GURPS Vehicles – Trifoil Design

Here's proof-positive of the efficacy of GURPS Vehicles (meaning it works really well!)

Date: Sat, 7 Sep 1996 16:44:42 -0700
From: sands@netcom.com (Sue and Sean)
To: GURPSnet-L@io.com
CC: sj@io.com
Subject: Vehicles Works!

Last weekend, I encountered a vehicle I was sure Vehicles would choke on. I actually rode in one of these things, and it is a blast. The ad is, in fact, totally accurate.

The ad:

DESIGNED FOR SPEED, IT'S SURE TO LEAVE YOU BREATHLESS.

Hobie Cat TriFoiler

When was the last time you went 35 MPH in a sailboat? With the Hobie
TriFoiler, your wildest dreams of speed with come true. The TriFoiler
is quite simply, the most amazing sailing machine on the water
today. Take the pilot's seat in the center cockpit with all the sail
and foil adjustments on the control panel in front of you and you're
off. All it takes is 12 knots of wind for the three self-adjusting
hydrofoils to lift off and you're flying! Check your speed on the
built-in speedometer as you streak past everything else on the water
while controlling your course with the steering pedals. From speed
runs, to the thrill of high G-force turn, the TriFoiler delivers
excitement like nothing else can.

--Standard Features--
o White Hulls with Colored Graphics     o Mast Rotators
o Colored Patented Multi-Sail           o Water-Tight Storage Compartment
  Zippered Reefing Sails                o "How to Rig" Video
o Center Cockpit Sail Controls          o Harken(R) Blocks
o Adjustable Pilot Seat                 o Black Anodized Aluminum
o Retractable Forward Hydrofoils
o Built-In Speedometer                  --Optional Features--
o Compass                               o Customer Trailer with Spar Storage
o Steering Pedal                        o Foil Covers
o Adjustable Shock Absorbers            o Mesh Spray Guards
                                        o Trailer Ties

--Specifications--
Length:                 22'             Main Hull Length:       16'3"
Beam:                   19'             Draft Foils Up:         5"
Sail Area:              215 sq. ft.     Draft Foils Down:       28"
Displacement:           280 lbs.        Beam on the Trailer:    44"
Mast Length:            18'             Designer:               Greg Ketterman

The GURPS Version:

TriFoiler (TL7)

Picture a kayak, with two surf boards as outriggers, and two *large* sails mounted on the surfboards. Now add hydrofoils fore and aft, and minimal controls. The TriFoiler is a new invention, available only from the designer. It is a flat-water toy; it would quickly wipe out in a heavy surf.

Subassemblies and Body Features:

Trimaran hull with fine lines. Two 18-foot masts. Hydrofoils. Floation rating 1,622 lbs.

Propulsion:

Two fore-and-aft sails, 215 sf of synthetic sails, average motive thrust 172 lbs.

Instruments and Electronics:

Compass, speedometer.

Controls & Crew Stations:

Primitive. "Driver" maneuvers by pulling ropes from exposed cramped crew station. Navigation is by seat of pants and a small compass.

Occupancy:

Short.

Passengers:

One.

Crew:

One.

Accomodations:

One exposed cramped passenger seat. Wet suits are highly recommended.

Cargo and Empty Space:

1 cf of cargo space, 55.6 cf of empty space (open framework, unarmored, unwaterproofed, etc.).

Volume:

Body 91.1 cf, two masts at 0.6 cf each.

Areas:

64.8 sf body, 4.2 each mast.

Structure:

TL7 light frame, standard materials (plastic), fine lines, trimaran.

Hit Points:

Body 49, each mast 8.

Armor:

Body and masts PD 2, DR 3 composite.

Surface Features:

Waterproof.

Vision:

Good.

Statistics:

Empty weight

450 lbs.

Usual payload

300 lbs.

Loaded weight

750 lbs.

Volume

92 cf assembled, breaks down to 41 cf.

Size modifier

+2.

Cost

$4,555.

price

$15,000.

HT

12.

Water Performance:

Can float.

Hydrodynamic drag:

5.

Aquatic motive thrust:

86 lbs / Beaufort number.

Speed at Beaufort number 1:

15.5 mph.

2:

19.5 mph (foils lift at 20.65 mph).

3:

33.5 mph.

4:

36.9 mph.

5:

39.7 mph.

wAccel:

2.3 mph/s.

wMR:

0.5.

MSR:

1.

wDecel:

3 mph/s.

Draft:

9.5 inches.

The commentary:

Mr. Pulver is a flaming genius. Noting that the "12 knots of wind" in the ad equates to Beaufort 4, every one of the specifications works out *perfectly* except two: the calculated draft is nearly twice the specified, and I can't figure out how to calculate the displacement. The spec sheet gives 280 lbs., which "feels" right, but the only reference to displacement in the book is 35 cf = 1 displacement ton, which doesn't make sense in this case.

 Susan and Sean (order optional)  Men may be bribed in
 S & S Enterprises                a variety of coin.
 sands@netcom.com

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