2001 400 Sedan Bridge Planing Problems w/Cat 3126's

L

lkrompier

Member
Aug 4, 2009
54
New Jersey
Boat Info
2007 44 Sedan Bridge
Engines
Cummins QSC 500 Diesels-478 HP
I have a 2001 400 Sedan Bridge w/Cat 3126's and have planing problems and speed problems since buying the boat in 2008. My avg speed at 2400 rpm's is a pitiful 19-20mph and planing is difficult without going over the safe 2400 rpm. The boat is not overly weighed down. I also have a hydraulic swim platform. I've heard this boat has problems getting out of the hole with these Cat motors. Props are supposed to be 22 x 24 but the previous owner had the pitch changed and they are now 22 x 23. The RPM's are right on at 2800 wot, where they should be. Anyone having this problem or resolutions?

Thanks, Larry
 
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Are you putting trim tabs ALL the way down when coming out of the hole?? All the way down means up to 15 to 20 seconds?? Then slightly ease up on them once on plane. Ric
 
Do you have 420hp 3126's? FrankW will come by but why cant you get 2800rpm? Something is not right. Did you survey the boat at sale? JC
 
WOT IS at 2800 rpm which is what it should be under load. I brought this up because re-pitching the prop to the specified 24 from the current 23 will reduce my RPM's from the current 2800 which is normal. It may get me out of the hole at a (supposedly) lower RPM but I'm now stressing the motor because it won't be able to reach the 2800 factory recommended max.
 
No, the tabs operate ok and the nose rides high regardless of how down the tabs are. I'm not getting the boat on plane and out of the hole.
 
I can't comment on the planing problem.
Horsepower is horsepower. Your 3126 at 350 hp is equivalent to my 355 hp 3208's, and my 390 cruises at 22 knots.
Given that your 40' bridge boat is undoubtedly heavier, I wouldn't be surprised at an 18 knot cruise.
Have you visually confirmed that the tabs are down- and stay down- under load
 
How do you visually confirm that the tabs stay down while the boat is under load (under way)?
 
Let me throw in the question of how clean is your bottom and the running gear? I am in fresh water, but have read a ton about salt water boats with dirty bottoms losing alot of speed with nothing needed to remedy it other than a good cleaning.
 
Larry,

I've got 3126TA at 420HP, 22x22 4 blade props with freshly cleaned haul and at 2400 run fully loaded with fuel and water 18-20kn depending on conditions. More often 18-19 than 20 till I burn off some fuel. I hold 350 gallons & 110 gallon of water so the 18-19 is more typically. At WOT which by my gauges which are pretty close can turn 2750 which is +- 23-24kn. I dont think you're going to get any more curising speed at 80% thottle with the 350HP engines you have.

You should be able to tell once you're at WOT & top speed if you trim tabs are working. If you raise them fully up your bow should rise enough to be able to tell it and if you put them all the way down your bow should drop and begin to plow enough to tell you have them down.

Your hydraulic swim platform added lenght to your boat and will decrease both top end speed and naturly raise the bow attitude somewhat over the same boat/power conditions with the extended lenght and weight of the platorm. This said, your boat is pretty close to fully loaded even without much fuel or water on board as a result of the platform extension and weight added.

Sorry but that's my 2 cents worth.
 
From Hampton -

"I think the problem goes back to before the boat was re-propped. If it had the correct props, but couldn’t spin them fast enough, then perhaps there was a problem with the fuel system, turbos, engines… The solution may have been to find the issue back then and get the engines to spin the recommended props at the recommended WOT. Does this make sense?

One way to get the correct WOT is to fix the problem. Another is to shave the props. The problem with shaving the props down is that you end up with a boat that will not meet performance expectations even though you are able to achieve WOT.

Just sayin’. Good Luck.

John"
 
Gimme Time said:
Larry,

I've got 3126TA at 420HP, 22x22 4 blade props with freshly cleaned haul and at 2400 run fully loaded with fuel and water 18-20kn depending on conditions. More often 18-19 than 20 till I burn off some fuel. I hold 350 gallons & 110 gallon of water so the 18-19 is more typically. At WOT which by my gauges which are pretty close can turn 2750 which is +- 23-24kn. I dont think you're going to get any more curising speed at 80% thottle with the 350HP engines you have.

You should be able to tell once you're at WOT & top speed if you trim tabs are working. If you raise them fully up your bow should rise enough to be able to tell it and if you put them all the way down your bow should drop and begin to plow enough to tell you have them down.

Your hydraulic swim platform added lenght to your boat and will decrease both top end speed and naturly raise the bow attitude somewhat over the same boat/power conditions with the extended lenght and weight of the platorm. This said, your boat is pretty close to fully loaded even without much fuel or water on board as a result of the platform extension and weight added.

Sorry but that's my 2 cents worth.
Click to expand...


Just to put some comparison to that, I run 350 HP CAT's and usually run closer to full fuel tanks rather than empty. Water and Holding tanks are typically 1/2 full or less. The props are at 20X24 (repitched from 20 X 25 to get to 2800 RPM's at WOT) and I typically cruise around 22 knots at 2200 RPM's. Granted that's a bit faster with a bit less RPM's, but mine is a whole lot less boat than yours too.

Gimme Time and Tobnpr may simply be onto the fact that this is a whole lot of boat to push with 350 HP X 2.
 
