Flush mount Through hull transducer issues on a 270 Islander

[Crgator]

I Just installed a Airmare 1kw flush mount transducer on my 270 Islander at the rear area of my transom , unfortunately It will not read when moving but works great when stopped and fishing .
Anyone else have any issues running a flush mount on these hulls ? Apparently the dealer thinks it’s air bubbles coming off the forward now streak ?
Any thoughts ?

 

[Sardinia306Canyon]

Your dealer is unfortunately right, what you see are the air bubbles travelling over the transducer surface.
Air bubbles from the bow area travel attached to the hull towards the stern but over the distance they tend to move side- and upwards and that makes the near stern keel area what is the deepest position the best place for flush mount transducers.
Worst transducer positions are behind any protrusion, water intakes, water outlets, paddel wheels, strakes, steps, etc, etc as they create turbulence and move/mix the stream of bubbles again.

That is what a High Speed Fairing Block is for, it keeps the air bubbles moving attached to the hull away from transducer surface, but they interfere with a trailer. High Speed Fairing Block is also to cut to the boats hull angle at mounting position to have a thru-hull transducer pointing straight down.
Some boats like some Grady-Whites have a flat transducer mounting pad, but in kind of a pocket what i would not use without fairing block, but the flat, horizontal surface makes cutting the fairing block to boats hull angle unneccessary.

Flush mount transducers will work at speed almost only there, rear, center keel.

Unfortunately here is nothing to do except removing the transducer again and position in a different location or add a spacer to have the transducer surface sticking out of the hull to be in cleaner water.

Can you show some photos, that would be very helpful to assess better, from side and back to show position and eventual protrusions.
Also what transducer did you installed, a big B265/275 or one of the flat mushroom shape B175 type ones?
I had a B165L on my RIB when i bought it used and it was reading perfectly up to 30 knots, but installer found perfect position.

Chris

 

[seasick]

I also would like to know what model transducer you installed, tilt angle if any, offset from keel line if any and confirmation that the arrow on the transducer faces the keel if offset from the keel or arrow points to the bow if 0 degree model and no offset.

One more question, how far off of the transom is the ducer positioned?
Chris asked about the transducer model and it will help to know in addition to the model, what the mounting surface on the hull is like. ( recessed raised, fairing block etc.

 

[Crgator]

Your dealer is unfortunately right, what you see are the air bubbles travelling over the transducer surface.
Air bubbles from the bow area travel attached to the hull towards the stern but over the distance they tend to move side- and upwards and that makes the near stern keel area what is the deepest position the best place for flush mount transducers.
Worst transducer positions are behind any protrusion, water intakes, water outlets, paddel wheels, strakes, steps, etc, etc as they create turbulence and move/mix the stream of bubbles again.

That is what a High Speed Fairing Block is for, it keeps the air bubbles moving attached to the hull away from transducer surface, but they interfere with a trailer. High Speed Fairing Block is also to cut to the boats hull angle at mounting position to have a thru-hull transducer pointing straight down.
Some boats like some Grady-Whites have a flat transducer mounting pad, but in kind of a pocket what i would not use without fairing block, but the flat, horizontal surface makes cutting the fairing block to boats hull angle unneccessary.

Flush mount transducers will work at speed almost only there, rear, center keel.

Unfortunately here is nothing to do except removing the transducer again and position in a different location or add a spacer to have the transducer surface sticking out of the hull to be in cleaner water.

Can you show some photos, that would be very helpful to assess better, from side and back to show position and eventual protrusions.
Also what transducer did you installed, a big B265/275 or one of the flat mushroom shape B175 type ones?
I had a B165L on my RIB when i bought it used and it was reading perfectly up to 30 knots, but installer found perfect position.

Chris

Your dealer is unfortunately right, what you see are the air bubbles travelling over the transducer surface.
Air bubbles from the bow area travel attached to the hull towards the stern but over the distance they tend to move side- and upwards and that makes the near stern keel area what is the deepest position the best place for flush mount transducers.
Worst transducer positions are behind any protrusion, water intakes, water outlets, paddel wheels, strakes, steps, etc, etc as they create turbulence and move/mix the stream of bubbles again.

That is what a High Speed Fairing Block is for, it keeps the air bubbles moving attached to the hull away from transducer surface, but they interfere with a trailer. High Speed Fairing Block is also to cut to the boats hull angle at mounting position to have a thru-hull transducer pointing straight down.
Some boats like some Grady-Whites have a flat transducer mounting pad, but in kind of a pocket what i would not use without fairing block, but the flat, horizontal surface makes cutting the fairing block to boats hull angle unneccessary.

Flush mount transducers will work at speed almost only there, rear, center keel.

Unfortunately here is nothing to do except removing the transducer again and position in a different location or add a spacer to have the transducer surface sticking out of the hull to be in cleaner water.

Can you show some photos, that would be very helpful to assess better, from side and back to show position and eventual protrusions.
Also what transducer did you installed, a big B265/275 or one of the flat mushroom shape B175 type ones?
I had a B165L on my RIB when i bought it used and it was reading perfectly up to 30 knots, but installer found perfect position.

