Filling the keel with cement

[skipperdude]

Has anyone filled the keel with cement?

If so did you use regular premix or something with an additive such as latex or poly resin?

Any issues with water trapped under the cement?

As I have heard thet water in the bilge can cause a sort of reverse osmosis simmilar to blisters only on the inside.

What about sealing it to the hull inside the keel?

SD

 

[Phil Fill]

Our keel and hull is filled with cement with a fiber glass mat over to keep the water/moisture out but more importantly to hold it in place.* The cement looks to be regular old cement with pea gravel and is not very hard to drill/dig out. A couple of time we have had water in the bilge, mostly domestic water leaking/spilling and water has gotten under, but I soaked and dried up the water as best I could.* There area couple of places I need to lay new fiberglass cloth.****


*
If I remember right, you took out some ballast when you got the boat.* What kind of ballast was that? **
** ******

 

[skipperdude]

Large tubs of dirt but was in the fish hold and did little to make her not so rocky tippy.
Just pushed her deeper into the water As the floor of the fish hold is above the keel and the dirt was set upon the bunks on either side. Not low and centered

SD

-- Edited by skipperdude on Monday 22nd of November 2010 02:51:24 PM

 

[jleonard]

My keel is also cement filled as Phil described but I don't know what the actual blend is.
I know it has water in it. I have been draining it every winter and it is mostly gone thanks to me sealing some bilge pump mounting screws that I believe breached the fiberglass "cap".
I had to drill a hole in the keel from below and tap for a pipe plug so I could drain when on the hard and seal up for launching.

 

[Datenight]

SD,

I cut the fiberglass cap, pulled out the stinking foam and poured concrete mix. Regular concrete from the hardware store. I'm sure sand mix would have been fine as well.

For the bilge pump I coated a piece of plywood with several coats of epoxy, drilled oversized holes for the mouting screws and filled them with thickened epoxy. The plywood was set in the wet concrete. The whole thing was covered with several layers of cloth and resin. Seems to work fine.

Rob
37' Sedan

 

[Delfin]

Skipper, is your vessel fiberglass?* With an existing hull, is there a reason you want to change trim by adding weight to the keel?

 

[koliver]

Cement is commonly used by cheaper builders, to encase the steel punchings or lead ingots that are the ballast in a sailboat keel. My first sailboat was done that way. I watched the builder hoist baking pan sized lead ingots up the ladder and into the hull, then lower them carefully to stand, wedged into the keel cavity, till no more would fit. Then steel punchings, then pour a thin mix of concrete to hold the whole works in place. It wasn't finished on top, so using the bilge for storage, your stuff would come out looking like it had been stored on the garage floor, the part under the car, as engine filth and shaft drippings would get it all dirty.
That was 1977. I saw the boat in 2007 and all was still well with it.
SD, if you are going to do it, I recommend adding a layer of FG on top, just to keep it clean.

 

[FF]

Pitch is as common as cement .

What ever is used be sure to curve the surface so the bilge water will usually settle in the center.

On steel boats this is critical , as a flat keel top will keep the steel wet constantly . and the usual curved shapes there make replacement costly.

 

[Larry M]

FF wrote:

Pitch is as common as cement .

What ever is used be sure to curve the surface so the bilge water will usually settle in the center.

On steel boats this is critical , as a flat keel top will keep the steel wet constantly . and the usual curved shapes there make replacement costly.

Doesn't the pitch stay soft and have no structural strength?* What happens if you heal significantly couldn't your ballast come rolling out?

*Larry

 

[skipperdude]

Delfin wrote:

Skipper, is your vessel fiberglass?* With an existing hull, is there a reason you want to change trim by adding weight to the keel?

I have been trying to determine why the boat is so tippy. The center of gravity seems to be high. With the engine amidships a cat 3208 and a 10,000# fish hold about the second quarter from the stern without fish she sets stern high.* The boat never had a letter of stability comprised for her.

I am attempting to figure out the math and measurements to determine if adding weight to the keel will help with the stability. I know I need weight low and centered.
I havent figured out the metacentris height of the boat to calculate the stability.

