Sailing boats' Stability, STIX and Old Ratios

[TeddyDiver]

I sended the question here just becouse it might interest someone.

Here’s some data of my motorsailer project. The first part is imperial, displacement with max load. Latter part containg values for STIX is metric, displacement with min load. Values with ? are questimates, either having some flexibility +- or just pure questimate.

Beam 10
LOA 33
LWL 31
Disp in lbs 13000
Disp in cu ft 203
Sail area 533 ?
Sa/D 15.5
MCR 29
CSF 1.7
D/L Ratio 195
SL Ratio 1.6


A gz 35 ?
A s 40 ?
h CE 7 ?
GZ90 0,6 ?
B wl 2,5
B h 3,05
L bs 9,5
F l 0,971104986
m sc 4800
F r 5,142857143
F b 1,920258142

Displacement Length Factor
FDL 0,96
Beam Displacement Factor
FDB 1,01
Knockdown Recovery Factor
FKR 1,33
Inversion Recovery Factor
FIR 1,23
Dynamic Stability Factor
FDS 0,7
FWM 1
FDF 1

STIX 34,9

Both FDF and FWM are 1 becouse of 90 deg downflooding value when the companionway door would submerge (max load). However I’m making the door watertight. The first question is if it makes a benefit for STIX calculation increasing the downflooding angle (actually there wouldn’t be any downflooding angle anymore if all ventilations are self closing).
In the ISO 11812:2001(E) are requirements for “watertight” cockpits in 5.2 “A watertight cockpit or recess shall: have its sills in accordance with clause 8, and  show a degree of watertightness in accordance with clause 9".
In clause 9 the watertightness requirements are:
"All surfaces of watertight cockpits up to hC shall have a watertightness degree 1".
For quickdrain cocpits theres a table of watertightness degrees for different opening places in the cockpit, but not for totally watertight cockpits.
In Annex E there’s tests only for openings in watertightness degrees 2 and 3 not for degree1.
So to my second question: Is it appropriate to use the same table (9.2.1 table 6) for watertight cockpits too, or should degree 1 be used fo all closing appliances, and if, how to test?

Teddy

Edit:
There's some inaccuracy (in my opinion) in the term "watertight" cockpit, or it might have a better description in some other part of the ISO standards. However there's two way's to understand it. Either it's it's a watertight "tub" open above the hight hC, or it can be understod as closed cockpit.
In the first case calling a bath tub without a drainage "watertight" is hilarious , and in the second case just it's just no adequatly prescribed..
Either way, it won't solve my quiz with the deg 1 watertight closing appliance. The links in Guillermos reply were about Solas watertight doors. A bit overkill in 10m motorsailer

[Guillermo]

Teddy,
If you provide me also with the following data:

Total Draught T
Body draught Tc
Moulded depth H
Ballast
Mast height (Over Wl)
Heeling Arm (Hce + Hclr)
Engine Power (Continuous)

I will produce my own guestimate on STIX (as well as some other numbers) and we can compare results.

About your question on watertightness of appliances in cockpit, I have to read first the rules at the office. Maybe next week.

Cheers.

[TeddyDiver]

Hola Guillermo!

Total Draught T 1.48m
Body draught Tc 0.48m
Moulded depth H 1.73m
Ballast 1 200kg cast iron Vcg -1.2m 700kg waterballast Vcg -0.7m
Mast height (Over Wl) 11m
Heeling Arm (Hce + Hclr) 6.8+0.7=7.5
Engine Power (Continuous) 18kW

The engine I currently have for the boat is rated 71hp at 3600rpm. I'm planning to optimize it for 2000 rpm/60-75% of the max power.


BR Teddy

Edit: Seems that there's allways something to add. The plan is for gaff rigg. The mast height doesn't include topsail spar. Hence the high Hce compared to the mast height.

[Guillermo]

OK, thanks.
Asuming engine's power as 40 HP, here some numbers for her.

