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View Poll Results: Thru hull open or closed while underway?
Thru hull open while underway 21 100.00%
Thru hull closed while underway 0 0%
Voters: 21. You may not vote on this poll

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  #1   IP: 174.254.192.157
Old 09-06-2020, 12:39 PM
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Thru hull open or closed underway?

Hereís a poll to ask if you religiously close the thru hull while underway or leave it open. I religiously close it...problem is that I didnít religiously open it (while battling high winds) and I think I will leave it open while underway just to have one less thing to do under scary circumstances.
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Old 09-06-2020, 01:14 PM
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Not sure why you would close the engine intake thru hull while underway?
There is a very high probability of needing to start your engine.
I can think of other reasons for closing it... but not while out sailing.
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Old 09-06-2020, 01:23 PM
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. . . and such practice dictates working anti siphon protection in the exhaust injection line for safety - either a valve or a vented loop (my preference).
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Old 09-06-2020, 01:54 PM
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Quote:
Originally Posted by roadnsky View Post
Not sure why you would close the engine intake thru hull while underway?
There is a very high probability of needing to start your engine.
I can think of other reasons for closing it... but not while out sailing.
The concern for me was flooding the engine
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Old 09-06-2020, 03:01 PM
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I found a checklist on my boat when I bought it that directed closing the raw water valve once shutting down the engine underway. The procedure to start was the same for starting at the pier and underway, and included opening the valve after the engine was running.
My practice is to leave the valve shut while starting next to the pier and then leave it open underway. I also get nervous about flooding the engine, and more often than not I will get antsy while cranking underway so I shut the valve then go back to starting. Iím sure takes less than three seconds to start, but it feels like minutes to me.
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Old 09-07-2020, 01:16 PM
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Bottom line - closing the thru-hull is a band-aid covering up an issue that should be fixed.
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  #7   IP: 100.36.65.17
Old 09-08-2020, 12:05 PM
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When I start the engine after its been sitting a day or more, I make sure the water intake is closed before cranking, in case the engine proves difficult to start (a frequent occurance in colder weather). I open the valve as soon as the A4 starts.

When the engine is warm, or has just been run within the last few houre, it always starts right up, so I leave the valve open while sailing. And yes, I do have an anti-siphon loop.
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Last edited by edwardc; 09-08-2020 at 12:10 PM. Reason: typo
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Old 09-08-2020, 11:34 PM
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I do much the same. It will often stay open for an entire extended cruise. Occasionally I may close it at anchor for the night for a cold start later on.

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Originally Posted by edwardc View Post
When I start the engine after its been sitting a day or more, I make sure the water intake is closed before cranking, in case the engine proves difficult to start (a frequent occurance in colder weather). I open the valve as soon as the A4 starts.

When the engine is warm, or has just been run within the last few houre, it always starts right up, so I leave the valve open while sailing. And yes, I do have an anti-siphon loop.
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Old 09-09-2020, 01:22 PM
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IMHO if cold starts take that much doing, perhaps track down why? In my case it was worn/dirty points.
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Old 09-10-2020, 12:31 PM
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No points: Electronic ignition.

A properly tuned updraft carb should be a little hard to start.

Years ago, I added an oxygen sensor and an air:fuel ratio gauge. Using an adjustable main jet, I have the ratio at cruise rpm set very close to the ideal 14.7:1.
At idle, I set the mixture slightly richer in order to make starting a little easier. In summer, a cold start with full choke always takes two tries. Very predictable. This increases in the fall as temperatures go down.

I did some experimenting, and found that adjusting the idle mix so it started cold on the first try was significantly richer than 14.7:1 and resulted in more fouled looking plugs.
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  #11   IP: 207.32.168.30
Old 09-13-2020, 12:57 PM
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Apparently I have the mixture adjusted rich, because my A4 almost always starts on the first try with a choke when cold, and without a choke once warm. Once it's warm it starts in less than a second. Cold with choke on, it starts in 4 seconds. If I prime the fuel line with the bail on the mechanical fuel pump before I start it cold, it starts quicker. It started on the first try this spring. I used engine fogging spray when closing down for the winter, and put a little MMO into the cylinders and let it soak in for a day before starting. I have EI, and an adjustable main jet.
It seems to be running well. I haven't checked the plugs for fouling since last year, but I change plugs every year, until this year. I have a water jacketed exhaust with an anti-siphon. I like the fact I can start up on a moment's notice without closing a thru hull first. I leave the water intake thru hull open all the time, except when I leave the boat for the winter. My definition of underway includes motoring, so closing the water intake underway never occurs to me.
If the engine ever didn't start within 5 seconds, I might close the thru hull until it caught, but I think the water jacketed exhaust prevents water from backing up into the cylinders. The problem many people have of water getting into the cylinders because they cranked it too much with the thru hull open has never happened to me. I don't run the starter for more than 5 seconds at a time with the thru hull open. If it doesn't start in 5 seconds, holding the starter in longer won't help, and may overwhelm your exhaust with water if the thru hull is open. If the fuel line has run dry, it might take several 5 second pulses to draw fuel from the tank to the carb. Manually pumping the mechanical pump will speed up that process, as will bypassing the OPSS on an electrical pump.
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