OD16 and foam / bilge water

[Palm Bay Chuck]

I'm going to start building the OD16 and it looks the gap between the keel and the sole is the 6" of the 2X6 stringers. I was not going to use foam to fill this space because the boat won't be in the water all the time and I fear that foam will just get saturated and heavy. Anyway, should this 6" space be treated like a bilge with a bilge pump and everything to ensure that it stays empty. The plans would seem to indicate that it should be 100% sealed, so there'd be no way to get in there and replace / repair the bilge pump unless some access panel were included. Just curious how you deal with this kind of enclosed space.

Thank you.

[OneWayTraffic]

In general the choices are sealed and foamed, or empty with inspection ports or hatches. Sealing with epoxy and fillets all around should be watertight if you carefully seal any penetrations. Everything under the sole and everywhere should have a minimum three coats epoxy, so water won't be a boat killing flaw. Water will only get into the foam if you let it. I understand the concerns but many (not all!) here have done that with no problems.

If not foaming I'd recommend that you make sure you have several independent chambers and ventilate them when not using the boat. Water vapour can penetrate epoxy over a long time in conditions of high humidity.

[jacquesmm]

It should be sealed but if you want a bilge space there, do what Onewaytraffic suggest.
I would keep it sealed, I see no benefit in having a bilge there.

[BWhalen]

When I built my OD16 I foamed and sealed everything below the sole. I have not had any issues (that I know of) but I also do not have any penetrations below the sole. If I was building one today, I would probably still foam underneath the sole but leave the space between the stingers without foam and treat as a traditional bilge adding limber holes where needed.

[fallguy1000]

There is also an in between option, but it carries some risks.

You can plan for a dry, foamed bilge, but design for a wet bilge. An inspection port or even a drywell can be added. Of course, the risk is that the well or port leak and allow water in.

Alternatively, you can only install a garboard drain and periodically open it which would be less likely to leak.

The most important thing is to ise sufficient glass on top of the sole seam. My designer recommended 1208 minimum. And avoid sole penetrations.

[VT_Jeff]

I'm going with sealed bilge, no-foam, no limber holes between compartments, no bilge pump, no inspection ports. I can drill a few small holes and check for water with a scope and then reseal if i suspect any water ingress. I have no sole penetrations outside of my 12v wire/steering cable "track" which is theoretically also sealed from the bilge. If I hole the hull, it SHOULD be pretty hard to sink the boat with all the other sealed compartments. Any water should leave through the hole it entered when the boat is hauled, and there won't be any foam to remove/dry out/replace. I may add styrofoam under the deck(not the sole) in a few places, this would be easy to install/easy to replace if needed, and help keep the boat upright if my guesses are wrong.

[fallguy1000]

I'm going with sealed bilge, no-foam, no limber holes between compartments, no bilge pump, no inspection ports. I can drill a few small holes and check for water with a scope and then reseal if i suspect any water ingress. I have no sole penetrations outside of my 12v wire/steering cable "track" which is theoretically also sealed from the bilge. If I hole the hull, it SHOULD be pretty hard to sink the boat with all the other sealed compartments. Any water should leave through the hole it entered when the boat is hauled, and there won't be any foam to remove/dry out/replace. I may add styrofoam under the deck(not the sole) in a few places, this would be easy to install/easy to replace if needed, and help keep the boat upright if my guesses are wrong.

Technically, there is an issue with this approach that I can warn about. If the boat were to fill with water; the sole is the most buoyant and this lends itself to a boat righting upside down. And thus, if you foam above the sole, as mentioned, the boat has a chance of staying in the normal position in heavy seas if partially submerged.

Production boats are required to have foam up along the sides so the most buoyant is not the boat upside down. A catamaran like mine, is of course most naturally stable with the cabin upside down, so nothing I can do besides good seamanship. And so, everyone understands, I am not chest thumping except perhaps imparting the small bit of knowledge I have learned on boatdesign.net.

[VT_Jeff]

I'm going with sealed bilge, no-foam, no limber holes between compartments, no bilge pump, no inspection ports. I can drill a few small holes and check for water with a scope and then reseal if i suspect any water ingress. I have no sole penetrations outside of my 12v wire/steering cable "track" which is theoretically also sealed from the bilge. If I hole the hull, it SHOULD be pretty hard to sink the boat with all the other sealed compartments. Any water should leave through the hole it entered when the boat is hauled, and there won't be any foam to remove/dry out/replace. I may add styrofoam under the deck(not the sole) in a few places, this would be easy to install/easy to replace if needed, and help keep the boat upright if my guesses are wrong.

Technically, there is an issue with this approach that I can warn about. If the boat were to fill with water; the sole is the most buoyant and this lends itself to a boat righting upside down. And thus, if you foam above the sole, as mentioned, the boat has a chance of staying in the normal position in heavy seas if partially submerged.

Production boats are required to have foam up along the sides so the most buoyant is not the boat upside down. A catamaran like mine, is of course most naturally stable with the cabin upside down, so nothing I can do besides good seamanship. And so, everyone understands, I am not chest thumping except perhaps imparting the small bit of knowledge I have learned on boatdesign.net.

100% agree on the upright flotation, that's exactly my thinking behind it.

[VT_Jeff]

A catamaran like mine, is of course most naturally stable with the cabin upside down, so nothing I can do besides good seamanship.

There was a pretty good docu-drama movie about some guys who were sailing a homemade cat in the south seas somewhere and flipped it, survived for months on it upside down. So what that cat lacks in righting moment, it more than makes up for in buoyancy! Maybe add an escape hatch in the bilge if you anticipate any inversions.

[Palm Bay Chuck]

Thank you everyone. I do appreciate the input.