1999 35 Open RPM's With Cummins 5.9 WOT 2700RPM

1999 35 Open RPM's With Cummins 5.9 WOT 2700RPM - Printable Version

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1999 35 Open RPM's With Cummins 5.9 WOT 2700RPM - torchlake99 - 10-03-2013

Hello
Just bought the above Tiara and we are very happy with the boat at this time. My only concern is that according to the specs on the diesel engines we should be turning 3000 RPM's . At WOT we only hit 2700, even with a light load (about 1/4 tank). At 2700 we are at about 32 MPH, the boat feels great and I am getting no signs that the we are laboring the engines (no black smoke). The specs show this boat and power package at 36 MPH at WOT. I have heard that the numbers from Tiara may be a bit optimistic and my boat is a 1999, not new. Wondering if the tach could be off or I have the wrong props on the boat. Is there anyone out there that could share some information on their real world experience with this 35 Open and Cummins diesels? It cruises at 27 to 28 MPH turning 2350 RPM's and feels great. Just trying to see what others with same boat feel.Thanks for any input you may have!

1999 35 Open RPM's With Cummins 5.9 WOT 2700RPM - South Sound Steve - 10-04-2013

are you measuring speed in knots or mph?

1999 35 Open RPM's With Cummins 5.9 WOT 2700RPM - torchlake99 - 10-05-2013

MPH

1999 35 Open RPM's With Cummins 5.9 WOT 2700RPM - anthem - 10-05-2013

Are those 370's or 330 hp? I had a 34 pursuit which is essentially the same hull as your 35 with the 370's. I would cruise at 2400 and 24 knots (about 27 mph) I could get pretty close to 3000 with a light load, clean bottom and clean running gear. The 330hp max out at 2700 I think.

1999 35 Open RPM's With Cummins 5.9 WOT 2700RPM - trit21 - 10-06-2013

You should turn over rated RPM to ensure long life from your engines. IF your MAX rpm is 2700, you should be able to turn 2800 + fully loaded as you use the boat, not a light load. If you max is 3000, then you should be able to turn 3100+. If you visit boatdiesel.com you will find many (including me) that agree with these numbers. Go to SBMAR.com (Tony Athens website) and look at the many many article and tips he has on the 6b engines and how to make them last a long time. My boat is a 2000 3500 with 370 6BTA's. She turns right at 3100 at WOT fully loaded. Cruise is 2400-2600 RPM at 23.5-25knots. My props are 23x28 and when I purchased the boat I removed 1"of pitch to achieve those number, especiallly the 3100 full loaded spec.

Tom

1999 35 Open RPM's With Cummins 5.9 WOT 2700RPM - torchlake99 - 10-06-2013

Thanks for sharing information! I do have the 370 6BTA's in the 35 Open. This is my project this winter to figure out, other than this everything is perfect with the boat. Either my tach is wrong or I have the wrong props on this Tiara it looks like. Thanks for the Athens info., I will check out the site.

Kent

1999 35 Open RPM's With Cummins 5.9 WOT 2700RPM - jmk - 10-06-2013

Before doing anything you need to verify your max RPM in neutral hits spec using a photo-tachometer (50 bucks, and you can't trust your dashboard tach). If your motor is not struggling, it is possible you just do not have the throttle all the way at the stops.

1999 35 Open RPM's With Cummins 5.9 WOT 2700RPM - Chris Burkard - 10-07-2013

Stop!!! If you are overloading the engines, you could do irreparable damage to the engines.

Your engines are rated to turn 3000 RPM under a full load. For safety, it is best to let them overturn about 50 RPM when fully loaded (100% Fuel, 100% Water, 4 people and gear) as this allows you to have a dirty bottom or dirty fuel and still fall within the safe range (3050 RPM). Light load, you should be turning 3100 to 3150 RPM.

At 2700 RPM light load, you have something wrong!

1) Make sure your bottom is clean!
2) Make sure your shafts turn freely when the engines are off and the transmissions are in neutral. You should be able to turn them by hand via the propeller.
3) Make sure your fuel is clean and fuel filters are clean.
4) Have engines checked (injectors?, turbos? fuel pumps?).
5) Props? The original props were likely 23"x29" - 3 Blade Federals with #7 Cup
6) If everything above is in order, as mentioned above, photo tach the engines for exact RPM. Gauges are notorious for being 50 to 100 RPM off. I've never seen gauges 300 plus RPM off, but I suppose it is possible. I would photo tach them under load (be careful!) it can be very dangerous to photo tach the engines while underway. You may want to hire a mechanic to do this for safety reasons.
7) If you truly are at 2700 RPM under load (everything above is good), I would pull the props first and verify the diameter, pitch and cup are close to factory settings. If they are, then you need to move to the engines.
8) If the above is all good and you are at 2700 RPM, then I would say you have a power problem, either worn cylinders and rings, bad turbos, bad fuel pumps, bad injectors or a combination.

I'm hoping it is something simple, but you need to figure it out before any damage is done.

1999 35 Open RPM's With Cummins 5.9 WOT 2700RPM - torchlake99 - 10-09-2013

Thanks all for the above information! Will be going out with a mechanic and check the rpm's at the motors vs what the tach says. From there we will get the boat to 3150 with a light load. This is our winter project. Prop company will pick them up and spec them out. Looking forward to spring already.
Thanks
Kent

1999 35 Open RPM's With Cummins 5.9 WOT 2700RPM - torchlake99 - 10-15-2013

Just a FYI, both tachs are good, within 1 or 2 percent accurate. Shafts turn free and everything checks out on the engines. We are going after the props and will make changes to them to again rpm's.
Thanks for all the help!