Category Archives: Tool Kit

Don’t Knock It!

Engine knock (aka “detonation”) is an undesirable phenomenon that occurs when a “left over” pocket of air-fuel mixture in the combustion chamber ignites after the spark plug has already fired. When this happens, cylinder pressure jumps as high as 25 times that of normal combustion, and in doing so creates a sharp metallic noise audible to the human ear.

So, what exactly is engine knock?  Well, put on your engineering hats for a moment, as we’re going to get a little technical here.  Simply put, engine knock (aka “detonation”) is an undesirable phenomenon that occurs when a “left over” pocket of air-fuel mixture in the combustion chamber ignites after the spark plug has already fired. When this happens, cylinder pressure jumps as high as 25 times that of normal combustion, and in doing so creates a sharp metallic noise audible to the human ear.  This noise is referred to as “knock”, and left unchecked, it can lead to engine damage ranging from relatively mild to complete engine failure. The extent of engine damage that can occur from knock is highly dependent on the specific output of the engine (horsepower/cubic inches or liters) . . . the higher the specific output, the more extensive the knock damage may be.  In addition, external factors influence an engine’s propensity to knock.  For example, higher air and/or water temperatures make it harder to cool the engine, and therefore create an easier environment for knock to occur, while higher humidity helps reduce the chances for knock.  By now you’re probably wondering “how can I protect my engine from the weather?”

Using high quality fuel with an octane rating that complies with your engine’s requirement is your single best defense against engine knock.

The good news is using high quality fuel with an octane rating that complies with your engine’s requirement is your single best defense against engine knock.  This is why certain Mercury Racing consumer outboards and sterndrives require a minimum of 91 octane (98 RON) pump fuel.  The higher-octane fuel allows your Mercury Racing engine to safely produce maximum power while protecting against engine knock.

Octane ratings at the pump are typically determined by the following equation: (RON + MON)/2; commonly written as (R + M)/2. This is called the antiknock index (AKI).

Octane, in fact, is a measure of gasoline’s antiknock performance. There are two test methods used to measure gasoline octane rating. One method results in the Research Octane Number (RON); the other produces the Motor Octane Number (MON). Octane ratings at the pump are typically determined by the following equation:

(RON + MON)/2; commonly written as (R + M)/2. This is called the antiknock index (AKI).  In general, a higher-octane fuel, such as 91, provides greater protection against engine knock than a lower octane fuel, such as 87 or 89.

400R and Automatic Knock Protection

The 400R produces its advertised horsepower at 7,000 RPM on 91-octane (98 RON) pump fuel; however, the engine control unit will automatically adjust spark timing on individual cylinders should it start to detect engine knock.

All Mercury Racing outboards and sterndrives require a certain minimum fuel octane to protect against knock while maximizing performance. The Verado 400R outboard takes it one step farther with an advanced computer controlled knock protection system. The 400R produces its advertised horsepower at 7,000 RPM on 91-octane (98 RON) pump fuel; however, the engine control unit will automatically adjust spark timing on individual cylinders should it start to detect engine knock. The amount of spark removed and subsequent power reduction is highly dependent on ambient conditions (water and air temperature, humidity) and other factors.

The 400R’s knock protection system provides the ultimate flexibility by allowing you to maximize performance on 91 octane without having to compromise where you run your boat based on available fuel grades at the gas dock.

The great thing about the 400R’s knock protection system is it is designed to always give you as much power as possible under all conditions while still protecting the engine from knock damage.  Running your 400Rs with the recommended 91 octane fuel will help ensure you always have the full 400 horsepower at your fingertips, but sometimes on the water, 89 octane or Rec 90 is the best you can find.  Don’t sweat it . . . your 400Rs will run safely and reliably on this fuel as well, you just may not see the same top speed you will with the premium fuel.  This knock protection system provides the ultimate flexibility by allowing you to maximize performance on 91 octane without having to compromise where you run your boat based on available fuel grades at the gas dock.

What About Other Race Product?

