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asked and answered

Design 101

We get lottsa questions and sometimes we actually respond. In this case we got the people who actually know something to do it! Britton Ward, from the Farr Design office enlightens us…

Q: Wondering if you think or what you have heard of the new VOR65’s are they faster than the VOR 70’s. Either Max speed and/or overall in most points of sail. I would suspect that the 70’s are faster in big sea state off of the wind.

A: The VO70’s are very impressive machines and we knew from the outset that it would be incredibly difficult to get the VO65’s close in performance given the challenging set of requirements that had to be met.  The short story: make them cheaper, build them faster, and make them significantly stronger and more reliable.  Also make sure they are more identical than any one design ever created and did we mention we would really like them to be able to knock out 500 + nautical mile runs in 24 hours?

Some quick numbers for comparison:

Variable

VO70

VO65

Length on Waterline [m]

21.0

19.5

Sailing Displacement [kg]

17500

16300

Righting Moment @ 25 Heel [kg/m]

38500

32100

So the VO65 is almost 5’ [1.5m] shorter on the waterline than the 70 and weighs 7% less but has 20% less stability at 25 degrees of heel.  Based on these numbers alone you can see that we should be slower in a lot of conditions and that bears up in real life.  Remember we’ve also got less crew, fewer sails, non-overlapping genoas, rig lifted daggerboards and a host of other details that needed to be juggled to balance construction and maintenance costs and a tight build schedule against performance potential.

As you’d expect with 20% less stability, in righting moment dominated sailing conditions the VO65 suffers being as much as 6 –8% slower upwind.  As you free up things get closer and we are seeing similar speeds at deep reaching and running angles in moderate to strong breezes – where stability is a bit less important and the inclined keel pin and off-center water ballast tanks of the VO65 start to light things up. These are the conditions where the big miles are put on the board and we have already seen 24 hour runs of 541 nautical miles and average 1hr speeds of 24 – 27 knots.

So why not just up the stability to close the gap? This is a question we get a lot and it is a critical piece of the design puzzle.  First off, the boat’s righting moment is one of the key cost drivers as it dictates directly how much load the structure must handle, loads on the mast and rigging and even deck hardware sizing which all can quickly drive the cost up and up.  We had a tight stability and cost window to shoot for and we wanted to produce the best performing boat we could in that window.

Because of the emphasis on robustness and reliability the boats have significantly more internal structure than the VO70’s [more bulkheads and longitudinals and a significantly more robust laminate adapted for series manufacturing] all of which means the hull and its structure are quite a bit heavier than a VO70’s.  Keeping displacement down is still the key to achieving the big mileage runs in these offshore races so we grabbed a bit of extra draft to lower the VCG and set about making sure we could satisfy the ultimate stability requirements [knockdowns with keel on wrong side etc.]  while trying to keep the overall displacement as low as possible. We got rid of the auxiliary engine to save weight and cost, added in the wing waterballast tanks to give us a sailing stability boost and tried to grab every performance improving thing we could within the constraints.

The upshot? The VO65 is not just a scaled down updated VO70. They are sensitive to sail trim and selection, weight positioning and ballast placement. They power up quickly and like to heel over both because of the lower stability and the inclined keel axis. Higher heel angles maximize their form stability and the effect of the canting keel and waterballast. (It’s worth noting that even the VO70’s sailed with heel angles in the mid – high 20’s a lot of the time).  The good news? They have survived plenty of gnarly conditions and come through in remarkably good condition.  The racing is incredible close and to top it off, in the right conditions the VO65’s could well get close to challenging the mono-hull 24 hour record.