Hi Eric,
The reason the SC17 was revisited/reinvented/put back into production is because it sold well once and it took no big bucks, no new tooling to bring it out again. The SC17 was designed 25 years ago. All that was done last year was to put new sails on the same rigging and spar and add a spinnaker as an option. This brought the 17 up to the same technology level as the other ARC products.
You asked about something to compare the ARC 17 to, Eric; here are some thoughts.
So, what is the correct PN for the new ARC17? Let's go to the Tradewinds Race results, 2004, and see what we can learn. I suggest we use the last four heats because in the first four heats boats were going around the wrong race course and the 17 used the spinnaker in three out of the first four so things are sort of scrambled. The last four heats are cleaner data and the 17 did not use the spinnaker.
Fifth heat analysis: Using a PN of 70.1 and not using the spinnaker, the ARC 17 finished second on corrected tine. That is 44 seconds behind the D18 and 2min and 27 seconds
in front of the T4.9.
Sixth heat: The ARC17 finished first on corrected time but only by a whisker. The 17 was 22 seconds ahead of the D18 and 1 min and 14 seconds ahead of the H20.
Seventh heat: The ARC 17 finished first again on corrected time. This time it was 50 seconds ahead of the D18 and 1 minute and 55 seconds ahead of the H20.
Eighth race: The ARC17 finished second on corrected time. This time it was 14 seconds behind the T4.9 and 30 seconds ahead of the D18. Tight race!
We could also use the fourth heat: Here the ARC17 finished second on corrected time in between the two T4.9s. The 17 finished 6 seconds behind the first T4.9 and 8 seconds in front of the second T4.9. Tight race again.
Summary: Assuming this crowd of sailors sailed their boats to their respective PNs, it looks to me like a PN of 70 for the ARC17 without spinnaker is a better number than 70.1 with spinnaker. This would make the PN for the ARC17 with spinnaker equal to 67.2.
Here is some more interesting information comparing PNs of boardless beach cats of similiar size.
H16, actual length 16ft and 6ins. PN = 76.1
P16, 16ft PN = 77.5
P18, 18ft PN = 74.5
SC17, 1980 intro. 17ft PN = 73.0
ARC17, 2004 intro. 17ft PN* = 70.0 sloop, new
sail plan
ARC17, 2004 intro. 17ft PN* = 67.2 with spinnaker
The 2004 ARC17 is the same boat as the 1980 SC17 with new sails and spinnaker.
Conclusion: The SC17 always has been outstandingly fast beach cat for its size. History tells us that. The new ARC 17 appears to be even faster.
* PNs calculated based on one,(1), regatta and subject to change as more data is accumulated.
Good Sailing, Eric
Bill
PS In the future, Eric, I am going to respond to questions on Aquarius products on the owners.aquarius-sail.com web site. When I talk about these products here, I get pounded with questions via e-mail from individual SC/ARC owners and I end up answering the same question at least 10 times. It is wearing me out.
Hi Carl,
I want to help you out a little with this SC15. The 15 plug was made from the 17 plug. Two feet was cut off the back end of the 17 plug and then the keel rocker in the aft end was increased, rolled up to a new transom at 15ft to add displacement in the aft end of the hull. The important thing for this discussion is that the front end of the hull was not changed. This means that the 15 like the 17 has the hull lifting surface, deep vee hull shape, in the front 6ft or so of the hull. The middle 5ft is transition shape from deep vee to round and the aft 4ft is a round hull bottom shape, therefore no lift here. Same 2x size rudder is on 15 and 17. This was all done in 1979/1980 to produce a boardless beach cat that would TACK. The aft end of any hull has to be free to slide sideways for a boat to tack quickly and easily. The no lift aft hull end automatically puts the lift burden on the rudder which is a high aspect ratio foil, therefore low induced drag. The rudder is like a steering daggerboard. This boat design is another example of shared lift done in 1979/1980 to make a boardless beach cat tack well.
Now here we are in 2004 and we want to put a spinnaker on this boat. Well how about that; aren't we lucky. This boat already has the hull CLR well forward, like 3 to 4ft back from the bow so adding the spin is "no problem". This boat will exhibit no lee helm with spin up because the sail plan CE will always be behind the hull CLR.
The motto of the best SC15 an 17 sailors is "drive those bows". By that they mean trim the boat out with the waterline halfway up the stem. Always keep the waterline tape underwater at the bow.
This hull design scheme has also led to an increased boat speed hull shape sailing to windward for boardless beach cats. The normal boardless beach hull shape has its lifting hull shape for the full length of the hull. The underwater aspect ratio for this hull shape is the average depth divided by the waterline length. These are numbers like .75ft deep by 16ft long. The induced drag due to generating lift is inversely proportional to this number. This number in this example has a value of 21.3 and it is a multiplier in the induced hull drag calculation. In the case of the SC15 and 17 this multiplier is made up of two parts. One is the hull induced drag and the other part is the rudder induced drag with each lifting body carrying half the total lift force. For the SC15 and 17 the hull induced drag aspect ratio is something like .75ft deep by 7ft long which leeds to a induced drag multiplier like 9.3. The rudder aspect ratio is like 2ft deep by .75 ft wide which leads to an induced drag multiplier like 0.375 acting on 50% of the lift force. So the induced drag coefficient for the hull plus rudder generating lift on a SC15 or 17 is equal to 0.5 x 9.3 plus 0.5 x 0.375 or a total of 4.84. This compares to 21.3 for a normal beach cat hull design. Needless to say, the hull drag on the SC15 and 17 is significantly less than the other beach cats. This shows up when comparing PNs between boats of similiar size. The SC17, which has a PN base, its PN is 4 to 5% lower than other beach cats of similiar size. The hull induced drag makes the difference.
I want you to understand what you have got, Carl, and why it sails like it does.
Good Sailing,
Bill