Descaling Engine Heat Exchangers [and other raw water plumbing...]

Is your engine starting to run warmer than usual?

Based upon this descaling article in Practical Sailor, we chose to use CLR (among several tested and rated products) annually to descale the raw water circuits on our propulsion engine and generator (which include several copper-nickle heat exchangers.)  

CLR is also safe to use on the dibghy outboard engine since there is aluminum to be found in its raw water cooling cirsuits.

We chose CLR because it is safer to work with, has no fumes (unlike muriatic acid...) and CLR won't harm any aluminum (or anodes) in the raw water circuit when used as directed in the above article and per manufacturer's instructions. 

CLR is also effective at removing rust stains, cleaning the shower floor and walls, clearing air conditioner/ heat pump raw water circuits, descaling coffee pots, outboard motor cooling circuit, etc., etc. (Everything on a boat should have more than one purpose, right?)

Instead of removing the various heat exchangers and soaking in a bucket, we leave them in place and use a small pump to recirculate 50% diluted CLR (per above linked article) through the raw water coolant loops of the main engine and generator annually.  

If you prefer to purge any raw water from the cooling circuits before descaling, pump some fresh water through first- discharging into the bilge instead of the bucket. Then put your hoses in the bucket of diluted CLR and turn on your recirculation pump.

Recirculating 50% diluted CLR clears the deposits in the raw water side of the heat exchangers. 

Keep it going until the discharge stops foaming.

       

The time elapsed between above photos was ~ 2 hours. (Severe deposits can take hours longer- even overnight...)

The red return line in the above photos is the disconnected exhaust elbow raw water injection hose on our generator (you wouldn't want to hydrolock your engine with the descaling recirculation pump...)

The black hose is the suction hose which normally goes to the raw water through-hull (strainer) for that engine.

 

This is a routine part of our annual maintenance. It also provides an opportunity to inspect the exaust elbow injection site for corrosion since we have to remove that hose to recirculate the descaling solution.

When we are finished with each engine, we dump the bucket of used CLR solution into the bilge with the primary (lowest or maintenance) bilge pump off. (We have several bilge pumps installed- each above the previous- and they are left on, so are covered in an emergency...) 

After adding the 2nd bucket full, we turn on the maintenance bilge pump for a few seconds to fill the discharge hose, and then turn it off again to let everything soak overnight. To empty the CLR from the bilge, capture the bilge pump discharge and dispose of properly. 

Three-way valves strategically placed in the bilge pump discharge and engine raw water hoses mentioned above make this annual maintenance quick and easy with no hoses to remove... (With well planned 3-way valves you could even use the bilge as the bucket, and the maintenance bilge pump to recirculate the descaling mixture...)

Win-Win.

 

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Links to related forum discussions:

Nauticat USA Forum 29-Jan-2023 

Cruiser's Forum 27-Jan-2023

Five year bottom paint?

We cruise N Pacific waters above 56°N. Aggressive hard growth (mainly barnacles and mussels) is very normal here. 

Water temps (°F) vary from mid 30's in some of the glaciated fjords, to as high as the low 50's in the Gulf of Alaska- with seasonal variations. You can see barnacles, mussels, etc. on the rocks at low tide everywhere. 

We can even judge the depth of tide by which intertidal growth layers are visible. (Sounds like fodder for a future post...)

Sometimes those cruising warmer waters think hard growth in minimized in cooler water. It isn't. Anyone who takes their dinghy (or kayak, etc.) to shore in these parts can attest to the razor sharp growth attached to any hard surface that spends at least part of the time underwater... 

The following photo we took in Jul-2022 demonstrates an extreme example of this. The image shows a small portion of Margerie Glacier (a tidewater, or fixed glacier at 59°N; 137°W), and barnacles growing on the (fairly) recently exposed adjacent bedrock. I can assure you this is not tepid water...

 

What antifouling paint do we use? Divers cleaning other boat hulls in the harbor often ask us this since ours has yet to need cleaning.

