dumping bilge through oar power

Yah, I'm not sure why the resistance to keeping the water out of the boat in the first place but it really seems to irritate the OP? The benefits are huge, including never swamping.

 

Why not do as sailing dinghies do, and have a raised bottom to the cockpit such that the cockpit sole is above the waterline? Then you can let the water run out through a transom flap. The sealed volume below the cockpit sole is your buoyancy tank for when you get swamped.

 

Mind your manners whitepointer, you don't need to act out in such a childish way.

You think I didn't read his post?

Besides, I wasn't talking to you.

 

Great idea but he doesn't want his sole above the water line...

 

While I'm not smart enough to put into design applied mathematics, I'm grateful for your effort, AK. It's rewarding that you're getting what I'm saying, but your figures aren't precise enough to help with design yet (again, not that I'm complaining). You're also not factoring in any hydraulic equations. It's valid to think that a large reservoir filled with fluid, under acceleration, with one small egress will experience a boost in pressure that can, and will give that fluid a serious altitude boost. Look at the goosenecks necessary for water and fuel tanks in sailboats (and the baffles in those tanks, to combat acceleration). I think we need a real pro to crunch some numbers, and I'll try to find him perhaps elsewhere.

*HOWEVER, I just realized there's a tremendous flaw in my premise. It also presents a solution, but I can't believe I missed this.

IF, given a long skinny light rowboat with a low center of gravity, but enough reserve buoyancy to sit in it and row even if swamped, IF SWAMPED, the waterline will be much higher. So for the moment, forget goosenecks and needing to lift the water. All one would really need is a strong locking gate / scupper just above the dry waterline. Boat gets swamped, pilot pulls a cable, opens flapped / gated scupper which is now BELOW WATERLINE, and starts to row. Water flows easily out of boat. This is a nice safety feature. Once the buoyancy is restored enough to lift the scupper above water line, we can go back to theorizing about accelerating the dregs out, but for now, I like the safety and simplicity of a design that can row out dozens of gallons with ease. Handling the swamped boat in chop or moderate swells wouldn't necessarily be easy, but it could be done (the boat would also need enough freeboard to keep from constantly shipping more water). This is what I'd like to design. A boat that could go ocean rowing, but wouldn't be helpless if swamped. Most Whitehalls would be helpless.

This suggests a two part 'rowing water out' design: One high capacity, to compensate for swamping, and one lower capacity, to constantly move small amounts with each stroke during regular rowing.

It's not really a low pressure type of principle we're shooting for here. We don't have energy to waste trying to generate speed to generate low pressure. We just need to lift the damm water.

Well, it will still be free in that the work provided to lift the water out of the boat will also (if marginally) be moving the boat forward. That's elegant.

Another complicated variable is the oar setup, boat design, and whether maximum acceleration is achieved by a power stroke on the boat at rest, or in motion. I'm imagining higher efficiency and more torque applied to the boat at rest, than would happen under a more horsepower / faster stroke at speed.

Thanks for that. There are people on this design / hydrodynamic forum who aren't grasping this, and should re-read your paragraph a time or two. Kayaks are fun, but not as efficient at covering distance, and that's the efficiency I want in a boat.

Oh, I agree. The wave will move everything backward. But it will also provide a lifting component to the bilge water. If the power stroke is coordinated with that exact moment, there will be a benefit to accelerating the boat just as the hull and bilge water go into a mild free fall.

 

It could even be like Formula 1's Kinetic Energy Recovery Systems (KERS). Charging a little battery, and then used as a docking engine when the oars are shipped approaching the dock. Kind of cool...

 

I'm not seeing it. Will keep trying.

 

I'm 6'5" and will be rowing oars with a sliding seat. The oar handles get pushed down to slide just over one's extended legs and knees. I've never seen anyone try to do that with a rubber skirt around their waist, covering their legs, so I'm not sure why you keep bringing this up. I think you haven't read the original post with comprehension, or perhaps don't know what an ocean rowing capable Adirondack guide boat or St. Lawrence river skiff or equivalent, more modern designs look like. The nature of rowing precludes a hermetic boat design.

