RMP and MPH at Full Throttle

D

David Erwin

New Member
Oct 1, 2018
6
Boat Info
2014 280 Sundancer
Engines
350 Mercruiser Bravo III Drive
In the process of purchasing a 2014 280 Sundancer that has 30 hours on it. This boat has the 350 mercruiser 300 hp engine and a 21" prop. The boat has not yet had its first service due to the low hours but maybe it still probably should have since it is 4 years old. I just had the survey done on the boat. During the sea trial at full throttle the boat reached a max of 4510 rpm and a max speed of 34.9 mph. There is a review of this boat on boattest.com that shows the boat reaching 5260 rpm and max speed of 41.5 mph. Is this something that I should be concerned about? On this same boattest.com review it does show at 4500 rpm it should be doing a speed of about 35 mph. So this makes me feel better about the situation but I just wonder if I should be worried that the boat was not able to reach 41.5 mph at 5260 rpm.
 
I would be, sitting around for 5 seasons doesn't bode well with internal combustion engines.
 
Well now I am seeing that the wide open throttle range for the 350 mag is 4600-5000 rpm's. Hitting 4510 rpm's on the sea trial on a boat that is 4 years old that has not been serviced would seem a little more in line with an engine that is rated at 4600-5000 rpm. So I am wondering with BoatTest.com gets their information from. Or are they just another review site that writes reviews without actually "testing" the boat.
 
I would imagine that the sea trial was done with a pretty light boat? Not much extra gear in it? How many people? Was the person operating the boat well versed in how to properly trim a boat? What were the conditions?
 
Unfortunately I was unable to be there during the sea trial but was in close contact with the surveyor during the survey. It was just him and the owner. The owner drove the boat. I do know that there was no extra gear on the boat and not a full tank of gas, they put enough gas in the boat just before the sea trial to cover them for the boat ride. The surveyor said that the owner/ driver of the boat did trim up slightly at WOT which is when they hit 4510 rpm. I know it is a possibility that the driver just did not know how to trim the boat properly but I am just not sure if this could have caused such as drastic difference between 5200 rpm and 4500 rpm. That is if BoatTest.com was actually able to hit 5200 rpm when what I am seeing now says this engine is rated 4600 to 5000 rpm at WOT.
 
I’d call that a good sea trial. They do this on not full fuel and light weight aboard. Real life additions add weight. Anchor onboard? Chain? Water? You don’t know if it’s propped differently? bottom dirty or painted? Is the tach not accurate (smartcraft, I know unlikely)?
 
The bottom is painted and I can say that it has no build up on it at all. There is an anchor on board and it does also have the optional generator. So I suppose this could have an affect on top speed.
 
Hi,

I just got my boat back from the mechanic. I asked him about the rpm range because i cannot get more than 4350 out of my 350 Mag. He said that motor is rated from 4100-4600 rpms. I've owned this boat for the last 9 years. Everything on this motor has been replaced. (block, risers, pumps, the last repair was cool fuel module and fuel injectors). So don't be worried about the rpms. Its within range.
 
For the longest time, the 350MAG was rated to 5,000RPM. However, in the last few years of it's lifespan it was uprated to 5,200.

Test sounds like it was done with the right load. However, an owner that has barely used it behind the wheel... probably tentative to go all out and may not know how to properly trim. The surveyor should have ran the boat to it's max. Period.

Regardless, even if the engine had still been rated for 5,000, it should have gotten much closer to that.

You mentioned that it hasn't had it's first service... which means 5-year old oil in it?

Dan... those numbers (RPM range) are wrong and your boat/engine should do MUCH more than 4350. I don't want to hijack this thread, but those numbers are wrong.
 
My ‘06 260DA with 350Mag and 300hp Bravo 3 was rated at WOT 4800-5200rpm. At any time during the 3 years I owned the boat, it would hit 5050rpms trimmed out. Proper trimming is a must to get all out of it she has.

Bennett
 
Well I really can’t say for sure if it hasn’t had a first service because the guy the I’m buying from bought it from an auction to solely flip the boat. It looks like it may have been a repo. It is a super clean boat and looks like you would expect a boat with 30 hours on it to look. And all the systems check out too. It seems that it was just a case of someone who bought a boat and never used it. But if I had to guess it probably does have old oil in it. First thing I will be doing is a full service.
 
David Erwin said:
In the process of purchasing a 2014 280 Sundancer that has 30 hours on it. This boat has the 350 mercruiser 300 hp engine and a 21" prop. The boat has not yet had its first service due to the low hours but maybe it still probably should have since it is 4 years old. I just had the survey done on the boat. During the sea trial at full throttle the boat reached a max of 4510 rpm and a max speed of 34.9 mph. There is a review of this boat on boattest.com that shows the boat reaching 5260 rpm and max speed of 41.5 mph. Is this something that I should be concerned about? On this same boattest.com review it does show at 4500 rpm it should be doing a speed of about 35 mph. So this makes me feel better about the situation but I just wonder if I should be worried that the boat was not able to reach 41.5 mph at 5260 rpm.
Click to expand...

Check to see that the prop size, and pitch are correct for that model boat. If the boat was laid up at
some point, Who knows if the prop was changed your RPM is close but not quite there. As far as speed i wouldn't be too concerned with that. The sea conditions play a big part in speed such as wind, current,
and chop. Get the top end off your mind with speed it will tear your boat up . Every boat has a sweet spot you treat it right it will return the favor. Good Luck and enjoy!
 
Lazy Dayz,
I agree with you. I always thought I should get more out of the engine. Iv'e owned this boat for 9 years and that's all I get. No matter how i trim it out. Like i said the motor has been rebuilt 4 years ago. When i got it back at that time I had the same results. This time the cool fuel module was changed along with 8 fuel injectors. All OEM. Big bucks. It is what it is.
 
scoflaw said:
That's a lot of boat for a single small block
Click to expand...

It's actually, basically, a 260 DA. I agree - not going to set the world on fire with a small block, but the hull actually does pretty decent with it as long as you're not loading it up with 10 people. I've even skied behind it many times! Not with 10 people in it, of course.

Lenny - I sent you a PM
 
Scoflaw,

The 270 Amberjack weighs about 1000 lbs more that the 260.

Lenny
 
Not sure if just an oversight by others or I missed something, but a fuel tank with little in it for 5 years has got to be holding some bad fuel? Adding just enough for a sea trial will not correct that.
 
dan313 said:
Scoflaw,

The 270 Amberjack weighs about 1000 lbs more that the 260.

Lenny
Click to expand...
Please double check me (SR lists specs for every boat online), but if memory serves, both boats are pretty close to the same weight.
 
Lazy Daze,

270 Amberjack 7325lbs dry. 260 Sundancer 6667lbs dry. This is from Sea Ray.

Lenny
 
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