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Old 15-09-2011, 00:18   #1
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Upsize Water and Fuel Tanks

I have a Cal 34 with a 10,000# displacement. I am planning to upsize the fresh water and diesel fuel tanks from the present 25 gal water and 28 gal fuel.

What are the 'Rules of Thumb' for water and fuel tank sizes for 2 people and 2 month cruises?

Thanks - Charles

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Old 15-09-2011, 00:41   #2
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Re: Upsize water and fuel tanks

Weight & placement are the big issue, of course. If you can afford a watermaker, I'd suggest going that way. I'm doubling the capacity on my Cal 2-30 & have moved my house batts forward and my anchors/chain aft & lower to compensate for the added weight of the tanks. You can never have too much water, right? If you went for 1 gallon/day you'd need 60gallons & would have no reserve. I managed to accommodate 80 gallons on my old 3-30 & that seemed like much too much when my brother or friend & I sailed, but not with my wife & I. But my wife smelled better! Fuel will really depend on how much you rely on your engine, some use it much more than others.

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Old 15-09-2011, 05:33   #3
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Re: Upsize water and fuel tanks

I think a lot depends on where you are cruising. Don't forget to increase the size of your holding tank as well.
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Old 15-09-2011, 07:02   #4
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Re: Upsize water and fuel tanks

Water weighs about 8-1/3 pounds per gallon. Gas weighs about 6 pounds per gallon. Every pound you add changes your boats sailing characteristics, weighs it down, and slows it down. And the Cal-34, at 9,500 lbs. displacement, is designed as a pretty light-weight 34 footer, so extra weight is going to affect it more than it would a boat designed with a relatively high D/L ratio.

As such, I personally would not add more than about 5% to the boat's displacement. That would be 475 lbs, and still allows you to add something like 20 gallons of gas and 40 gallons of water.

Now you have to consider where you are adding this weight. Obviously you're creating a problem if it is all on one side, so you have to balance it port and starboard to avoid listing. You need to get it down as low as possible, though the Cal-34 has a ballast ratio of almost 40%, so it won't be the end of the world if the weight is not right down in the bilge.

The general rule of thumb for water is 1 gallon per person, per day. Are you really thinking of spending two months away from facilities where you can refill? Then you need 120 gallons, which is really too much for this boat. If you are going to be doing a more typical cruise, where you are usually able to refill every 2-3 weeks or so, then 60 gallons becomes plenty. If you are cruising through the Caribbean, where you can fill up every few days then the 25 gallons you have is enough. In fact, that's exactly what a boat like the Cal-34 was designed for.

As for gas, only you can decide how much and how often you will run the engine. Some cruisers do it all the time. Some hardly ever. I'm one of those "the boat was made for sailing" types. Some people, you wonder why they didn't just buy a powerboat to begin with. I used to dock next to a guy who--quite literally--ran his engine all the time, even when he had the sails up (which, frankly, I think he spent more time motoring with his sails down than he did with his sails up). I'm quite sure that he burned as much diesel in the course of one day of day-sailing as I would burn during a 2-week cruise.
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Old 15-09-2011, 15:21   #5
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Re: Upsize Water and Fuel Tanks

You might want to consider increasing the fuel capacity, leave the water capacity as it is and install a small watermaker.
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fuel, fuel tank, water

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