Re: [bolger] now hull speed, was Re: mast options for Ruben's Nym ph
In a message dated 6/4/02 7:46:17 AM Central Daylight Time,
nickerb@...writes:
and I can't get the jokes because I don't understand the "AIA's" ("AIA" being
an new "initialism" for me.) (Thanks for including the definition in
parantheses, BTW. :-)) (The AIA "BTW" and "emoticon" are my attempt at
cyber-humor.)
I'll try to provide a de-coder for my AIA's, in the off-chance that you are
actually interested and not just setting me up as a figure of fun:
S/L = "speed to length ratio"; mathematically this is a boat's speed in
nautical miles per hour ("knots" or "Kts.") divided by the square root of its
waterline length (LWL) in feet. The significance of this ratio is that the
energy expended in creating the surface waves generated by boats that
progress through the water at "displacement" speeds is what limits their
speeds. A 16' boat at 4 Kts. will produce the same wavelength relative to its
length as a 36' boat at 6 Kts. Both boats would be moving at an S/L of 1.0.
At that S/L ratio the wavelength of the wave and the length of the LWL
coincide. Above that S/l the boat has to start climbing up its own bow wave
to go faster. Above an S/L ratio of 1.0, the amount of power required to
increase speed increases at an accelerating rate as speed increases.
D/L = "displacement to length ratio"; in the form used by Gerr, this is the
displacement of the boat in "long tons" (2240 pounds per "long ton") divided
by the cube of one percent of the LWL in feet. The dividend is a
dimensionless number, which is perfectly arbitrary, as far as I can tell, but
commonly used to compare boat designs. The higher the ratio, the heavier the
boat is for its length and the more power it takes to drive it to a given
speed. Unless the boat is designed to "plane", there is an S/L ratio where
adding additional power results in rapidly diminishing returns.
O/B = outboard motor
Kts. = "nautical miles per hour"; a nautical mile is about 1.15 statute
(U.S.) miles
C ("Crouch Formula") = this is just a constant; George Crouch was an eminent
designer of high performance planing power boats in the '30's and this is
derived from his work. Gerr gives values of "C" ranging from 150 ("average
runabout") to 230 ("racing power catamarans").
Kts. = "nautical miles per hour" a.k.a. "knots"; a nautical mile is
approximately 1.15 statute miles; an hour is an hour, I think.
SHP = "shaft horsepower"; this is the power available to turn the propeller.
With inboard engines deductions from crankshaft horsepower have to be made
for power losses to accessories, transmission, bearings and etc. O/B motors
are now rated for SHP, but I have recently purchased a 1983 vintage Mercury
O/B "40" that was subsequently marketed as a 35 SHP model when Mercury
changed its ratings from "crankshaft" HP to SHP.
LWL = I believe this is an "intialism" for "Load Water Line"; for purposes
like calculating S/L and D/L, it is the distance between the stern of the
boat and that portion that contacts the water at its most forward point.
Overhangs, bowsprits, pulpits, etc. do not interact with the air/water
interface and so "LWL" is used as a reference datum, rather that "LOA"
(Length Over All), a different dimension, with its own valuable uses. (e.g.
docking fees, trailer length, storage facilities, etc.)
Ciao for Niao,
Bill in MN
[Non-text portions of this message have been removed]
nickerb@...writes:
> These AIAsOh Dear Me! I see I've inspired our humorists to new levels of cyber-speak,
> (acronyms, initialisms and abbreviations) are not only confusing to me, but
> I sometimes cannot understand if they are technical terms from the topic
> under discussion, or cyber-speak (like BTW).
and I can't get the jokes because I don't understand the "AIA's" ("AIA" being
an new "initialism" for me.) (Thanks for including the definition in
parantheses, BTW. :-)) (The AIA "BTW" and "emoticon" are my attempt at
cyber-humor.)