Currently the 400R is the only Mercury Racing engine with a built-in knock protection system.  This means with other Mercury Racing outboards and sterndrives, it is absolutely necessary to comply with specified fuel requirements for each engine. Using a fuel with an octane number lower than an engine’s specified rating will likely result in engine failure, which is not covered by Mercury Racing’s limited warranty. While most fuel grades are readily available for boats that are trailered, it is important to understand what is sold at the gas docks for boats that are kept in the water or run for long distances.

The 600 SCi is one of three Mercury Racing sterndrives designed to run on 87 octane fuel.

Fortunately, all but three of Mercury Racing’s outboard and sterndrive products are designed to run on 87 or 89 octane (see chart below for octane requirements by engine model).  Since most gas docks carry 89 or Rec 90, the vast majority of Racing product may be operated virtually anywhere.  The consumer Race product which requires 91 octane includes the 300XS outboard and the QC4 1350 sterndrive.  Finally, the dual cal 1350/1550 QC4 consumer model requires 91 octane in 1350 mode and 112 octane race fuel in 1550 mode.  Typically race fuel (112+ octane) is not readily available and must be ordered in advance for speed runs or competition race activities.  Recommended race fuels per the chart below are Sunoco Supreme 112 AKI or Sunoco 117 MON, VP C16 or equivalents.

Can’t I Just Add Octane Boost?

As previously mentioned, most marinas today are carrying Rec 90; a cross between 91 and 89 octane pump fuel. In other areas, the highest available fuel rating is often 89 but sometimes 87-octane. This is a huge gamble if your engine requires 91-octane fuel and is not equipped with knock control, one that often leads to serious engine damage.

As a result, it comes as no surprise that many of our customers turn to aftermarket products (fuel additives) promising to raise the octane in their boats to acceptable levels which comply with our specified fuel requirements.  Internet forums are full of discussion threads arguing whether these products actually work.  Here at Mercury Racing, we are frequently asked for our opinions on these additives. To date, we have not been able to validate the effectiveness of any aftermarket octane boosting products on any Mercury Racing product.  Thus, we do not recommend or support using them as a substitute for using the specified minimum octane fuels our products require.

Higher volume fuel tanks found on most powerboats or center consoles would likely require a substantial amount of octane booster, and even at that, there is risk the final octane in the tank may still not be enough to meet the specified requirement.

Many of these products advertise that they boost the octane by a certain percentage or factor when mixed with the fuel at a certain ratio.  It is unclear how much of the product is truly required to boost the fuel octane in the tank by a full point.  Higher volume fuel tanks found on most powerboats or center consoles would likely require a substantial amount of octane booster, and even at that, there is risk the final octane in the tank may still not be enough to meet the specified requirement. This is a major risk to take with your high dollar investment, and one that would not be covered by Mercury Racing’s limited warranty.

Our advice?  Don’t risk it.  Top off your tanks with the correct fuel grade specified for your Mercury Racing engines prior to your day on the water. Plan your route to ensure you have access to your required fuel when needed. Your engines will thank you with top performance and unwavering reliability.

 

 

 

 

 

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Prop Slip? We Have an App for That!

Home screen of the all-new Mercury Racing Propeller Slip Calculator.
Home screen of the all-new Mercury Racing Propeller Slip Calculator.

We’re excited to announce the release of our new Propeller Slip Calculator App. Available for both Apple or Android devices, the app provides all of the functionality of the calculator featured on our website. The app enhances the versatility of the tool – making prop testing much easier and a ton more accurate. Download it for free from Google Play Store or Apple iTunes.

Results for any of the five fields can be determined by populating four of the five fields.
The Mercury Racing word mark is hyperlinked to the Mercury Racing website.

 

I use the slip calculator daily when assisting customers with propeller questions. It is a great tool that provides much more information than just slip. Results for each of the five fields can be derived by populating the other four. Following are a few examples of what this powerful app can do.

Outboard Example

Speed results from plugging in Pitch, Ratio, R.P.M. and Slip.
Speed results from plugging in Pitch, Ratio, R.P.M. and Slip.

