SJ23 Tech Tip H02 - Hull & Rigging Specifications + Profile Images for the SJ23 Mk I & II

SJ23 Tech Tip H02, (Updated 2024-06-08) Bob Schimmel, Rudy Mayer & Charlie Olden

Hull & Rigging Specifications + Profile Images for the SJ23, Mk I & II.

There are three North American versions of the SJ23;
- the Mk I is equipped with the shoal draft keel and center board. Designed for trailer launch.
- the Mk II is equipped with the fin keel, reinforced floor and 2' taller mast. It goes fast. See Tech Tip H10.
- the Mark III is equipped with a winged keel, reinforced floor and 2' taller mast. It goes like hell. See Tech Tip H10.
The New Zealand version is equipped with a shoal draft keel, a reverse transom that creates room for the outboard in the cockpit & has an inboard rudder. See Tech Tip H10.
The Australian version is equipped with a shoal draft keel, double lower shrouds & two large windows. See Tech Tip H10.

INDEX - Hull, Standing Rigging, Spar, Sails.

NOTE: The article below was excerpted from a SJ23 Mk I brochure that came with Panache when I bought her.

"The trailerable San Juan 23 is a performance oriented cruiser designed for the family, single handler or sailing with friends. The hull lines are a modification of the latest (1977) thinking in level class racing boats with a reasonably generous waterline beam for stability and additional interior room.

A rather flat run reduces pitching in seas and increases performance off the wind. The ballast to displacement ratio is high for a boat of this size to increase stability in heavy airs.

The sail plan is tailored to provide the largest sail area to displacement ration of any production boat her size range. A centerboard is used to optimize windward performance. The San Juan 23 sailboat should easily be the fastest boat of her size and type for those interested in performance and one of the most comfortable for those interested in on board living convenience.

Her deck is styled to optimize the interior spaciousness and be extremely appealing to the eye. The slope of the deck is carried well forward to maximize the V-berth area in a way that a conventional coach roof cannot.

The San Juan 23 was designed to appeal to those who demand maximum sailing ability, comfort, beauty and fun." Don Clark, 1983.

