Iron Keel/Fibreglass Hull joint
Hugo 'NOx' Tyson
My boat is a Trident 24, 30 year old 24' glass fibre sloop with cast iron
keel. The keel's not encapsulated, but the heads of the keelbolts are, as
a line of large swellings in the bilge. It's anode protected by a wire
from the aft keelbolt bulge off to the engine/electrics ground and the
external anode mouted aft.
Inspecting out of the water, I can see a join or crack running along the
line where the metal keel joins the plastic hull. It only runs parts of
the way in several runs, not all round, and looking at another Trident
nearby I see no such thing. It doesn't look as if it's moving, or the
keel's coming off or anything, just that however that join was sealed or
smoothed from new is no longer watertight/smooth. I expect it doesn't have
to be watertight, the keelbolts are all encapsulated in the sole anyway.
The bolts should also be protected from corrosion by the anode just like
the keel itself. Should I worry? Should I scrape that join out and fill
it with epoxy or something? Any thoughts?
I'm also considering drilling through the thin fin part of the keel above
the bulb and adding a pair of doughnut anodes there, just like the rudder
has, to increase the protection to the keel; it looks fairly rusty.
Opinions? Should I disconnect the keel from the electrics if I do this so
it's fully standalone?
TIA,
- Huge
The_navigator©
that at a minimum you should scrape out the join to a good depth and seal with
5200 then repaint. A layer of flexible fill is the only way to stop the seal
breaking, now that movement is taking place. If you see evidence of rust -eg.
bubbles of rust or rust stains you may need to pull a keel bolt to establish
the extent of the corrosion. Lets face facts, the keel HAS moved and you should
ponder why... At this age you should probably pull a keel bolt anyway to be on
the safe side. Just 'cos they are buried does not mean they are not corroding.
I like the idea of separate anodes for the keel and isolating it from the
engine/electrics by the way. If in doubt seek professional advice, keels are
important.
Cheers MC
Tony of Judicious
the hull) failed.
Rust takes up about 8X the volume of the original metal. If the top surface of the keel is rusting
this could stretch the keel bolts, perhaps fracturing them.
The Navigator has a point - why is there rust in the first place? Has the keel moved? Twisters are
pretty tough boats, I'd be more worried if it was a fin keel, but it may be worth getting expert
advice.
Tony Howard
www.yacht-judicious.co.uk
Hugo 'NOx' Tyson
(And thanks to Oz and the Navigator too - all helpful comments)
Tony of Judicious<po...@thoward.plus.com> writes:
> A question - is the rust just on the surface or has the bedding on the
> top surface of the keel (to the hull) failed.
I don't know. I suspect just the surface - the rest of the keel especially
right at the bottom on the bulb where it rubs the mud[1] also has rust. BUT
the whole thing looks no better nor any worse now out of the water than it
did when I last looked in May - including the crack where the keel joins.
> The Navigator has a point - why is there rust in the first place? Has
> the keel moved? Twisters are pretty tough boats, I'd be more worried if
> it was a fin keel, but it may be worth getting expert advice.
"Trident" not Twister - and it *is* a fin keel.
I shall ask advice from the marina engineering shop when I'm next down
there, then.
My conclusion from what you've all said is (at least)
a) do re-seal the join, even if protected from corrosion by anodes, sealing
it with some sikaflex-like sealant then painting over (antifoul) is
useful.
b) given the keel is corroded generally, add more anodes and isolate from
rest of boat. Easy and cheap and a good thing.
and depending on what the experts say (I've also got this question out with
the Trident Owners' Association as well as getting pro advice) I may get
the keelbolts checked/replaced. (Eeeeek! Scary stuff.)
Thanks again all,
- Huge
[1]very soft mud. Fin keel, not bilge. Our berths at Hoo are not well
dredged and get rather silty, but the boats always manage to carve a slot
OK, so it seems. It dips into the mud at low water.
Graham Frankland
news:m3adjgw...@foo.surfingsuggestion.co.uk...
It sounds as if there is some movement there so if it were my boat I would
be dropping the keel to check the state of the studs and re-bed it. You
could also grit-blast the rust off and epoxy it at the same time. A pair of
anodes would seem a good idea but I'm not sure whether the bonding wire
should be removed or not - is there any lightening grounding which runs to
the keel?
Graham.
The_navigator©
lot of strain on the keel/hull join and may explain the movement. Fin keels are
not generally designed to take the ground in this way and if the keel is stuck
in mud while the boat hull is twisted ... Remember a fin keel is not designed
to act as a mud shovel but to part water and survive a 'head on' impact with
rock (possibly with some structural damage).
Cheers MC
Simon Brooke
> (And thanks to Oz and the Navigator too - all helpful comments)
>
> Tony of Judicious<po...@thoward.plus.com> writes:
> > A question - is the rust just on the surface or has the bedding on the
> > top surface of the keel (to the hull) failed.
>
> I don't know. I suspect just the surface - the rest of the keel especially
> right at the bottom on the bulb where it rubs the mud[1] also has rust. BUT
> the whole thing looks no better nor any worse now out of the water than it
> did when I last looked in May - including the crack where the keel joins.
>
> > The Navigator has a point - why is there rust in the first place? Has
> > the keel moved? Twisters are pretty tough boats, I'd be more worried if
> > it was a fin keel, but it may be worth getting expert advice.
>
> "Trident" not Twister - and it *is* a fin keel.
>
> I shall ask advice from the marina engineering shop when I'm next down
> there, then.
