Performance

F

fullhouse

New Member
Apr 14, 2008
9
cape cod
Boat Info
380 Sundancer 1999
Engines
3116 cats
1999 380DA-640 with 3116TA cats. I have always been concerned that my boat just does not go as fast as it should. I Recently found some information on "BOATTEST" that indicated that I should be able to make 24.3 knots at 2250 rpm and top out at 30.8 knots at 2800 rpm. I am not sure if the props. are the correct size or why it just doesn't move. We try running it on empty with just a few people aboard and the bottom clean and still average only around 15 knots cruising and 21 opened up. Speed is not so important but fuel economy is. Does anyone know first hand how fast I should go? Anyone suggest some things to try? Is there a wood core that could be wet? Wrong tranny? Is there a kit that can be installed in these engines to calculate gph? Thanks
 
Welcome to CSR. There are a few members here that are quite knowledgeable about your hull, and others that are knowledgeable about your engines.

I have a few questions for you to start with; What rpm are you currently toping out at? How well does your boat come up on plane? Do you know the HP of your engines? Do you know the HP of the engines in the 30 knot test that you referred to?
 
Thank you for the welcome.

We top out at 2800 rpm and it seems to come up on a plane o.k. Should I time it? The rating plate on my engines says 350 and the test boat was 340. They seem to be working pretty hard.
 
Yes, you should be faster.
A big gas powered boat does better than that.

Email searay and ask for the factory spec sheet.
Tranny
Props
Ect.
 
I sent Sea Ray an email last night asking for prop size and have not heard back. I will send them another looking for remaining specs.
I determine my speed by the GPS and my brother in his 360 who said he has never travelled so slow. He said he normally burns 45 GPH and burned 30 GPH following me. Is it difficult to add fuel consumption metering?
 
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15 kts at 2400 sure doesn't sound right, as Ron said I'm sure there's someone else here that has your setup.

But- we need to back up and start at square #1...

You say you've "always been concerned"- how long have you owned the boat?
It also sounds (please say it ain't so) that you purchased without a sea trial and surveyor aboard?

Assuming that's the case, it's water under the bridge now. Since you state it has always run at that speed, it likely can't be a fouled/dirty bottom.

Here's the rub- unless you've got some kind of props that are slipping like crazy, it doesn't make sense. If the engine is turning 2800 max- where it should be- the boat should be moving at "x" knots based on the props' pitch. It's not rocket science- and there are online calculators which will tell you what the boat's speed should be based on engine rpms, gear ratio, and prop size.

Something isn't adding up.
 
So he's making rated rpm (2800) out of each engine. He is most likely putting all of the 700 hp to the props. If the engines were overloaded they would struggle to make rated rpm. I he was under propped, the engines would overrun.

Did you burn more fuel than your brothers 30 gph, I'm thinking you filled up together?
 
Have you tried adjusting your trim tabs to see if that makes a difference?
 
I wish I could answer the gph question. We do not fill the tanks full when refueling. Trying to minimize the weight. He has a metering device that tells him gph. I have actually never calculated it. I will work on that this weekend.

We had a marine surveyor do a sea trial with us and he did not find an issue with the speed. The boat is a bit of an oddball where there were so few made with the cats. Whenever I looked at specs they pertained to the gas engines. It may not be as bad as I indicated. We were probably bucking a 2 knot current when we only made 15 knots. The speed at 2300 is closer to 17 knots. What rpm should we cruise at?

I just found a 2000 380 da with 3116's 350 hp that indicates cruising speed is 24knots
 
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Carver370 said:
What does the bottom look like? Any growth?
Click to expand...

We get a late start every year. Just before July 4th. We do not have any growth yet. When we paint it each year I wonder about the depressions left by the chips. Would they slow it down much? Should we strip all the paint off and start over?
 
I am wondering about the tachs some. They read a few hundred different. Do they usually read high or low? Is it easy to connect an instrument to the engine to get a better reading? They do seem to top out at 2800.
 
I ride butt heavy with the TNT lift and dinghy. when i put full tabs down, I can gain 2-3kts.
 
fullhouse said:
I am wondering about the tachs some. They read a few hundred different. Do they usually read high or low? Is it easy to connect an instrument to the engine to get a better reading? They do seem to top out at 2800.
Click to expand...


ahhh, the tachs, they are crap. have you tried tapping on them to see if they change?
 
Turtlesboat said:
ahhh, the tachs, they are crap. have you tried tapping on them to see if they change?
Click to expand...

Ditto.
Forgot about that variable...that's the "real" square "1"- confirming the rpms.

Do yourself-and your boat- a favor. Get a set of Aetna digital tachs, every diesel boat should have them.

Otherwise, you need a mechanic with a photo-tach to confirm your gauges are correct. That's gotta be it...

If there were growth or problems with the bottom/gear, the engines would be smoking like hell from being overloaded.

If they're reading a few hundred low, the 2400 cruise you think you're running at would only be 2100- which would explain the slow speed.
 
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How difficult would it be to get the rpm's to display on the E120?(called cat and they said no way)
I order to leave the dash intact can I run an additional tach in a remote location?
 
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A…24 @ 2250 30 @ 2800
B…17 @ 2300 21 @ 2800

From the above: I would say the ratio between cruise/wot from A/B is roughly the same. I would prognoses that; 1)…your not putting total rated power to the water and the boat has been reproped to get rpms. 2)… the load applied to the total rated power is all it will do.

If I came to your boat to check your engines for rated power, here’s what I would do.
1)… check both governor controls for full throttle.
2)… check both engines for bare engine high idle speed no load (some what higher than the rated 2800 rpm)
3)… sea trial test with turbo boost and fuel pressure gage installed. Rated rpms and rated boost pressure equals rated hp every time.
4)… finally I would test each engines torque rise by; at wot, backing off one throttle until her sister loads down good 2600-2400. Looking for good boost and fuel pressure, also some black smoke as she goes into a deep lug.

If I was satisfied with the data above as it compared with Cat’s data when your engines were first run, I would tell you there is nothing wrong with your Cats.


I do understand your need for a fuel flow meter as a test instrument. Perhaps when you get back to your boat, you could put a mask on and look at your props to see what they are. Also maybe look at your trans to see what gear ratio your running.
 
Anyone with dual engines should own and know how to use a photo tach. Throttle position and gauges are only as good as the cables and wires that they use to operate them. Another cheap item to own is a temperature gun. You can pick a descent one up for around $50.00 and alleviate a lot of anxiety.
 
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