Albatross Marine Python Drive UK Marine dealer

Python-Drive flexible driveshafts by Albatross Marine Python-Drive UK main dealer

Tel: + 44 (0)24 7632 9841 Fax: +44 (0)24 7632 9914

Email the author: ian.oliver@albatross-marine.com

Albatross Marine look at how installing a flexible drive unit can help reduce both wear and vibration to your engine and boat.

In times past when engines were much heavier and far slower running, they had large diameter heavy flywheels which put a lot of inertia into the system, this inertia is crucial in helping to eliminate vibration from the engine. In those days it was standard procedure to mount the engine on solid bearers usually of seasoned oak or elm, and to connect the gearbox to the prop-shaft via a half coupling making it a solid connection all the way through from the gearbox to the propeller.

On more traditional engines such as Russell Newbery and Gardner this is still general practice, and providing the alignment is absolutely correct, and the length of the shaft is not too long without being supported by bearings, they cause no problem. Enthusiasts own most of this type of installation today, and any vibration that may occur is usually acceptable to them.

With modern engines it is far more complicated as they are the exact opposite of the older engines. Firstly, they are of a much lighter construction, secondly, their rpm is a lot higher, and thirdly because of this light construction they are not able to support that much needed heavy flywheel, theirs being a lot smaller in diameter and consequently much lighter in weight.

Modern engines

Those offering marinising services for today's engines do a very good job: the diameter of their flywheel is by and large restricted by the manufacturers design criteria, and when one looks at the number of engines produced for the generator / automotive market, and compare it with the number used in the marine market, the percentages are pretty low. It is obvious therefore that the manufacturers of these engines are not going to change their spec; for what is to them, a low volume product.

Exponents of marinisation ease their way where possible, by adding weight to the flywheel, whilst keeping it balanced, in addition to fitting engine mounts and drive plates of varying hardness and softness. These devices are designed to take out the vibration: in case of the damper plate it absorbs some of the vibration from the engine, whilst the engine mounts have a cushioning effect permitting the engine to move thereby reducing the vibration.

The driveline

Without flexibility in the line, what happens when a gear is selected? As the propeller bites into the water, it has the effect of trying to screw itself into the boat, and is only being held in position by the engine mounts. At his point the engine is being asked to work harder so the vibration becomes greater, coupled with the vibration from the engine from the opposite direction makes the engine mounts work even harder. As the rpm increases centrifugal force takes effect, and the movement begins to even out so it is not so noticeable. However, with the prop-shaft connected directly to engine, and there being no flexible joint available, the whole driveline has to move with the engine as the mounts flex.

Whilst the engine mounts are doing their job what is not so noticeable is the movement of the prop-shaft backwards and forwards through the stern tube.

Premature wear

Due to the weight of the prop-shaft this continual movement wears the stern tube at its lowest point, gradually elongating the stern tube, causing shaft to develop a wobble, and run eccentrically. This movement wears the shaft prematurely at the point it is located in the stern tube, and as the wear gradually gets worse, so the water drips in ever increasing amounts, and vibrations begin to occur that were not present previously.

It reasonable to expect there to be some wear at this point of the shaft and stern tube because of the natural friction, however the continual backwards and forwards movement of the driveline will cause it to wear much quicker than would be the case if there were some flexibility within the system, and the prop-shaft was prevented from sliding in the stern tube.

The cure

The way to get around this is to fit a Python-Drive constant velocity flexible output shaft with a CV joint at either end. One end connected to the gearbox and the other connected to a thrust assembly block.

This allows the engine total flexibility permitting movement in any direction. Whilst the two constant velocity joints absorb the engine movement, the output shaft speed remains constant. The thrust assembly block being rubber mounted permits only rotational movement of the prop-shaft, by putting the thrust coming back up the driveline into the hull, thus preventing the backwards and forwards movement of the whole driveline.

Advantages

The other major advantage in fitting Python-Drive flexible driveshafts is, it makes aligning the engine so easy. On an installation without a flexible output shaft the actual process of getting the engine

aligned with the prop-shaft can be a time consuming job. It is done by continually adjusting all four engine mounts, and checking the gap as each adjustment is made, between gearbox output coupling and the connecting component on the prop shaft until the gap is even around the whole circumference to within 5.000th inch.

Python-Drive simplifies this enormously. The design of the CV bearings is on a slow spiral, this means they require some angle to work effectively. Fitting a Python-drive does not eliminate the necessity of making adjustments, one still has to ensure the engine load is divided equally over the four mounts, but it does mean the actual alignment is not so critical, and the time saved is considerable.

Summary

Python-Drive makes the alignment far easier, both on new and old installations, where it greatly reduces the vibration in addition to providing a longer life to the driveline by reducing the wear. No one likes to a make change for the sake of it, but where a fully flexible Python-Drive output shaft is concerned this is definitely a necessary piece of equipment.

New Python-Drive

To assist boat owners with current vibration problems where space is at a premium, Albatross Marine have announced a new short version to fit 1.25in & 1.5in prop shafts. The overall length of the P60-K is 296mm with the mounting plate being located 237mm from the gearbox flange. The new model P60-B is 246mm long with the mounting plate @ 181 mm from the gearbox.

The main Distributor for the Python Drive is Albatross Marine Ltd., Unit 24 Hammond Close, Attleborough Fields Industrial Estate, Nuneaton, Warwickshire

CV1l 6RY Tel: 024 7632 9841. Fax: 024 7632 9914. Mob: 07734 080990.