The owner of a commercial fishing boat across from our slip told us about a time he couldn't back out of his slip. He thought his transmission had malfunctioned. A diver revealed he had over a foot of mussels and barnacles coating both sides of his 48 inch 4 blade prop. All was well after the diver used a spud bar to peel off the growth- which had accumulated over 5 months of sitting at the dock in winter. 

We first applied this ablative antifouling paint in Apr-2017. 

Our next haulout was 4 years later in May 2021 (because we needed an insurance survey.)

Note that Denali Rose spends all of her time in the water- except during routine, ~1 week haulouts every few years. 

Following are a couple of photos of the hull as it is still dripping from being hauled-out after sitting at the dock for 4 months over winter: (4 years and 1 month since it was last painted...)

Denali Rose is 50 ft. OAL. This is the smallest travel lift in the yard @ 150 tons.  
We prefer it when our boat looks like a toy in the travelift...

Pre-pressure wash image demonstrating the clean hull [after 49 months in the water full time] with hard growth on some of the metal components.

We coat UW metals with Pettit Prop Coat. It lasts us about 3+ years when overcoated with Hydrocoat per the manufacturer's directions.

Note a bit of greenish slime on the hull and keel from sitting unmoving at the dock for 4 months over winter...

In the above pre-pressure wash images, you can see the 4 year old black Hydrocoat paint would likely have lasted at least another year, but there was some hard growth on some of the underwater (UW) metals (which represents about 13 months growth since the last time a diver cleaned the zinc spray coated UW metals and replaced the anodes. No diver hull cleaning. Ever.)

We have never had a diver clean the bottom since we started using Hydrocoat, but every year or two we do have a diver renew the anodes and remove any hard growth on underwater metals as needed. (We inspect the hull every 6 months or so using a GoPro camera mounted on a boat pole.)

Of course, since we were hauled out for the insurance survey, we renewed the bottom paint in May 2021.

We started using water-based Pettit Hydrocoat ablative bottom paint  in Apr-2017. (NOT the ECO version without copper...) We re-applied Hydrocoat during our insurance survey haulout  4 years later (in May-2021) the day after the above photos were taken. (And the hull is still pristine as of the publishing of this post on 19-Jan-2023...)

Our next haulout is currently planned for 5 years after the last painting in May-2021; spring of 2026.

Stay tuned...

Of course, YMMV...

PS: Other advantages of using a water based (low VOC) bottom paint include we can have it mailed USPS-  which is typically our most ecconomical shipping choice in remote locations. And we can use it to coat through-hull transducers that specify water-based antifouling paint only. (Most potted transducers.)

PPS: What about bottom paint considerations in areas with warmer waters?

In case you aren't familiar with Practical Sailor's [continental US] regional bottom paint testing results, here is a representative article that may be useful. (Scroll to bottom to see extensive rating tables...)

Jamestown Distributors [JD] also conducted bottom paint surveys for several years in a row, and I found this recap article in case it is of interest.

Following are a couple of informative graphics from the JD article linked above:






I couldn't find their live Google map, but I remember you could drill-in and read individual submissions, so asking JD for access may prove useful if you are interested in what boaters reported using (and their ratings) in specific regions of the world.



I recall using a hard, high copper bottom paint (Trinidad?) when I spent 7 years in the S Pacific tropics decades ago on a different boat. Cleaning the bottom monthly was good exercise...


More FWIW info.

Hull strainers can be blocked too...

Recently, while running the generator at anchor, I noticed the gen exhaust water splash had abrubtly stopped, and shut it down right away...

I started troubleshooting by looking at the raw water strainer for the gen set. It was full of bits of jellyfish- but not so full as to prevent water flowing still...

The boat has external strainers [images below] on the hull for engine intake through-hulls, so the suction must have extruded pieces of the unfortunate organism.

Generator

 Engine

 

Backflushing with pressurized water didn't work. I had to fire up the engine and run the prop in reverse to blow the jellyfish off the strainer. 

I doubt this would happen while underway, and was surprized it did while sitting still... 

Murphy prevailed- to the detriment of the jellyfish...

Moon Jellyfish [Aurelia aurita]