Raw water pump impeller sudden failure

[kapnd]

Originally Posted by capt jgw

Could be the intake got temporarily blocked, plastic bag, jellyfish, etc stuck on the intake. Does the intake have a scoop shaped screen on the outside? It's counter intuitive but those should be installed with the scoop facing AFT, not forward. That way the boat's motion through the water will help slough an obstruction off the screen. Facing forward it's held in place.

Aft facing scoop will not work on a fast moving boat, as low pressure area develops behind it. The SCOOP design is intended to scoop water with forward motion.
It’s more frequently done on sailing vessels and auxiliary motors such as generators to avoid stuffing water up them when underway.
A scoop is most streamlined when facing forward, making it less likely to pick up damaging debris.

[David Mathis]

If it ran dry long enough and hot enough to destroy the impeller, small streaks of the melted impeller may be attached to the housing. This will result in a high friction point which will place additional stress on the new impeller resulting in a significantly shortened service life. The advice is to replace the pump.

[Bluechart]

If you are going to continue to close the intake, do you turn off starting battery, close head intakes?

Create a laminated “Check-off” list for leaving the boat, and on the back of the card a “Check-on” list for when you arrive.

[eroc]

Many years ago after rebuilds due to charter customers overheating a Yanmar , I installed a flow sensor on the raw water intake, can't recall the brand, but it has a fine flow adjustment. Connected it to the "water in saildrive" alarm circuit on the replacement Yanmar 3YM which was unused since the boat has a shaft drive. It issues an impossible to ignore alarm for any condition stopping raw water flow. Not very costly- highly recommend.

[rpackard]

i installed a micro switch which gets closed when the seacock is opened. That switch operates a relay in series with my ignition. So the engine cannot be started unless the seacock is open. I installed it 40 years ago and never had a problem.

[SailingHarmonie]

Originally Posted by kapnd

Aft facing scoop will not work on a fast moving boat, as low pressure area develops behind it. The SCOOP design is intended to scoop water with forward motion.
It’s more frequently done on sailing vessels and auxiliary motors such as generators to avoid stuffing water up them when underway.
A scoop is most streamlined when facing forward, making it less likely to pick up damaging debris.

It is not at all clear if you are making any kind of recommendation here, but on a sailboat a “scoop” on the drive engine should NEVER point forward. A flexible impeller pump is a positive displacement pump, but it does NOT guarantee a pressure tight seal. Water can trickle past it, and if it is damaged, water can flow past quite easily.

Having the boat sailing forward stuffing water into the scoop risks filling the engine with water. On generators, the scoop should NEVER face forward, on any boat, for the same reason. Even on twin engine motorboats, if the scoop faces forward, running on one engine is a serious risk to the idle engine.

I KNOW many boats have these installed incorrectly. The engines in all of them are all living on borrowed time. Someday, they will flood.

[smacksman]

I fitted a brand new, shrink wrapped, raw water impeller. Ten days later I luckily spotted the engine temperature rising and checked the cooling circuit. Half the new impeller was trapped upstream of the oil cooler. Old stock I suppose.

[GrowleyMonster]

Originally Posted by Jolly Roger

This is what the impeller looked like after an attempt to drag my boat off a grounding in the intracoastal. It resulted in me having to strip and clean out the whole of the raw water engine system, including two heat exchangers, and the heavy exhaust.
During the repair I installed a filter directly after the pump, which will now capture any bits of impeller or other debris.
The moral is: if you must use your engine to get off a grounding, inspect the impeller directly afterwards. Better still: kedge an anchor and pull her off - more difficult, but a darn-sight easier than stripping a Perkins 4.326, believe me!

A filter or strainer downstream from the water pump of some sort should be in the ABYC standards. It can seriously prevent a bad day or ten.

[GrowleyMonster]

Originally Posted by rpackard

i installed a micro switch which gets closed when the seacock is opened. That switch operates a relay in series with my ignition. So the engine cannot be started unless the seacock is open. I installed it 40 years ago and never had a problem.

