330 Express Performance Question

[Cregan13]

I have an '06 330 Express with 2018 Yamaha F300s that were installed new on the boat late last summer. I have 87 hours on the engines. All of the sudden, I have noticed a loss of power. To clarify, the engines are still turning the same RPMs and do not sound like they are struggling. I am, however, getting 6-7 mph (14%) less at WOT and 3-4 mph (11%) less at my cruise rpms. I am also getting .2 mpg (20%) less fuel efficiency at my cruise rpms. I am thinking I have some growth on the hull. It sat for two weeks, which is the longest it has ever sat for. I have ablative bottom paint that is close to the end of its useful life, but at the last haul out in October I was told it would be good until the 100 hour service. I went down there today and ran the heck out of the boat to see if I could clean the hull off, and it seemed to get a little better at cruise but not at WOT. It is still "dragging" at cruise.

Like I said, the engines are still able to hit max RPMs, there are no alarms, and they sound okay. I thought the ride today might have been a bit rough, but I am so hyper-focused on every little thing right now that it is hard to say. The only other thing of note is that I topped the tanks off on Memorial Day. I typically use fuel I bring down from the local BP, which is 89 octane non-ethanol. This last refuel, however, I was almost completely empty, and I filled up at a marina with what they told me was 89 non-ethanol. Not sure if maybe the octane wasn't as advertised and that is causing the performance decline.

I still think it is bottom growth, and I am going to have new bottom paint applied when it is pulled for the 100 hour service. However, I am headed 65 miles offshore on Saturday, and I wanted to see if the above raised any red flags with the brain trust here before I left sight of land.

Thanks.

 

[georgemjr]

No red flags to me considering what you said (full rpms, not struggling). Is the boat heavier now than when you were hitting the better numbers (full fuel, full water)? If not, growth might be the ticket. It certainly can reduce by at least 5mph+. I don't think octane would change the power, it would prevent preignition (knocking).

 

[magicalbill]

1.) Make sure your tabs are not stuck in the "down" position; The same bottom growth that could be causing your performance loss may have your tabs glued down at least partially, although that's unlikely.

2.) If you know your boat's running attitude and are certain your tabs are fully retracted while under way, have the boat hauled and scrub the bottom, or have it scrubbed by someone. It would only be a couple hours on a rack in your marina and I'll bet that fixes it. Just running the boat won't get the scum off. While she's on the hard, clean the bowthruster cavity & blades if so equipped.

I wouldn't be able to wait to get this rectified. I would stew the whole time about it.

 

[wspitler]

A full fuel load (350gal) versus a lighter load, say 150-200 gallons is significant difference on my boat. Sea conditions have an impact. Also the way it is loaded makes a big difference on the 330. Full fuel 2500+ lbs, full water another 320 lbs, could that be the difference? I have the F250s on my 2007, wish I had F300s, but mine run so good I can't justify the upgrade! Don't worry they will get you there and back in style!

 

[Flot]

Let's be clear on one thing - if your engines are turning the same RPM as they ever did, and your props are unchanged - then there is nothing wrong with the engine side of the equation. 6000 RPM spinning a given prop in good shape is just as much thrust as it ever was.

That leaves two things left on the hull end - weight, and drag. It sounds like you may have a little bit of both going on. Just my $0.02 but I've never had much luck running a boat to clean it. It'll knock the worst off but fresh paint can be a big difference.

Also remember that wind and current (and waves) play into your speed and mpg calculations, if you're using GPS as your speed source. Down here that can easily be +/- 5 mph, so don't forget to make that run both ways and average your numbers.

 

[WiltonGrady232]

My money is on growth. It doesn't take much to really hurt performance. My bottom is painted on my sailfish and if I let it sit for more than a week without taking her out, I will lose performance.

 

[Cregan13]

Let's be clear on one thing - if your engines are turning the same RPM as they ever did, and your props are unchanged - then there is nothing wrong with the engine side of the equation. 6000 RPM spinning a given prop in good shape is just as much thrust as it ever was.



Thanks for the reassurance. That is what I figured. I fill it all the way up regularly before running offshore, so I know what to expect when all 350 gallons are on board, and this is different. I was planning on re-bottom painting at the 100 hour service, so I can live with this. Something mechanical on new engines, however, would have a different story.

Work tied me up for two weeks, and I could not get down to the dock for a quick run, which I typically do at least once a week. I will not let that happen again if this is what results!

Thanks again, and I will post some pictures of the bottom when it is hauled and performance numbers after it is back in.

 

[HMBJack]

These are some of the longest sunlight days of the year. Add warm water, and your growth on the hull is at maximum output.
You know your boat - you're initial thoughts are probably spot on. You might have a Diver do a scrub job before going offshore. Or at least have someone take a swim and do an inspection. My two cents...

 

[Cregan13]

Pulled it today for bottom paint and service. Here's what she looked like on the bottom. Hoping to get my MPGs and MPHs back! As an aside, I am glad the shop felt comfortable rolling it down the street on those tires, cause I wouldn't have!
service. Here's what

 

[magicalbill]

So the growth in the pics is the result of the boat sitting in the water for how long?

You wrote in your opener it sat for two weeks, but I assume you mean it sat in the slip without running.

I'd be interested to know how much time it took for that much marine growth to accumulate.

 

[Cregan13]

Yes, it is in a slip, and I usually run it once or twice a week. Noticed the decreased performance after about two weeks of it sitting in the slip without getting down there to run it. The last time it had been out of the water was around late October or November.

 

[Cregan13]

And I'm back! Pressure wash and bottom paint was the answer. It felt great to fly down the ICW again!

 

[nodima]

Nice that it was a simple solution. But damn, that was a lot of growth!

 

[Cregan13]

Still crazy to me how everything was fine and then suddenly it wasn't. Most surprising effect was how much my fuel efficiency dropped.

 

[magicalbill]

Congrats: Glad your back in the zone; I would be happy as well!

I looked at your RPM's VS MPH numbers and thought, "hmm, that 330 is pretty light on it's feet for having 250's."

Then I re-read your initial post and saw you had 300's.

Got it....

 

[stripedo]

I have twin 300's on my 330 Express and she runs a bit faster than that at 4500. Are you trimming up your engines?

 

[Cregan13]

I have twin 300's on my 330 Express and she runs a bit faster than that at 4500. Are you trimming up your engines?

Yup. How fast are you getting? Do you have your enclosure up? Yamahas or Zukes? bottom paint? full tank? I get 42-43 at top end. What about you?

Just curious.

 

[stripedo]

I'm around 32 at that RPM. Enclosure curtains down.Yami's. Bottom paint. I'm about 43 MPH as well.