[Rhodes22-list] adding keel weight

Roger Pihlaja cen09402 at centurytel.net
Fri Oct 17 11:22:19 EDT 2003


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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