Let’s look at a single engine OptiMax 250 ProXS outboard powered hull.  When communicating with customers, I always first ask for baseline information such as the pitch of prop they are running,  gear ratio and engine RPM at wide open throttle. Using the app, I can plug information I’m provided (pitch, gear ratio, engine rpm and speed) to first determine slip.

 

Decreasing the pitch by two inches results with an improved hole shot and acceleration while sacrificing 2 mph off top end speed.
Decreasing the pitch by two inches results with an improved hole shot and acceleration while sacrificing 2 mph off top end speed.

Now – after getting some additional information, the customer informs me the rig is under a heavy load and thus he is looking to increase RPM for enhanced hole shot and mid range acceleration to carry the load. Let’s see what happens when we drop the propeller pitch by two inches. Typically, one inch change in pitch affects engine speed by 150 RPM. In this case – dropping two inches of pitch will increase engine speed by 300 RPM. I plug in the new RPM and pitch size into the app – leaving everything else the same.  The engine is running at the upper end of it operating range. This will provide the added thrust needed for the enhanced hole shot and mid range performance the customer desires. Note the top end speed drops by 2 mph.

Getting close to what the customer needs for his application.
Getting close to what the customer needs for his application.

The customer sometimes runs under lighter loads and he is concerned with it being so close to the rev limit using the smaller wheel. Lets see what happens when we go back up one inch in pitch. I go to the app and change the pitch to 24 and decrease the engine speed by 150 RPM. I again select Actual Speed and find a gain of one mph in top end speed.

With help with the app - the 23.5" pitch is perfect size for what the customer expects from his application.
With help with the app – the 23.5″ pitch is perfect size for what the customer expects from his application.

Let’s see what happens when we go down one-half inch in pitch. Knowing the engine speed will increase 75 RPM, I change the RPM  to 5925 and pitch to 23.5 and select the Actual Speed button.

Top speed is comparable to what is achieved with using the 24″ pitch prop. The higher engine RPM will enhance the hole shot and mid range performance. There is enough of a gap between the actual engine speed to the upper engine operating range to allow for occasional light load applications without worrying about hitting the rev limit. This is the prop I would recommend for this application.

Sterndrive Examples

NXT6 Application 

The information supplied here results with 12.8% slip.
The information supplied here results with 12.83% slip.

Here I wanted to share a couple of examples. The first is regarding a boat originally equipped with twin 800 h.p. engines coupled to our dry-sump NXT6 drives. The customer has supplied us with gear ratio, engine RPM,  pitch and speed. By inputting our known data, we find the slip to 12.83%.

The customer then decides to have his engines rebuilt and updated to 1,000 H.P. He would like to know the pitch size he could run with the updated engines.

The increase in speed by 10 mph, with everything else constant, results in a larger prop pitch.
I would suggest he start out by running his existing 36-inch pitch cleavers

Running a conservative calculation we can expect a 10% increase in speed (1.10 x 103 mph) for a total of 113 mph.

The new engines need to rev to 5800 rpm. I plug 5800 into the App and change mph to 113. Keeping everything else the same and select pitch, which changes to 35.42″ pitch.  Here, I would suggest he start out by running his existing 36-inch pitch cleavers. He can break the motors in and then check wide open throttle to see if he can get to the recommended 5800 RPM.  If he gets there and finds he has more throttle – he can consider higher pitch props.

A new speed of 123 changes the prop pitch to 38.55 inch.
A new speed of 123 changes the prop pitch to 38.55 inch.

Using the old general rule of thumb, it takes 10 additional hp for a gain of 1 mph – for both single and multiple engine applications. Remember – this is the old rule of thumb. In this case – we bumped the power from 800 to 1,000 h.p. or 200 h.p./10 h.p. = 20 mph.

Let’s see what the results are with that. When I change the speed to 123 mph in the slip calculator the pitch comes in at 38.55-inch. Now the customer needs to make a decision to go up to either 38-inch or 39-inch pitch props.

 

Bravo Application 

Performance data of the 42-foot Fountain with twin 525 EFIs and lab Finished Bravo I propellers.
Performance data of the 42-foot Fountain with twin 525 EFIs and lab Finished Bravo I propellers.

