> > > As always, thank you Rhodies, for your experienced opinions.  I
welcome
> > all suggestions on this topic you have to offer.
> > >
> > > PT
> > > __________________________________________________
> > > Use Rhodes22-list at rhodes22.org, Help? www.rhodes22.org/list
> > >
> > >
> > >
> >
> >
> > __________________________________________________
> > Use Rhodes22-list at rhodes22.org, Help? www.rhodes22.org/list
>
> __________________________________________________
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>
>