dumping bilge through oar power

I'd like to design a rowboat hull with a smooth bilge that could take surf splash. I'd like to be able to row in ocean swells without having to stop and bail water out manually.

My idea is to create a smooth tubular bilge that runs the length of the hull. At the stern, there would be a through-hull a few inches above waterline, and internally, this bilge-tube would smoothly bend up to it. The through-hull would have a sprung (and optionally locking) scupper gate to allow water out but not in (I’m aware this would be tricky to get right on tension, and would probably not be completely effective in keeping water out in a heavier swell.

But under a strong pull of oars, and especially if timed while climbing a wave-face, I’m hoping the water’s inertia would shoot it down the tube and up and out the gate. The floorboards would be glassed-in above the bilge so water would have no place to stay other than flowing down to an opening at the boat’s mid-point.

I'm imagining a hydraulic effect with a tube full of water, but if only the tube accelerates, and there's no pressure on the water (other than atmospheric), I think it's likely any water that exits the scupper will climb up just under inertial resistance, and that the shape of its container will be irrelevant.

In any case, I'd love to hear a pro opinion of this concept. I've never seen it before, so it's probably got some flaw I'm not seeing that makes it impractical. Any thoughts most appreciated.

 

You can buy and automatic bailer. Elvstrom designed them in the 50s and are readily available.

 

Thanks but the Anderson / Seasure Super suck self bailers don’t seem to be optimal designs. I haven’t been impressed with them on sailing dinghies, or rowing shells. Through hulls (below the waterline) on thin-skinned rowing craft don’t seem a good idea anyway. They also require speed for effect, and I want something that works on acceleration. I want to be able to row the water out of a swamped boat.

 

Turn your foot rest into a bilge pump. Every pull of the oars would pump out a little water.

 

Thanks sam, that could work, I've thought of it, but I'd have to build it, and I'd have to use extra mental and physical energy. I'm more interested in using energy I'm already expending.

 

"Turn your foot rest into a bilge pump. Every pull of the oars would pump out a little water."...no, you would not even know that you are doing it, this is a very good idea.

 

Couldn't agree more. A mini gusher pump that pumped every stroke simply from foot rest pulsing pressure. Minimal stroke length.

-Tom

 

I have seen and copied a really old system, that might be enough.

A large car (so it has a dual action pump ) fuel pump is mounted so the operating lever faces down.

A lead weigh is mounted on the lever that will operate the pump when moved side to side.

The weight is stopped at the end of its travel with usually a ply piece cut into a U.

Now any movement , with you aboard , or wave action on a moored boat will operate the pump.

Its only a teaspoon at a time , but an hour of operation gets a lot of teaspoons out of the boat.

FF

 

Okay, a teaspoon at a time is not enough for my ambition. I do like a weighted swivel, but think a better application for that would be controlling a water gate / scupper door. And when one is using a sliding seat on an open water rowboat, your feet are the connection to the boat. Any play would detract energy from the rowing motion, and require significant concentration and coordination (too much).

I'm actually looking for a hydrodynamic analysis of my concept. It seems workable to me, but I can't understand why I haven't seen it before.

Maybe I need to be thinking in terms of velocity. A tube running the length of the boat, accelerating from 2 to 5 knots with a strong pull of the oars will create a 3 knot difference in potential energy between the stern and the water in the tube. So I need to calculate what that would translate into in terms of kinetic lift to get water up and out the scupper. Again, I don't know whether the shape of the bilge / container / pathway makes any difference there. I'm suspecting not, but I'd like a pro opinion.

 

This on the seat..

 

Your system would only work when you are accelerating. Once you reach maximum speed, the water will slosh back and forth. Bailers work because they use pressure differential.

 

Yeah, one of those under each foot, some hose and Bob's yer Uncle!



dcnblues, it sounds like your thinking along the water ram sort of idea where a lot of moving water pumps a little uphill....
http://www.ncollier.com/rams.html

 

But in a rowboat, you accelerate with each stroke of the oars, and decelerate with every recovery. It'll also 'slosh back' with a gravity boost when climbing a wave or swell.

 

Well, as I said, that'd be hydraulic force where mine will just be inertial resistance.

 

i can see what you are after, just build your self draining cockpit and make a flap out of insertion rubber to go on the scupper outlet , it will work fine. the flap stops water rushing back in but also lets it out with out much resistance. i would not curve the drain up to the scupper though. i would make the floor a bit higher so it can run down to the scupper.