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Old 04-05-2021, 02:56 PM   #1
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Boat Balancing

After many years of sailing I recently joined "the dark side" by purchasing a 1998 Offshore 48.
I am almost overwhelmed with all the systems.
My first question relates to balancing the craft.
There are 4 fuel tanks. three have about the same level of fuel. (Down about 1/4 to 1/3) The forward port tank is almost full. I have a list to port.

If I open all 4 valves and the crossover will the levels even out? Should I open the fill ports to assist?

More questions to follow.
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Old 04-06-2021, 12:48 AM   #2
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Welcome to TF.

Re the tank levelling. Yes, if they are connected side to side, they will level. If there is a difference in fluid level between the for'd and aft tanks, they will attempt to level to the level of the highest placed tank, which might mean overfilling the lower tanks.

Just check that is not going to happen. If the tanks are all mounted about the same level it should not be an issue. Otherwise, only level them in pairs. That is, just for'd tanks, keeping any connection to the aft tanks closed, then do likewise to the aft tanks, keeping the for'd tanks isolated. That would then mean you only draw from either for'd or aft tanks at any one time, of course. And, no, you would not need to open the fillers to any of them.

Does that make sense..?
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Old 04-06-2021, 05:21 AM   #3
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It has been my experience that keeping fuel tanks within about a quarter of each other will not effect trim much.

My boat, like many trawlers, rides low in the bow. I try to keep heavy stuff at the stern but it isn't always possible, especially if I have guests up front. I just go with it and keep my stern water tanks as full as I can.

I just don't let it bother me.

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Old 04-06-2021, 06:59 AM   #4
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“Open the fill ports?” Do you mean deck fill caps? No! Bad idea. The tanks have vent lines.
You should have an engine supply and engine return line from/to each tank. Where each line meets the tank there should be a shutoff valve. You need to trace out each line. Wrong alignment can cause an engine shutdown or worse, a big fuel spill.
Thoughts on high tank:
Tank outlet closed.
Tank outlet clogged.
Tank level gauge wrong or broken.
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Old 04-06-2021, 10:01 AM   #5
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Quote:
Originally Posted by Peter B View Post
Welcome to TF.

Re the tank levelling. Yes, if they are connected side to side, they will level. If there is a difference in fluid level between the for'd and aft tanks, they will attempt to level to the level of the highest placed tank, which might mean overfilling the lower tanks.

Just check that is not going to happen. If the tanks are all mounted about the same level it should not be an issue. Otherwise, only level them in pairs. That is, just for'd tanks, keeping any connection to the aft tanks closed, then do likewise to the aft tanks, keeping the for'd tanks isolated. That would then mean you only draw from either for'd or aft tanks at any one time, of course. And, no, you would not need to open the fillers to any of them.

Does that make sense..?
As Peter noted, watch for the lowest opening on the top of all of the tanks. there will be no adverse consequence to having all interconnections open, with the result that all go down at the same rate.
If yours is a planing boat, however, the vents must all come to the same location, or when on a plane the forward tanks will drain out the vents for the aft tanks. There, you can't open the forward pair to the aft pair, but must be sure to balance them side to side.
I have a non-planing boat. My water tanks are a two very different heights, one pair being high in the lazarette and a second pair below the bed in the aft cabin, so the bottoms of the upper tanks are above the tops of the lower tanks. This all came with a complicated interconnection system that had the former owner in knots. When I located the vents and found that they were all at the same height and within 1' of the transom, I simply opened all of the valves in the complicated system and all is well with the tanks lowering as you would expect. The same would be true of fuel tanks if a pair are forward of a second pair.
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Old 04-06-2021, 10:48 AM   #6
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Many (approaching most) trawlers and cruisers are not well trimmed.
My own boat is stern heavy and I haven’t “fixed it”.
But if it was bow heavy I would.
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Old 04-06-2021, 01:56 PM   #7
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I have moved my spare anchors to the port side of my lazarette (sp?) and I am balanced that way. I am bow heavy with 500' of chain and a couple of non-standard additions: Bow mounted hydraulic davit and bow thruster. I have tried to use up my mid line 260 gallon fuel tank before my aft 400 gallon fuel tank with no discernible effect. She does cut the waves well but I would prefer that the doors not always shut themselves.
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Old 04-06-2021, 02:50 PM   #8
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It’s nice to have fixed weights amidships but moving heavy things around is tricky RickyD.

