The Boston Whaler company introduced a new 19-foot center console, the 190 NANTUCKET, at the Miami Boat Show in February of 2003. (See Cetacea Page 71 for more photographs, specifications, and pricing of the boat.) The engineers and designers of this boat conducted performance tests with a number of different Mercury engines and propellers. The data from these tests is reproduced below in tabular and graphic form.
Boston Whaler boat tests of their new 190 NANTUCKET model provided a gold mine of information, interesting for prospective owners of the new model, but also as a comparison of different types of engines and propellers on the same boat. At the most fundamental level, the data show how the boat performs with five different combinations of engine type, horsepower, and propeller. Closer analysis allows comparison between engines of the same horsepower (115-HP) but of three different designs: conventional carburetor 2-stroke, low-emisison Optimax 2-stroke, and fuel injected 4-stroke. Also, variations of the same engine with different styles of propeller can be seen. In total, three different types of propellers are used in these tests: Black Max (aluminum), Vengeance (stainless steel), and Mirage (stainless steel). All are three-blade designs without venting.
The table below shows the raw data from the tests conducted by Boston Whaler in February, 2003. Speeds are reported in miles per hour or revolutions per minute, as appropriate. Propeller dimensions are in inches (pitch x diameter). All tests were reported to be conducted with a full fuel tank (60-gallons) and two people aboard. I have added additional data for engine displacement (in cubic inches), lower unit gear ratio (1:X), and transom mounting height (hole position), which may help to understand some of the results seen in the data. Hole position refers to which hole in the engine mounting bracket is used, counting down from the top or first hole. An engine mounted in the "3rd" hole is mounting higher on the transom than an engine mounted in the "2nd" hole.
Make your own analysis and interpretation of the data. Why not? Everyone can find something to like in these results.
|Boston Whaler 190 NANTUCKET|
|MOTOR||115 XL Classic||115 XL Optimax||135 XL Optimax||150 XL Optimax||115 XL EFI
|PROP||13 x 19||13.12 x 16||15.5 x 17||15.5 x 17||13.37 x 14||13.75 x 15|
|TYPE||Black Max||Vengeance||Mirage||Mirage||Vengeance||Black Max|
|MTG POS||2nd Hole||2nd Hole||3rd Hole||3rd Hole||2nd Hole||2nd Hole|
The chart above shows overlaid plots of this data. The colors of the plot lines are coordinated with the table's color headings. Note that the curves drawn are simply connections between the various data points. The program which created the graphed lines has added curves to them between the data points.
As is quite normal with moderate vee-hull boats, the 190 Nantucket boat appears to need about 20-MPH to get onto hydroplane. In comparing all engines, the most powerful (the 150-HP Optimax) has the boat on plane at the lowest engine speed (3000-RPM), a result of its larger pitch propeller and gear ratio (only engine less than 2:1). Curiously, one of the least powerful engines (115-HP 2-stroke) appears to be able to get the boat on-plane almost as well! And even more interesting, the other 115-HP engine (the 4-stroke) needs the most engine speed to have the boat up on plane (however it has the least propeller pitch, so this is expected). Note that all the 115-HP engines have the same gear ratio. The reason the 2-stroke engines are able to reach plane at lower engine speeds may be more torque at those lower engine speeds. The 115-HP Optimax is not as fast as the 115-HP classic 2-stroke, which has quite an edge in engine displacement (113 vs 93 cubic-inches).
Another interesting comparison buried in this data is the similarity in the propeller performance once on plane between the Black Max (aluminum) propellers and the Vengeance (stainless steel) propellers. Both styles are three blade propellers. The pitch ratings seem to be slightly different. If one allows that a 19-inch rated pitch of a Black Max is about the equivalent of a 17-inch pitch in a Mirage, then the very similar slope of their performance curves is explained. A similar relationship is seen in the curves for the 15-inch Black Max and the 14-inch Vengeance.
The data presented here is simply a record of boat speed versus engine speed. It can be resonably assumed that the instrumentation used to obtain engine speed and boat speed was accurate, but there are other considerations. As in every other presentation of this type of informaton ever seen in boating literature, there is no notation of time. Time to reach a certain speed, say 30-MPH, is another measurement. It is one that is often used to compare acceleration, but that data is not provided here. These data points cannot tell us which engine and propeller combination reached a particular speed the fastest, however I think it safe to bet on the ones with the higher horsepower, particularly the 2-stroke engines.
Propeller performance may not be properly judged just from comparison of data points. The propeller can also affect how the hull rides when on plane. Propellers that provide bow or stern lift can change the boat's characteristics when on plane, bringing the stern up and out of the water, or moving the whole boat upward so that the planing surface is elongated yet at the same time made smaller. This often causes a difference in the feel of the boat to its occupants.
The ability of the propeller to maintain good "connection" with the water can also vary. These properties are not seen in the data presented here. They could have considerable affect on boat handling.
Thanks to the Boston Whaler company for making these tests and distributing the data, which are faithfully reproduced here.
DISCLAIMER: This information is believed to be accurate but there is no guarantee. We do our best!
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Author: James W. Hebert from data supplied by Boston Whaler.
This article first appeared November 24, 2003.