CONTINUOUSWAVE

A water hose from the gear case of a [1989 Yamaha two-stroke-power-cycle outboard engine of unknown horsepower] and runs into the rigging tunnel, bundled with the steering cables and engine cables. I do know where it goes.

The hose appears to have been chewed by a varmint.

Water streams out of this hose.

Q1: where did this water hose used to connect?

Q2: is the hose for cooling engine fuel?

This is the hose from the [Pitot speedometer pickup] in the outboard engine lower unit that runs to the speedometer gauge at the helm.

This type of speed measurement is not very accurate and has been supplanted by GPS instruments and mobile apps.

While you can reconnect or add additional hose (1/8" diameter tubing) to reach the back of the gauge, you can also just plug the hose and leave in place.

I don't think the speedometer ever worked. I just want to make sure that water line wasn't providing cooling for fuel or anything else.

You should not see much water flow from the hose until the boat begins to make forward way, unless there is a siphon effect taking place. Increase in water flow with boat forward way is a sure sign the hose is from a Pitot tube pickup on the engine gear case below the waterline. Often the hose is a plastic material. With age the plastic loses its resiliency, and it falls off the back of the speedometer gauge. Or someone puts a bit of tension on the hose while manipulating some boat rigging, and pulls off the hose from the gauge.

Pitot tube speedometers can be very accurate for measuring speed through the water, but ones that are very accurate usually have a large diameter dial face, a long arc of pointer movement, very fine scale graduations, and are expensive.

The dial graduations will give you an idea of the accuracy. If the dial can be read to less than 1-MPH, the speedometer is probably very accurate. If the dial is small diameter, the pointer arc limited, the graduations coarse and can be read only to about 5-MPH, the Speedometer won't be very accurate.

The measurement of speed by a GNSS receiver only speed over ground, not speed through the water. The accuracy of GNSS speed measurement depends on the particular receiver, the satellite constellation, the boat maintaining a straight line course, the course line direction relative to the satellite geometry, the number of satellites in the position fix, and the use of any augmentation systems to enhance precision of position fix. More precise speed can be measured by specialized GNSS receivers, but the typical receiver included in an inexpensive chart plotter won't be reliably accurate to more than about ±1-MPH, and in best conditions perhaps ±0.5-MPH.

JBell4 wrote:Q2: is the hose for cooling engine fuel?

Generally any engine with a carburetor would never have a fuel cooler. Fuel coolers are only typical in fuel induction systems where the gasoline fuel is pressurized and circulated among multiple fuel injectors. The fuel tends to become warmed by the injectors, which produce a lot of heat in their electrical operation. A fuel cooler for an outboard engine would never be located outside of the engine cowling. And water would never intentionally be introduced to the inside of large volume main fuel tank to reduce fuel temperature. When fuel cooling is necessary, it is only necessary for the small volume of fuel that circulates in the fuel induction system and is getting warmer than ambient temperature by the engine heat picked while circulating.

JBell4 wrote:I just want to make sure that water line wasn't providing cooling for fuel or anything else.

What other possible element of an outboard small boat would require cooling water provided from the engine? Did you have something in mind?

Do you have a water pressure gauge on your console? That hose [could] connect to a water pressure gauge.

There would only be “flowing” water if the hose were no longer connected. The force of the water inside the tube is driving the gauge.

The water in the hose is not cooling anything.