 

As this is my thread, I must insist you read the posts here with more care. Sail boats, dinghies especially, need wide hulls for righting moment against the mast/sail.

High performance rowboats can't afford the drag of being wide, so they need to be deep for stability. That means A SEAT ON OR BELOW THE WATERLINE. Perhaps this pic will help:

 

I was surprised to read this.

My own designs of ultra-light canoes do indeed have the seat below the waterline, they are paddled using a kayak style double-bladed paddle, which is held quite high. Knees don’t interfere with the stroke and the paddler sits very low - the seat is less than an inch above the bottom plank.

Although using a sliding seat for rowing allows a lower body position than a fixed seat, the geometry of the human body and the need for a sustainable and efficient position for rowing must require a seating position several inches off the bottom. That being the case, it should be possible to add a false bottom to prevent the water running all the way to the bottom of the boat. Then a well could be added for the feet, which would both limit the amount of water than can trickle below the waterline and concentrate the water for pumping out by whatever means desirable.

 

I'm surprised that you're surprised, as we seem to be in agreement.

I don't disagree with anything you just wrote. However, to build such a design would mean less space and room in the boat, and the only reason to have such a 'false bottom' would be if you had open scuppers which would let water flow out (like an aussie surf boat [see below]). Such scuppers, in any kind of chop, would then fill your footwell with water, negating the goal of this thread.

And while I like kayaks and canoes, and double bladed paddles, I have a problem sitting on my tailbone with my legs bent 90 degrees to my torso for any length of time. I can handle a high seat in a canoe if I can get room for my legs to move around under me (I actually quite like such a canoe), but that's a still water solution. Not for the SF Bay. I like the range of motion and lack of strain on the coccys you get with a sliding seat. I'll take the penalty of pitching the hull. I don't mind.

I'm more interested in your reaction to my most recent proposal: A locking swing gate, which could be unlocked in the event of a swamping, allowing the natural rowing action to quickly empty the boat of a large majority of water. This would be the best of both worlds: the speed advantage of a shell-like narrow hull, with the ability to reasonably quickly drain large amounts of surf / swell water in rough conditions (like a wide aussie surf boat. See pic below).

A tube bilge using hydraulic pressure and a gooseneck to void small amount of water could be a separate system. But I think any hydraulic effects would only work with a full tube of water. There'd come a point when air in the system would render it ineffective. Thus it would need to be kept small.

 

I didn't comment on the locking swing gate because I don't really have a picture of it in my mind. Perhaps a sketch might help to visualize it.

 

Here's one way to get your sole above the waterline but I'm confident you wont like it:

http://www.youtube.com/watch?v=9BXxL9gztO8&feature=youtube_gdata_player

Just out of curiousity, why are you so opposed to keeping the water out in the first place?

I'm not the only one who has suggested it so it can't be personal.

 

dcn-

You seem to be having some trouble relating the potential energies and kinetic energies. You appear to be expecting way too much in terms of being able to row the boat out from under the water. The water only needs a tiny bit of height behind you to out accelerate you and fill the boat from behind. The water hammer I mentioned is designed to transfer a lot of energy from a five foot long pipe of water to a much smaller amount, maybe 5% as much, and thus give it the necessary energy to escape. But it causes nearly the same resistance as not pumping. That is where the energy for pumping comes from- the resistance to acceleration. All your water removal methods must expend a certain amount of energy to lift the bilge water. If you eject the water after you have lifted it above the local wateline, you lose the energy that it could have transfered back to the boat. You really want to pump it up and out when it is in a low energy state, not dump it overboard in a high energy state.

 

swamped

I've purposley swamped one of my boats on a calm day to see what the rescue effort would be. Rowing out of it seems impossible. The weight of water precludes even getting the boat moving. If the boat floats high enough a large bucket is the way to go. In bad conditions, I don't think a self rescue would be possible without a raised sole and large scuppers like an Aussie surf boat. For small amounts of water over a short time duration , a couple of guys I race against have fitted a small bilge pump with a motorcycle battery for power. For our races, it works well. I hope you come up with a workable idea but from my practical experience, I doubt that you will. With a good sea-worthy boat and sound judgement, you should never be in such a situation. Prove me wrong, it will be great to see your solution