Depth loss at speed

[Dill et Bound]

I have to rely on accurate depth readings due to a large tidal range, and a large area between France and Jersey and the Bay of St Malo where you can often get off and walk, a mile or two..

My Sealine 255 was originally fitted with a Stowe depth sounder, later replaced by a small Raymarine unit using the same transducer. I needed to replace an ageing GPS. Garmin 126 so

put an additional GPS Chartplotter in the form of a Garmin 551 S attached to a stern mounted Garmin transducer onboard 2 years ago..

I find no problem with either unit at speed.. They read to about 1/2 metre of each other in depths up to about 8 meters up to 22 kts.

I never rely on the split screen visuals on the 551, but tend to use the Raymarine for Harbour and anchorage work.. I have a shallow water alarm set for 2.5 meters..

In depths over 8 meters they do vary slightly more, but still give an acceptable idea of depth at higher speeds, although I have never tested with a lead and line..

I also kept the old Garmin Gps attached to my Radio on a separate circuit to the new 551,giving me DSC.

Therefore ensuring that should I blow a fuse, I have Gps available on the other circuit, and usefully depth..

 

[RogerRat]

Usually means the transducer has been positioned somewhere where the water flow over the hull is too turbulent for a reading when travelling at speed. I had this on my Targa 40; I repositioned the transducer and the problem was solved.

Interesting Jimmy, I never had a depth reading on the plane on my Targa and just guessed it was due to turbulence. Above 26 knots (minimum plane speed) I was never very concerned about depth although sometimes, it would take several minutes to stabilise again when approaching an anchorage.

I only touched once, and that was on a certain 'Pirate's' birthday celebration at East head.

RR

 

[MapisM]

Above 26 knots (minimum plane speed)

Wow, that sounds pretty fast as a min planing speed. What hull size are you talking about?
With apologies to the OP for the o/t, just curious...

 

[BrendanS]

Does anyone want to explain why my depth sounder worked fine on my Regal 2150, even when I was doing 44knts. Never had any problems at all. Spent some time with various forumites some years back using the transducer in a bag of water to find the ideal spot which often involved hanging head down in engine bay at low to high speed!

 

[RogerRat]

Wow, that sounds pretty fast as a min planing speed. What hull size are you talking about?
With apologies to the OP for the o/t, just curious...

Fairline Targa 40, same as Jimmy's. (pictured on the wake in the 'favourite picture thread'):

http://www.ybw.com/forums/showthread.php?383137-Show-us-your-favourite-pic-of-your-own-boat


It would plane at lower speeds, even down to 23ish but it never liked it. Best speed around 3000 rpm 32-33 knots when clean was spot on. She also ran very flat & smooth at 40.

She felt wallowy and unresponsive and certainly less efficient, even with a lot of bow down tab at the slower speeds. The extra weight of the D6- 370s' over the original Kad44 or Kad 300s' made the stern sit lower.

RR

 

[gjgm]

Yes

Actually I couldnt be bothered to take one of them back out, so I now have one on each side of the hull. I do find that if I slalom very hard at 40 knots or so, I do seem able to get a reading from one then the other. The drawback is that this seems to cause intense panic from any sailing boats nearby

 

[jimmy_the_builder]

Spent some time ... using the transducer in a bag of water to find the ideal spot

That's exactly what I did as well.

 

[jimmy_the_builder]

I only touched once, and that was on a certain 'Pirate's' birthday celebration at East head.

Aha, happy memories... that was unbelieveably six years ago!

 

[spannerman]

Having installed 100+ transducers both transom mounted, through the hull, glued to the inside of the hull, and oil bath, they ALL drop out around 20-24knts, its what I always check for when testing the boat, what speed it loses the signal as the owner will invariably have high expectations of his new equipment.
I just installed a monster Chirp transducer which needed a 6" hole in the hull and that dropped out at 23 knts on a semi displacement boat.
The problem is either the hull gets air under it on planing boats which interrupts the signal or there is turbulence due to the design of the hull.
Often the ideal location has no internal access or there is internal structure/machinery in the way.
The best I ever saw was 38 kts on a transom mounted transducer on a 20 ft boat, it defied all logic.

 

[RogerRat]

Aha, happy memories... that was unbelieveably six years ago!

Shuuuush, don't remind the old' feller, he's listening and watching you know...:disgust:

Notice, I kept us out of this!

 

[MapisM]

It would plane at lower speeds, even down to 23ish but it never liked it. Best speed around 3000 rpm 32-33 knots when clean was spot on. She also ran very flat & smooth at 40.
She felt wallowy and unresponsive and certainly less efficient, even with a lot of bow down tab at the slower speeds. The extra weight of the D6- 370s' over the original Kad44 or Kad 300s' made the stern sit lower.