That's smart sailorproofing. Much better than hanging the "key" from the seacock handle. Some of us, like me for example, don't have a start key.

[stormalong]

Originally Posted by David Mathis

If it ran dry long enough and hot enough to destroy the impeller, small streaks of the melted impeller may be attached to the housing. This will result in a high friction point which will place additional stress on the new impeller resulting in a significantly shortened service life. The advice is to replace the pump.

Really??? You would replace a multi-hundred dollar pump because of "small streaks of of melted rubber"? In the unlikely event of that happening it would be easy to clean with a scotchbrite pad.

BTW: Some Teflon grease will make impeller installation easier and extend it's life. It does not wash out.

[BBill]

Originally Posted by SailingHarmonie

It is not at all clear if you are making any kind of recommendation here, but on a sailboat a “scoop” on the drive engine should NEVER point forward. A flexible impeller pump is a positive displacement pump, but it does NOT guarantee a pressure tight seal. Water can trickle past it, and if it is damaged, water can flow past quite easily.

Having the boat sailing forward stuffing water into the scoop risks filling the engine with water. On generators, the scoop should NEVER face forward, on any boat, for the same reason. Even on twin engine motorboats, if the scoop faces forward, running on one engine is a serious risk to the idle engine.

I KNOW many boats have these installed incorrectly. The engines in all of them are all living on borrowed time. Someday, they will flood.

Wow, this is news to me. Is this some type of aybc code or personally inspired? I've owned many sailboats with fwd facing scoops and never a problem. It seems after 50+ yrs and 1000s of cruising hrs it would have reared its ugly head with at least one of my boats. Can't remember seeing a sailboat with the scoop facing aft. If a fwd facing scoop fills the engine its a pixx poor exhaust design.

[Disailor]

I remove the impellor for the winter then coat with "SuperLube" when re-installing in the spring. I also have a small strainer (with a see-thru bowl) between the pump & the heat xchanger.

[deblen]

Originally Posted by skwanderer

Yes!! I greatly appreciated your remark here, as I had my seacocks closed once when I set out, having forgotten to open them. I felt like such an idiot, I'm heartened to hear I'm not alone making this mistake. The result was I saw my engine temp gauge climbing, and considering not trusting my instruments, I ignored it. I finally decided to open the engine hatch and whoosh! Big plumes of steam! Aigh!!! I quickly jumped down and opened the seacocks on the raw water intake when I saw they were still closed, and kept the engines running, thinking this may ensure the now flowing raw water may help cool the engines (that did), and I returned to my silp. The result was the impeller had disintegrated into tiny bits and got lodged in the system, resulting in a costly repair by my diesel mechanic. My point here is that I now use Google Keep notes for a departure checklist for everything, from checking coolant to pfd to vhf on to Seacocks open! You can use the list with checkboxes beside each, and then reset it to untick the boxes and reuse the list. Highly recommend, and I don't have to think if I did everything, I just follow the checklist every time. Screenshot s of my departure checklist attached. Hope this helps someone in the future.

++ As soon as you start engine,look over the side & make sure water is coming out the exhaust

[BBill]

Those vintage bronze gear water pumps with grease cap on top were great. Never a worry about rubber impellers. I had them on gas and diesel sailboat engines in the past. When they got worn and wouldn't prime all you had to do is turn the grease cap a quarter turn and you were good to go.

[stormalong]

Originally Posted by BBill

Those vintage bronze gear water pumps with grease cap on top were great. Never a worry about rubber impellers. I had them on gas and diesel sailboat engines in the past. When they got worn and wouldn't prime all you had to do is turn the grease cap a quarter turn and you were good to go.

Interesting idea. Just did a google search on grease cups. Pricey little devils.

An alternate idea would be to use a stainless steel grease nipple and occasionally pump a little grease in. Downside is that you would have to remove the pump to drill and tap for the nipple. Maybe on the next rebuild. In my case probably coming up soon.