going to install a pumpless ballast system

im tired of jacking w/ my fat seat and front sac. looks like we are gonna build a stainless steel tanks for the rear and bow and get a pad for upholstered for the g/f to lay out. instead of using ballast pumps i have been talked into using intake strainers. one face the to bow of the boat(intake) and one to the rear of the boat for draining. gonna rely on natural vacuums to fill and drain the tanks. also a a couple of valves to turn the water on and off. god a hope this works. my friend says it will.

well after a lengthy conversation and some pounding into my dense head. we are gonna just use one strainer. since the tanks will sit above the water line theyll drain naturally. and fill naturally when the boat is in motion. im getting pretty psyched. ill post a pic or two once the project gets underway in a couple of weeks.

interesting? Where did you get the plans? parts?

Sounds good, I'd be interested to see some pics too.

What kind of boat and how much weight are you thinking?

definitely interesting... I was planning to cut my raw water intake and install a reversible pump this winter. The "natural draining" sounds like it would work, but would make me nervous. I would consider a fat sac self-priming pump for back up, but thats up to you. You at least need some check valves for your drain, or else your boat will sink.

It should work, but it might be slower than pumps depending on your design. Some obvious things:
1. You must be moving to fill
2. You should vent your tank for faster draining, and for overfill protection
3. You must not be moving to drain
4. You should use the largest diameter scoop and hose you can, and keep the hose as short and straight as possible
5. The intake/drain of your tank must be on the lowest part of your tank
6. If you did use a second scoop, rear-facing for the drain, you might be able to drain on your way back to the dock

Report back on what you do and how it works.

well i emptied my fat seat into five gallon buckets this morning and it filled 20 buckets so im looking at a weight of about 800 lbs for the rear tank. i didnt fill a bag in the front but im guessing i probably use about 250-300 in the front. i own a 95 ps 190. i found a 1 1/2 scoop last night at west marine which should provide for a little faster filling. the tank will be vented for the purposes stated above. my boat has a cooler built into it between the motor and the front seating. this is where the valves are going to be placed. the plans/idea came from my friends head. it helps to know people alot smarter than yourself i removed the back padding today so i will be coming up with demensions for the tank shortly. im still tossing around the idea of whether to make additional storage or a rear seat since the weight of the fat seat was far less than anticipated. ill keep you guys posted.

I have a 96 PS 190 and would love an easier way to fill the sac up in the bow. Definatley post pics.

Alan,

I am sure your plan will work. I used help with a drag race boat that used this approach to cool the motor of the boat. The pickup was actually incorporated into the rudder assembly. It worked very well since it allowed the boat to warm up quickly at the starting line then cool on the way back from the pass. No power losses from pumps and no thermostat needed.

I had been thinking of rigging some kind of attachment under my swim platform for some time now, just haven't spent the time to build it. You may have issues with the draining if any of your plumbing runs uphill, you may need to eliminate the vent or include an interior bladder in the tank.

Good winter project, let us know how it turns out.

sounds like the system will work, but i bet it'll be pretty slow to fill and drain (even with a rear-facing scupper) unless you're moving pretty fast. i suggest when you're designing the system, do it so that it will be easy to add pumps later if you need them.

Mike:

Regarding the drag boat: They didn't need much water for cooling, and when they need it the most is when they are going really fast. By having the pickup integrated into the rudder they would get a lot more pressure because they are also directly behing the prop!


Alan:
I highly recommend that you build your system so that you can easily retrofit pumps at a later date because I will bet that you will want them!

If you want to help your natural fill and empty along then I recommend that your fill line enter at the top of the tank and the empty line from the bottom of the tank. You definately should put valves on both fittings to shut the flow of water off. If you don't shut off the fill line you may never get them to empty while underway.

You can get valves that are remotely controlled via a control cable. I have these on my Nautique, if i remember I will take a look and see if I can spot a manufacturer. They make it handy to operate the valves from the driver's seat.

