Planing off with Detroits

[madhatter1]

My 34 with 270HP Cummins planes off very easily by progressively increasing throttle. No need for full throttle.

I had a 46 Bertram years ago with 435HP DD's that was a bit underpowered. The only way to plane off was full throttle until turbo's spooled up and then back off throttles.

Bought Dave's 46 HP with 650HP 8-92's. Clearly not underpowered (except by todays need for mega HP). Still needs a lot of throttle until turbos spool up, just like the 8-71's. Guessing this is normal due to size of turbos. Not getting boost until around 1500 RPM.

My question is what is the proper way to plane off. Should I just go full throttle and back off as soon as they make boost/power? Or is 3/4 throttle good and just wait a little longer? Just feels weird waiting to get over the hump.

Thanks for any responses.

 

[SeaEric]

Are the trim tabs working?

 

[racclarkson@gmail.com]

In my case with 1271Ti’s, I work the throttles up gradually (+\- 5 to 8 secs) so as not to over-fuel. As the bow starts to come down, I engage the synchronizer and pull the master back to a mark I scribed on the control head that will produce 1,800 RPM when the power stabilizes. RPM reaches 2,050 or so before settling back and well on plane. Fuel flow then stabilizes at 26.5 to 28.5 GPH X 2 for 18.5 knots. Aslan always runs most efficiently with full tab. No doubt that gets her up faster.

 

[Boatsb]

The 34 is 19k lbs and a large flat stern so no comparison .


Detroits will take time to spool and make power I'm not sure the full throttle position while it's coming up will do any damage. It's not like their cold and their not making all that power as the crank up.

 

[madhatter1]

Tabs work fine. Other than leave in position for best cruise while in use I have never tried putting them down further to plane off. Sounds like maybe that is something I should be doing. Using the boat tomorrow. Will pay close attention to actual throttle positions as I run her up. Maybe I am babying it too much and not giving enough initial throttle. Not smoking or any other issues. Probably just me.

 

[Pascal]

On most boats you need full tabs down to get on plane quicker. Then once there gradually retract to reduce drag and increase speed until speed peaks

From hull speed I always increase power gradually about 100 rpm every 5 seconds till whatever RPM it takes to get the boat up on plane and to the target speed. Less stress on the drivetrain, no cavitation. If the boat is underpowered you may need to push the throttles further and then back off

 

[madhatter1]

I am used to the 34 which needs zero tab to plane off or run at best speed. The only tine I ever use tabs on the 34 is to level out or get bow down along with slowing down for very choppy water. Will try tabs down tomorrow.

 

[pdog]

On my 46 with 871 TI's I gradually increase power till I get to 1950 or so and engage synchronizer and then pull back a little to my cruise rpm. I always use full tabs until on plane and set at proper rpm.

 

[SKYCHENEY]

Don't be afraid to go to WOT. These engines were designed to do that. But, as stated, don't horse them up there too quickly.

 

[madhatter1]

So with tabs down and synchronizer on I slowly and progressively applied throttle just enough that slave was not lagging the lead. At about 13 smph both turbos kicked in closer than I was ever able to get them to. Planed off effortlessly other that short turbo lag 1400 just under 1500 RPM. Worked great. Still disengage synchronizer to drop off plane.

Yes, I know I am overthinking some of this but for me better to underthink and screw up.

Thanks for all suggestions.

 

[racclarkson@gmail.com]

So with tabs down and synchronizer on I slowly and progressively applied throttle just enough that slave was not lagging the lead. At about 13 smph both turbos kicked in closer than I was ever able to get them to. Planed off effortlessly other that short turbo lag 1400 just under 1500 RPM. Worked great. Still disengage synchronizer to drop off plane.

Yes, I know I am overthinking some of this but for me better to underthink and screw up.

Thanks for all suggestions.

Negatory. Do not engage synchronizer until both motors are well up to speed or the master will be doing most of the pulling with the slave lagging. You want them both churning. I work the throttles up in sort of a wrist twisting motion. But that's just a personal thing. No reason to disengage sync slowing down; it'll come off plane straighter synced.

 

[spartonboat1]

Don't be afraid to go to WOT. These engines were designed to do that. But, as stated, don't horse them up there too quickly.

Haven't been on here in a while. I have owned my old 1972 43' DCFB, since 1997, which I view as very reliable. They are non-turbo 6-71N's, 310hp and original, with full 50#'s oil pressure above 900 rpm, as a function of the lift off valve; right engine in -framed in 1995 and they have 2,400 hrs.

My suggestion/policy is to allow them to run at 11-1,400 rpm, until their temperatures come up, i.e. at hull speed. Any internal combustion engine should near full temperature, before heavy loading, to ensure internal clearances are stable. Once temps are up, don't slam the throttles to wide open, but bring up rpm's to allow 10-15 secs to reach full throttle. When on-plane, set the trim tabs to level out. Finally, engage syncros.

My 2cw.

 

[jrbrein]

My suggestion/policy is to allow them to run at 11-1,400 rpm, until their temperatures come up, i.e. at hull speed. Any internal combustion engine should near full temperature, before heavy loading, to ensure internal clearances are stable. Once temps are up, don't slam the throttles to wide open, but bring up rpm's to allow 10-15 secs to reach full throttle. When on-plane, set the trim tabs to level out. Finally, engage syncros.

My 2cw.

Spartonboat,

I'l take your advice!!

I do not have synchronizers so instead I listen for (and can almost feel) the humming of the engines like a slow Wha...Wha...Wha as I am looking at both Tachs. Your thoughts please.

Jon