For this example I wanted to share an example of an air entrapment vee-bottom hull and the how it affects propeller performance. The subject boat is a 42-foot Fountain equipped with twin 525 EFI sterndrives. The customer provides me with the baseline information. He tells me his is running 34-inch pitch Lab Finished Bravo I props with a 1.50:1 gear ratio. The 525’s turn 5200 RPM at wide open throttle. His slip is high at 22% – resulting with a top speed of 87.05 MPH.

Stepped hulls such as that featured on the Fountain aerate the water just forward of the propeller blades. This creates slip as the propeller is not large enough overall  – or in blade area specifically – to grab clean water. Here I would suggest the customer switch from the four blade Lab Finished Bravo I to the five blade Lab Finished Maximus. Let’s go to the app and see if what we find out.

Prop slip is greatly reduced when moving from the Bravo to the Maximus.
Prop slip is greatly reduced when moving from the Bravo to the Maximus.

I know from experience the pitch will go down two inches when switching from the 4 blade Bravo I to the  larger 5 blade Maximus. I also know the the slip will go down to approximately 12%. I plug in the constants; 5200 RPM, 1.50:1 gear ratio, and revise the pitch to 32-inches and plug in the 12% slip. The resulting top speed calc is impressive and representative of what the Fountain with 525s is capable of producing. The customer is pleased to learn he will gain five MPH when switching to the Maximus. He’ll also gain that speed in the mid-range offering a great cruising speed.

I hope these examples provide a sense of the various calculations you can perform with our new app. Remember, the calculator is a tool to help us better understand a number of variables. It provides a base from which to test the results for your particular application.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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Cat Nip!

The very first Skater catamaran powered by Verado 400R outboards.
The very first Skater catamaran powered by Verado 400R outboards. Photo credit: speedonthewater.com

The Verado 400R has fueled the resurgence of the outboard performance boat market. Multiple outboard (two or more) installations capable of speeds in excess of 85 mph require the use of an external rear tie bar assembly to keep the motors parallel and equalize loading. 

Factory Installed Tie Bar Kit

Verado 400Rs destined for go fast cats come with a factory installed rear tie bar mounting kit.
Verado 400Rs destined for go fast cats come with a factory installed rear tie bar mounting kit.

400Rs destined for go fast duty on catamaran hulls are equipped with a custom Mercury Racing designed rear tie bar kit. The factory installed kit includes custom rear engine mounts and a heavy duty, stainless steel tie bar wing plate.  The engine mounts feature an addendum for the mounting of the wing plate. A tie bar is not included.

A view of a port rear engine mount.
A view of a port rear engine mount.

The custom rear mounts are critical for safe and secure installation of the wing plate. They serve a function and –  at the same time – maintain the integrity, form and function of the 400Rs’ Advanced MidSection. Most people mount aftermarket rear tie bar wing plates via the powerhead studs. This places a great amount of stress on the studs, engine mounts and the powerhead which could lead to cylinder distortion and possible engine failure.

A view of the starboard engine mount.
A view of the starboard engine mount.

Verado 400Rs with factory installed tie bar kits are backed with a full warranty.  The Mercury product warranty does not cover any damaged related to the use of tie bar kits or other accessories not manufactured by Mercury Marine.

Sport Master

The 400R is the first Verado available with the race proven Sport Master gearcase.
The 400R is the first Verado available with the race proven Sport Master gearcase.

One of the features which differentiates the Verado 400R from all other four stroke outboards is the availability of the Sport Master gearcase. Designed  for boats capable of speeds in excess of 85 mph, Sport Master 400Rs deliver fresh adrenaline pumping excitement to the go fast cat world.

The factory installation process includes cutting custom slots into the AMS covers to allow room for the tie bar wing plate.
The factory installation process includes cutting custom slots into the AMS covers to allow room for the tie bar wing plate.

