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Old 13 June 2021, 06:31   #1
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Freshwater/ saltwater

Hi,

Sorry if it sounds like a silly question but is there a difference between a saltwater and freshwater rib/engine?

I am looking at buying a rib that has only been used for freshwater and it has an aluminium deck.

I just wanted to know if there's any different or anything I should be mindful of as I plan on using it on the sea.

Thanks
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Old 13 June 2021, 13:13   #2
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Buyers often like a freshwater only craft as the corrosion problems are usually far less on the engine and possibly boat fittings too. But... and it's a big but... many boats of 10-20yrs old have been through the hands of several owners and the seller may not actually know for sure even if claimed.
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Old 13 June 2021, 14:01   #3
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Just need to make sure the engine's got aluminium anodes.

Zinc are no good in freshwater and magnesium are no good in sea water. I had new aluminium ones side by side with zinc and couldn't tell the difference visually even when rubbed on some coarse emery.
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Old 13 June 2021, 14:08   #4
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You might want to check with the seller any anodes fitted as there are differences & those currently fitted may not be suitable for salt water use.

^^^^Beaten to it!
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Old 13 June 2021, 15:28   #5
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So manufacturers state fresh or salt water use only then? I thought anodes were material mix to suit both ?
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Old 13 June 2021, 15:46   #6
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Quote:
Originally Posted by Limecc View Post
Just need to make sure the engine's got aluminium anodes.

Zinc are no good in freshwater and magnesium are no good in sea water. I had new aluminium ones side by side with zinc and couldn't tell the difference visually even when rubbed on some coarse emery.
The weight is a pretty good indicator aluminium is about half the weight of zinc
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Originally Posted by jeffstevens763@g View Post
So manufacturers state fresh or salt water use only then? I thought anodes were material mix to suit both ?
Magnesium freshwater only
Zinc saltwater only
Aluminium brackish or saltwater
I think personally I'd go with zinc on an aluminium boat but I'm no expert so maybe worth the op doing some homework to be sure which is best
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Old 14 June 2021, 01:15   #7
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The weight is a pretty good indicator aluminium is about half the weight of zinc

I think personally I'd go with zinc on an aluminium boat but I'm no expert so maybe worth the op doing some homework to be sure which is best
Good point about the weight thanks, but they weigh practically nothing and I don't have fine scales.
OP said aluminium deck not aluminium hull, I guess we are mainly concerned about the engine.

I once questioned how aluminium anodes could work in an engine that's basically well.. aluminium, but I guess not all alloys are the same and these are designed to be sacrificial.

https://www.yachtingmonthly.com/gear...m-anodes-70157

Pictured: Non-working zinc engine anode after just 218 hours, trailered boat, flushed regularly after use I was told (reliable source).
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Old 14 June 2021, 02:38   #8
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Good point about the weight thanks, but they weigh practically nothing and I don't have fine scales.
OP said aluminium deck not aluminium hull, I guess we are mainly concerned about the engine.

I once questioned how aluminium anodes could work in an engine that's basically well.. aluminium, but I guess not all alloys are the same and these are designed to be sacrificial.

https://www.yachtingmonthly.com/gear...m-anodes-70157

Pictured: Non-working zinc engine anode after just 218 hours, trailered boat, flushed regularly after use I was told (reliable source).
Anodes only work when in water, once removed they should be buffed to remove oxidation which prevents them working which probably explains why they dont work well on trailered boats. Just because they are there doesnt mean they will work.
The op stated his Rib has an aluminium deck hence my assumption it was an aluminium boat but it's possibly not a rib at all its more likely a sib, never seen a rib with an aluminium floor & another material for the hull.
Anodes are realy only useful on boats kept in the water for longish periods so for a sib thats left in for hours at a time not weeks the choice of anodes isnt realy a great concern imho
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Old 14 June 2021, 03:38   #9
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Anodes are realy only useful on boats kept in the water for longish periods so for a sib thats left in for hours at a time not weeks the choice of anodes isnt realy a great concern imho
But even boats on a swing mooring have the prop tilted clear of the water, the internal engine anodes being exposed to air regularly.

Probably often overlooked, I think there's no substitute for a yearly visual, especially when they're so easy to remove. I'm glad I changed mine out for aluminium and happy I found them before any serious corrosion took place.
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Old 14 June 2021, 06:03   #10
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for info

https://www.boatus.com/expert-advice...al-anodes-work
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Old 14 June 2021, 10:56   #11
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Quote:
Originally Posted by Limecc View Post
But even boats on a swing mooring have the prop tilted clear of the water, the internal engine anodes being exposed to air regularly.

Probably often overlooked, I think there's no substitute for a yearly visual, especially when they're so easy to remove. I'm glad I changed mine out for aluminium and happy I found them before any serious corrosion took place.
Yep the key is maintenance whether its in or out of the water. If its left in the water the anodes deteriorate by corrosion but being left dry they build up a coating & loose their effectiveness, either way they should be changed or if still good buffed to remove the skin that prevents them working
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