Safe to go WOT?

[jitts3]

When an engine is over-reved, the camshafts are spinning fast enough that the valves overcome the pull of the valve springs and "float" off the camshaft (or rocker or whaever). In a non-interference engine it isn't necessarily a catastrophe. In an interference engine (meaning the pistons occupy the same space at the top of the bore as the valves do when they are open), it is bad news bears as it can lead to bending a valve/snapping the head off, and the ensuing carnage.

Basicly the cam asks the valve to open before the valve spring can close it. Another way of saying that.

Do they make interfienance marine engines even with the high proablibility of overreving? My little 200 had and will continue to be a non interfierance engine. But it is a 1978 Model

 

[Gunn]

I must definetly have something wrong! My boat won't plane loaded without full tabs, everyone elses will....my boat tops out about 42, and that's with a bottom with no bottom paint and looks like new, and everyone has more topend:huh: You have me curious now:smt101:smt021

Edit: I should add that she runs perfectly when she runs!

I get to 40knots on the GPS when at full throttle...that's about 46mph. No bottom paint here either. Have never used tabs to plane, but the last time I had a pretty full load with guests, it was the first time I experienced any difficulty. Next time I'll remember to set the tabs first and give it a shot...

 

[Dick Whetstone]

I must definetly have something wrong! My boat won't plane loaded without full tabs, everyone elses will....my boat tops out about 42, and that's with a bottom with no bottom paint and looks like new, and everyone has more topend:huh: You have me curious now:smt101:smt021

Edit: I should add that she runs perfectly when she runs!

I have a 2001 270DA which is basically the same boat as yours. I have a single 7.4 with Bravo III and factory 22P props. My boat will plane easily with a full load of passengers (8 people), 28 gallons of water, 100 gallons of fuel, and provisions, with no help from the trim tabs. Under the same conditions cruising speed is 30MPH at 3500RPM and top speed is around 40+ at 4400RPM.

 

[floriduramax1]

I have a 2001 270DA which is basically the same boat as yours. I have a single 7.4 with Bravo III and factory 22P props. My boat will plane easily with a full load of passengers (8 people), 28 gallons of water, 100 gallons of fuel, and provisions, with no help from the trim tabs. Under the same conditions cruising speed is 30MPH at 3500RPM and top speed is around 40+ at 4400RPM.

Longer, wider and twin engine. Do you have a/c and gen? I bet we are at least 2k lbs apart. Hardly a good comparison. My buddy has a 270 and side by side the difference is quite noticeable regardless of online specs.

 

[SCORPIO]

I use tabs to get on plane and then retract them almost all the way and trim my drives. I find bringing up the tabs will increase my speed by about two miles per hour with the same throttle settings. My boat takes a while to plane with a full fuel load, full water and six or more adults plus gear and provisions. I don't firewall the throttles at all, I just advance them to about 3200 and drop the tabs and wait a few seconds and she will pop up and then I can adjust the trim.

 

[rcmafgny]

i was told by the mechanic at my marina that running WOT is good in small doses, especially after being off for a while, It helps the engine survive the crappy ethanol we have to use

 

[tdappleman]

I run mine at WOT in short doses to make sure they both run up to the same RPM and oil/temp stays steady. Full load on mine with drives and tabs trimmed up is 44mph on a calm day. It's fun to watch boats who think you are a slow cruiser just get smaller in your wake... When I repowered I expected a bit more out of the top end but ended up with better low end and can cruise at 28-30mph at about 300-400 less RPM than before so not too bad.

 

[bajturner]

My boat won't plane loaded without full tabs....my boat tops out about 42

Maybe an obvious question, but are your drives trimmed fully down? Even trimmed up to 1 or 2 can make it hard or impossible to get onto plane.

Fully loaded last weekend (6 big guys, one small gal, a lot of gear and "liquids"...and a canoe in the cockpit (long story)) and I was able to get onto plane with no issues at all with no tabs. With tabs, about the same amount of time but less drama and less throttle.

Weekend before, forgot the engines were trimmed up a bit (2), two couples in the cockpit and two little kids (110lbs combined) in the cabin and the boat took about 20s to come onto plane (no tabs) at full throttle. I was about to stop to see what was wrong when it finally jumped up, then I realized the trim position.

You need to qualify the speed measurements as well. I consistently hit about 41-42mph with a family full of stuff on board. Trim up ~2 and I get another 1mph. Tab port or starboard for levelling off and I lose ~1-2mph. These are GPS readings while at the same time the speedo says I am going somewhere over 45mph.

 

[floriduramax1]

Maybe an obvious question, but are your drives trimmed fully down? Even trimmed up to 1 or 2 can make it hard or impossible to get onto plane.

Fully loaded last weekend (6 big guys, one small gal, a lot of gear and "liquids"...and a canoe in the cockpit (long story)) and I was able to get onto plane with no issues at all with no tabs. With tabs, about the same amount of time but less drama and less throttle.

Weekend before, forgot the engines were trimmed up a bit (2), two couples in the cockpit and two little kids (110lbs combined) in the cabin and the boat took about 20s to come onto plane (no tabs) at full throttle. I was about to stop to see what was wrong when it finally jumped up, then I realized the trim position.

You need to qualify the speed measurements as well. I consistently hit about 41-42mph with a family full of stuff on board. Trim up ~2 and I get another 1mph. Tab port or starboard for levelling off and I lose ~1-2mph. These are GPS readings while at the same time the speedo says I am going somewhere over 45mph.

Yes, drives full down. Your speeds are consistent with mine.