The system will work, but I bet that you won't be happy with it. I like to cruise out to our riding spot with the tanks empty because the boat doesn't ride well at 30 MPH with the tanks full. When we get to the desired spot I throttle down and then start filling the tanks. By the time the rider has his board on and we are ready to go the tanks are about half full, and then they fill the rest of the way before he is ready for his first jump.

Without the pump the filling process will start when the rider starts and it will be slower. The first rider may be done before the tanks are full.

Emptying isn't so critical, as long as the tanks will empty on their own. The only time it is an issue is when you switch to a rider that doesn't want the ballast, in which case they may be done before the tanks are empty.

If you have a separate fill and empty line then it would be easy to add a pair of pumps to the system so you can make that call later if you wish.

Rod

www.flow-rite.com for the valves.

i appreciate all the tips and advice. since its still in the design phase everything is being taken into consideration. the idea of retro fitting the pumps was talked about and we plan to do that. i think.
jim you can chime in at anytime if you like.

Isn't this the same way early air nautiques fill and drain?

My friend has a 98 air and we have to run at 25 or so for 5 mins to fill the onboard ballast.

take a look a calabria system. It works with out pumps at half the fill and drain time of pumps.

Alan, I don't want to rain on your party but the laws of physics will factor into how effective your system works. As you have figured, while the boat is sitting in the water, the tanks will only fill to a level equal to the elevation of the lake water. To get the water in the tank to a higher elevation you have to use the velocity pressure of the boat moving across the water. Keep the intake and piping as large as possible or the flow rate will be poor (duh). You will want to close the valve before you even slow the boat down or you will start losing your water. Or use a check valve but that will hurt the flow rate.

Your tanks will not drain below the elevation of the lake water unless you use a devise that takes advantage again of velocity pressure. A device that does this is the water bed drain thingey that uses a garden hose and water flow to create a suction. Sorry, but a rear facing bottom intake won't do much good.

To maximize the benefit of what you are doing, look at the Calabria system and copy the principles- keep the tank low in the boat (theirs is below the water line) and the drain outlet is out the back of the boat (so when moving the outlet is above the water level).

I'm not saying it won't work, there just are some limitations that you should understand or expect. Maybe someone else who has had fluid mechanics more recently than 28 years ago could figure out how high water could be forced into the boat at 30 mph. Good Luck!

Here are two scenario's illustrated both of which should work. My SAN ballast vent hoses will shoot water out of them if I leave the fill valves open while driving/boarding. The level of the outlet is just below the rub rail so the pressure from driving is capable of over coming the head pressure due to the elevation. I can either use my pumps or drive the boat to fill the tanks. Alan's boat will have the tanks located on top of the floor since there are not any other options due to limited space. Once the tanks are full then valves will be shut, off either vent or inlet, to maintain the water in the tanks. When it is time to leave, open the valves and water will run back out of the tanks through the bottom of the boat into the lake if the boat is not moving, down to either the water level of the lake or the bottom of the tank, which ever is highest. Drive it onto the trailer and the remaining water, if any, will drain.





I would kind of like to try the vent control valves since you can run small hoses up near the driver and use small valves controlling the air in the tank. If the air can't get out the tank, the water can't come in. Once the tank is full and air can't come back into the tank, water can't go out. Kind of like holding your thumb on a straw with water in it, it stays in the straw until you take your thumb off and let it run out.

Keep the hoses short. The longer they are the more pressure drop you will have and also try and limit the amount of bends in the line.

Rod had a good point. If you fill from the top you will have more of a zero back pressure system and it will work more like a syphon as the water drains down to the lower elevation in the tank.

