Iw 31
IW Varvet · Sparkman & Stephens · 1975
Updated
The Iw 31 is a 9.30 m heavy displacement racing yacht designed by Sparkman & Stephens and built by IW Varvet, first launched in 1975. It races in Class C.
Length
9.30 m
30′ 6″
Beam
2.68 m
Draft
1.68 m
Displacement
3.7 t
Sail area
46 m²
On the podium
Where a Iw 31 finishes when she goes racing.
0
Wins
0
Seconds
0
Thirds
1
Starts
Not enough races yet for a percentage — these are the counts so far. We keep collecting results, so this will fill in.
Read from 1 start by 1 boat between 2023, counting races with six boats or more.
Recent regattas
The latest events where a Iw 31 was on the start line, named as the organisers publish them.
KaaVe Marskär Open2023
Raced one we are missing?
Report a regattaRound the buoys, or offshore
A short windward-leeward and a night at sea ask different things of a boat. Here is how this one does in each.
Round the buoys
—
Not enough data yet: no races of 10 NM or less carry a published distance.
Offshore & coastal
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Not enough data yet: no races over 10 NM carry a published distance.
Who she races against
The designs a Iw 31 actually lines up with, most often first. The bar shows how those meetings ended.
Met too few times for a figure:
X-35 (2 meetings), X-332 (1 meeting), Arcona 340 (1 meeting), Bavaria Match 35 (1 meeting), Ridas 31 (1 meeting), Swan 36 (Stephens) (1 meeting), Finngulf 41 (1 meeting)
Speed at every angle
The shape of this design's speed, drawn from the measured fleet. Pick a wind and watch it stretch.
Upwind VMG
4.28
40°
Beam reach
6.99
90°
Broad reach
7.62
135°
Downwind VMG
6.83
170°
Speed in knots at 20 knots of true wind. Green marks the angles that pay: the closest useful beat and the deepest run worth sailing.
Where it wins and where it pays
Every boat is judged against its own measurements — length, weight, sail area. The quicker those say it should be, the more it has to deliver just to break even. Going fast is not enough: it has to go faster than its own numbers promised.
There is no obvious weak spot here. It rewards preparation and crew work more than it rewards picking the right day.
Where it gains
Its best ground is on the beat in the light stuff, where it outruns what it looks like on paper. It holds that advantage running deep as well, so the gain is not down to one leg of the course.
Where it pays
It falls short off the wind when it blows, giving away time it never gets back. That is weight that has to be driven rather than released.
Above the line it delivers more than promised and gains on the fleet. Below, it falls short. Move the wind: plenty of boats sit on one side in the light and the other when it blows.
Full width is 0.4 kn either way.
At 10 knots this design makes back more than its rating asks on the upwind.
How fast is a Iw 31
Boat speed in knots, by true wind angle and wind strength.
| Angle | 6 kn | 10 kn | 14 kn | 20 kn |
|---|---|---|---|---|
| Beat VMG | 2.94 | 3.92 | 4.24 | 4.28 |
| 52° | 4.45 | 5.70 | 6.08 | 6.16 |
| 60° | 4.67 | 5.88 | 6.26 | 6.36 |
| 75° | 4.81 | 6.04 | 6.46 | 6.69 |
| 90° | 4.71 | 6.07 | 6.55 | 6.99 |
| 110° | 4.77 | 6.23 | 6.79 | 7.25 |
| 120° | 4.61 | 6.19 | 6.83 | 7.53 |
| 135° | 4.20 | 5.92 | 6.70 | 7.62 |
| 150° | 3.63 | 5.42 | 6.43 | 7.34 |
| Run VMG | 3.15 | 4.73 | 5.88 | 6.83 |
How they are set up
The range each sail spans across the fleet.
Roughly half carry a folding propeller. Crew weight is declared around 330 kg.
Rigging
Iw 31 rig and sail dimensions
A Iw 31 carries 9.94 m of mainsail hoist on a 2.98 m boom, a forestay 11.55 m above the deck. Typical figures across the 2 boats measured under the current VPP, with the range each one spans.
Rig
Sails