-
This site contains eBay affiliate links for which Sea-Doo Forum may be compensated.
Safe rpm the boat
- Thread starter Polcat
- Start date
- Status
Sportster-2001-951C-Stock
Well-Known Member
Full throttle specification is 5500~6000, so you're at the upper limit. 52 is pretty fast. sounds like it's running fine.
Lumps
Active Member
I am interested in this as well. I once asked my friend why boat engines don't last as long as car engines. He said because boat 'only run at full out'. I know what he meant but when does the stress on an engine start? How many hours can one go at 6000 rpm? 5000? 4000? I would like to see a chart of expected life per rpm range so I can better judge how mean I am being.
With the kids in the boat I go as fast as can stay on plain. I don't really go full out. But when I do I would like to know the consequences
With the kids in the boat I go as fast as can stay on plain. I don't really go full out. But when I do I would like to know the consequences
Sportster-2001-951C-Stock
Well-Known Member
Yep, I agree to go just fast enough to remain on plane, my boat planes at 20MPH and I run about 30MPH b/c that's where the RAVE exhaust valves open up, about 5200RPM keeps them open.
Think about how much heat is made in a boat engine, burning 10PGH or more instead of just 2GPH like in a car, you can see in the boat the 100% duty cycle and no coasting creates a lot more heat and fuel consumed so boat engines have to be tougher than car engines, that's why you see mostly good quality parts and techniques used.
Still, there are some outboards like Johnsons more than 20 years old, they can last 2 generations seems like. I've seen Yamaha 4-stroke outboards with a couple thousand hours on them still running great, and mercruisers with over 3,000 hours. I'd bet you the owners don't run them wide open for long periods.
But it's important any engine isn't overloaded with too much prop for instance, this will make them last much longer if the spec of WOT is correct. An outboard engine for instance can last only a few hundred hours if the prop has too much pitch, it's important to test WOT on these ans we fill out this WOT RPM and lots of other info on the warranty registration forms to certify we checked everything.
I also will say most boat engines don't die due to they're worn out, most of the time they're broken due to some kind of abuse.
Think about how much heat is made in a boat engine, burning 10PGH or more instead of just 2GPH like in a car, you can see in the boat the 100% duty cycle and no coasting creates a lot more heat and fuel consumed so boat engines have to be tougher than car engines, that's why you see mostly good quality parts and techniques used.
Still, there are some outboards like Johnsons more than 20 years old, they can last 2 generations seems like. I've seen Yamaha 4-stroke outboards with a couple thousand hours on them still running great, and mercruisers with over 3,000 hours. I'd bet you the owners don't run them wide open for long periods.
But it's important any engine isn't overloaded with too much prop for instance, this will make them last much longer if the spec of WOT is correct. An outboard engine for instance can last only a few hundred hours if the prop has too much pitch, it's important to test WOT on these ans we fill out this WOT RPM and lots of other info on the warranty registration forms to certify we checked everything.
I also will say most boat engines don't die due to they're worn out, most of the time they're broken due to some kind of abuse.
Lumps
Active Member
I just read an interesting post on a "whaler" forum on this topic. If I were to sum up the parts that weren't flames... yes running at WOT reduces the life span of your boat at a greater rate then at lower speeds, the average boater doesn't use their boat enough to reduce the life of their boat's engine to the point that it makes a difference. I would say read the post but only the first half has posts that are reasonable.
if you buy in to the logic from the other forum, if you are using your boat every day all summer and you are at WOT I am sure it will eventually make a difference. for me, I really only get 10 days out a year.
I hardly ever get the chance to go full out so maybe the debate is moot. I guess I am just curious. also I am worried maybe the engine is on its last legs and maybe I'll push it over the edge.
if you buy in to the logic from the other forum, if you are using your boat every day all summer and you are at WOT I am sure it will eventually make a difference. for me, I really only get 10 days out a year.
I hardly ever get the chance to go full out so maybe the debate is moot. I guess I am just curious. also I am worried maybe the engine is on its last legs and maybe I'll push it over the edge.
Sportster-2001-951C-Stock
Well-Known Member
It's hard to know what they're saying, do they expect 3,000 hours running full WOT or are they happy with 500hrs?
Sportster-2001-951C-Stock
Well-Known Member
8700 hours, probably not while going 120MPH? - "Yamaha Marine Group announced today that the Charleston Water Taxi has re-powered for the second time in two years with a pair of Yamaha F150 outboards. This time, the outboards they are replacing are still running strong after 8,700 hours of use each."
Lumps
Active Member
I think that is what they are saying. I see boats on kijiji all the time that are 6 years old with 150 hours. If you can get 1500 hours at a conservative usage then 500 hours at wot would still be18 plus years.
