after asking the same question when i put my 585 transducer in last year, i ended up trying the cooking oil.

Works great and gives good clear readings.

cheers 

 dont run cooking oil as it kills ali when it ages.The guy to talk to is on here as PGFC he has forgotten more about this stuff than most will learn.I think i will run glycol when i build mine in unless i get told different by Rhyss.

Have just done a fair bit of internet surfing on the subject. Your boat is fiberglass, you cant run a through the hull transducer with alloy. Aparently the first thing you do is establish whether if the fiberglass is solid or a composite consruction. Assuming that it is fiberglass, and your sounder is installed, put about 20 litres of water in where you intend to fit the transducer. Take the boat for a spin with the transducer hooked up and hold it where you intend to mount it. If the reading is good mark the spot. If the reading is bad, try other spots until the best reading is found.

The wet box seems to be the best system, and I was just reading about the liquid on another forum, they said just use plain water. Top it up when required.

not ethylene glycol ,but basicly you just want somthing that wont grow bacteria and crap as your tranny will read the sediment ,they only use the glycol in cold climates so your tranny 

dont freeze  up and crack in cold climates , i used g propylene glycol in mine , only place i could find it was a fuchs sicolene anti freeze,aparently sigma chemicals sell it aswell 

I use salt water ,seems to be plenty out there and it free .I get a great clear picture .when the transducer is on the back of the boat its in saltwater not oil or coolant,don't see how these can make that much differance .Its all in the head i think/.

Is it mounted on the keel centre line or off to one side. I was intending to mount the unit off to one side as the fibreglass maybe thicker on the keel line (no keel though), but the centerline area is quite flat and would make things easier.

Intending to use a PVC sewer fitting c/w screw lid housing a modified transom mount transducer. All sitaflexed in place.

 Thanks fellas. Most installation instructions say to fill it with propylene glycol but I didn't know how hard it is to get or even where to get this from.

Spot on 225mm storm pipe with lid transducer fitted through lid stiaflexed in $160 works a treat.

Did you try the water in the hull trick B4 mounting, or a plastic bag of water,(dont really know if that would work). Or you just took the plunge and mounted it with out trial?

hey tim

i had one in my boat and i run the cooking oil(never again) messy and a prick to clean up if you change options later, also if you spill abit, even harder to seal.

i have since gone to a differant in hull tranny and is filled with collant now, much easier  to clean up.

or as paul said and use salt water.

i have got a better pic with my inhull wetbox that the one out back, allthough i think it had alot to do with my hull, just make sure you have a solid hull and not the one with foam inbetween.

good luck

Tim,

PM sent  Cheers Rhyss

 as said above coolant will work but from experience you only need a small amount to stop the growth in the water, as i have found out if you fill wet box full of coolant it will actually expand in the heat and try and escape, very similar to a radiator hence having an overflow

biggest advantage of coolant is it does not allow bubbles to form in rough seas or pounding over waves, the bubbles that can occur in sea water can disrupt your signal.

I have a 2kw 200hz in one wet box and on the otherside of the keel a 1kw 50 / 200hz as well.

In both cases sides of container are made from a modified wetbox housing I bought of a fellow Fishwreck member, but I have put allie tops on both for a good reason.

1, the allie blocks off any unwanted signal noise from the engine and deck electronics above and

2, the allie lid allowed me to mount the trannies directly onto it, so they submerge straight into the fluid.

For a relief system, I used standard fittings used for HD eletrical wirirng, the type that clamp tight like a quick fit hose coupler when fitted, this allows a breather tube to exstend above the top level of the housing, so easy to see if the level drops and if you need to refill.

Biggest trick in the book is to find your sweat wpot of your hull. I used a transducer in a plastic bag of water that I moved around the hull bottom, till I got the best signal when cruising at 10 knots, then repeated it at 15 knots, to see if any disturbances occured when going onto the plane.

for me the sweat spot is just ahead of the inboard motor and about 4 inch's from the keel line. further out is gets noisy and closer in the keels thickness dampens signal. Not every boat is the same. So do the checks, play around with different areas before making the final choice.

Not sure I want to find the sweat spot of anything tony ;)