Water pressure/flow

[gungadin]

I would like to know if anyone can tell me what kind of water pressure and flow I could expect at cruising speed of 25 kph if I was to put a 1/2 inch water inlet just under the stern of my boat directly facing the bow. I realise the flow and pressure will vary with speed, so 25 kph is just an arbitrary figure.

 

[Viking]

Wash down? Interesting idea.

 

[gungadin]

Well that was not my initial idea, but it would work I would think. The reason I ask is: I now only have one engine on the boat, but it has a fresh water flushing attachment. I have a water puppy for a wash down with a pipe that ends just above the bottom of the boat (to not allow it to create any spray when travelling. In a situation where my water pump on the outboard ceases to function, I was wondering if I could just extend the pickup into the water stream and connect it to the flushing point to keep the engine cooling so I could at least get home, without calling for help. Obviously it would not work at idle, I would use the Jabsco for that, but don't really want to idle all the way home. Just curious if the pressure and flow would be enough to cool the engine either through the wash down or teed of it (relying only on water flow under the boat to provide flow and pressure).

 

[Viking]

Sounds like it could work. I wonder if the motor would pee. That would tell you there is enough.

 

[gungadin]

When I hookup the flushing attachment to house water pressure it "pees" like a Kentucky Derby winner. But I think that is because it is the first outlet from the flushing attachment. I also think that the flushing attachment is a reverse flush, that is the flow is opposite to what it would be if the water were pumped by the water pump impeller. The manufacturer (Yamaha) warns against running the engine with the flushing attachment on. Should not make any difference to the actual cooling as there is a thermostat bypass (I think). However removal of the thermostat is a 2 minute job if necessary. Just to be clear I am not referring to ear muff style flushing attachments, but rater a direct connection to a hose just below the cowling area.

 

[Wild Bill]

Sounds like it would be easier and cheaper to just replace your water pump at a period of time you are comfortable with.
Water pumps are pretty reliable, and who needs the extra drag for something you may never use?

 

[gungadin]

I would not have it extended until needed, just trying to avoid Murphy's Law.

 

[Wild Bill]

Search and see if you can find coolant flow diagrams for your engine.
IF it circulates completely at a high enough volume your golden! Try it with the hose to see how good the flow and pressure is.

 

[gungadin]

I am not certain what you mean. Water flow under normal conditions would be through the water pump up the tube to the lower part of the engine, filling the block and head through various passageways and restrictions, then diverting some to the tell tail before exiting by cooling the exhaust. When I attach the garden hose to the flushing port, I am pretty sure that the flow is the reverse as I am essentially putting water through the outlet toward the inlet. water flows through the head and out the exhaust but not through the water pump as the vanes would be blocking passage. Of course if the vanes were gone, then flow would not be blocked and water would flow out the intake, albeit somewhat restricted by the broken pieces of rubber from the pump. Now on Suzuki outboards (some at least) you can run the engine with a fresh water hose connections without destroying your water pump, but Yamaha says Do not Run with flushing hose attached.

 

[Wild Bill]

I'm guessing your assumptions are correct, and I'm guessing engine running with home water pressure you could essentially create a situation of no coolant flow with a serviceable water pump. Should work with a torn up water pump unless the pieces plug the inlet (now outlet lol!). Life and death I would probably go for it but you have a radio and friends out there. Water pump probably the least of your worries regarding Murphy!

 

[Rockfish]

It would make me nervous experimenting on a very expensive large newer outboard. The newer ones are increasingly run by lots of sensors, computers and AI. I would be concerned that if you try reversing cooling water flow with a ram scoop, that the AI could take offense and decide something was so out of spec. that it is best to throw error codes and alarms and protectively shut down completely or perhaps put itself into limp home mode and limit hp/rpm and then demand you take it to the dealer.

 

[gungadin]

Yes, this engine has a few sensors, but the only ones that would apply in a scenario where the coolant flow was reversed would be the water temperature sensor, two possible codes could be thrown. Code 15 incorrect cooling water temperature and code 49 which is an overcool signal. If the temperature runs too hot the ECM will not permit the engine to run past 2000 rpm . This could happen with reverse flow I suppose if the coolant was unable to bypass the thermostat in any great volume due to restriction. Of course removing the thermostat would remove the restriction, but probably trigger code 49 which would not initiate any response other then the code. I would at some point need to get the codes cleared.
I like to be as prepared as possible when on the water, and I feel that this low cost spare part might come in handy.
I remember back in the day I used to run a 1/4 in piece of copper tubing from under the boat into my live bait well to keep the herring aerated while travelling at speed (20hp on a 16ft Thornes), if you can call that combination speedy.

 

[profisher]

I would go for an electric pump that you could put into a 5 gallon bucket kept on board...use you wash down pump to keep the bucket topped up...you would be able to check to see that there is a balance maintained so that the bucket never empties.