blocked pitot tube -- cutaway diagram of F40 lower unit??

[TownsendsFJR1300]

If your not worried about it working, I'd flush with fresh water from both ends, (LU off) let dry or blow dry, then as posted, seal each end with 5200, epoxy, etc.

[99yam40]

My thoughts were directly to the LU, (which would have to be removed), NOT going thru any hoses. High pressure anything would likely blow the hose off.

I understand, but still that drilled hole coming down into the LU where it meets the pitot would get filled with grease and be hard to get it back out.
but then being filled up with grease would be better than filled with saltwater

to the OP.
we all have seen a lot of old motors that the pitot were never used or flushed, but never did the lower unit metal get ate up with corrosion. there is a good chance there was something more going on to do something that bad

[boscoe99]

I understand, but still that drilled hole coming down into the LU where it meets the pitot would get filled with grease and be hard to get it back out.
but then being filled up with grease would be better than filled with saltwater

to the OP.
we all have sen a lot of old motors that the pitot were never used or flushed, but never did the lower unit metal get ate up with corrosion. there is a good chance there was something more going on to do something that bad

I must say that this is the first time I have ever heard of it happening. But I don't doubt for a minute that it did in fact happen. I believe that it happened. I just don't think that it happens very often.

I oft wonder how aluminium can last as long as it does in salt water.

[99yam40]

Yamaha paint jobs do well until they do not.

could it be that not making sure the paint stays in place be the problem?

[Mike Topaz]

The way the alloy split then calved off on my old Yammie suggested to me that the corrosion was inside a void or gallery in the lower leg and was causing expansion, then cracking, then more corrosion. It was ugly, but not as horrifying as sucking out a mouthful of "West Texas crude" after inserting the drill bit progressively and then sucking out the debris (by mouth) from the pitot tube each stroke!

So maybe there was something else going on down there as boscoe99 says?

I should have cut the old leg open with a grinder to do a post-mortem before taking it to metal recycling.

I have to say that, other than that issue, I have never had a problem with Yammies. The fact I purchased another is proof of my trust in them, but given the low price of modern GPS combos, their popularity, and the accurate speed over ground they give, I cannot see the need for a pitot tube nowadays on tiller steer models.

If you are running into a current, the pitot-tube speed will be an overestimate of speed over ground. This would lead to errors in planning trip duration and trip fuel consumption if those plans were based only on pitot-tube speed. GPS-sonar combos give you speed over ground, course over ground, distance travelled, and time/distance to destination without any link to the motor.

[99yam40]

the flaw in you thoughts is the motor is pushing thru that current that is flowing against it, so the fuel used would be more than that using the GPS distance and the speed thru the water would be more than the GPS speed.
I think that was said correctly

[boscoe99]

There is speed through the water and there is speed through space (over ground). Completely different. Just depends upon what people want.

The highest tech most advanced airplane in the world, with maybe three GPS and other navigation systems installed, is always gonna use a pitot tube derived speed for landing and take off.

[boscoe99]

If you are running into a current, the pitot-tube speed will be an overestimate of speed over ground. This would lead to errors in planning trip duration and trip fuel consumption if those plans were based only on pitot-tube speed. GPS-sonar combos give you speed over ground, course over ground, distance travelled, and time/distance to destination without any link to the motor.

Depends upon the direction of the current and the heading of the boat. A boat heading down a 30 mile per hour fast flowing river at a boat speed of 30 MPH will indicate via pitot tube a speed of 30 MPH. When in fact it is moving over the ground at 60 MPH. As the GPS will indicate. The pitot tube is underestimating ground speed. But a pitot tube speedometer is not for ground speed in the first place.

[TownsendsFJR1300]

I bought a used marine Hummingbird GPS "just removed from a boat" excellent condition a couple years ago from E-Bay.

While changing the settings to match my exact, older unit(screen failing), I found the TOP RECORDED speed well over 175MPH!!!

Most of the "tracks" (not erased) was between Miami and the south Keys.

I suspect it came off a sea plane....