Tag: Engine Mounts

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How to install an inboard engine?

Are you going to install or re-install an inboard engine yourself? Then prepare yourself well, start with the basics and start measuring. Then you can replace an engine with minimal adjustments. For recent engine types, you often know the installation dimensions or they are easy to find. Pay particular attention to:

In any case, consider what you will need.

Propeller shaft height

First check if the engine matches the propeller shaft height. Are the reverse clutch output and the crankshaft at the same height? If the reverse clutch output is lower than the existing propeller shaft, the engine will ‘rise’.

Engine mounts

On some inboard engines, adjusting the existing engine mounts is not a problem. In case of a steel ship its foundation can be adjusted. In a polyester ship, this is more difficult. Therefore, please check in advance what is possible. Especially with a saildrive, you are often bound to prefabricated through-hulls.

Maximum tilt

Also check whether the inboard engine can handle the maximum tilt when sailing. The maximum tilt can often be found in the manual. A homokinetic drive solves the problem in a different way.

Reverse gear

The Velvet, PRM, Hurth, ZF and Twindisc reverse gears are well known common types. The ratio is often given as engine speed divided by the output speed, e.g. in the ratio of two to one (2:1). This ratio means: Two engine revs / one propeller shaft rev (or simply half).

Often the direction of rotation is indicated with L or R. L 2:1 therefore means: a two-to-one left-hand reverse gear for a left-handed propeller.

You may also come across gears, e.g. for Volvo Penta, with an A for Angle. The axis of these reverse gears is rotated by 7 degrees. Then the motor does not have to tilt as much.

Propeller

Note the direction of rotation of the screw. There are left-hand and right-hand reverse gears. The direction of rotation of the gearbox is determined with the ship moving forward and you looking at the bow.

Be careful with a ‘Z-drive’. The engine will then be reversed, so check the specifications carefully.

AB marine service can carry out the power requirements calculation for your ship.

Power

If you keep the power in the same direction, you can often use the same supply and return connections, such as the exhaust gas outlet, cold water inlet or circulation pipes.

If you are going for larger or smaller power, check the diameter of the connection on the engine. This is already a good indication of the required size.

If the exhaust manifold has a 45 mm diameter, you can use that one. Do not use smaller diameters, this will cause the engine to brake, with all its consequences. Bigger ones are often not a problem.

Propeller shaft and bearing

Also think about connecting the propeller to the reverse gear. Some brands are interchangeable, but this is not always the case. In that case you will need an adapter flange. These are available separately on request or are supplied ready to use with a homokinetic drive.

Want to prevent vibration and save time when connecting? Consider the advantages of a thrust bearing with a homokinetic drive.

What do I need?

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A flexible engine set-up

Vibration-free sailing is for relaxation!

Ever made a lovely boat trip, but eased down on the throttle after a while because of all the noise? After all, for a stress-free yarn we want to be able to hear one another. A flexible engine set-up with engine supports will minimise any noise and vibration. But what is the basis of vibration-free (relaxed) sailing? The principle is simple: remove the fixed connection between the engine and the bedplate. This makes that vibration of the engine is felt throughout the boat. Allow the engine to float on its bedplate to get rid of the noise. But how is that done? Start at the base;

beeld

Why do engines vibrate?
Engines have internal parts that quickly move back and forth. It takes only milliseconds for the piston to be pushed down by an explosion and then back up again, driving the crankshaft at the same speed for a new compression stroke. Modern engine blocks are compact and lightweight thanks to a short piston stroke and aluminium construction. This has many advantages, such as saving space and lower production costs. However, due to its lightweight construction, vibrations are less attenuated and absorbed by the dead weight, and the shorter engine stroke also requires a higher RPM to keep running. And we know from experience that the further we open the throttle, the more noise we create.

Detached engine mount
All the more important to ensure a good and solid bedplate with soft engine mounts, which detach the engine from the bedplate, as it were. The principle is an engine mount as soft as possible, but still strong enough to carry the weight of the engine, the reverse clutch and a part of the propeller shaft.The softest possible rubber
The softness of rubber is expressed in SHORE with a hardness number. In addition, the letters A through to D determine the category of rubber, on which we will not elaborate in this article. SHORE 10 rubber is very soft, and the higher the number the firmer it becomes. A heavier engine also needs stronger rubber to make sure that the rubber is not squeezed out by its weight. Engine mounts are often SHORE 35 and up. It is a matter of finding soft rubber that is firm enough to support the engine. Hardness and quality of the rubber often determine the price and lifespan of the product. Good advice! It would be wise not to look at the price when purchasing engine mounts. Cheap engine mounts from other sectors (washing machine mounts) may be able to do the job, but are not always resistant to oil, grease and diesel fumes that we encounter in engine spaces.

dempers

Too soft?
If the engine mounts are too soft, sturdiness will be lost due to the pull and push movement of the propeller shaft and engine when manoeuvring. V-shaped engine mounts lock the engine in place under load due to their V shape. However, since the engine pushes itself against the rubber, it will also lose some of its muffling effect.

But what is the best solution
For optimal muffling, a combination of flat vibration isolators with a thrust bearing would be the best solution. A thrust bearing keeps the propeller shaft in place. It is a bearing that can absorb forces from any direction. It also hangs in rubber and is mounted between the reverse clutch and the propeller shaft. After installation, it has to be set exactly straight and level to prevent overloading of bearings and propeller shaft sleeves. Even better is to put a flexible (homokinetic) joint between the coupling and the shaft, so that even when under pressure and shifting, all parts can still be running stress-free.

tekening

Example of a homokinetic engine arrangement:
propeller shaft; brown
clamping hub; blue
thrust bearing; pink
homokinetic coupling; green
adapter flange; red
engine mount / vibration isolator; yellow

Advice
Looking for less vibration and more relaxation? In other words: a better engine set-up? We suggest you take a good look at the bedplate of your engine set-up and think about possible improvements. We advise to have this done in consultation with our experts. All engine and clutch makes require their own power calculations. Based on such data, we will be able to draw up a plan.

We supply arrangements for any brand, engine model and reverse clutch. Feel free to ask for your own smooth sailing.