Do you need to bond your transom ?

The Dock · 14 April 2010, 23:24

Checked my outboard the other day and found pitting on my tilt rams again ! Checked all wiring and found all connections sound and clean . Then I traced a cable from the negative on the battery to the transom mounting bolt . Could anyone tell me if this is correct ? Religiously turning off power isolator switch and raising prop and leg out of water when tied to the marina . All anodes metred out and continuity is good . Tilt rams are stainless and under water level constantly . Going MAAAADDDDD here !!!!!!!!!!!!! Please help me !

Nos4r2 · 14 April 2010, 23:32

I'm assuming the paintwork on your motor is spotless so there's no exposed aluminium in contact with the water?

If so:-
1)Have you checked for continuity between your PTT anode and the powerhead?

2)Could there be a power 'leak' near your boat from a pontoon or another boat?

3)Silly question, but is your battery switch in the -ve lead?

The Dock · 15 April 2010, 00:11

EFFICIENCY of the highest order ! I have checked continuity all over the boat and all is correct . My buddy's boat with a yamaha on the back is on the same finger as me on the marina and his trim rams are fine . I compared my wiring layout to his and basically the same . Is the positive the VE lead ?

Nos4r2 · 15 April 2010, 01:33

Quote:

Originally Posted by The Dock

EFFICIENCY of the highest order ! I have checked continuity all over the boat and all is correct . My buddy's boat with a yamaha on the back is on the same finger as me on the marina and his trim rams are fine . I compared my wiring layout to his and basically the same . Is the positive the VE lead ?

No the -ve is negative. +ve is positive.

Trim rams really shouldn't corrode at all-the ally should go first.

9D280 · 15 April 2010, 12:34

The other option is disconnect the lead to the mount bolt & let the anodes do their job alone.......

That will remove any "external" influences. Also your Engine should be connected to the _ve by the starter cable somewhere under the hood. If not and it;s connected to the mount bolt, I would imagine to get power to anything useful inside would need a lack of paint under siaid bolt........

doggypaddle · 15 April 2010, 12:40

Quote:

Originally Posted by 9D280

The other option is disconnect the lead to the mount bolt & let the anodes do their job alone.......

That will remove any "external" influences. Also your Engine should be connected to the _ve by the starter cable somewhere under the hood. If not and it;s connected to the mount bolt, I would imagine to get power to anything useful inside would need a lack of paint under siaid bolt........

Thats what I got the impression of, The battery negative connected only to the transom clamp?
That would be a good way of inducing electrolytic corrosion. Battery negative should go straight to the starter motor or star earth point or near to it as possible, so no current flows through any part of the engine/leg.
where a current flows there will be a voltage drop, and the electricity will take an alternative path, ie out of the rams, into the prop/anode carrying a little bit of the ram with it, up the leg to the powerhead.
also if your lead only goes to the transom clamp the steering bearing and tilt bearings will be carrying current which won't do them any cood. They are bypassed by a small earth strap, but thats to prevent corrosion by bonding across the very high resistance bearing, theyre not designed to carry current, theyr'e thin, and stainless which isnt a very good conductor so could fry up when you crank the engine on the starter.
Technically the transom should be bonded, but in reality the chances of it not being with four tight m12 bolts holding the engine to it are slim.
if it is bonded it should be to the clamp and nowhere else that could be at a different potential, even if it is only 0.1 volt over time it will take its toll

Nos4r2 · 15 April 2010, 16:01

Quote:

Originally Posted by doggypaddle

The battery negative connected only to the transom clamp?

That possibility didn't occur to me-I assumed it was an extra lead.

However, I guess if the main negative connection to the powerhead was a bit dubious it could cause some corrosion.

The Dock · 15 April 2010, 22:49

Guys I think ye hit the nail on the head!!!!! The negative bonded to the transom is an extra lead but the negative going to the powerhead must be damaged . It definitely adds up cos +VE is being broken on isolating switch and absolutely everything on board is isolated except for auto bilge which has no interference on transom . Should i remove negative from transom as this could be becoming part of the starter circuit for the motor and even for the tilt and trim system . Current will obviously take the shortest route

Nos4r2 · 15 April 2010, 23:22

Quote:

Originally Posted by The Dock

Guys I think ye hit the nail on the head!!!!! The negative bonded to the transom is an extra lead but the negative going to the powerhead must be damaged . It definitely adds up cos +VE is being broken on isolating switch and absolutely everything on board is isolated except for auto bilge which has no interference on transom . Should i remove negative from transom as this could be becoming part of the starter circuit for the motor and even for the tilt and trim system . Current will obviously take the shortest route

I would. If you're going to do it, get the multimeter out too and see what (if any) difference it makes to the resistance between the powerhead and the battery negative terminal.