[Bluto]

I recently purchased a 28ft steel pilot house sailboat. The previous owner did not use a galvanic isolator nor an isolation tranformer and did not have any problems . However the surveyor recommended an isolation transformer . While I am leaning towards an isolation transformer the cost in Canada is about $1,200 plus my install. Any advice, or recommendations on the matter is appreciated.

 

[miatapaul]

I recently purchased a 28ft steel pilot house sailboat. The previous owner did not use a galvanic isolator nor an isolation tranformer and did not have any problems . However the surveyor recommended an isolation transformer . While I am leaning towards an isolation transformer the cost in Canada is about $1,200 plus my install. Any advice, or recommendations on the matter is appreciated.

I think it depends on where your boat will be. If you will rarely be in a slip (likely the case of the former owner if they did not have issues) then I don't think the transformer would be worth it. If you plan on keeping it in a slip then it will. Though a steel boat would be the last construction I would want if I were keeping it in a marina. Too much stray current to do damage. You will need to be very careful about the marinas you keep the boat in, some will eat up zincs s in a month or two on a fiberglass boat, and on a steel boat they will not stop at the zinc!

 

[Faster]

I think it depends on where your boat will be. If you will rarely be in a slip (likely the case of the former owner if they did not have issues) then I don't think the transformer would be worth it. If you plan on keeping it in a slip then it will. Though a steel boat would be the last construction I would want if I were keeping it in a marina. Too much stray current to do damage. You will need to be very careful about the marinas you keep the boat in, some will eat up zincs s in a month or two on a fiberglass boat, and on a steel boat they will not stop at the zinc!

We had a long-neglected steel boat in our marina.. when the owner finally hired a diver to clean the bottom of several inches of mussels etc, they had to to an emergency haulout (fortunately only a 100 feet away) when the diver opened up a thumb-sized hole in the steel that had, up to that point, been 'plugged' with growth!

 

[Bluto]

The boat will be kept in a slip in a small marina on Georgian Bay. It had previously been kept in a marina on Lake Ontario. The boat also needs it wiring cleaned up so I thought the isolation transformer would add a degree of saftey as well as corrosion control.

 

[Bluto]

P.s. thanks to both of you.

 

[celenoglu]

A galvanic isolator can be used. Normally the active wires are not in contact with the boat, and ground wire is not connected to the boat. But in case the ground wire is connected to the boat hull, a galvanic isolator should be the selection.

 

[Bluto]

Thankyou. Would the isolation transformer not do the same thing and protect the boat from being accidentally electrified in case of a shore power short? This is my first metal boat and I want to be carefull. Ideally I would not use shore power at all but for now it is convenient.

 

[k7el]

An isolation transformer is the best practice - nearly all commercial vessels use them. For a steel hull, I'd seriously consider the transformer. But in addition to the cost, you need to consider the weight - it will be heavy and take up precious space in a 28 foot boat.

 

[Faster]

Have you seen this? Good discussion.

SmartGauge Electronics - Isolation Transformers or Galvanic Isolator? 1/2

 

[Skipper Jer]

Just how much power do you need to push across the transformer? If all you are running is a battery charger then maybe just a few hundred watts are required in which case the isolation transformer is not that expensive. If you are pushing a couple of thousand watts thats a different story. A quick check at Newark has xformers from about $100 US (200 watts) to $525 US for 2.5 KW.

 

[Bluto]

3600 watts the boat has a lot of toys. Over time I will rationalize things but during the fix up period I think I will want to use the full 30amps available I.e. a/c , fridge etc
But I thank you for the idea.

 

[k7el]

So a 5000 VA encapsulated transformer is about 120 pounds - less than I thought. I'd advise getting copper windings instead of aluminum. A 7500 VA unit weighs about 133 pounds.

Losses at full load are about 200 watts are so.

 

[mitiempo]

The isolation transformer has to be sized for the shorepower connection - typically 30 amps for a 28' boat. Victron makes one that would do the job nicely.

With an isolation transformer you are protected from stray current caused by other boats and entering the boat through the green earth wire. The only issues would be those on your own boat.

A galvanic isolator will minimize stray current - up to 1.2 volts - but will not stop a stray current if it is over 1.2 volts.

 

[Skipper Jer]

"The isolation transformer has to be sized for the shorepower connection"

Why is that? If he installs a double pole breaker for the expected load wouldn't that be ok?

 

[mitiempo]

If not sized properly the transformer will fry. It is installed before the breaker.

 

[Skipper Jer]

I understand how one can fry the transformer when the breaker is 20 amps and the transformer is rated for 10 amps. I'm not sure I like the breaker after the transformer. I would want the breaker between shore power and transformer in order to protect in case of transformer malfunction. Maybe its code for the breaker to be after the transformer.

 

[desert rat]

Sorry Mitempo, what fries an isolation transformer is a short or drawing to much current on the secondary (a short again). With the secondary open you could connect the smallest transformer with no worry.
The major concern is that an isolation transformer leaves you with a floating ground. Not a problem in itself but any piece of electrical equipment improperly grounded, especially on a boat in salt water, can become a galvanic disaster.

 

[mitiempo]

I understand how one can fry the transformer when the breaker is 20 amps and the transformer is rated for 10 amps. I'm not sure I like the breaker after the transformer. I would want the breaker between shore power and transformer in order to protect in case of transformer malfunction. Maybe its code for the breaker to be after the transformer.

The isolation transformer is the first item after the shorepower inlet. It's purpose is to totally eliminate any electrical connection between shore and the boat. This is the best solution for eliminating any issues caused by other boats connected to shore power.

They are sized for the service - 30 amp, 50 amp, etc.

Victron, Charles, and Mastervolt are companies making quality marine isolation transformers.

Regarding Desert Rat's comment above, if you expect to use the current supplied by the shore power connection it has to be rated for that current.
I am sure pulling 30 amps through a 10 amp transformer isn't good for it if it would work at all.

 

[pjs1554]

The transformer needs over current and short circuit protection. Weather it is up stream or down stream to the transformer is not as important as being properly sized to protect it from overloads and faults.