Saturday, July 1, 2017

Can Wharrams Go To Windward?

Of course I know that they can, but I keep coming across "informed" commentary stating as received wisdom that Wharram cats perform very poorly to windward.

This issue has interested me for a long time. When I was growing up sailing with my Dad, I was often told that multihulls, and Wharrams in particular, were death traps only good for off the wind sailing (also that fiberglass would never take on as a boat building material!).

After reading a new thread on this recurring topic on "Wharram Builders and Friends", I decided to record another gps track directly up wind the next time the opportunity presented itself.



Last October I was in the North Bay off San Quentin, and diverted from my journey for a run of several nautical miles directly into a NW breeze coming out of San Quentin Bay (see first image). The wind at the start of the run was about 10 knots true, and built to around 15 knots true by the end of the run next to the Corte Madera marsh (i.e. from right to left in the picture). The tide had just turned, and so we were heading directly into about a knot of outgoing tide, and there was a small chop.




Running the video of the run (above) recorded in GPSAR software there is a legend showing:

- V = speed in knots
- Angle = angle to the wind in real time
- Average Speed = average speed in knots measured over 1,000 meters (1 kilometer, or just over 1/2 of a nautical mile)
- Average VMG = average velocity made good in a direct line upwind over 1,000 meters
- Average Angle = average angle to windward measured over 1,000 meters

The streaming graph at the bottom of the window is a second measurement of average VMG, this time over the default GPSAR distance setting of 500m.

Over the run, speed ranges up to 8 knots and the angle to the wind in real time swings widely from the the mid 30s to high 60 degrees. The problem with using software for measurements like this is that it cannot account for windshifts in the real world - it records the numbers as if the wind was fixed at 290 degrees (in this case). So the boat is not really sailing at 35 degrees to the wind (or 69 degrees), instead the wind has veered in real time in the real world. To get around this problem I set the average angle and speed recordings over 1,000 meters - using a large distance will correct for the small swings in sailing angle caused by wind shifts.

This means that the last two numbers are the most useful: average angle to the wind and average VMG over 1,000 meters. The average angle of the (true) wind ranges from 48 to 58 degrees, and actual progress to windward (VMG) ranges from around 3 to over 4 knots.

Note that progress to windward is about a knot slower on the northerly tacks than it is on the westerly tacks. This reflects how much the boat is sailing into the outgoing tide - the northerly tacks are more directly into the tidal flow.

So what does it all mean? On this day, Little Cat was tacking through from a best of 96 degrees to a worst of 116 degrees, and maintaining an average 3 - 4 knots progress directly to windward. Is this any good or not?

Working in our favor was a breeze in the golden range of 10-15 knots true, and Little Cat had a freshly painted (smooth) bottom. Working against us was a one knot tidal current, a small short chop in San Quentin Bay, and a mainsail which no longer has such a great shape after a lot of use. In other words, conditions were a good approximation of real world conditions.

In my opinion, these tacking angles are pretty good, and compare favorably to most sailing company - even performance multis can be hard to tack though better than 50 degrees when conditions are less than ideal.


Ideal conditions for a Wharram cat are flat water, no tide, and wind in the golden range of 10-15 knots. In such conditions, I think a a Tiki should tack through 90 degrees. With all of the water movement in The Bay, such conditions don't occur often, so Little Cat doesn't get many opportunities to try. In fact, conditions in The Bay, are more often "anti-Wharram" with strong tide and currents, a shallow-water chop and very high winds, very light winds, or constantly changing between the extremes. In these more typical conditions, tacking performance on the Tiki can be disappointing - for example, on a recent trip to Drake's Bay we were tacking through 130 degrees.

However, most sailboats (except racing boats) find strong head currents, short chop, or very light winds, hard to tack through; so overall I think that the Tiki can hold its own to windward when conditions allow. One caveat is that the Tiki is not an easy boat to trim to windward, in my opinion. I have sailed other boats that sail as well or better to windward with a lot less attention to trim and tiller.

1 comment:

  1. This is an interesting and informative article. Your tacking angles aren't that bad at all. Tiki 21 looks like a pretty capable boat.

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