The Calabria system is below the water line as it fills. It will only fill until the water in the boat equals the level of the water out of the boat. In theory, you will not see the boat get lower in the water. The advantage is, when the boat goes in motion, the boat will now try and come on plane and then the water will be above the lake level and will now be counted as weight. It will displace water until either the boat displaces it's weight in water or the water in the bottom of the boat reaches the level of the lake. Depends on how much water, displacement and so on; but, water that low in the boat may not be as effective as water higher up in the boat. You may have twice as much water in the very bottom of the boat, but, it it reaches lake level, it is no longer pushing down on the boat. So, it may be misleading that the Calabria system says it has so much volume, but, it may not effect the boat as much as hard tanks with the same volume or even less volume.

i see what you're saying & agree re filling; there's no way Calabria's system could work with tanks above the waterline. the way i see it, though, once the boat is trying to plane out, the vertical location of weight inside the boat doesn't matter as long as the weight is there. the boat is still heavier. placing weight lower in the hull does make the boat more stable.

re bringing fill hoses into the top or bottom... IMO this is going to be a tradeoff, and probably a little slower with hoses in the top because the lines will have to be longer (more pipe loss). you still have to overcome the elevation change to get the water to the top of the tank. siphon effects would be a wash, because they would only make up for the height difference back to the bottom of the tank, which is still above the waterline, and will see the same head pressure as a bottom entry when the tank is full.

drains should definitely come out the bottom, and short runs with few fittings. if you cut a couple large holes in your transom & use the electric gate valves (like Rival), it should drain pretty quickly.

also, i do think you would see a Calabria sink lower in the water when the tanks are flooded. you would essentially be making the freeboard a bit lower. it would be the same as cutting large notches in the hull where the tanks are, which would displace less water and thus make the boat less bouyant.

Im not sure I agree with you Rod. Water in the boat (when sealed) will be weight and it shouldnt have anything to do with the exterior water line.

Water level (freeboard) is an equation of Weight and Bouincy (sp?). The water internal to the boat will weigh the boat down regardless of the exterior water level.

But when filling the tanks you are correct. The boat will 'sink' to equalize the inner and outer water levels.

I am always amazed at how confused people get about ballast and buoyancy. You're basically right, Chris (and trace).

Archimedes' Law tells us that the weight of liquid displaced by a floating object is equal to the weight of the object. When you increase the weight of the object, e.g. by adding water inside the hull, the amount of water displaced increases. This means that the boat sinks lower in the water. It doesn't matter where you add the weight (above or below the waterline).

The only time there is a special relationship between the external water line and water inside the boat, is when you have water flowing between the inside and the outside. Water will not flow uphill so if you want a gravity-fed ballast system, the level of water in the tanks must be below the water line at all times while it is filling. If this is not the case, you will need to supply some kind of force to push the water uphill into the tanks.

The genius in the Calabria system is that the tanks sit below the water line when standing still but above the water line when on plane. Thus, you get gravity fill and gravity empty.

Here is how I see it happening.

The boat displaces water until the weight of the water displaced is the same as the wieght of the boat. Basic physics.

Matter of fact, if you know how much your boat weighs and how many square inchs the hull is, you can calculate how many PSI will come up through the fill hole that Alan want to put in his boat to fill his tanks. PSI does not matter how big the whole is. The whole size will only tell you how much flow for the amount of PSI of water. Then consider there is usually a 1 PSI drop for every foot you go up and you may have a pretty good idea of how long it will take to fill if it will without moving. But, back to topic.

The boat is no longer displacing water. The boat will try and sink. It will sink up to the point of the top of the floor tanks. I assume it is a floor tank made by the stringer system and floor. At that point you are back to displacement again. The boat will not sink further. What I imagin happens is the boat below the new water line does one of three things. It has a little weight but maybe close to the density of the water and at that point does not count to the weight of the boat. At that point it is neutral and is acting as a water trap if you will.
OR... The bottom section of the boat is less density and will try and float a little
OR it is more dense and will just add to the wieght total and displace just a little more water.
Basically, I think the bottom of the boat that is now under water does not add much or subtract much from the wieght and is negligible in the water displaced. I think the new displacement is based on the new hull (if you will call it that), that is defined by the top of the tanks/ bottom of the floor.

That is the case for the boat being stopped.

