Where is the thrust?

[Confused]

This may seem dumb, but for a first time boater this is a good question. Where does the thrust from the prop get transferred to? The prop pushes on the drive dog, but where does it go from there?

 

[topfuel443]

ummm..... not sure what it is your asking, but if the drive dog is stationary and there is thrust cuming off of a prop, it would have to go to the rear of the boat.......providing the propulsion for the boat to go forward.

am I misunderstanding the question?

~ James

 

[Propjockey]

Chris, can I borrow a pic to demonstrate? Thanks.

Let's see...the prop pushes on the drive dog, which pushes on the strut (green), which pushes on the strut bracket (purple), which pushes on the hull (usually at the transom)...and VOILA! Boat goes forward.

 

[Zimmerman]

Yah...But... If it is a straight thru flex drive system, then the thrust goes to the engine. Unless there is not enough gap between the drive dog and the strut, then there is no thrust as the shaft will fail and what is likely your best prop will go to the bottom of the pond. the good side is... if the prop is shiny you'll get some of the best bass hits ever on the way down. 8)

 

[Ian Inverarity]

I keep hearing that sort of thing, but I know a guy who ran flex hex's on his twin 90 hydro and used to deliberately set no gap between the drive dogs, thrust washers and struts. He told me the engines moved forward too much if he didn't......

Nitrocrazed racing: Does the cable really shorten that much or does the engine get pushed forward on the rubber mounts...

 

[Zimmerman]

Back in the bad old days of hard motor mounts and even today with the relatively long shafts on hydros you get a lot of compression and torque shrinkage on the launch when the prop hooks up. Having the drive dog collide with the strut under these conditions seems to aggrevate rather than relieve the stress on the cable. A few episodes of this in a strong 45 or bigger will definitely lighten your wallet a tad.

 

[confused]

What about electrics? How much space should you leave? I heard that the endbell can be damaged by the thrust going to it, is that true?

 

[Mark Anderson]

What we used to do on our electrics is put a thrust bearing between the motor and the collet. Thrusting on the strut or thrusting on the engine make no difference in the way the boat runs. It is personal preferance. With a rubber mount seems to me that the motor is going to move forward and you would be thrusting on the strut anyway.

Mark

 

[nitrotoys]

I tried the thrust bearings on a couple, they work, but ****, they RUST. Steel ballbearings. LOL

I leave about 1/8 inch between strut and dog.

I have a real torquey gass boat, and well the crank is shimmed so theres no forward to back movment.

So i would say ALOT of it goes against the BEARINGS.

as several people have the front bearings leaking on there boats.

NT