4 blade vs 3 blade torque

[dingbat]

It has a 14x20” Enertia prop. If I let go of the steering wheel at anything trimmed down to neutral or anything below 25-30mph...the boat will violently throw itself to starboard for certain

Interesting. Other than when transitioning from off to on plane, I get very little if any prop steer.

My 15 x 15 Enertia does not exhibit the characteristic problem nor does the 14 x 17, Offshore Renegade (4 blade).

Then again, I don’t use trim to control the running angle of the boat. Trim is kept neutral and tabs are used to adjust the running angle of the boat.

 

[flyingscott]

Maybe you guys should check out the Sharrow prop. I heard it almost eliminates torque steer.
Torque steer is normal usually on an outboard it can be trimmed up to eliminate it or reduce it. On an I/O could be the prop itself something not aligned something bent or broke.

 

[JimS123]

Interesting. Other than when transitioning from off to on plane, I get very little if any prop steer.

My 15 x 15 Enertia does not exhibit the characteristic problem nor does the 14 x 17, Offshore Renegade (4 blade).

Then again, I don’t use trim to control the running angle of the boat. Trim is kept neutral and tabs are used to adjust the running angle of the boat.

Prop steer is a function of the trim angle and the trim tab position. In other words, if you optimize the "system" for neutral pull, once you trim up or down you'll throw it out of balance and get some prop steer again.

OB or I/O, you basically have the same leg in the water. In my experience both needed to be adjusted if you wanted zero torque on the steering wheel.

Some I/Os that have power steering use a flat anode with no tab. Since you don't feel the torque I guess Merc feels that the tab is not necessary.

Some years ago with my I/O the first time out in the Spring I felt an unusual steering pull on a rig that had previously been optimized. When I got home I saw that the tab had broken clean off. A new part fixed it back to normal.

 

[dizzy1]

I can speak from what i found on my 20' I/O Reinell 5.0GL. Had 3 blade prop when i bought it, never listed but lacked pulling power for a 4 seat tube or pulling wakeboarder up fast enough. Went to a 4 blade few years later. Boat instantly had the listing issue you described but pulling power was impressive with little to no impact on top speed. I moved batteries and equipment around in boat to try to offset list, but still happened. Year after put on Smart Tabs and even tried a softer actuator on the high side. Still listed under power. This past year got a different 4 blade and still had list. For fun, put the old 3 blade back on one day and list was completely gone. So either deal with list if you want that extra holeshot for watersports or put on a 3 blade and stay level. Just my 2 cents from experience.

 

[Fed]

QBhoy, if you can't fit a trim tab to the motor I think you will have to be more aggressive with your trim up position to neutralise your steering. Having said that you may have to also move a bit of weight forward to keep the hull's attitude nice.
It's all to do with the blade angle of attack difference between the up stroke blade vs the down stroke blade.
I liken it to herding cats.

 

[Fed]

Nearly forgot the OP, yes mate a 4 blade prop will make it lean more.

 

[QBhoy]

Maybe you guys should check out the Sharrow prop. I heard it almost eliminates torque steer.
Torque steer is normal usually on an outboard it can be trimmed up to eliminate it or reduce it. On an I/O could be the prop itself something not aligned something bent or broke.

Haha. I nearly bit the hook you’d cast out there !

 

[QBhoy]

QBhoy, if you can't fit a trim tab to the motor I think you will have to be more aggressive with your trim up position to neutralise your steering. Having said that you may have to also move a bit of weight forward to keep the hull's attitude nice.
It's all to do with the blade angle of attack difference between the up stroke blade vs the down stroke blade.
I liken it to herding cats.

Thanks Fed. You’re totally right. I had mentioned as much just not long ago. It needs trim to sort it out for sure. Just that occasionaly the sweet spot is a little faster than ideal in rough stuff.

 

[QBhoy]

Interesting. Other than when transitioning from off to on plane, I get very little if any prop steer.

My 15 x 15 Enertia does not exhibit the characteristic problem nor does the 14 x 17, Offshore Renegade (4 blade).

Then again, I don’t use trim to control the running angle of the boat. Trim is kept neutral and tabs are used to adjust the running angle of the boat.

Interesting. Do you have fancy steering or power steering ?
i think my case is further amplified by a narrow deep v hull. She is easily unsettled...but also a superb hull in the rough.
sorry to hi jack the post.

 

[QBhoy]

Merc makes 3 types (I guess after Jim's comment about a flat one). One is full width, the second is about half width and effective for high rake prop clearance like you would have with a bass boat and the other is flat....per Jim.