We are excited to see our high performance boat builders embrace the 400R. The response thus far has been phenomenal. The biggest kick I get is people seem to be as awestruck by the pure power and torque of the engine as they are its  drivability and and overall  quietness. People are as excited to be able to carry on a conversation at 80 mph as they are going for the big number. These are exciting times for sure.

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Hush the Magic 520!

The 520 sterndrive comes with cast iron manifolds with stainless steel exhaust elbows.
The 520 sterndrive comes with cast iron manifolds with stainless steel exhaust elbows.
Mercury Racing 520s with Axius Joystick Piloting technology is a popular option for their 400FX Sport Cruiser.
The 520 with Axius Joystick Piloting technology is a popular option for Formula’s 400FX Sport Cruiser.

Our new 520 sterndrive has been a resounding success since it was introduced one year ago at  the LOTO (Lake of the Ozarks) Shootout. It’s become even more popular since the release of a  Joystick Piloting for Sterndrives – Axius option for selected models fitted with the Bravo Three XR sterndrive. Formula boats have been early adopters of the engine package. They are also the first OEM boat builder to install the potent engines with joystick control. A Formula 400FX used to demonstrate joystick 520 maneuvers at the Miami Boat Show had standard through transom exhaust fitted with aftermarket mufflers. For our traditional sport boat crowd – they had a nice exhaust note. For those looking for enhanced performance without all the rumble – it might have been a bit much.

Alpha maleness without all the barking!
Alpha maleness without all the barking!
This CAD drawing shows the the port and starboard exhaust connected by a custom y-pipe.
This CAD drawing shows a 520 engine fitted with the starboard X-haust Noise Reducer System – Stage 1.

We took note, no pun intended, and went to work to create an X-haust Noise Reduction system designed specifically for the 520.  The system will appease our friends at Formula and a variety of our OEM boat builder partners, dealers and consumers looking to take advantage of the 520’s performance value.  It will also be adopted in European Union countries where the engine is certified in meeting the stringent RCD (Recreational Craft Directive) exhaust emissions standards. Read more

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Vital Fluids

Dyno technician, Dave Dins, running a 1350 for DCB.
Dyno technician, Dave Dins, puts a 1350 through its paces.
OptiMax 300XS powerheads await their turn on the dyno.
OptiMax 300XS powerheads await their turn on the dyno.

We spend a lot of time validating our products. This is because we are responsible for entire propulsion systems – not just independent components. Everything (engines, transmissions, drives and propellers) must work together and be tolerant of each other. This includes oils and lubes. They are the system’s lifeblood.

We validate our engines using specific oil types and weights. Same goes for the drives and  lubes. Over the years, our two-stroke outboards have evolved from carbs to electronic fuel injection to OptiMax low-emissions direct fuel injected technology. Similarly, our higher horsepower sterndrives have evolved from traditional 2-valve, push rod engines to a quad cam, four valve engine of our own design. Oil and lube requirements have evolved along with the products. Read more

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Bravo for Go Fast Charters

Captain Sam (L) and his son Joe.
(L-R) Go Fast Fishing Charters Captains Joe and Sam Maisano.

It’s been a year since we introduced the Bravo I FS outboard propeller. It was originally developed for single engine four stroke outboard applications. We’ll, it didn’t take long for the word to spread regarding the prop’s performance. Folks running multiple four stroke outboard rigs started asking for right and left-hand rotation sets of the popular prop.

Bravo I FS test boat: 32-foot Donzi ZF center console.
Twin Verado 300s with 1.75: HD gearcases.

Being the conservative person I am, I opted to first work with a handful of people running various hull types to prove the concept before releasing the counter rotation Bravo I FS models. It took longer than I thought to get feedback from the field.

I  grew frustrated because I wasn’t getting any details regarding performance results. All I would get was, “They’re great! Thanks. ” or more often than not – no news at all. It was like pulling teeth. I found out over time the props worked so well that they wanted to keep their performance secret to themselves. Eventually, I got the detailed information I was looking for and I am happy to share it with you here. Read more

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Bravo on the Bayou

Mercury Marine reps celebrate another BASS Classic victory. (L-R) Scott Reichow, Kevin "KB" Brown, Mike Shedivy, Randy Qualls (Legend Boats), Chris Lane (2012 Classic Winner), Michelle Kilburn, Steve Miller
The Pro Finish Bravo I XS outboard propeller features a tuned exhaust tube with large one-inch vent holes for enhanced 2-stroke outboard performance.

