Lavro Dory Foam Core Discovery

One of the big concerns I have had with this Lavro Dory project is that there is foam below the floor, but the hull has no drain plugs. This seemed really stupid to me, given that the manufacturer, and owners after, had drilled holes in the floor to attach hardware, and water has certainly gotten below.

Not knowing exactly how it was constructed, or what foam was used, I thought that there was potentially a lot of water weight below the deck. Other owners have reported a rather wide range of top speeds, with the same horsepower motors. And I feared that the reason for that may be lots of weight in water saturated foam below the floor. I thought it was certainly possible that I might have to remove the entire floor and the foam below, if I found wet foam.

What to do? I considered lots of options, the simplest being installing a drain plug in the stern. But normally water saturated foam will not drain, so this would likely do little good. And the lowest point in the boat is actually up in the bow, and I was not keen on installing a drain through the hull up in the bow.

So I decided to cut a 6″ diameter access hole in the floor, directly over the lowest point in the bow. I wanted to see what the foam was like, and if it was wet. I could either re-cap it later, or install an inspection hatch for the future.

Well, after cutting it out, I discovered that it had a very well bonded structural foam core below. It was really hard stuff. And when I plopped it into a bowl of water, it did not absorb any. I even drilled a hole in the top of the plug and left it full of water overnight. And the water level was only slightly lower in the morning. So the good news was this foam was not damaged by water, nor does it hold much water.

After some internet sleuthing, and asking boat builders, it appears the foam is Divinycell H. That is good news. It is a very good core that in fact will hold very little water.

So it appears this boat is made with a structural foam core, bonded to the bottom and the floor, with no stringers. And that is really a good thing, because it is a lightweight way to build, and it provides enough positive buoyancy that the boat will not sink. And I don’t have to tear it all out.

Next I drilled a hole down through the foam core, down to the fiberglass in the bottom of the hull. I then stuffed a towel down into the hole. And sure enough, within a few hours the towel was wet, having wicked water up it. So although the foam is not damaged by water, it is certainly holding a bit of water. And it does seem to have moved to the low point in the boat, because a similar wicking test of another hole where a seat was mounted yielded no water.

It probably is not a lot of weight in water, but it would still be nice to dry it out. Having talked about this problem with some composite construction experts, it is not easy to remove. It likely will not drain out by itself, because of all the surface tension in the tiny spaces that it resides.

I considered setting up a vacuum system to pull the moisture out. But it was explained to me that in order for this to work, I would need to create a very high level of vacuum, so that the water would essentially boil, allowing it to be sucked out as vapor. That high of a vacuum made me nervous about the structure of the boat being damaged. Plus it would cost a bunch of money to get the equipment to achieve it.

Ultimately I decided that continuing to wick water from the core with a towel would do a good enough job. I can keep changing it out for a long time, until no more water comes out, and cap it up at a later date. And the floor will have no holes in it when I am done. All hardware connections will be glued.

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