Subfloor - Drainage - Questions - 1448

JoeDiesel · Aug 10, 2021

I'm an experienced DIYer, I can weld, woodwork, plumb, etc, but novice boater this will be my first non-canoe/kayak. So I apologize if I use improper lingo/sound stupid

I got some questions about proper Jon boat drainage. I'm looking at modifying a 1448 to have a subfloor with flotation foam underneath. This boat will be used in rivers and on the Texas coast for inshore redfish. So both fresh and saltwater.

I haven't found much information on building a subfloor/deck. My main concern is drainage. It appears there's two types of flotation foam methods. Either free-draining? (water can escape under the foam and under out the back to the bilge). Or have a air/moisture tight foam cavity

The free draining makes sense, but in the event of running the boat in saltwater would you want to flush out the underside after use? Maybe I'm overthinking this, but it seems important.

Any insight or additional information would be helpful! Thank you!

LDUBS · Aug 11, 2021

"So I apologize if I use improper lingo/sound stupid "

Read a few of my posts and you will come to the realization you have nothing to worry about.

To me the "free-draining" option seems the way to avoid issues down the road. For small open boats there are fewer options for floatation. Seems there is a conflict between the need for positive floatation and the need for good drainage under the floor boards. A lot of folks leave an open channel through the under-floor foam for drainage.

JoeDiesel · Aug 12, 2021

LDUBS said:
"So I apologize if I use improper lingo/sound stupid "

Read a few of my posts and you will come to the realization you have nothing to worry about.

To me the "free-draining" option seems the way to avoid issues down the road. For small open boats there are fewer options for floatation. Seems there is a conflict between the need for positive floatation and the need for good drainage under the floor boards. A lot of folks leave an open channel through the under-floor foam for drainage.

Thanks for the response! But yes that seems to be the route I've been seeing. Free draining, and allowing plenty of room under the foam so water can easily travel to the back.

onthewater102 · Aug 12, 2021

I poured foam between the ribs in my 16', but I lined the cavities with painter's plastic and put a round object along the center of the bottom of the cavity so water could still drain from the sides of the boat to the center. There are pictures on my build thread.

If I were to do it again I'd rip a piece of PVC pipe down the centerline on my bandsaw and cut it to fit as a form for the lateral channel on the underside of the foam, it wouldn't stick up as high off the bottom of the boat as simply dropping a round section of pipe would, but that's just to get a bit more thickness in the foam board, I haven't had any issues with it.

CedarRiverScooter · Aug 12, 2021

Another factor is providing airflow to the bilge. Consider adding a scuttle facing fwd. Will help dry it out.

wmk0002 · Aug 12, 2021

I've wondered in the past if you could set up a form outside of the boat to pour foam in. Something kind of like what the use for concrete tables/countertops using that engineered wood with the laminate layer on the faces. If it would work, you could put something in where the strakes run so they have a larger opening when the form is laid in. Probably a stupid idea, but I'm throwing it out for better or worse lol.

CedarRiverScooter · Aug 13, 2021

Why not just put pipes in, then plastic sheet, pour foam, lift out the big block when cured & remove pipes.

LDUBS · Aug 13, 2021

Or, if it is in an enclosed area, like under the floor board, you could use cut up sheets of closed cell foam instead of the two-part pour in stuff. Leave as many openings as needed for drainage. Benefit of this is the foam will be much easier to remove if needed for any future modification, repairs, etc.