TEDDY'S MOTORSAILER RATIOS AND PARAMETERS
Length/Beam Ratio (2Lwl + Lh)/3B = 3,16
Lwl/Bwl Ratio Lwl/Bwl = 3,78
WL beam/Body draught Bwl/Tc = 5,21
Mould. D/Hull draught H/Tc = 3,60
Breadth/Mould. D Bmax/H = 1,76
Length/Mould. D Lh/H = 5,81
L float / Lhull Lwl/Lh = 0,94
Ballast/Disp Ratio W/Disp = 0,32
Displacement/Length Ratio D/L = 195,36
Sail Area/Disp. Ratio SA/D = 15,43
SA (metric)/ Power (Imp.) SA/HP = 1,21
Power/ Disp. Ratio HP/D = 3,14 HP/ton
Hull speed HSPD = 7,46 Kn
Potential Maximum Speed PMS = 7,93 Kn
Velocity Ratio VR = 1,06
Best motoring speed (1.1) CSPD = 6,12 Kn
Capsize Safety Factor CSF = 1,70
Motion Comfort Ratio MCR = 29,37
Roll Period T = 3,43 Sec
Roll Acceleration Acc = 0,06 G's
Stability Index SI = 1,13
Angle of Vanishing Stability AVS = 120 º
Upright Heeling Moment UHM = 13624,76 Ft*pound
Righting Moment at 1º HM1º = 325,76 Ft*pound
Heeling Moment at 20º HM20 = 11581,31 Ft*pound
Righting Moment at 20º RM20 = 5846,79 Ft*pound
Dellenbaugh Angle DA = 41,82 º (14 kn wind)


I have more numbers for her I do not dare to post, as they still need serious checking and further development.

As a first impression she seems to be a tender boat, needing more beam at the WL, although this is totally speculative.

Are you sure Hce is as high as 6,8 m?

Cheers

[TeddyDiver]

Thanks Guillermo! It's really big help to get some number crunching and opinion about the project. Some of the ratios are somewhat unknown to me, so I'll make a search and study them a bit..
The beam is allready what it is, and I got to live with it. It was actually restricted to 3m becouse I'll maybe have to trailer it twice a year some 20km.
The Hce 6,8m is my "worst case scenario" in this case with the largest top sail for light air. Without a top sail Hce is 4,8m and sail area 10m2 less.
The tenderness is actually a bit less than looks obvious at first sight. Aft part being very beamy compared to Bwl. It worsens somewhat helm, but is a compromise with the actual purpose of the boat mostly as a coastal cruiser & dive and sportfishing boat (occasionally making passges).

Teddy

[Guillermo]

Asuming Hce = 4,8 m (Anyway, you wouldn't fly the top sail in a 14 kn wind) if you bring beam on the waterline to 2,75 m instead of 2,5 m, the Dellenbaugh angle comes down to around 22º, which although still being somewhat high for a boat this size, is a much more reasonable figure than 41,82º.

Cheers.

[TeddyDiver]

I haven't before paid attention to Dellenbaugh Angle. Quite interesting and shows that I must pay more attention to GM and also consider ways to lower CE. With GM it helps increasing the amount of casted ballast and shaping it to get Vcg lower. Actually I expected, and can live with, some 20-30deg (old fashioned way) heeling angle in avarege sailing conditions but some reconsidering I got to do.

[TeddyDiver]

Looked bit more closely Dellengbaugh Angle. The formula does work realisticly to maybe 25deg heel depending somewhat on the hull geometry. Perhaps with larger heels (tender boats) a preheel should be considered. Let's say 15deg preheeling and measuring then half Bwl from lee side and using this doubled as a virtual Bwl. At the end the preheel angle and calculated angle sum up a more realistic angle.
Any thoughts?

[Guillermo]

But, what's the use for that? Dellenbaugh angle only intends to give a clue on how stiff or tender a boat is, this is, simply an indication on her initial stability, that's all. It does not -and cannot- pretend to say nothing about stability at greater angles.

Cheers.

[TeddyDiver]

Originally Posted by Guillermo

But, what's the use for that? Dellenbaugh angle only intends to give a clue on how stiff or tender a boat is, this is, simply an indication on her initial stability, that's all. It does not -and cannot- pretend to say nothing about stability at greater angles.

Cheers.

Got a though that it could give also some additional information about the stiffness under sails in stonger winds/seas? It's allready obvious in the GZ curves, but maybe as a secondary method.

[Antonio Alcalá]

Hi Guillermo. What do you think about the STIX of this sailboat?

