Boat steers really hard after prop swap,

[vxdude21a]

I just bought a new Solas propeller for my 1980 OMC 400 Stearn drive from , the old prop was a little out of balance, the new prop same size and pitch does not have that outer ring with the little gap in it on the outside of the propeller on the very end where the exhaust exits, (diffuser ring" )

I put that new prop on its nice and smooth but I cant hardly turn the wheel to the right it feels like if i had to turn fast and hard i might break the steering cable its so hard,

Its like day and night how the 2 different propeller effect the steering!!,

its nice and loose until i get up on step,

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Update on that reason for such a difference in the way the boat steers after swapping prop,

The new Solas propeller although the same diameter and pitch also seems to have a different blade design besides also not having a what I now know is called a "diffuser ring" the new prop uses a flair at the end too diffuse exhaust gas's,

I'm thinking that the radical change in the way it steers is the blade design,

The boat always pulled to the left and the trim tab is turned quite a bit to compensate, I'm going to back off on that and see if it helps, but I'm thinking I'm probably going to have my old prop rebuilt or get one with the same bade design to be back to having a easy to steer boat.

Anyway hope this helps anyone else that has this mysterious steering problem.

 

[SparkieBoat]

Re: Boat steers really hard after prop swap,

I never heard of a prop effecting steering that much. did you move the little trim tab??

 

[vxdude21a]

Re: Boat steers really hard after prop swap,

No I used it on one weekend, swapped the prop took it out the next weekend, the was like What the Heck?? I thought I was dragging a buoy line or something at first, its dramatically different.

 

[Texasmark]

Re: Boat steers really hard after prop swap,

Your diffuser ring prop was one of the original OMC SS designs...bet it was (Teflon) black too with a brass/bronze diffuser. They were designed as high performance props for the time. I ran one on a 125 OB for years.

Since then things have changed and so has prop technology. Only know what you told us, but yes, you experienced the effect of prop technology changes and yes, the trim tab may help overcome the problem. The tab is only so large and can only be moved so far. Trim position also plays a part in the effect of the tab....I set mine for best steering at the trim setting where I normally run. Reducing or increasing trim will have opposite effects on steering. It sets into the turn....if boat turns to the right (starboard) move the rear of the tab to the right.....with what you said, as far as it will go......which isn't all that far.

Mark

 

[vxdude21a]

Re: Boat steers really hard after prop swap,

You know I might have actually moved the trim tab the wrong way a while back,

I tore out and re glassed the Deck,transom and all the motor mounts, when I re installed the motor and drive I later found it was not perfectly aligned so I monkeyed around with the trim tab,

Evidently the new prop design is not as forgiving to a maladjusted trim tab,

I will try moving the rear of the trim tab the way it pulls,

thanks a bunch

 

[wellcraft19]

Re: Boat steers really hard after prop swap,

That little trim tab (or as I call it "trim fin") can be the difference between a safe day on the lake or a horrible accident. With too much torque steer due to an incorrectly adjusted fin, not hard to see a Teleflex (wire) steering literally falling into pieces and rendering a boat unmaneuverable.

Follow Texasmark's advice and you'd be fine - after a couple of trial runs followed by minor adjustments.

 

[vxdude21a]

Re: Boat steers really hard after prop swap,

Well I re adjusted the trim tab as per recommendations and the boat steers GREAT! ,

I'm still amazed how forgiving the old prop design was to a Mal adjusted trim tab as compared to the newer design,

thanks all for you help an comments,

 

[Texasmark]

Re: Boat steers really hard after prop swap,

thanks all for you help an comments,

Glad we were able to help and thanks for sharing your success with us. It certainly helps when considering a similar problem for the next boater that asks.......like, you had the right answer.

Mark