water ballast

[Andre Emmenegger]

I was lucky and was able to keep my boat on a lift. It looks like that may change soon, and it will go into a slip. Whenever I drained the water ballast, I could drain an additional 5 to 10 gallons, if I tilted the boat, to make the drain side of the hull bottom was parallel to the water. Since fiberglass is not waterproof, and will retain water, my question is what prevents the hull from getting water logged, or blistering from the inside?

[March]

The blisters will occur only if the fiberglass is covered with a gel coat, I think, which is not the case within the interior of the tank. As for the fiberglass itself becoming waterlogged, you may be right here, but I wouldn't worry too much about it. It would be like worrying that the entire hull is not indestructible and will be affected by water eventually: well, it isn't, neither fiberglass, nor wood, nor metal. Nothing is, but the amount of passive damage over time in the boat's life is minor. I would worry more about 'active damage' (exterior blisters, cracks in the gel, scratches, screws and bolts in the fiberglass that become loose, etc. etc.)

[mastreb]

I think the question is regarding water migration from the un-gelled ballast tank through the bottom glass and then blistering the exterior gelcoat. The answer is that there's no need to worry as there is no osmotic pressure gradient as long as the ballast tank water is the same type (fresh or salt) as the outside water, which it always is unless you're carrying water around with you between lakes and oceans. A fiberglass hull can be completely water saturated without the water causing any issues.

Also, because the layup on MacGregor's is large sheets of woven roving, water will not tend to migrate from layer to layer as it migrates along the glass weave due to capillary action. Finally, the resin used may be more waterproof than others; resins vary widely in their absorption characteristics.

Here's an article on the subject, but the most important information is that there's no evidence of even very old Macgregor hulls having problems with long term water migration from the interior.

http://www.yachtsurvey.com/WetLaminate.htm

[Ixneigh]

My 73 v222 has a few on the outside.
It's been in the water the last five years.
I've dealt this this problem before. If the hull is prone to them, no amount of paint will fix it permanenIt has to be a new layer of glass and vinyl ester resin.
In the ballast tank, who knows? I might someday be inclined to pour a few gallons of vinegar in there. Not sure if it would help. The sure fire way is cutting open the ballast tank, and using the space for four big batteries and fuel or water tanks. And however much lead needed to make up the difference. I'll let you know how that works out if blisters ever become a problem.

[seahouse]

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 (chronically speaking... there might be a bit on heel) acting to force water into the walls of the ballast tank.

The selectively-permeable membrane in the hull sandwich for the purpose of osmosis discussions is identified as the gelcoat on the exterior of the hull, rather than the polyester matrix, or any internal layers of it. Osmosis draws the water through the porous gelcoat, into the polyester matrix, and forces it to accumulate and be retained there until the blisters we all know about form.

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 at all deep in thicker structural layers, as anyone who has sanded and repaired blisters will tell you.

Gelcoat by comparison is unreinforced, weak, brittle, and much less able to withstand expanding 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 gelcoat.

Combine the above with this fact - if blisters 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!

- Brian.

[mastreb]

if blisters 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!

- Brian.

The proof, as they say, is in the lack of pudding.

[Ixneigh]

Hahaha so these boats could go down in history as proving or disproving that water inside the hull causes blisters.
I concur with the bad skin layer theory advanced in the posted link. Mat type fiberglass sucks up resin like a sponge, making for added expense and weight. The temptation is to make the resin go as far as possible. All of my blister issues on other boats started in that layer, although some also had really bad delam issues as well. I went clean through the hull on my old yawl once, looking for good glass.
One wonders about just leaving off with the gel coat, and using a good heavy coat of plain resin instead, at least on boats that will be bottom painted.
Ix

[BOAT]

Roger claimed to have the best record in the business in regards to the blistering issue; he was quoted in a publication. I guess he probably could say that since he has so many boats out there that are very very old.

I like the water ballast because the ballast tank makes the bottom stiffer and you can take a hole in the bottom of the boat and it will not make the inside of the boat flood. You still have that ballast tank between you and the rock you just hit.

A full lead bottom is of course much stronger but if you put a hole in the hull the water seeps around the lead plug and floods the inside of your boat and makes it sink.

Has anyone ever read of a MAC sinking? I have only read of them turning over in a turtle, but I have never read of one sinking. Are there any cases? I was curious because I know of MANY cases of sinking in my old boat model and other popular brands.

[RobertB]

Has anyone ever read of a MAC sinking? I have only read of them turning over in a turtle, but I have never read of one sinking. Are there any cases? I was curious because I know of MANY cases of sinking in my old boat model and other popular brands.

Probably they turn turtle since so many take out the foam under the mast step

[mastreb]

This is the only thing I know of: Deliberately sunk.

http://www.youtube.com/watch?v=mah5vwVQ384

[BOAT]

I can't find ANY Macs that have sunk! Now I KNOW of three A23's that sunk - one hit the rocks in Mexico and went down - the family of 4 were friends - they were okay - another in Canada caught fire and went down, and another sunk under circumstance that were not detailed to me.

You can find lots of stuff about jensen CAL boats sinking and Catalina's and others (mostly from pilot error) but I can't find any MACs that sank.