Marine Starter Motors???

[Gary Fox]

The connection between the name of that boat and this discussion has just reminded me that I once read somewhere that when aircraft were imported from the US during WW2 they all arrived with an earth return electrical system but had to be rewired to comply with the RAF's standard two wire standard.

Why? Why would the RAF do that? Totally re-wire all of them? Not believable sorry.

 

[geem]

Hello

I am a basic mechanic and can normally get there at the end of the day. Is there really any difference between a "Marine" Starter motor and an ordinary agricultural one except of course price.
I would have thought a starter motor is a starter motor is a starter motor. The difference in price between Volvo parts and JCB is staggering. Am I missing something or is a "Marine" thing.

Sean

I am no expert but there are two basic types of starter motors on boats. Isolated return and pretty normal automotive type none isolated return. If your boat is made of steel or aluminium then there are distinct benefits of an isolated return. You don’t want current flowing through your engine and possibly your hull. My engine has an isolated return starter motor but my engine is commonly installation in steel fishing boats. Quite a few different Perkins engines come with isolated return for this reason.
I think if you have a grp boat then the negative return is less important and a standard automotive starter will work fine. You may have to modify your wiring slightly if you already have an isolated return.

From my experience small marine engines from Yanmar, Beta, etc just use regular automotive type starters

 

[Tamar]

I am no expert but there are two basic types of starter motors on boats. Isolated return and pretty normal automotive type none isolated return. If your boat is made of steel or aluminium then there are distinct benefits of an isolated return. You don’t want current flowing through your engine and possibly your hull. My engine has an isolated return starter motor but my engine is commonly installation in steel fishing boats. Quite a few different Perkins engines come with isolated return for this reason.
I think if you have a grp boat then the negative return is less important and a standard automotive starter will work fine. You may have to modify your wiring slightly if you already have an isolated return.

From my experience small marine engines from Yanmar, Beta, etc just use regular automotive type starters

Well I'm learning new stuff everyday.
I didn't realise there was all this stuff about earthing, when electrical stuff wear out on my boats engine I just put an automotive spare back in, my alternator was bought from a car spares shop, still going strong 5 years later, guess I have been lucky.

 

[PaulRainbow]

Well I'm learning new stuff everyday.
I didn't realise there was all this stuff about earthing, when electrical stuff wear out on my boats engine I just put an automotive spare back in, my alternator was bought from a car spares shop, still going strong 5 years later, guess I have been lucky.

You had a little luck when you fitted a standard alternator, in that your engine obviously isn't isolated return, if it was, the alternator would not have worked. Once fitted and working, your alternator is no different to the millions of other standard alternators fitted to boats. In fact, it's little different to all of the isolated return alternators, these are nothing special compared to yours, they just use a different path for the negative return. They use a cable from inside the alternator, isolated from the case and the block, all the way back to the battery, yours connects to the block, the return goes through the block to a single cable and then to the battery. The only difference is that yours has a current running through the block. No reason for it not to last decades.

 

[Tamar]

You had a little luck when you fitted a standard alternator, in that your engine obviously isn't isolated return, if it was, the alternator would not have worked. Once fitted and working, your alternator is no different to the millions of other standard alternators fitted to boats. In fact, it's little different to all of the isolated return alternators, these are nothing special compared to yours, they just use a different path for the negative return. They use a cable from inside the alternator, isolated from the case and the block, all the way back to the battery, yours connects to the block, the return goes through the block to a single cable and then to the battery. The only difference is that yours has a current running through the block. No reason for it not to last decades.

Thanks Paul.

 

[fushion julz]

It was not someone at Perkins or Fairey that specified that system

That would be believable if it was ONLY the MoD vessels that had the system in question... but all (that I've seen) Perkins T6.354 installs in Fairey craft have a similar starter motor...
TBH, I don't really care. I agree that, in the real world, my boat is unlikely to explode or catch fire due to any spark generated at the starter motor.
However, I didn't buy a classic wooden power cruiser to go and change the features and systems. I might improve what is there, but not just for change sake and certainly not to downgrade the equipment!

 

[ghostlymoron]

One of my friends had to replace his starter motor due to corrosion on a 3 cylinder Yanmar. Yanmar quoted over £300. Another friend got one for him from a local tractor dealer for under £100 identical except the colour.

 

[Laminar Flow]

Just to be clear: Isolated ground/negative return is not required, even on steel and aluminium boats. The hysteria by aluminium boat owners and builders that their pride and joy would disappear in a fizz like an Alkaselzer in a glass of water on the morning of the hangover was just that, hysteria, (egged on, no doubt, by an industry keen to sell the much more expensive upgrade.

The Germanic Lloyd demands that all electric and electronic installations have automatic switch-off.
To this point they require: "That the negative terminal of the battery shall be connected to the hull via a cable with sufficient cross section and in an easily accessible area."

This kinda puts the kibosh in the whole isolated ground argument.

This information is extracted from a book by Kurt Reinke, a very prolific German designer of steel and aluminium yachts.

 

[Tranona]

Reading through this thread and note that moat of the stuff on galvanic action and anodes has been glossed over and not challenged. Owners (and builders) of MOBOs have a tendency to think that because of their big complex engines and often equally complex electrics and electronics they are going to fizz away - even with wood or GRP - hulls so scatter anodes around, often linking them together in a circuit. The reality is that many of their engines do suffer from galvanic action simply because they have a lot of mixed metals in their seawater cooling systems - but the action is nothing to do with the electrics in the boat. The anodes in the circuits need regular checking because they can have a long life.

Otherwise the only parts of the boat that need consideration for possible galvanic action are stern gear and steering systems again because of mixed metals. However there are well established methods of protection using anodes. stern drives have similar problems, but arguably worse because of the metals used in their construction but again there are established ways of protection. Trim tabs and bow thrusters can also suffer but manufacturers usual make provision for anodes. Through hulls and skin fittings/seacocks do not need any protection if fitted in the normal way with non metallic hoses.

The key thing is that there is no need for a "bonding circuit" as used to be advocated by some. Each individual potential cell has to be considered on its own and an anode added where required.