publicId: "32bf3437d1346295e03ebcf545f9c839", Raising the motor increases the speed of the boat while decreasing the effort needed to turn the boat. The brackets can add 1 inch to the overall mounting height of the outboard. For over five years he has worked as a newspaper reporter and historic researcher. This will ensure the best performance. But, how do you measure it? If you have an outboard motor, the distance from one end to another will be found on the side or on a label near its bottom. | Sitemap, The Marine Parts Warehouse Outboard Museum, OBR Powerhead / Shortblock Warranty Claim Form, Remanufactured vs. straight edge from the center of the pad, but this time you're measuring This provides seaworthiness and offers maximum protection from large seas. A reverse transom that sits too high can impact the propellers of the motor and motor bracket. Owners of bass boats, RIBs, or offshore fishing boats need to get this right. Increased RPM and additional horsepower feed the need for speed. When the right length motor is hung on the transom of a boat, the cavitation plate (the large plate that extends out over the propeller) should be even with the very bottom of the boat. One of the main concerns is causing the engine to overheat if not enough water reaches the engine to keep it cool. Gear case sits just below or at the hull depth due to the deep v. straight edge on the top of the transom to "extend" it out Is my outboard long or short shaft? What matters is the actual measurement in the specifications, not the name. Tilt your motor until the bullet of the gearcase is Extra-extra long shafts are 30-inches long. To do so, measure from the stern (back) of the boat to the midpoint of the hull on both sides. The correct shaft length for your boat depends on a few factors. On the downside, a higher mount can interfere with the boaters steering capabilities. If the propeller fails to ventilate, the motor is mounted to low. You dont have to be a mathematician to determine the correct boat transomangle. var addyd53b59933f6c3f2e8b59f1b4a6d41fa5 = 'info' + '@'; The first step is to determine the height of your boat's transom. Also, the boat will be more likely to hit bottom or submerge objects such as rocks or logs. h[0].appendChild(s); Or measure from the main engine prop up to the water line? On the downside, a higher mount can interfere with the boaters steering capabilities. The transom is the "back wall" of your boat, the most rearward part of your hull. A big NO. A1: Broadly speaking, the outboard motor shaft length for pontoon boat, bass boat, or other larger boats should be long shaft. Attention: Remember to measure the outboard shaft length straight up and down instead of measuring along the transom. The engine must be linked to the transom at the proper height for a propeller to best meet specific boating demands. Boats with extended transoms, brackets that extend the mounting bracket for the outboard motor behind the back of the boat, can use a higher outboard height. Other boats that need extra long shafts are: Read my other articles on outboard motors. If you are running a slower boat, the exact location of the ventilation plate is less important. For slower boats, its less critical to. mpeInit(); endobj center of the propshaft. your motor will be higher.) The propellers will also have trouble reaching the water. debugMode: false, One of the great things about an outboard motor is how versatile it is. Thats a fairly simple list of symptoms, but if your motor is too low, youll probably notice at least one of them. This restriction includes most fishing boats and longer sailboats. if (PayTomorrow) { An outboard motor can drive just about any sort of boat with proper mounting. The prop will be in cleaner, harder water as it advances farther aft, making it more efficient. Some fishing boats can handle the motor being underwater. And thats usually the case since the electric outboards are designed with larger and more efficient propeller that needs longer shaft. If so, send me an With it comes a lot of responsibility and new things to learn includingboat maintenanceand boat basics. If it measures anywhere from 17" to around 22", then your going to want to go with a long shaft motor. Say the 20 shaft is a long shaft length for gas engines, but it is a short shaft length for electric outboard motors. Displacement hulled vessels like sailboats and workboats can benefit from a little more space between the hull and cavitation plate, but not much. Before we get started lets see what a boat transom is and what it does. For vee-shaped hulls, the lowest spot of the hull will come to point, while on flat-bottomed boats it will be more or less level. maxMicroAmount: 0.0, The boater must also consider if the boat transomsupport is designed to bear the weight of a higher mount. A reversetransom that sits too high can impact the propellers of the motor and motor bracket. Transom Outboard Engine Position - YouTube 0:00 / 0:56 Transom Outboard Engine Position BOATING SCENE 763 subscribers 609 211K views 5 years ago www.boatingscene.com.au Sometimes when your. steel ruler, etc. window.dataLayer = window.dataLayer || []; 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. This could also affect your travelling capabilities on the boat trailer. I would also recommend finding your maximum horsepower rating which is located on the yellow coast guard tag towards the back of your boat. Bass boats, ski boats, or center cockpit vessels will want to double-check their measurements to get it just right. Chances are the boat was designed with a specific size of outboard in mind. Measure from the top of the straight edge to the center of the front In step 3, add another 10 cm (4") to the previous calculation in order to develop the ideal shaft length. former editor at Boating Magazine and contributor to many national publications However, you will need an understanding of how the degrees will alter the boats usability. The same is true for the newest, high-powered offshore fishing boats, where triple or quadruple motor setups are becoming