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Catalina/Capri 25/250 Sailor's Forums

Catalina 250 Specific Forum

Bottom aft concaved

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suttergold
1st Mate

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USA
49 Posts

Initially Posted - 10/13/2008 : 20:53:33

Yesterday I pulled my Catalina 250 WB out for the season. This was the third year that I have done so. I was power washing the bottom and noticed that the bottom, aft of the cable area was concaved. I can only speculate that it has something to do with the draining of the ballast.

I tapped the area and it was not soft. Any suggestions?

"Knot On Call"

Edited by - on

Steve Blackburn
Master Marine Consultant

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Canada
1091 Posts

Response Posted - 10/14/2008 : 00:09:21

Pictures please. for the pictures maybe you could hold a ruler to show how concave it is? I can then post pictures of mine for comparison.

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zebra50
Captain

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USA
408 Posts

Response Posted - 10/14/2008 : 15:47:41

I have a 250 WB 1998, and pull it out every year draining the ballast. I have never had a concave area in the hull. Did you hit something during the time in the water?

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suttergold
1st Mate

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USA
49 Posts

Response Posted - 10/14/2008 : 19:16:14

I have not hit anything that would cause the concave, there is not any damage to the area. I can only theorize that the concave is related to the pressure of the water in the tank area and when it drained maybe the pressure change caused the concave in the hull.

I will try to get to the boat this weekend and take photo's and post them.

Edited by - on

jbkayaker
Captain

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USA
299 Posts

Response Posted - 10/15/2008 : 23:07:14

It sounds like the air pressure inside the tank was maintained lower than the outside air pressure for an extended period. One caveat: I am only familiar with the water ballast plumbing on a MacGregor. Did you allow water to exit the bottom drain without opening the top vent to allow air in ? Or has the temperature dropped while both the top and bottom holes were closed ? This could happen if you launched on a hot day and sealed the tank before cold water or cold air cooled the air inside the tank. A partial vacuum would be created IF the tank was perfectly sealed. Over time the fiberglass might yield.

Edited by - on

Al
Captain

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USA
269 Posts

Response Posted - 10/16/2008 : 03:09:10

I've never even seen a water ballast C250, but if it is a pressure differential problem and assuming it's an airtight tank, it seems like you could seal the valves/vents and install a tubeless tire valve in the tank somewhere accessible and stop by a gas station and pump it up till the dent pops out.

Edited by - on

britinusa
Web Editor

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USA
5404 Posts

Response Posted - 10/16/2008 : 06:06:39

We flood and drain the WB every trip on JD, no dings here! I'm pretty familiar with the underside as I had to install a water inlet for the AC and did a repair on the keel swivel. I agree with Steve --- pics! ----

paul

Edited by - on

jbkayaker
Captain

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USA
299 Posts

Response Posted - 10/16/2008 : 10:33:37

Some heat to soften the fiberglass and low air pressure inside the tank might do the trick. But that approach seems very risky to me. I was back flushing the water filter for my little water garden with a garden hose. Without thinking I put my thumb over the outlet. That created enough force to blow the top off the fiberglass filter tank. That's the beauty and danger of hydraulics and pneumatics. A small force is multiplied by the ratio of the areas involved. My thumb probably created something around 5 psi, but multiply 5 psi by the area of the tank top and that was easily 150 pounds of force. So it broke several of the top hold downs until water escaped relieving the pressure. From my experience I believe YOU COULD CRACK A SEAM ON YOUR BALLAST TANK WITH RELATIVELY LOW PRESSURES ! Or you could pooch out and stretch the fiberglass beyond the original contour.

A direct attack on the concave area would be safer. Applying a vacuum pump and a form would be one approach. I think it would be difficult to get that to work.

Drilling holes to attach folding anchors (like those used to mount things on drywall), followed by suspending weights would be another.

The least risky solution would be filling in the concave volume with Bondo or foam and fiberglassing over it to restore the contour.

All of these are untried solutions and may be worth what you paid for them or less.

Edited by - on

JohnMD
Navigator

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USA
207 Posts

Response Posted - 10/16/2008 : 11:48:04

I have a 95 wb with a 'dent' in the bottom much like you describe. It's starboard of the cable area you're talking about. As you said, it's not soft, it's not cracked and it doesn't make the tank leak. So, if it's not causing any structural problems, why mess with it at all? No one will even know it's there but you. By messing around and trying to get it to pop back out, you could cause a real problem. My two cents.

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bill bosworth
Navigator

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USA
172 Posts

Response Posted - 10/16/2008 : 19:22:27

I have a 250 WB, I've never seen a concave area on the bottom. I would also caution against putting pressure in the balast tank, I think you would be asking to blow a seam, a problem that could be difficut to fix.
Bill
c250wb #134 SERENDIPITY on beautiful Kerr Lake, NC

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OLarryR
Master Marine Consultant

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USA
3477 Posts

Response Posted - 10/16/2008 : 22:16:21

It would seem to me the best thing to do before taking any action on your boat is to send an EMail to Catalina Yachts Technical Services and see what they have to say.

