optimum speed for fuel economy m26

[niel passet]

where can i get a taper bore with bobel flow indicator no calibration for finding best speed vs flow alt fuel graph for a yamaha 50 hp high thrust 14x11k 5500rpm

[mastreb]

where can i get a taper bore with bobel flow indicator no calibration for finding best speed vs flow alt fuel graph for a yamaha 50 hp high thrust 14x11k 5500rpm

I don't really understand this post. firstly, your prop seems probably best for a Mac with a 50hp motor, but what a "bobel flow indicator" is baffles me. I'm supposing I just haven't heard of this instrument. I too do not want to calibrated anything, but why would anybody try to "bobel" flow anything when you can get real actual numbers out of your engine? Just put an EMM cable to a chartplotter and you've got real, actually usage numbers that don't require you to "bobel" anything.

I'm not trying to be disrespectful, but eyeballing something is not a way to tune, in my humble opinion.

[Ormonddude]

Google never heard of it either but I am very curious

[K9Kampers]

Try "bubble" flow indicator. Suspect he wants a fuel flow meter.

[Ormonddude]

Actually Google did redirect me to bubble flow meter however that instrument just confirms flow and does not monitor flow amount at all. Unless I am missing something.

[drams_1999]

Since we are on the subject and waiting for further feedback....

I always thought that for displacement hulls, the hull speed would be optimal (provided you have enough power).

I figured that would account for our M's and X's, since we typically have plenty of "excess" engine power. I thought hull speed works best regardless of loading on the boat, ballast, propeller, etc., at any given time.

In my case, around 5 knots. Naturally, other options exist (take less people, less provisions, change prop size, etc) but these choices are done before departing and can't be changed while on the water (unless making people walk the plank is an option ).

Am I right or is there more to it?

I figured if we want to go faster than hull speed, we will consume more and more fuel per mile travelled until travelling at WOT.

Surely we have data available among our vast collective experience and measurements to determine the "sweet spot" of our boats, regardless of loading, ballast, engine horsepower, etc.

Any thoughts? (forgive me if this has been discussed elsehwere but since we were in this thread I figured it would be ok to ask)

[Tomfoolery]

I've been under the impression that something less than hull speed would give the best mileage, as even under hull speed, the faster you go, the lower the fuel mileage. Once it starts to plow, fuel efficiency drops off rapidly, but when fully on plane, it's better than that no-man's land where it's plowing a huge bow wave. I don't think my really gets fully on plane, though. More hp would be better. Of course.

But I could be wrong. I'm really not a power boat kind of guy, so I've never bothered to dig into it deeply.

[Boblee]

drams_1999
Think you hit the nail on the head but with our it's about 1200-1500rpm and as a simple rule of thumb if you are creating a bow wave you are getting too high for maximum efficiency which needs to be measured on engine speed not water speed as wind and tide etc have too much effect.
Too cover maximum distance when replacement fuel is not available we normally plan our trip around wind and tide conditions not speed.

[DaveB]

You are correct, with a 50hp high thrust best rpms are at 2200-2500 rpms useing around .7 gals a hr and running 5.2-5.6 mph in a 1 ft. sea and no current.
All depends on seas and how fast you want to get there.
Lot of X's and M's like the 3000 rpm's before plane but this only gets you 1.25 mph faster and use approx 1.1 gals a hr.
I like the 2500 rpms in reltively calm waters and get 6mph @2500 rpms and use .5 gal. per hr. on my New Merc. Bigfoot. My Honda 50 had to be at 2800 rpms to get same speed and more fuel.
Big Foot does make a big diffrence and also larger prop. and fuel injection.
I don't have a fuel meter but have recorded lots of distance and waves/wind over time and amount of fuel used.
Going to windward in a 3ft chop will cut your fuel by 50% or more even if you do 3000 rpms to do 4-5mph.
I am doing mph and should be doing Knots but many don't know the calculations.
I should also mention I am Heavy weight with refig,3 batteries,4 anchors etc. for cruiseing.
Dave

I've been under the impression that something less than hull speed would give the best mileage, as even under hull speed, the faster you go, the lower the fuel mileage. Once it starts to plow, fuel efficiency drops off rapidly, but when fully on plane, it's better than that no-man's land where it's plowing a huge bow wave. I don't think my really gets fully on plane, though. More hp would be better. Of course.

But I could be wrong. I'm really not a power boat kind of guy, so I've never bothered to dig into it deeply.

