Need 2 Questions Answered: Shoot-Thru Hull & Prop Thrust

[Tuck]

okay you wonderful carbon-based life forms (that's people to those not sure ), I have a couple of questions I need answered, and I know you're the group to ask.

1: I have a Garmin 530S that I've had hooked up for a few weeks (thanks to g3), minus the transom mount transducer. I've decided to mount it on the inside of the hull with epoxy, but I need your opinion as to the BEST place to secure it to the hull on a '77 F-32 in order to get the best signal, etc. (My initial thought is the center of the hull, in between the engines in the bilge.)

I'm assuming someone here already has a shoot thru the hull setup?

2: I've noticed that my boat's props put out an unequal amount of thrust at low speed. It's especially noticeable while spinning the boat to back into the slip. It seems the port puts out a lot more than the starboard.

(Now let me also add this tidbit. While at complete idle, the starboard engine's RPM gauge does read a bit lower than the port, they "sound" equal, and when I bump up the RPM on the starboard to make them even, the "sound" isn't right.)

I've spoken with a couple of people who have older boats (one is a Silverton '34 and the other is a Chris Craft) and they say theirs does the same thing. However, I have also heard others suggest that either I have a prop issue, or even need to fix the idle on the engine(s).

What are your thoughts as veteran Trojaniers?

Thanks in advance, yet once again.

[prowlersfish]

Check your tachs with a photo or lazer tach

[JuiceClark]

I mounted my Garmin transducer next to the stringer aside the shaft in the bilge. So, if you're looking down into the bilge, you'd see it a foot or so behind one of the transmissions. Figured that's as far forward you can go without getting air in seas.

Also, my last "shooting through the hull" transducer didn't work right because I didn't sand the roving woven down flat enough - there must have remained a little air under the transducer. Make sure and sand it flat as a pancake before epoxying to the hull. I put a bead of 5200 around the spot to corral the expoxy in the right spot.

[randyp]

Save yourself the hassle of epoxy, dams, etc and just spooge that sucker down to the floor with a big blob of clear marine grade "Goop". I did this 8 years ago and it works fine. Location on an F-32 I defer to the 32'ers out there....same with your engine/prop issues, although it sounds like it may be prop/pitch related (oops, couldn't help myself....)

[LSP]

Tuck ....if you don't mind me asking, where'd you get your transducer? I'm looking for the same type to fit a Garmin 498 I have.

[Tuck]

hey lspmiester....

the transducer came with the unit. it's a 530s...a gps/sonar combo.

the garmin site has what you need, but they're more costly than other places i've browsed. i would go to the garmin site and find out exactly what model of transducer you need for your unit (not sure if it's specific or not on what you require), and look on ebay. chances are pretty good you'll find what you need.

if i recall, transducers aren't very expensive.

[Tuck]

randy, can you explain a bit more?

is there a product actually called marine goop? (i'm about to google it. hehe)

also, another silly question...

i just cleaned a place in my engine bilge, dead center, and layed the transducer there to see if i'd get a single. nohting. yet, when i put it in a small puddle of water in my rear bilge...in the center behind the watertank, it works. so, my question is thiis: does the transducer have to be in water water for it to work when using as shoot thru hull, or does the epoxy serve that purpose?

stoooopid question i know, but i'm just making sure before i do something that'll be a mess to fix.

[rossjo]

Never tried the GOOP, but the damns, epoxy etc. that they recommend Do work ... It needs to be density similar to water all the way through - no coring, no bubbles ... Yahoo! it (Google sux) ... there are aton of aritcles on how to o it right.

[randyp]

Yes Virginia, there is a Goop. You can usually find it in hardware stores, etc. Basically a clear flexible adhesive that stays pliable when cured. It will flow into the roven mat voids and will give you an air-tight medium in which to bed the transom mount transducer (these are usually either standard with many sounders or the least expensive). Just laying the transducer on the floor of the bilge may not get it tight enough. Also, you may have placed it over the dreaded/infamous Trojan "hollow keel" that runs from about midships back to the prop shaft on some models.

