Pitot tube extension?

[johnbo]

Hi,

I'm moving my speedo and fishfinder transducers to make room for a set of SmartTabs.. Running into a problem that I can't get enough slack on the speedo tube.

Can I just cut this (inside the boat) and extend it with some similar diameter plastic tube? If so, how careful do I need to be about the diameter of the fittings and the new section of tube?

Thanks,

johnbo

 

[Reel Poor]

Re: Pitot tube extension?

It's really not that critical. You can use those little plastic vaccum hose splicers (avaliable at any auto parts supplier) and just add in the length of hose you need. Slightly smaller or larger will not effect the speed-o-meter accuracy.

 

[tashasdaddy]

Re: Pitot tube extension?

a lot of marine supply stores, have it by the foot, with the splicers. just cut a piece off your, and match it. all it is, is an air pressure hose, the pressure of the water into the pitot , compresses the air in the tube, thus reading on the speedo.

 

[johnbo]

Re: Pitot tube extension?

Great news,

Thanks,

johnbo

 

[Silvertip]

Re: Pitot tube extension?

The splicers are called hose barbs and are also available in various sizes at any home improvement or hardware store.

 

[johnbo]

Re: Pitot tube extension?

Follow up question. Is there any reason not to place the pitot tube assembly close to the outdrive leg?

There seem to be some concerns over the position of the fishfinder/sonar transducer near the leg, but the pitot system shouldn't really care, right? As long as it has a relatively smooth flow of water past it, it should work fine.

My boat has about a 8-9" wide flat spot on the bottom of the hull, I'm thinking about right at the edge of this. This would still give me some room for the sonar transducer.

The Smart Tabs sure do complicate the placement of things back there. First it was the tie down straps, then the sonar and the pitot.

Thanks,

johnbo

 

[tashasdaddy]

Re: Pitot tube extension?

buy an tie down that goes over the boat. the solves that. i see no reason not to put the pitot there, it will get clean water, before the prop.

 

[Dhadley]

Re: Pitot tube extension?

You don't want anything in front of the prop. About 10 to 12" from the center of the motor to each side should be clear.

 

[johnbo]

Re: Pitot tube extension?

I gotta ask. Why?

I can understand not wanting to disturb the flow of water with something like a kicker motor which could really mess up the flow. But, a pitot tube is going to stick a 1/4 inch wide stick into the flow about an inch or so deep. Hardly seems likely to foul the water flow past the prop.

Am I missing something here?

Thanks,

johnbo

 

[Dhadley]

Re: Pitot tube extension?

You don't want anything in the prop path that will aerate the water. Disturbed or "dirty" water can lead to cavitation and poor performance. On an outboard it can lead to water injestion in the powerhead too.

The cooling water intakes are on the gearcase too. You don't want air bubbles in the cooling water.

A stern drive like your Cobra is typicaly mounted pretty low so the effect may be minimal. Anytime we do anything like this we would install the tabs and test without anything being replaced on the transom. Then once we establish the new baseline we would install the transducer and the pitot. Usually you want the tabs mounted as far to the outside as possible which leaves plenty of room.

 

[johnbo]

Re: Pitot tube extension?

OK, that makes a certain amount of sense.

On my boat the stern is getting a little crowded. The back of the boat has a kind of catamarran effect with the outer edges of the hull sticking out past the transom surface. This covers the chine areas, but eats up about a foot on either side of the boat.

I've got the smart tabs within about 4" inches of these extensions, to allow the tie down straps a place to pass. Still there is a foot or so between the outer edge of the outdrive and the inside edge of the SmartTabs. I may move the pitot tube to the opposite side of the outdrive to give the transducer more room. I just want to avoid drilling more holes in the back of the boat, if I can avoid this.

Later,

johnbo