I'll try to provide a de-coder for my AIA's, in the off-chance that you are
actually interested and not just setting me up as a figure of fun:
S/L = "speed to length ratio"; mathematically this is a boat's speed in
nautical miles per hour ("knots" or "Kts.") divided by the square root of its
waterline length (LWL) in feet. The significance of this ratio is that the
energy expended in creating the surface waves generated by boats that
progress through the water at "displacement" speeds is what limits their
speeds. A 16' boat at 4 Kts. will produce the same wavelength relative to its
length as a 36' boat at 6 Kts. Both boats would be moving at an S/L of 1.0.
At that S/L ratio the wavelength of the wave and the length of the LWL
coincide. Above that S/l the boat has to start climbing up its own bow wave
to go faster. Above an S/L ratio of 1.0, the amount of power required to
increase speed increases at an accelerating rate as speed increases.
D/L = "displacement to length ratio"; in the form used by Gerr, this is the
displacement of the boat in "long tons" (2240 pounds per "long ton") divided
by the cube of one percent of the LWL in feet. The dividend is a
dimensionless number, which is perfectly arbitrary, as far as I can tell, but
commonly used to compare boat designs. The higher the ratio, the heavier the
boat is for its length and the more power it takes to drive it to a given
speed. Unless the boat is designed to "plane", there is an S/L ratio where
adding additional power results in rapidly diminishing returns.
O/B = outboard motor
Kts. = "nautical miles per hour"; a nautical mile is about 1.15 statute
(U.S.) miles
C ("Crouch Formula") = this is just a constant; George Crouch was an eminent
designer of high performance planing power boats in the '30's and this is
derived from his work. Gerr gives values of "C" ranging from 150 ("average
runabout") to 230 ("racing power catamarans").
Kts. = "nautical miles per hour" a.k.a. "knots"; a nautical mile is
approximately 1.15 statute miles; an hour is an hour, I think.
SHP = "shaft horsepower"; this is the power available to turn the propeller.
With inboard engines deductions from crankshaft horsepower have to be made
for power losses to accessories, transmission, bearings and etc. O/B motors
are now rated for SHP, but I have recently purchased a 1983 vintage Mercury
O/B "40" that was subsequently marketed as a 35 SHP model when Mercury
changed its ratings from "crankshaft" HP to SHP.
LWL = I believe this is an "intialism" for "Load Water Line"; for purposes
like calculating S/L and D/L, it is the distance between the stern of the
boat and that portion that contacts the water at its most forward point.
Overhangs, bowsprits, pulpits, etc. do not interact with the air/water
interface and so "LWL" is used as a reference datum, rather that "LOA"
(Length Over All), a different dimension, with its own valuable uses. (e.g.
docking fees, trailer length, storage facilities, etc.)
Ciao for Niao,
Bill in MN
[Non-text portions of this message have been removed]
Technically, an acronym is an initialism which makes a pronouncable word.
Thus AVCO, from Aviation Corporation, is an acronym, while TLA is an
initialism. St. for saint or street, is an abbreviation.
-----Original Message-----
From: Richard Spelling [mailto:richard@...]
Sent: Tuesday, June 04, 2002 1:28 PM
To:bolger@yahoogroups.com
Subject: Re: [bolger] now hull speed, was Re: mast options for Ruben's Nymph
Three(or Two) Letter Acronym
Thus AVCO, from Aviation Corporation, is an acronym, while TLA is an
initialism. St. for saint or street, is an abbreviation.
-----Original Message-----
From: Richard Spelling [mailto:richard@...]