Edited by - on

Steve Blackburn
Master Marine Consultant

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Canada
1091 Posts

Response Posted - 10/17/2008 : 10:59:20

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by britinusa
 We flood and drain the WB every trip on JD, no dings here! I'm pretty familiar with the underside as I had to install a water inlet for the AC and did a repair on the keel swivel. I agree with Steve --- pics! ----

paul
<hr height="1" noshade id="quote"></blockquote id="quote">

Paul, didn't you mention the bottom was about 2" thick fiberglass around that area when you installed your AC? If so, how can that even bend? Obviously I'm wrong about the 2", I'm guessing it's much thinner.

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britinusa
Web Editor

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USA
5404 Posts

Response Posted - 10/17/2008 : 16:13:14

Steve, correct, the hull was very thick in the area aft of the water ballast tank. I can't see it being much thinner fwd of the tanks aft bulkhead.

Paul

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suttergold
1st Mate

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USA
49 Posts

Response Posted - 10/18/2008 : 14:22:30

Went to the boat yard this morning to take photo's of the aft hull area to post, the concave area in now gone, vanished. I cannot explain why!

Edited by - on

Al
Captain

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USA
269 Posts

Response Posted - 10/18/2008 : 15:30:03

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Steve Blackburn
Master Marine Consultant

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Canada
1091 Posts

Response Posted - 10/18/2008 : 20:46:06

Optical illusion? Did you actually pass you hand on the area? How concave was it when you saw it? Still I can see how 2" thick fiberglass can concave. The boat is designed to be trailered and if it would be so easy to concave we would experience all sorts of beer can effects.

Edit: I meant I CANNOT see how 2" thick fiberglass can concave.

Edited by - Steve Blackburn on 10/19/2008 14:50:22

suttergold
1st Mate

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USA
49 Posts

Response Posted - 10/18/2008 : 22:11:38

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by Steve Blackburn
 Optical illusion? Did you actually pass you hand on the area? How concave was it when you saw it? Still I can see how 2" thick fiberglass can concave. The boat is designed to be trailered and if it would be so easy to concave we would experience all sorts of beer can effects.
<hr height="1" noshade id="quote"></blockquote id="quote">
I ran my hand in/on the entire area. I tapped the entire area with my knuckles and pushed. It sounded solid and felt solid. It seems to me that it was like a large dent and then without any thing done to it, it popped out.

Edited by - on

OLarryR
Master Marine Consultant

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USA
3477 Posts

Response Posted - 10/19/2008 : 07:50:14

This is sounding like the fish that got away story.

Good news is that you can get a good night sleep again and enjoy sailing with no concerns !

Edited by - on

suttergold
1st Mate

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USA
49 Posts

Response Posted - 10/19/2008 : 14:46:32

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by OLarryR
 This is sounding like the fish that got away story.

Good news is that you can get a good night sleep again and enjoy sailing with no concerns !
<hr height="1" noshade id="quote"></blockquote id="quote">
It did not pop out when I ran my hand on the area. I did that when I first discovered the concave area. One week later when I returned to take a photo to post I noticed that the concave area was gone.

I don't fish and I don't tell stories, what I saw last week was what I saw.

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OLarryR
Master Marine Consultant

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USA
3477 Posts

Response Posted - 10/19/2008 : 21:16:52

Well...I was only kidding. Seems the two most likely causes, you already mentioned one of them - Draining the water and it pulling a vacuum; The other that was mentioned - A difference in air temperature between the inside and outside. Either of these could have initially occurred but not if the tank was vented.

Edited by - on

Nauti Josh
Deckhand

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USA
7 Posts

Response Posted - 10/20/2008 : 19:45:23

I've got a book titled Inspecting the Aging Sailboat by Don Casey. In this book what you have described he calls a FLAT SPOT. He states that thin fiberglass depends upon curvature too make it stiff, designed flat areas of the hull will be thicker and/or stiffened to compensate. Flat spots in the curved parts of the hull indicate trouble. They occasionally occur because the manufacturer removed the hull from the mold too soon, but more often they indicate weakness, damage, or poorly executed repair. Rigging tension can dimple a flimsy hull around the chain plate attachment points. A weak hull may permanently deflect if stored in a cradle or supported by screw stands for a long time. Any impact that flattens the hull has broken or delaminated the fiberglass. Amateur repairs often "bridge" a hole rather than matching the original contour of the hull. All of these require corrective measures.

If your sure that your boat has never suffered an impact in this area. Than it must be a weak spot in the hull. I personally don't think that pressure differential from filling and emptying the tank would ever cause this. Nor pressure from temperature fluxuations in the water tank. Unless it is a weak spot. I would not recommend trying to pop out the spot by putting the ballast tank under pressure. If you do want to "try" to pop the area out. Try this low tech approach. Use a toilet plunger on the spot. I once pulled a big dent out of a car door with a toilet plunger.

Edited by - on

willy
Captain

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USA
422 Posts

Response Posted - 10/20/2008 : 20:43:35

Dent on dents...you can't beat that!

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