Do I want to avoid buying a saltwater boat for freshwater use?

[Tim.M]

I see a lot of boat ads advertise "freshwater only." What's so bad about saltwater on a fiberglass powerboat?

[TeddyDiver]

Some aspects to consider.
1. Some boats are manufactured for freshwater use only. It means there might be some corrosion issues in saltwater.
2. In fresh water wooden structures are more exposed to decay as in saltwater metals are for corrosion..

[Fanie]

I think it's more a matter of construction and how the boat has been designed.

A house boat is suitable for fresh water use only. Sure it will float on a calm sea, but when the weather picks up a bit then the rougher water becomes a problem, and the house boat may make water.

In some cases the owner put one motor on the boat, this makes it a fresh water boat since legally for a sea boat you require two motors, as well as certain equipment not required for inland or protected waters.

If you are going to the expenditure of buying a sea going boat pls get something decent. No one like putting the money up, so I see many buy this little ski boat that is really more of a threat to life than a sea boat.

[alan white]

One thing I see is Zamac fittings on what I'd term fresh water boats. It's a pot metal that has little strength and little resistance to salt water corrosion. Stainless cleats won't normally rust but they are much more expensive. Other fittings from ski-pull rings to lighting fixtures to chocks to windshield metals to bimini fittings can be built to deal with fresh water or salt environments with attendant differences in strength and corrosion resistance.
Beyond that, the design and build of so-called freshwater boats is not generally intended to deal (if called upon) with 6 foot waves, dropping from a height to crash into troughs without damage, and stay relatively dry while doing so.
I've seen many runabouts that have seats that just set in place atop boxes, something I'd not want in a rough seaway. But this appears to be common.
The list goes on, and mostly there isn't any black or white but a lot of gray in between the two extremes. It's possible to have quite a mix of design and construction ideas where the judgement of what category of boat type is pretty subjective. For me, the hull scantlings and quality of build, and the general shape of the hull would top the list of requirements for a good salt (or big water) boat. you can alter or replace the little things, but the hull is the foundation and you can't change it much without extreme cost.

If the advertised type of boat is commonly used in saltwater and the ad says "freshwater only" that means nothing else than "garage stored" in a car ad. The seller tries to make a sort of "additional plus point", which it is´nt really.
But take care, if the engine has "fresh water cooling" (no heat exchanger), that means "fresh" water due to corrosion issues in salt water.
And to the question in the thread title, NO, you buy the better boat if you buy a saltwater boat.

Regards
Richard

[Tim.M]

Thanks guys. What I'm looking at is a 25 to 30' sportboat (~30 knot cruise with ~50 knot top end) that's sold for both freshwater and saltwater. There are a lot more on the market that have been used in saltwater and price seems to be about 50% cheaper for a saltwater boat than a freshwater boat.

There aren't many thru hull fittings on these as they're sterndrive boats.

Will look at the aluminum sterndrives closely for corrosion issues.

Main thing seems to be that some of the saltwater boats have raw water cooled engines. I take it this is a very bad thing for engine block life.

Would you consider a raw water cooled io that's been used in saltwater for 200 hours, or is that too much corrosion from the salt water if raw water cooled?

In terms of the fiberglass hull, does saltwater affect the life vs. freshwater? Do barnacles create cracks or bore through the gellcoat? Is osmosis or blistering worse in salt than fresh water?

[Guest62110524]

boats -- engines do rarely wear out, they rot out
For instancre, if you boat si left with the exhaust open, then over time the valves will start rusting If the block has jacket cooling, enclosed then it will not rot IF a corrosion inhibitor has been used and the filter in the jacket water , replaced regularly
Petrol engines usually have no filter If the jacket water has no inhibitor in it(easy to tell) then probably it is poorly maintained
So if I were buying I would first, get a compression check done on the power plant and a thorough test on the cooling, you do not HAVE to go to sea to do thsi, tie the boat to a spring line and run it at say half ahead for as long as it takes to run up to temperature, then leave it there running for awhile
Wooden boats fare best in salt, frssh water kills unprotected wood

[alan white]

Fresh water only would be a negative if claimed of a wooden boat, except for the engine's cooling system, which will always do better in fresh water if raw water cooled. However, many engines last for decades with raw water cooling, like one I had. No discernable corrosion when inspected through the freeze plug holes. But it was low-powered. I'd suspect a raw water-cooled inboard with any kind of heat-generating power.