disregard the "hooks" at the front of the Outboard Motor Shaft Length: How do I measure? This illustration depicts four different outboard mounting height options (courtesy Mercury Marine). on How to Measure Outboard Shaft Length: The Only Guide You Need, ePropulsion vs Torqeedo: An All-Round Comparison, 55 lb Thrust Trolling Motors: All You Need to Know Before Purchase, Spot Lock Trolling Motor: Is It Worth It & Best Options in 2022, Wiring 24V Trolling Motors: 24 Volt Wiring Diagram (with Video), LiFePO4 Battery: Why Lithium iron Phosphate Batteries Are Your Best Options in 2022, Minn Kota vs MotorGuide: Best Option in 2022. To achieve this, the motor itself has to be attached at the correct height. function gtag(){dataLayer.push(arguments);} Since the length of the shaft of your outboard is associated with the size boat, smaller engines will generally have shorter shafts. What's the best height for my boat motor? bracket forward with a straight edge to where you can then measure up Owners of bass boats, RIBs, or offshore fishing boats need to get this right. Boats with more engine power and weight require longer shaft outboards for better balance. This is simply a measurement taken from the top of the transom (top of Here we look at the effects of standard, lower and higher mounting. To achieve this, the motor itself has to be attached at the correct height. var xmlHttp = new XMLHttpRequest(); The boater must also consider if the boat transom support is designed to bear the weight of a higher mount. Now that you have a better understanding of boat transom heights its time to take out the ruler and get the perfect measurements. Keep these numbers in mind if you ever have a need for a new outboard motor for your boat. They operate as a planing surface, allowing your boat to climb to the top more quickly. However, youll notice a little increase in drag and a decrease in top-end performance. The motor is what powers the boat so the two go hand-in-hand. Charles Plueddeman is Boats.com's outboard, trailer, and PWC expert. Next, measure from your centerline to where the outboard will be mounted on each side. Generally, the anti-ventilation plate on most engines is aligned with the bottom of the vessel. hulls, such as Allisons, Bullets, Strokers, etc., this measurement could What is Transom Height? Boats that use longer outboard shafts include: Height Measurement: Recommended Shaft Length: 14" - 17.25" 15" Shaft (Short) 17.25" - 19.5" Varies by application 19.5" - 22.5" It is extremely important that the boater understands the significance of the transom's height. The greater the number, the more the drive may sway (also called tuck under or negative trim). The height is approximately six inches higher than with a propeller. The how to measure the shaft length of an outboard motor is a question that many people have asked. The boat transom can be flat with zero degree angles. It moves an outboard up and down to optimize performance and enable a boat to venture into shallower water than it might otherwise. Take the center measurement from the top to the bottom of the hull. |. When you measure the width of the stern, mark the center with a grease pencil. (1) Multiply the overall length of your boat (in feet) by it's widest beam at the stern (excluding any Fins and or Shear) (2) Locate that value on the left hand vertical column of the chart below. Boaters who consider going with a higher mount can see increased speeds. Raising an outboard higher on the transom can reduce drag and raise top speed. As summer approaches there will be more boaters taking to the water. The anti-cavitation plate above the prop needs to be within an inch of the bottom of the transom, therefore, the prop should be well below the transom. Mounting the motor lower on the boat transomcan createexcessive spray, increase case drag, reduce underwater clearance, and negatively impact faster boats. To measure the transom height, measure from the center on for transom (rear of the boat). Basically, there are three main ways to measure motor I show you how to consistently measure your prop to pad height. This alone can outweigh the negatives when deciding to adjust the mount upwards. To achieve 35 mph with a 6 hp engine, the total weight is 135 lbs (boat motor fuel passengers). If you are running a twin-engine setup, then measure the same distance from each clamping plate to the bottom of the hull. To sum up, there is a simple calculator of the shaft length for outboard motors: Outboard Shaft Length = Transom Height +/- Factors. An outboard motor can drive just about any sort of boat with proper mounting. If you are running a slower boat, the exact location of the ventilation plate is less important. The boat transom height is measured from the lowest point on the keel along the center line to the spot where the outboard motor's mounting holes bracket rests. I would ask you to go back and measure the transom of your boat. Not to measure boat speed, but to gauge the mounting height of the outboard motor on the boat transom. Measure