Controls for balancing tanks

What, what , what???? Submarine Tom, what I won't give up on is the idea that boats should be for people, not people should be for boats. For twentyfive years in this business that creed has worked for me anyway, so yeah, I'm not giving up on it.

 

Based on the boat design, we really need some more details about the conditions of use.

Number of crew, passengers, payload, displacement, performance, purpose and sea state operation, etc.

Mark

 

After doing some Salmon fishing with 'customers' and 'reletives' on board, walking about etc, I wonder if you can move any kind of ballast quickly enough to keep the level on a smaller boat, less than 30' or so.

The ladies will soon line up for the potty. Most men will sit and watch, but if they are fishing they will move quickly to make sure they can land the fish.

Maybe with a few more details of your craft.....?

 

Thanks thudpucker and Mark Cat.
This is a social boat--its main feature is its quietness and is designed mainly for wine and cheese cruises at diplacement hull speeds. The first boat will be used on the Eastern Shore of Maryland and it can get rough there at times although mainly it will be used in calm waters--at least the cruise will start out that way. Still, I don't plan on this being a one-off for long so I want to design in as much flexibility as possible.

I expect the passengers will sit in the open cockpit forward in nice weather and in the aft cabin in less than nice weather--although the cabin windows do open so it should still have a nice breeze going through it--the main problem is passengers in the cabin will not be in the same conversation as those in the open cockpit. Most trips won't last longer than 2 hours--I'm not planning for a head area on hull #1 but that may change. The cabin will be heated and AC is still an open question. I am trying to achieve seating for 8 in each area but that will be tight so there may be times when both areas are occupied. This will not be a fishing boat--at least not with this cabin arrangement. I plan to be able to incorporate various cabin arrangements on future boats and some of those may not be quite to sensitve to seating arrangement as this one.

I most likely will end up using a completely manual water ballast system but thought maybe there was an exsisting auto control system that could be incorporated without me having to design every aspect of it. This application would have the same input parameters as a system for movable ballast on larger boats and also for stablizing fins but not dealing with those types of boats I was not sure how elaborate their controls were. After a little more research it sounds like an automatic system might have to involve some very costly sensors. Any input appreciated. Thanks again.

 

Interesting problem.
Any weight shift would or should equal the weight shift from CG.

So if the whole Passenger list wanted to see somthing on the port side, you'd need a lot of weight for the Stb side eh?

The Higher above CG the 'compensation weight' could be would make it more effective.
I'm thinking tanks in the Gunnl's.
Big two or three inch pipes from Gunn'l tank to Gunnl' tank.

A Mercury switch would be to 'energetic or active' so that just about leaves it up to the Helm to make the transfer dont it?

Although maybe you could put a slow moving fluid in a Tubing across the boat way low down.
That slow moving fluid might take some time to settle on the low side representing a stable lean time, instead of a rough Sea time like a Mercury switch.

A curved tube like a Spirit level has, might do the trick. If the heavy slow fluid moves far enough and stays there long enough, a switch at that end would activate the pump moving the Ballast fluid to the othere Gunnl'.

I know I'm gonna catch some crap for this cockamamie idea

 

Although I don't design boats, I do design material handling equipment, and this is more in my line of expertise.

I don't know the laws in your country but if a boat that size capsized here and you had 16 people on board, you would go straight to jail without collecting $200.

Anyway 16 on board would not be a problem with them moving about because they don't have much room to move. 6 people would be worse where 3 people could walk from one end to the other very quickly.

Before I start designing something I normally have a feel for what will work and what won't. This I feel a won't.

To design you need to be able to imagine what will happen in different scenarios.

So 2 people walk from one end of the boat to the other. Add up their weight, and calculate the amount of water you need to pump from one end to the other. Then calculate the time it will take them, you now have the volume and velocity of the water in Litres per minute. Or toes.

You would be looking at a large pump.

You can minimise this by putting your central tank back in.

1/2 fill each tank. To get the weight from back to front, pump half the weight from the back tank to the central tank and half the weight from the central tank to the front tank.

 

Failure to communicate and it is my fault: I said "I am trying to achieve seating for 8 in each area". I should have said "either area". I am planning on only eight passengers which I am quite sure will not send me to jail. I am NOT trying to instantly compensate for their every movement. I am trying to allow all 8 passengers to SIT in one area and still keep the boat trim. Sorry for the confusion.

 

Tom,
Maybe you can clear up how fast you expect this to work and just how important it is from a safety standpoint.

It seems that some people are picturing a boat that is so tender that if all the passengers go to one area the boat may swamp without the help of active ballast.

I'm picturing a boat where everyone can safely move from one area to the next, and the water ballast is there to keep ideal trim for both looks and efficiency. So there is no real need for speed in the transfer of ballast. If it takes 3 minutes to level out, fine, being a little unlevel won't sink the boat.

Personally I would try to make it safe even if the ballast system stopped working at the worst-case setting. When fully trimmed for everyone aft, if everyone rushes forward ("Look! A whale!"), the boat should still be safe. Add fixed ballast as necessary to accomplish this (more batteries!).

I mean, this boat isn't so light and fine that it'll be like a canoe with both people at one end, right? Been there done that, and she wasn't thrilled about the surprise dunking halfway through .

 

srimes,
I am not worried about safety--the boat will not swamp. It already has 1500 lbs of batteries under the cabin and cockpit soles in the boxed keel. I'm worried about the boat:

1. Looking right--(if you can't look good doing it then don't do it.) Also keeping it trim as you say for efficiency.
2. Being comfortable for the passengers with all the tables and seats level fore and aft.

A couple of minutes to adjust the ballast would be just fine. I started out looking for an auto control system so the pilot did not have to concern himself with that task. That may end up being more of an extravagance than costs permit but wanted to try none the less. Thanks.