Engine replacement

[doug9846]

Replacing a solid mounted Volvo with a vetus with rubber engine mounts, intend using flexible coupling thought this would be OK however someone has put some doubt in my mind. Should I do something more sophisticated like CV drive shaft or a dripless seal maybe more tolerant of movement(vibration), really wanted to keep the simplicity and reliablity of a stuffing box, any thoughts?

[Nineteen]

Hi,
We put in a R&D flex coupling and a PSS dripless seal in with our Yanmar 3JH3 about 8 years ago and the combination has been great. No issues even with the Yanmar mounts that are quite soft. It has definetly reduced noise and vibration transmitted into the hull.

I still check the alignment each year and will look at changing the bellows next liftout.

If we had the space then I would have done a thrust bearing and CV setup but I think the current arrangment works great. We also have a 11/4 shaft and Hydralign feathering prop FWIW.

Cheers
Tom

[skipperpete]

Is your traditional stern gland rigidly mounted or attached to an extension hose?
If you decide to use a CV shaft( aquadrive or python) a rigid shaft seal mounting is ok but you might find the installation work a problem, there needs to be a bulkhead created to absorb the propeller thrust (and the CV shaft assemblies are fairly expensive). There are some very good flexible couplings in the Vetus catalogue that allow 1 to 2° of angular mis alignment for continuous duty. The other installation considerations are the clearance below the coupling and the distance from the coupling to the stern seal, ....what you can do is defined by these measurements.

[kapnd]

Originally Posted by skipperpete

. There are some very good flexible couplings in the Vetus catalogue that allow 1 to 2° of angular mis alignment for continuous duty. .

You don’t want to allow any misalignment, even if the coupling is said to have the ability to absorb that. It will come back to haunt you!
1 to 2* of misalignment should be fairly easy to work out in the motor mounts, possibly some shims, if it’s that close already, why not make it right?

[doug9846]

Thanks for the replies, I believe I can get the alignment right, guess my concern is that I was advised by the previous owner " don't let anyone talk you into soft mounting the engine" the flexible coupling would be to absorb vibration movement fed down the shaft, rather than compensating for misalignment.The stern gland is traditional rigid mount stuffing box, 1" shaft, sounds like Tom has a similiar instal to what I am considering operating successfully over a number of years? Like to get out of the instal under $14k USD or thereabouts but reliable of course.

[Pete7]

Doug, tell us more about the boat. Is this a yacht or powerboat?

Pete

[skipperpete]

Mostly I’d agree about the alignment, especially with the polyflex and similar “Drivesaver couplers but sometimes it’s simply not possible to eliminate a degree in alignment.
I took out a Volvo with a down angle gearbox and replaced it with a Yanmar and their own down angle gearbox. The difference in the down angle between the different gearboxes was enough to put the front of the Yanmar down by about 1½ ° with no room overhead to use a straight drive Yanmar transmission. The Yanmar installation instructions specify 0° of down at the front so there were only 2 choices .... cut and raise the cockpit floor by over 4” or just ignore Yanmar and drop in the engine with the down angle to the front and negate the warranty. Bought a “ Uniflex “ type coupling after consulting with Vetus and the boat did the trip from Thailand to Europe..... no problems and it still has the same coupling.

[doug9846]

Hi Pete the boat is a 30' sailing sloop, 5 ton, swing keel, 1985. Already purchased the engine , Vetus 3.09 3cyl 27 Hp. Autostream 3 blade feathering prop. Comes with some bits for the instal, ie fuel filter,raw water filter, water lok muffler & engine panel. Maybe a tad overpowered but wanted the smootheness of 3 cyls and the previous 16 hp was well under powered.

[skipperpete]

Hey congratulations on the new engine, excellent choice. Nice propeller too.
Pete.

[Q Xopa]

Originally Posted by kapnd

You don’t want to allow any misalignment, even if the coupling is said to have the ability to absorb that. It will come back to haunt you!

1 to 2* of misalignment should be fairly easy to work out in the motor mounts, possibly some shims, if it’s that close already, why not make it right?

Alignment is a moving target. I consider it a good start approximation.
But consider the following.
When we align our engine to our propeller shaft it's not running.
I dont know if you have watched a motor when you rev it. It moves.
It moves more with more torque trying to twist a propeller pushing against water.
Then the propeller tries to move forward to push our boat forward. This pushes the motor forward.
Then think about our motor flopping from side to side in a seaway.
We might think our boat hulls are solid, but they do flex to varying extents. This is often shows up most when the boat is on the hard.
Anyway, it's a good start, but there are limitation. It's probably the best we can practically do.
But keeping things perspective how much these things matter. This is the way things have been done for ever. And let's face it, it works.

Anyway just some ramblings.

[doug9846]

Thanks kapnd, I agree that chasing down the last couple of thou is he right way to go and
I will bear in mind Q Xopa words which strike a chord as the reality of the situation, there are quite a few forces at play, appreciate your perspective.

[malbert73]

Everyone uses soft mounts I think. I personally did install a Sigma Drive this off-season mainly as when motorsailing and heeling (ie if I want to head very close to wind with reefed mainsail to make a heading) there was some vibration, probably as engine shifts slightly. And it certainly took all vibration out of my drivetrain. A pretty slick set-up though not cheap, but I recommend it

[Q Xopa]

Seeing chasing down alignment percision is being sought. Generally 0.004" ( 4 thousandths of an inch), or better, is what is suggested. Usually done with feeler gauges between coupling mating faces. This is the way most yard mechanics will do it.

Just to be aware, there are also some limitations to this method.
Firstly it requires some disassembly.
Secondly it's a bit of a lengthy process as you need to adjust and then check. Readjust and re check until it's where you are happy with it.
The other trouble is that you have only got the shaft axis's the same angle. It doesnt actually measure the shaft centre axis's are concentric. Ie the shafts could be the same angle but one could be higher, or left or right of the other.

If you are chasing alignment perfection. I use a set of a couple of dial gauges. They cover the above 3 limitations.

Anyway not to be over dramatic, but more to consider the whole picture.

At the end of the day if you do a good alignment you are in a much better place than I would hazard to say many.