Air bubbles from a transducer???

[itsaboattime]

Hey everybody..............I have an 83 16' 4winns marquise with an '83 Johnson 50 hp. I picked it up last year and I have only recently really had time to get on the water. The thing is, the boat feels like it looses all power and ummmph after it comes up out of the hole on it's way to plane. It never makes it to plane. It just goes along at about 5 mph with the bow up in the air. A buddy suggested that the depth finder transducer, mounted in front of the lower unit, is creating air bubbles and making the prop ventilate. Is this possible?? And if I move it, what do I use to fill in the old screw holes?? And where would be a good spot to move it to??


THANKS!!!

 

[HighTrim]

Re: Air bubbles from a transducer???

Seems possible but i cant see it slowing you down to the speed you say. Is your boat fibreglass, if so fibreglass cloth and resin will easily fill the holes. Seems like a bad place to mount it anyways. Have you checked your prop and hub to see if its not thrown. Might also want to check the height of your motor in relation to your boat. GL

 

[F_R]

Re: Air bubbles from a transducer???

Anything in front of the lower unit is apt to make it ventilate. Move it. Or at least take it off temporailly and try it. You can always put it back on.

 

[itsaboattime]

Re: Air bubbles from a transducer???

I just put on a new prop thinking tat the prop was thrown. I will check the motor height as well.

Thanks

 

[Marc III]

Re: Air bubbles from a transducer???

I'm assuming it doesn't have power tilt and trim. Your motor may be need to be adjusted in some at the bottom of the mount. Set the "tilt pin" in the hole closest to the transom and try it again. Through trial and error you will find which hole is the best compromise between quick planing and top speeed, probably the second one.

 

[iwombat]

Re: Air bubbles from a transducer???

At the very least, the transducer mounted that close to your motor will read all kinds of noise while the motor is running. You should be moving it for that reason alone.

You can fill the holes with marine tex.

 

[itsaboattime]

Re: Air bubbles from a transducer???

Yeah..........no power tilt or trim. The tilt pin is set closest to the transom. The hull is fiberglass and I will pick up some filler this afternoon after work. The depth finder transducer was mounted there when I got the boat and it does pick up some noise while underway. There is a set of fins on the anti-ventilation plate and I am wondering if they are mounted correctly. The back of the fins are cut out to allow for adjusting the trim tab. The fins are mounted back so far that the cutout is past the trim tab. The back of them is flush with the back of the lower unit. Mabe I should move them forward at least enough so that the cutouts are where they are supposed to be?? I have never had a boat with these fins before and not sure how they are supposed to act.

 

[ezeke]

Re: Air bubbles from a transducer???

Try running without the fins.

 

[iwombat]

Re: Air bubbles from a transducer???

Not sure what brand of fishfinder you have, but look in the manual (can probably find it online at the manufacturer's site) under mounting the transducer. There's usually a minimum distance from the lower unit given.

And yeah, lose the fins.

 

[jtexas]

Re: Air bubbles from a transducer???

is the engine revving up while this is happening? engine running fast but boat going slow?

if the answer is yes: any obvious damage on the prop needs to be repaired first. Then scribe a line on the end of the propeller across the hub and rubber insert. Run the motor, then look to see if your marks still line up. If they don't, take the prop to a prop shop to be re-hubbed. If they do, then move the transducer about 18" one side or other of the motor. Fill the holes with marine-tex. Use 3M 5200 to seal the mounting screws in the new location.

if the answer is no (engine not revving up): you are describing classic symptoms of clogged carburetors. Remove, disassemble, soak overnight in carb cleaner, blow through all passages with compressed air (or aerosol carb cleaner), reassemble with new carb kits, reinstall, link & sync, adjust idle speed screws (if equipped).

 

[itsaboattime]

Re: Air bubbles from a transducer???

I just put a new prop on last weekend. I don't think it's slipping. The engine is running at 5500 - 5800 rpm. I don't think the power head is the trouble because it fires up and runs strong. The owners manual tells me that optimum operating range is 4500 to 5500 rpm.
I will move the transducer tonight. See if that is the trouble. If that is no help then I will take the fins off and see if that is any help. You know, try one thing at a time. lol

Whats the deal with the fins anyway?? What are they supposed to do?? I have seen boats with them before and never figured them out.

 

[iwombat]

Re: Air bubbles from a transducer???

The fins are supposed to give you more speed, better hole shot, cure cancer, seduce all the women on the dock, and wash your dog.

They do a decent job of washing the dog.

 

[jtexas]

Re: Air bubbles from a transducer???

good - just wanted to be clear on the symptoms. I was skeptical at first about a transducer causing that, but any time the water flow into the prop blades gets interrupted, you'll get cavitation.

Hydrofoils are useful for helping underpowered or overloaded boats get on plane.

 

[itsaboattime]

Re: Air bubbles from a transducer???

The fins are supposed to give you more speed, better hole shot, cure cancer, seduce all the women on the dock, and wash your dog.

They do a decent job of washing the dog.

too funny..............................

 

[itsaboattime]

Re: Air bubbles from a transducer???

The fins are supposed to give you more speed, better hole shot, cure cancer, seduce all the women on the dock, and wash your dog.

They do a decent job of washing the dog.

Tooo funny....................

 

[itsaboattime]

Re: Air bubbles from a transducer???

OK..........Checked the engine height and the antiventilation plate is flush with the bottom of the boat. I also was able to view the owners manual to my vintage humminbird super sixty(came with the boat) depth finder. It tells me that I need to move the transducer up or down to adjust for top speed.

 

[ezeke]

Re: Air bubbles from a transducer???

The 1983 Four Winns 16' Marquis F&S was rated for 120 HP. The motor that you have would still get on plane with a very low pitch prop, but you probably would not get much in the way of top speed.

http://www.iboats.com/Four_Winns_Boats__160_Marquise_F&S__1983/bp/64b34156r1

 

[itsaboattime]

Re: Air bubbles from a transducer???

Just to follow up.......................Moved the transducer to starboard about 16 inches. And I tried running the boat without the hydrofoils. That was a laughable experience. No plane, not even close. Way underpowered. Sooooo I put the hydrofoils back on and moved them forward so that the trim tab slots are where they need to be. The boat planes and runs pretty smooth. I won't break any speed records but I don't need to. I am pretty satisfied with where it's at. I have seen what kind of damage can happen to a boat going to fast on the Rock river. In the future if I get some cash and don't know what to do with it,(yeah, right) I think an 80 horse may find it's way to my house.

Thanks to all of you with your suggestions!! They helped me out!!