John Tiger does some prop swapping on two STV/Merc combos. Once more, we embark on yet again another interesting (and fun!) propeller comparison, this time using a very popular outboard powered Mod-VP-style tunnel hull as our test platform. Our intent was to compare several similar propellers from different manufacturers and tuners to see what effect they might have on the acceleration, handling and top-speed characteristics of our Summerford Tunnel Vee. We actually ended up running 14 (!) different over­hub-style high-speed pro­pellers over a three-day period using two almost-identical STV Euro tunnels with Mercury power. The results were closer than we all thought and revealed inter­esting traits of the props tested, as well as the rigs they were run on. 

TEST BOATS
     The two STV hulls were owned by upstate New York hot-boaters Mac Hadden and Steve Neander, who bought them one after another a few years back after owning a succession of vee-bottom hot rods. Tiring of the rough­water antics the old vees served up, the hot-boating pair traveled to Long Island to purchase their rigs from well-known STV/Mariner dealer Diamond Marine (since relocated to Fort Lauderdale, Florida). The only difference in these two boats is the color and choice of power; Neander's '93 is a mean flamed green with white trim while Hadden's '94 is a red/white combo with yellow, orange and black trim. Power for Neander's green meanie is served up by a Merc 2.4 Bridgeport (carbureted model), circa 1990; the engine's basically stock, save for a set of milled 32cc cylinder heads. Hadden opted for the carbureted 2.5 model, which is (still) stock. As such, the rigs were ideally matched; during testing, they were consistently within one mph of each other at top speed, and acceleration was dose as well. However, the edge would go to Haddon's 2.5, where the  extra displacement helped kick the boat into the upper speed ranges just a shade quicker than the 2.4-powered boat. In all, though, two closer-matched rigs would be tough to find. As test platforms, they provided smooth, consistent runs with great stability and a very good ride. These boats are excellent “'family" tunnels, as close as they can get to a multi­ purpose hot boat. The interior is fairly roomy, with four contoured and padded buckets and a fully carpeted flat floor. Storage space is surprisingly abundant for this type of boat. The only drawback is a slightly wet ride at speeds below 25 mph, especially in choppy, windy conditions; when the speed is raised to 30­plus, this problem disappears. Both engines performed flawlessly testament to their running quality as well as longevity (neither had been as much as touched internally since new, with estimates of 100-plus hours per season logged already!). Haddon's 2.5 required a bit of carburetor tuning the result of a missing fuel needle retainer; once this was replaced, the engine ran consistent 7,500-plus-rpm runs all day for three days on end. We were lucky to be blessed with three days of sunny, warm and calm days, with very close temperature and humidity conditions throughout the test.

 TESTING PARAMETERS
     Our intent was to find the best overall propeller for these two rigs, taking into account not just top speed but acceleration, handling and weight-carrying ability. The top speed numbers are always exciting and alluring to be sure, and a lot of extra "fun time" was spent trying to eke out that last mph, but overall, the best propeller was not the fastest (as is usually the case). Our testing procedures involved first taking a midrange "joyride" with each prop, to determine its midrange handling characteristics (and to get a good feel for the prop's idiosyncrasies). Next, Mac (or Steve, depending on the boat being tested) took the rig through several acceleration runs, with me manning the radar gun, digital tachometer and stopwatch simultaneously to record the runs on a notepad. Copious notes were recorded (and almost lost one stiff wind took an entire pad out of my hands and slapped it to the lake's surface; we quickly retrieved it, saving over a day and a half's worth of work!). We used my standard recording instruments: Stalker radar gun and Medallion 125-mph speedometer for speed, digital OMC ShopTach and Mercury Hi-Performance analog tachometer for rpm’s and calibrated digital Heuer stopwatch for acceleration runs. Finally, I climbed to another boat to record the full bore, driver-only top-speed runs from a clean vantage point. Our test area was upstate New York's Schroon Lake, reported on last year in these pages as having unusually smooth waters. As a "test track," it proved perfect, with only a slight wind chop and occasion­al boat wakes to contend with. Each wheel was run through a rougher part of the lake right in the face of the wind to evaluate its rougher water capabilities. Temps were in the high 70s to low 80s for most of the test, and humidity was low the entire time-perfect conditions for optimum performance. Our engines both peaked in the 7,000 to 7,500 rpm range, with the 2.5 revving perhaps just a bit more than the Bridgeport for maximum performance. Both rigs were equipped with 14 ¼ x29" Spinelli three-blade round-ear props, so we baselined both rigs back-to-back with these wheels first. 

PROP #1
SPINELLI 14 ¼ x 29' THREE-BLADE CHOPPER
     This propeller proved tough to beat in any test and showed that both boats were set up very well as is. We tried both wheels on their respective boats and then swapped; performance differences were so slight that they weren't worth recording  Hadden's 2.5 showed a penchant for strong acceleration, good top speeds and consistent running. Bottom-end acceleration numbers were good; certainly not best-of-test but very satisfying just the same. Midrange and top-speed handling was very good; the wheel held the boat steady in turns as well as straight-aways. Overall, the per­formance of this propeller was very good on either rig. Blade design was similar to the other round-ears in this test, except that the blade width (as measured across the face midway up the blade) was narrower than the others. Theory would hold that this design might allow more rpm than another prop of the same pitch and larger blade area, but it wasn't so with the Spinelli; top end rpm never passed 7,400, even with just the driver aboard. With a retail price of $880, this prop cost more than most of the three-blade round-ears we tested. Only the Merc Lightning ET cost more. That alone is its downfall; the performance, finish and warranty (one year, with a free rework within the first 30 days if performance isn't as expected) were just about as good as any of the other contenders. Spinelli Props is a true custom shop, building and hand-finishing custom props at their shop in Rochester, New York. Regular readers will recognize their name as one that's been around for a while; Mod-VP racers, as well as weekend hot-rodders, have been using Spinelli props for at least two decades. 

