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Author Topic:   Yamaha water tube
DanT posted 03-10-2002 11:11 AM ET (US)   Profile for DanT   Send Email to DanT  
I have a used 90hp Yamaha that I installed on my Eastport. There is a water tube that runs from the lower unit, just forward of the shift shaft, up to the area of the tilt tube. It terminates at this point with a plug. Does anyone know the purpose of this tube? Thanks
Tom W Clark posted 03-10-2002 11:29 AM ET (US)     Profile for Tom W Clark  Send Email to Tom W Clark     
Speedometer pick up. Many motors in the 1980's had a pitot tube built into the gearcase. It was one of those great ideas that didn't work too well.
DanT posted 03-10-2002 06:02 PM ET (US)     Profile for DanT  Send Email to DanT     
Thanks for the information guys. The motor is an '87. Were the problems with this type of pitot setup prone to failure or just not accurate?
Tom W Clark posted 03-10-2002 07:07 PM ET (US)     Profile for Tom W Clark  Send Email to Tom W Clark     
They worked great when they worked. OMC came out with this idea in 1982 and when I saw it I thought "That's such a sensible idea. Why hasn't somebody thought of this sooner?" It's clean looking and eliminates the need for an unsightly hose and pitot tube running down your transom. No extra screws to drill too.

The problem comes when the gearcase hits any kind of debris. The pickup gets clogged. Unlike a separate pitot tube which kicks up when it strikes something, the gearcase just slams into whatever little stuff is in the water. Yes, if your hit a big piece of driftwood, the motor will kick up too, but by then it's too late for the speedometer pickup in the gearcase.

In the case of my 1982 Johnson 90 hp on my first Montauk, the gearcase pitot got clogged up the very first time it struck something. No amount of picking and blowing ever cleared it out. I simply installed a separate Teleflex pitot as I had always done before and left it at that. In the case of the OMC motors, the speedometer hose hooked up at the top of the gearcase on a plastic barb. This plastic part was very easily broken, which in fact happened to mine eventually.

I didn't know the Yamahas still used this idea. I know in the case of the OMC motors, they abandoned the gearcase pitot before the end of the 1980's. I suspect Yamaha has a more robust system and, hopefully, a way to clear a clogged pickup. Like I said, when it works, it works great. Probably more accurate than a transom mounted pitot because itís running in cleaner water and because of its added depth will stay in the water too.

Salmon Tub posted 03-19-2002 02:17 PM ET (US)     Profile for Salmon Tub  Send Email to Salmon Tub     
DanT, actually, that tube has a dual purpose. It was originally designed to be hooked up to another hose that went into the console of a boat and ended with a little valve. It was originally designed for skippers who took out unruley friends with them. When an impatient passenger would start to complain about the length of the boat ride or make a comment like "look at that boat" as they point to some Fish/Ski job, the skipper could take the tube by the end, open the valve, point at the delussional passenger and spray him with water. The effect on the person is said to be sobering in the least. The skipper could also have his now "enlightened" partner use the same set up to help wash down the boat on the ride home, before the scales and blood have a chance to dry. But, I guess you could hook it up to a speedo. I actually have seen some rigged to small bait tanks in smaller boats like the Montalk.
Bigshot posted 03-19-2002 02:25 PM ET (US)     Profile for Bigshot  Send Email to Bigshot     
It is plugged because it was never used probably. try it. My 1999 Evinzuki has it and it works great...unfortunately the Donzi Speedo is off by 4mph(at least it reads fast).

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