Pitot Tube - Motor vs. Hull mount?

[trxxx250r]

I have a 1995 Stratos 20ft. with a Johnson 175.

The boat came with a pitot tube for the speedo mounted on the bottom of the transom. However, the speedo has never worked since I got the boat, it's dead.

Since I've been looking into a new set of gauges I've learned that there is a fitting coming off my lower unit that is a pitot built into the lower unit of the motor.

Question - Which should I use? A new pitot installed where the old one was on the transom or come off the fitting on the lower unit? What are the differences and which one would be more accurate?

Thanks!

 

[F_R]

Re: Pitot Tube - Motor vs. Hull mount?

Use the one on the motor. Transom mount ones are generally in the same category as garbage.

 

[Bosunsmate]

Re: Pitot Tube - Motor vs. Hull mount?

i like motor ones as they lift up with the motor. i find them more brittle though

 

[trxxx250r]

Re: Pitot Tube - Motor vs. Hull mount?

It's actually built in to the lower unit, there's just a small stainless tube flush on the leading edge of the lower unit. Then the tube outlet fitting is right above the anti ventilation plate.

It seems to me with the motor always turning and being trimmed it would give a skewed reading as opposed to a fixed unit on the hull. Why am I wrong?

 

[Faztbullet]

Re: Pitot Tube - Motor vs. Hull mount?

Hull mount....rarely stops up and kicks up if it hits a object.

 

[Fed]

Re: Pitot Tube - Motor vs. Hull mount?

In a post the other day I read a link that said the inbuilt pitot on a mercury will read 10% higher (I think) than a transom mounted one. I'll look for the details for you.
Anyway that would suggest the speedo should be matched to the pitot, merc to merc or aftermarket to aftermarket. The same may apply to your OMC.
The only problem is that it doesn't make sense, water pressure is water pressure unless the variation is caused by the extra depth on the inbuilt one.

Had a quick look, can't find the thread so far.
Edit: http://www.v3instruments.com/trouble_shooting_guides/speedometer_pitot_ts.pdf
Point #8

 

[trxxx250r]

Re: Pitot Tube - Motor vs. Hull mount?

thanks fed.

 

[trxxx250r]

Re: Pitot Tube - Motor vs. Hull mount?

What brand gauges do you guys like? Reasonably priced ones, anyway.

I like the look of the Sierra or Teleflex (not sure who makes them) Amega's

 

[boobie]

Re: Pitot Tube - Motor vs. Hull mount?

Teleflex or BRP (OMC).

 

[F_R]

Re: Pitot Tube - Motor vs. Hull mount?

A speedometer is nothing more than a pressure gauge marked in MPH instead of PSI. A pitot is nothing more than a pipe pointing forward. As the speed increases, the water pressure on the pipe end increases. Result: Gauge reads water pressure and displays it as MPH. The hole size in the pitot makes no difference, be it 1/8" or 1/2". Reason: Pressure PER SUARE INCH in the guts of the gauge is what counts.

I called transom mounts garbage because I live in Florida, and they won't go five minutes before a weed or something gets snagged on it, disrupts the water flow direction and PSI shown to the gauge.

EDIT: Following up, speedometers are nice dashboard decorations, but virtually useless and a waste of money. If you really are interested in knowing how fast you are going, spend your money on a GPS. Even the cheap hand held Garmins, etc, will accurately display speed. And direction. And mark that great fishing hole for future reference. And even leave a bread crumb trail so you can find your way back home. Just my 2c

 

[phillnjack2]

Re: Pitot Tube - Motor vs. Hull mount?

why not buy a gps gauge that looks like a original old type and be accurate (within 10%).
nothing to snag on no pipes to go brittle and no worries about a leak anywhere ?


phill