Well, you know, getting the keel bolts out and replacing them is going
to be one horrible job and may of course not be justified. On the
other hand if it is justified and you don't do it one of these fine
days when the going is bumpy the keel is just going to fall off, which
could be a little embarrassing. It used to be common practice to x-ray
keel bolts in place to check their condition. Otherwise, get one out
and inspect is carefully and if you're sure it's alright put it
back. Yes, I know, horrible job - but not as horrible either as
getting all of them out and replacing them or as having your keel fall
off.
--
si...@jasmine.org.uk (Simon Brooke) http://www.jasmine.org.uk/~simon/
,/| _.--''^``-...___.._.,;
/, \'. _-' ,--,,,--'''
{ \ `_-'' ' /
`;;' ; ; ;
._..--'' ._,,, _..' .;.'
(,_....----''' (,..--''
Karlheinz
> Well, you know, getting the keel bolts out and replacing them is going
> to be one horrible job and may of course not be justified. On the
> other hand if it is justified and you don't do it one of these fine
> days when the going is bumpy the keel is just going to fall off, which
> could be a little embarrassing. It used to be common practice to x-ray
> keel bolts in place to check their condition. Otherwise, get one out
> and inspect is carefully and if you're sure it's alright put it
> back. Yes, I know, horrible job - but not as horrible either as
> getting all of them out and replacing them or as having your keel fall
> off.
what if it's a long keel, weighing 8500lbs?, shows just a bit of
surface rust when out for painting but the hull (FG) to keel (castiron)
joint seems fine. Would I have to undoe all the interior glassed
over nuts (including one under the engine) and then lift the boat off
the keel for inspection?? I'm assuming that how it was built in the
first place, keel down and then the glass hull placed on top and
glassed in place.
this is a moody halberdier 36', built in 67.
opinions??
karlheinz
plu...@altavista.net
> I'm also considering drilling through the thin fin part of the keel above
> the bulb and adding a pair of doughnut anodes there, just like the rudder
> has, to increase the protection to the keel; it looks fairly rusty.
> Opinions? Should I disconnect the keel from the electrics if I do this so
> it's fully standalone?
no, bonding is to connect everything together, so that there are no electrical
differences between parts. If you can separate the electrics from the salt
water then good, but I doubt you can, the engine will not be isolated.
The rust that you have on your keel, is this from when the boat has been out
of the water? I had bare steel showing under the water for a couple of
years and no rust ever grew there..
and yes, seal the crack - maybe you should tighten the keelbolts aswell just
to be sure they are tight
plu...@altavista.net
> You should worry a bit. The encapsulation does not prevent corrosion. I suggest
> that at a minimum you should scrape out the join to a good depth and seal with
> 5200 then repaint. A layer of flexible fill is the only way to stop the seal
> breaking, now that movement is taking place.
if you are on 3M products, then I think 4200 is the one to use if you want to
paint over it, 5200 went gooey when I painted it last year. (in fact, I have
seen it go that way several times on different occasions)
The_navigator©
then 4200 then paint ... The 5200 has better adhesion and can give more (I think...)
Cheers MC
Hugo 'NOx' Tyson
For clarity, the crack is hairline, you know, just a rusty line partway
along in the old layers of antifoul that's down there, not like something
you could get a knife or sheet of paper into, not broken fibreglass nor
even gelcoat AFIAK.
Thanks for the comments folks - I will be definitely doing this: adding
extra anodes directly on the keel; *not* isolating it from the rest of the
system earth wires (though there is no lightning grounding explicit that I
know of); asking for advice from the local boat-engineers. I might also
fill it the gap, and/or ask the local boatyard to examine the keelbolts
depending on their advice. The bolt heads are glassed over in the bilge,
such is life.
Some owners of the same type of yacht (and they're all of similar age)
indicate that the same thing has been seen - with no problems known.
So wasn't a "fly poster" (asking a qn and reading the answers but not
reporting back conclusions) - I just haven't had time to *do* anything more
yet on the matter. More info back here when I do.
Hugo 'NOx' Tyson
Hugo 'NOx' Tyson <hm...@surfingsuggestionx.co.ukx> writes:
>>>> Summary: I asked for advice about some hairline cracks in the antifoul
>>>> where the iron fin keel joins the glassfibre hull. Keelbolts are all
>>>> glassed over on the bilge.
> Some owners of the same type of yacht (and they're all of similar age)
> indicate that the same thing has been seen - with no problems known.
...and that the keel is bedded in some very tough mastic that'll actually
hold it on with the keelbolts removed! (In the shed, I mean, not at sea)
And it's a devil's own job even getting through to the keelbolts.
> So I wasn't a "fly poster" (asking a qn and reading the answers but not
> reporting back conclusions) - I just haven't had time to *do* anything
> more yet on the matter. More info back here when I do.
Having finally got down to the boat and had a go at the "crack" with a
wire-brush electric drill, in a couple of places, there's no sign of
problems under the paint (antifoul). Just a joint with mastic in it, all
sound looking.
I'm not even sure that filling the crack is possible, since it's only a
surface paint crack - maybe caused by years of very slight movement.
Possibly also provoked by the mud - our berths aren't very well dredged, so
she dips into (very very soft) mud, in the same place, twice a day. But
I'll ask advice from the local yard later. I suppose for best results I'll
go all along it with a wire-brush electric drill and cover the exposed
glassfibre with epoxy, or maybe new mastic. Not decided for sure yet, but
now far less concerned than I was earlier!
What I have done (yesterday) is added a pair of doughnut anodes to the keel
itself, so it's not relying on the other anode (prop &c) by an old-looking
wire. That should arrest any tendancy for the keel to rust, so I can be
confident it's not rust in the keel bedding causing a problem.
Wishing a good Xmas and Happy New Year to all, thanks again,
- Huge