Full Tanks or Not?

I'm interested in what TF'ers think about this question. Let's assume you are at a floating dock in good condition. A windstorm is heading your way--high to hurricane force winds. You decide that where you are tied up is reasonably protected and so the boat will stay where it is. Your fuel and water tanks are near empty but you have the option to fill them before the storm hits. Do you fill them or leave them near empty.

One caveat--this is question about boat safety/stability in the storm, it is not a question of having fuel and water after the storm passes.

Might depend on the configuration of the boat. For my boat, I have two fresh water tanks, 50 gallons each, port and starboard. That's just 800 lbs., but I'd fill them for a little more weight, balance, and to sit slightly lower in the water. My 300 gallon fuel tank is about 1/3 full right now and I'd probably leave it that way. Gas is what, about 6 lbs. per gallon? That's awfully expensive ballast.

My boat is so tall for its weight (26,000 fully loaded) I don't know that full water tanks would make much difference though. On balance I love our boat, but the thing is a giant fiberglass sail. I would imagine other boats with different profiles and tank configurations, you'll get a very different answer.

I have 4700 litre fuel capacity, almost 4 tonnes. Water is about 1100 litre. At the dock I normally am not more than half of fuel capacity but full of water. I would not change anything (re: liquids) ahead of wind coming. Securing/stowing stuff would be my priority.

The boat does not sit that much lower in the water full of fuel, so little reduction in windage. But, it does handle more sluggishly, and has more kinetic energy/momentum. If banging against a dock that increased energy is a negative.

Insequent said:

I have 4700 litre fuel capacity, almost 4 tonnes. Water is about 1100 litre. At the dock I normally am not more than half of fuel capacity but full of water. I would not change anything (re: liquids) ahead of wind coming. Securing/stowing stuff would be my priority.

The boat does not sit that much lower in the water full of fuel, so little reduction in windage. But, it does handle more sluggishly, and has more kinetic energy/momentum. If banging against a dock that increased energy is a negative.

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My thoughts, also. In a big blow, the boats going to move around. In my case, I'd rather have 35,000 pounds pulling against the lines and cleats (low volumes of fuel and water) rather than 42,000 pounds (full of water and fuel).

Giggitoni said:

My thoughts, also. In a big blow, the boats going to move around. In my case, I'd rather have 35,000 pounds pulling against the lines and cleats (low volumes of fuel and water) rather than 42,000 pounds (full of water and fuel).

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My opinion is the heavier boat will move around less, and/or less violently.

Less room in the tank for water intrusion, which is a concern in TS/hurricane conditions.

My opinion is fill her up to the nuts and make her as heavy as you can, we are all hoping that everyone is safe in this very nasty time.

If you have a gasoline boat, perhaps hoarding the fuel might be useful in the aftermath? Godspeed to you all.

Imo, any added weight below the waterline is a plus as it lowers the center of gravity. I might fill all tanks to the boat's waterline.

Ted

Without any experience of an hurricane I would say that it would not make any difference considering the forces in action. My boat is 6 tons empty, 7 or 8 with full fuel, water, our stuff and our fat bodies, but I still can move it by pushing it... imagine 200km/h wind... Full fuel tanks would only add to pollution mess if by any bad luck (and I sincerely hope this will not be your case) the boat is destroyed.

L

Water tanks and two of four fuel tanks of mine are above waterline. The boat is heavy with a low profile, so believe filling the lower fuel tanks would not have much affect. However, if future availability of water and fuel was questionable, I'd take on water and some fuel.

I like to have water tanks full, in case I need to move the boat and then might stay aboard for an extended period. (This would generally be after a move to more safety but then being without ground transport. I'm NOT staying aboard in the direct path of a hurricane.)

I like to keep the fuel tanks somewhere around half full during our season anyway, so that gives me some significant mobility if necessary. If it looks like I might need to make a serious move, full fuel tanks (more range) make me slightly less nervous.

-Chris

I think the "it weighs more so pulls more on lines / hits dock harder" logic is potentially not accurate.

IMHO The net effect would be zero as it won't get gain as much kinetic energy due to being heavier.

What I think *would* happen is frequency will decrease, and I think that's a good thing.

I'm full up on all tanks, and thankfully latest forecast Savannah is out of the cone.