Sent: Tuesday, June 04, 2002 1:28 PM
To:bolger@yahoogroups.com
Subject: Re: [bolger] now hull speed, was Re: mast options for Ruben's Nymph
Three(or Two) Letter Acronym
----- Original Message -----
From: "Nickerson, Bruce " <nickerb@...>
To: <bolger@yahoogroups.com>
Sent: Tuesday, June 04, 2002 12:17 PM
Subject: RE: [bolger] now hull speed, was Re: mast options for Ruben's Nymph
> When I managed a tech writing department in the defense industry, we were
> inundated with abbreviations, acronyms and initialisms. I even had a 400
> page book listing all these AAIs. My favorite was PLU (Preservation of
> Locational Uncertainty) which referred to storing ICBMs on flat bed rail
> trucks so that their location could be changed frequently. Some managers
> who could never be found were then said to be managing by PLU. However
used
> I got to using AAIs, I will admit to having trouble understanding what
"The
> TLA's like BTW or D/L are part of the WWW, though D/L is a boating TLA..."
> means. I think WWW is world wide web, BTW is by the way, but fall apart
on
> TLA.
>
> -----Original Message-----
> From: Stew Miller [mailto:junkmail@...]
> Sent: Tuesday, June 04, 2002 12:00 PM
> To:bolger@yahoogroups.com
> Subject: Re: [bolger] now hull speed, was Re: mast options for Ruben's
Nymph
>
>
>
> Richard,
> You forgot to define TLA, which is yet another TLA.
>
> FYI, when you hire on at SUN Microsystems you must memorize three pages
> of TLAs.
>
> Richard Spelling wrote:
> > The TLA's like BTW or D/L are part of the WWW, though D/L is a boating
> TLA,
>
>
>
> Yahoo! Groups Sponsor
>
> ADVERTISEMENT
>
>
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http://us.adserver.yahoo.com/l?M=226014.2032696.3508022.1829184/D=egroupmai
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> l/S=1705065791:HM/A=1000239/rand=417682374>
>
> Bolger rules!!!
> - no cursing, flaming, trolling, spamming, or flogging dead horses
> - stay on topic, stay on thread, punctuate, no "Ed, thanks, Fred" posts
> - add your comments at the TOP and SIGN your posts and <snip> away
> - To order plans: Mr. Philip C. Bolger, P.O. Box 1209, Gloucester, MA,
> 01930, Fax: (978) 282-1349
> - Unsubscribe:bolger-unsubscribe@yahoogroups.com
>
> Your use of Yahoo! Groups is subject to the Yahoo! Terms of
> <http://docs.yahoo.com/info/terms/<http://docs.yahoo.com/info/terms/> >
Service.
>
>
>
>
> [Non-text portions of this message have been removed]
>
>
>
> Bolger rules!!!
> - no cursing, flaming, trolling, spamming, or flogging dead horses
> - stay on topic, stay on thread, punctuate, no "Ed, thanks, Fred" posts
> - add your comments at the TOP and SIGN your posts and <snip> away
> - To order plans: Mr. Philip C. Bolger, P.O. Box 1209, Gloucester, MA,
01930, Fax: (978) 282-1349
> - Unsubscribe:bolger-unsubscribe@yahoogroups.com
>
> Your use of Yahoo! Groups is subject tohttp://docs.yahoo.com/info/terms/
<http://docs.yahoo.com/info/terms/>
>
>
>
Bolger rules!!!
- no cursing, flaming, trolling, spamming, or flogging dead horses
- stay on topic, stay on thread, punctuate, no "Ed, thanks, Fred" posts
- add your comments at the TOP and SIGN your posts and <snip> away
- To order plans: Mr. Philip C. Bolger, P.O. Box 1209, Gloucester, MA,
01930, Fax: (978) 282-1349
- Unsubscribe:bolger-unsubscribe@yahoogroups.com
Your use of Yahoo! Groups is subject to the Yahoo! Terms of
<http://docs.yahoo.com/info/terms/> Service.
[Non-text portions of this message have been removed]
When I managed a tech writing department in the defense industry, we were
inundated with abbreviations, acronyms and initialisms. I even had a 400
page book listing all these AAIs. My favorite was PLU (Preservation of
Locational Uncertainty) which referred to storing ICBMs on flat bed rail
trucks so that their location could be changed frequently. Some managers
who could never be found were then said to be managing by PLU. However used
I got to using AAIs, I will admit to having trouble understanding what "The
TLA's like BTW or D/L are part of the WWW, though D/L is a boating TLA..."
means. I think WWW is world wide web, BTW is by the way, but fall apart on
TLA.