I ran a TP 14" diameter 3 blade wheel on my last engine (2002 2 stroke 90ELPT) for a test with the half thickness anode and just cut a chunk out of it for the prop to clear.

i had NFB steering on that boat and liked it....it's my avatar. Current boat apparently doesn't and steering is very sensitive to trim position, being Port favoring above mid trim, pretty well compensated at mid trim (tab all the way to Port....which isn't but 10-15*) and Starboard favoring below. With my engine now down on the transom, more of the LU is in the water and as a result, the tab position is more pronounced. When up in the 4th hole I just ran it amidship as I wasn't in the water much.

Thinking about where I am now with finding the clogged fuel filter, I might jack that sucker back up to the 4th hole, put that Ballistic 22XL back on there and see if she will top 50. Slip on the TPS is running around 5%. GO-Fast PSC says that 50 is a piece of cake with it.....but once I prove the point (that the PO did in fact run the Ballistic as his every day prop), it would be back down on the transom and the 17P 4 blade for my soft ride in a good chop at a moderate speed. Yak yak, gab gab. Bed time. Bye!

Good wee read there. Good to hear.
think I’ll try a tab, even if it’s a cut down one for clearance. It’s a bit of a pain. I’ve gotten used to it now but was certainly a pain if I have driven the other fast boat not long before jumping into the cuddy.
I pretty much used the cuddy for most of the year. Really taken by it. Managed to get it propped perfectly with only a little slip. About 4 or 5 from memory. Likely bored you all with it by now. But can’t tell you enough how good the mercury 115 2.1l command thrust is. So powerful. Certainly putting out more than 115hp for sure. Incredibly managing 44 mph gps with that power is amazing. It’s 19ft cuddy and a deep v hull. It’s a fact that fletcher boats are always known to be quick, but wasn’t expecting that at all from it. The same hull in the open version and a 225 will be touching 70. Amazing things.

 

[Texasmark]

Thanks for the replies. Chris, you are correct that tracking is part of it. We correct with rudder in a subtle way that goes unnoticed by most boaters but I disagree that props don't cause list. List and tracking are related. A right hand prop will "twist" the boat down on port up on starboard. This is the same reason helicopters have tail rotors. If not for the tail rotor they would spin in circles. I believe the center console crowd deals with this more than guys like me due to the weight being centered. This is why lots of center consoles come standard with trim tabs. Yes I'm probably overkilling this but what the heck it's cold out and I like thinking about boating situations haa.

Take the function to the limit. If the prop were to instantaneously lock to the engine, like say at WOT, since it's delivering the thrust against the water, the opposing water pressure would be (is normally) against the face of the blade, since the face of the blade is physically "thrust" against the resisting water. Were it to lock up, the prop, aka engine, aka boat would be "thrust" backwards (Physical law of forces-reactions) which would push the Port side of the boat down.

I just talked myself out of what I said last night. I was 180* out all these years wondering whey they moved the helm to the Starboard side and now I know and agree with all the yeah sayers here that Starboard helms help to counteract yawing caused by Rt. hand driven props.

Don't believe it, grab a spinning shaft (keeping it within reason for safety's sake) and see which way your had goes/wants to go.....opposite to the direction of rotation. Doing that to a boat puts the Port side down in the water, opposite to the direction of rotation of the prop.

Another example and surely most of you have been drilling a hole to have the bit lock up in the material like steel while the motor was at high speed......which way did the handle go? On the normal right hand drill bit, it went CCW and I have hurt myself while using hand held battery operated drills with the ½" chuck (Ryobi) and a ⅝ or so, cut down shank drill bit, at high speed, lock up ....when the tip of the drill just attempts to pass out of the metal, and jerk my wrist.

 

[QBhoy]

Take the function to the limit. If the prop were to instantaneously lock to the engine, like say at WOT, since it's delivering the thrust against the water, the opposing water pressure would be (is normally) against the face of the blade, since the face of the blade is physically "thrust" against the resisting water. Were it to lock up, the prop, aka engine, aka boat would be "thrust" backwards (Physical law of forces-reactions) which would push the Port side of the boat down.

I just talked myself out of what I said last night. I was 180* out all these years wondering whey they moved the helm to the Starboard side and now I know and agree with all the yeah sayers here that Starboard helms help to counteract yawing caused by Rt. hand driven props.

Don't believe it, grab a spinning shaft (keeping it within reason for safety's sake) and see which way your had goes/wants to go.....opposite to the direction of rotation. Doing that to a boat puts the Port side down in the water, opposite to the direction of rotation of the prop.

