DFF3D Transducer and GPS Setup Offsets

[MarMax]

After reading the post by flowmotion on DFF3D cross section display movement I thought a check of my offsets was in order. Sure enough I had a couple things that seemed wrong in terms of positive or negative offset.

My TM54 transducer is mounted 2 feet starboard of centerline and my GPS is on top of the house on the centerline. Here are my settings so please let me know if I have any + or - mixups.

TD mismount = OFF
TDP Bow/Stern = +8 '
TDP Up/Down = -1.5'
TDP Port/Starb = -2'

GPSP Bow/Stern = -16'
GPSP Up/Down = +9'
GPSP Port/Starb = +2' (this is the one I had originally set to minus)

RS Offset = -2'
PS Offset = +8'

It's confusing to say the least. The transducer relative to the centerline is minus 2 feet, yet the transducer relative to the GPS (since the GPS in on the CL) is plus 2 feet.

Have I done this correctly?

Edited to add a question I asked in a different thread that was never answered regarding the MFD changing the offset. For the TDP Bow/Stern setting of +8.0 feet the MFD changes this to 7.9 feet. I'll enter 8.0 and check done and the unit changes it to 7.9 after a couple seconds. Is this some internal software conversion to metric units an then rounding back?

 

[C-Bass]

Good afternoon Marmax,

Thank you for your inquiry.

So based on the numbers I want to follow up with you.

TDP Bow/Stern: 8'. So you are saying the transducer is located 8' towards the stern from the Center of Gravity of the vessel correct? The value you gave is in feet did you convert to metric?

TDP Up/Down: -1.5'. So the transducer is located 1.5 feet below the Center of Gravity correct? In the units menu did you choose "Feet" or "Meters" for the length and height section?

TDP Port/Starbard: -2'. The transducer is located 2' to starboard from the Center of Gravity correct? In the units menu did you choose "Feet" or "Meters" for the length and height section?

GPS Bow/Stern: -16'. You are saying the GPS sensor is 16' forward of the transducer location correct? In the units menu did you choose "Feet" or "Meters" for the length and height section?

GPS Up/Down: 9'. The GPS sensor is located 9' above the transducer correct? In the units menu did you choose "Feet" or "Meters" for the length and height section?

GPS Port/Starboard: 2': The way I have been taught is this is the correct measurement. The GPS sensor is located 2' to port of the transducer.

I am not sure about your add on question. I have not experienced this?

 

[MarMax]

TDP Bow/Stern: 8'. So you are saying the transducer is located 8' towards the stern from the Center of Gravity of the vessel correct?

Yes

The value you gave is in feet did you convert to metric?

No did not convert to metric. Since I've selected Feet as my units I would think that I enter this measurement in feet.

TDP Up/Down: -1.5'. So the transducer is located 1.5 feet below the Center of Gravity correct? In the units menu did you choose "Feet" or "Meters" for the length and height section?

Yes and Yes for "Feet"

TDP Port/Starbard: -2'. The transducer is located 2' to starboard from the Center of Gravity correct? In the units menu did you choose "Feet" or "Meters" for the length and height section?

Yes and Yes for "Feet"

GPS Bow/Stern: -16'. You are saying the GPS sensor is 16' forward of the transducer location correct? In the units menu did you choose "Feet" or "Meters" for the length and height section?

Yes and Yes for "Feet"

GPS Up/Down: 9'. The GPS sensor is located 9' above the transducer correct? In the units menu did you choose "Feet" or "Meters" for the length and height section?

Yes and Yes for "Feet"

GPS Port/Starboard: 2': The way I have been taught is this is the correct measurement. The GPS sensor is located 2' to port of the transducer.

Yes

 

[C-Bass]

Good morning MarMax,

To verify based on what you provided to us I feel you provided the correct offsets based on the measurements that you provided.

We will continue to research your anomaly concerning your second question. Something does not feel right about it. You also provided another forum question concerning contour lines that is similar to what your are seeing correct?

 

[flowmotion]

Marmax is correct about the DFF3D changing the tenths unit on the offsets. I have observed exactly the same thing. I put in 6.0, go to the previous screen and the 6.0 shortly changes to 5.9 for no apparent reason. I only happens on certain inputs.

