An outboard that is mounted too low will limit your boat's optimal operation. You can often tell that an outboard is too low if you are experiencing sluggish speeds, poor handling, excessive spray, porpoising, or even water pushing up into the cowling.
What happens when your outboard is too low?
If the outboard is too low, it creates excessive drag, which cuts into speed and fuel efficiency. If it's too high, the propeller tends to ventilate, losing its bite on the water and blowing out while turning and in steep seas.
How far below the bottom of the boat should the prop be?
If you have a short shaft motor, the top most part of the transom and the lower most part of the boat should be about 15 to 16 inches. For a long shaft, I think 20 to 21 inches is correct.
How low should my outboard sit in the water?
Industry standards dictate that for short shaft engines the transom height should be 15″. A long shaft engine requires a height of 20″ and extra-long shaft engines will need a transom height of 25″. While this is the case there is certain saltwater motors that are extra extra long at 30″.
How do I know if my outboard is mounted too high?
Too high usually results in low water pressure, prop letting go in turns, or lack of bow lift are usually the telltale signs. Sometimes porpoising is caused by too much bow lift and dropping the motor will give it more bite and make it worse.
29 related questions foundShould cavitation plate be underwater?
your cavitation plate should be right at the water level. As a rule of thumb it should be 1 inch above the hull for every 12 inches back. (if you have a eurotransom, or bracket or something.) If your cavitation plate is under water you might get better performance if you raise the motor.
Will raising my outboard stop Porpoising?
By changing the engine setback, propeller selection and motor height, you adjust the dynamic balance of the hull. All of these can have a great effect on the porpoising movement. By raising the prop shaft higher, you shift the Dynamic Configuration forward and further reduce the trim angle.
How should an outboard sit on a boat?
A boat rigger's rule of thumb is that the motor can be raised one inch for each eight to 10 inches of distance between the transom and prop. As the prop moves further aft, it's also likely to be in cleaner, “harder” water, and be more efficient.
Why put a jack plate on a boat?
Jack plates perform two key functions. One is setback, which distances an outboard from the boat's transom, allowing the propeller to run in less-turbulent water. Jack plates also move an outboard up and down to optimize performance and enable a boat to venture into shallower water than it might otherwise.
What angle should my outboard be?
There is no one ideal angle -- it always varies by boat. Put the motor into a neutral trim, where the propeller is parallel to the back of the boat. In an evenly weighted craft this should be a fairly fast position and in a craft with only the driver, it will likely be the fastest.
How far should the cavitation plate be below the boat?
The dealer set it at 1/2" above the bottom of the hull when the motor is sitting level or straight up and down. When the motor is trimmed all the way down it is 1/2" below the bottom of the boat but when trimmed up just a little there is slippage or some cavitation.
How far should my propeller be below my boat?
Determining the proper trolling motor shaft length is one of the key aspects of finding the right motor for your boat. It will help ensure that the motors' shaft is long enough to keep the propeller submerged at least 12" below the water line in your specific fishing conditions.
How far should the cavitation plate be?
Re: Cavitation plate location
The cavitation plate should be nearly even with or slightly below the bottom. For a short shaft the vertical measurement of the transom should be about 15 inches.
Will raising outboard increase RPM?
Will Raising My Outboard Increase Rpm? Every engine can be raised to maximize speed, rather than having too little pressure applied to the engine. With too much moisture in your room, the top speed will drop, but the top RPM will increase as it is exposed to more slip, with less ventilated room.
How far in the water should an outboard motor be on a pontoon?
A boat rigger's rule of thumb is that the motor can be raised one inch for each eight to 10 inches of distance between the transom and prop. As the prop moves further aft, it's also likely to be in cleaner, “harder” water, and be more efficient.
What is porpoising in a boat?
Porpoising is a sustained, repetitive motion that causes a boat's bow to bounce up and down out of the water, even in calm waters. While porpoising can be merely uncomfortable for passengers, it can also cause loss of control, which may result in injury or damage to the structure of the boat.
Will a jack plate increase speed?
Jackplates allow improved performance in bass boats, raising the prop to maximum height for reduced drag, improving speed as well as fuel economy. What's more, the setback also effectively lengthens a boat. Setting the motor farther back should improve the ride in a chop coming at the bow.
What RPM should I run my boat at?
Most mechanics and engineers suggest the best cruising speeds are achieved at 3400 and 3800 rpm respectively.
Is a jack plate worth it?
Although they may be a bit pricey, hydraulic jackplates can vastly improve the performance of your bass boat — both at the top end and in the ability to run shallower at low or high speeds. They can even improve the ride.
Why does the front of my boat go up?
Porpoising, or the bow bobbing up and dow, is caused by over-trimming at cruising speed; there's no longer enough hull in the water to support the weight of the boat. Either trim down a little until the porpoising stops, or increase boat speed slightly to create more lifting force under the hull.
How do you find the transom angle?
Measuring The Transom Angle (Degrees):
Slide forward until the short side of the rule (16") touches the transom straight up. Measuure the distance from the keel point to the inside corner of carpenter's square ruler (see sketch). Each 1/4" is equal to 1° degree.
Will a Jackplate help with Porpoising?
A jack plate does not help with porpoise, only somewhat makes it worse, but with the right prop and setup, it will work. Never had this issue with aluminum boats and motor and kicker mounted on transom, also most new glass boats now have stepped hulls, which is a jack plate in its self.
Why does my boat hop?
What Causes Porpoising? Porpoising is the result of the motor's outdrive pushing the boat upwards, essentially boosting it out of the water – albeit for a short period of time. Once the boat comes back down, the outdrive will once again push it back out of the water.
Will a 4 blade prop stop Porpoising?
4 blade props tend to give you more transom "lift", as well as increasing holeshot (via the "rear lift"). It would help with the porpoising you are experiencing by lifting the back of the boat more.
