Ballast Tank Plumbing
 

What are the options for plumbing the ballast tank in a catamaran ?

The present schematic follows;

1. Water comes from both motors to a "T", a larger hose goes to a 12 volt solenoid valve,the larger hose then fills the tank.

2. The tank is drained by opening a solenoid valve. The drain hose exits to a fitting located on the upper inside of the sponson. The fitting is located far forward in the tunnel.

3. Control of the valves is through a three position, momentary-off-momentary, panel mounted switch.

4. An analog, water level gauge is dash mounted.

Your critique would be appreciated.

Ours is filled from a manual pick up that drops down from the transom and fills the tank. There is a hose to a small vent in the deck and when it is full water shoots up in the air (you can see it is full in my avaitar. To drain it we have too very large pumps that pump it dry in 31 seconds. Simple and fast to fill and empty

Wahoo was a good system. The small vent does two things it lets you know its full and it prevents an air lock. His discharge system is fast, very important. Gauge is a toss up chances are it won't read in the rough any way. I wouldn't use any electric valves. If you want to use engine water to fill the tank just use a manual valve. I don't know if outboards will fill it fast enough.

On my skater the lines off the sea strainers come to a common manifold which supplies water to the motors and to the ballast tank. The line to the ballast tank has a manual valve with lever next to the throttleman/port seat. Open the valve, water flows to the ballast tank. Close it it stops. Electric pumps on ballast tank to empty it by a switch on the dash.

We used manual fill and dump valves. The dump valve was a big 2" ball valve with a clam shell, it helped suck the water out. The water fill was off the engine discharge with a deck vent. Can't tell you how long it took to drain but it was fast enough for us.

The deck vent was funny with the stand-up open boat, you knew all to well when it was full the water would come back and get you right in the face!!!

Guys, Your input is great !

The deck vent is interesting. However, the closed canopies have been removed. People in the back seat would definately report "FULL" after the first time the tank filled, while they were on board.:D

Seriously,it didn't occur to us,a vent is required. Therefore, one possibility, a light weight/low pressure, piston accumulator. The accumulator would accept pressure from the ballast tank, eliminating hydraulic restriction. However,the accumulator CU. Ft. capacity should equal that of the ballast tank capacity. The pressurized accumulator/ballast tank would also expidite dumping.

Or, what would you think of venting from the tank top to a point behind the fuel tank vents and blower scoops ? The vent hose would exit above an up angled line between the tank top and the vent, discouraging siphoning. The vent line could also have a valve that closes simutaneously with the fill valve.

Another point you have identified, the water fill source. We were planning on using water before the engines. However,now we're thinking of using water from a balance line between the header distribution tubes. CMI is fabricating prototype dry tail pipes with water flow orifices. The design will keep the exhaust system cool from blueing but warm enough to discourage thermal shock. The remaining water flow is dumped over board. That dump is after a pressure relief valve. The ballast tank fill hose would be before the pressure relief.

MOBILEMERCMAN, Why do you recommend we NOT use solenoid valves ? The sending unit we have is the vertical tube design from Gaffrig,which seems to create a stable gauge reading.

I think as others agree use ball valves. simple, effective, dependable. Electric components, water and salt don't work well together. Just my preference. The gafrig sender is as good as it gets but assumes water is not bouncing around. Time to full and adjust as needed. We used water from the header rail before worked good. Not as fast as a scoop but pretty good. Another thing about the vent on tank. Keep it vented, if your vent valve hanges up or is mis operated you may blow the tank up.

On my old 36' Cig I put the vent in the side of the hull right below the rub rail. The fill was from the sea strainer, had a ball valve set up with a morse cable. Only problem is it would not fill unless the boat was on plane. Used 3 pumps to empty, 2 big Rule bilge pump & a little centri-puppy to get the last few gallons out.

No tank, I took the front 2 bulkheads and covered them. Also filled it with fuel cell foam to keep the slosh down. I wish I had the tank for the 2 years I actually raced the boat, made a heck of a differance.

I agree, electric valve sounds like trouble. We recently did a fuel system with some air actuated industrial valves, worked out great. If I ever put the boat back together that's what I plan to use.

Thanks again Guys,

I find myself constantly fighting tunnel vision, especially with these boats. Perhaps, that keeps boats intriguing,for me.

Marc, your shared experience with the expanded Ballast Tank causes me to utter another DUH ! There should be little reason a second tank couldn't be included in the hull design. A high X and/or an aft CG causes planing problems. Therefore, if the second tank was only used to get on plane,life would be simpler. The downside, design liability, if the second tank was not drained before running,it would be easy to stuff it.

Marc how many gallons does your tank hold ?

I calculated it to be about 90 gallons. The cg on boat was OK, it was flighty however. With the 9 1/2 beam there was a bit of aerodynamic lift up front. The 600 lbs in the very nose took care of that :) Adding the tank was like buying a new boat as far as handling.