-----Original Message-----
From: Stew Miller [mailto:junkmail@...]
Sent: Tuesday, June 04, 2002 12:00 PM
To:bolger@yahoogroups.com
Subject: Re: [bolger] now hull speed, was Re: mast options for Ruben's Nymph
Richard,
You forgot to define TLA, which is yet another TLA.
FYI, when you hire on at SUN Microsystems you must memorize three pages
of TLAs.
Richard Spelling wrote:
Yahoo! Groups Sponsor
ADVERTISEMENT
<http://rd.yahoo.com/M=226014.2032696.3508022.1829184/D=egroupweb/S=17050657
91:HM/A=1000239/R=0/*http://ads.x10.com/?bHlhaG9vaG0xLmRhd=1023206582%3eM=22
6014.2032696.3508022.1829184/D=egroupweb/S=1705065791:HM/A=1000239/R=1>
<http://us.adserver.yahoo.com/l?M=226014.2032696.3508022.1829184/D=egroupmai
l/S=1705065791:HM/A=1000239/rand=417682374>
Bolger rules!!!
- no cursing, flaming, trolling, spamming, or flogging dead horses
- stay on topic, stay on thread, punctuate, no "Ed, thanks, Fred" posts
- add your comments at the TOP and SIGN your posts and <snip> away
- To order plans: Mr. Philip C. Bolger, P.O. Box 1209, Gloucester, MA,
01930, Fax: (978) 282-1349
- Unsubscribe:bolger-unsubscribe@yahoogroups.com
Your use of Yahoo! Groups is subject to the Yahoo! Terms of
<http://docs.yahoo.com/info/terms/> Service.
[Non-text portions of this message have been removed]
inundated with abbreviations, acronyms and initialisms. I even had a 400
page book listing all these AAIs. My favorite was PLU (Preservation of
Locational Uncertainty) which referred to storing ICBMs on flat bed rail
trucks so that their location could be changed frequently. Some managers
who could never be found were then said to be managing by PLU. However used
I got to using AAIs, I will admit to having trouble understanding what "The
TLA's like BTW or D/L are part of the WWW, though D/L is a boating TLA..."
means. I think WWW is world wide web, BTW is by the way, but fall apart on
TLA.
-----Original Message-----
From: Stew Miller [mailto:junkmail@...]
Sent: Tuesday, June 04, 2002 12:00 PM
To:bolger@yahoogroups.com
Subject: Re: [bolger] now hull speed, was Re: mast options for Ruben's Nymph
Richard,
You forgot to define TLA, which is yet another TLA.
FYI, when you hire on at SUN Microsystems you must memorize three pages
of TLAs.
Richard Spelling wrote:
> The TLA's like BTW or D/L are part of the WWW, though D/L is a boatingTLA,
Yahoo! Groups Sponsor
ADVERTISEMENT
<http://rd.yahoo.com/M=226014.2032696.3508022.1829184/D=egroupweb/S=17050657
91:HM/A=1000239/R=0/*http://ads.x10.com/?bHlhaG9vaG0xLmRhd=1023206582%3eM=22
6014.2032696.3508022.1829184/D=egroupweb/S=1705065791:HM/A=1000239/R=1>
<http://us.adserver.yahoo.com/l?M=226014.2032696.3508022.1829184/D=egroupmai
l/S=1705065791:HM/A=1000239/rand=417682374>
Bolger rules!!!