Now as the boat begins to move the pressure being pushed against the hull is no long that of a body of water, but the force of the water pushing against the boat hull giving it lift. That is defined by the speed, weight of the boat, and shape of the hull. The laws of physics still have to apply for the boat to float in that the boat has to still displace it's weight in water to float. That is proved by the fact if you were running at speed, you would never have a wake. Wake is created by water displacement.

At the point where the hull trys to lift out of the water, the weight trapped in the old hull (the sunken section) will come into play because the force of the boat running across the water will try and add lift to the hull. The boat will only lift as high as the boat needs to create the balance of physics properties. The lift of the hull at speed plus the displacement of hull needs to counter the weight of the boat in order to float.

Only thing you would have to try and model would be this. Water under water is nuetrally buoyant. So, I doubt it adds wieght to the hull when it is submerged. Only problem is the original hull (the boat without water in it) used to sit higher in the water. It used to be more effiecient, but, since the new hull sits lower in the water; it is not as efficient. Now the hull efficiency has changed, that makes the lift of the hull less. With a less efficient hull, it takes more water displacement to make the boat float.

My argument is the curve for hull displacement per amount of water in the boat will be shallower (meaning less effect) for the under floor vent system than a similar boat with fat sacks. I could be wrong, but, I layed out my case. I am not absolutely claiming I am right that is why I put out my thought process.

Is a fat sac dropped in the water nuetral or still heavy? I think you will be suprised.


(Message edited by deltahoosier on October 28, 2004)

--- The sac should remain nearly nuetral and float near the surface --

The whole exersise of weighting a boat with lead/chicks/sacs is to force more of the hull below the water line. The makes the boat push more water (not always displace -- Cal system) when underway and therefore create more wake.

So the buoyancy of the hull or what is causing it be under the waterline should be irrelevant. It should be a question of hull shape, object (boat) mass, and speed.

Where the water is placed in the boat makes no difference,it is still weight. If you add water under the floor of the boat, which lets say is below the water line it will sink the boat the same as if you put the same amount of water on top of the tower. Come on common sense!!

Then why is a fat sac nuetral buoyancy when dropped in the water? It is contained just like in a boat right? Soon as it hits the water level it no longer is heavy. Common sense right?

boats have to be lower density than water, or they don't float. since sacks are placed inside the sealed hull of the boat, which is a much larger volume than a sack, they increase the density (lbs/in³) of the boat and decrease its bouyancy.

here's another way of looking at it: you know that gasoline (6.1 lbs/gal) is lower density than water (8.33 lbs/gal), right? following that theory, your boat would actually be lighter and the wake would be smaller with a full tank of gas compared to empty!

"boats have to be lower density than water, or they don't float."

Aircraft carriers are made of steel which is more dense that water and they float. It is called displacement. We are not talking density. We are talking about liquids wanting to come to a similar level.

You can take a tank and hard bolt it down in a swimming pool. Put water in the pool surrounding the tank. Then put water in the tank and fil it let's say two to three feet above the level in the pool. Now take a hose and put it in the tank to the pool with the lower water level. Now create a syphon. Which way is the water going to flow? It will flow to the pool. When will it stop? It will only empty the tank until the level of the pool and the level in the tank are equal. The tank is a complete sealed system from the pool as far as a structure. You can even take the tank and dig a hole next to the swimming pool and put the tank in the hole. THen fill the tank with water and then do the same experiment. It will work the same.

(Message edited by deltahoosier on October 29, 2004)

---

quote:

here's another way of looking at it: you know that gasoline (6.1 lbs/gal) is lower density than water (8.33 lbs/gal), right? following that theory, your boat would actually be lighter and the wake would be smaller with a full tank of gas compared to empty!

---

Wrong premise. The gas will be wieght until on of two things happen. The boat displaces the additional wieght in water that the gas adds in weight

or

The boat will sink to a point it no longer displaces the water and will in effect sink. If the boat sinks the gas in the tank will want to float to the surface. It will not be able to float because it is tied to a system that actually is more dense than that of the water. The reason the boat will not sink is it has buoyant matterial designed into the stringer system.

