Reply
 
Thread Tools Search this Thread
 
Old 31 July 2017, 18:23   #1
Member
 
Country: Ireland
Town: Cobh
Make: Cobra
Length: 6m +
Engine: Mariner 200HP 2-St
Join Date: Jul 2017
Posts: 4
Water getting into under-deck tank

Hi Folks,

Just bought my first used rib - a Cobra 6.5m. Not sure of exact year but guessing late 90s.

I've had a few teething problems so far, the most significant being that at times, there seems to be water getting into the under-deck tank.

All was OK for a few days while the bilge pump was doing it's job.
Then the Bilge pump failed a couple of times - turns out it was dodgy wiring to the switch.

After heavy rain, there was a few inches of water on the deck. Once I drained the deck, I went for a spin. After a few minutes, I lost power and worked out that there was a lot of water in the fuel. I drained the tank and took over 100L of water out of the tank - plus 40L of Petrol. Same happened a few days later.
So, clearly when there's a lot of water on the deck, it's somehow getting into the tank. There's no sign of fuel coming into the bilge.

I'm not that familiar with Ribs, so I don't know the normal setup. In my boat, the solid stainless pipes come up from the tank a few inches above the deck and the hoses join to them - this is all in the drivers jockey seat. When the deck was flooded, the water seemed to be coming up from the bilge and a couple of inches deep. So, the joints between the hoses and fixed pipes were under water.

Sorry for the long post, but there are a few separate issues contributing to the problem. Ive sorted the bilge pump, but I'm assuming that I can't depend on not having water on the deck in the future.

My guess is that this is probably down to a leak in the tank, possibly around the seal with the hoses , but possibly elsewhere. Other posts about tank leaks talk about fuel getting out rather than water getting in.

I see from other threads that diagnosing / repairing / replacing under-floor tanks is not trivial. Am I right that the first step is a pressure test? Someone mentioned a smoke test is a possibility?

Some side questions:

- Should water be coming up from the bilge - there are three holes for cables to run to the stern.
- Is there any of getting a layout diagram / drawings for the boat - to see where the tank etc is?
- Should cables, lines be running front to back through the bilge?

Thanks in advance

Colum
__________________

__________________
Daoirse is offline   Reply With Quote
Old 01 August 2017, 02:09   #2
Member
 
Country: UK - England
Town: Chesterfield
Boat name: Sea Quell
Make: Picton Cobra
Length: 5m +
Engine: Mercury 150 4 Stroke
MMSI: 235038298
Join Date: Sep 2003
Posts: 997
I would guess that the water is getting into the tank through the sender unit gasket. The connection will most likely be under the seat pod. I don't think Dave fitted an inspection hatch inside the seat base as standard then. You will have to try and remove the seat assembly - it's secured by 4 nuts onto captive studs in each corner. ASAP Supplies have rubber gaskets for the 5 hole senders at good prices. Once done and checked I would fit a screw down inspection hatch in the seat base.
Water on the deck may be getting in through either of the two 4" standpipes that the cables run in and out off. Probably the stern one where the sealant into the deck has failed,,, unless you had so much water on the deck that it over-topped the pipes that are about 4" tall
Good luck
Jeff
__________________

__________________
Jeff is offline   Reply With Quote
Old 01 August 2017, 02:13   #3
Member
 
Country: UK - England
Town: Chesterfield
Boat name: Sea Quell
Make: Picton Cobra
Length: 5m +
Engine: Mercury 150 4 Stroke
MMSI: 235038298
Join Date: Sep 2003
Posts: 997
Another thought,,,,, was this from when the boat was on the water... If so, it could well be a leaking transom drain bung and it's entering through there. You can soon get a hull full of water then! ,,, or check the elephants trunk for a split . If you have one of those dreadful ball scupper valves instead,,, get rid 😊
__________________
Jeff is offline   Reply With Quote
Old 02 August 2017, 10:06   #4
Member
 
Country: UK - England
Town: plymouth
Make: Ribtec
Length: 6m +
Engine: Mercury 175 optimax
Join Date: Feb 2008
Posts: 394
Second the gasket on the fuel sender...I had someone pressure test my tanks in situ and told me they had massive holes and were letting in water....I ripped the deck off and took the tanks out only to find that it a perished gasket around the sender.....I wasn't a happy bunny!!
__________________
Miller is offline   Reply With Quote
Old 02 August 2017, 11:40   #5
Member
 
Country: Finland
Town: Helsinki
Boat name: Harmaakarhu
Make: Avon SR6
Length: 6m +
Engine: Yamaha F150
Join Date: Feb 2009
Posts: 75
How about a split breather hose? Since the amount of water is so huge it has to be a substantial leak. Or a smaller leak, but constantly under water.
__________________
Stresspill is offline   Reply With Quote
Old 02 August 2017, 18:36   #6
Member
 
Country: Ireland
Town: Cobh
Make: Cobra
Length: 6m +
Engine: Mariner 200HP 2-St
Join Date: Jul 2017
Posts: 4
Hi Folks,

Many thanks for the responses so far.
I'll take some photos to be more clear.
Under the jockey seat, I can see 3 pipes about 4" above the deck. They all come through a panel about 4" x 10". Interestingly, there is no sign of a fuel sender. My guess is that the panel has been added later or modified. That panel is screwed down with 4 or six screws. So, I think if I lift that panel I expect to see the sender blanked off and I hope the source of the problem. My preference is obviously to re-install a fuel sender. Is there anything specific I should be looking for in sourcing a sender?