I mounted mine just to starboard of centerline and about 2-1/2 feet forward of the prop. When in reverse I get some crazy readings due to prop wash, and at high speeds the sonar will not register, but at anything under 10mph I'm good to go, with the occasional bouts of "dumbass" on the monitor, but only temporarily. It worked flawlessly for nearly 500 miles of canal cruising last year.

[wowzer52]

West Marine has the transducer for a Garmin 498, though the 498 is not produced anymore.( I have one on my flybridge). The 498 and the newer Garmins all take the same transducer, though there are many different models, they all interchange. I have a 498 on the bridge and a new 400c and a 545s at the lower helm. I am a Garmin freak.

[Tuck]

okay...need more advice, specifically regarding placement.

i've mucked about with the transducer this afternoon, and the only place i can get a reading is in the rear bilge, just behind the watertank/forward of the transom. i tried using a baggie full of water to test areas in the engine bilge, but can't get a reading.

i spoke with g3, and he mentioned something about the keel of this model basically not allowing a reading due to a hollow section. so, it seems if i want a centerline placement, the only option left is the rear bilge.

with that, my question is this: how is the position of the props going affect the readings if i were to place the transducere there? is this too far back to expect a good reliable reading? are there other places in the forward/engine bilge i can place the unit, other than off center?


update; i think it'll work.

for those of you following in case you ever want to do this on a f-32...

i placed the transducer in the rear bilge, between the water tank and transom. secured it loosely with the bilge pump hose, and took off. while i had some 'clutter' on the screen, it gave accurate (based on what i remember of the local depths...coupled with the old sonar downstairs) readings. only draw back...a lot of fuzz on the screen...but again, the depth seemed right, and i had a good picture of the bottom.

i'm hoping that once i get the unit secured with epoxy, that'll take care of some of the fuzz. either way, if it gives decent readings, i'm a happy duck.

for those following who may want to try something like this, i'll keep ya's posted.

tks again for the advice from those who offered it.

[rossjo]

Two issues with the transducer in the bilge by the transom:

• 1) Prop wash can affect readings,
  2) When moving forward in unknown waters (shallow rock pile for example), by the time you get a low depth reading, you're boat will already be over the obstruction.

I think it is more important to get the transducer midships than ti have it centerline. You should be good to mount the transducer about a foot off center around the front of the engine room. Just my 2 cents ...

Mine is mounted externally at the transom, and works poorly. I have 2 transducers from previous owners glud inside, but they're not compatible with my Garmin (2 units). As I finish up my radar arch, I plan to install Garmins at both helms, with separate transducers,

Where does everyone else have their transducers mounted?

[Dan Faith]

I use garmin's on both my boats on my F32 it had a transom mounted and I used the transom mount for my Garmin works great accurate and a clean picture on the screen. On my F30 I put a through the hull one foot to the starboard side of the centerline and even with the aft part of the engine it also works great. This area has very little deadrise so it points staight down without a block.

I tried in both cases to stay clear of the props and potential bubbles they cause.

[wowzer52]

I have two transducers, (I drilled the hull) one foot out on each side of the keel, forward engine room. they both work perfect. but I can only use one at a time (lower helm or bridge) or I get clutter. The signals interfere with each other if I try to use them both at the same time. My buddy has an F-32 with the transducer glued on the starboard side one foot off the keel, forward of the engine room bulkhead (shoot through) and it works great also in all conditions.

[rossjo]

Can you run one at 50khZ and one at 200kHz? I'm surprised you're having "clutter" when running both - bbut it makes sense. I have 2 unts on my 25 - a Garmin and a Furuno dual frequency. I can run boht at 50 or 200 with no interference, but they're separated by about 7-8' at the transom.

For "shoot-thru" - how is everyone gluing to the bottom?

• Goop?
  Epoxy?
  Airmar housing epoxied to hull and filled with mineral oil?