SPECIFICATIONS from the CLARK FACTORY MANUAL. (with some additional info to make it more useful)
HULL SPECIFICATIONS	SJ23 MKI - (shoal draft/Cbrd), 1975 Designer - B Kirby/D Clark Builder - Clark Boat Co. (USA)	SJ23 MKII - (fin keel), 1977 Designer - Bruce Kirby Builder - Clark Boat Co. (USA)
LOA - Length overall.	23' / 7.01 m	23' / 7.01 m
LWL - Length water line.	20' 4" / 6.2 m	20' 4" / 6.2 m
BEAM - Hull width at its widest.	8' / 2.44 m	8' / 2.44 m
WATER DRAFT - How deep the hull sits in the water.	(center board up - 1' 11") (center board down - 4' 9")	4.3' / 1.31 m
DISPLACEMENT - Total weight of empty hull.	2700 lbs. / 1,225 kg	2900 lbs. / 1315 kg
BALLAST - The early hulls had lead pellets encapsulated in resin. The last hulls had lead ingots encapsulated in resin. There might be a small air gap above the ballast.	960 lbs. / 435 kg	1100 lbs. / 499 kg
HULL CONSTRUCTION - Solid fibreglass hull below the toe rail. Above the toe rail the deck is wood cored with 1/4" plywood throughout and solid fibreglass in the major structural areas. The greater curvature of the cabin top and sliding hatch have 3/8" end grain balsa core.		The MKII has a force grid on the cabin sole to support the heavier fin keel of the SJ7.7. It reduces the cabin height a bit.
FREEBOARD - Measured at the front of the cockpit.	~33" / 1 m	~33" / 1 m
CARRYING CAPACITY - There is no capacity plate on an SJ23 but you should restrict how much weight is in the cockpit during rough weather.	3 adults in the cockpit is not a problem provided 2 sit at the front with the third at the helm. While it may be tempting for 2 crew to sit at the aft end of the cockpit, the narrow transom cannot support their weight in anything rougher than "grandmother weather." The extra weight will cause the stern to squat dangerously low. The boat must be sailed level on its lines to achieve hull speed.
AIR DRAFT ON THE WATER - To float under a bridge, (Allow extra for Windex, antenna or waves).	~32.5' / 9.91 m	~34.5' / 10.52 m
TRANSPORT CLEARANCE ON A ROAD - To drive under a bridge.	~12' / 3.66 m	~14' / 4.27 m
STANDING RIGGING - All measurements with turnbuckles 3/4 open. (taken from SJ23 MKI manual). NOTE - While compiling this info, I learned that early version SJ23 spreaders and mast heads are rigged different from later ones. Who would have thought! Unfortunately it would clutter up this document to include all versions, not that I even know them. Shown below is Panache's factory standing rigging from deck to mast head. Panache is the first version SJ23.
MKI (shoal draft keel), 1977	SJ23 MKI - (shoal draft/Cbrd), 1975	MKII (fin keel), 1977
FORESTAY TOP - Swaged eye, e/w 1/4" pin. Locked with a cotter pin. BOTTOM - Swaged 1/4" stud screwed into a Ronstan RF354, body & lower jaw turnbuckle. Fastened to chain plate with a 1/4" T-bolt toggle e/w 1/4" pin. Locked with split ring.	1x19, 1/8" wire, 316 SS. 29' 3-1/4" - top eye to turnbuckle toggle.	1x19, 5/32" wire, 316 SS. ~31.47' - top eye to turnbuckle toggle.
STEM CHAIN PLATE The Stem chain plate is (1/4x1)" SS strap bolted to the hull with 7/16" bolts. It protrudes 2" up from the deck with a 3/8" hole for the forestay.	3/8" hole, 1/4" from top of chain plate.	3/8" hole, 1/4" from top of chain plate.
UPPER SHROUDS TOP - Swaged fork e/w 3/16" pin though a 3/16" tang hole. Locked with cotter pin. BOTTOM - Swaged 1/4" stud screwed into a Ronstan RF354, body & lower jaw turnbuckle. Fastened to chain plate with a 1/4" T-bolt toggle e/w 1/4" pin. Locked with split ring.	1x19, 1/8" wire, 316 SS. 25' 10" - top fork to turnbuckle eye. First version SJ23 - Top of Nicropress sleeve is ~12' 3 3/4" from fork eye at top.	1x19, 5/32" wire, 316 SS. ~27' 10" - top fork to turnbuckle eye.
LOWER SHROUDS TOP - Swaged fork e/w 3/16" pin though a 3/16" tang hole. Locked with cotter pin. BOTTOM - Swaged 1/4" stud screwed into a Ronstan RF354, body & lower jaw turnbuckle. Fastened to chain plate with a 1/4" T-bolt toggle e/w 1/4" pin. Locked with split ring.	1x19, 1/8" wire, 316 SS. 13' 5-5/8" - top fork to turnbuckle eye.	1x19, 5/32" wire, 316 SS. ~15' 5-5/8" - top fork to turnbuckle eye.
SHROUD CHAIN PLATE The Shroud Chain Plates are (1/4x2x9.5)" SS straps bolted to the plywood bulkhead with 1/4" bolts. Plates protrude 1 6/8" up from the deck.	3/8" hole, 3/8" from top of chain plate.	3/8" hole, 3/8" from top of chain plate.
BACKSTAY TOP - Swaged eye e/w 1/4" pin. Locked with a cotter pin. BOTTOM - Swaged 1/4" stud screwed into a Ronstan RF354 body & lower jaw turnbuckle. Fastened to chain plate with a 1/4" T-bolt toggle e/w 1/4" pin. Locked with split ring.	1x19, 1/8" wire, 316 SS. 30' 3" - top eye to turnbuckle eye.	1x19, 5/32" wire, 316 SS. ~32' 3" - top eye to turnbuckle eye.
BACKSTAY CHAIN PLATE The Back Stay chain plate is (1/4x1)" SS strap bolted to the hull with 1/4" bolts through the transom. - A hull could have 2 chain plates if a split backstay adjuster is installed.	1/4" hole, 1/4" from top of chain plate.	1/4" hole, 1/4" from top of chain plate.
SPLIT BACKSTAY ( See Tech Tip F09)	1/4" hole, 1/4" from top of chain plate.	1/4" hole, 1/4" from top of chain plate.
SPAR (measured)	SJ23 MKI - (shoal draft/Cbrd), 1975	MKII (fin keel), 1977
Masthead - Cast aluminum pop riveted or machine screwed to mast.	- Equipped with two 1/4" OD x 1 7/8" long pins to which the forestay & backstay swaged eye fittings terminate. - 4 sheaves (7/16" x 1 3/4" OD) for 3/8" halyard. Turning on 1/4" shaft.	- Equipped with two 3/8" OD x 1 7/8" long pins to which the forestay & backstay swaged eye fittings terminate. - 4 sheaves (7/16" x 1 3/4" OD) for 3/8" halyard. Turning on 1/4" shaft.
