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Old 09-09-2020, 05:07   #1
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Keel Void - "Black Hole" - What to do

I had posted a question on repowering my Liberty 28 (diesel inboard vs outboard) and results were excellent for my decision making process. I have another issue I would like to throw out there for ideas.

This boat is full keel. Underneath the engine all the way down to the end of the keel (aft) there is what I call "the black hole" some 3' wide closer to the boat's cabin, to some 4" wide down there at the end as the boat's hull tapers off. The thing is around 4' deep. I have been at the task of cleaning probably 40 years of sludge and who knows how many wrenches, tight-wraps, pieces of cable, and who know what creatures I might find. The water I use to clean I take out with a 110V pump since there is no other way out. I am still wondering why this cavity is down there as it has no use and has no structural sense. This could have been filled with fiberglass when the boat was constructed. Guess they saved on that.

Any comments on how this can be "filled" that does not present later headaches? Here is a photo of the area.
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Old 09-09-2020, 05:27   #2
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Re: Keel Void - "Black Hole" - What to do

If it were capped off level with plywood then GRP, is there an area were you could fit a small inspection hatch to look in once a year just to check?

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Old 09-09-2020, 05:33   #3
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Re: Keel Void - "Black Hole" - What to do

It looks like the normal bilge on a full keel boat.

Mine has the same thing except a bit wider than yours maybe

If I do start to cruise full time offshore, my plan is to place a bilge alarm down there near the bottom which is also where my bilge pump and float switch are located.

I cleaned out tons of old sludge etc from my "bilge" also after I removed the diesel.

The propeller shaft was down in there a bit also when the diesel was in the boat.

From the bristol27.com site.

http://www.bristol27.com/projects/bilge

http://www.bristol27.com/projects/engine-compartment
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Old 09-09-2020, 05:52   #4
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Re: Keel Void - "Black Hole" - What to do

You might could build a cover with fiberglassed plywood and screw it in place with just 4 or 6 screws (?). Including a small hole to run wires for a bilge alarm. Put the alarm in, screw down the cover. A few screws is all you should need because there shouldn't be any stress on it. This allows you to remove it easily to check things out, but keeps it covered. If your hull isn't thick enough for the screws you can fiberglass a 1"x2" frame around it, giving you more depth for the screws.

I wouldn't permanently seal it up. Others have mentioned the problem with permanently sealed keels after years and years of use and finally opening it up.

Just an idea from looking at the photo. You'll probably think of something better because you're right there.
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Old 09-09-2020, 06:13   #5
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Re: Keel Void - "Black Hole" - What to do

Perhaps it would be possible to partially fill that void with epoxy or concrete?

My Pearson 365 ketch has the aft portion of the keel hollow which has led to some cracked hulls from blocking during haulout. Some have reported using concrete (or other material) to partially fill the void then glassing over the fill to provide extra strength in this area.
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Old 09-09-2020, 06:17   #6
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Re: Keel Void - "Black Hole" - What to do

Storage. I would build some boxes/crates that fit the space. Keep it dry (or at least to only an inch or so) with good bilge pumps.
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Old 09-09-2020, 06:21   #7
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Re: Keel Void - "Black Hole" - What to do

Another good thing about that deep bilge is that if your boat does develop a leak the water has some place to go besides the cabin sol while you go about stopping the leak.

BTW, does your boat leak? Or allow rain in?

Or if somehow you took a wave over the stern and had your hatch open, the water could drain down into that deep bilge and then be pumped out easily with your bilge pump while you go about closing the hatch etc.

Not sure why anyone would want to block, fill, or close it off.

Mine will hold many, many gallons of water before even getting near the cabin sol. So with a bilge alarm also installed near the bottom you are good to go.

And now that I have an outboard on the stern instead of some nasty, leaky old diesel in that area the bilge stays pretty nice and clean.
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Old 09-09-2020, 06:21   #8
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Re: Keel Void - "Black Hole" - What to do

I suspect that any cover you can mount is still going to allow oily water to accumulate. Consider two possible routes. In the first, place a cover over it to keep large junk out. Then from time to time lift the cover and stick the narrow nozzle on your wet/dry vacuum in there to suck out the accumulation. In the second, clean it out carefully and thn fill the void with floatation foam - the mix and pour type, not aerosol. The careful cleaning is the allow the foam to adhere to the sides so that there isn't a crack for the oily water to sneak in. Foam such as this:

TotalBoat Pourable 2 Part Polyurethane Expanding Flotation Foam

But, I have a concern. If indeed your prop shaft is down there, you probably are stuck with the first alternative to consider, or fill with foam only to the level of the shaft.
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Old 09-09-2020, 07:34   #9
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Re: Keel Void - "Black Hole" - What to do

Quote:
Originally Posted by commander500 View Post
I am still wondering why this cavity is down there as it has no use and has no structural sense.
It absolutely has a use - it's called a "bilge" and is meant to allow ingressing water to be pumped out before it gets as high as your cabin sole.
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Old 09-09-2020, 09:50   #10
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Re: Keel Void - "Black Hole" - What to do

Quote:
Originally Posted by Phantom Jim View Post
Perhaps it would be possible to partially fill that void with epoxy or concrete?

