Reverse Engineering

There has been a great deal of discussion on this forum about the merits of designing within a rule. I figure that the class rules are written to achieve 2 purposes:
(1) to prevent one boat from acquiring an unfair advantage through design; and-or,
(2) to provide a minimum level of safety.

I own a Sandpiper 565 - a 18.5ft mini-pocket-cruiser. I do not have a PHRF certificate but PHRF-Lake Ontario has issued certificates at 300 Spinnaker & 318 White Sails. This boat has not been manufactured since the early 80s (however, it may still be popular in Britain where the design originated under a different name). There is no effective class rule. I have made significant modifications to this craft:
- installed a rotating mast;
- machined a NACA rudder section;
- reduced weight throughout; and,
- currently changing the 20ft x 8ft mainsail for a Hobie 16 main (24ft x 8.75ft full batten, broad roach).

It is my objective to take this boat to the Levels Regatta in Youngstown, NY in 2004. The PHRF-13 start featured:
- C&C Redline 25 (PHRF 249)
- MacGregor 25 (PHRF 270)
- Narthstar 500 (PHRF 219-246)
- Jeanneau Fantasia 27 (PHRF 216-234)

What are the most significant modifications that may be effected in order to decrease the PHRF rating of this boat?

I call this reverse engineering because: if it breaks the class rule or solicits a PHRF penalty, then it must be a go-fast modification.

[SuperPiper]

I have used Terry Schell's IM-S-Timator to determine the benefit of various modifications. His estimator uses sail area, draft, displacement, sail aspect ratio and hull length to calculate a seconds-per-mile number.

Marginal reductions in hull weight accomplish little according to his estimator. Sail area and aspect ratio changes will create some benefit. It is hull length that generates the biggest bang for the buck.

Does extending the hull skin beyond the transom (in style on newer dinghys and Open class ocean racers) create a longer effective hull length? Or, does it just add wetted surface area to the existing design?

[tonyr]

We used to have a Sandpiper.

Some suggestions, only more or less practical.

1. Add 300 pounds lead to the retractable keel. Modify trailer as needed.

2. Increase mast height, sail area (fully battened as you seem to be doing), and add a drifter (flat cut spinaker) for downwind performance.

3. Add two feet to transom.

4. Move mast as found to be needed.

Have fun, Tony.

[gonzo]

An easy way to decrease your PHRF rating is to race badly for a season. It is self adjusting. The real way to beat that rule, is to buy a different boat every season. The seller should be a bad sailor who never won a race. After a succesful season, sell the boat and buy a new boat from another bad sailor. PHRF is like inheriting the golfing handicapp from the previous owner of your clubs.

CL Boatworks says Sandpipers were produced until 1991.
The Brit boat was a Sailfish.

[SuperPiper]

I am reading in Scuttlebutt that the ISAF will perform swing tests to determine the gyro-rotational weight of the Olympic boats this summer. The tests are to determine that boats are not light in the ends even though they meet the overall weight specification.

Just how significant an advantage is unweighting the ends of a boat? Which end, bow or stern, provides the greatest advantage from being unweighted?

[redcoopers]

Originally Posted by SuperPiper

Marginal reductions in hull weight accomplish little according to his estimator. Sail area and aspect ratio changes will create some benefit. It is hull length that generates the biggest bang for the buck.

Actually, VPPs and other parametric resistance tools are quite ineffective at predicting the performance of a well-modified sailboat. For instance - you can make sure the keel is faired correctly, but there is no "checkbox" in any progam for this parameter. I highly doubt you could even enter in the NACA foil type into the program.

The basis of this is because these programs are built off of tests from fully designed hullforms. The tests assume that you have a hull that approximates the hulls that were tested. In another 'for instance,' if you had a bustle in your transom and you faired it out yourself, there would be no VPP which could predict the change in performance which this makes.

The only option would be to run tank tests (or a good CFD) of the original hull, and then the modified hull.

Modifying the LWL is a parametrically defined quality in LPPs (Lines processing program) which does have *huge* implications. Most of us, however, can't just tack on a few extra plys of fiberglass to the transom or the bow. You will get more efficient performance improvements by continuing to do what you are doing - making smart modifications of the foil, rig, etc - which are beyond the scope of VPPs.

Keep making the smart improvements, and let your results on the racecourse be your VPP.
-Jon

[SuperPiper]

You are correct. It is difficult to redesign the hull. But relocating the fuel tanks from the lazarette to somewhere adjacent to the keel is quite possible. Stowing the anchor in the cabin rather than in the bow is practical during racing. I can move the battery, safety equipment, dock lines, spare sails . . .

What will the result be? By lightening the ends of a little boat will it not tend to bob over waves rather than plow through them? Is bobbing faster than plowing?

[tonyr]

A follow up to the earlier post. The discussion on weights Vs performance is interesting. We found that in any kind of serious wind, our Sandpiper was too light to keep going well in chop, so we added about 100 pounds in sandbags in the wing "lockers" roughly level with the daggerboard.

This noticibly improved the stability (marginal at best with the original 250 pounds of ballast), and let the boat keep going nicely. It did not seem to be any wetter.

The merit of this approach is that you can always remove the sand bags on a light day.

Tony.

[SuperPiper]

A water-ballasted 'Piper? I get wet just thinking about it . . .