I’m fortunate to annually represent Mercury Racing at the Bass Master Classic in the Mercury booth. This year, a fisherman named Rick asked me if there was a Mercury prop that would work for him. He had recently purchased a 2012 Triton 19XS powered by an OptiMax Pro XS 200. Rick was frustrated with the performance. The sharp turns and switchbacks on the Bayou where he runs were causing his propeller to break loose. This forced him to back off the throttle, causing the boat to lose speed and drop off plane. Rick had contacted his Triton representative regarding the issue. Although they discussed various options, the rep suggested Rick continue using a three blade prop.

The performance facts that I gathered in our conversation pointed me to a Bravo I XS. I told Rick the prop is designed specifically for low-emissions 2-stroke OptiMax outboards. Rick responded, “Isn’t Bravo I a sterndrive prop?” Read more

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Hi-Performance Boat Operation – Part 3: Prep & Drive

Pre-run inspection of a 700 SCi powered DCB catamaran. Photo credit: Tres Martin's Performance Boat School.
Twin OptiMax 300XS outboards rigged on a 30-foot Spectre catamaran.

In my previous post (Part 2) regarding high performance boat operation, I reviewed basic information on rigging fit and function. Now its time to head to the ramp.

While the boat is still on the trailer, walk around for a visual inspection of the hull.  Next, climb aboard for a visual inspection of the interior and engine compartment (motor well for outboards): ensure everything is in place and secure. Don’t forget the drain plug(s)!  Check your other safety accessories: aboard? In secure locations?

Helm of a DCB M35 catamaran powered by twin 700 SCi sterndrives.
Helm of 50-foot Cigarette Marauder with twin 1350 sterndrives.

Once your boat is launched,  review the helm to familiarize yourself with the location and function of all instruments and controls. Make sure the steering wheel, throttle and shift controls are well within your reach and that you are comfortable with their operation.

If your boat is fitted with K-Plane trim tabs, be comfortable with the location and operation of the tab trim switches. The driver needs to know the location and function of accessory switches such as bilge blower, bilge pump, running lights, horn, courtesy lights and related fuses, or circuit breakers. Read more

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Hi-Performance Boat Operation – Part 2: Rigging Fit & Function

Spring is a great time for newbie and veteran performance boaters alike to get familiar with their craft. For starters, you should review your owners manuals — really, you should — and review the key components of your new boat.

The 300XS is very popular for singe and multiple engine applications.
The 300XS on this Hydrostream features a 20-inch mid section and Sport Master gearcase.

Performance boats vary widely in propulsion and size. Outboards come in 20, 25 and 30-inch drive shaft lengths to accommodate a variety of applications. Mercury (and other brand) outboards are fitted with a standard gearcase for most applications. Hulls that can take advantage of the high power-to-weight ratio of a 300XS may benefit from its wide range of gearcase options. Similarly, Mercury Racing offers a variety of sterndrives for differing power capacities and hull types.

Mercury Racing’s high styled Zero Effort Digital controls.

Mechanical control: High performance outboards are usually rigged with with dual steering cables, a shift cable, throttle cable and fuel line. With performance sterndrives, throttle and shift are accomplished with cables, but steering is hydraulic. These include 600 SCi  and 700 SCi Mercury Racing packages.

Digital control: On Digital Throttle & Shift compatible outboards, such as the 400R and sterndrives including the 520, 540, 565, 860, 11001350 and 1550 mechanical throttle and shift cables are gone — replaced with a single electronic cable. Steering is either electric (Verado) or hydraulic (MerCruiser). Read more

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Hi-Performance Boat Operation – Part 1: Introduction

A Nor-Tech catamaran boat powered by twin 850 SCi sterndrives. Photo credit. Florida Powerboat Club.
The boys from Sunsation enjoy their time on the water. Photo credit: Naplesimage.

