2000 380 Sundancer WOT confusion

Gallf1

Well-Known Member
Sep 26, 2018
316
Palm Coast, FL
Boat Info
2000 Searay 380
Engines
Mercruiser 454 MAG MPI 7.4L
Custom Forward Hardtop
Whaly 270 Hard Dinghy, 4hp Honda

Bahamas Veteran
Hello all;
I tried searching the archives and I can’t seem to find an answer...

I am in the process of finalizing the purchase of a 2000 SR480 DA with 7.4L MAG MPI motors with 21x22 props. Engines passed compression tests and has a very clean bottom.

At WOT it is only reaching 3800rpm....I am thinking the pitch is off and needs to be adjusted to reach at least 4400rpm?

Is their a definitive WOT/ RPM prop chart that I can show the owner and broker?

The links to prop charts in the forum appear to be dead?

Thanks in advance!
 
If memory serves, there were slightly different specs based on whether it's a "7.4" or "454". And if it's truly a "MAG", as well. If it's the "7.4", I believe you are right that you'd want at least 4400... I think the "range" is 4200 to 4600. The 454 MAG has a higher range - which I believe is 4600 to 5000.

I just went to Sea Ray's website and looked at the spec sheet for your boat... it shows the 454 MAG MPI as the only gas engine available. So, if you actually have the 454 MAG, then you'd, ideally, be able to run up close to 5000. Of course... the spec sheet can occasionally be wrong.

Either way, 3800 is WAY too low. I'm not sure what props would have been on there - I have hard copies of the prop but I won't be able to get to them till later this week. I wouldn't expect a prop to INCREASE is pitch with age, though. If anything, it should decrease in pitch... resulting in HIGHER RPMs than expected.

A compression check is only a basic check... might need to do a leak down. How do the props physically look?

If you want to find out for sure, call Merc with the engine serial number. They can definitely tell you the proper MAX RPM range for those specific engines.
 
Last edited:
Thx for the reply...
Yes, you are correct in that I have the 454 MAG MPI in the boat with 4-blade 21x22 props. Seatrial with this setup gave me “cruise” at 3500 with 21.7 mph
And WOT at 3800 with 25.7 mph.

One of the props ended up being needed to be reconditioned due to slight vibration. I am thinking it is overpropped and the pitch on the props need to be adjusted to at least reach 4400 at WOT?

If you can send me any documents with the info from SeaRay or? I would be very grateful!
Thx
Felix
 
Not entirely germane but my 400 with 7.4's cruises at 27mph at 3600-3700rpm +/- (24kts). WOT is 4200-4300 +/-.
 
Thx!
 
You don't specify, but where are you measuring RPM? Sea Ray dash tach's are notoriously inaccurate. If you are not measuring your RPM's at the flywheel/on engine, a $15 tach from Amazon will get you a much more accurate reading.

I have this one - ttps://www.amazon.com/AGPtek%C2%AE-Professional-Digital-Tachometer-Contact/dp/B004Q8L894/ref=sr_1_1_sspa?ie=UTF8&qid=1541343247&sr=8-1-spons&keywords=laser+tach&psc=1

If you are already doing this, disreagard, but you could be chasing "ghosts" if the dash tachs are giving false information.

Might want to order hearing protection for the guy in the engine room measuring @WOT!

Let us know how it works out, the 380 is one great, sexy SR!
 
Thx....rpm was measured by surveyor using digital tach. We are thinking previous owner had wrong pitch on the 21x22 four blade props so they are being checked and balanced
 
By the time Thursday came around, forgot about checking prop charts. What did Merc say - did it match up with what we were thinking above and what Doc found for you?
 
Tech said 4400-4600 with average load and average bottom condition, so once props are checked we will do another WOT run
Thx
 
Tech said 4400-4600 with average load and average bottom condition, so once props are checked we will do another WOT run
Thx
By "tech", do you mean "Mercruiser"?
 
yes....sorry
 
You don't specify, but where are you measuring RPM? Sea Ray dash tach's are notoriously inaccurate. If you are not measuring your RPM's at the flywheel/on engine, a $15 tach from Amazon will get you a much more accurate reading.

I have this one - ttps://www.amazon.com/AGPtek%C2%AE-Professional-Digital-Tachometer-Contact/dp/B004Q8L894/ref=sr_1_1_sspa?ie=UTF8&qid=1541343247&sr=8-1-spons&keywords=laser+tach&psc=1

If you are already doing this, disreagard, but you could be chasing "ghosts" if the dash tachs are giving false information.

Might want to order hearing protection for the guy in the engine room measuring @WOT!

Let us know how it works out, the 380 is one great, sexy SR!

Getting one of those. Thanks,

MM
 
Assuming the Merc spec is that 4600-5000, the recommendation of 4400 to 4600 with an average load is still be a little on the low side. That means you're 400 to 600 underneath the top end. Ideally, for the best efficiency we want to be able to get the engines as close to max as possible. Personally, I like to prop a boat for the way the boat is run "most" of the time - referring to the normal load in a boat. For those times when you're running light, you can adjust with the throttle - for those times when you're running heavy, it gives you're still running safely and not lugging the engine.

Take this in to account with the load that is on the boat during the test rides - often the boat is on the light side for test rides.
 

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