"boats have to be lower density than water, or they don't float."

by the way are you suggesting that ducks are less dense that water? I think I have it. Ducks float. What else floats? Wood!!! Now lets see. Since wood floats like a duck, the duck must be made of wood! While we are on the subject of wood. What does wood do as well? It burns. Now what else burns? Witches burn right? So, if a woman weighs as much as a duck, she must be made of wood and since wood burns, she must be a witch because witches burn too. I think we have a logical conclusion to all of this. Glad it is all figured out.

Oh...And coconuts are no migratory as well.

ok, by "density", i didn't mean the sum of the volumes and densities of the materials in the boat, but instead the ratio of the weight of the boat to how much volume the sealed hull can displace. somewhat misleading, i guess. when you add any type of weight inside the sealed hull, you increase this ratio.

if you're taking on water, all bets are off and it sinks (to the gunwales if it has flotation foam).


edit:
i like the the pool & tank analogy, how about this?

fat sacks: you have a bucket floating in the pool, and you put a 1 gallon milk jug full of water in it. the bucket sinks a little. replace the jug with an 8.33 lb hunk of lead. the bucket sinks the same amount, there's just more room left in the bucket.

Calabria system: you have a bucket floating on water with a 1 gallon chamber/false bottom and a valve. open the valve, and the chamber floods until the bucket sinks to the level of the false bottom. lift the bucket out of the water, open the valve, and the water runs back out.

i think we're saying the same things, just hard to describe verbally.

and ducks are less dense than water!

(Message edited by trace on October 29, 2004)

Next time at the sink.

Fill the sink with water. Take a kind of tall clear glass cup maybe 6 inchs tall and put it on top of the water bottom first. What happens? The cup will float. It will sink only to the point to where it displaced the same weight in water. It will most likely want to fall over because it is top heavy.

Now add in some coins to the point to where the cup will sink enough that it will be stable and sit up on it's own. Call it our lead. Maybe sink it at least a few inches even if it is stable.

Now add water to the glass. Add just a little so it is noticably below the water line. Note what happens.

Now add it to the water line and not what happens.

Now start to fill above the water line and watch it sink to try and displace the water weight above the water line.

I will try it too. I am interested to see if I am correct. Should be fun. Could be wrong, but, I am interested and this should bring some closure.

I see what you are saying, but, I am talking about adding water into a already sunken hull. What happens if you leave in the lead and then add water in the bucket to take up the volume left by the lead up to the water line? Do you get a one to one change in level per known amount of wieght? Does it move at all before getting to the water line? I am going to try my experiment and see. It is killing me now.

More weight things to think about.

You have an air tight box that has a bird sitting on the bottom of the box and it is setting on a scale and it weights X. If the bird flies in the sealed box, what happens to the weight shown on the scale? Remember the box is sealed air tight.

Rod/Trace,
Instead of thinking in terms of density think in terms of displacement. I physics terms the bouyant force is equal to the weight of water displaced. It takes 8.33 pounds of force to hold one gallon of air under water. Our boats bouyancy is caused by their displacement. Anytime you replace the "air" in the boat with something heavier you increase the wake. Did that make sense or help?

Rod Mc,
As always you provide a solid voice of wisdom. Back then (80s) I was surprised how much water flow this system produced even when we were puttering around tuning the thing, especially considering the rudder was offset. But as you said it was probably not producing much pressure. One more thing, those boats were very low to the water so less water column.

Alan,
You might want to PM the Wakejunky. His sacks filled without pumps as we wakesurfed a couple months ago. I know he is also considering a rework of his ballast system so it might be good if you bounced some ideas.

Jim,
I think your ideas are very good, please keep us updated as you progress with your project. Search E-Bay for "Tanks & More" I have been very happy with thier spiral hose and fittings.