Chris

Thanks for all that great info ,it’s all in line with what my dealer was telling me . Unfortunately the boat originally came with a high speed fairing block and transducer but I was worried about hitting debris or a log and causing more damage , and it was also a low power transducer . So I had it removed and replaced it with a 21 degree B175M thinking bigger the better .
It’s only a couple feet at most from the stern area . I hate to remove it again , but I think it will be a winter project now .

 

[SkunkBoat]

Thanks for all that great info ,it’s all in line with what my dealer was telling me . Unfortunately the boat originally came with a high speed fairing block and transducer but I was worried about hitting debris or a log and causing more damage , and it was also a low power transducer . So I had it removed and replaced it with a 21 degree B175M thinking bigger the better .
It’s only a couple feet at most from the stern area . I hate to remove it again , but I think it will be a winter project now .

but I was worried about hitting debris or a log and causing more damage
This is not a thing...

Thats a big hole to fill...Leave it where it is. Use it trolling and drifting.

Assuming you have two inputs on your sonar...Get a thru hull with a 50/200khz. (B265LH) Put it centerline about 1-2 feet from transom. The 50khz will read bottom best at speed and deepest bottom.

You didn't say what brand/model sonar. If you have available sidescan, get an All-in one thru hull with the lowest frequency they have. mount centerline without a fairing.
Unfortunately, the lowest freq is probably same as your B175M.

 

[Crgator]

but I was worried about hitting debris or a log and causing more damage
This is not a thing...

Thats a big hole to fill...Leave it where it is. Use it trolling and drifting.

Assuming you have two inputs on your sonar...Get a thru hull with a 50/200khz. (B265LH) Put it centerline about 1-2 feet from transom. The 50khz will read bottom best at speed and deepest bottom.

You didn't say what brand/model sonar. If you have available sidescan, get an All-in one thru hull with the lowest frequency they have. mount centerline without a fairing.
Unfortunately, the lowest freq is probably same as your B175M.

but I was worried about hitting debris or a log and causing more damage
This is not a thing...

Thats a big hole to fill...Leave it where it is. Use it trolling and drifting.

Assuming you have two inputs on your sonar...Get a thru hull with a 50/200khz. (B265LH) Put it centerline about 1-2 feet from transom. The 50khz will read bottom best at speed and deepest bottom.

You didn't say what brand/model sonar. If you have available sidescan, get an All-in one thru hull with the lowest frequency they have. mount centerline without a fairing.
Unfortunately, the lowest freq is probably same as your B175M.

Ok thanks . I’m running the new Furuno TZT13 . Love it when trolling but it would have been nice to read also when cruising . We tried play with the frequency down to 80 but still no luck .
I’m also running a smaller Garmin with a transom mount out the back between the twin motors and it hasn’t missed a beat cruising or trolling . It’s a 9” echomap .
Thanks for all the great info . Wish I would have asked first before I did all this work .

 

[Sardinia306Canyon]

Wish I would have asked first before I did all this work .

Yep!

Yes there is a risk to hit something floating with B265/275 or similar transducers on their high speed fairing, but damage would be limited.
There are boaters who boat in lakes full of drift wood and there it's something to consider, but in the sea i would not and never did.
I lived and worked 14 years November to May in Costa Rica and floating logs are common and in thousands and thousands of hours i hit once one of this logs.
The damage was at the outboard who hit the log with the midsection and lower unit vertical, a log would just get pushed away by a high speed fairing.
But yes, shit can happen, but i would not consider that as reason to remove a fairing block and my B265LH is center keel on full hight fairing block.

I also would not remove and glass the hole, doable but a lot of work to do it right, if the hole is the same of the old transducer, just wider then you may reduce it's size and install again a B265/275 LH or the LHW.

The stem of your B175M should be long enough to add a fairing block/spacer between hull and B175M to get transducer surface in cleaner water.
I did a quick search and could not find one ready to buy, however it should not be difficult to make a spacer, basically a big, conical washer about 1 inch thick.
If it works i can't tell you, but it probably does if there is nothing in front of the transducer what produces turbulence or bubbles.

As SkunkBoat already mentioned, installing a second one would be much less work.
B265LH or B275 LHW would be the option, the model just depends on how you fish as the B275LHW has extra wide high frequency cone for drifting/trolling but that is not very useful for bottom fishing as the cone is so wide that you see fish or structure but don't know exactly where they are. However you could use low freuency for bottom fishing isntead of high wide frequency.
I have the B265LH and can read bottom deep as 1000ft at 29 knots and 5500 ft when stopped/drifting using the Garmin GSD26 blackbox.
My second transducer is a GT51M-TM Side-Scan transducer on the transom and love it, but same problem as you have, it will not read at 12 knots +.
My problem is that i have to install the GT51M-TM between the engines but about 15 inch in front is the B265LH on the fairing block what 99% is the culprit as it creates turbulence to the GT51M-TM. However not reading at speed does not matter to me as i have the B265LH for that and to get best Side-Scan images speed should be below 12 knots.
You may use the GT51M-TH and install it center line or if you have nothing in front same GT51M-TM on the transom just right hand of the drain plug and between the outboards. That would be the least intense installation and once you have height and inclination set correct the GT51M-TM should read up to 25/28 knots if not more.

Chris