My Pearson 365 ketch has the aft portion of the keel hollow which has led to some cracked hulls from blocking during haulout. Some have reported using concrete (or other material) to partially fill the void then glassing over the fill to provide extra strength in this area.
I was thinking poly for financial reasons and microspheres. Cement might have an adverse effect on the design stiffness and would not bond.
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Old 09-09-2020, 10:19   #11
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Re: Keel Void - "Black Hole" - What to do

Commander:

That "black hole" is called a "sump", and it is there to collect bilge water of sufficient depth, though of little volume, so it may be sent overboard while the volume is trivial via a "real" bilge pump with a suction hose. When your boat was young, and where it was engendered, those deplorable little "Rule" centrifugal pumps we all suffer with when we have fin keels rather than full keels, had not yet been invented.

I long for a set-up like yours :-)!

Now, there is nothing to making up a frame that drops into the bilge as a lid to the black hole. It can rest on the curve of the hull moulding where it begins to flare. That will keep "good stuff" like tools (as well as beer bottle caps and deceased bits of pizza) out of your sump.

All you need to let the water get from the actual bilge to the sump is a little scupper 'ole at the bottom of the sump cover.

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Old 09-09-2020, 10:26   #12
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Re: Keel Void - "Black Hole" - What to do

Our boat has the same thing except here it is capped with a grp pan so there is zero leak from below the engine to the deep bilge.


I think its function was a possible water or diesel tank. It does not need filling, but it should be dammed as any breach in this part will flood your boat without any chance of plugging it from inside!


So either add a tank and glass it all around, or add foam blocks and then cap with a grp layer, etc.


Do not leave it as is.


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Old 09-09-2020, 10:43   #13
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Re: Keel Void - "Black Hole" - What to do

I have the same thing x2. I was thinking the same thing. AFter reading the other posts, I have come up with my solution.

Clear Acrylic! Fiberglass attachment blocks with screws.

That way you can see down into the bilge as well as prevent tools, wire ties, wire fittings, etc. from dropping down into it.
On my boat we pour Dawn into the bilge for any fuel or oil. About once a year, I take the hose and a scrub brush to clean the black hole. Nasty place.
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Old 09-09-2020, 10:50   #14
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Re: Keel Void - "Black Hole" - What to do

The part of the boat you describe is the thickest, toughest part of my boat. The fiberglass is very thick in the whole area.

The forward section is where the 2575 lb chunk of lead ballast is housed. This comes down near the end of the bilge area and right at the end of that is where my bilge pump and float switch are located.

I have looked at fin keel boats that have almost no bilge what so ever and it seems quite strange after having my "deep bilge."

Also, my boat was built in the 1970's like yours so I doubt you need to be in a big hurry to change/fix? the bilge since it's been that way for 40 plus years.

https://sailboatdata.com/sailboat/bristol-27
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Old 09-09-2020, 11:01   #15
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Re: Keel Void - "Black Hole" - What to do

my first boat had a steel hull like that. it required lead ballast in all but the last void in the keel...ie, from last keel frame to back of keel..I could not sand blast down there to clean it, nor could I reach down in there to paint it...so I poured concrete in there...to within about 12" from the hull, so I still had somewhat of a "bilge". The problem I had with that was the concrete drying.....I had to drill a small 1/4" hole at the bottom of the keel to drain the water...surprisingly, that hole weeped water for many days....ok, my boat was on land, so that was not an issue......once the concrete hardened I slather the top of the concrete and sides of the keel plate with coal-tar epoxy...the hole got welded shut.

That void was directly under the engine, so getting to it in the future would have been impossible. The 12" "bilge" space was more than adequate and put it in line with the top of the ballast in the other spaces...it all worked just fine....but certainly recommend leaving about a 12" space for some "bilge room"

a friend of mine built a similar boat and was faced with the same problem....his solution, was to get some two part polyurethane foam.... and pour it down there, much like I did with the concrete...it was sanded flush once it go to the top, then it too got painted with coal-tar epoxy...it also worked fine....there is little likelihood of anything ever puncturing that foam...kinda wished I did that...wouldn't have to deal with the water problem.

my next boat also has the deep keel void under the keel, right under the engine. It was a giant PITA. anything dropped in there, stayed in there...plus it stank with oil and whatever else found it's way down there.....I hated it, so much so, I sold the boat....as I could not think of a way to get to it to fill it. I could have poured foam in there, but it would have been a hit or miss thing...

On the flip side, the Beneteau has that classic flat French planing hull....the hull is a scant 9" below the sole. The " bilge" is about the size of a shoe box. it is also a PITA, as any water in there just runs to the low side of the hull, exactly where you don't want it and can't pump it out either...
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