There is some confusion about the power required to move a boat at various speeds. Most boaters do not appreciate the very low power required at slow speed and the rapid increase in power required as the boat moves faster. Remember that a boatyard worker can push a heavy trawler at a speed of less that one KT without really putting his back into it and a single mule could haul a 30 ton barge on the Erie Canal at 2 KT. Yet it would take 100 mules to haul the same barge at 8 KT. The best way of characterizing boat speed of a displacement type hull is to convert speed measurements into S/L ratios. S/L ratios are calculated by dividing the actual boat speed in knots by the sq. rt. of the LWL in feet. Hull speed is usually considered to be a S/L ratio of 1.34. Naval architects use a rule of thumb in powering displacement hulls, estimating that the power necessary to achieve hull speed is approximately equal to 1 HP per 500 LB of displacement. My 16,000 LB trawler would thus require 32 HP. In fact this rule of thumb is pessimistic since my boat with a clean bottom can reach hull speed in calm water with only 23 HP. Dave Gerr once told me that the conservative NA rule is based on the realization that the ocean is not a mill pond, that boat hulls and props are often fouled, and that engines are not always in the best of tune. So he and most other NAs add a safety factor of about 1/3 to the theoretical required HP. To move a boat at a S/L of .34 requires only 2% of the power necessary to move it at hull speed. Reaching a S/L of .45 requires 4% of the hull speed power. Moving the boat at a S/L of .56 requires 7% of hull speed power. You can reach a S/L of .67 with only 12% of power. A S/L of .78 takes 20% of hull speed power. A hull speed of .89 requires 30% of hull speed power. Reaching a S/L of 1.0, the speed recommended for most economical cruising, requires just 43 % of the power necessary for hull speed. Going faster to a S/L of 1.12 requires 60% of hull speed power. A S/L of 1.2, recommended by Beebe in a time when diesel cost pennies per gallon, requires 74% of hull speed power. Finally at a S/L of 1.34, hull speed, the boat requires 100% of hull speed power. Following the NA rule of thumb this is 1 HP per 500 LB. If you want to push your displacement boat faster, increasing to a S/L of 1.45 requires 1.28 % of the power necessary to move it at a S/L of 1.34 and almost 3 times the power necessary for a S/L of 1.0. Since the T&T list is unkindly to graphs, I plotted a regression equation so you can calculate all the foregoing for yourself. Don't be afraid. If you passed 8th grade math you can do the sums. Y = the fraction of Hull Speed HP required to reach a given S/L ratio. X = the S/L ratio desired. The equation is: Y = .309 - 1.167X + 1.275X^2 The last term is 1.275 times X squared. If you know how much power your boat takes to reach hull speed, you can estimate the power required to reach any lesser S/L ratio. I ran several checks on the actual fuel consumption at various speeds on my own boat and all are within a few percent of the calculated values. So this explains why reducing speed saves fuel. Dropping your 8 KT trawler speed to 6 KT will cut your fuel consumption in half - or double your range. It's all a matter of hydrodynamics. Or it might let me run the air conditioner without guilt in this 94 degree, 70% humidity weather. Larry Z ************** Get fantasy football with free live scoring. Sign up for FanHouse Fantasy Football today. (http://www.fanhouse.com/fantasyaffair?ncid=aolspr00050000000020)

