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pitot tube question? |
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62 wood 
Grand Poobah 
Joined: February-19-2005 Location: NW IL Status: Offline Points: 4527 |
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 Topic: pitot tube question?Posted: February-10-2009 at 12:50am |
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I understand the larger tubes (just above the platform) are stabilizers for the speedos, on this 72 SN ?
I see the speedo tubing runs into them, but how do they actually work? |
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critter
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Joined: January-11-2008 Location: New Hill, NC Status: Offline Points: 1227 |
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Posted: February-10-2009 at 1:20am |
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I understand that they are equallizers and the water from the pitot displaces the air in the equallizer. This causes pressure at the speedo and results in needle movement.
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1980 Ski Nautique
1966 Barracuda |
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Gary S
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Joined: November-30-2006 Location: Illinois Status: Offline Points: 14096 |
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Posted: February-10-2009 at 1:55am |
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Steve , they can also be mounted anywhere ,mine is mounted on the stringer behind the toe board
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8122pbrainard
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Joined: September-14-2006 Location: Three Lakes Wi. Status: Offline Points: 41045 |
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Posted: February-10-2009 at 10:02am |
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Steve,
They can also be called pulsation dampeners. They smooth out the air pressure coming from the pickup so you don't get as much needle bounce on the speedo. |
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TRBenj
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Joined: June-29-2005 Location: NWCT Status: Offline Points: 21190 |
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Posted: February-10-2009 at 11:33am |
True- but you want them to be as close to vertical as possible. |
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DrCC
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Joined: April-12-2004 Location: at home Status: Offline Points: 2868 |
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Posted: February-10-2009 at 10:21pm |
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They can also be referred to as Ballast tubes.
They (CC) moved them to the inside of the transom around 1975 or 1976. ____________ '74 Ski Nautique '73 Ski Nautique '66 Mustang '88 Mustang |
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bkhallpass
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Joined: March-29-2005 Location: United States Status: Offline Points: 4723 |
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Posted: February-10-2009 at 11:46pm |
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Good info. I always called them "those speedo things on the back of the boat."
BKH |
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Livin' the Dream
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62 wood
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Joined: February-19-2005 Location: NW IL Status: Offline Points: 4527 |
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Posted: February-11-2009 at 12:03am |
 me too Brian..
Does anyone know, Do all speedos use them, or are they just for the boats requiring more accurate readings? (ie: tournement ski boats) |
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sethro
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Joined: February-11-2009 Location: Sterling, IL Status: Offline Points: 30 |
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Posted: February-11-2009 at 5:09pm |
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I don't know about all boats, but I did a bunch of trouble shooting with pitot driven speedos on an 85 MasterCraft last summer. I learned that the tubes (I was calling them ballast tubes) didn't seem to have any effect on the readout. I didn't see a difference in anything...bouncing or time to register the speed.
I ended up keeping them on the boat just because and replaced the pitots with the new venturi style from skidim.com My friend's 84 MasterCraft has never had the tubes and his speedos function just fine. |
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Tellarico
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Joined: June-17-2008 Location: United States Status: Offline Points: 118 |
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Posted: February-12-2009 at 7:58pm |
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When my speedos were out being serviced water ran out of the end of the tube that attaches to the speedo. I read above "air pressure" where is my problem if I have water instead of air? have not run them since.
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8122pbrainard
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Joined: September-14-2006 Location: Three Lakes Wi. Status: Offline Points: 41045 |
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Posted: February-12-2009 at 9:53pm |
Paul, Water ran out of them BEFORE you sent them out for restoration, correct? Air pressure is created by the water pushing in at the pickup. Inside the speedo is a bellows that changes the air pressure into a mechanical needle movement. The bellows are known to break. When this happens, the bellows won't hold the air pressure so there's nothing to hold the water back. Now, the water makes it all the way up to the speedo and then usually pis** on your legs!!!! |
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65 'cuda
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Joined: July-12-2005 Location: Cincinnati, OH Status: Offline Points: 1091 |
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Posted: February-12-2009 at 11:11pm |
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Last spring after having the speedometer out,I left the line off the back. Running across the lake during first trip I noticed the water pissing on my legs. I was amazed how much pressure was there, I had a difficult time holding back the water with my thumb on the way back to the dock. Be sure to blow all the water back out of the tubing before hooking back up the tubing.
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Tellarico
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Posted: February-13-2009 at 1:02pm |
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Thanks Pete, It was before I sent the speedos out and during the time they were out. I will blow the water out before I hook them up again. My motor should be back in after a rebuild next week and I will gewt to run it and check it out. Paul
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Gary S wrote: