Hi, All.
This week I decided to explore the maintenance readiness of the seawater pump on my newly-acquired R-29s Yanmar 6BY2-260 engine. Engine coolant temperatures have been entirely normal on trips since we acquired the boat in November, but I have no information whether the original owner ever replaced the impeller, or how long it's been since the last replacement, so investigation was in order.
With my trusty assistant/chief engineer at wrench, we found that the factory-original pump was dripping from the front housing, indicating a failed mechanical seal. After much grunting and foul language from the chief engineer, the pump was out and on the bench for closer inspection to find that the impeller in all likelihood had never before been removed, and that the mechanical seal likely had failed a few hundred hours ago.
My initial inclination was to obtain an OEM replacement pump for installation, and to rebuild the failed pump for a spare when the new pump inevitably fails on a trip. But after watching the extreme discomfort of the chief engineer as he worked that pump off the engine, it became obvious to me that a combination of my size 2XL hands, the protective coating on my rock-hard abs, and my general distaste for working with my head lower than my ankles would combine to make it utterly impractical for me to ever plan to replace that pump at sea by myself.
That sobering reality brought me to where I am now, planning to engineer a redundant backup seawater pump into my engine's cooling system so that when the mechanical pump next fails, I can simply flip a valve and switch and have an electrical pump delivering seawater to my engine's cooling system until I'm safely back at the dock where chief engineer can repair the failed mechanical pump without the threat of emergency, and I can enjoy a cold beer while he works.
My current plan is to plumb ball valves and a tee into the seawater piping to connect a 12v washdown pump with quick connect hardware, and wire the pump so that it runs from a manual switch powered from a relay connected to the oil pressure switch, so that it can only operate while the engine is running (and perhaps with a manual override so that it can run even if the engine has ceased making oil pressure in an extreme emergency). That way I can have instant backup seawater cooling at all times if the main pump fails, and minimize the risk of a temperature-induced propulsion emergency. The cost of keeping spare electric washdown pumps is a tiny fraction of a spare Yanmar seawater pump for these BY-series engines, and if I'm feeling extra paranoid about loss of seawater cooling, I can always hook up two or three spare electric pumps in a standby array. :geek:
So, my question to the group is: have any of you done this sort of custom mod on your own boats? If so, I'd love to hear your thoughts and strategies. Or, have you thought about doing this mod and changed your mind, and if so then why?
Your plan may work if the if the wash down pump is not sharing the same sea strainer as the engine. My strainer is for both engine and wash down pump.
As far as a back up sea water pump, redundancy is always a good idea for safety. The sea water pump designs used in the Yanmar and Volvo are simple and for the most part very dependable. Like any rotating equipment there is wear and required preventative maintenance. The preventative maintenance comes in two forms Visual inspection for leaks, belt condition, and hose condition which should be done on a regular interval. The second is disassembly for inspection and replacement of damaged rotating parts. A minimum replacement should be the rotating element ( impeller) and O-ring. If a Mechanical seal is used and shows signs of leakage replace, or if lip seals are used and show evidence of damage or leak replace, if the internal wear plate or eccentric pump housing are worn its time for a complete pump replacement. The second inspection is recommended by the manufactures every 200hrs or 2 years (Volvo) I believe Yanmar is the same. If this is done the chances of pump failure are minimal but I suppose possible but any failure is possible at any time. Preventative maintenance is the key to reducing failures.
In the event that a pump failure does happen while under way because of a obstruction in the water pick up, bag, running aground ( sand and silt) and damaging the impeller. A back up pump would be great to have on board. It could be has simple as a large bilge pump with a bracket to submerge off the swim platform and run a hose to a connection in the raw water system (After the water pump, it can not be before the water pump). Or a more permanent installation that you described. Or keep a spare impeller on board and make modifications to the boat to ease in the repair of the pump. This was my method, If I have a pump failure ( damaged impeller) I can replace it in 10 minutes. The original boat design before interior modifications it was an hour. Good luck in your project, If having an additional back up pump gives you piece of mind while cruising it is a worth while project.
BB marine":p390qpxq said:
Your plan may work if the if the wash down pump is not sharing the same sea strainer as the engine. My strainer is for both engine and wash down pump.
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Or keep a spare impeller on board and make modifications to the boat to ease in the repair of the pump. This was my method, If I have a pump failure ( damaged impeller) I can replace it in 10 minutes. The original boat design before interior modifications it was an hour. Good luck in your project, If having an additional back up pump gives you piece of mind while cruising it is a worth while project.
Excellent points! My wash-down pump has a separate seawater strainer. I'm sure that I could not change that impeller myself in 10 minutes, and that when it fails I probably won't even have the luxury of that much time.
