diesel saturation of Fiberglass

[LH44]

The Little Harbor 44 has intregal FG diesel tanks. The hull exteriro has been peeled and there are signs of diesel fuel beneath one of the tanks. Since the hull is cored it appears that the fuel has found its way thru a joint in the airex core and between the core and the outer laminate. Mositure meter readings are dry and tapping produces a solid sound. Does not appear to be any delamination.
Any experience with such a situation or ideas as to the long term effect?

[waltward]

I will be interested in what folks have to say here. I have a Capri 30 with a similar problem, taps solid except for a small area. I know if you cut one of these out you have to go far enough to get to totally dry material, could be a pretty big hole. I think my other option is to barrier coat the bottom, paint it, put on a life jacket & go sailing.

Walt -- Northern Lower MI.

[jparker11]

LH44,

Well, the biggest problem will be developing the repair procedure for putting the exterior skin back in place and having the repaired area perform structurally in a manner similar the surrounding cored laminate.

Baltek/Airex apply a fiberglass surface layer during manufacture of the core to facilitate bonding of the polyester/vinyl ester resins to the core. Polyester and VE resins have notoriously poor adhesion properties to PVC (Airex). By removing the exterior skin you have broken that bond and torn the fiber mat from the airex.

There are epoxy resins with good bond capabilities to PVC. Now, the skin layups need to be applied with huge edge tapers (20 to 30 to 1) to prevent hard spots in the interface between the repair area to existing laminates. All in all it will (or should be) a very sophisticated repair done by pros that have built cored laminates.

I must add that you stated you chased diesel down an airex seam by removing the exterior skin. So, I am assuming your peeled area exceeds 2 square feet.

Now, your question was about the diesel. It would have had little effect on the core material (Airex) or the fiberglass laminates (refinery storage tanks are protected by fiberglass overlays over carbon steel in the lower 6'' of each tank - read total immersion). Again, the bad actor here will be the effect it will have on the repair. Diesel seepage from the core area will affect secondary bonding to the core and the fiberglass laminates unless it is staunched.

You might want to scare the hell out of yourself and have the tanks tested by soaping them and pulling a small vacuum on them to locate the leak sources. Some material testing labs can do this type of test. Bet you are looking at a hard wall stand alone tank, unless you enjoy diesel taste in your fresh crab.

You would have been better served had they used a much less invasive inspection procedure.

Industrial tank producers have been trying to build cored tank bottoms for years to no positive experiences. I don''t know why a boat builder would think they are any smarter!!

[LH44]

Thanks for your replies.
When I mentioned the bottom has been peeled, I meant that the bottom paint, barrier coats, and gel coat had been removed. What remains is the exterior laminate, the core and the interior laminate. Prior to emptying the tank, diesel was finding its way thru the outer laminate through a pin hole and onto the surface of bottom. After the fuel was removed from the tank, the exterior was degreased and sanded. Signs of diesel can be seen THROUGH the exterior laminate and on top of the core. It is obviously finding its way through the interior laminate and the airex core to get to this location.
The decision that has to be made is whether or not to remove a small (5" diameter) area of the exterior laminate and the core, and then glass the interior laminate so as to prevent fuel from following the same path.
If the core and laminate will not be damaged as you suggest, it might be best to fill the exterior laminate pin hole and leave well enough alone.

[jparker11]

LH44, Sorry for over reacting a little. I have just seen bad experiences with repairs of cored laminates and then had to forensically develop repair procedures with computer modeling to save the structure. Your actions thus far, now that I understand them, will minimize repair costs.

If the diesel impregnation of the Airex is keeping you up at night, removing a 2-4" diameter section of exterior laminate with a hole saw (round holes - important) as a vent would be an easy repair. Drive the diesel out with small heat application.

If you can locate the tank leak and it is a manufacturing type defect in the lay up, fine. But, if it is integral with a tank/bulkhead intersection with the hull form, life gets a whole lot more complicated. These are the ultimate hard spots in laminate designs. Overstressing the interior core laminates at these locations is very easy. You may get the leak fixed until you lift the boat off the cradle!! If a metal tank is not in your future, what about a custom bladder for the tank? Have this type of tank in the plane and they seem to a have a life of about 20 years. Just a thought.

Good Luck,