from there down to the top of the cavitation plate, also known as the anti-ventilation plate. Displacement hulled vessels like sailboats and workboats can benefit from a little more space between the hull and cavitation plate, but not much. Happy boating! All you need to do is measure how much to rise. The outboard comes with mounting holes and brackets. These cookies track visitors across websites and collect information to provide customized ads. (616) 364-0666, On all contiguous US part orders over $100. Functional cookies help to perform certain functionalities like sharing the content of the website on social media platforms, collect feedbacks, and other third-party features. displayPrimeOffers: true, If you have a small boat with a 15 to 17 inch aft transom, youll most likely need a short shaft outboard. })(); a Detwiler manual jackplate. In addition, motor totes will not harm the finish of the lower unit. Step 2 requires the propeller's radius (check the user manual and then the technical drawing). It varies between different motors and boats. h[0].appendChild(s); A reverse transom that sits too high can impact the propellers of the motor and motor bracket. However, there may be times when a boater strays away from these recommendations. document.getElementById('cloakd53b59933f6c3f2e8b59f1b4a6d41fa5').innerHTML = ''; Two years ago, I bought a Boston Whaler to fish off the coast. A1: Broadly speaking, the outboard motor shaft length for pontoon boat, bass boat, or other larger boats should be long shaft. There is a simple test to see if your outboard motor is set at the best height. measuring; you may have to "extend" the flat part of the How to Measure Transom Height For vessels with transom-mounted outboards, you can easily figure out which type of outboard you need to get. Simply start with the engine in idle, followed bytrimming the motor out by one-half to full trim. If the height of the boat transom is off it can cause major issues. Commonly, the transom angle ranges from 0-30 degrees, with the average transom angle set at 14 degrees. Boat Transom Heights The Beginners Guide, Buying a boat can be an exciting purchase. But, how do you measure it? While this is the case there is certain saltwater motors that are extra extra long at 30. mpeSelector: ".pt-mpe", When it gets to the short side (14), When the inner corner of the square comes into touch with the transom, measure the distance between the inside corner of the square and the boat bottom (see drawing below). Simply start with the engine in idle, followed by trimming the motor out by one-half to full trim. 2019s List of the Best Recreational Pontoon Boats for Sale. Disclaimer: As an affiliate I may earn a commission on any qualifying purchases, including those from Amazon.com, at no extra cost to you read more. If it measures between 17 and 22, youll want to go with a long shaft motor. var h = d.getElementsByTagName("head"), and I'll explain it better, (or point you to someone that can help. motor brackets window.dataLayer = window.dataLayer || []; Doing this can have adverse effects. The vertical distance between the interior of the clamp and the cavitation plate is the shaft length specified by the outboard manufacturer. Copyright 1999-2023 Boats Group. The transom is the boats flat vertical part at the back. Among them will be first-timers or those who have recently purchased their boats. endobj The most common percent angle is probably 12, however spec sheets for O/B and I/O boats may show 10 percent, 12 percent, and 14 degrees. Top 10 Choices for Boaters, Mercury Introduces 600HP V12 Verado Outboard Engine, The Outboard Expert: Tohatsu Propane Outboard Engine. Engine Oil Mixing Ratio Fuel 50: Engine Oil 1. Rest the yard stick or another suitable straight edge along the keel on the bottom of the boat so that it makes a straight line aft to the outboard. Higher mounting decisions should be left to the professionals. Step 3: Add another 10 cm (4'') to the previous calculation for the final ideal shaft length. Having the cavitation plate a bit lower than the transom is preferable to having it too high. If youre looking for a bracket that can handle motors of up to 10/15 horsepower, go no further. Smaller boats may use adjustable jack plates that can be changed to fit any outboard. 