re F2xx "dry exhaust" corrosion

[fairdeal]

so it is frequently mentioned,
usually in the context that "flushing" is irrelevant to the issue,

that the corrosion occurs in the "dry side" of the exhaust.

Certainly, while the engine is running,
there is no cooling water discharged onto those surfaces -
and there is presumably "exhaust pressure" present.

However - when the engine is not running,

am I wrong in thinking that "the sea" will "seek its own level" within that area?

On my F225, moored in calm water, the "water line" is just below the top bolt of the tilt/trim unit:



about the level of the bottom of the oil pan:



Now granted, there is "trapped air" present which would resist compression

But - say, at anchor, engine off, boat rising/falling in a strong swell -

is not seawater going to be forced well up into that "dry" area?

[boscoe99]

Certainly water will seek its own level. Exactly as you have described when your boat is at rest.

Take take the case of a boat that is trailered and is being launched from a steep ramp. I have seen instances where the water level came up over the back of the transom when trying to get the boat to float off the trailer. For maybe just a moment or so the water level rose quite high within the exhaust system of the motor. Salt water. Now the aluminum exhaust system has been covered by salt water with no good way to rinse those aluminum parts. Along comes some corrosive exhaust gasses and the situation is made worse.

Yamaha cautions about engine mounting heights for four strokes because of possible engine damage. Not due to a boat being launched but merely while at rest.

And now that I think about it, it seems that the majority of motors are mounted on the low side. Lower than they would be for optimum performance. Seems that by raising them a hole or two Yamaha would be killing two birds with the same stone.

[boscoe99]

[pstephens46]

I have seen several new boats lately where the motor couldn't be tilted up completely without hitting baitwell, etc. Foot still in the water...

[fairdeal]

Fascinating!

I don't know exactly what dimension "H" is for the F225TXRD -

but if I followed that drawing - to raise the lower motor mount out of the water

that's another 7-8 inches higher.

half my prop would be above the keel -

I would expect some cavitation / ventilation issues?

Here's how it runs now:

[pstephens46]

The boat is resting on foam blocks? Is that one of the transducers that sprays water and had to be modified?

[boscoe99]

Fascinating!

I don't know exactly what dimension "H" is for the F225TXRD -

but if I followed that drawing - to raise the lower motor mount out of the water

that's another 7-8 inches higher.

half my prop would be above the keel -

I would expect some cavitation / ventilation issues?

Here's how it runs now:

It is 100 mm. 3.9 inches for those that have not yet joined us in the 21st Century.

[fairdeal]

The boat is resting on foam blocks? Is that one of the transducers that sprays water and had to be modified?

yes, styrofoam - I never saw it done before I moved to the Keys - but quite common here.

At the stern that was a 2'x2'x4' block
I cut it with a hot wire to make two halves matching the deadrise.

The transducer is a Garmin GT50 thru-hull - "Typically" installed in pairs, one on either side

I wanted to safe effort & money by putting just one flat on the keel

but I was worried that - with my single engine - it might disrupt the prop

So I made & installed a wooden mock-up to test it first.

There is no noticeable negative effect - and the sonar performance is perfect.

From what I've read, it's the transom mounts that cause problems with "roostertails"

[pstephens46]

H is what? 100mm? Or 100mm between mounting holes in bracket?

[pstephens46]

I thought I was looking at a transom mounted black something, in line with the bracket anode. I assume you don't have the sandbars we do around here. I would eventually break mine if mounted there. Inshore fishing.....

Nice work!

All of those boat supports make me nervous, wood blocks or whatever...

[fairdeal]

It is 100 mm. 3.9 inches for those that have not yet joined us in the 21st Century.

I'm confused.
The distance from "the clamp bracket seating point" to the water surface?

[boscoe99]

I'm confused.
The distance from "the clamp bracket seating point" to the water surface?

Yes.

[Colpatten]

I have a 2014 Yamaha F150 with 360hrs on the clock. With exhaust corrosion out through the exhaust guide plate and nearly through to the water jacket on the block side. I will repair the motor but would like to stop this problem recurring.
The motor is a 20” shaft and is set to 120mm height. It is always used in salt water. I use Caltex 91 fuel.
I see that 2000-2004 motors had this corrosion problem. Can any one tell me what Yamaha did at that time to address this problem?
Is the recommended height too low?

[boscoe99]

There is little to no correlation of the early V6 3.3 liter F200/225/250s to the inline F150. Completely different design
.

For the V6 models different alloys and surface finishes were used.

[boscoe99]

A motor can be mounted at or above the optimum height. However, with a steep ramp water can go well up into the exhaust section while the boat is being launched from or retrieved onto the trailer.