A good friend has a interesting offer but sincerely i´ve never heard something about her: The Neptun 32 .

http://www.boatsandoutboards.co.uk/view/F181112

I have tried to find some information about her, but today i´m not a lucky man

Thank you friend

[TeddyDiver]

Originally Posted by Antonio Alcalá

The Neptun 32 .
I have tried to find some information about her, but today i´m not a lucky man

I found something:

Model Year: 1975
Length: 9,60 m / 31,49 '
Beam: 3,00 m
Draught 1,59m
Weight: 5.000,00 kg or 3,6t? (different source)
Speed 7,29
Material hull: GRP
Material superstructure: GRP
Cabins: 2
Beds: 5
Number of sails: 3
Sail Surface: 40,00 m ²
Tank volume: 160,00 l
Motor: 1 × 14,71 kW or 14hp

BR Teddy

[Antonio Alcalá]

Thanks a lot Teddy, you certainly are a lucky man!!! i suppose this will be fine for Guillermo in order to calculate an estimative stix.

Best winds

[TeddyDiver]

Originally Posted by Antonio Alcalá

Thanks a lot Teddy

Thanks to Google
One remark conserning google searches. Somewhat different results with same search parameters when the country selection is changed. Like google.fi or google.no etc.. even when the search results are in english

[Antonio Alcalá]

Länge über alles: 9,60 m
Länge CWL: 7,50 m
Breite über alles: 3,00 m
Tiefgang: 1,40 m
Segelfläche am Wind: ca. 40 m2
Großsegel: 16 m2
Genua(Rollfock): 22,5 m2
Blister: 51,6 m2
Yardstick: 112
Gewicht: 5.000 kg
Verdrängung: 3.600 kg
Ballast: 1.500 kg
Material: Kunststoff GFK
Baujahr: 1975
Kabine(n): 2 Kabine(n), 5 Kojen, Nasszelle: mit WC und Waschbecken
Anz. Motoren: 1 Diesel mit Welle
Motor/Fabrikat: Bukh
Leistung: 14,71 kW (20 PS)
Brennstofftank: 160 l
Frischwassertank: 180 l
Kategorie: Motorsegler
Liegeplatz: Hooksiel, Nordsee, Deutschland
Ausstattung:
Ballastkiel,Balanceruder mit hydraulischer Radsteuerung und Notpinne, Steuerstand mit Motor-Bedienung und Kompass, selbst lenzender Ankerkasten
Besegelung & Rigg:
Mast, Baum, 1 Vorstag, 1 Babystag, 4 Wanten, 1 Achterstag, Fallen, Fockschot, Großschot, Niederholer, Yachtblöcke, Dirk, Hebelwinschen, Fockleitschienen, Groß-Segel mit Segelpersenning, Rollfockeinrichtung mit Segelpersenning (Anlage und Segel, Neu 1999) , Blister (Neu 1980)
Einrichtung & Aufteilung:
Salon, Polsterbezüge Stoff, Gläserbord , Vorhänge, Kartentisch, Pantryschrank mit Spüle und Pumpe, Achterkajüte, Duschraum/Sanitärraum mit aufstellbarem Vorluk, WC manuell, nach Außenbord abpumpbar, Waschbecken, Kleider- und Wäscheschränke, Schiebeluks für Salon und Achterkajüte sowie Steckschotten mit Flügeltüren,
Pantry:
Gas-Herd 2-flammig, Spüle, Schränke für Geschirr- und Besteck
Nautische Instrumente:
Echolot, Sumlog, Kompass, GPS, Windmessanlage, UKW-Seefunk, Barometer
Planen & Persenninge:
Plichtpersenning, Sprayhood
Technische Ausrüstung:
Schalttafel mit Batterie-Hauptschalter, Sicherungen Ampere-und Voltmeter, 1 Bordnetzbatterie 12 Volt, 105 Ah, Radio, Wassertank mit elektrischer Pumpe und Entlüftung, Tanoylüfter, Innen- und Außenbeleuchtung mit Decksbeleuchtung
Zubehör Badeleiter, Seereling, Bugkorb, Heckkorb Niro, Anker mit Kette und Leine, Bilgepumpe mechanisch, Flagge mit Stock und Halter, Cockpittisch, inkl. Bootsanhänger ungebremst (ohne Straßenzulassung)