I thought if I figured out the center of boyancy I could get a more stable ride.
*
Any one know a easy way to calculate the roll*responce?
I have tried using the Navier Stokes*equation but I keep getting lost in the math.

This is the problem with reconfiguring a commerical fish boat to personal use.*

SD*

*


-- Edited by skipperdude on Tuesday 23rd of November 2010 02:13:17 PM

 

[Delfin]

Ah, I see the problem.* I assume the fish hold is water tight.* If so, have you tried filling the hold with H2O to see the effect on roll?*

I was going to do a stability test on Delfin, but didn't end up doing so as she draws 7 ' and it probably would have been pointless.* When I spoke to an architect, the procedure described was basically loading weight onto the sided deck and measuring the amount of deflection from horizontal.* My impression then was that there was no easy way to determine stability, which is why they just pile weight on to see what happens.* Someone more knowledgeable on the subject can add to this, I'm sure.

 

[skipperdude]

Delfin wrote:

Ah, I see the problem.* I assume the fish hold is water tight.* If so, have you tried filling the hold with H2O to see the effect on roll?*

Negative. I could I suppose but as I use it for storage and have mounted my flow scan on the bulkhead I would have to remove that first.

There has been bilge keels added and they are at about 4%

The roll is remarkably quick in the order of about*2.3 seconds.

Of course the Paravane's *change the whole equation.

SD*



*

 

[RickB]

skipperdude wrote:The roll is remarkably quick in the order of about*2.3 seconds.

*How are you measuring that period?

 

[skipperdude]

RickB wrote:

*
*How are you measuring that period?

*I had a 300 lb friend stand on the gunnal next to the dock and jump off.
*I should have timed it to the stop I just timed it to the the virtical.
SD


-- Edited by skipperdude on Tuesday 23rd of November 2010 02:47:27 PM

 

[RickB]

I mean from what to what are you counting the time? If you start the timer when the guy jumps off the heeled boat, when do you stop it?

 

[skipperdude]

when the roll comes from when he jumped off the port to when it rolls to starboard and back to vertical. I am probably doing this wrong.*
I tried suspending a plumb bob from the center of the saloon with a yard stick running transversly athwartships to get an idea of the angle of heel. I don't recall the number now or exactly how to apply it in the calculations. unfortunatly I have all that info on the boat.



SD

 

[RickB]

Yeah, you quit too soon.

Time the roll from the moment the weight is removed until the boat returns all the way back to that point. In other words, if the STBD side is down all the way, time it rolling from STBD to PORT and back to STBD again. Do this 3 or 4 times and get the average.

Since a 300 pounder puts a large force onto the boat by jumping off the boat it might work better to just have her push down on the gunwale with a foot to get the boat rolling at its natural frequency.

What is your beam? Is it around 10 feet, maybe a couple inches over?

Do you know the displacement?*

 

[RickB]

Delfin wrote:Ah, I see the problem.* I assume the fish hold is water tight.* If so, have you tried filling the hold with H2O to see the effect on roll?*

I take it you have never heard of "free surface effect"?

It has a tremendous effect on roll and the life expectancy of those who ignore it.

*

 

[skipperdude]

RickB wrote:
Do you know the displacement?*

I do not.

*Just gross 16 ton *and net 10 ton. *She is 31 &9/10*ft* waterline* 11 and 9/10 beam

Thanks for the info on timing the roll. Sooner or later I will have all the numbers and hopefully get the math right.

SD

-- Edited by skipperdude on Tuesday 23rd of November 2010 04:07:52 PM

 

[Delfin]

Yes, RickB.* I have heard of 'Free Surface Effect,' which is why I suggested that Skipper fill the tank to eliminate the effect.

 

[RickB]

skipperdude wrote:*Just gross 16 ton *and net 10 ton. *She is 31 &9/10*ft* waterline* 11 and 9/10 beam

OK, judging by the beam and extrapolating your roll period, the boat is a bit stiff. It*may have*too much weight down low already, probably because someone worried about the top hamper.

And since you mentioned it, gross tonnage is enclosed volume, net tonnage is the volume available for cargo. Neither has any connection with the displacement of the boat., they are regulatory and taxation figures.

