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Tom Mitchell 04-08-2008 02:58 PM

What are the issues in moving a boat from fresh to salt water?



MMNETSEA 04-08-2008 11:49 PM


Originally Posted by Tom Mitchell (Post 19764)
What are the issues in moving a boat from fresh to salt water?



Tom ,

Hard to answer without knowing the context. However, a few important issues that come to mind :-

#1. Salt air environment - gradual corrosion.

#2. Osmosis is seldom seen in boats kept in fresh water.

#3. Barnacles & the Termites of the Sea - Teredo Worms.

#4. Depending on the size of boat - Lifting >> Transport >> Launching.

#5. Removing and Replacing Mast.

#6. Additional safety gear.

#7. Cost.

It will be interesting to see what other members have experienced in making the transition.


Aquaria 04-09-2008 04:28 PM

Hi Tom,

here is #8

Your boat will swim higher up in salt water, you can either put more gear on the boat to meet the cwl (construction water line), or you can lower this line the next time the boat is on the dry.

And #2 is special problem of glassfibre boats only:

I'm not sure about Richards #2. I'd say: Osmosis is seldom seen on boats in salt water. I've had a centerboarder on an inshore lake long time ago, that after years suffered Osmosis. I took care of a swedish double ender that has not had Osmosis for the time it was sitting in salt water (even brackish) of the western baltic sea for about 15 years. Then it was moved into a river environment ant it started to develope Osmosis pretty soon after.

My explanation: the gradient between freshwater outside and the "water" inside the is the driving force to dilute the solvent residues and it is higher, than in salt water: pure water outside and a high share of residues inside the laminate forces the water into the laminate for dilution. In saltwater you have no pure water outside, so the process of osmosis runs (more) in both direction.

So, I'd say, the saltier the water, the less the danger of catching this disease...

I must say I am far away from being a chemist and the process of Osmosis might be more complex... and maybe there is a chemist/sailor/boatbuilder on this forum who can say how things really are between the water outside our hulls and the moisture that is inside the grp-structure.>/blush.gif




MMNETSEA 04-09-2008 10:59 PM

Hi Uwe,

You may be quite right, my experience has been 95% warm sea water - where I have seen possibly hundreds of boats with "blisters" as a result of osmosis. On recollection, the boats built in the period 1980 >> 1995 were the most infected. I don't know of a comparative survey which found osmosis favouring fresh over salt - but I must admit seeing passing reference to it.

A very good article on the whole subject (where they agree with you) is to be found

by clicking here

Stay well


Aquaria 04-10-2008 04:17 PM

Hi Richard,

thank you for this link. A very informative article - I learned alot!

Especially, that temperature plays another big role in the decision if your hull will be affected, or not.

Now it makes sence that the boat i mentioned never showed any signs of osmosis, as long as it was moored in rather cold brackish water of the Baltic and then within one summer in the water showed severe signs of osmosis on the entire hull: fresh river water that got very warm through the summer months!

Good for you, Tom, if you should own a fibreglass yacht: no higher danger of osmosis, when moving the boat into the salty elements and normally open sea water does not heat up as much as an inland freshwater.

best wishes



MMNETSEA 04-10-2008 07:56 PM

1 Attachment(s)
Hi Uwe,

At this time 11th April - not yet summer, the waters around the cruising areas of South East Asia are averaging around 27 degrees Celsius . Here is today's synoptic chart produced by the Meteorological Division of the N.E.A. Singapore Government (note: an aside - when the temperature exceeds 26 C Typhoons are happy)

Attachment 400


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