Another example and surely most of you have been drilling a hole to have the bit lock up in the material like steel while the motor was at high speed......which way did the handle go? On the normal right hand drill bit, it went CCW and I have hurt myself while using hand held battery operated drills with the ½" chuck (Ryobi) and a ⅝ or so, cut down shank drill bit, at high speed, lock up ....when the tip of the drill just attempts to pass out of the metal, and jerk my wrist.

I love to read something like this, but without being cheeky. A RH rotation prop will throw to the starboard side of not a force of counter action to stop it.
the drill is a good theory, but it’s slightly different. The outboard has another axis to move on if you like. The force of the prop trying to walk to the right means the engine will throw to the right, steering the boat to starboard.

 

[Texasmark]

I love to read something like this, but without being cheeky. A RH rotation prop will throw to the starboard side of not a force of counter action to stop it.
the drill is a good theory, but it’s slightly different. The outboard has another axis to move on if you like. The force of the prop trying to walk to the right means the engine will throw to the right, steering the boat to starboard.

Well it's not pristine, cut and dried, and I dare not try it but it is a theory.....might be hard to prove......no proof, no puddin: "The Proof is in the Pudding" (source unknown....to me...assume it means the pudding's taste will prove out it's worth to the consumer) On the grab the rotating shaft thing, after thinking about it, I don't think that is a good analogy.

So, backing the truck up (don't know that one either), why the industry shift from Port to Starboard and remaining there for decades to date?

 

[JimS123]

I love hearing engineering stuff to prove a point. But sometimes the answer is right in front of you because you saw it with your own eyes. First hand knowledge trumps all (no pun intended).

Why does the lake freeze over, while the fast flowing river does not? It's moving too fast! (kinetic energy)

Why did Lyman put a port steering wheel on my boat when RH props were the norm in that era? I dunno.

Why does a boat list to port with a RH prop? Every boat I ever owned worked like that. (except the Bravo 3)

 

[Stinnett21]

Thanks dizzy and Fed. That's what I was wondering. I would love to install tabs to play with and counteract but my boat has huge sponsons at the transom. They prohibit mounting anywhere but toward the center between the keel and the chine and I'm hesitant to spend money and drill holes only to find out the port tab buries the bow before any meaningful lateral adjustment occurs. Thinking I may stick with my 19 Vengeance. Yes I know it's ancient technology but my numbers are excellent and tbh I'm very satisfied with it. Then again I don't have anything to compare it to other than a 21 Vengeance.

 

[dingbat]

http://www.killcaremarina.com.au/commonly-asked/60-boating-performance

 

[Stinnett21]

Very good article dingbat. Thanks for that.

 

[Fed]

Figures 8-24 and 8-26 are wrong, I advised Mercury many Years ago & they removed that article from their website.

In addition to Copyright or Copywrong? © 2019 Killcare Marina

Shame on Killcare to claim it as theirs.

 

[Texasmark]

Jim on my outboard powered cuddy. It has a command thrust gearbox so takes the big merc props. Unfortunately it has no power steering so you feel every effect.
It has a 14x20” Enertia prop. If I let go of the steering wheel at anything trimmed down to neutral or anything below 25-30mph...the boat will violently throw itself to starboard for certain. It’s a RH prop.

What you said is right out of the Mercury service manual (the one I quoted a few days ago covering my 115 carbed). In the front are detailed explanations concerning using and maintaining your new engine. Trim tab is specifically mentioned with respect to trim positions and it clearly states that at mid trim positions, tab is neutral....for high trim positions (with right hand turning props which this engine turns) it has to be set to the left (Port) to offset the torque and for negative trim positions it's just the opposite. It goes on to say, what we well know in that the higher the AV plate is mounted, the less the effect of the tab.

My current boat has that personified: The PO, as it's proving to me, not somebody swapping parts at the dealership, had a 22P Ballistic SS, engine jacked up in the 4th (highest mounting position) hole and the TT was centered.

When I was dropping my engine I noticed that at high trim positions, the Port steering tendencies got heavier and I had to put the tab as far as it would go to the left after I got to the last hole )engine sitting on the transom), which helped but still had a good (undesired) feedback at higher rpms. Course the more you compensate for that the worse the negative trim right feedback. I had a Teleflex no feedback steering in my last boat. Don't know what's in this one, but being a Crestliner I would expect it to be no feedback.

 

[dingbat]

Figures 8-24 and 8-26 are wrong, I advised Mercury many Years ago & they removed that article from their website.

In addition to Copyright or Copywrong? © 2019 Killcare Marina

Shame on Killcare to claim it as theirs.

The copyright is on the website. No credit on the article.

Please explain how the figures 8-24 and 8-26 are incorrect