more and more common. As summer approaches there will be more boaters taking to the water. Plus, a low transom cut is an invitation for the water to flood the boat. To do so, you will want to measure at the exact center of the transom from the very top to the very bottom. boats.com, 1221 Brickell Avenue, 23rd Floor, Miami, FL 33131, USA. The cavitation plate is the horizontal surface of the lower unit immediately above the propeller. Smaller 12-14 foot boats can require either a short or long shaft outboard depending on the style of the boat and the brand. In the second photo, we've measure down from the top of the Detwiler Usually speaking, the farther the outboard is set off the transom, the higher the propeller should be in the water (or the higher the outboard can be mounted). If possible for your peace of mind and not let down that magnificent purchase opportunity, place that 08 kicker at back transom and test for yourself. It is extremely important that the boater understands the significance of the transom's height. "brackets". With the long side (22 1/2), place a carpenters square ) in opposition to the keel. Should I take the raft onto the water and measure the exact distance from the top of the transom to the water line? Problems with getting the ventilation plate too low include slower hole-shot and lower top-end speeds. You may wonder how deep your prop should be in the water. Pretty easy to figure out but like I said its crucial to pairing a motor with a boat. Each one has a totally different effect on the boats performance. Always weigh the risks of making adjustments. It can also improve the experience of driving a faster boat. There are a series of four to six holes at the top of the bracket, and the lower bolts actually fit into slots. Knowing how this can affect the overall operation of the boat is a factor to be considered. All rights reserved. If you went too long it would still work but it may lack in performance. The Effects of Standard, Lower and Higher Mounting. To sum up, there is a simple calculator of the shaft length for outboard motors: Outboard Shaft Length = Transom Height +/- Factors. Here we will guide you in how to get the right boat transom height. a Detwiler manual jackplate. The height of the boat transom dictates the size of the outboard motor. I believe 20 to 21 inches is the optimum length for a lengthy shaft. Sailboats use these sometimes, as well as some boaters who want to install a much smaller auxiliary motor to use in case of primary engine failure. Be sure to measure carefully and research thoroughly before diving in. Beyond motorboats designed for large outboards, you will see outboards hanging on the sterns of everything from small canoes to large cruising sailboats. A long shaft engine requires a height of 20 and extra-long shaft engines will need a transom height of 25. Some may call it a standard length while others may call it a short or a long shaft. This email address is being protected from spambots. Offshore vessels are often equipped with a large mounting bracket so that the transom can be left at full height. Generally, short shaft outboards are 15 inches, long shaft outboards are 20 inches, and extra-long outboards are 25 inches. These are vertically aligned so the boater can make adjustments. This, however, is not recommended for the beginning boater. A transom saver, which can change the spacing between the lower unit and the trailer, negates some of the support. August 9/08). Ten years ago I bought my first boat. At least if its too long you can raise the motor or "build up" your transom. But in many cases, its a little more complicated than that alone. Any questions? The motor is what powers the boat so the two go hand-in-hand. Another important measurement is the transom angle. 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. xmlHttp.open('POST', 'https://bes.gcp.data.bigcommerce.com/nobot'); Necessary cookies are absolutely essential for the website to function properly. Mounting the motor lower on the boat transomcan createexcessive spray, increase case drag, reduce underwater clearance, and negatively impact faster boats. The current measurement is the ventilation plate is about 1 1/2" above the true keel line which is about 24" in front of the motor edge. parallel with the straight edge. Height Measurement: Recommended Shaft Length: 14" - 17.25" 15" Shaft (Short) 17.25" - 19.5" Varies by application 19.5" - 22.5" Small portable outboards ranging from 2 to 20 horsepower are usually sold only in short or long shaft versions. So from there, I will try to help out by asking questions about your boat such as what type it is and the length. Remember, if you use a longer outboard shaft than you need you will be increasing your draft. (3) Move horizontally across the chart until you hit the graph curve. The transom is the rear wall of the boat where the outboard engine is mounted in the middle. If you go too short your more than likely going to cavitate and loose power. Step 3: Add another 10 cm (4'') to the previous calculation for the final ideal shaft length. This also means it can affect the safety of the boat. Cavitation is when the propeller is out of the water due to the boat forming a wake of "air bubbles" or "vapor cavities" around the prop. The propellers will also have trouble reaching the water. Engine Oil Mixing Ratio Fuel 50: Engine Oil 1. With more than a decade of experience cruising the lakes in my Crestliner Grand Cayman pontoon boat and my Boston Whaler, I now want to share everything I've learned with my community here at Boating Hub. Actual shaft length is 21.5" on those. ), Al Shields These cookies ensure basic functionalities and security features of the website, anonymously. When the boat transom is too low, the motor could end up underwater. How high exactly do you have to raise the transom?-. They operate as a planing surface, allowing your boat to climb to the top more quickly. :$I>M W$h"%U_yzIb?]NHg_G|r@nX eTf."SQ Its still smart to measure it yourself though, just in case, the design changed over the years. Boaters who consider going with a higher mount can see increased speeds. If the propeller fails to ventilate, the motor is mounted to low. Eq*^?6R83e+j}UY.