Our second test boat was a new 1987 Cruisers model 337 Esprit which we named GRID II.
This test boat had an overall length of 36 feet an a beam of 11 foot 8 inches with a displacement of 12,500 pounds. This type of vessel was chosen for its greater size and
displacement than
GRID I.
The original propulsion was provided by two 350 Crusader raw water cooled engines producing a total of 700hp at 4400rpm.
After an
adequate break-in and boat familiarization period, our speed trials began on October 20, 1986 with the original raw water cooling and factory painted hull. The tests were
conducted over the same measured mile as GRID I's, and were made at the same four RPM settings (2500, 3000, 3500, and 4000). Every attempt was made to standardize the
environments in which the tests were made so that the comparison of test results would be meaningful. We found the craft without
GRIDCOOLERS capable of sustaining 31.61 knots @ 4000 RPM and 13.02 knots @ 2500 RPM.
In the spring of 1987, the raw water cooled engines were converted to a closed fresh water cooling for the engine jacket water system. This was accomplished by adding a
GRIDCOOLER®, expansion tank, and manifold baffles (separators). The raw water pump
was retained to cool the exhaust elbow and muffler. Initially we wanted dry exhaust, however, this would have been complicated to install in the existing engine compartment.
Speed trials during 1988 were with
GRIDCOOLERS
mounted on the hull with fairing blocks fore and aft of the
GRIDCOOLERS.
The
GRIDCOOLERS were mounted directly forward of the propellers. We would have
preferred to mount them farther out on the sides of the boat, but the fuel tanks blocked that kind of installation. The
GRIDCOOLERS also could not be recessed on this boat due to the lack of space for a
recess in the pre-configured engine room. To recess the
GRIDCOOLERS in
the proper location, the recesses would have to be formed when the fiberglass hull was laid up.
The mounting of the
GRIDCOOLERS aided the speed of the boat at lower RPM settings by directing the flow
of water towards the propellers. Unfortunately, this location also starved the propellers for water at higher RPM settings. This lowered the speed more than would be expected
with
GRIDCOOLERS mounted away from the propellers.
Over the testing period the
following effects to hull speed were noted.
|
RPM
|
HULL SPEED
MPH
|
GRlDCOOLER
W/FAIRING BLOCKS
MPH
|
| ..2500......................................
13.02 ........................ 13.51 |
| ..SPEED CHANGE
.................................................... +0.49 |
| ..PERCENT CHANGE
................................................ +3.61% |
| ..3000 ......................................
19.49 ....................... 19.28 |
| ..SPEED CHANGE
..................................................... -0.21 |
| ..PERCENT CHANGE
................................................. -1.08% |
| ..3500 ......................................
26.77 ........................ 25.43 |
| ..SPEED CHANGE
...................................................... -1.34 |
| ..PERCENT CHANGE ..................................................
-4.99% |
| ..4000 ......................................
31.61 ........................ 30.19 |
| ..SPEED CHANGE
...................................................... -1.42 |
| ..PERCENT CHANGE
.................................................. -4.52% |
All speeds listed have been averaged over several runs on a measured mile. All speeds are in miles per
hour.
Since we couldn't recess the
GRIDCOOLERS,
and because we wanted an independent appraisal, we also had drag tests run by the Vienna Model Test Basin. The test results we received from them are available upon request. The
next boat we test, GRlD III, will be a 40+ foot vessel with diesel engines and a dry exhaust system. The design of the vessel will have to be more closely monitored than GRID II,
due to the incompatibilities encountered when we considered recessing
GRIDCOOLERS. GRID
III will allow us to recess
GRIDCOOLERS and
place them closer to the sides of the boat, away from the propellers. It will also allow us to test a boat with a dry exhaust system.
|
