Mr. Roberts RE: ARC-17

Hi Dave,
I will try to answer your questions on the ARC17.
The ARC17 is the same boat, hulls, mast etc., as the SC17 with rigging upgrades.
The boat is 8.5ft wide. PN adj = 0.995
It has a square top mainsail. PN adj = 0.980
The self tacking is smaller in area than the old SC17 jib. No PN adj. factor?
Does a 1.005 factor apply?
It has a spinnaker with launcher and retraction system.
PN adj = 0/.960
This is the boat with all the bells and whistles.

Therefore the adjusted PN = .960 x 0.98 x 0.995 x 0.73 =
0.68335 for two persons sailing the boat.
For single handing add the 0.974 factor and the PN is 0.66558.
Since the same boat is sold as a one person or two person boat, sailing it either way is well within class rules.
As far as the difference in boat feel goes, there should be very little. The boats are the same width so the roll inertias are very similar and the quickness that the boats fly a hull will be very similar. Fore and aft the boats will feel similar because even though the 17 is shorter it has taller bows, which tend to restore the pitch inertia lost due to the shorter hulls. Also the 17 has clean, elliptical topsides, decks, that will split the water just as easy as the keel. Therefore you don't get the "slam on the brakes effect" when you drive the bow under. The boat recovers really sweetly.
Look at the one picture of the SC20TR in the Steeple Chase Race in Cat Sailor. The leeward foredeck is underwater. Are the sailors in that picture diving for the rear beam? No, there is no problem and no reason for alarm on this hull design. The elliptical foredeck splits the water easily and this boat just keeps right on ripping. Another hull design would be doing a forward cartwheel in this same situation.
Good Sailing,
Bill

Hi Bill,
I want to thank you for taking the time to answer my questions. I didn't realize that going "smaller" with regards to a boat was going to a more difficult decision that if I were looking for a "bigger" boat.

With a lot of solid input from yourself and other helpful sailors....I am going in the right direction with this project.

Thanks again,
Dave

Bill,

How was the DPN of 70.4, that was used at Tradewinds this weekend, arrived at?

Good question Stingo!
I was sailing open class this weekend on my stock H-20 and got killed by the PN#. However, the course felt short and the wind was good, the ARC 17 may have not have been depowering as much as the H-20. The H-17'2 were also very fast upwind this weekend, many rounding A mark before the Arc, but then got clobbered down wind.

I'm really sorry here but what happened at Tradewinds ?

First we calculated the rating of the Arc-17 at :

"adjusted PN = .960 x 0.98 x 0.995 x 0.73 =
0.68335 for two persons sailing the boat"

therefor = 68.3

(At one time I saw number like 66.5 fly past)

Than we sail the boat in the tradewinds off 70.2 ?

Whats up ?

Wouter

Results would have looked like this if the DPN of 68.3 was used.

R1 R2 R3 R4 R5 R6 R7 R8 TOTAL
OPEN D18 4203 Terry Fondrk Judy Fondrk 1 2 3 5 1 2 2 2 13
OPEN ARC17 1700 Bill Roberts Bobbie Adrien 5 1 5 2 3 1 1 3 16
OPEN T4.9 274 Hollis Caffee Janet Caffee 2 4 2 3 2 5 4 1 18
OPEN TF16U 221 Seth Stern   3 3 1 1 5 4 5 5 22
OPEN H20 911 Eric Arbogast Tom Wilson 4 6 4 4 4 3 3 4 26
OPEN ORCA ORCA 3 Victor Pogrebnov Sasha Suren 6 5 DNF DNS DNC DNC DNC DNC 46

The Sailwave results list 3 modifications, MN B SP. The MN mod (only 0.995) implies that the main is different (square vs pin) but of the SAME AREA, not larger as in the previous calc. Mr. Bill, what are those areas, anyway?

There is no "B" in the tables but if it's really "BM" (sic) then that is 0.995. The SP is the spinnaker at 0.96. That leaves us at

73.0 x 0.995 x 0.995 x .096 = 69.4

Where did the 70.2 come from? If you put in a "fat boy" H3 at 1.01 it gets closer. Were they...chubby?

Granted, it's a small difference but one wonders. Whenever Portsmouth is used I think of the priest saying, "Let us proclaim the mystery of Faith."