From my point the valves cost almost as much as the Simer pumps (8.5gph $65 shipped from BE Atlas vs. the flow-rite valves). Since these pumps can also work as valves I tend to keep it simple and just use a direct operating pump for each tank/sac. They can be slow so I might make a 2 pump/sac system this winter. Hopefully you guys will figure the scupper system so I don't need to.

Mike

when the bird flies, the weight on the scale would still show the total weight with the bird. the bird's weight is still there, but instead of reaching the box floor through its legs, it would be transmitted through the air in the box that's providing lift for the bird to fly. good stuff!

Well if all goes well the custom stainless tanks and all the parts should be done be end of next week and we can start the install. My choice was to do the system with the vent control valves so we can mount miniture ball valves by the driver for air control. Alan is skeptical but it is easy to change the hoses and add more valves so it will be fun to test.

Spot on with your answer Trace with the bird in the box. That is a fun one to get people thinking.

It is all about displacement. anything you put inside the boat causes displacement, be it feathers or lead.

The best way I can explain is like so..
Take a large tub and put a small tub inside of it. fill the small tub to the very top with water.
take an 8.33 pound chunk of lead (for arguments sake, lets say that it is the exact same size and shape as half a can of soda) and drop it into the small tub of water. The water in the small tub will overflow enough to fill half a can of soda, because with no bouyancy, it will only displace its own volume of water.

Now, put a bowl into the small tub of water that is capable of holding the lead weight, and fill the small tub to the very top again. then put the same lead weight into the bowl. The amount of water that overflows will be exactly one gallon. on a bouyant object, the lead displaces its weight worth of water instead of its volume.

The displacement of water in water works the same way, although it is on roughly a one to one basis. Fill a ziplock baggie with 12 ounces of water, and drop it into the tub of water, and 12 ounces of water will overflow.
put the baggie into a floating object in the pan of water, 12 ounces will overflow.

It even applies below the water line.
weight a tennis ball can so it floats upright, with half the can below the water, half the can above the water. if you pour 10 ounces of water into the can, 10 ounces of water will overflow out of the tub.





(Message edited by upupnaway on October 31, 2004)

so mike do you have your hoses run throughout the boat and just hook them up to the sacs when needed? also what did you use to attach the hose to the sac. i dont have a lot of confidence in the little blue nipple thing alas we are using a tank in the front. however it would be nice to use a sac in the front as this is all the storage i have.
jim have you been dropping acid? that bird riddle is crazy

All I gotta say is a coupla Rule 1100's, 1" hose, two handvalves, giddy yup. Go wakeboarding.

Alan,

Any flow/pressure tests with your scupper yet? I am curious to see how much water column the scupper will produce. In the case of the system that I am working on with pumps this pressure may or may not require me to add a gate valve. I am trying to avoid putting any valves in my system (except an emergency ball valve in case of plumbing failures).

I might just mount my scupper backwards or just use a thruhull and strainer.
Mike

Salmon Tacos has it right. Archemedies law of Boyancy is stated correctly in his post. Read it carefully. If you're trying to fill the tanks and they are above the waterline, without some sort of force to push the water up, it's not going to work.

The scoop under a moving boat provides the force.

If you look up Calabria on the patents website you have a detailed description of how they do it, you're just infringing patent if you copy it!

that only matters if you sell the product. you can infringe all the patents you like for personal use. also, this is not a copy of Calabria's system anyway.

It won't be when he gets tired of waiting for it to fill and puts in a couple Rule 1100's!

If you haven't seen the related post, here's the link.

http://www.wakeworld.com/MB/Discus/messages/3183/199086.html?1100401634

The system overall works great and when we actually timed it, it takes under 6 minutes to fill cruising about 20 mph. No need to add pumps or large valves.

I'd like to see some pictures of the boat when full. I'm skeptical that the scoop can provide enough force at 20 mph to push the water up that pipe, through the valve, across the T fitting to two tanks. There's probably at least one more 90 degree fitting between the T and the tank it would have to cross also. All of it above the water line and against Archemedies principal.

Since you can't see how full the tanks are, how do you know when they are full?

