I563 Design data : interpretation

[Andrew]

G'day all, hope you are not holed up too much! (as i have)

Been studying Design data to compare different boats.

Studied it because i'm interested in where the safety envelope may be for coastal cruising, boat performance and comfort (or not)

Found the Investigator 563 made it onto the world-stage within the "Sailboat data" website!

https://sailboatdata.com/sailboat/investigator-563

Here are some figures with interpretations i got from the internet (notebook form at the moment). Most are good (but the capsize screening seems a bit contradictory.)

SA/D = sail area/displacement ratio. I563 = 21 : "good sailing performance"

B/D = ballast/displacement ratio. (righting moment) I563 = 46 : "heavy bluewater boat" (high righting moment)

D/L = displacement/length ration. I563 = 165 : "Moderate displacement"

Comfort ratio. I563 = 11.4 : "Lightweight racer" (this is where it doesn't sound quite right to me, for its size it seems fairly comfortable..but then they're comparing it to large yachts)

Capsize screening. (Bought in for racing yachts after fastnet disaster) below 2 is good. I563 = 2.33 (could be prone to capsize offshore). This is understandable due to its very short length)

I was interested in studying this design stuff to quantify to good feeling i have of the design for coastal cruising (while picking the weather and wind direction etc). I have taken "Teria" upto what i think are near her upper limits so far (beating into >30 knots with sharp >2m waves of a headland, which got so uncomfortable/ plain scary! and required a turn-tail downwind run back to shelter! never looked like capsizing. perhaps smaller headsail and extra reef in mainsail could fix this and make an I563 operate above 30 knots)

This sailboatdata is also very useful if you are thinking of a larger cruising boat design, how seaworthy it is and whether its an overweight slug vs good performer. (So far i've found Tophat25's, H28's tick the good coastal cruising boxes plus sail well).

[snoopebj]

Interesting study Andrew. I’m not good at number crunching but one stat that always stood out for me in the Investigator was the ballast displacement. A huge 46.16 ratio. That’s more than most keel yachts and almost double most trailer sailers. I also discovered a compare section in saildata where you can search up to three boats and compare data. I put in the careel 18 and sonata 6 popular t/s boats. You can then understand why the Investigator is a good choice for limited offshore work.
My experiences crewing in other t/s careels mcgregors castles etc is they’re often faster, point better, roomier than the Investigator but still have that t/s feel. I’m much more confident in the Investigator as it handles like a yacht not a large sailing dinghy.
Obviously there are are limitations with a 563 length boat and like yourself have pushed its limits a few times much to my missus’ horror. I have to admit though when out there on my own in the swells off the Five Islands I get the thrill and excitement of a boat completely at home fighting the elements. It’s very hard after that just sailing and pottering around on the lake.

[Ozzie]

The few times I’ve been sailing or motoring in really crook weather the boat design has not worried me as much as the possibility of gear failure. Limits, when found are often at a rather inconvenient time. Also on the lake there is often not a lot of time between gear failures and running out of water failures.

Even well maintained gear/rigging/ motor can fail if pushed hard enough. I remember the PITA getting my mast back on board when a shroud broke on the mooring and that was calm still water. That is why in a serious situation you have wire cutters and use them before your mast takes up residence on your v berth via your hull . Obviously seagoing sailboats are rigged heavier and serviced more......but of course that’s not always true and the results are regularly reported and sometimes tragic.

My main issue personally is I don’t sail in heavy weather enough to be confident I’m going to handle it well if things did go wrong. Sorry Emrys, disregard this post ...I’m not trying to add more to your paranoia file

I should add that even when I’ve been over canvassed and clobbered by a bullet I always felt confident the boat wasn’t going anywhere bad. Poseidon bless Kevin Shepherd.

[Andrew]

Thanks for finding the comparison function. Yes the Investigators main numbers are quite good, and compare favourably with some small coastal cruiser keelboats eg. Albin Vega 27fter. Though these small keelers have about 2-3x the comfort ratio of the Trailer sailers. The Investigators comfort ratio of 11.4 seems relatively good for a small TS, compares with 10.6 for a Careel 18 and 7.68 for a Princess 18. So even when it chops up a bit it's easier on the crew.

So we will probably pop backup from a bullet-knockdown no matter where the crew ends up (like in the lee scuppers!)

[Andrew]

Delved a bit more into "Sailboat data".

"S#" is another 'calculation' value (But they haven't calculated the S# for Investigator's as yet, its there for many other sailboats though)

On the right top of the "sailboat calculations" box, i clicked on "definitions" link..(which revealed..)

S# is approximately "boat performance"

<2 = slow, under canvased
2-3 = cruiser
3-5 = cruiser racer
> 5 = fast racer

In the "definitions" link, There are also all the definitions of SA/D, Bal/D, Displ/L, Comfort ratio, Capsize sf, (and S#) in huge detail, (including all the formulas used, the realm of maths gurus.)

Below that is for multihull enthusiasts.
BN = "Bruce number" = power to weight ratio
KSP = "Kelsall sailing performance" = (speed the cat/tri does in 10knots of wind).