*

 

[RickB]

Delfin wrote:

Yes, RickB.* I have heard of 'Free Surface Effect,' which is why I suggested that Skipper fill the tank to eliminate the effect.

*It wasn't a tank you suggested he fill, it*was the*fish hold. Big big difference!

 

[skipperdude]

RickB wrote:

OK, judging by the beam and extrapolating your roll period, the boat is a bit stiff. It*may have*too much weight down low already, probably because someone worried about the top hamper.

I am going to redo the roll test and get it right this time.* I assume a roll*period should be about 4.0*seconds or there about. for my boat.

SD

*


-- Edited by skipperdude on Tuesday 23rd of November 2010 04:35:34 PM

 

[Marin]

RickB wrote:

*
Delfin wrote:

Yes, RickB.* I have heard of 'Free Surface Effect,' which is why I suggested that Skipper fill the tank to eliminate the effect.


*It wasn't a tank you suggested he fill, it*was the*fish hold. Big big difference!

Isn't the free surface effect present in a tank, too?* As I understand it, this is one of the things truck drivers who haul fuel*trailers have to understand and be careful of.* Isn't the free surface effect the force(s) generated by the sloshing of a fluid in a defined space like a tank or fish hold?* The fluid gets moving back and forth by the movement of the container and once it's moving it*begins generating unbalancing forces independent of what the container is doing?

Or do I have the definition wrong?

*

 

[RT Firefly]

Hiya,
* I think the free surface effect is much more pronounced in a boat as opposed to a tanker truck.

 

[markpierce]

My*last vessel, a pocket cutter*(Bluewater Blackwatch), had sand as ballast, well sealed.* Never a problem.

 

[Delfin]

If the tank is full, the effect is nil.* If it is not, you have to deal with a moving center of gravity.* Mypoint was to determine whether adding weight easily with water to what one would presume was designed to add significant weight below the waterline effected the apparent stability.* If it did, then it might make sense to go to the trouble of adding ballast.* If not, why bother?* However, it sounds like that might be a problem for Skipper, so please assume I never said a thing....

Next, we'll get a lecture from RickB on the subject, to be sure.

 

[RT Firefly]

Hiya,
** I think Mr Delfin you've hit the nail on the head.* If the tank is totaly FULL, there's no free surface and thus no effect.** I'm ready to be corrected.* I recall boating in a leaky canoe.* Even 1" of water in the bottom completely destroyed stablility.* That was when I was a lot younger and HAD a sense of balance.* Now, I'd be swimming.

 

[RickB]

Delfin wrote:
Next, we'll get a lecture from RickB on the subject, to be sure.

If you tell someone to do something very dangerous and stupid and I read it I will post the reasons why it is dangerous and stupid. Too bad if it offends you.

It's a fish hold, not a tank. Most of the volume of that hold is above the vertical CG. If it were pressed in order to avoid free surface effect the boat would probably be dangerously overloaded with a GM that made it liable to capsize without warning. If it was only filled to some arbitrary level then the very large free surface would flip it in a heartbeat. That is why your "advice" is dangerous and stupid.

To top it off, what has the waterline got to do with CG?

And for Marin, the sloshing you mentioned is also very dangerous, especially to a road vehicle where the tank is a separate structure. On tankships it can cause structural damage when the ship is subject to surging in a seaway. Both tank trucks and tankships use multiple smaller tanks with baffles and divide them on the centerline to minimize free surface and sloshing problems.

The difference in it being a hold rather than a tank is that, except for fishing vessels that use a refrigerated seawater fish hold like you see on the Bering crab boats, the boat is not designed to operate with the hold completely full of water and "batter boards" are used to prevent fish and ice from causing a free surface effect.

Tanks are calculated for their stability effects in the design stage and the vessel stability is calculated with tanks in empty and pressed condition. The stability documentation may include prohibitions against operating the boat with certain tanks part full, empty, or pressed.

*


-- Edited by RickB on Wednesday 24th of November 2010 06:21:00 AM

-- Edited by RickB on Wednesday 24th of November 2010 06:28:07 AM

 

[Delfin]

Thanks for the correction RickB, and for being so predictably true to character.