Mast - Anodized aluminum.	26' 7" long aluminum extrusion. Cross section (3.5 x ~5)" For Class Racing - A 1/2" wide black band (upper) is to be maintained on the mast, so that the lower edge of the band is to be no higher than 26’ above the mast step. The sail, when hoisted, shall not extend its topmost portion above the lower edge of the band. Another black band (lower) must be maintained on the mast 24’ from the lower edge of the upper band to the upper edge of the lower band. The sail shall not be down hauled down past the upper edge of the lower band.	28' 3"aluminum extrusion. Cross section (3.5 x ~5)" For Class Racing - A 1/2" wide black band (upper) is to be maintained so that the lower edge is no higher than 28' above the mast step. The sail, when hoisted, shall not extend its topmost portion above the lower edge of the band. Another black band (lower) must be maintained on the mast 26’ from the lower edge of the upper band to the upper edge of the lower band. The sail shall not be hauled down past the upper edge of the lower band. NOTE - I doubt there was ever a class created for the MKII. The above measurements are my SWAG.
Mast Foot - Cast aluminum. Pop riveted or machine screwed to mast.	STANDARD FOOT - 5/16" tall (external halyards). OPTIONAL FOOT - ~4" tall (equipped with internal turning blocks for factory internal halyards).
Spreaders - In line, round anodized aluminum.	1 3/16" OD, 1 1/16" ID and approximately 27" long with a metal or vinyl cap on the end to lock the shroud to the spreader. For Class Racing - A spreader shall hold a shroud 26 ¾” from mast (minimum). Cut a replacement tube 26 1/4" long.
Boom - Anodized aluminum.	The original aluminum extrusion, without the goose neck or end cap, is about 10' long. However, the length of a boom may depend on the foot length of your mainsail. Since there are so many different mainsail designs available these days, some owners choose to cut off the excess, preferring to clear the cockpit. Its an easy thing to do. See Tech Tips F20, F12. For Class Racing - A black band, 1/2" wide, shall be maintained on the boom, the inner edge of which shall not be greater than 8’ 9” from the aft edge of the mast. The sail must not be hauled past the inner edge of the band.
Spinnaker Pole - Any type of material but usually aluminum.	For Class Racing - The spinnaker pole shall not exceed 9’ 6”, measured from end to end. A lanyard is permitted. The spinnaker pole must be used and connected to the mast when the spinnaker is set, and must be used on the side opposite to where the boom is carried. See Tech Tip F15.
Whisker Pole - Any type of material but usually aluminum.	A (6-12)' adjustable pole is ideal. Best to have a hook at both ends with a release cable in the middle. For Class Racing - The whisker pole may be of any length and type. It is to be used only with a jib and must be attached to the mast on the side opposite to where the boom is carried.
Pulpit & Stanchions - Polished Stainless Steel.	7/8" diameter tubing. (1" OD).
Toe Rail - Black Anodized aluminum.	1/2" holes spaced 4" apart beside the cockpit and 8" apart forward of cockpit.	1/2" holes spaced 4" apart beside the cockpit and 8" apart forward of cockpit.
SAILS	SJ23 MKI - (shoal draft/Cbrd), 1975	MKII (fin keel), 1977
NOTE - Cloth weight shown below is from the 1980s. Sail cloth today is lighter and stronger than when Clark Sails were made. Don't be fooled into buying the same weight cloth as shown below. Talk to your sail maker.
Main Sail (Clark) - 5.5 oz Dacron. 1 reef. (2 reefs is better). (Reef when heel exceed 20⁰).	105 ft²- luff 24' / foot 8' 9" / leech x' - sheet ?'.	unknown
CLARK JIBS WITH HANKS
A1, Genoa 153% (Clark) - 3.8 oz Dacron with piston hanks. (up to 12 knots wind).	201 ft² - luff 27' 3" / foot 15' / leech 25' 4" - sheets 29'.	unknown
A2, Genoa 135% - 4.5 oz Dacron with piston hanks. (up to 16 knots wind).	~161 ft²- luff 27' 3" / foot ~13' 8" / leech ~23' 8" - sheets ?'. (See NOTE below).	unknown
A3, Genoa 115% - 5.5 oz Dacron with piston hanks. (10-18 knots wind).	121 ft²- luff 24.8' / foot 10' 8.5" / leech 21' 5" - sheets ?'.	unknown
J1, Working Jib 110% (Clark) - 6 oz Dacron with piston hanks. (12-18 knots wind).	95 ft²- luff 24' 10" / foot 8' 6" / leech 22' 4" - sheets ?'.	unknown
J2, Storm Jib - 10 oz Dacron, wire luff with piston hanks. (18+ knots wind).	40 ft²- luff 16' / foot 6' 10" / leech 12' 7" - sheets 31'.	unknown
CLARK JIBS CONVERTED TO FURLING
A1, Genoa ~150% (full hoist) - 3.8 oz Dacron with luff tape to fit foil. Flat cut for roller furling. (up to 12 knots wind).	~199 ft² - luff 27' / foot 14' 10" / leech 25' - sheets 29'.	unknown
A2, Genoa ~120% (full hoist) - 5.7 oz Dacron with luff tape to fit foil. Flat cut for roller furling. (up to 16 knots wind). Tech Tip F21.	~130 ft²- luff 27' / foot ~11' 3" / leech ~23' 9" - sheets ?'.	unknown
J1, Working Jib 110% (full hoist) - 6 oz Dacron with luff tape to fit foil. Flat cut for roller furling. (12-18 knots wind). Tech Tip F21.	~105 ft²- luff 27' / foot 10' 7" / leech 23' 3") - sheets ?'.	unknown
J1, Working Jib 110% (7/8 hoist) - 6 oz Dacron with luff tape to fit foil. Flat cut for roller furling. (12-18 knots wind). Tech Tip F21.	95 ft²- luff 24' 10" / foot 8' 6" / leech 22' 4" - sheets ?'.	unknown
J2, Staysail (Tech Tip F36) - 10 oz Dacron. Wire luff hoisted on Solent stay. (18+ knots wind).	40 ft²- luff 16' / foot 6' 10" / leech 12' 7" - sheets 31'.	unknown
SPINNAKERS
Tri-Radial Spinnaker - 3/4 oz Nylon, 75 Stabilkote.	400 ft²	446 ft²
Tri-Radial Head Spinnaker - 3/4 oz nylon.	350 ft²	~375 ft²
Cruise Spinnaker - 3/4 oz nylon.	380 ft²	~400 ft²
North Sails G-2 Cruise Spinnaker - Big powerful runner. Light to medium wind speed.	368.9 ft² - luff 30' 3" / foot 16' 1" / leech 26' 4"	unknown
North Sails G-3 Cruise Spinnaker - Flat reacher. Medium to heavier wind speed.	313.9 ft² - luff 29' 11" / foot 13' 11" / leech 25' 9-1/2"	unknown
North Sails PHRF Max Asymmetric Cruise Spinnaker	399.5 ft² - luff 30' 6" / foot 16' 11" / leech 25' 8"	unknown
North Sails Cruise Spinnaker - G-0 Very flat genoa like a reacher. Light to medium tight reaching.	399.5 ft²- luff 29' / foot 13' 11" / leech 24' 11"	unknown
STANDING RIG DIMENSIONS
RIG I - Fore triangle height (measured from the toe rail height).	28' / 8.53 m	30' / 9.14 m
RIG J - Fore triangle base.	9.5' / 2.9 m	9.5' / 2.9 m
RIG P - Mainsail luff.	24' / 7.32 m	26' / 7.92 m
RIG E - Mainsail foot.	9.5' / 2.67 m	9.5' / 2.9 m
SA Fore: - Jib.	133² ft / 12.36² m	142.5² ft / 13.24² m
SA Main: - Mainsail.	105² ft / 9.75² m	123² ft / 11.47² m
TOTAL SAIL AREA - (100% fore sail + Main)	234² ft / 22.1² m	266² ft / 24.71² m

