Re-powering from VP to Beta - advice on earthing please

[Bobc]

My current VP engine (TMD-22) has return wires for the alternator, and sensors I believe, and only earths when the plugs are heating, when the starter is running, or when the stop solenoid is energised (or so I believe).

I am thinking about re-powering with a Beta engine, which I believe has the battery negative connected to the engine block and uses the block as a negative earth for everything.

Assuming I have a solid coupling to the propshaft, what would I need to do to ensure that the engine is electrically protected.

 

[pvb]

My current VP engine (TMD-22) has return wires for the alternator, and sensors I believe, and only earths when the plugs are heating, when the starter is running, or when the stop solenoid is energised (or so I believe).

I am thinking about re-powering with a Beta engine, which I believe has the battery negative connected to the engine block and uses the block as a negative earth for everything.

Assuming I have a solid coupling to the propshaft, what would I need to do to ensure that the engine is electrically protected.

The VP isolated earth system is usually seen on saildrives, not shaft drives. There's no great corrosion risk with shaft drives, especially if you fit a galvanic isolator.

 

[Kukri]

Isolated return is also a good idea on wooden boats. Not essential, but nice to have.

 

[PaulRainbow]

My current VP engine (TMD-22) has return wires for the alternator, and sensors I believe, and only earths when the plugs are heating, when the starter is running, or when the stop solenoid is energised (or so I believe).

Probably does, but the block often has a -12v connection too, especially on shaft drives.

I am thinking about re-powering with a Beta engine, which I believe has the battery negative connected to the engine block and uses the block as a negative earth for everything.

Assuming I have a solid coupling to the propshaft, what would I need to do to ensure that the engine is electrically protected.

A hull anode wouldn't do any harm, most likely negate the need for shaft and prop anodes.

If shore power is fitted and the earth is bonded to anything on the -12v circuits, then you should have a galvanic isolator as well.

 

[VicS]

My current VP engine (TMD-22) has return wires for the alternator, and sensors I believe, and only earths when the plugs are heating, when the starter is running, or when the stop solenoid is energised (or so I believe).

I am thinking about re-powering with a Beta engine, which I believe has the battery negative connected to the engine block and uses the block as a negative earth for everything.

Assuming I have a solid coupling to the propshaft, what would I need to do to ensure that the engine is electrically protected.

Yes you are right about the blocks on the 22 series being electrically isolated, only being earthed via a relay for the glowplugs and the engine stop solenoid during preheating, starting and stopping. Even the starter motor is isolated
It comes about because there is no electrical insulation between the block and the transmission as there is on many other VP engines since IIRC the "B" series MD 2010/ 2020 etc series. Important for saildrive leg protection although not really relevant to shaft drives and nothing to do with engine protection

You will be able to connect the battery negative directly to the Beta block in the usual way .... Beta engines come with a good Installation Guide and Owners Manual, which you can find on the Beta Marine website if you wish. It gives full details of the required electrical connections.

https://issuu.com/betamarine/docs/heat_exchanger_om_221-20031_rev-02_?e=15614309/66188182

The extra thing you will have to do for engine protection is routine replacement of the heat exchanger anode .

If you normally connect to shorepower for lengthy periods a galvanic isolator is next to essential, unless the earth is not bonded to the DC negative ( it wont have been with the TMD22) and the anodes etc . You may have to look at how your shorepower earth is bonded.

A hull anode may be a worthwhile for additional protection of the stern gear in addition to any prop or shaft anodes but no change there from the existing situation. Unless an " Electroeliminator" or similar is used to make contact with the shaft a flexible coupling will need to be bridged. Some couplings ( R&D ??? ) use a special conductive insert.

 

[Bobc]

Thanks chaps.

At the moment the boat doesn't have a hull anode and nothing is bonded. It just has an anode on the propshaft.

So effectively you're saying that I won't have to do anything much, other than fitting a hull anode?

 

[PaulRainbow]

Thanks chaps.

At the moment the boat doesn't have a hull anode and nothing is bonded. It just has an anode on the propshaft.

So effectively you're saying that I won't have to do anything much, other than fitting a hull anode?

If you leave the shore power un-bonded, no need for, or any point in having, a galvanic isolator.

If you stick a decent hull anode on you know the drive train is covered (note Vics comments ref flexible couplings, if you fit one). With a hull anode there isn't usually a need for a shaft or prop anode, providing of course there is electrical continuity between the prop, shaft and hull anode.

 

[Bobc]

Thanks Paul

 

[VicS]

Thanks chaps.

At the moment the boat doesn't have a hull anode and nothing is bonded. It just has an anode on the propshaft.

So effectively you're saying that I won't have to do anything much, other than fitting a hull anode?

A hull anode is purely optional if the prop has its own anode(s), as most folders do, or a shaft anode. No more necessary with the Beta than with the Volvo.

 

[PaulRainbow]

A hull anode is purely optional if the prop has its own anode(s), as most folders do, or a shaft anode. No more necessary with the Beta than with the Volvo.

But he didn't mention a folding prop, or indeed a flexible coupling. He specifically said "Assuming I have a solid coupling to the propshaft", so fitting a hull anode and connecting it to the transmission/engine negates the prop anode. Prop and hull anodes are disproportionally expensive, a good size hull anode will likely last years.

 

[zoidberg]

Commercially-available bonding straps, for bridging a flexible coupling, seemed rather expensive. I fitted a short length of heavy-gauge copper welding cable between boltheads 'fore and aft' across the coupling. I was so pleased at having saved so much mullah that I fitted a second length about 180° removed, as 'belt and braces'.

Have I done bad, or can I feel a little glow of smug?

 

[Bobc]

But he didn't mention a folding prop, or indeed a flexible coupling. He specifically said "Assuming I have a solid coupling to the propshaft", so fitting a hull anode and connecting it to the transmission/engine negates the prop anode. Prop and hull anodes are disproportionally expensive, a good size hull anode will likely last years.

ATM I have a fixed prop, but will be fitting a folding/feathering prop, so it sounds like good advice to fit a hull anode. Thanks for the feedback on this.

 

[Bobc]

I was initally going to simply replace the old VP Perkins Prima with a new VP, but am definitely leaning towards the Beta option now.

 

[NormanB]

My current VP engine (TMD-22) has return wires for the alternator, and sensors I believe, and only earths when the plugs are heating, when the starter is running, or when the stop solenoid is energised (or so I believe).

I am thinking about re-powering with a Beta engine, which I believe has the battery negative connected to the engine block and uses the block as a negative earth for everything.

Assuming I have a solid coupling to the propshaft, what would I need to do to ensure that the engine is electrically protected.

I believe BETA also have an option for isolated earth wiring harness.

 

[Bobc]

I believe BETA also have an option for isolated earth wiring harness.

Thanks, yes, just seen that on their price list of options. Sounds like I'm going to be fine without it though. I think the VP engine that I have has it, simply because they all did, not because the boat needed it.

Stared at the drawings and done some maths and it looks to me like it will fit fine, but the front of the engine will be 77mm further forward than the VP and I will need to have 35mm spacer pads under the feet. This should put the centre of the gearbox output flange in exactly the same place an at exactly the same angle as the current one.