Is Full Throttle BAD For Outboards?

[dlandersson]

Is Full Throttle BAD For Outboards?

[ris]

I never run anything wide open except for a few minutes. Our Honda 60 on the Mac tracks our time spent around 2500 rpm, 4000 rpm and wide open. In 2000 hrs + of operating time, 95% was spent at 2500 or less.

[NiceAft]

Full throttle at short spurts is fine. When I was having 40 & 50 miles between marinas, I kept the speed to 7 ~ 7.5 knots. If I got bored, I would run crease to 8.7 knots for awhile, then back to 7.5.

P.S. Sunshinecoasting’s post reminded me to post I have a four stroke.

[sunshinecoasting]

Four stroke.....probably shouldn't
Two stroke?........YESSSSSSssssssssss go for it.

[dustoff]

I've spoken with outboard engine mechanics and one person who formerly worked at BRP. What I've been told is similar to the first video, outboards are purposefully engineered to run at max power for long periods of time, unlike car engines. However, with modern 4-stroke outboards that doesn't mean you can't run them at less than max power for long periods also without any problem. It also doesn't mean that overall engine life won't be impacted by running at max power most of the time.
Another thing is that, compared to car engines, the number of hours a typical outboard actually runs over its age is a small fraction of what most car engines endure. Most people are putting 10-20 hours of wear on their cars every week (500 to 1000 hours a year). For a small(ish) recreational sailboat outboard that has a user that's still working a land-based job, its maybe 50-150 hours a year. With that kind of hour usage, even running at WOT most of the time, the engine should last for 10-15 years without a major overhaul.
That's why the newer outboards are perfect for most recreational boating uses, whereas long-distance cruising sailboats and power boats still opt for inboard diesels. Those have much much longer hour lifespans, at a cost of weight and interior space.

[OverEasy]

Hi All!

WOT or NotWOT. That is the question….

Think of the engine like a bucket, engine speed like holes in the bucket and the fluid level like the useful horsepower life of the engine.
The more holes (engine speed and hence horsepower) you make the faster the fluid leaks out and the shorter the useful life time span.
If you never use the engine there would be no holes so there is no impact to useful life.
Make a sieve out of the bucket (lots of holes) and while one gets lots of power one doesn’t get much useful life time.

That’s sort of the general philosophy of engines and systems….
The more time at max horsepower one demands out of an engine it’s gonna wear out sooner.
There is a caveat though in that if you only dribble out the fluid from tiny hole(s) it’s apt to get clogged.
That’s why most newer engines have over speed limiters and the manufacturer generally recommends running about 60-to-80% of rated horsepower. That will give the engine enough power to be useful for purpose and clean off the internal cylinder surface deposits.
Idling all the time is not recommended as that will lead to carbon build up and incomplete combustion (which is also why the manufacturers recommend shorter oil change intervals for engines that operate at lower RPMs.

It’s why one sees a smaller auxiliary’trolling’ motor on many of the fishing boats.
It saves having the big engine from running at idle while the littler auxiliary trolling motor can run at a reasonable speed…
At least that’s the thought behind it… there are many people don’t think like that though and are only looking at initial costs or looks.
Sizing an engine to fit the purpose is key to getting what you need for a more optimal solution.

It’s why traditional cruiser sail boats have smaller inboard engines. As sailboats they aren’t particularly interested in speed perse… they generally feel that 6 knots is a good average speed based upon its optimal hull speed… so why have an engine that tries to push the boat faster than hull speed? These folk see excess power as a waste of space and range… a smaller engine that gets the sailboat close to hull speed will actually move the vessel further for the same amount of stored fuel than a larger engine that plows through the water.

A MacGregor is a hybrid hull to let us take advantage of the options… sail or power.


The newer four stroke engines with computers have various ‘tricks’ to expand the lower rpm operational range that older engines can’t do.
A hotter spark at lower RPMs helps get better combustion and less carbon build up.
Variable carburetor mixtures is another.
Combining the two is another.
So the traditional paradigm is changed to some extent.

Best Regards,
Over Easy

[Starscream]

I wouldn't have bought a Mac if I was going to worry about this. Life's too short to not wot when you want to.

[OverEasy]

I wouldn't have bought a Mac if I was going to worry about this. Life's too short to not wot when you want to.

That Too!!

[dlandersson]

Note that it's an X. Just sayn'

I wouldn't have bought a Mac if I was going to worry about this. Life's too short to not wot when you want to.

[Be Free]

Also note that it is clearly running ahead of its bow wave. There is no doubt that it is planing. The large amount of spray is due to the hull shape on the forward portion of the boat.

I can get up on the bow wave but can't quite get fully in front of it with my 40hp. I still like the way it looks (and the looks it gets) when I'm running at WOT (but usually not more than a couple of miles at a time).

[Starscream]

This was with full ballast at about 24mph. I agree that we must be on a plane of sorts, mostly, but in this configuration it still feels like its smashing the bow wave instead of riding over it. Something interesting happens without ballast at somewhere around 25 or 26mph: after a short time at that speed, the nose will drop noticeably and the boat will quickly accelerate up to 29 or even 30mph. At that point it feels like a real plane, with less splashing and smashing.

I don't have a video at unballasted wot yet, but I'll fix that this season.

[Be Free]

This was with full ballast at about 24mph. I agree that we must be on a plane of sorts, mostly, but in this configuration it still feels like its smashing the bow wave instead of riding over it. Something interesting happens without ballast at somewhere around 25 or 26mph: after a short time at that speed, the nose will drop noticeably and the boat will quickly accelerate up to 29 or even 30mph. At that point it feels like a real plane, with less splashing and smashing.

I don't have a video at unballasted wot yet, but I'll fix that this season.

That's an impressive speed with full ballast! It also explains why you are still throwing up so much water along the sides. You are still sitting relatively low in the water (for a boat that is beginning to plane).

The first requirement for "planing" is to get the boat in front of the bow wave. You have achieved that in the picture. The second is transition from plowing through the water to skimming the surface. That is what you are describing without ballast. The boat speed will increase noticeably and you will even be able to throttle back a bit and still keep the boat on a plane.

[TrailerTrash]

All internal combustion engines are designed around an optimal RPM range. The physical dimensions of the rod/piston/crank/camshaft, bearing design, moving mass etc..etc.. all play a role in what RPM range the engine is optimized around. Engineers must also consider transmission/gearing needs and the speed/mass of the vehicle they power. There is some correlation between operational RPM and lifespan, but that is just one of the variables in engineering.

For a boat, you also have to size the prop correctly, as it is like the final drive ratio for the boat. Outboards have been engineered to operate within an RPM range, and as long as you keep them within that window, it likely isn't going to be the deciding factor in the longevity of the engine.