Earthed engine consequences

[roaringgirl]

There's an earth strap from the battery to the engine. There's a strap across the cush drive which electrically joins the propshaft to the engine. Therefore there's a potential difference (of around 12V) between the battery positive terminal and the sea surrounding the boat - is this right and normal, or am I missing something?

 

[Boater Sam]

There's an earth strap from the battery to the engine. There's a strap across the cush drive which electrically joins the propshaft to the engine. Therefore there's a potential difference (of around 12V) between the battery positive terminal and the sea surrounding the boat - is this right and normal, or am I missing something?

Normal.

 

[roaringgirl]

Normal.

Thank you.

The Victron MPPT connects the negative side of the PV directly to the battery negative, which means there's 37V between the PV positive and the sea. I got a mild shock the other day when holding the guard rail with one hand and touching the PV positive output. I guess this means that the guard rail is grounded - is this a good thing?

 

[VicS]

"Earth strap" to engine is the battery negative connection for all the engine electrical equipment.

Strap across the flexible shaft coupling is there to complete an electrical circuit between the prop and a hull anode bonded to the engine or gearbox.

Battery negative is therefore earthed to the water and as a result there will be 12 vlts between the water and battery positive

 

[vyv_cox]

It is quite normal to have the negative side of the battery earthed via the gearbox and prop shaft. It is when the positive side is connected to the sea that serious problems occur. Several examples of these are illustrated here Electrolytic corrosion

 

[Offshore57]

Working from Boat (WFB) and this thread prompted me to go and check engine start and aux batteries conditions.......engine start ones seemed dead, but it was a sticky isolator solenoid.....phew. Power restored....back to laptop. (well it was lunchtime)