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1980 San Juan 21 MKII

Listed
Expired
$4,600 USD

Seller's Description

1980 San Juan 21 MKII with Trailer

Good Sails, Swing Keel, Mercury 3.5 HP

ACCOMMODATIONS:

V-Berth Forward Two Quarter Berths Room for a Porta-Potti Capable of Overnighting

SAILS/RIGGING:

Mainsail with Cover in good Condition Two Headsails Transom Mounted Rudder with Tiller Swing Keel Trailer

Equipment: The following observations were posted on Sailnet Forum and provide insights from a San Juan owner:

The Mark II is distinguished from the Mark I by the fact that coach roof & the deck are all at one level continuous to the edge of the boat.

San Juans are moderately well built.

It is a light boat compared to many of its competitors which makes it quick in light airs as the keel is only about 400 lbs. It is a retractable keel that swings up into a raised trunk inside of the cabin. When fully retracted, the boat only draws about 12 inches of water, allowing it to beach easily.

The cockpit on the Mark II is reasonably spacious. The mainsheet is on the floor at the stern of the cockpit when traditionally rigged.

There is a lazarette in the back of the boat for storing gas, anchors, etc. It is sealed off from the rest of the cabin so you can store semi-noxious materials there without concern.

There is a basic electrical system that consists of cabin lights, accessories and running lights.

In general, this boat should be considered a daysailor with the potential for overnight excursions.

Putting in and taking out is easy since you do not have to have a deep water ramp and no tongue extension is required for this boat.

Parts are no problem with this boat as there is still an active aftermarket and most parts have found modern replacements by major manufacturers.

In general the SJ 21 is somewhat unique in its class. There are an abundance of 21 foot pocket cruisers, but only a few other large scale manufactured boats offer the flush keel in this length. It does well in races in light airs, but is pretty tender in heavier air. It is a great boat to step into from dinghies given the easy of trailerability and the ability to overnight.

Specs

Designers
?
Builders
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Associations
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# Built
?
Hull
Monohull
Keel
?
Rudder
?
Construction
?

Dimensions

Length Overall
20 11 / 6.4 m
Waterline Length
?
Beam
6 11 / 2.1 m
Draft
4 0 / 1.2 m
Displacement
?
Ballast
?

Rig and Sails

Type
?
Reported Sail Area
?
Total Sail Area
?
Mainsail
Sail Area
?
P
?
E
?
Air Draft
?
Foresail
Sail Area
?
I
?
J
?
Forestay Length
?

Auxilary Power

Make
?
Model
?
HP
?
Fuel Type
?
Fuel Capacity
?
Engine Hours
?

Accomodations

Water Capacity
?
Holding Tank Capacity
?
Headroom
?
Cabins
?

Calculations

Hull Speed
?

Hull Speed

The theoretical maximum speed that a displacement hull can move efficiently through the water is determined by it's waterline length and displacement. It may be unable to reach this speed if the boat is underpowered or heavily loaded, though it may exceed this speed given enough power. Read more.

Formula

Classic hull speed formula:

Hull Speed = 1.34 x √LWL

A more accurate formula devised by Dave Gerr in The Propeller Handbook replaces the Speed/Length ratio constant of 1.34 with a calculation based on the Displacement/Length ratio.

Max Speed/Length ratio = 8.26 ÷ Displacement/Length ratio.311
Hull Speed = Max Speed/Length ratio x √LWL

?
Classic formula: ?
Sail Area/Displacement
?

Sail Area / Displacement Ratio

A measure of the power of the sails relative to the weight of the boat. The higher the number, the higher the performance, but the harder the boat will be to handle. This ratio is a "non-dimensional" value that facilitates comparisons between boats of different types and sizes. Read more.

Formula

SA/D = SA ÷ (D ÷ 64)2/3

  • SA: Sail area in square feet, derived by adding the mainsail area to 100% of the foretriangle area (the lateral area above the deck between the mast and the forestay).
  • D: Displacement in pounds.
?
<16: under powered
16-20: good performance
>20: high performance
Ballast/Displacement
?

Ballast / Displacement Ratio

A measure of the stability of a boat's hull that suggests how well a monohull will stand up to its sails. The ballast displacement ratio indicates how much of the weight of a boat is placed for maximum stability against capsizing and is an indicator of stiffness and resistance to capsize.

Formula

Ballast / Displacement * 100

?
<40: less stiff, less powerful
>40: stiffer, more powerful
Displacement/Length
?

Displacement / Length Ratio

A measure of the weight of the boat relative to it's length at the waterline. The higher a boat’s D/L ratio, the more easily it will carry a load and the more comfortable its motion will be. The lower a boat's ratio is, the less power it takes to drive the boat to its nominal hull speed or beyond. Read more.

Formula

D/L = (D ÷ 2240) ÷ (0.01 x LWL)³

  • D: Displacement of the boat in pounds.
  • LWL: Waterline length in feet
?
<100: ultralight
100-200: light
200-300: moderate
300-400: heavy
>400: very heavy
Comfort Ratio
?

Comfort Ratio

This ratio assess how quickly and abruptly a boat’s hull reacts to waves in a significant seaway, these being the elements of a boat’s motion most likely to cause seasickness. Read more.

Formula

Comfort ratio = D ÷ (.65 x (.7 LWL + .3 LOA) x Beam1.33)

  • D: Displacement of the boat in pounds
  • LWL: Waterline length in feet
  • LOA: Length overall in feet
  • Beam: Width of boat at the widest point in feet
?
<20: lightweight racing boat
20-30: coastal cruiser
30-40: moderate bluewater cruising boat
40-50: heavy bluewater boat
>50: extremely heavy bluewater boat
Capsize Screening
?

Capsize Screening Formula

This formula attempts to indicate whether a given boat might be too wide and light to readily right itself after being overturned in extreme conditions. Read more.

Formula

CSV = Beam ÷ ³√(D / 64)

  • Beam: Width of boat at the widest point in feet
  • D: Displacement of the boat in pounds
?
<2: better suited for ocean passages
>2: better suited for coastal cruising

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