You know when the tanks are full since there is an air vent line out the top of the tanks out through the side of the boat above the rub rail. Drive until water is flowing out air vent lines, then shut the mini ball valves off for the vent lines and the water stays in the tank like holding your thumb over a straw with liquid in it. If the boat is sitting still and you open the air vent valves, you can hear the tanks gurgle as the water runs out the bottom fittings through the bottom of the hull. The head pressure you have to overcome is probably about 2' so it doesn't take much speed to flow water to that height with the scoop. The estimated flow rate is about 1300 GPH with the given tank volumes and fill time. Pretty simple and not much to go wrong.

This is the system in my boat.
It brings water onboard at the rate of aboat 4000gph and pumps out at the rate of 3500gph.
Thats 2000lbs if weight in 2.5mins in and about 3 mins out.

Loading the boat : 2" water scoop , 2" electric solonoid valve screws straight onto the top of the thread of the scoop. Switch on the dash opens and closes valve. 2" tee reduced down to 1.5" outgoing. Plumb to the tanks.

Make sure you have twice the breather capacity of the intake , so two 1.5' breather for each tank. This will keep the flow going and also wont blow up the tank. All water outlets at gunnel height.

Pump out : use the Rule 3800 general pump , just tee the tanks together and connect the pump. Connect to a skin fitting at gunnel height.
Be aware that when this puppy runs it will throw water 10ft.



(Message edited by chaoswake on December 09, 2004)

Shane, can you post a link to the 2" solenoid valve?
also, are there any more valves that are not shown in the diagram? how do you control the levels in the tanks individually? it looks like everything would just go to equilibrium.

Jim, on a similar note, if you want to fill one tank more than the other, are you building much pressure in the tank with the vent blocked, when the other is filling? do you have any way of knowing any level in the tanks except completely full?

is there no ball valve between the intake and the solenoid?

Trace, we were not concerned with part full, just either wanted the tanks empty or full. If that was a concern, it would be easy to install a sight guage on the side of the tank with a clear hose to view the water level. If you wanted to get fancy guages are also an option. The whole thought to this system was to make it as simple as possible with no moving parts, wires or switches. The pressure on the tanks does not seem to be a problem. Visually you can not see distortion with excessive pressure at full speed of the boat which would be the highest pressure. If there was an issue, the main brass valve at the scoop could be shut off. Since filling and draining both happen through the bottom, the air vent lines could be sized small, since all it needs to do is let air in and out. Kind of like poking a pin hole in your water jug when camping, once you allow air in, the water rushes out.

so you theroetically never actually shut the inlet valve, except in an emergency? i'm surprised you're getting 1300 gph at a low enough pressure that doesn't hurt the tanks when you shut the vent valves. what gauge stainless are they made of?

Nope, we leave the main inlet valve open at all times. The tanks are 16 GA. If it were a problem a check valve could always be installed in the vent line so water could continiously overflow then have the vent valves bypass the check to allow air in for draining. My SAN just spits water out the vents if I don't shut the inlets off once full.

Trace, here is a link to some large (relatively) cheap 12vdc valves, you may have seen it already but if not....

http://www.1valves.com/electricvalves.html

thanks Psy. yeah, i've seen those, but Shane said his is a solenoid valve, which are usually smaller, restrictive, pilot operated, etc. i think the best thing i've seen is the RV dump valves, but don't know if they're ignition protected or submersible. anyone know?

Jim - that's a very clean design, probably almost impossible to fail, and self-winterizing to boot. i really like seeing completely different approaches. one more question, i promise: how long does it take to drain?

Trace,
We haven't timed the drain time, but it seems to be faster than the fill time, probably 3-4 minutes.

wow seems to be a hot topic jim, thanks for answering questions.
john- there are no other 90 fittings. i dont know why you would be skeptical.
trace along the lines of what jim said we havent timed the drain we just usually let the boat drain while someone runs to get the trailer. its always empty by the time we trailer the boat. next time i take the boat out ill try filling just one of the tanks for you.