SEA TRIAL COMPARISON - During a one hour impromptu "sea trial" in 1999 to compare the performance of the MK I & II, both boats carried the working jib and a single reefed full battened main of approximately equal condition. I sailed Panache, a MK I, solo and was lightly loaded for day sailing. A buddy sailed Our Juan, a MK II, carrying three people and was loaded for family weekend cruising. The two boats sailed together in worsening weather with a thunder storm approaching, so we were cautious. The wave height averaged about 1.5'. On close haul, the MK II pointed about 5⁰ higher than the MK I, stood up better in the heavy puffs, and therefore maintained its heading with slightly more speed. This is due to the lift generated by the deep fin keel and the higher righting moment exerted by the lower extra ballast. The MK I heeled slightly more and was pushed downwind with the heavy puffs. This is partly due to the fact that I was busy and not able to trim things at their optimum when it needed to be done. I hate being held captive by the tiller. The two boats appeared to sail equal on all other points of sail. By the end of the trial both boats were double reefed, dodging the thunder storm as we slid back into the anchorage. Not very scientific, but it illustrates the point. Unfortunately we have never been able to repeat this test in fair weather as the MKII was sold shortly after.

SAIL SELECTION, UPWIND				SAIL SELECTION, DOWNWIND
APPARENT WIND			SAIL SELECTION	APPARENT WIND			SAIL SELECTION
KNOTS	M/H	KM/H	SAIL SELECTION	KNOTS	M/H	KM/H	SAIL SELECTION
0 - 14	0 - 16	0 - 26	Main & 153% genoa.	0 - 12	0 - 14	0 - 22	Main & 153% genoa.
5 - 16	6 - 18	9 - 30	* Main & 135% genoa.	0 - 16	0 - 18	0 - 30	* Main & 135% genoa.
12 - 18	14 - 21	22 - 33	Main & 110% jib.	10 - 18	12 - 21	19 - 33	Main & 110% jib.
15 - 20	17 - 23	28 - 37	Single reefed main with 110% jib.	15 - 25	17 - 29	28 - 46	Single reefed main with 110% jib.
20 - 30	23 - 35	37 - 56	Single or double reefed main with 110% jib.	22 - 30	25 - 35	41 - 56	Single or double reefed main with 110% jib.
30 +	35 +	56 +	Double reefed main with storm jib.	30 +	35 +	56 +	Double reefed main with storm jib.
NOTE: The wind speed and sail selections are suggested by Clark. * Since the 135% genoa was not an option for the SJ23 when Clark created this chart I simply fit this sail within the wind speed range. If you have a 135% genoa then I suggest reducing the top wind speed use of the 153% to save it and prevent heeling beyond 20⁰.