(M7k]~4g)g ~wmS{ O7t/o(W|X? To make the yard stick long enough to measure the length of all the clubs, tape the ruler to the top. Ask a friend to hold one end of a measuring tape at the extreme outer edge of the top of the transom while you pull the tape across its width to the opposite outer edge to measure the "length of the taffrail," which is the width of the boat across the top edge of the stern. Your goal is to measure how the outboard will sit, so start from the clamping plate and follow the centerline of the hull. When the boattransom is too low, the motor could end up underwater. 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. Adjusting the mounting height of an outboard on the boat transom can affect performance and every boat can be different, so actual on-water testing is best. Finding the right size is a matter of looking at what youve got and taking out the measuring tape. It was a 23-foot Crestliner Grand Cayman pontoon boat. 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). Basically, there are three main ways to measure motor Knowing how this can affect the overall operation of the boat is a factor to be considered. since 1986. By clicking Accept, you consent to the use of ALL the cookies. Pad to bottom of If your boat is newer and the manufacturer is still in business, you might also want to try to give them a call. For vessels with transom-mounted outboards, you can easily figure out which type of outboard you need to get. So its easier and safer to communicate with the dealer with the exact measurement of outboard shaft length in order to get the right model. And the rule of thumb is that you should keep the cavitation plate level with the bottom or keel of the boat. Boat hulls are designed in three basic types that range from slow displacement and semi-displacement hulls to the fastest planing hulls. Why wont Touch ID be under the screen in the iPhone 15 and iPhone 16? You will also risk hitting bottom or submerge objects more frequently such as rocks or logs. In the photo above, we've measured from the motor bracket to the top of Take the center measurement from the top to the bottom of the hull. The transom angle is the vertical incline of the transom and is measured in degrees. Among them will be first-timers or those who have recently purchased their boats. 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. Shaft lengths are available in increments of 5. Measure the area of the transom directly where the engine will be mounted. Here are several situations on how you should adjust the outboard shaft length: Mounting the outboard a little bit higher than the standard point could reduce drag, improve RPM at full throttle, and therefore improve speed and make it easier for the boat to get on plane. These allow the mounting of a standard length outboard behind the transom. Lubrication System Engine Oil Mixed Gasoline. Charles Plueddeman is Boats.com's outboard, trailer, and PWC expert. Other boats that need long shafts are. 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. Your at your local outboard dealer shopping for a new motor and the salesman hits you with the question, "short or long shaft?". (127 mm). from the transom. Copyright 1999-2023 Boats Group. Check the literature about your model boat online, and you may be surprised to find that the number is published for you. Since the ventilation plate & foil are burried under water it is obviously too low. height (that I'm aware of); probably the most common is: If you decide to make some custom adjustments we have theexperience and know-howto make it happen. So you should just measure the height of the boat's transom from the center down to the lowest point of the hull, and compare transom height with the outboard shaft length numbers. 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. With the outboard shaft length too long, meaning the prop is too deep in the water, the engine wont be as efficient, and the fuel burn is high. Its important to note that manufacturers call their models different things. These are vertically aligned so the boater can make adjustments. s = d.createElement("link"); When trimming your motor, they provide you a greater bow response. These cookies track visitors across websites and collect information to provide customized ads. Now that you have a better understanding of boat transom heights its time to take out the ruler and get the perfect measurements. function loadScript(script) { Some outboards have a serial number that tells you which shaft length to go for. As with anything, there are exceptions to the rule. Analytical cookies are used to understand how visitors interact with the website. var ptScript = "https://cdn.paytomorrow.com/js/pt-mpe.min.js"; I would ask you to go back and measure the transom of your boat. All things considered, sticking with the industry standard is best for the beginner. An inch or two probably wont make a big difference, but any more than that will lead to trouble. The form of a boats transom varies depending on the manufacturer and model. s.setAttribute("rel", "stylesheet"); All rights reserved. Check out the Westshore Marine & Leisure Youtube page! When mounting the engine, you want the cavitation plate to be 1 above the boat bottom for every 12 away from the transom. With such an important, long-term, and expensive upgrade, its never a bad idea to double-check. Which Navigation Lights Does Your Boat Need? Keep these numbers in mind if you ever have a need for a new outboard motor for your boat. If mounting directly to a boat transom: Measure from the top of the transom down to the bottom of the hull or keel (lowest point). 3 0 obj <>/Metadata 127 0 R/ViewerPreferences 128 0 R>> This is probably the worst case scenario out of the two. Picking the right shaft length for your outboard is an essential step in getting the best performance from your boat.
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