HELP!!! Gelcoat leprosy, is my season over?

[mrron_tx]

Russ ...... Without consulting an almanac .....I wouldn't know about the rain part... But I seem to recall a song saying it never rains in southern California Ron.

[Russ]

Russ ...... Without consulting an almanac .....I wouldn't know about the rain part... But I seem to recall a song saying it never rains in southern California Ron.

but don't they warn ya
It pours, man, it pours

[u12fly]

After reading this, I wonder how the new Florida built Tattoo boats will do with this issue?

[Catigale]

The fear uncertainty and doubt of blisters compromising hull integrity is the 'ka-Ching" of many a boatyard

Ignore them and sail your boat. When someone tells you water will infuse your fiberglass ask them why the ballast water doesn't do the same thing from the inside.

[Doug W]

When someone tells you water will infuse your fiberglass ask them why the ballast water doesn't do the same thing from the inside.

I had wondered about the water ballast tank.

[seahouse]

I had wondered about the water ballast tank.

I pondered the same thing before I bought my boat and concluded that the ballast water was not a threat to the integrity of the gelcoat on the outside of the hull. For several reasons.

Other than osmotic pressure, there is also an inward-directed hydrostatic pressure acting on the exterior surface of a boat's hull when it is in the water. This is the pressure that actually keeps the boat afloat, and its magnitude varies depending on its location on the hull. Drill a hole in the hull to experience first-hand evidence of this.  

There is no such pressure acting to force water into the walls of the ballast tank, the shallow water supports its own weight, not the additional weight of the boat.

The selectively-permeable membrane in the hull sandwich is identified as the porous gelcoat on the exterior of the hull, rather than the polyester matrix, or any internal layers of it. Osmotic pressure draws the water through the porous gelcoat, into the polyester matrix, and forces it to accumulate and be retained there until the blisters you see, Doug.

Only the ones that are formed near the surface will actually cause visible blisters or bubbles, deeper ones will cause cracking, but the pressure buildup needs to be much greater for a blister to form from even deeper layers – and that's much rarer, and doesn't happen deep in thicker structural layers, as anyone who has sanded and repaired blisters will have seen.

Gelcoat by comparison is unreinforced, weak, brittle, and much less able to withstand expanding burst pressures from within.

Since there is no gelcoat layer inside the ballast tank, there is no selectively-permeable membrane across which pressure can build to lift. The water that moves in is driven to dilute, among other compounds, the unreacted solutes that remain in the polyester matrix. Once it dissolves these, it it not as inhibited from simply migrating back out into the ballast water by a layer of selectively permeable gelcoat. 

Combine the above with this fact - if blisters on the exterior were in fact caused from within the hull, then the pattern of their distribution over the hull would prominently betray that fact, given that the ballast water is not in contact with the entire hull surface that is wetted from the exterior. You'd be able to see the layout of the ballast tank from outside the hull! No one has reported this yet.

The salt vs fresh water train of though is this...Blistering is caused by osmotic pressure, and osmotic pressure is caused by movement of water along a concentration gradient. The greater the concentration gradient, the greater the osmotic pressure is. The osmotic pressure gradient is greater in fresh than salt water, which is why blistering is a more serious problem in fresh than salt water.

Overall, you can draw parallels between the blisters on a boat and rust on a car. Nobody wants them, they're not cosmetically appealing, they don't cause any great deal of damage or structural weakness (at least initially, but make no mistake, at some point in the future they will if the causative conditions remain in place), you can take measures to prevent them from the outset if you buy them new and plan on keeping them for a while, or you can repair the damage after the fact if you choose to. Or not.

Some people worry about a bit of rust on a car, and some don't. I would also say to just go out and continue to have a blast in your boat, Doug, blisters or no blisters.

- Brian . 

[seahouse]

After reading this, I wonder how the new Florida built Tattoo boats will do with this issue?

I thought I heard mention that vinylester resin was being used in their construction, which is a superior, but more costly material. It is also known to be more resistant to osmosis and blistering than polyester resins, so they should fare even better than the Macs.
- B.

[Doug W]

I would also say to just go out and continue to have a blast in your boat, Doug, blisters or no blisters.

- Brian . 

That's my plan now, Brian! I intend to get the leper into the water this weekend!

[seahouse]

I'm sure there will be others just like it there as well, to make it a colony, but nobody's telling, and nobody knows!

[sirlandsalot]

Holy blister!

I just pulled my boat out after a summer in the water, exact same blisters on the entire bottom. Guess I will leave it for now and see if it worsens after next summer. Lot s of money to fix it and no where near by to do it.

Hope it doesn't get worse.

[Russ]

Holy blister!

I just pulled my boat out after a summer in the water, exact same blisters on the entire bottom. Guess I will leave it for now and see if it worsens after next summer. Lot s of money to fix it and no where near by to do it.

Hope it doesn't get worse.

My first year had the same issue. It never got worse. In the spring, I popped a couple to see what's going on inside. Nothing came out. If they ooze creepy acid like substance, you may have concern.

Yea, expensive to sand them all down and epoxy over them. If they don't get worse, I wouldn't worry too much.

[Seapup]

I'm sure there will be others just like it there as well, to make it a colony, but nobody's telling, and nobody knows!

Ignorance is bliss I helped a buddy strip and paint his new to him mac 22 that has lived in a slip 30+ years last summer. It was covered (Mostly on one side and not the other???). I casually mentioned them, but I can guarantee he has not thought of them since and that they have had zero impact on his boat enjoyment.