Confused by stringers, water drainage design

[tmh]

OK, here's the situation. I had rotten section in back of boat floor. Removed back half of floor and pulled out lots of wet foam underneath. As I now look at it, I can't for the life of me figure out how any water that does get under the floor can ever escape.

1985 19' Mark Twain BR. The stringers run lengthwise and across the width, basically creating boxes with approx. 3' lengths and 8" cross pieces. These are nicely glassed into the hull. The foam was in these sections. I ASSUMED there would be a way for water to flow to the back bilge to be pumped out. However, each of these sections seems totally closed (glassed in) with no hole connecting to the next section.

Is this a common design and is it assuming no water ever gets beneath the floor? Should I drill some holes to connect the sections and allow flow if water gets under there again? Do I need to glass those holes or just slop some epoxy in there to seal the drilled wood?

Also, am I safe to ASSUME the natural low point is the back where the bilge pump is? or could it be the water won't flow there even with the holes?

Please offer advice! Sorry, no pictures because my dig. camera died recently.

 

[andy6374]

Re: Confused by stringers, water drainage design

Yes it is a common design. When people pull rotten stringers and recreate the stringer grid system they often sleeve pvc through the stringer for draining to the bilge.

This is a nice example

Making limber holes in the stringers is another option (that's what I did).

 

[drewpster]

Re: Confused by stringers, water drainage design

I can tell you on the old thundercraft I have there is a separate lower drain plug at the bottom where water is allowed to drain from under the floor. It is a more permanent screw in type pipe plug as opposed to the rubber expanding plug above it used to to drain the deck. I remove both while the boat is out of the water and tilt the trailer up slightly to keep water out and theses areas dry. Question: Did you refill the spaces between the stringers with floatation foam when you rebuilt them? Is it necessary to?

 

[tmh]

Re: Confused by stringers, water drainage design

ahhhh.....those PVC pipes look interesting. However, in the photo I don't see and way for water to flow the the back? Am I missing something?

What is a "limber hole"?

I have not replaced the foam and will likely not finish the project until spring. I want to get the stringers done now though. I have a problem putting the poured in foam in again as it will block and possible water flow and eventually create the same problem. Soda bottles are a possibility, but I wonder how much the foam helped with ride quality, vibration and noise reduction?

Anyone ever take it out and not put new foam back in? How did it work ride quality wise?

 

[seven up]

Re: Confused by stringers, water drainage design

Limber holes allow water to drain from longitudinals as well as drainage between fore and aft frames to the lowest bilge. Often a small chain is threaded through for clean-out.

us composites website offers some explanation of pourable foams: 2 lb to 16 lb densities.

The foam was a coast guard requirement after a certain year in manufacture.



Enjoy

 

[Bob_VT]

Re: Confused by stringers, water drainage design

I would design and drill holes for drains. Contour all edges to facilitate the flow of water, they block the areas with plastic to prevent foam from filling those spots in.

Just because people were not thinking ahead and thinking with their focus on profits we should not create the same problems under the decking...... unless you enjoy stringer work.

 

[croSSed]

Re: Confused by stringers, water drainage design

Here's another option: After you have drilled drainage holes in your stringers and properly glassed around the holes so that no water that does need to drain ever touches wood, install your floor with NO floatation foam in the false bottom. Then, after your floor has set up and is completely solid, drill holes in your floor where the voids in the false bottom are, and pour in liquid polyuretane foam, in amounts that ensure there is no voids left. The whole false bottom would be filled with the foam in such a way that no water CAN get it. But, in case some somehow does, you have the drainage holes down there already. After you have drilled the holes in the floor, and poured the foam, fill them properly.

TG

 

[tmh]

Re: Confused by stringers, water drainage design

Thanks again for all the ideas. I'll be drilling some holes when I get back to the boat. I'll have to assme that when the boat is in the water the flow goes to the stern and collects near th bilge pump. On the trailer, it's not really obvious where the lowest spot is on some of the side "channels".

If I put foam back in there it will not be the pourable type i don't think as it will bloack water flow causing the same problem. I may use soda bottles or use pieces of closed-cell foam layed in in such a way so as to not block the bottom inch or so of each section.

Richt now i need to make a decision on whether to tear up more of the floor to get the foam out or leave it. The wood is fine and the wetness is not nearly as bad as the back section so I may just dry things as best I can and leave the rest of the floor in place. Then again, what's another piece of plywood in the big scheme of things. Maybe I'll go another few feet until I get to the end of the coackpit area. I sure don'e want to try doing under the bow seats - I don't even know how I'd go about doing that.

 

[croSSed]

Re: Confused by stringers, water drainage design

I guess I'm just thinking that if you put enough pourable foam in the voids, so that there is NO voids left at all, how is any water going to get in? The foam will have expanded and will be pressed against the back side of the floor, the sides of the stringers, and the bottom of the boat. There would be no space for anything else to get in.

TG

 

[Bob_VT]

Re: Confused by stringers, water drainage design

Foam absorbs water. Want flotation? Use empty soda bottles..... been discussed here alot.

 

[tmh]

Re: Confused by stringers, water drainage design

Bob VT, I have read that here which is where I got te idea from. I haven't seen anything about how using bottles vs. foam effects the ride of the boat. Does foam help absorb shocks, dampen doise, etc? Or would the ride be identical with the Soda bottles?

Thanks

 

[Solittle]

Re: Confused by stringers, water drainage design

Foam will add to the rigitity of the hull. More rigid results in a firmer ride.

 

[tmh]

Re: Confused by stringers, water drainage design

OK, for a more rigid construction it's easy just to add a few more cross-brace boards. That should do the job fine I would think,

 

[salty87]

Re: Confused by stringers, water drainage design

how about drilling your drainage holes and sealing the wood properly, filling them with closed or capped sections of pvc, laying the floor, pouring foam and then pulling the pvc sections to leave voids for any water flow?

 

[tmh]

Re: Confused by stringers, water drainage design

Good idea, except how would I pull the PVC after layinhg down the floor? I can't see how I'd get at it. Could use PVC with holes drilled in it though and leave it in there to collect and drain the water, maybe.

 

[salty87]

Re: Confused by stringers, water drainage design

except how would I pull the PVC after layinhg down the floor? I can't see how I'd get at it.

i was thinking you might be able to cut the pvc so that they are long enough to hang out into the bilge. once it's all together, they'll still be sticking through the stringer and you could pull them through. the foam might grab them though. maybe wax em up first? i remember having read about someone using wax rope that would disintegrate leaving voids behind. i dunno, i'm in the planning stages too.