With Spring in the air, the timing is right to review the basics of high performance boat operation to ensure you and your passengers have a safe and enjoyable Summer on the water. We include a Guide to Hi-Performance Boat Operation with every engine we ship. We encourage new and current owners to review the book and then get some in-boat driving lessons from your local high performance dealer. Those who do not have a qualified driving instructor in their area may want to consider Tres Martin’s Performance Boat School.

Our operation guide is packed with general performance boating information including a list of descriptive terms relating to propellers, hull types and overall boat performance.  Let’s first review the various performance boat hull configurations.

Read more

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On Their Own Plane

The cover of the original K-Plane Trim Tabs brochure.
K-Planes continue to prove themselves in offshore powerboat races around the globe. Photo credit: Paul Kemiel Photographics.

I was going through my literature archives the other day and came across a copy of the original Kiekhaefer Aeromarine, Inc., K-Plane Trim Tabs sales brochure. I’ve always respected the quality and functionality of Kiekhaefer’s literature.  I  thought a blog post regarding the history of K-Plane trim tabs would be of interest. More importantly, it will serve as a refresher regarding the fit, form and function of the world’s most durable trim tabs.

Kiekhaefer Aeromarine Motors first introduced K-Plane Trim Tabs in 1970.  They were designed to keep the fastest, hardest running racing boats on an even keel in just about any water condition. US (APBA) and World Offshore (UIM) champions, Doc Magoon and Carlo Bonomi ran nothing else. In the mid 70s, Fred Kiekhaefer upgraded the product for recreational use. Read more

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Prop School – Part 6: Slip

Bob Teague uses Mercury Racing Pro Finish CNC Cleavers exclusively on his 525 EFI powered Skater 388 Super Cat Lite race boat. Photo credit: Paul Kemiel Photographics.

Response to my Prop School series has been been gratifying. It has generated a lot of good discussion (online and off) regarding  propeller design, function and application. One of the most common questions is about prop slip. It is the most misunderstood of all propeller terms.

A wing moving through air produces a pressure differential: low pressure above the wing, with high pressure below it, creates lift.

Propeller blades work like wings on an airplane. Wings carry the weight of the plane by providing lift; marine propeller blades provide thrust as they rotate through water. If an airplane wing were symmetrical (air moves across the top and bottom of the wing equally), the pressure from above and below the wing would be equal, resulting in zero lift.   The curvature of a wing reduces static pressure above the wing — the Bernoulli effect — so that the pressure below the wing is greater. The net of these two forces pushes the wing upward. With a positive angle of attack, even higher pressure below the wing creates still more lift. Read more

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Prop School – Part 5: Blade Efficiency

 

 

Turning out.

Rotation. Propellers come in both right and left-hand rotation. Standard rotation for both outboards and sterndrives is right-hand: the prop spins clockwise when in forward gear.  Left-hand props spin counter clockwise.  Left-hand props are typically used with multi-engine applications. The counter-rotation prop works to balance (or reduce) the torque effects from the right-hand prop. Most twin engine applications are setup with the the props “turning in”; the port engine spinning right-hand and the starboard engine spinning counter clockwise. Read more

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Walleye Prop

Mercury Racing Lab Finished Bravo I Outboard Propeller.
Mercury Racing Pro Finish Bravo I XS outboard propeller.

You may wonder how we go about testing props. We have a number of our own outboard and sterndrive boats that we use for initial testing. Nevertheless, I’m a firm believer of getting feedback from those who use the product everyday in the real world. Recently, I wanted feedback on performance differences between our Lab Finished Bravo I and Pro Finish Bravo I XS outboard props. My target applications were Walleye and bass anglers.

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Prop School – Part 4: Blade Cup

Illustration of cup added to the trailing edge of a typical thru-hub exhaust prop.
Blade cup location on our Lab Finished Maximus prop.