- no cursing, flaming, trolling, spamming, or flogging dead horses
- stay on topic, stay on thread, punctuate, no "Ed, thanks, Fred" posts
- add your comments at the TOP and SIGN your posts and <snip> away
- To order plans: Mr. Philip C. Bolger, P.O. Box 1209, Gloucester, MA,
01930, Fax: (978) 282-1349
- Unsubscribe:bolger-unsubscribe@yahoogroups.com
Your use of Yahoo! Groups is subject to the Yahoo! Terms of
<http://docs.yahoo.com/info/terms/> Service.
[Non-text portions of this message have been removed]
In general, I agree with you. The one that gets me is abbreviated boat
names, tho I also originally thought OSB mean "one sheet boat".
In this case, there is an explicit definition of the D/L ratio we are
using (though actually it is NOT just displacement/length) in an
earlier post in this same thread. I seem to recall it is displacement
in long tons (2240lbs?) divided by the cube of .01 times the waterline
length in feet, IF I remember correctly. S/L is speed/waterlinelength
(knots and feet, I think).
I think SHP is shaft horsepower, and O/B must be outboard motor.
LWL is a common and conventional abbreviation for waterline length.
BTW, I forget where it is on the web, but a guy in Australia or New
Zealand or someplace south of the equator like that (I forget which,
it's not that I think they're all the same) has a free program which
purports to calculate resistance for hulls like this and even has an
"evolution" algorythmn (sp?) to come up with low resistance shapes.
Unfortunately, I don't remember the URL.
names, tho I also originally thought OSB mean "one sheet boat".
In this case, there is an explicit definition of the D/L ratio we are
using (though actually it is NOT just displacement/length) in an
earlier post in this same thread. I seem to recall it is displacement
in long tons (2240lbs?) divided by the cube of .01 times the waterline
length in feet, IF I remember correctly. S/L is speed/waterlinelength
(knots and feet, I think).
I think SHP is shaft horsepower, and O/B must be outboard motor.
LWL is a common and conventional abbreviation for waterline length.
BTW, I forget where it is on the web, but a guy in Australia or New
Zealand or someplace south of the equator like that (I forget which,
it's not that I think they're all the same) has a free program which
purports to calculate resistance for hulls like this and even has an
"evolution" algorythmn (sp?) to come up with low resistance shapes.
Unfortunately, I don't remember the URL.
--- In bolger@y..., "Nickerson, Bruce " <nickerb@p...> wrote:
> While I find this technical stuff interesting, I am a bit boggled by
the
> abbreviations, initialisms and acronyms here abounding. These AIAs
> (acronyms, initialisms and abbreviations) are not only confusing to
me, but
> I sometimes cannot understand if they are technical terms from the
topic
> under discussion, or cyber-speak (like BTW). Anyone else have this
concern
> and some suggestions about how to ease this pain?
>
> -----Original Message-----
snip
While I find this technical stuff interesting, I am a bit boggled by the
abbreviations, initialisms and acronyms here abounding. These AIAs
(acronyms, initialisms and abbreviations) are not only confusing to me, but
I sometimes cannot understand if they are technical terms from the topic
under discussion, or cyber-speak (like BTW). Anyone else have this concern
and some suggestions about how to ease this pain?
-----Original Message-----
From:wmrpage@...[mailto:wmrpage@...]
Sent: Monday, June 03, 2002 10:25 PM
To:bolger@yahoogroups.com
Subject: Re: [bolger] now hull speed, was Re: mast options for Ruben's Nymph
In a message dated 5/31/02 9:43:14 PM Central Daylight Time,
lincolnr@...writes:
of
311 lbs. gives a D/L of 15, so I think you got your sums right. I was
surprised and intrigued by your observation!
Gerr's formulae indicate that this hypothetical scull has a maximum S/L of
3.6, which translates into a "non-planing" top speed of 16.5 Kts. His
displacement SHP formula indicates that it would take approx. .6 SHP to go 6
Kts., possibly attainable by a highly-trained and strong rower, I suppose.
