On Thu, 3 Aug 2000 12:29:00 -0400 "Wright, James C." <jcw@rti.org> writes: > > > 1000 gallons of fuel weighs about 8000 pounds. That is a lot of > weight > > to distribute around the hull. > > 1000 gallons of diesel fuel weighs more like 6000 pounds. In the interests of expediency, I did not bother to check the exact weight of diesel. According to the specifications given to me by the U.S.Navy, #2 diesel weighs exactly 7.3 lbs. per gallon. I should have said, "1000 gallons of fuel weighs about 7,300 pounds. That is a lot of weight to distribute around the hull." tempus fugit Patrick

pgslo@juno.com writes: > I should have >said, "1000 gallons of fuel weighs about 7,300 pounds. That is a >lot of >weight to distribute around the hull." 6000 or 7300 lbs still leaves me with the impression of a possible large imbalance. What are you going to do when you eventually go for that long ocean cruise and one by one your tanks run dry (as was your plan). How do you propose to compensate then for the imbalance, perhaps in the middle of the North Atlantic? Will you fill the empty tanks with salt water or stay unbalasted and bounce around like a cork in a bathtub?

"6000 or 7300 lbs still leaves me with the impression of a possible large imbalance. What are you going to do when you eventually go for that long ocean cruise and one by one your tanks run dry (as was your plan). How do you propose to compensate then for the imbalance, perhaps in the middle of the North Atlantic? Will you fill the empty tanks with salt water or stay unbalasted and bounce around like a cork in a bathtub?" Well that certainly is an issue, but the critical factor would be the proportion of the total displacement represented by the weight of the fuel. If a hypothetical 45 - 50 footer displaced around 45,000-50,000 lbs (and it could be more depending on the D/L ratio), the weight of 1000 US gallons of fuel would represent about 14-15% of the displacement. Depending on the hull shape and water plane area, that would only push the hull down into the water by an inch or so which shouldn't be critical. Presumably a long range motorboat should be designed to float "deep" when fully loaded and fuelled rather than "high" when running light. Disclaimer: I am not a naval architect or designer, and anybody who relies on my statements needs their head examining. There's a discussion of this issue in "Voyaging Under Power" which has the advantage of being written by people who know what they're talking about. Regards, Robert Bryett Sydney, Australia. mailto:rbryett@ibm.net

Actually Robert raises a very good point. If we can't run well with empty tanks what do we do at the end of a cruise? If I had a boat that went squirelly on the last 25% of fuel I would find it unacceptable. So I think it likely our naval architect types try to design these systems so that one can run close to empty and still manage the boat stability. Note that cruisers often carry a ton or two of other consumables that may be gone at the end of a voyage. So it would in fact seem perfectly plausible that the boat would run perfectly reasonably at least down to 10% of capacity. If this were me and I was getting that low I would be working out of no more than two tanks and probably one. So the empty tank strategy should work fine - given that your boat was seaworthy in the first place. I would admit to concerns about water in empty tanks though. Dessicant filters on the vents? Jim > -----Original Message----- > From: owner-trawler-world-list@samurai.com > [mailto:owner-trawler-world-list@samurai.com]On Behalf Of Robert Bryett > Sent: Friday, August 04, 2000 4:15 PM > To: trawler-world-list@samurai.com > Subject: TWL: Leaving some fuel tanks empty > > > "6000 or 7300 lbs still leaves me with the impression of a possible large > imbalance. What are you going to do when you eventually go for that long > ocean cruise and one by one your tanks run dry (as was your plan). How do > you propose to compensate then for the imbalance, perhaps in the middle of > the North Atlantic? Will you fill the empty tanks with salt water or stay > unbalasted and bounce around like a cork in a bathtub?" > > Well that certainly is an issue, but the critical factor would be the > proportion of the total displacement represented by the weight of > the fuel. > If a hypothetical 45 - 50 footer displaced around 45,000-50,000 > lbs (and it > could be more depending on the D/L ratio), the weight of 1000 US > gallons of > fuel would represent about 14-15% of the displacement. Depending on the > hull shape and water plane area, that would only push the hull down into > the water by an inch or so which shouldn't be critical. Presumably a long > range motorboat should be designed to float "deep" when fully loaded and > fuelled rather than "high" when running light. > > Disclaimer: > > I am not a naval architect or designer, and anybody who relies on my > statements needs their head examining. There's a discussion of this issue > in "Voyaging Under Power" which has the advantage of being written by > people who know what they're talking about. > > Regards, Robert Bryett > Sydney, Australia. > mailto:rbryett@ibm.net > >