new prop and right turn

[swaycleveland]

So, i finally pulled the trigger on a new prop. the boat is a 85 4 winns 21ft 3.8 omc stringer with a 14.25x 19 ss 3 blade.. so i pulled the trigger on the 4 blade solas. I was hedging my bets on the 14.5x15 4blade for a couple of reasons. My reasons, addition of kicker motor ( 93 9.9 evinrude mounted on a omc 15hp bracket mounted on port side.) Next reason is i run with a convertible top and it adds some drag and dropped me down where with a full load i could just barely make it up to WOT rating. Next reason for the 15 pitch was going from the SS 3 blade to the 4 blade alum i was trying to compensate for that. All that being said, NOTHING CHANGES UNLESS SOMETHING CHANGES.
The only thing ive changed is the prop everything else is the same. However now she is pulling to the right i have adjusted the steering tab on the outdrive and does not help. The only adjustment i can make is my bennett trim tabs. I can adjust those to make her run straight, but that is not fixing the problem.
So.... While the 4 blade pulls nicely and got me back to the right RPMS. I do notice a bit of prop slip. I know running the tabs so out of wack to compensate is costing me preformance, plus the constant right turn is pissing me off.
Anyone think i should buy a 3 blade 17 or 4 blade 17? heck at this point ill take any ideas i can get
thank you iun advance

 

[jimmbo]

Try trimming the engine out

 

[Sea Rider]

The issue going on is when light, medium or heavily loaded. What about moving load, passengers to port to compensate, Is it possible to adjust load on wheel mechanism to help boat maintain a straight water course ?

Happy Boating

 

[Starcraft5834]

the problem is not your prop choice, sounds to me like you made a good choice there.. your at recommended rpm range now... you had increased weight in need of more punch.. the 4 blade does that for you, when you add weight such at kickers and things to the rear end, naturally it's going to toss the balance out of whack... that's what Sea's saying, moving load around.... that's more of hastle, move fat people to one side, skinny to the other...... answer? get rid of kicker?? tough one.. trim tabs?..

 

[swaycleveland]

well ive got trim tabs. and i can adjust those to compensate. as far as the load is concerned check this out. Just me- steers right Me plus someone equal size - steers right even better the kicker is on the left side !!!!!!!!! logic would say the boat should be bias to the left. Thats whats got me. I have tried what i thought to be the low hanging fruit, but i keep coming up empty on results.

 

[Fed]

Did you adjust the trim tab TRAILING EDGE towards the STARBOARD side, often people go the wrong way because they think the tab steers the boat when in fact it turns the outboard which then steers the boat. Sort of works in reverse to what you'd first think.

Failing that refer to Post #2.

 

[swaycleveland]

yes i have adjusted it in both directions an it does not seem to influence it for better or worse

 

[Fed]

Then try trimming the engine out as suggested in Post #2.

 

[swaycleveland]

OK, took the wife of perch fishing. Got our limited! Tried trimming the motor, yeah that did nothing. But thanks for the advice. Anyone got anything else that I should try.

 

[Sea Rider]

Seems that combo doesn't like being propped with a 4 blade, if with previous 3 blade prop didin't have those issues, I would go back to a 3 blade of different pitch. As usually loaded, what were your wot numbers with previous SS 3 blade 19 pitch ?

Happy Boating

 

[swaycleveland]

4k top rpm with My normal load. I forget what speed . But I don't normally run all out. I generally try to run about 3000 to 3500 at about 18 to23 mph is live to get those numbers to 2800 tpm and 20 mph but I don't think that number is possible

 

[jimmbo]

Sounds like you are over propped. An 1985 engine was probably supposed to run between 4200 - 4600 rpm.

 

[Sea Rider]

4k top rpm with My normal load. I forget what speed . But I don't normally run all out. I generally try to run about 3000 to 3500 at about 18 to 23 mph is live to get those numbers to 2800 tpm and 20 mph but I don't think that number is possible

With your "normal load" OB should be propped to achieve the max wot rpm range, say 4600 if that's the max. Once there, can throttle at your preferred boating speed. That way you'll be getting the max HP out of that OB including an incredible hole shot.

Happy Boating

 

[Fed]

I'd think being over propped or the addition of an extra blade would only cause the hull to lean to the Port rather that pull the steering to the Starboard.
When viewed from the rear does the prop go clockwise in forward gear, could you have a counter rotating one? Don't know if they made them.

 

[swaycleveland]

Yeah, I'm confused too. I'm gonna change back to my 3 blade and rethink this. I consider myself a fairly mechanically incline person and I totally gonna work this out

 

[Fed]

Assuming you maxed out the trim tab in the correct direction and trimmed the drive to the max at the same time then you're running out of adjustment options.
Something's not right that's for sure.

Steer to the right is usually a trim tab setting.
Pull to the right is usually a drive trim setting.
Lean to the right doesn't happen with standard rotation props.

I expect you can discount any hull deformations as it's fine with a 3 blade prop.

Keep us updated please.

 

[swaycleveland]

To keep everyone up to date, i went out today with my old prop ( ss 14.5x19 omc 1985 vintage ) boat steered straight as an arrow. totally under propped. With the full tank of gas, kicker and the wife sitting on the doghouse the boat could barely get out of the hole and the prop slip was so bad in the 2 to 4 ft waves i stop at the beach and put the 4 blade back on just to get some UMPH out of it.
SO here is the 10000000.00 question 3 blade 17 or 4 blade 17 both aluminium

 

[jimmbo]

You never said what Rpms you got with the old prop

 

[swaycleveland]

You never said what Rpms you got with the old prop

old prop stats
omc 14.5x19 4400 wot without kicker
omc 14.5x19 4000 wot with kicker

best speed with kicker 25 mph sog

 

[airshot]

OK something is not right here....loosing 400 rpm by adding a kicker motor? I have a 22' alum hull with a 9.9 jonnyrude and by removing the kicker I barely change 50 rpm, almost not noticible. If you getting a 400 rpm drop is the kicker to much weight for the back of your boat? Or is it mounted to far to one side? Just throwing out some ideas here as their should not be a 400 rpm drop for 100 lbs of motor weight unless it is mounted in an extreme position. Any chance of posting a couple pics for us to look at?