Just how reliable Gerr's formulae are for very low D/L boats at high S/L
ratios is questionable, however, as application of the formulae to the
Stillwater catamaran shows. The displacement formula seems to overstate
power
requirements at high S/L ratios, while the Crouch (planing) formula seems to
understate power requirements at lower S/L ratios.
The Stillwater catamaran is 26' LWL. It has a claimed top speed of 18 Kts.
w/15 SHP long-shaft O/B motor. I assume that the claimed top speed is
accurate, probably a bit conservative - obviously it is a quantity
relatively
easily verified by a buyer who could be expected to complain if the claim
was
not met. (Do you have any insight into why the design requires a long-shaft
motor?)
I've estimated it's gross displacement at 1300# (4 x 200# adults + 15hp O/B
motor + 5 gal. gas tank) or 900# (2 x 200# adults + 15hp O/B motor + 5 gal.
gas tank). This gives D/L ratios of 33 and 23, respectively, S/L maximums of
2.8 and 3.1, which translate to 14.3 Kts and 15.6 Kts top speed. Gerr's
displacement SHP formula gives, respectively, SHP requirements of these
speeds as 23.9 SHP and 22.4 SHP. Conversely, calculated top speeds for 15
SHP
are 12.2 Kts and something in excess of 13.8 Kts.
Crouch's formula for planing boats (I'm rather arbitrarily using C = 200)
gives speeds of something less than 16 Kts. and 19.4 Kts. respectively for
15
SHP. Interestingly, at this power level, the lighter-loaded boat approaches
the 60#/SHP ratio that is the highest #/SHP ratio that Gerr shows on his
Crouch chart.
One could reasonably infer that the performance of low D/L boats at high S/L
ratios falls somewhere in between the displacement SHP curve and the Crouch
SHP curve, perhaps approximating the first up to a certain speed and
approximating the second after that, but I've run innumerable graphs
comparing the two curves for various hypothetical boats and have not
detected
any significant relationship in where the divergence point between the two
curves occurs.
Gerr does not discuss the source of the displacement formula he uses. I
suspect it is derived from tests on full scale naval and maritime merchant
vessels, supplemented by model tests of similar types at the U.S.N. Taylor
basin. Crouch's formula seems to be empirically derived from the performance
of boats of low #/SHP ratios. If I am correct, there is a gap in the data
for
boats of low D/L ratios like Bolger's "Sneakeasy" and others of its ilk.
I believe that the University of Illinois did some wind tunnel testing of
airfoils at low-Reynold's numbers that is of considerable interest to model
airplane builders, while totally devoid of pertinence to commercial airplane
designers. One can hope that perhaps, someday, some suitably equiped
engineering faculty might turn its sights on the phenomenom of low D/L
boats,
like "Sneakeasy".
Ciao for Niao,
I've epoxy to mix,
Bill in MN
[Non-text portions of this message have been removed]
Bolger rules!!!
- no cursing, flaming, trolling, spamming, or flogging dead horses
- pls take "personals" off-list, stay on topic, and punctuate
- add your comments at the TOP and SIGN your posts, snip all you like
- To order plans: Mr. Philip C. Bolger, P.O. Box 1209, Gloucester, MA,
01930, Fax: (978) 282-1349
- Unsubscribe:bolger-unsubscribe@yahoogroups.com
Your use of Yahoo! Groups is subject to the Yahoo! Terms of Service
<http://docs.yahoo.com/info/terms/> .
[Non-text portions of this message have been removed]
abbreviations, initialisms and acronyms here abounding. These AIAs
(acronyms, initialisms and abbreviations) are not only confusing to me, but
I sometimes cannot understand if they are technical terms from the topic
under discussion, or cyber-speak (like BTW). Anyone else have this concern
and some suggestions about how to ease this pain?
-----Original Message-----
From:wmrpage@...[mailto:wmrpage@...]
