Some random BSing and status

[rslifkin]

Originally Posted by Chotu

So one of the things I had to do today to do some diagnostics without the software is to take a wide-open throttle temperature reading.

That came out nominal.

not only that, I am currently into about two hours wide-open throttle already today.

well, about half an hour ago I backed it down to maybe 90% throttle. That’s my cruising RPM. The one where I get 3.5 miles per gallon.

estimating that to be about 4800 RPM. And I’m at 6.1 kn.

The engine is running like a champ and not leaking oil today. That’s the difficulty. It’s so intermittent.

I’m also getting pretty decent speed because I got a free bottom cleaning in the fresh water. A lot of the growth of course died in there. And those fish were eating it. But not so much. I only had a few of those fish. They weren’t really attacking it like they did it my old Marina and the freshwater.

Out of curiosity, now that the outboards are doing better in the cavitation department, what do you get for a top speed under power with both outboards running?



And at a steady 6 kts, I'd be curious what your fuel economy is on 1 engine vs 2. With the somewhat small outboard props, I have to wonder if having 2 props pushing (and getting rid of the slight drag from rudder offset when on 1 engine) might out-weigh the efficiency losses from having a second engine running (especially if they're still under enough load to be fairly efficient).

[Chotu]

Originally Posted by rslifkin

Out of curiosity, now that the outboards are doing better in the cavitation department, what do you get for a top speed under power with both outboards running?



And at a steady 6 kts, I'd be curious what your fuel economy is on 1 engine vs 2. With the somewhat small outboard props, I have to wonder if having 2 props pushing (and getting rid of the slight drag from rudder offset when on 1 engine) might out-weigh the efficiency losses from having a second engine running (especially if they're still under enough load to be fairly efficient).

I am also a big fan of optimization. I like the spirit of your post. But I can’t practically test this.

I only have speed over ground. I don’t have speed through the water.

so there is no way for me to isolate that minute of a difference with the speed changes. Any small Current would throw the comparison off.

what I know from many years of Catamaran experience in the past is running one diesel certainly uses less fuel than two of them at the same speed.

I don’t know if that’s the case for an outboard or not. I just carried the same philosophy over.

it would seem to be the same situation. My outboard legs act exactly saildrive units. They are positioned in the exact same spot.

and remember, I run out of RPMs before I run out of power. It is propped lower than it should be. I have the big four blade Hydrus props with 7 inch pitch.

this is in order to be able to punch through bad weather, in order to be able to maneuver with more power at the dock and whatever. in order not to slip and to really grip well at low speeds. So the sacrifice is top end.

[MicHughV]

for my money....I'd consider trading them in for Yamaha's....I've owned several of them from 5 to 150 hp...they all run like swiss watches without a hiccup......

you are likely to keep having issues or problems along the way, if you re already having them now.

further up the east coast, tides and currents can be serious, the last place you'd want engine troubles...

[Chotu]

oh yeah. And I think I’m like eight or nine knots with both Outboard‘s wide-open throttle.

however, that is something like 8 gallons per hour.

These are just numbers off the top of my head. You can easily see online how much the Evinrude E tech 25s at least use at different RPMs.

[rslifkin]

Originally Posted by Chotu

I am also a big fan of optimization. I like the spirit of your post. But I can’t practically test this.

I only have speed over ground. I don’t have speed through the water.

so there is no way for me to isolate that minute of a difference with the speed changes. Any small Current would throw the comparison off.

what I know from many years of Catamaran experience in the past is running one diesel certainly uses less fuel than two of them at the same speed.

I don’t know if that’s the case for an outboard or not. I just carried the same philosophy over.

it would seem to be the same situation. My outboard legs act exactly saildrive units. They are positioned in the exact same spot.

and remember, I run out of RPMs before I run out of power. It is propped lower than it should be. I have the big four blade Hydrus props with 7 inch pitch.

this is in order to be able to punch through bad weather, in order to be able to maneuver with more power at the dock and whatever. in order not to slip and to really grip well at low speeds. So the sacrifice is top end.

Being underpropped might increase the fuel penalty for 2 engines (as you're running more lightly loaded at a given RPM). But just speed over ground should be good enough to tell if firing up the second engine makes things better or worse. The numbers don't need to be exact, just taken under similar enough conditions to see if there's a meaningful difference.

Especially with gas engines, the outright engine efficiency will be worse at a given speed with both running (as the load on each engine gets lighter). But because the outboards have somewhat small props, I have to wonder if the change in prop loading, etc. might gain enough to offset that. I'd expect the saildrives you're comparing to likely have larger props than your outboards. I wonder mostly because while 3.5 mpg at 6 kts is pretty decent, I would have expected better from your boat.


Thinking about the prop situation, are you underpropped when running on 1, or just with both running? If you can get a similar prop with an inch more pitch, you might gain some efficiency. Ideally, you'd be a little underpropped with both engines running (to leave more margin for bad weather, etc.). But also a little overpropped on 1 engine, which would likely leave your best running condition as single engine up to a certain speed, then both engines above that speed. I'd expect fuel economy at lower speeds would increase with a bit more engine load (and you'd get a bit higher top speed under power too).

[Chotu]

Originally Posted by MicHughV

for my money....I'd consider trading them in for Yamaha's....I've owned several of them from 5 to 150 hp...they all run like swiss watches without a hiccup......

you are likely to keep having issues or problems along the way, if you re already having them now.

further up the east coast, tides and currents can be serious, the last place you'd want engine troubles...

Why?