[Tomfoolery]

That's consistent with what my BF50 does in the Erie Canal. I do about 5 mph typically for a leisurely booze cruise with friends. I've never measured gas mileage, but it goes for hours and hours (pretty much all day) on a 6 gallon tank at around 2500-3000 rpm (closer to 2500 if memory serves) with the common 3-blade prop. I remember the engine speed sort of because I know my 4-blade howls in that speed range, so I don't use it for that.

Now I'm going to have to track it next time, 'cause you've got me wondering.

I like the 2500 rpms in reltively calm waters and get 6mph @2500 rpms and use .5 gal. per hr. on my New Merc. Bigfoot. My Honda 50 had to be at 2800 rpms to get same speed and more fuel. <snip>

I've been under the impression that something less than hull speed would give the best mileage, as even under hull speed, the faster you go, the lower the fuel mileage. Once it starts to plow, fuel efficiency drops off rapidly, but when fully on plane, it's better than that no-man's land where it's plowing a huge bow wave. I don't think my really gets fully on plane, though. More hp would be better. Of course.

But I could be wrong. I'm really not a power boat kind of guy, so I've never bothered to dig into it deeply.

[BOAT]

Is it okay to run WOT for like 20 miles at a time or would that be bad for the motor? (I was just wondering if I was out in the middle of the San Pedro Channel and loat wind and wanted to get home in a hurry if it would be okay.) I wonder how much gas that would take?

[Ormonddude]

Is it okay to run WOT for like 20 miles at a time or would that be bad for the motor? (I was just wondering if I was out in the middle of the San Pedro Channel and loat wind and wanted to get home in a hurry if it would be okay.) I wonder how much gas that would take?

if the engine is operating with in its RPM range its actually sort of good for it blows out a lot of carbon and at that speed the engine can burn any moisture in the tank without stalling - running at idle speeds for prolonged periods on the other hand can cause problems like fouled plugs and engine deposits.

[yukonbob]

Is it okay to run WOT for like 20 miles at a time or would that be bad for the motor? (I was just wondering if I was out in the middle of the San Pedro Channel and loat wind and wanted to get home in a hurry if it would be okay.) I wonder how much gas that would take?

if the engine is operating with in its RPM range its actually sort of good for it blows out a lot of carbon and at that speed the engine can burn any moisture in the tank without stalling - running at idle speeds for prolonged periods on the other hand can cause problems like fouled plugs and engine deposits.

I also remember reading here that a guy had been doing a lot of putting about at low rpm, and started burning a oil. He told his mechanic everything and was told to go out and open it up wot. No more oil consumption. I think around 2500 is the best fuel economy, but I usually run at 3000 just to get where I'm going. If there are three foot seas, the sails will be up and i think thats the best gas mileage; and much more comfortable for everyone.

[BOAT]

Thanks for the tips - I want to do some night runs to Avalon too so I figured on a lot of WOT on those legs during the times of night that the wind might die.

[seahouse]

The biggest variable in determining the rpm for maximum range in our boats (below our high-drag plane) is the engine itself. A modern 2-cycle engine (= E-tec) will run (and they do run this way – fishermen regularly idle all day trawling without issue) all day long at just above idle and not foul the plugs because oil is not deliberately injected excessively (or not at all) above the piston. There is much more precise control over the specifics of the engine's operation. I believe that such engines achieve best range at, or slightly above, idle speed.

Less oil is required at idle speeds, and many engines cannot adjust oil precisely enough to reduce it to the volume needed to prevent plug fouling at the cooler plug temperatures. A 4-cycle fouling plugs has other problems.

Any engine design has its ideal operating conditions, and therefore it logically follows that it also has a less than ideal operating range. A modern engine computer can measure and adjust a large number of operating parameters (for example fuel mixture, valve timing and duration, ignition timing, fuel injected timing and duration, oil flow to various components, air intake temperature, engine load) to a much finer degree than was ever possible before, so its ideal operating range is considerably widened, right up to, or including, idle speed.

For obvious reasons, older engines were made to operate ideally at higher rpms, but were made to run slower by literally “strangling” the engine at the carburetor by means of a throttle valve. Think if humans worked like that. You would run as fast as possible from place to place and would slow yourself down by strangling yourself around the throat to let less air into your lungs! Not a efficient way of operating. I think this example illustrates why older engines run less efficiently at, or above idle, and must be run at higher rpm for best range (= best mpg).

Another historical example, 4- barrel carburetors had 2 small throats for efficient operation at lower rpms, and 2 larger throats to kick in at higher rpms. They were capable of running more efficiently at lower rpms than a 2-barrel (with 2 intermediate sized barrels), which at lower rpms cannot provide the air velocity needed for efficient mixing and good mpg. New technology at that time, as it continues to be now as well, was focused on widened the range of conditions over which an engine can operate at efficiently.

-Brian.