Sent: Monday, June 03, 2002 10:25 PM
To:bolger@yahoogroups.com
Subject: Re: [bolger] now hull speed, was Re: mast options for Ruben's Nymph
In a message dated 5/31/02 9:43:14 PM Central Daylight Time,
lincolnr@...writes:
> BTW, if I got your equations right, a good single scull would have<http://www.stillwaterdesign.com/Pics/older25c.jpg>
> "D/L" of less than 15. I have seen a "wakeless launch" which probably
> has a "D/L" of around 30, scoot around at maybe 15 knots or so with
> practically no wake. See:
>http://www.stillwaterdesign.com/Pics/older25c.jpg
>My Lotus 1-2-3 spreadsheet tells me that a 21' scull with an all-up weight
of
311 lbs. gives a D/L of 15, so I think you got your sums right. I was
surprised and intrigued by your observation!
Gerr's formulae indicate that this hypothetical scull has a maximum S/L of
3.6, which translates into a "non-planing" top speed of 16.5 Kts. His
displacement SHP formula indicates that it would take approx. .6 SHP to go 6
Kts., possibly attainable by a highly-trained and strong rower, I suppose.
Just how reliable Gerr's formulae are for very low D/L boats at high S/L
ratios is questionable, however, as application of the formulae to the
Stillwater catamaran shows. The displacement formula seems to overstate
power
requirements at high S/L ratios, while the Crouch (planing) formula seems to
understate power requirements at lower S/L ratios.
The Stillwater catamaran is 26' LWL. It has a claimed top speed of 18 Kts.
w/15 SHP long-shaft O/B motor. I assume that the claimed top speed is
accurate, probably a bit conservative - obviously it is a quantity
relatively
easily verified by a buyer who could be expected to complain if the claim
was
not met. (Do you have any insight into why the design requires a long-shaft
motor?)
I've estimated it's gross displacement at 1300# (4 x 200# adults + 15hp O/B
motor + 5 gal. gas tank) or 900# (2 x 200# adults + 15hp O/B motor + 5 gal.
gas tank). This gives D/L ratios of 33 and 23, respectively, S/L maximums of
2.8 and 3.1, which translate to 14.3 Kts and 15.6 Kts top speed. Gerr's
displacement SHP formula gives, respectively, SHP requirements of these
speeds as 23.9 SHP and 22.4 SHP. Conversely, calculated top speeds for 15
SHP
are 12.2 Kts and something in excess of 13.8 Kts.
Crouch's formula for planing boats (I'm rather arbitrarily using C = 200)
gives speeds of something less than 16 Kts. and 19.4 Kts. respectively for
15
SHP. Interestingly, at this power level, the lighter-loaded boat approaches
the 60#/SHP ratio that is the highest #/SHP ratio that Gerr shows on his
Crouch chart.
One could reasonably infer that the performance of low D/L boats at high S/L
ratios falls somewhere in between the displacement SHP curve and the Crouch
SHP curve, perhaps approximating the first up to a certain speed and
approximating the second after that, but I've run innumerable graphs
comparing the two curves for various hypothetical boats and have not
detected
any significant relationship in where the divergence point between the two
curves occurs.
Gerr does not discuss the source of the displacement formula he uses. I
suspect it is derived from tests on full scale naval and maritime merchant
vessels, supplemented by model tests of similar types at the U.S.N. Taylor
basin. Crouch's formula seems to be empirically derived from the performance
of boats of low #/SHP ratios. If I am correct, there is a gap in the data
for
boats of low D/L ratios like Bolger's "Sneakeasy" and others of its ilk.
I believe that the University of Illinois did some wind tunnel testing of
airfoils at low-Reynold's numbers that is of considerable interest to model
airplane builders, while totally devoid of pertinence to commercial airplane
designers. One can hope that perhaps, someday, some suitably equiped
engineering faculty might turn its sights on the phenomenom of low D/L
boats,
like "Sneakeasy".
Ciao for Niao,
I've epoxy to mix,
Bill in MN
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