What is the point of doing all that extra work and spending all the extra money?

These motors have about 2300 miles on them right now. they have been sitting a lot.

I really don’t see why I would go through all the hassle of having to haul this boat out or get a crane to move these outboard off the boat. Waste a ton of money buying new ones. Have to re-cut the holes and change all the geometry of the outboard wells. What a disaster!

this is the worst plan you have ever come up with. Lol. I like you. I’m kind of giving you a hard time. But this is a terrible idea.

I don’t need to add weeks of work to my to do list. I think it’s long enough already.

also, I’m going to my home waters. Not to some strange far away land. I’m going to where I learned to sail.

[Chotu]

Originally Posted by rslifkin

Being underpropped might increase the fuel penalty for 2 engines (as you're running more lightly loaded at a given RPM). But just speed over ground should be good enough to tell if firing up the second engine makes things better or worse. The numbers don't need to be exact, just taken under similar enough conditions to see if there's a meaningful difference.

Especially with gas engines, the outright engine efficiency will be worse at a given speed with both running (as the load on each engine gets lighter). But because the outboards have somewhat small props, I have to wonder if the change in prop loading, etc. might gain enough to offset that. I'd expect the saildrives you're comparing to likely have larger props than your outboards. I wonder mostly because while 3.5 mpg at 6 kts is pretty decent, I would have expected better from your boat.


Thinking about the prop situation, are you underpropped when running on 1, or just with both running? If you can get a similar prop with an inch more pitch, you might gain some efficiency. Ideally, you'd be a little underpropped with both engines running (to leave more margin for bad weather, etc.). But also a little overpropped on 1 engine, which would likely leave your best running condition as single engine up to a certain speed, then both engines above that speed. I'd expect fuel economy at lower speeds would increase with a bit more engine load (and you'd get a bit higher top speed under power too).

Interesting set of theories. This will have to get analyzed a different time. What I could do right now though is give you a little data.

I am running at some given RPM that I can’t see. Maybe 4800 or 5000. I’m doing 5.8 kn over the ground. Current or wind or something change things.

I can turn on my other motor and match RPMs and tell you the speed differential. I will do that now.

[Chotu]

1 engine at 4800ish rpms is 5.8 knots uses about 2GPH

2 engines at 4800ish rpms is 7.7 knots using about 4gph

2 engines WOT is 8.2 knots using 8 gph

2 engines at unknown RPM (guessing 3500) is 5.8 knots using about 2.5GPh

Without changing props, it looks like that data definitely supports common knowledge and experience.

I think my current cruising speed is the most efficient way to use the boat without changing any props.

although running both at 5.8 does seem to be pretty close. Given that everything is an estimate who knows?


The only other issue is you have all of the extra wear and tear and hours adding up if you use both engines all the time. However, maybe both engines at a lower rpm is less wear and tear. I have no idea. I feel like splitting these hairs is impossible to reason out.

I think the only way this would be easier to figure out would be if I was putting together a power cat. Then it would be going for a top end fuel efficiency. That would be a little more straightforward.

[Chotu]

And I am under propped on one of them I guess? I only use one at a time. I run out of RPMs before I run out of push power.

[rslifkin]

Originally Posted by Chotu

And I am under propped on one of them I guess? I only use one at a time. I run out of RPMs before I run out of push power.

If you can still hit the rev limiter when running on one engine, then yeah, I'd say you're underpropped on one. If you can get working tachs on them, I'd ideally aim for propping so that you're in the low to middle part of the rated RPM range at full throttle with 1 engine running. You'll probably be able to hit the rev limiter at full throttle with both running. That'll almost certainly gain you some fuel economy for normal motoring on one engine, but you'll still have plenty of reserve power for motoring in rough weather if you fire up the second engine.



I'm guessing your current prop is this guy? https://www.boatpropellerwarehouse.c...peller-5008225

[Chotu]

interesting. I will check this out. The one time I could use this is right now. Lol

Later, I won't be using the engines really. It's a serious sailboat. So engines will be to get in/out of harbors.

Bummer. Would have loved to set this up for this trip.

PS:. Yes…. Rev limiter hit on one

[Chotu]

Cooking right along now that the wind has picked up significantly enough to heel monohulls a bit under bare poles.

God I wish I had a rig!

[Chotu]

Wind still picking up in my favor. Guess I’ll run all day to take advantage of this!

Still just 4800RPM or so. Same output that had me at 5.8 before the wind picked up.

That’s 1 30HP outboard not even at full output on a 50ft boat with growth on the bottom.

This thing is going to do pretty well with the rig I think

[gonesail]

it's been hot and dry in NE Florida for the past few weeks. Wonderful really. Front passed thru today. Once you get north of Vero it gets better

[MicHughV]

Each to his own, Chotu...in my neck of the woods it would be rare to see an Evinrude outboard on any boat....it's 99.9% Yamaha.....probably for the singular reason they are known to be very reliable and many Yamaha dealers up and down the coast.. There are, off course, a few other engines seen on boats....Mercury probably the next on the list...but not many....
Should you eventually make it to the B'mas and beyond, you'll likely find Yamaha to be the top dog there as well.

Which would bring up my next question.....where would you service your Evinrudes in the event you have a serious malfunction or need an engine technician come to the boat??

True, swapping engines this late in the game might cost a few bucks..not sure what you'd get for those engines as a trade in.....but if you're planning to motor 1,000's of miles....reliability would certainly weigh on my mind.

Nonetheless, should you ever consider to re-power for whatever reason, my 2c would be to give Yamaha a looksee.