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Old 28-03-2020, 07:07   #1
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Had boat hauled, refloated, no raw water flow?

After bottom job, had boat relaunched. Noticed very little water flow from exhaust. Boat yard turned us loose, no choice, half a mile later engine over temp alarm. Got to our marina and pulled the water pump">raw water pump to find the impeller in perfect shape. What happened?


Bob
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Old 28-03-2020, 07:19   #2
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Re: Had boat hauled, refloated, no raw water flow?

Probably an air lock in the system that it couldn't clear. If you've got a strainer on the raw water inlet, crack the lid on the strainer loose with the seacock open after launch to bleed the air out of it. Worst case, you might need to loosen the hose at the pump inlet on the engine to bleed the system.

If it turns out not to be an airlock, make sure the thru hull didn't get partially painted closed.
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Old 28-03-2020, 07:19   #3
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Re: Had boat hauled, refloated, no raw water flow?

Bob,
Can you tell us what motor you have?

Did you close your engine intake before you hauled out or open it while on the hard, draining the engine raw water? Either of these could have caused an air lock.

Assumed you checked the raw water valve is fully open, strainer flow good? Possibly blocked heat exchanger?
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Old 28-03-2020, 08:36   #4
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Re: Had boat hauled, refloated, no raw water flow?

I’m in agreement with Rslifkin & Bill O that it’s likely an air lock. Also agree with their recommended solutions.
The only addition is that when flexible impeller pumps are new they do a good job drawing water up through the system. Truth is that under normal conditions a raw water pump you should never have an air lock. As the pumps age the Impeller, pump face, and seals wear allows water to pass around the impeller reducing the efficiency. It is possible that when the system was fully drained the pump could not draw enough to restart the flow. To investigate pull the pump face inspect for wear. The photos show a Sherwood raw water pump that had the exact same problem that was resolved with a new pump face.
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Old 28-03-2020, 09:06   #5
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Re: Had boat hauled, refloated, no raw water flow?

Hope no damage-
lesson learned-

If the engine is to be started after launching a quality yard should at least mention to the owner to check the raw water flow. The airlock is the culprit and particularly on vessels with strainers above the waterline. The easiest solution fills the strainer if reachable. Closing intake seacock permits this to be done prior to launching, then immediately after starting open seacock. Opening prior may permit water to drain out wrong way. Every vessel is differnt.
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Old 28-03-2020, 09:28   #6
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Re: Had boat hauled, refloated, no raw water flow?

Years ago, may be my first season with my first boat, a 27 footer with Volvo MD5A a similar thing had happened - no water coming out of the exhaust. Lucky for newbie me I had a boat builder buddy on board - he was there to teach me the ropes. He shut the engine off, while we drifted, disconnected the intake hose from the strainer side and blew into it. A plastic shopping bag floated from under the hull. I would've never guessed had I been there by myself.
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Old 28-03-2020, 09:29   #7
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Re: Had boat hauled, refloated, no raw water flow?

Quote:
Originally Posted by BobHorn View Post
After bottom job, had boat relaunched. Noticed very little water flow from exhaust. Boat yard turned us loose, no choice, half a mile later engine over temp alarm. Got to our marina and pulled the raw water pump to find the impeller in perfect shape. What happened?


Bob
Maybe you forgot to close all seacocks before hauling out?
Your most likely air locked.
Remove the strainer cap and fill with water.
In most yards this is the Protocal, close before hauling, open and engine running, raw water flow, before launching, especially if engine work or the raw water loop has been serviced
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Old 28-03-2020, 09:41   #8
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Re: Had boat hauled, refloated, no raw water flow?

BobHorn , I know your problem .I suggest to check :
seacock open
amount water in the exhaust output
time temperature alarm turn on
If the first is yes and second is low volumen
and the third is more than 1 min , probably you have a reduced fluid transfer due to calcium or salt deposits in the hoses and heat interchanger and that produced a slowly engine heated
good luck
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Old 28-03-2020, 09:56   #9
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Re: Had boat hauled, refloated, no raw water flow?

Agree with all of the above. The boat is fairly new to us and judging by the lack of maintenance on other items, I immediately assumed a bad impeller. The boat yard picked the boat up at the slip so I have no idea if they closed the seacock. They were supposed to deliver the boat back to the marina but drug their feet for two weeks, "can't find a captain because of the virus", so went down to do it ourselves. I suspect they noticed the issue with the reduced water flow and that's why they didn't want to deliver the boat back. I had barely started the engine when they untied us and turned us loose, not much chance to check much of anything. Had some other issues with them, like painting over some barnacles on the hull, they claimed it was a gel coat issue, little mound with a hole in the middle. Sure looked like a barnacle to me.
Used them because of the convenience of them picking up the boat and then taking it back. Never again.
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Old 28-03-2020, 10:14   #10
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Re: Had boat hauled, refloated, no raw water flow?

One time the cork gasket on my bronze raw water filter dried out in only 2-3 days. Airlock. I had tried everything else twice looked for hours. Sometimes the simplest things.
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Old 28-03-2020, 11:18   #11
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Re: Had boat hauled, refloated, no raw water flow?

I once had similar issues though not after a launching. It took quite a while of head scratching to find that the problem was a sheared impeller shaft bushing to impeller! Not obvious just looking at it. I took the impeller out and had in my hand and looking closely saw suspicious signs around the bushing in the center of the impeller. Replaced the impeller and all was fine. Foufou
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Old 28-03-2020, 11:26   #12
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Re: Had boat hauled, refloated, no raw water flow?

That happened to my toilet intake last haulout. Insect nest inside the hose. Might want to check aomething like that isnt clogging intake.
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Old 28-03-2020, 14:21   #13
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Re: Had boat hauled, refloated, no raw water flow?

With the thru-hull closed take the hose off the intake side of the pump. Open the thru-hull you should have a sizable flow of raw water. If not blow back into the hose with a garden hose full force.

If that is good take off the discharge hose on the pump. Then the hose before the exhaust mixing elbow and attach a garden hose. This time use gentle pressure to backwash your system.

Hope that helps.
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Old 28-03-2020, 16:53   #14
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Re: Had boat hauled, refloated, no raw water flow?

Of COURSE you have opened the sea cock to the heat exchanger raw water supply--so if your boat has been painted, it sounds as if it could be the old masking tape over raw water inlet through-hull trick. They sometimes put it there to stop mud wasps.

Slip over the side and check--it may be clogged with a mud wasp nest if there is no covering anyway. Sometimes one can poke a Go-Pro on a stick down and have a shufti--

Do not try to back-flush through the boat system using a hose. Only flush FORWARDS through the impeller inlet, and for a short time because if the engine is not running, water could possibly get into your cylinders.

You will probably have to prime the system-- I used to do that by tipping fresh water into the raw water strainer, then screwing the lid back on. Gravity takes it to the impeller, then it has enough suck to work and draw in sea water. While you have the strainer open, give it a clean.
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Old 29-03-2020, 14:16   #15
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Re: Had boat hauled, refloated, no raw water flow?

make sure your thru hull is cleaned out. They could have painted a coating over the valve or existing barnacles and plugged it up. Standard operation procedure before starting engines, take screwdriver and cleaning out barnacles in thruhull. If the boat sits 3-4 weeks, it will have buildup and needs to be cleaned out. Of course, check flow in strainer. Some sailors attach hose to thruhull so it is above water line and jab long stick to clear barnacles. I just dive and clean props at the same time.
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