From: Paul Goyette <paul@whooppee.com> On Mon, 4 Apr 2005 scottstrickland@comcast.net wrote: > The only comment I would like to offer after doing 5,000 miles > in the Pacific last year is that range is more dependent on > sea state the one would expect. Yup, that's basically why I won't even try for the Marquesas if we don't get fuel in Kiritimati. It would be an uphill 1200 nm run, into winds and seas. > At 1,800 rpm we made between 8 knots and 2.8 knots. Hopefully, that was 8.2 kts, not 2.8 ? :) 2.8 would be excruciatingly slow! ==================================== No I mean 2.8 knots. The point of the message was that in serious head seas I have seen a 60% drop in speed for a given RPM. The was the purpose of the message. When planning a passage, you need to be aware that sometimes your range decreases 60%! An important fact that was left unsaid in the message, but I will make more clear for those that missed it. 3 knots is barely enough to maintain steerage. I was turning 1,800 rpm. If I slowed down to conserve fuel I would not have been able to maintain steerage, hence slowing down was not an option. Not to mention stabilization does not really work at 3 knots! The point I was trying to make is that if you are doing a long leg, where the weather might change on you, the fuel reserves required for a safe trip are greater then it would seem if you have not expereiced10-20 foot head seas. People who assume that they can always throttle back to extend their range, need to realize that is not always true!

This matter of displacement-mode speed vs. fuel economy seems to get an interesting twist with catamarans. I'm guessing it's a physics thing -- two slender hulls requiring less effort to be moved through a fluid than one wide hull -- that accounts for the fact that displacement-type power cats operate at just about 100% faster speeds than do displacement-type monohulls. Whereas 40 to 45-foot displacement monos (Nordhavn, Grand Banks, Selene, et al) appear to do about 8 to 10 knots, all of the displacement-type cats (Endeavor, Lagoon, Fountaine Pajot, Ted Hood's Portsmouth cats, etc.) do 16 to 20 knots. Of course, they, too can proceed slower in order to conserve fuel, but "slower" never requires such a dimishment in speed that maneuverability becomes an issue. (It appears that even when operating on just one of their two engines -- which typically cuts the speed by about 30% but increases fuel by 40% to 50% -- maneuverability remains high because the two rudders are so far apart: anywhere from 13 to 18 feet.) Further, the inherent stability of two, widely spaced hulls makes the addition of a stabilizing system a moot point. Cats are stable underway or at anchor. Unfortunately, there don't seem to be any production-built cats yets produced that offer the same ergonomics/liveability/sales-price of the current most popular cruising monohulls. Anybody have any ideas why that is? scottstrickland@comcast.net wrote: >From: Paul Goyette <paul@whooppee.com> >On Mon, 4 Apr 2005 scottstrickland@comcast.net wrote: > > > >>The only comment I would like to offer after doing 5,000 miles >>in the Pacific last year is that range is more dependent on >>sea state the one would expect. >> >> > >Yup, that's basically why I won't even try for the Marquesas if >we don't get fuel in Kiritimati. It would be an uphill 1200 nm >run, into winds and seas. > > > >>At 1,800 rpm we made between 8 knots and 2.8 knots. >> >> > >Hopefully, that was 8.2 kts, not 2.8 ? :) 2.8 would >be excruciatingly slow! > >==================================== >No I mean 2.8 knots. > >The point of the message was that in serious >head seas I have seen a 60% drop in speed for a given >RPM. > >The was the purpose of the message. > >When planning a passage, you need to be aware that >sometimes your range decreases 60%! > >An important fact that was left unsaid in the message, >but I will make more clear for those that missed it. > >3 knots is barely enough to maintain steerage. >I was turning 1,800 rpm. If I slowed down to conserve >fuel I would not have been able to maintain steerage, >hence slowing down was not an option. > >Not to mention stabilization does not really work at 3 knots! > >The point I was trying to make is that if you are doing a long >leg, where the weather might change on you, the fuel reserves >required for a safe trip are greater then it would seem if you >have not expereiced10-20 foot head seas. > >People who assume that they can always throttle back to extend >their range, need to realize that is not always true! >_______________________________________________ >Passagemaking-Under-Power Mailing List > > >

I see that I left out a crucial word below, which I'll now insert in bold, to make the statement factual: Rod Gibbons wrote: >This matter of displacement-mode speed vs. fuel economy seems to get an >interesting twist with catamarans. I'm guessing it's a physics thing -- >two slender hulls requiring less effort to be moved through a fluid than >one wide hull -- that accounts for the fact that displacement-type power >cats operate at just about 100% faster speeds than do displacement-type >monohulls. Whereas 40 to 45-foot displacement monos (Nordhavn, Grand >Banks, Selene, et al) appear to do about 8 to 10 knots, all of the >displacement-type cats (Endeavor, Lagoon, Fountaine Pajot, Ted Hood's >Portsmouth cats, etc.) do 16 to 20 knots. > >Of course, they, too can proceed slower in order to conserve fuel, but >"slower" never requires such a dimishment in speed that maneuverability >becomes an issue. (It appears that even when operating on just one of >their two engines -- which typically cuts the speed by about 30% but >increases fuel conservation by 40% to 50% -- maneuverability remains high because the >two rudders are so far apart: anywhere from 13 to 18 feet.) > >Further, the inherent stability of two, widely spaced hulls makes the >addition of a stabilizing system a moot point. Cats are stable underway >or at anchor. > >Unfortunately, there don't seem to be any production-built cats yets >produced that offer the same ergonomics/liveability/sales-price of the >current most popular cruising monohulls. Anybody have any ideas why that is? > > > > >scottstrickland@comcast.net wrote: > > > >>From: Paul Goyette <paul@whooppee.com> >>On Mon, 4 Apr 2005 scottstrickland@comcast.net wrote: >> >> >> >> >> >>>The only comment I would like to offer after doing 5,000 miles >>>in the Pacific last year is that range is more dependent on >>>sea state the one would expect. >>> >>> >>> >>> >>Yup, that's basically why I won't even try for the Marquesas if >>we don't get fuel in Kiritimati. It would be an uphill 1200 nm >>run, into winds and seas. >> >> >> >> >> >>>At 1,800 rpm we made between 8 knots and 2.8 knots. >>> >>> >>> >>> >>Hopefully, that was 8.2 kts, not 2.8 ? :) 2.8 would >>be excruciatingly slow! >> >>==================================== >>No I mean 2.8 knots. >> >>The point of the message was that in serious >>head seas I have seen a 60% drop in speed for a given >>RPM. >> >>The was the purpose of the message. >> >>When planning a passage, you need to be aware that >>sometimes your range decreases 60%! >> >>An important fact that was left unsaid in the message, >>but I will make more clear for those that missed it. >> >>3 knots is barely enough to maintain steerage. >>I was turning 1,800 rpm. If I slowed down to conserve >>fuel I would not have been able to maintain steerage, >>hence slowing down was not an option. >> >>Not to mention stabilization does not really work at 3 knots! >> >>The point I was trying to make is that if you are doing a long >>leg, where the weather might change on you, the fuel reserves >>required for a safe trip are greater then it would seem if you >>have not expereiced10-20 foot head seas. >> >>People who assume that they can always throttle back to extend >>their range, need to realize that is not always true! >>_______________________________________________ >>Passagemaking-Under-Power Mailing List >> >> >> >> >> >_______________________________________________ >Passagemaking-Under-Power Mailing List > > >