 

[Bob & Sue]

When an engine is over-reved, the camshafts are spinning fast enough that the valves overcome the pull of the valve springs and "float" off the camshaft (or rocker or whaever). In a non-interference engine it isn't necessarily a catastrophe. In an interference engine (meaning the pistons occupy the same space at the top of the bore as the valves do when they are open), it is bad news bears as it can lead to bending a valve/snapping the head off, and the ensuing carnage.

With Mercruiser 5.0, 5.7 engines at least from 98 on they run a roller camshaft with retaining plate and large valve springs to eliminate any valve float with a rev limiter set a couple hundred rpm over wot specs. This kind of a setup can easily run 8000 rpm at short burst with no floating of valves the rev limiter is never going to let you get that high.

 

[LetsRock]

On a somewhat related topic, at times I tend to have a bit of weight (although not over the posted capacity) on the boat between people, fuel, water, coolers...etc and my boat sometimes struggles to get on plane right away. I can tell in the first 3 seconds if she is going to stuggle or get right up. My question is how long is it ok to let her "struggle" while at WOT? I tend to leave it at WOT until I feel her starting to get up but sometimes it takes a little while. Am I doing any damage or is it ok for a reasonable amount of time until she gets going?

BTW - I have a Mercruiser 5.7, 265HP I/O

 

[terminaldegree]

I tend to run the boat at WOT once or twice a season... Always at least once at the beginning of the year to be sure the engine makes the spec'd rpm and runs smoothly. I watch the water temp, tach, and speedometer gauges pretty closely when I do. Otherwise, I may goose it if I'm trying to outrun a rainstorm and get back to the dock if I'm nearby.

When I ran smaller boats, I ran WOT much more frequently for short bursts (maybe a minute), as it cost less to do so. In addition to the good advice already given, with outdrives I would be careful to tweak the drive trim before getting to 100% throttle to avoid ventilation and bumping the rev limiter. Also, I don't run outdrives at WOT if there's a chance of "catching air" for safety reasons, and to preserve the gears in the drive...

 

[blaster]

On the days you struggle to plane out have you run to max speed to see your max rpm's? I know you don't take your friends out and just run full blast all the time but the numbers will tell you how much your lugging the engine. If it's safe to do so try and see if you are in the wot powerband for your engine. If not then you may be causing damage to the engine.

On a somewhat related topic, at times I tend to have a bit of weight (although not over the posted capacity) on the boat between people, fuel, water, coolers...etc and my boat sometimes struggles to get on plane right away. I can tell in the first 3 seconds if she is going to stuggle or get right up. My question is how long is it ok to let her "struggle" while at WOT? I tend to leave it at WOT until I feel her starting to get up but sometimes it takes a little while. Am I doing any damage or is it ok for a reasonable amount of time until she gets going?

BTW - I have a Mercruiser 5.7, 265HP I/O

 

[blaster]

How many gallons per mile do you get running wide open?

I tend to run the boat at WOT once or twice a season... Always at least once at the beginning of the year to be sure the engine makes the spec'd rpm and runs smoothly. I watch the water temp, tach, and speedometer gauges pretty closely when I do. Otherwise, I may goose it if I'm trying to outrun a rainstorm and get back to the dock if I'm nearby.

When I ran smaller boats, I ran WOT much more frequently for short bursts (maybe a minute), as it cost less to do so. In addition to the good advice already given, with outdrives I would be careful to tweak the drive trim before getting to 100% throttle to avoid ventilation and bumping the rev limiter. Also, I don't run outdrives at WOT if there's a chance of "catching air" for safety reasons, and to preserve the gears in the drive...

 

[LetsRock]

On the days you struggle to plane out have you run to max speed to see your max rpm's? I know you don't take your friends out and just run full blast all the time but the numbers will tell you how much your lugging the engine. If it's safe to do so try and see if you are in the wot powerband for your engine. If not then you may be causing damage to the engine.

I dont think I have ever gone to max speed. I will cut back on the throttle just as she gets up and will max out about 20-25 knots. I believe my RPM's might be around 3500-4000 at that speed.

 

[blaster]

It's not a bad idea to open it up once or twice a season like Terminaldegree said. It will tell you a lot about your engine and prop health.

 

[terminaldegree]

Hi blaster,

I'm not sure what my gph/speed are at WOT; if conditions are good next week, I'll give it a shot and report back with the results... I'll take a wild guess now: maybe 30 gph per engine and top speed in the high 30's (but it'll make a glorious noise like a speedboat)!

 

[Theresamarie11]

Well, through 4 boats, which have never had an issue, we do it probably more frequently than most. But then I've never had a boat that'll go much above maximum rated RPM either. With the 300 DA, which is actually our fastest boat top end boat yet by 3mph, we probably do it once per weekend but usually not for really long times. But we'll run a 40-42mph for extended periods. The issue with wide open is that it's a diminishing returns issue. But it is fun to go fast now and then. If anything, I suspect you may have to worry about canvas more than motors. I think there's a recommended maximum speed for various canvas configurations but don't recall where I read it.

 

[Bucit]

I always use the tabs to get on plane. I was told by a long time mechanic that the Alphas were "bullet proof" but why add the extra stress on the outdrives while getting on plane. The tabs take a few seconds to lower and raise so I always use them. While on plane (and less than 2' waves) I rasie the tabs and trim up to 2-3 at the max. I will usually gain a couple miles per hour while increasing my mpg. I'm not able to boat this Saturday but hopefully on Sunday. If so I will run WOT again to see what the GPS says. Last time out I hit 48 but depending on water conditions 46 is average.