Cutting your fuel consumption in half (gals/hr) does not double your range, because you also cut your speed significantly. Larry Cruzen On 7/22/08, LRZeitlin@aol.com <LRZeitlin@aol.com> wrote: > There is some confusion about the power required to move a boat at various > speeds. Most boaters do not appreciate the very low power required at slow > speed > and the rapid increase in power required as the boat moves faster. Remember > that a boatyard worker can push a heavy trawler at a speed of less that one > KT > without really putting his back into it and a single mule could haul a 30 > ton > barge on the Erie Canal at 2 KT. Yet it would take 100 mules to haul the > same > barge at 8 KT. > > The best way of characterizing boat speed of a displacement type hull is to > convert speed measurements into S/L ratios. S/L ratios are calculated by > dividing the actual boat speed in knots by the sq. rt. of the LWL in feet. > Hull > speed is usually considered to be a S/L ratio of 1.34. Naval architects use > a rule > of thumb in powering displacement hulls, estimating that the power necessary > to achieve hull speed is approximately equal to 1 HP per 500 LB of > displacement. My 16,000 LB trawler would thus require 32 HP. In fact this > rule of thumb > is pessimistic since my boat with a clean bottom can reach hull speed in > calm > water with only 23 HP. Dave Gerr once told me that the conservative NA rule > is > based on the realization that the ocean is not a mill pond, that boat hulls > and props are often fouled, and that engines are not always in the best of > tune. > So he and most other NAs add a safety factor of about 1/3 to the theoretical > required HP. > > To move a boat at a S/L of .34 requires only 2% of the power necessary to > move it at hull speed. Reaching a S/L of .45 requires 4% of the hull speed > power. > Moving the boat at a S/L of .56 requires 7% of hull speed power. You can > reach a S/L of .67 with only 12% of power. A S/L of .78 takes 20% of hull > speed > power. A hull speed of .89 requires 30% of hull speed power. Reaching a S/L > of > 1.0, the speed recommended for most economical cruising, requires just 43 % > of the power necessary for hull speed. Going faster to a S/L of 1.12 > requires > 60% of hull speed power. A S/L of 1.2, recommended by Beebe in a time when > diesel cost pennies per gallon, requires 74% of hull speed power. Finally at > a S/L > of 1.34, hull speed, the boat requires 100% of hull speed power. Following > the NA rule of thumb this is 1 HP per 500 LB. If you want to push your > displacement boat faster, increasing to a S/L of 1.45 requires 1.28 % of the > power > necessary to move it at a S/L of 1.34 and almost 3 times the power necessary > for a > S/L of 1.0. > > Since the T&T list is unkindly to graphs, I plotted a regression equation so > you can calculate all the foregoing for yourself. Don't be afraid. If you > passed 8th grade math you can do the sums. > > Y = the fraction of Hull Speed HP required to reach a given S/L ratio. > X = the S/L ratio desired. > > The equation is: > > Y = .309 - 1.167X + 1.275X^2 > > The last term is 1.275 times X squared. > > If you know how much power your boat takes to reach hull speed, you can > estimate the power required to reach any lesser S/L ratio. I ran several > checks on > the actual fuel consumption at various speeds on my own boat and all are > within a few percent of the calculated values. > > So this explains why reducing speed saves fuel. Dropping your 8 KT trawler > speed to 6 KT will cut your fuel consumption in half - or double your range. > It's all a matter of hydrodynamics. Or it might let me run the air > conditioner > without guilt in this 94 degree, 70% humidity weather. > > Larry Z > > > > > > > ************** > Get fantasy football with free live scoring. Sign up for > FanHouse Fantasy Football today. > > (http://www.fanhouse.com/fantasyaffair?ncid=aolspr00050000000020) > _______________________________________________ > http://lists.samurai.com/mailman/listinfo/trawlers-and-trawlering > > To unsubscribe or modify your subscription options (get password, change > email address, etc) go to: > http://lists.samurai.com/mailman/options/trawlers-and-trawlering > > Trawlers & Trawlering and T&T are trademarks of Water World > Productions. Unauthorized use is prohibited.

Larry Cruzen wrote: > Cutting your fuel consumption in half (gals/hr) does not double your > range, because you also cut your speed significantly. In my example of the Hatteras 48 LRC, it almost does. Nautical MPG is: 1.2 @ 8.4 k 2.3 @ 6.2 k Bob ________________ Robert Calhoun Smith Jr in DC M/V MARY KATHRYN Hatteras 58 LRC South River Annapolis, MD

In the car forums, we call it "magazine racing". People take all the numbers for their car that are in their favor and conveniently forget about the ones against them and then claim victory based solely on a set of numbers. Pretty much what y'all are doing here. Trawler on, John Please visit www.trawlerforum.com --- On Wed, 7/23/08, R C Smith Jr <rcsmith@garrett-smith.com> wrote: From: R C Smith Jr <rcsmith@garrett-smith.com> Subject: Re: T&T: Low boat speed = low power. To: "T&T T&T" <trawlers-and-trawlering@lists.samurai.com> Date: Wednesday, July 23, 2008, 9:26 AM Larry Cruzen wrote: > Cutting your fuel consumption in half (gals/hr) does not double your > range, because you also cut your speed significantly. In my example of the Hatteras 48 LRC, it almost does. Nautical MPG is: 1.2 @ 8.4 k 2.3 @ 6.2 k Bob ________________ Robert Calhoun Smith Jr in DC M/V MARY KATHRYN Hatteras 58 LRC South River Annapolis, MD _______________________________________________ http://lists.samurai.com/mailman/listinfo/trawlers-and-trawlering To unsubscribe or modify your subscription options (get password, change email address, etc) go to: http://lists.samurai.com/mailman/options/trawlers-and-trawlering Trawlers & Trawlering and T&T are trademarks of Water World Productions. Unauthorized use is prohibited.

Ok, these are real numbers on my Krogen, I got them straight off of my Electronic Engine interface. 156 hp John Deere Tier II in a Krogen 44 GPH Speed Nmpg .9 6 knots 6.67 1.7 7 knots 4.11 3 8 knots 2.66 Granted I can't run with the fast boys, but just looking at these numbers makes me wonder why I run it at 8 knots. John Ford KK44 Feisty Lady On Jul 23, 2008, at 12:55 PM, John Baker wrote: > People take all the numbers > for their car that are in their favor and conveniently forget about > the ones > against them and then claim victory based solely on a set of numbers.

I just had it pointed out to me that my tabs didn't work.. So maybe spacing this out will help clean it up. On Jul 23, 2008, at 5:02 PM, John Ford wrote: > GPH Speed Nmpg > .9 6 knots 6.67 > 1.7 7 knots 4.11 > 3 8 knots 2.66