A bit more detail on the source of the water - once it was pure stupidity on my part - forgot to install the bung in the bilge! After an hour, the deck was full of water. The second time, the bilge pump failed and it rained constantly for 2 days. Both times, under the console, the water was about 2-3" deep. The boat had been fine for a few weeks sitting in the water and hadn't leaked water into the fuel. So this all points to a leak at the top of the tank when the deck is flooded.

A side-issue is that there seems to be no separation between the deck area and the under-deck bilge area. In the area under the jockey seat over the tank , there are three holes from the deck to the bilge. Two of them are being used to run cables and flexible fuel line to the outboard. Am I right to assume that this isn't original and that the deck and bilge should be isolated? If that's the case, then I'm assuming that the area under the jockey seat should be dry. Any reason why I shouldn't try to reverse these modifications and just run a cable conduit over the deck?

One final question, how do I confirm that I've found and fixed the leak? I assume the easiest option is a pressure test. Do you know who I could use to do this? I also assume I'd have to take lots of precautions of emptying the tank and ideally rinse with water ( I have lots of that!)

Many thanks for the input so far. I have another question about another modification that's been done to the stern creating a "well" that temporarily holds water coming in over the gunnel by the engine, but I'll create a seperate post for that.

Colum
__________________
Daoirse is offline   Reply With Quote
Old 03 August 2017, 04:22   #7
Member
 
Country: UK - England
Town: Chesterfield
Boat name: Sea Quell
Make: Picton Cobra
Length: 5m +
Engine: Mercury 150 4 Stroke
MMSI: 235038298
Join Date: Sep 2003
Posts: 997
Some photos may help,,, the 3 pipes you refer to are usually a larger filler pipe and 2 small - one for supply to the engine and the other a vent. The panel is fitted as standard - it covers a larger hole in the deck over the tank. I assumed these came up inside the console not seat but perhaps yours is a single jockey configuration as opposed to Side by side bench?
The well at the back is a sump and standard and where the pump should be sited,,, it keeps the deck a bit clearer whilst the pump operates.
The better fuel senders IMHO are WEMA,,,,, make sure the sender and gauge are the same US or UK resistance spec. Mercury / Smartcraft are US.
If it is the gasket, which from your issue with leaving the bung out may indicate, it will be pretty obvious. Tear or mounting nuts loose. The sender mount is usually mid way along the tank
__________________
Jeff is offline   Reply With Quote
Old 03 August 2017, 04:44   #8
Member
 
Country: UK - Scotland
Town: Glasgow
Boat name: Thunder
Make: Halmatic Arctic 22
Length: 6m +
Engine: 2 x 150 Etec
Join Date: Oct 2008
Posts: 517
If all the obvious things are ok check the welds on the tank, I had issues with a similar age of stainless tank where the welds had hairline cracks.
__________________
GordyP is offline   Reply With Quote
Old 08 August 2017, 14:32   #9
Member
 
Country: Ireland
Town: Cobh
Make: Cobra
Length: 6m +
Engine: Mariner 200HP 2-St
Join Date: Jul 2017
Posts: 4
Just a quick update - I'm still trying to work out how to share pics:

Big issue is that after taking off the cover , there is still no sign of a fuel sender. A few other points.
- The pipes up from the tank are at the front of the tank - I assume that the feed pipe must be routed backward from the top of the tank to the rear internally?
- While there is no fuel sender visible, it is possible that it's been blanked off and fibreglassed over. There is however no obvious sign of this. Has anybody seen an internal tank with no sender?
- I can't see any obvious sign of any damage to the hoses or the rising pipes.
- The rising pipes are stainless steel, so am I right to assume that that means that the tank itself is stainless?


Will post photos when I can

Thanks,

Colum
__________________
Daoirse is offline   Reply With Quote
Old 08 August 2017, 17:23   #10
Member
 
Country: Ireland
Town: Cobh
Make: Cobra
Length: 6m +
Engine: Mariner 200HP 2-St
Join Date: Jul 2017
Posts: 4
Here are some photos.

This shows the fuel tank under the pilot jockey seat.

Click image for larger version

Name:	IMG_20170803_130510(1).jpg
Views:	88
Size:	51.3 KB
ID:	121301

Click image for larger version

Name:	IMG_20170803_130521(1).jpg
Views:	97
Size:	46.5 KB
ID:	121302

Click image for larger version

Name:	IMG_20170803_130537(1).jpg
Views:	88
Size:	46.5 KB
ID:	121303

Click image for larger version

Name:	IMG_20170803_131938(1).jpg
Views:	81
Size:	86.0 KB
ID:	121304

Click image for larger version

Name:	IMG_20170803_133629(1).jpg
Views:	83
Size:	100.5 KB
ID:	121305
__________________

__________________
Daoirse is offline   Reply With Quote
Reply

Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off





Copyright 2002- Social Knowledge, LLC All Rights Reserved.

All times are GMT -5. The time now is 08:13.


Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2019, vBulletin Solutions, Inc.