I still don't know if these numbers are realistic. I suspect people really don't know the actual effects. Especially since real world usage is never at wot 100% of the time. The most you could do is wot when conditions allow.
Lumps
Active Member
Some of the other posts I read talked about this too. It's amazing the usage you can get if the engine is always warmed up and you go nice and slow.
One of the other points discussed is proper maintenance for longevity
Dr Honda
Well-Known Member
Physical time is harder on an engine that "Running Hours". That's why I say that a low hour boat, that is 10 years old, almost doesn't matter.
When you have a lot of running hours in a year... that means that engine has been running in it's proper temp range, and is always covered in oil, and is having any moisture boiled out. SO... it's well protected. But when you get that boat that isn't pushed much, and sits around... well... then you get an engine where the seals dry out, and the internals start to rust.
As far as RPM's... on the 240... 6000 RPM's is fine. It has a rev limiter that will cut you off at 6200.
When you have a lot of running hours in a year... that means that engine has been running in it's proper temp range, and is always covered in oil, and is having any moisture boiled out. SO... it's well protected. But when you get that boat that isn't pushed much, and sits around... well... then you get an engine where the seals dry out, and the internals start to rust.
As far as RPM's... on the 240... 6000 RPM's is fine. It has a rev limiter that will cut you off at 6200.
Sportster-2001-951C-Stock
Well-Known Member
Those outboards were being run 10 hours daily, probably by now a third set has been rigged. There are plenty of them out there, the BRP 2-stroke outboards obtain high hours too.
Don't get me wrong, short WOT blasts are necessary to confirm the engine is running correctly and often to lift a skier out of the water (low power boats like my Sportster).
Lumps
Active Member
The guy I bought my boat from said he didn't like skiing behind it because he felt like it was ripping his arms out of the sockets when it pulled him out of the water
Sportster-2001-951C-Stock
Well-Known Member
That's what you want, the boat should be strong enough to do that. Then it's up to the driver to moderate the power and of course not go too fast. If the water is reasonably smooth about 25MPH is a good speed for me on a single ski, the smoother water the faster I can ski but it can hurt when you fall going too fast. Never would I ski at top speed. Barefoot skiers need a high speed, wow I can't imagine.
I would say based on your description your boat is more powerful than mine, these two are completely different boats and those M2's run pretty strong.
My Sportster is difficult to get up behind b/c it's not powerful enough to pull me up on a single ski with authority, this makes for a slow start and a little too much dragging the skier, the boat should be strong enough to "do all the work".
It's especially important for learning how to ski, I don't think my boat could pull someone who's learning on a single ski b/c they have to hang on longer than they should have to before speed increases. It is strong enough to pop a skier right up on doubles.
I insist on having a 100ft rope, anything shorter and you spray the skier with the jet blast.
Last edited by a moderator:
Lumps
Active Member
I had a really hard time with my challenger (dual 717 engines). If you tried to pull too hard the pumps would cavitate and you would totally lose power. my wife was really good at applying the power just right. I am hoping the new boat is better. we haven't had a chance to go skiing yet. living in Atlantic Canada its too windy too often to go skiing much.
Sportster-2001-951C-Stock
Well-Known Member
Yep, that's about the same as mine. It's still okay just not great, I didn't expect it would be super strong anyway and I can get up so I'm pretty happy. 
Dr Honda
Well-Known Member
If you put zip-ties on the seal boots, and change over to Skat-Trak "Swirl" impellers... you can mash the throttle as hard as you want without cavitation.
Sportster-2001-951C-Stock
Well-Known Member
Is this the case with a slalom or wake board skier behind the boat? There's a difference.
Dr Honda
Well-Known Member
Not really..... It's still a lead behind the boat.
Anyway... in the Rotax boats... as you clean up the pump, and use a good impeller... you make enough suction that you will pull air past the carbon seal. (suck the boot back) If you have a good (new OEM) boot then it's not normally a problem. But if you have an older boot, and the rubber has shrunk, and is getting a little stiff... then you loose pressure on the seal. Putting a couple zip-ties in the valley of the boot helps keep it in place... but doesn't totally restrict the flex.
Works great. Give it a try.
But, since this is the Mercury section... we should keep it on track wit those drive systems.
Anyway... in the Rotax boats... as you clean up the pump, and use a good impeller... you make enough suction that you will pull air past the carbon seal. (suck the boot back) If you have a good (new OEM) boot then it's not normally a problem. But if you have an older boot, and the rubber has shrunk, and is getting a little stiff... then you loose pressure on the seal. Putting a couple zip-ties in the valley of the boot helps keep it in place... but doesn't totally restrict the flex.
Works great. Give it a try.
But, since this is the Mercury section... we should keep it on track wit those drive systems.
- Status