Mike you are correct the auxiliary pump would need to be plumbed after the raw water pump housing outlet. The water flow would be more of an issue of not enough flow with a raw water wash down. The raw water pump used on my D3 pumps 1 cuft per minute = to 7.4 gallons per minute @700rpm. A raw water wash down has a max flow of around 5 gallons a minute at 40 psi 1/2" hose. If you were to attach a garden hose 1/2" id to the dock and run it to your strainer At 40psi it would flow 6 gallons per minute given the larger flow source is 100 ft away. Normally the garden hose can not keep up with the raw water pump. At rpm my D3 raw water pump provides 2.7 cuft per minute= to 20 gallons a minute. So your thought of how much water will the auxiliary pump put out is a good Idea to check and match to the raw water pump capacity but most small 12 volt pumps will not provide enough water flow and engine rpm will be = to limp mode at best for proper cooling. At rpm the D3 pump flows 30 gallons a minute which in the Ranger/ Cutwater design with 1" hose attached to the thru hull it is hard to flow that much It really needs a 1 1/4" hose to be matched up properly to the Raw water pump.
Back in my marine technician days I had a customer that had a boat on a mooring with a damaged impeller. (stern drive) I needed to get the boat from the mooring can to the boat ramp about 5 miles away.( Taunton River MA. to Fall River launch ramp) I installed a gph bilge pump on a plate and mounted it to the swim platform support bracket at its lowest point. I had to lift the water up 5' to get to the location were I was teeing into the raw water side of cooling at the engine. This reduced my water flow 25% but still enough to be equivalent to the stern drive pump output running at rpm. I was able to get the boat to the ramp without the cost of a tow for my customer. A very simple aux.pump to get a boat home.
BB marine":1ea6w61f said:
Mike you are correct the auxiliary pump would need to be plumbed after the raw water pump housing outlet. The water flow would be more of an issue of not enough flow with a raw water wash down. The raw water pump used on my D3 pumps 1 cuft per minute = to 7.4 gallons per minute @700rpm. A raw water wash down has a max flow of around 5 gallons a minute at 40 psi 1/2" hose. If you were to attach a garden hose 1/2" id to the dock and run it to your strainer At 40psi it would flow 6 gallons per minute given the larger flow source is 100 ft away. Normally the garden hose can not keep up with the raw water pump. At rpm my D3 raw water pump provides 2.7 cuft per minute= to 20 gallons a minute. So your thought of how much water will the auxiliary pump put out is a good Idea to check and match to the raw water pump capacity but most small 12 volt pumps will not provide enough water flow and engine rpm will be = to limp mode at best for proper cooling. At rpm the D3 pump flows 30 gallons a minute which in the Ranger/ Cutwater design with 1" hose attached to the thru hull it is hard to flow that much It really needs a 1 1/4" hose to be matched up properly to the Raw water pump.
Back in my marine technician days I had a customer that had a boat on a mooring with a damaged impeller. (stern drive) I needed to get the boat from the mooring can to the boat ramp about 5 miles away.( Taunton River MA. to Fall River launch ramp) I installed a gph bilge pump on a plate and mounted it to the swim platform support bracket at its lowest point. I had to lift the water up 5' to get to the location were I was teeing into the raw water side of cooling at the engine. This reduced my water flow 25% but still enough to be equivalent to the stern drive pump output running at rpm. I was able to get the boat to the ramp without the cost of a tow for my customer. A very simple aux.pump to get a boat home.
Thanks for that detailed consideration, Brian! Getting sufficient backup flow from an electric pump is definitely a challenge, and has me thinking of installing a more robust pump than the standard washdown unit, but even then I may have to consider it at best to be a short-duration emergency pump for a (hopefully-rare) situation where shutting down to change out an impeller is simply not an option.
I considered a similar modification for the same reasons. We also operate around rocky shorelines in remote areas where it is typically too deep to anchor and time required to conduct repairs may not be available much less waiting for a tow. We ultimately opted for auxiliary power since it covers loss of primary power for any reason, not just cooling pump failure. That's a whole separate discussion but I do have a couple of thoughts on the pump scheme.
As BB marine pointed out there's no reason it won't work but likely won't provide enough flow for much above idle speed. Which is still way better than zero.
Regarding the design of such a system, I've been afloat all my life plus spent my career working on system reliability. And the one principle that nearly always holds true is that simple is more reliable. So if it were me I'd avoid all of the protective relays etc and simply valve it in. You'll only use it in an emergency when you're paying attention to what's going on so chances of leaving it running with the engine shut down are minimal. Relying on operator intervention is typically accepted as a valid design philosophy in reliability systems that don't involve potential for immediate threat to human life.