[Rhodes22-list] adding keel weight

[Rob Lowe]

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
> >
> >
> >
>
>
> __________________________________________________
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