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Larry,

There don't appear to be any mechanical problems with the engines since they both turn up 2800 rpm. You hardly ever see fuel delivery, turbo, etc. problems affect both engines at the same time and in the same way, and you did not indicate that in your post.

The bottom isn't fouled or you would not see 2800 rpm.

Your boat's previous owner's re-ptiching the original props is quite normal since Sea Ray tweaks the wheels with a very light load. At some point most mid 90's-early 2000's owners did the same thing to get the engines to turn rated rpms without overloading. "Shaving", whatever that is, or messing with pitch or cup in this case serves no purpose since the engines are performing as they should.

Most likely, you have a normal 400DB, and based on your comments, you may have expected it to perform like a Sundancer, which isn't going to happen. The 400DB is a big, stern heavy boat. Compounding that is the hydraulic swim platform which adds even more weight well aft of the COG. It is what it is and, short of moving the COG and using a lot of tab, there isn't much you can do about it other than adapt to a stern low attitude and speeds of about 20 kts.

One of the things all the 400DB owners in our area have done is to go to an all chain anchor rode to put several hundred pounds right on the nose of the boat. It helps, but not as much as you probably want.

Sorry, but I don't have any ideas that will add to the positive side of the equation........
 
As Frank said, The 400DB is a big stern heavy boat. Especially with a hydraulic platform on it. I run with a buddy who has an '03 version of 400DB but with the 480CE Cummins engines. Even with that power set up, she takes quite a bit of time and effort to get up on plane.

I will take minor issue with Frank W (at my peril, I know) with the broad characterization that all DB's are slow out of the hole [edit: OK Frank Didn't say that all DBs are slow, but he did imply that all dancers are not!]. My boat jumps up on plane in a few short seconds with virtually no bow rise. She gets out of the water as fast as, if not faster than, similarly sized dancers and even smaller dancers. My brother has a 320 and when we start off together he says all he hears is a little turbo whine, and then I am gone.

As Hampton would say: "Just sayin'"
 
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Larger tabs might help (if they can be fitted)?

They add a lot of drag, but if it improves the running angle of the hull and gets the stern out of the hole it could end up on the + side.

Maybe Frank knows if anyone's done this or if it's even possible.
 
Read more carefully Tim.............I said "Based on his comments".........he may be expecting the 400DB to perform like a DA, but it isn't going to happen. And, all my comments are based on the 400DB.

For my taste, the 400DB is a good boat, but she represents the ownership threshold for Sea Rays for DB's due to the whole weight and balance thing. As the boats get bigger, they handle and perform better. Other than the diesel 370DB, those under 40 ft tend to be stern heavy and slow. If you like the 44DB, go run a 480 sometime and the old 6V92 powered 550DB is a tremendous boat.

I'm just sayin.....................
 
I hear what yer sayin' Frank.

I just get a little touchy on the "dancers are 'sporty' and bridge boats aren't" theme. And you are right, the bigger they are, the better the seem to perform.
 
I'll start with my basic mantra....if you are using the factory analog tachs to determine your motors rpms then you may or may not have accurate readings...most likely not! IMHO, they suck. Replace them with a pair of Etna digitals and you will never look back. All RPMs numbers should be confirmed with a laser tach or properly calibrated digitals.

Specifically with the 3126TA motors, there are two main RPM numbers to concern yourself for basic diagnostics purposes....

1st---- "bare engine hi idle" rpms or the "no load" rpms....each engine is factory calibrated to reach this number and then the number is posted on the valve cover....Every engine is unique....my 350HP 3126TAs are 3132 RPMs and 3120 RPMs.

You check this number by putting the boat in neutral, start the motors, and hit throttles to the wall. don't forget the ear muffs.

2nd---- loaded WOT RPMs. That number is also posted on the valve cover and will read " 350 BHP AT 2800 RPM". All 350HP 3126 TA marine motors have the same loaded RPM number...2800.

As FW satated, the Sea Ray 'recommended' props are not necessarily real world props ....IMHO, they are a very generic props, tested in ideal and extremely lightly loaded conditions as a means to sell a specific model with lower (read less $$$) powered motors. Having Sea Ray 'recommended' props on the boat does not mean a specific boat is correctly propped.

For example....I'll bet ALL 400DBs with 350HP CATs came from the factory with the same props...regardless of the way the boat was optioned....add an open array radar, hydraulic platform with a dink, all chain anchor rode, etc,....and you have added significant weight and weight not necessarily very well distributed. Then fill the fuel tanks and fresh water tank and you've added total close to two tons more in weight than the way the factory most likely test that specific model.

Also, Just because a motor reaches the Bare Idle Speed doesn't meant it will reach the rated WOT rpms under load. There are a whole host of issues that can cause a loaded motor to miss rated RPMs: low fuel pressure, Air in fuel lines, dirty fuel filters, dirty bottom, coked up turbos, low boost, bad injector, etc, etc.

You need to know that the motor's air, cooling and fuel systems are working per spec. You then have to 'work' the props the reach rated WOT RPMs. Most will suggest you reach rated WOT RPMs +/- 25-50 rpm. Once your props have been correctly pitched/cupped to reach the rated loaded WOT RPMs, you will then have dialed into the cruising speed for that specific boat. It is what it is. If you can't reach the rated loaded WOT RPMs, you will be overpropped and overloading the motors. Depending on the level, the overpropping could also cause a boat to plane slowly.
 
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