# Rule of thumb for water pressure



## fjmaverick (Sep 18, 2015)

Running a jack plate on a tunnel hull without a water pressure guage. How can you tell if your running low pressure?


I havnt started using the jackplate until recently and want to be sure before I bring it way up.


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## Vertigo (Jun 3, 2012)

Easiest way is to get a gauge. They're cheap and installation is easy. Without a gauge, if water is coming from the telltale, you've got pressure, but it's not smart to be looking over your shoulder to watch it. In my experience with tunnel hulls, it's hard to get the motor so high that you lose pressure. The thing that causes me most pressure loss is weed. You can be running full down and pickup enough weed to lose pressure, especially this time of year in my neighborhood. Just get a gauge.


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## fjmaverick (Sep 18, 2015)

Thanks that is good info.

What are you guys running for a guage?


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## devrep (Feb 22, 2009)

Depends on the motor. Tohatsus only run like 6lbs of water pressure so the gauge isn't that helpful. I just keep an eye on the stream. And yes grass and weeds can be a problem. Fortunately these new motors will let you know if they are running hot before damage occurs.


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## fjmaverick (Sep 18, 2015)

Motor is a 2015 f70. I think it has decent pressure, when I flush it, it shoots 15+ feet

I would prefer a nice analog unit. Is the connection already in the motor block or is that something that has to be done?

I looked at the lowrance digital unit (i think it uses nmea2000). Was considering running that with a shoot through tranducer.


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## lemaymiami (Feb 9, 2007)

I won't rig a skiff without a water pressure gauge.... it's that important - particularly if you run at night. If you run into weed (or wrap a plastic bag around your lower unit) - you'll never know you've lost water pressure until your motor overheats and you hear that warning buzzer. By then it might be too late... More than one guy running a jackplate has burnt up a motor when they didn't notice that they were running it too high to pick up water properly.... I don't run a jackplate (and don't particularly like them - but that's another story) but I'll still have water pressure gauge on any skiff if I can. An additional benefit is that your gauge will show you when your water pump is getting weak and needs replacing....

Water pressure gauges, on any motor, are purely mechanical with a water tube that connects to the front of your lower unit to allow the water to run up to the gauge itself... Different makes (and different model motors) have different requirements as to what pressure the system requires to be operating in the safe range. Talk to your dealer, they'll be able to tell you the parts you need if you're going to install one yourself - or what it will run to install one for you. The guage should be somewhere between $50 and $100, the hardware (tubing, fittings, etc.) shouldn't cost much either. The biggest hassle I ever found was the additional wiring needed so that the gauge is lit for night-time running. Hope this helps


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## Skiff Junky (Oct 6, 2015)

Check with your dealer to find out what pressures to expect. Like devrep stated, they are very low pressure. If you are under 15 lbs (you most likely are less than 12), get a 15lb gauge. It will be easier to notice the variations easier to read at a glance than a 30 or 45lb gauge. A quick google search will show your options.

The good catp'n LeMay offers sound advice.


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## Smackdaddy53 (Dec 31, 2012)

I would recommend a gauge with a needle. That F70 is Low volume High pressure so you need a 0-30psi gauge. High volume low pressure motors only need a 0-20psi.


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## fjmaverick (Sep 18, 2015)

Think 0-35 is too much? I like the livorsi guage but thats the smallest they make. Any other recomendations on a quality guage? Prefer a white face.


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## ADicus (Feb 15, 2013)

Unsure of what brand my gauge is but it's a 0-30psi on my 14' F70 I generally run around 25-30psi up or down on the plate but I am still tinkering on the plate setup


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## commtrd (Aug 1, 2015)

My F70 will carry on at around 23 psi with motor lifted all the way up but the only thing that really affects it is floating grass that plugs off the water intakes.


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## Sublime (Oct 9, 2015)

I am all ears if someone knows how to mount one on a 30 etec. There is NO factory port to hook one up to.


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## Sublime (Oct 9, 2015)

I am all ears if someone knows how to mount one on a 30 etec. There is NO factory port to hook one up to.


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## Smackdaddy53 (Dec 31, 2012)

Sublime said:


> I am all ears if someone knows how to mount one on a 30 etec. There is NO factory port to hook one up to.


Drill and tap!


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## hunterbrown (Feb 17, 2014)

Look into gaffrig gauges, you can get them from gaffrig or their sister site monster marine which is much less expensive. I have been very happy with them, they come in 0-15 and 0-30 with all of the mounting hardware and tubing included.


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## Jim Lenfest (Jul 20, 2016)

Sublime said:


> I am all ears if someone knows how to mount one on a 30 etec. There is NO factory port to hook one up to.


Maybe you could place a tee in the Tell Tale hose inside the cowl. I know on my Mercury, Near the top of the water jacket, they placed a hole threaded to NPT with a plug in it, just for the purpose. Thinking it is 1/4" NPT. A rear view mirror could be used for watching the telltale as a quick solution rather than looking back all the time. I always also try to tell guests to keep an occasional eye on that as well.


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