Cup is a curl formed or cast into the trailing edge of a propeller blade.  When done correctly, The face of a cupped prop blade is completely concave. Cupping is most beneficial on blades which are surfacing, either from transom height (X-dimension) or trim angle. The cup retains water on the blade for a longer period of time, enhancing thrust and efficiency. Racers and performance boaters were the first to realize the benefits of cupping. Now, most recreational props come standard with some cup.

Read more

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Prop School – Part 3: Blade Rake

Rake is the relationship of the blade face and the propeller hub.

Rake is the angle of a propeller blade face relative to its hub. If the blade face is perpendicular to the hub, the prop has zero-degree rake. As a blade face slants back toward the rear of the prop, blade rake increases. Rake is either flat (straight) or curved (progressive). Most lower horsepower (“lower” by Mercury Racing’s reckoning) outboard propellers, like Black Max aluminum and Vengeance, have 15-degree rake and are designed to operate fully submerged to push a boat across the water. Typically, higher horsepower outboard and sterndrive propellers have a higher flat or progressive rake.

A good view of our CNC cleaver prop on a NXT1 drive.

A greater rake angle generally improves the ability of the propeller to operate in a ventilating situation. Ventilation occurs when blades break and re-enter the water’s surface — such as occurs with 1) a Bravo sterndrive installed with a high “X” dimension, 2) a surfacing drive (NXT1NXT6 SSM or M8) or 3) an outboard installed or jacked high on a transom. In surfacing operation, higher rake can hold the water better as it’s being thrown into the air — deflecting it aft and creating more thrust. Read more

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Prop School – Part 2: Terminology

Continuing from Prop School….Part 1… Here, I will explain basic propeller terminology and fitment.

Diameter: In “prop speak,” diameter is the distance across a circle made by the blade tips as a propeller rotates.  The proper diameter is determined by the power that is delivered to it and the resulting prop RPM.

A 17 1/2 inch diameter Pro Finish 5-blade CNC prop on an M8 sterndrive.

Type of application is also a factor. How much propeller is in the water (partially surfaced vs fully submerged) plays a role in determining diameter: The more of the prop that is surfacing above the water, the larger the diameter needs to be (so what’s left under water can still push). On rare occasions, diameter may be physically limited by drive type or in close, staggered installations where tips can touch.

Within a specific propeller style, diameter is usually larger on slower boats and smaller on faster boats. Similarly, for engines with a lower maximum engine speed (or with more gear reduction), diameter will tend to be larger. Also, diameter typically decreases as propeller blade surface area increases (for the same engine power and RPM): a four bladed prop replacing a three blade of the same pitch will typically be smaller in diameter.

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Prop School – Part 1: Introduction

I’m Scott Reichow. I manage Mercury Racing’s propeller department (see my previous post, Bravo for Outboards? YES!). Working in performance boating is exciting: It’s fast paced. Propulsion systems and hull designs are in continual evolution. Our customers are generally astute, technically oriented and often quite colorful characters. We’re all performance freaks! We’re all continually learning. That’s what makes my job so much fun!

The prop knowledge guide book. Circa 1980.

If you are like me, your first boating experiences were in lower horsepower boats used primarily for family recreation, fishing, skiing, wake boarding, or general cruising. And like me, your boating experiences and knowledge have evolved through time.

When working with high-end performance boats and experienced customers, one tends to assume people have basic product knowledge. However, a propeller is complicated. Because our backgrounds vary widely, our levels of understanding vary widely, too. So, we’ll revisit the basics and then dive deeper on propeller form, fit and function. Read more

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Refreshed & Rejuvenated

Is your propulsion system in good shape and ready for another season? Now is the time to check over your equipment. If your engines have reached a maximum of 150 hours, now is the time for a refresh to insure a hassle-free 2011 boating season.

We introduced the Factory Fresh engine refresh program in 2006 as a service for owners of our big block sterndrive engines (850 SCi, 1025 SCi, 1075 SCi and 1200 SCi). We’ve learned how our customers from around the world use the product, how various applications relate to engine wear and the affects maintenance (or lack of) has on engine life. More importantly, we have built valuable relationships with our consumers, OEM boat builders and dealers.

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