Edit: Also +1 for more fuel in an apocalypse is a good investment.

I'll add a different view:

If the boat breaks away or sinks and you've just spent $500 filling up the fuel tanks, you're not going to be happy about that.

I keep my fuel tanks full so I don't have that choice but my boat is hauled and in a building so my situation is different anyway.

What percentage of displacement is the added fuel?

I personally dont think it will add much to stability. The dock linesv will probably reduce rolling to the point where the real righting force of that added fuel may not be much.

OK, so I see both sides of this coin. Bottom line is nobody knows. Perhaps an NA will chime in. Fortunately for us we are still in CT so it is not a big issue. What triggered the question is yesterday I filled our fuel tanks to capacity in anticipation of our trip south. I reasoned that diesel prices may go up due to the storms so buy now. Then I got to thinking about it and it gave rise to my query.

Good luck and safe passage wishes to all those in harm's way.

We're full but that's just the way they were anyway. Probably a little stability gained but I don't see that it's enough to really matter. I see one big plus in being full and that is post storm fuel deliveries for marinas are not likely to be a high priority. Also, might need to use the boat in some relief effort. The negative is that if you sink, then the environmental issue has been increased.

hmason said:

OK, so I see both sides of this coin. Bottom line is nobody knows. Perhaps an NA will chime in. Fortunately for us we are still in CT so it is not a big issue. What triggered the question is yesterday I filled our fuel tanks to capacity in anticipation of our trip south. I reasoned that diesel prices may go up due to the storms so buy now. Then I got to thinking about it and it gave rise to my query.

Good luck and safe passage wishes to all those in harm's way.

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No. We do know.
The KK42 with full tanks add 15% to the displacement weight.
The boat will sit about 5 inches lower in the water compared to almost empty.
She bobs around much more when empty.

I'd have all the tanks full.

I thought about this and decided if my boat sank, I didn't want over 100 gallons going with it. I left thr boat with about 1/3rd tanks.

Steve91T said:

I thought about this and decided if my boat sank, I didn't want over 100 gallons going with it. I left thr boat with about 1/3rd tanks.

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Wifey B: I prefer to plan for it not to sink.

BandB said:

Wifey B: I prefer to plan for it not to sink.

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Ha right. But I figure if she's going to sink, 100 gallons isn't going to make a bit of difference.

Lou_tribal said:

Without any experience of an hurricane I would say that it would not make any difference considering the forces in action. My boat is 6 tons empty, 7 or 8 with full fuel, water, our stuff and our fat bodies, but I still can move it by pushing it... imagine 200km/h wind... Full fuel tanks would only add to pollution mess if by any bad luck (and I sincerely hope this will not be your case) the boat is destroyed.

L

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I'm with you and Brian, above, Lou. As you say, the extra weight will not help - inconsequential in the proposed scenario, as we are talking of a boat tied to a dock in a strong wind and surge situation. To me the less weight tugging against those mooring lines the better.

I don't know the answer. I just know it's irrelevant to me. I always keep the boat full. You can fill empty tanks but you really can't empty full ones.

Full tanks always improve stability and decrease strain on lines. It is the quick snap of velocity on lines that causes problems. The same is true for anchoring. You'll notice it's almost always the smallest boat in an anchorage that drag. The boat bounces more with less weight and pulls out the anchor. A heavier boat is also easier to dock as the motions are slower and more predictable dockside.

There is an other consideration. If you leave the tanks half full the fuel will slosh around in a bad storm and mix any junk on the bottom of the tank into the fuel, which could make moving the boat after the storm interesting. Full tanks don't slosh. Of course you can compensate for the lighter weight of the half full tanks with the weight of all the fuel filters you are likely to need after the storm.

I have 1,000 gals capacity diesel tanks, 300 gals fresh water. Fuel tanks are half full. Very expensive to fill up plus I spent time securing the boat rather than running to the fuel dock and back. I did fill the fw tanks before I left though.

IMO - All tanks 1/2 full. That's if you feel fuel tanks have at least fairly clean bottoms and sides

Art said:

IMO - All tanks 1/2 full. That's if you feel fuel tanks have at least fairly clean bottoms and sides

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+1

Cheers.

H.