PROFILE IMAGES - Shown below are the profile images of the original Mark I and later Mark II SJ23s from a 1983 San Juan brochure. The Mark I on the left is the original shoal draft version and the Mark II on the right is a later fin keel version. Several thousand MK I's were manufactured, but only a dozen MK II's were ever manufactured, mostly as an experiment over beer, as I understand it. The MK II did not replace the MK I despite the fact that the hulls are identical. The differences are in the shape of the keel, the amount of ballast and the taller mast, all listed in the specifications below. The mast on both models is made from the same extrusion.

SJ23 MKI - (shoal draft/Cbrd), 1975

SJ23 MKII - Fin Keel, (1977)

The "anchor locker" shown in the picture above is of the MK I hull. Access is through an opening from the forward berth.
The deck accessible anchor locker shown at right is for the later versions of MKI and all MKII & MKIII hulls. Access is through a deck lid held down with a bungee cord. The bulkhead is completely sealed to the cabin. The drain is through the stem. A much improved system.

The dotted line outlining a fin keel was never installed. This is likely a conceptual drawing that was abandoned in favour of using SJ7.7 fin keel that was installed. The 7.7M keel was already in production and it is much cheaper to use an existing keel than build a new one. The cabin sole was reinforced with ~2" thick ribs to handle the heavier keel. I think Clark kept the outline of the shoal draft keel on this diagram for comparison purposes. The SJ23 MKII is a fast boat.

This cut away line drawing is an excellent side view of the interior. It applies to the Mark I, II & III. The center board crank was never produced. I presume it was someone's brainchild that never became reality. To function without adding fatigue it needs to be mounted on top of the pedestal and this would get in the way of the table. Nice idea though.

The line drawing of a MKI on the right shows a good profile of the hull and rigging. The dimensions of the small jib reflect 1970s thinking of lowering the height of the sail to lower the centre of effort in a strong wind. The current trend is to use a blade or a tall skinny jib to maintain consistent drive, speed and control during those strong winds. The blade style jib has proven itself over many single handed races through the Southern ocean. It works because there is more steady wind just a bit higher above the waves!

This is the rest of the 1983 brochure showing the teak & holly cabin floor, boarding ladder, transom cockpit drains and aluminum trim on the coach roof and companionway. All these features are part of the later version of the SJ23 MK I. They are all good low maintenance features that lead to greater enjoyment and less maintenance. While I enjoy working on the boat, I don't enjoy being a slave to it which is the reason why I have installed all these low maintenance features on Panache. Although, it took a few years.

The text that was chopped from the top of the image goes as follows.
"Take the performance features of the San Juan 24, add the necessities of easy handling, trailering and launching, add the ability to sustain a cruising family and you have the San Juan 23. Strong due to her unitized hull and deck structure. Stable with her high lift 960 lb. keel centerboard. Superbly equipped with aluminum toe rail, winches, boom vang, mainsheet traveller, fairleads and anchor locker, all standard and comfortable. The competition doesn't come close. More boat for the buck."

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