PROP #2 
DAH/MERCURY 14 ½ x 32  THREE-BLADE CLEAVER  
This was the "big blade" of the bunch; at 32 inches of pitch, it easily outpaced the rest of the field in sheer blade twist. As such, it was easy to see why Mac and Steve elected to try it first after the base­line runs when the Spinelli props were fin­ished; they wanted to see the "big numbers" come up right away! The big cleaver didn't disappoint anyone; a best top speed of 98 mph after several tries was clearly the fastest we would achieve (and a full two mph faster than the next closest prop). Bottom-end and midrange times were poor comparatively but not nearly as bad as was expected from such a tall prop. This wheel started life as a Mercury Hi­Performance propeller, then was modified by DAH Propellers in Burlington, Wisconsin. The workmanship was excellent; DAH wheel­man John Janaky has been tweaking props for years under the expert tutelage of former OMC propeller whiz Don Henrich (hence the DAH moniker), and the results show; time after time, Janaky's props really shine. Cost on this prop was a hefty $870-$795 retail from Merc and another $75 for the DAH blueprint job. Workmanship was excellent; the prop shined like chrome, and blade thickness was still stout enough so that the strength was still there. Clearly, this was too much blade for these engines however; 7,250 rpm  was shy of our desired 7,500 rpm tar­get range. A great prop but not the right one for these rigs. More horse­power, and who knows? 

PROP #3  
MAZCO RE-3 14½ x30-­THREE-BLADE ROUND-EAR
     Mazco makes a lot of props for STV owners, as the Outboard Tech letters and phone calls can attest. However, this RE-3 was not the best overall prop or these boats, for this test. Acceleration and top speeds were right in the thick of the best numbers, but the Mazco wheels didn't shine head and shoulders above the rest the way they have so often in the past. Pitch is probably the culprit; had we stepped down to a 28- or 27-inch RE, these STVs would have snapped to attention. The 30-inch pitch RE accelerated well, had solid top speeds in the low to mid 90s and held the boat well in rough water with a two-man load. Wheel torque was substantial and tiring. As usual, finish and workmanship was impeccable. With a retail price of $550, the RE-3 represents a great value for excellent performance. Mazco offers a free rework within 30 days of purchase, and a one-year warranty against failure Outboard Tech readers know that Mazco is one of my favorite prop builders, for good reason; his props work so well on so many applications it's tough to go wrong when recommending one. This application was not tough to prop for, but a smaller wheel would have been the way to go (as the OMC, Mach, Mercury and Performance Propeller test runs showed-read on)

Prop #4
MAZCO RE-4 14 ½ x30" FOUR-BLADE ROUND-EAR 
     If 30 inches of pitch was too much with the RE-3, it certainly was way over propped with the same size RE-4. This prop gripped like an eagle with sharp claws, but the tall blades just wouldn't let the Mercs wind up. Lower midrange punch was excellent as expected, but the prop suffered after 50 mph (see chart), as evidenced by the slow 0 to 60 and 40 to 70 times. Top-end rpm was lower than most and, therefore, so were the speeds achieved. As with the RE-3, workmanship was absolutely beautiful; at $690, it better be! Mazco's one rework and one-year warranty apply to this prop as well. Wheel torque was almost nonexistent with this prop a benefit of that fourth blade. It held the boat tight even in brutal turns and had no tendency to blowout even with a heavy load aboard. Again, a step down in pitch-my guess would be a 26-inch­er-would improve its performance on these rigs by a large margin.

PROP #6  
MAZCO/OMC SRX 14 1/2 x29" THREE-BLADE ROUND-EAR
     This old salt has been a forgotten performer for years; OMC prop wizard Don Henrich designed it in the late 1970s, and it's been in the OMC parts catalog since the early 1980s. First covered in a Teflon black coating, it's been produced in a high-polish finish for some time now. The props have excellent top-speed characteristics when stock but lack sorely in acceleration. Both Mazco and DAH perform fine reworks and really wake up the bottom end, so we elected to try one from each builder. This 29-inch speci­men was tweaked by Mazco, with truly excellent results; acceleration easily matched or outpaced the other 29­ and 30-inch props and beat many of the 28-inch wheels as well. Top speeds were at the top of the class; 89 mph with two aboard was a bit light, but solid 94.5-mph clockings with dri­ver only was near the best of the bunch. This prop just felt right; it handled beautifully, punched well, and minimal wheel torque was noticed. All felt it would be tough to improve upon. The price isn't cheap but certainly not out of line for such great performance; OMC retails it for $404, and Mazco adds $210 to blueprint and modify it, bringing the total to $614. Mazco, however sells them worked for $575.The workmanship was  excellent, all in all, this prop was a good contender for the best of test.

Propeller Test Results- STV/Mercury