JEM Watercraft

I know how to figure pressure head, I'm not sure how to figure lateral pressure on a dry compartment.

Say you are building a Southwind 15, and plan to put dry storage in both ends with hatches using the #2 and #5 frame locations. Say you roll it and fill it most of the way with water. Now it's setting we'll assume mostly underwater. Wow much force is on the bulkheads and hatches? Would that be about the same as the pressure head, height x .433? Thanks .

Joe

Hhhmmmmmmm............ Good question Joe.

Pressure in a liquid at a particular depth is the same in any direction and the maximum pressure will be the same as the pressure head at the bottom of whatever depth of water you have in the boat. The width of the water column has no effect so filling the cockpit of a Laker 13 to 8" will give the same pressure as filling a Sasquatch 18.5 to the same depth.

Pressure is force divided by area so conversely the total force on the bulkhead wil be the pressure multiplied by the area. The problem here is that the pressure increases from the top of the bulkhead to the bottom and the shape of the bulkead is irregular so I think you need some sort of integral calulation to work it out exactly. From the practical point of view I would say that if you take the pressure at half height and multiply that by the area of the bulkhead panel it will be a good approximation of the total force. Just from looking at the Southwind study plan I'd be surprised if there was more than 40lb on each bulkhead with the boat completely filled.

I assume you are asking this so you can be sure that your bulkheads are strong enough not to break and are mounted in the hull securely enough not to be dislodged in the event of a capsize.
Given that the panel is :
- glued in all the way around with epoxy,
- reinforced with battens, glass tape or both,
- positioned such that it is in a tapering section of the boat so any pressure from the outside will force it up harder against the hull.....
....and that the force is distributed so that a fair portion is near the supported edges ....
I doubt that it would be a problem unless it is very thin ply.

Anyhow, when the boat is finished do a capsize drill and let us know if she sinks

Good luck with the build.

Yeah, Ditto to what Bob said.

No idea mate. we are building canoes and kayaks, not nuke subs.

I haven't calculated it like that but it would help if you explained your concern. Are you worried the bulkheads will cave in if the main hull is filled?

I glued plywood bulkheads into a kayak with silicon caulk. It filled with water and they held fine so I would assume epoxy would be even better.

I dont use foot pegs just push against the bulkhead ,never had a problem even in races.
Ron

Thanks for the replies guys, I didn't see them till this AM. I'll take a couple of photos and tell what I have in mind this PM.
Matt the hatch caving in is my concern, I want compartments as floation mainly. I thought I would make hatches in case I ever hauled camping cargo. I know wood floats and I'm allways in my PFD, just wanted the boat to ride a little higher in a capsize. I'll post some photos in the builders log and show my thoughts. See ya.

Joe

bronco302 wrote: Matt the hatch caving in is my concern, I want compartments as floation mainly.

Joe

I'd need to see you hatch design... assuming you're making your own.