 

[MarMax]

To verify based on what you provided to us I feel you provided the correct offsets based on the measurements that you provided.

Thank you C-Bass

We will continue to research your anomaly concerning your second question. Something does not feel right about it.

This is really not problematic, I just pointed it out because computers are exact so there must be some internal conversion from feet to meters then back to feet in the programming. I'll bet that if they add one more significant digit to the algorithm it may solve itself.

You also provided another forum question concerning contour lines that is similar to what your are seeing correct?

Yes, this is also not really problematic, just that it seemed unusual for you to not have consistency among the MFDs. The question is in the TZT forum regarding the shallow, safety and deep contour settings for the vector charts.

 

[MarMax]

Marmax is correct about the DFF3D changing the tenths unit on the offsets. I have observed exactly the same thing. I put in 6.0, go to the previous screen and the 6.0 shortly changes to 5.9 for no apparent reason. I only happens on certain inputs.

I'm providing this screen shot to corroborate the rounding claims. The 7.9, 1.6, 16.1 and 8.9 were all entered as 8, 1.5, 16 and 9.

 

[C-Bass]

Thank you,

I will kick them to our engineering department for review.

Kind Regards,

 

[MarMax]

I've done some more exact measuring of offsets and also started with a better estimation of the center of gravity for my boat. It's all reflected in the image below. And I'm still unclear on the +- value for transducer to GPS bow/stern. The manual says "for a stern location set a positive value". Sorry to beat this to death. Thanks for any feedback.

 

[C-Bass]

Your drawing looks good. No problem that is why we are here is to confirm your questions. So looking at the DFF3D manual the setup requires to know the location of the transducer when looking at the center of gravity of the vessel. If the transducer is located to the stern from the COG point then the value is positive. I think you measured this at 9’. You question also asked the location of the transducer to GPS sensor? So from the transducer where is the GPS located, towards the bow or towards the stern. Your drawing indicates the GPS is forward or towards the bow so it will be a negative value, I think you measured at -14.6 so that is correct.

 

[MarMax]

Thank you C-Bass!

 

[MarMax]

I'm bringing this back to life because I've been going through my notes again and just don't understand why the "+" or "-" convention for the offsets would be different for transducer to GC or transducer to GPS. Intuitively, the factory must use the same convention for both, which is how the manual seems to be written.

- for transducer to the stern of GC the value is positive "+"
- for transducer to the port of GC the value is positive "+"
- for transducer below GC the value is positive "+"

- for transducer to the stern of GPS the value is positive "+"
- for transducer to the port of GPS the value is positive "+"
- for transducer below GPS the value is positive "+"

Please clarify this again for me. Thanks.

 

[C-Bass]

Good morning Marmax,

Please see the attached photo that may help.

 

[MarMax]

Thanks again C-Bass . . and as they say . . a picture is worth 1,000 words.

 

[C-Bass]

Marmax,

Yes I know, every time I look at the explanation I scratch my head. We are in the process of reviewing the language in the manual. We may decide to add a supplemental document on the website for download that shows the picture I attached to the previous post.

 

[MarMax]

Yes, putting the example diagram in the manual or providing it separately in the same location as the manual would be very helpful. I would recommend that you make the numbers in the diagram bigger and clearer, and include the "+" and "-" convention with each number.

Here is my diagram as modified based on your instructions. I just use the CG convention vs. GC. To me it's center of gravity, which is how I learned it in school. Maybe gravity center is a Japanese thing.

 

[Bayhouse]

Marmax,

Yes I know, every time I look at the explanation I scratch my head. We are in the process of reviewing the language in the manual. We may decide to add a supplemental document on the website for download that shows the picture I attached to the previous post.

C-Bass - was this 'supplemental document' ever generated? I'm REALLY struggling with the +/- terminology and trying to reconcile it with these pics.

For example, it looks like you're taking measurements from the xducer (which is presumed higher than the keel) for CG while the manual clearly says from the Keel :questions :questions

 

[C-Bass]

Good afternoon Bayhouse,

The supplemental document was never created.

We have used the following example with good success. This example is from the TZ Pro User Guide, and we have had good success with it.