Doh! Now I remember your boat.
Yep, getting flatter as the speed increases is actually true for most P boats, and even more so for Olesinski hulls, most of which have a more than average bow high attitude.
But a higher AoA at slower speed doesn't mean that they aren't actually on the plane.
In fact, also 23 still sounds a tad high, I would have guessed that a T40 could stay on the plane already at 20 or so, at least with trim and flaps down.
Mind, not that there's anything wrong with cruising at 30 kts, particularly when you're not getting any better MPG by slowing down...
...aside from a bit bumpy ride in the rough stuff, I guess.

Great Med boat, btw. Ever considered to follow JTB route?
.
.
.
Hang on. On second thought, forget that. You must have been asked already a zillion times....

 

[MapisM]

Does anyone want to explain why my depth sounder worked fine on my Regal 2150, even when I was doing 44knts.

LOL, you are not seriously meaning that there must be an explanation for all boat-related equipment behaviours, are you?

Truth be told, I also had a similar experience with my Fountain, and without making any effort with the installation.
In fact, she came with a factory installed depth sensor glued inside the hull, right above the keel, placed just inside the cabin door, therefore much more forward than most installations.
And when it was in good mood, I saw the display working at unreal speeds.
The explanation (well, sort of) I gave to that is that the in-hull placement allowed the sensor to work with a thick solid layer first, before passing through the turbulence inevitably connected with fast speed.
Not something I would count on, or hope to replicate, anyway.

 

[Dill et Bound]

I have checked this morning when I was out on the boat, and the figures I gave are fairly true, but it was a little rough..
I have a single installation, so the stern mounted transducer has little or no turbulence.
I said that it had the original Stowe transducer, mounted just in front the engine.. May not be, It may be a Raymarine item.. difficult to say..
Main thing, they both work fine, at planing speeds, which I realize now may be in my case a bit slow!!!

 

[RogerRat]

Doh! Now I remember your boat.

In fact, also 23 still sounds a tad high, I would have guessed that a T40 could stay on the plane already at 20 or so, at least with trim and flaps down.
Mind, not that there's anything wrong with cruising at 30 kts, particularly when you're not getting any better MPG by slowing down...
...aside from a bit bumpy ride in the rough stuff, I guess.


Great Med boat, btw. Ever considered to follow JTB route?


Hang on. On second thought, forget that. You must have been asked already a zillion times....

I agree MM, 23Knts does sound high, but she just didn't like it. You know when they feel right and it can be different nearly every day.
30+ knots is fine when fairly flat, wind and tide opposing and forget it. I took her up to 35 in a 5-6 on the nose in the Solent once and it was horrible and I doubt if it was any good for the hull either.



Great Med boat, btw. Ever considered to follow JTB route?

Not been asked very often actually, as most people that know me know that I like to be on the boat every week if possible. If the boat was berthed in the Med, I would hardly get a chance to use her as I can't take the time from work. I have to work hard to play hard if get my drift.

RR

 

[jimmy_the_builder]

Notice, I kept us out of this!

Well played!

 

[Pinnacle]

Well played!

So.......only four years to the next "big" birthday!

 

[peterjaw]

Mine lost the depth when faster than 9 ~ 10 knts. It is a transom-mount transducer.

I am thinking about relocate it, but don't know where to go.

 

[Piers]

Usually means the transducer has been positioned somewhere where the water flow over the hull is too turbulent for a reading when travelling at speed. I had this on my Targa 40; I repositioned the transducer and the problem was solved.

Jimmy is absolutely correct. Turbulent waterflow and/or air bubbles, often caused by the transducer housing/fairing block itself, can stop the depth read-out. Another is the transducer being out of the when on the plane.

One other point, many is the time I've seen a transducer painted over with the same anti-foul as used on the boat's hull itself. This is 100% wrong. You need a special anti-foul for transducers available, for example, from MDR (https://www.westmarine.com/buy/mdr--transducer-antifouling-paint--128225). I last pot I bought (they last ages) was from BT Marine (Electronics), Falmouth, t 0800 612 6731, sales@sea-kit.co.uk

More info from Airmar: http://www.airmar.com/sitesearch.html?search=mdr

Piers

 

[Glenlivet]

I’ve got two transducers, Airmar P58 to a Raymarine A50D and Simrad Totalscan to a Simrad NSS evo2, both transom mounted. The P58/Raymarine set up is quite old tech and will keep bottom up to max hull speed on my semi d Orkadian. The Simrad starts to break up at around 18 knots, despite being on the ‘correct’ side of the engine (starboard on a rh prop).

I’ve come to the conclusion that the new tech stuff is more sensitive therefore more likely to suffer at speed.

Edited to say; oops, just seen the date on the OP!

 

[Momac]

Yes its an old thread but peterjaw has brought it back to life
My depth transducer is just forwards on the engines in my stern drive boat and I have not experienced any issues at speed.