For a manufacturer it’s impossible as most every boat is different. And a big problem is the pointy shape of boats that don’t support weight well at the pointy end for lack of buoyancy due to the pointy shape of the hull. All considered the bow is the worst place for lots of weight ... like chain.

Somebody should create a system that measures a drop in fuel level in a lazerette mounted fuel tank so it could be pumped aft into the laz tank. Over time that would make the best of a difficult situation.
And from a standpoint of broaching a big heavy fuel tank aft can be a small plus in that it would resist movement aft but once movement started ... it would be bad.

And re generally having weight amidship is considered a plus but it can be really bad in extremes. You never want to fly in an airplane w lots of weight at both ends. Same for a boat. Both turn by yawing and yawing is difficult to start and hard to stop in both cases. But a boat w all the auxiliary equipment amidships (weight) will turn very easily if (taken to an extreme). Mid-engined cars do very well turning.
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Old 04-07-2021, 12:14 PM   #9
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The galley, cabinets, fridge and stove are all port on my boat. Plus we use the guest cabin (port side) as a storage area. We have a list to Port. I used bags of reclaimed lead and stored amidships on Stbd tucked away in bilge spaces. That balances the list.

I don't like using things that will get moved "coolers, portable generator, outboard, spare gear. All of a sudden you re-introduce the issue when you use or move the gear.
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Old 04-07-2021, 12:50 PM   #10
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Shrew,
Mainship should’a put batteries and other heavy stuff to stbd.
You could run the port fuel tank most all the time and kept the starboard tank full except for long trips. You could have a transfer pump to fill the stbd tank from the port w perhaps an inner-connecting vent. A low volume pump pumping fuel anytime the engine is “on” would keep the stbd side full and a connecting vent hose would keep the excess constantly “draining” to port. But you’d need a shutoff switch for the port side. And ideally you’d have a pump and float switch that would keep the stbd tank full drawing off the port tank. But float switches are known for failure so you’d prolly get fuel all over the place in time.

I kind’a like dream’in things up. But you may have a CL mounted tank in the laz like NT. haha
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Old 04-07-2021, 01:15 PM   #11
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Quote:
Originally Posted by RsPolarBear View Post
After many years of sailing I recently joined "the dark side" by purchasing a 1998 Offshore 48.
I am almost overwhelmed with all the systems.
My first question relates to balancing the craft.
There are 4 fuel tanks. three have about the same level of fuel. (Down about 1/4 to 1/3) The forward port tank is almost full. I have a list to port.

If I open all 4 valves and the crossover will the levels even out? Should I open the fill ports to assist?

More questions to follow.
How is your fuel return handled? Can you select which tank it goes to?

My fuel return tees into both tanks. However, the port side line has significantly more restriction. Hence, drawing from the port tank effectively transfers fuel from port to stb while drawing from the stb tank reduces that tank's level very slowly.

It can take forever to correct a list to stb. I do have tank interconnects which is by far the quickest solution to get 90% level.
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Old 04-07-2021, 01:33 PM   #12
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A rounded bilge, soft chined, tender hull will tend to list more readily with an uneven port/stbd weight distribution. On these boats, leaving the fuel or water crossover lines open will not necessarily decrease the list. It can make the list worse.

Look at it this way.

If the tank volumes are equal and the weight is equally distributed, the boat will sit level with no list. If we then add 200kg of gear on the port side, this side will drop a bit, let's say one inch. . If the crossover line is open, the stbd tank (which is now higher) will start draining to the port tank. This will continue until the levels are equal in hight above the water line, not equal in tank volume.

With the extra fuel 100kg of fuel and/or water have moved to the port side, it makes the list even worse, causing more fuel and water to transfer to port.
Eventually it all equalizes, but the list would be less if the crossover line was left closed.

My boat behaves this way, and I manage any list by simply drawing fuel and water from the high side, with the crossover lines left closed.
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Old 04-07-2021, 02:01 PM   #13
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My two tanks are the same size port and starboard. The boat has a list to port because of fit out. I have valves on return lines and on cross over pipe. I close of both cross over and fuel return to stbd tank effectively using one tank. When needed i can add from the other full tank by opening cross over and watching sight glass. Of course on a longer trip i end up with the same list to port!
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