My boat's speedometer occasionally stops working or reads very low.  The lake I usually boat in is full of silt, weeds, wood, etc. and the pick-up hole for the pitot on the lower unit of my outboard gets plugged fairly often.  

 

I keep a large sewing pin stashed in the carpet near the motor well for the purpose of picking debris out of the opening.  So far, that has always got my speedometer working again.  Except for this time.

 

I'm wondering what my next course of action should be.  I was thinking of trying to blow some pressurized air back out through the lower section of the pitot tube from the joint near the well, but I'm not sure how to disconnect it (or if it is able to be disconnected there).

 

Any thoughts?

Boat speedometers are highly inaccurate and finicky. I don't pay much attention to mine. 

I rely on the GPS based speedometer on my fishfinder.

I use an eighth inch drill bit and small vice grips to clear my pilot hole. It will pull out anything in there. Had mine filled with dirt, weeds small wood, the bit cleared it out.

I use my GPS for accurate speed readings, speedo is off 3-4 mph.

2 hours ago, Smalliefan2 said:

I use an eighth inch drill bit and small vice grips to clear my pilot hole. It will pull out anything in there. Had mine filled with dirt, weeds small wood, the bit cleared it out.

I use my GPS for accurate speed readings, speedo is off 3-4 mph.

I started to do exactly that, but it felt like the bit was up against something hard and I didn't want to risk going too deep with it.  With my luck, I'd drill a hole into the gear case...  

 

I wonder exactly how deep it's safe to go in a Mercury ELPT 40HP four-stroke's pitot hole?

 

?

Im ready to remove mine.  It either reads 20mph or 55mph.  It's useless.  No reason to have it with a GPS.

Water speedometers are useless pull it out and put in a digital gauge or a radio.

Mine hasn't worked for about 5 years. The other day my wife and I were going across the lake and she said it seemed like the boat was bouncing a lot for 10 mph. I looked at her kind of strange and said what are you talking about? She said the speedometer said 10 mph. I told her that hasn't worked for a couple years now. She said I thought this whole time you were just driving at 10 mph. I got a great laugh out of it and probably won't let her forget it anytime soon. 

The hole diameter is less then .125D, suggest you use a smaller size #89 or 3/32 (.093D). No need to use a drill motor. Tape the drill with duct tape about 1” long on the drill shank. Twist the drill by hand to remove debris in the hole.

You can run a .046D wire in the hole to clean out whatever is in it after hand rimming with the drill.

Tom

 

I’ve always accidentally pinched the hose while lowering and raising the motor, my console depth finder gives more accurate speed anyhow. In my small boat with nothing electronic, I use an app on my phone called speedbox. And I go like 11 mph so I have no idea why I want to know that