Sustainable Max RPM?

T

Tortuga

New member
I am delighted to say that my new Yamaha EFI 90 will be rigged this weekend. :D The specs report that the designed RPM range is 5000-6000.

Am I therefore correct to prop the boat for a 5500 WOT target? (probaby will start with a 13.5x15 aluminum)

And, what would be a sustainable max RPM (sustainable in the sense of not damaging the engine)?

I vaguely remember some discussion that 85% of WOT is a safe RPM. In the ocean out here in So Cal we often are limited by chop, but on glassy mornings it's always nice to get across the channel in as short a time as possible. So I guess I'm asking, how fast can I go, and for how long, without frying my new baby?

Matt
 
Tortuga":1m1vjsua said:
And, what would be a sustainable max RPM (sustainable in the sense of not damaging the engine)?
Click to expand...

I have found that if I run my 150s over ~3500 RPM for extended periods the operating temperature rises from midpoint on the scale to 75%. However, I have not been able to find anyone who can tell me if this is hard on the engine or not. Obviously, this is way below 85% of WOT.

Warren
 
Matt,

When we get a day that allows us to open the throttle, I like to run my Honda 90 (carbs) at about 4100-4400 rpm. This gives a speed of about 21-22 mph, and is nice and comfortable. The miles per gallon is probably in the plus/minus 4 mpg range. My guess is that you will find that to be a comfort zone, too.

Steve
 
I often run the Honda 90 EFI around 4500 rpm which gives 19-20 knots of speed. I only have 130 hours on it but so far it has run perfectly.

I have a Yamaha carbeurated 2 stroke on the Whaler and run that at 4200-4500 rpm typically. The engine is 11 years old and still runs well, but I burn 12-16 gallons an hour at those RPM's.

I don't think you will cause any damage by running an engine hard, but with the C-Dory 22 you will have a hard time finding conditions that will allow you to run it at really high RPM's for a long time. As long as you maintain it properly the engine should last for a very long time.
 
Matt

We usually run out of CIH and make the short jaunt over to the Arch and go up the front side of Anacapa, unless we are heading for Santa Cruz.
It gets us across quicker and it is usually calmer.
Not sure how much time you have spent on the water, but once you get out in deeper water (closer to the rigs) you will be out of the ground swell and the water tends to lay down a bit.

I hope to be out this weekend-- need some H2O therapy.

I try to run my Honda 90 between 4500 - 5000 rpm.
 
If the water is smooth enough I usually run at about 5100 rpm (Carbureted 06 Honda 90), our boat’s usually heavy with gear so I’m lucky to make 22 to 24 mph at that RPM.
Even when loaded with full fuel, extra fuel, ¾ water, 4 shrimp pots, extra this and extra that, all the other stuff, etc, etc, I’m able to make 5500 RPM at WAT.
When your motor’s broke-in you should be able to run it all day approaching WAT without harm, not to say anyone would do that.
First time we took out the Triple J WAT got us about 34MPH, now I’m lucky to get 28.
My overall fuel economy is about 3.75 to 4.00 mpg, so can’t complain.
 
Load your boat up with full fuel, water, gear and persons when testing for the proper pitch prop. When you can attain close to the 5800-6000 rpm at wide open throttle, in calm water, with the trim up as much as you can, then you have the correct pitch. I like to size my props to attain the high end of the rpm range because it will compensate for when I have an extra load to carry or if my boat bottom has a lot of growth (this will drop rpm).

For sustained high rpm, you can easily run at 80-85% all day long (approx. 4800-5100 rpm). I would not run at WOT for more than half hour.
 
We run our Honda 130 on the C Dory 25 between 4500 and 5,000 RPM when on a plane. I don't see this as significantly shortening the life span, as long as you are compulsive about maintance. (WOT is about 5800).
 
Matt, I've never heard that an 85% RPM is maximum sustainable RPM on any outboard I've owned. Yamaha specs say 5-6k, then 5-6k is maximum sustainable with the only caveat that the ambient intake water temperature does not increase engine temp above it's temperature rating. Never happen in So Cal seawater. MTBF (Mean time between failures) is based on some pretty stringent environmental testing, including long periods of WOT and, if Yamaha tests engines like Emerson Electric used to test military systems, they get multiple WOT testing with the highest and lowest intake coolant temp specs all the way to failure and MTBF is spec'd out well below that just to "cover their - uh - bases." For the micro critical, run to failure isn't the only factor used to develop MTBF, just the one I use here as an example.

With that said, of course an outboard that is run at lower RPM's will last longer but even if you push the specs every time yer heading for Catalina chances are good you'll upgrade the boat long before the engine will develop problems as long as you do like the Doc says . . . maintain it.

A C-22 is happy with 75 hp, 90 hp, even 100hp. I think Bill and El had 2,000 hours on their 40's when they died. I wouldn't worry a bit. So Cal waters will inherently cut your speed more often than not, but if the opportunity is there, go for it.

Again, my opinion is worth every penny you paid for it. :wink

Don
 
We run our cc23 with an f115 Yamaha about 4200-4500 rpm about 20-23 mph about 4-4.5 gallon an hour . If we open it up 5800 rpm I use about 9 gallons an hour 32-22mph. So at 4200 -4500 this is the sweet spot . Thats our story and we are sticking to it.
 
Thanks to everyone for your insights and experience! My last engine (a '94 Yami 70 2 stroke) gave up the ghost after (actually during) two days of running close to WOT (4500 RPM) between Roche Harbor and Victoria BC... so I'm a little RPM shy at this point... course that was a 14 year old engine that I've been running hard for years and with a rebuilt powerhead would probably run for another 14 years. I know the new technology is far superior.

Matt
 
Ill buy you a 12 pack if you can break that Yammi in normal recreational use at any throttle setting assuming its maintaned according to schedule,propped correctly ,use factory filters and oil, has a working water pump ,and you WARM IT UP before you see how fast you can go.
Marc
 
Go for it !You bought a great motor. Make sure you have the giant blue 10 micron fuel water separator that Yamaha now requires as well .
Marc
 
Try to prop the engine to get close to the 6000 rpm mark. Getting lower in the range can lug the engine a a bit, and if you wind up heavy for some reason you might wind up closer to the low end of the range.

The smaller prop to get to 6000 will also give a better hole shot as it will spin up faster. Of course proping can be a bit science and a bit luck.

If you did wind up at 5500-5600, and happy with how the boat runs, I would not lose sleep over it.
 
I'm no expert but it would seem that the most logical approach would be to load your boat as lightly as you expected to use it and then find a prop that would give you 6000 rpm. Then whenever you load it more heavily your WOT rpm will be lower, keeping you below the maximum allowable (making sure to keep your WOT rpm above 5000 rpm to obviate lugging).
 
I agree. Here are my most recent numbers with the 13.5x15 aluminum prop:

4500 RPM -- 24 mph*
5000 RPM -- 25-26 mph**
5500 RPM -- 26 mph**
5700 RPM -- 29 mph**
5800 RPM -- 30 mph**
WOT -- 5800 RPM

* Surprisingly comfortable;
** In general this was not comfortable, but with the bow down there was little slamming.

Later, when the water flattened out more:

4500 RPM -- 26 mph
4700 RPM -- 27 mph
4900 RPM -- 28 mph
5000 RPM -- 28-30 mph
5100 RPM -- 29-31 mph
5500 RPM -- 31-33 mph
WOT -- 5800 RPM

This seems to me to be a comfortable place. I'll see when I run with a heavier load. I may need to drop down to a 13" pitch for very heavy loads.

Matt
 
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