2 0 obj Always weigh the risks of making adjustments. Industry standards dictate that for short shaft engines the transom height should be 15. (Putting a This is handy if youre shopping for second-hand outboards or looking to sell the one that came with your boat. All things considered, sticking with the industry standard is best for the beginner. On the downside, a higher mount can interfere with the boaters steering capabilities. As mentioned above, the operation of the propeller relies on the transom height. For most boaters this is a no brainer, but for the novice or inexperienced boater it may be a tougher question. In lower mounting, the engine is set lower than the recommended standard. xmlHttp.setRequestHeader('Content-Type', 'application/json'); <> There is a simple test to see if your outboard motor is set at the best height. In the case of a larger offshore boat, it may be to the top of a cutout on the . Most transom savers can support up to a 150HP motor, which is sufficient for most regular boats. He is also a certified marine technician and the author of a popular text on writing local history. Advertisement cookies are used to provide visitors with relevant ads and marketing campaigns. Long shafts are 20-inches long. You also have the option to opt-out of these cookies. Other factors to consider when determining the mounting height of an outboard are related to performance. The first order of business is to measure your boat for the ideal fit. Or measure from the main engine prop up to the water line? Extra-extra long shafts are 30-inches long. If measuring an existing outboard: Measure from the inside top of mounting bracket down to anti-cavitation plate above propeller (this is the largest plate/fin directly above the propeller). Analytical cookies are used to understand how visitors interact with the website. The transom is the back of the boat where the motor is hung. The height of the transom is calculated by measuring from the bottom of the hull to the top of the transom, using the center line. The prop will be in cleaner, harder water as it advances farther aft, making it more efficient. To do so, measure from the stern (back) of the boat to the midpoint of the hull on both sides. The motor length corresponds to the transom height of the boat, measured from the keel to gunwale at the transom. However, your boat will have slightly more drag which will reduce your maximum speed. When the boat transom is too low, the motor could end up underwater. Place the bracket on the transom to the left of the main outboard or rudder. maxMicroAmount: 0.0, This allows the engine to idle without the flow of the exhaust being restricted. These are vertically aligned so the boater can make adjustments. For slower boats, its less critical to. Buying a boat can be an exciting purchase. former editor at Boating Magazine and contributor to many national publications To do so, take a measurement from the very top to the very bottom of the transom in the precise center. height (that I'm aware of); probably the most common is: Offshore vessels are often equipped with a large mounting bracket so that the transom can be left at full height. Trimming in, trimming down, and trimming out are all terms that a beginning boater should learn. Once you know what will fit on your hull, you can fine-tune your choice based on the performance youre looking for and how you use the boat. If it measures between 17 and 22, you'll want to go with a long shaft motor. With the motor trimmed so that the propshaft is parallel to the keel, the anti-ventilation plate should be just about even with your straight edge, and thus even with the boat bottom at the keel. This, however, is not recommended for the beginning boater. Doing so, will put the propeller right below the boat. The boat transom can be flat with zero degree angles. To break it down a bit more for you: Short shafts are 15-inches long. How the outboard will sit on the back of the boat depends on how the transom is designed. Ill also explain the difference between short and long shafts and how they vary by type of boat. Amazon has plate extensions to allow adjustments without buying a new motor: T-H Marine Jack Plate Extension. Set the end of the tape on the outside edge of the taffrail at the center and measure inward to the inside edge of the taffrail. If it measures anywhere from 17" to around 22", then your going to want to go with a long shaft motor. Some may call it a standard length while others may call it a short or a long shaft. A2: Instead of changing to the short outboard shaft, you can try the Jack Plate first. No one wants to have issues with a new transom or boat repairs. With it comes a lot of responsibility and new things to learn includingboat maintenanceand boat basics. The distance between the ends of a transom is measured in inches. Repowering your boat is one of the most expensive upgrades you can make. For example, you can have the Mercury outboard shaft length by model code. boats.com, 1221 Brickell Avenue, 23rd Floor, Miami, FL 33131, USA. Step 2: After you get the transom height, add the radius of the propeller (check the user manual, and then technical drawing for the number) to calculate the minimum shaft length needed to make it work. The height of the transom is calculated by measuring from the bottom of the hull to the top of the transom, using the center line. His works have appeared in regional newspapers in North Dakota and in "North Dakota Horizons" and "Cowboys and Indians" magazines. So from there, I will try to help out by asking questions about your boat such as what type it is and the length. Sluggish speeds, poor handling, heavy spray, porpoising, or even water pushing up into the cowling are all signs that an outboard is set too low.