|
|
20-05-2019, 17:34
|
#1
|
Registered User
Join Date: Dec 2018
Boat: C&C 27 Mk V
Posts: 153
|
How's your math?
SA/DSPL for a 4400# boat w/283 sq ' sail area?
|
|
|
20-05-2019, 18:23
|
#2
|
Moderator
Join Date: Sep 2014
Location: Channel Islands, CA
Boat: 1962 Columbia 29 MK 1 #37
Posts: 14,262
|
Re: How's your math?
My ol' Columbia 24 had a SA of 285 and a D of 4000 or a little over which supposedly gave it a SA/D of 18 so I'll bet yours is 17 as a guess. Otherwise here's the formula, good luck!
To then find the boat's SA/D ratio, just divide its sail-area in square feet (SA) by its displacement in cubic feet taken to the two-thirds power (SA/D ratio = SA ÷ DCF↑.667)
__________________
DL
Pythagoras
1962 Columbia 29 MKI #37
|
|
|
20-05-2019, 18:24
|
#3
|
Registered User
Join Date: Jun 2018
Location: stuck in Florida for vaccinations, bot stuck in the Chesapeake
Boat: Vanguard 33
Posts: 103
|
Re: How's your math?
15.5
Sailboatdata.com will give you all the answers ye seek
|
|
|
20-05-2019, 18:29
|
#4
|
Moderator
Join Date: Sep 2014
Location: Channel Islands, CA
Boat: 1962 Columbia 29 MK 1 #37
Posts: 14,262
|
Re: How's your math?
OK, got it, 16.8. Hey I was pretty darn close!
What did I win?
https://wavetrain.net/2011/03/17/cru...acement-ratio/
__________________
DL
Pythagoras
1962 Columbia 29 MKI #37
|
|
|
20-05-2019, 19:22
|
#6
|
Registered User
Join Date: Feb 2015
Location: Sweden
Boat: 73´ULDB custom ketch
Posts: 1,069
|
Re: How's your math?
Quote:
Originally Posted by Drinky Crow
|
Reasonable is the word 17 is not bad for a small cruising boat.
|
|
|
20-05-2019, 19:49
|
#7
|
Senior Cruiser
Join Date: Nov 2013
Location: Port Moresby,Papua New Guinea
Boat: FP Belize Maestro 43 and OPBs
Posts: 12,888
|
Re: How's your math?
Quote:
Originally Posted by Drinky Crow
SA/DSPL for a 4400# boat w/283 sq ' sail area?
|
DCuft = 4400 / 64 = 68.75 ft^3
DSPL = DCuF ^2/3 = 16.78
SA/DSPL = 283 / 16.78 = 16.87
|
|
|
20-05-2019, 19:53
|
#8
|
Registered User
Join Date: Mar 2013
Location: Slidell, LA
Boat: Beneteau First 375
Posts: 447
|
Re: How's your math?
You'd be surprised how much that ratio can vary with fairly small changes in the displacement.
|
|
|
20-05-2019, 20:01
|
#9
|
Registered User
Join Date: Jun 2016
Location: Brisbane Australia
Boat: Schionning Waterline 1480
Posts: 1,987
|
Re: How's your math?
Is this to give a performance comparison ?
What if your comparing a short fat boat to a long skinny one.
__________________
Regards
Dave
|
|
|
20-05-2019, 20:03
|
#10
|
Moderator
Join Date: Sep 2014
Location: Channel Islands, CA
Boat: 1962 Columbia 29 MK 1 #37
Posts: 14,262
|
Re: How's your math?
You're comparing it to an Olson 25?
__________________
DL
Pythagoras
1962 Columbia 29 MKI #37
|
|
|
20-05-2019, 21:40
|
#11
|
Senior Cruiser
Join Date: Nov 2013
Location: Port Moresby,Papua New Guinea
Boat: FP Belize Maestro 43 and OPBs
Posts: 12,888
|
Re: How's your math?
Quote:
Originally Posted by sandy stone
You'd be surprised how much that ratio can vary with fairly small changes in the displacement.
|
On a percentage basis, I'd be surprise if it wasn't less than linear.
Let's see.
-20% = 3520lb = 19.57 = +16%
-10% = 3960lb = 18.09 = +7%
-5% = 4180 = 17.45 = +3%
100% = 4400lb = 16.86
+5% = 4620 = 16.32 = -3%
+10% = 4840lb = 15.82 = -6%
+20% = 5280lb = 14.93 = -11%
|
|
|
21-05-2019, 00:16
|
#12
|
Registered User
Join Date: Dec 2018
Boat: C&C 27 Mk V
Posts: 153
|
Re: How's your math?
Quote:
Originally Posted by Don C L
You're comparing it to an Olson 25?
|
Comparable insomuch as price and fit-to-the-slip but no, completely different animals....all boats being a compromise.
.........
|
|
|
21-05-2019, 02:49
|
#13
|
Senior Cruiser
Join Date: Mar 2003
Location: Thunder Bay, Ontario - 48-29N x 89-20W
Boat: (Cruiser Living On Dirt)
Posts: 49,085
|
Re: How's your math?
According to Carl’s Sail Calculator v3.55. Performance Comparison
➥ Sail Calculator Pro v3.54 - 3200+ boats
Mirage 25 vs Olson 25
SAIL AREA*: Mirage 25 =275 ~ Olson 25 = 308
DISPLACEMENT: Mirage 25 = 4226 ~ Olson 25 = 2900
SA/DISP*: Mirage 25 = 16.83 ~ Olson 25 = 24.23
*The sail area is the total of the main sail and the area of the front triangle. I cannot be sure that this datum was entered correctly for each listed boat.
High performance boats would be around 18 or higher SA/D.
__________________
Gord May
"If you didn't have the time or money to do it right in the first place, when will you get the time/$ to fix it?"
|
|
|
21-05-2019, 03:28
|
#14
|
Registered User
Join Date: Feb 2015
Location: Sweden
Boat: 73´ULDB custom ketch
Posts: 1,069
|
Re: How's your math?
Just one basic fact regarding boats (there are exceptions):
Faster = less comfortable
|
|
|
21-05-2019, 04:59
|
#15
|
Senior Cruiser
Join Date: Nov 2013
Location: Port Moresby,Papua New Guinea
Boat: FP Belize Maestro 43 and OPBs
Posts: 12,888
|
Re: How's your math?
Quote:
Originally Posted by MartinR
Just one basic fact regarding boats (there are exceptions):
Faster = less comfortable
|
That kind of goes against the concept of hull speed as a factor of LWL.
As a general rule:
The bigger the boat, the faster.
The bigger the boat, the more comfortable.
|
|
|
|
|
Thread Tools |
Search this Thread |
|
|
Display Modes |
Rate This Thread |
Linear Mode
|
|
Posting Rules
|
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts
HTML code is Off
|
|
|
|
Advertise Here
Recent Discussions |
|
|
|
|
|
|
|
|
|
|
|
|
Vendor Spotlight |
|
|
|