noob question about setback?

[pcrussell50]

i know it allows you to run the motor higher, and i know it's usually good for some speed. BUT i can't visualize why? because whether the motor is set back or not, the nose cone has to be at more or less the same depth in the water, [shallower if you have a lwp, deeper if you don't]. so as long as the prop is at the same depth relative to the water, why is it faster if it is also further back?

gonna guess: is it because the water further back is "cleaner" in an aerodynamic sense?

-peter

[Riverman]

Setback moves the C of G aft allowing the bow to fly without using positive trim.

[transomstand]

i know it allows you to run the motor higher, and i know it's usually good for some speed. BUT i can't visualize why? because whether the motor is set back or not, the nose cone has to be at more or less the same depth in the water, [shallower if you have a lwp, deeper if you don't]. so as long as the prop is at the same depth relative to the water, why is it faster if it is also further back?

gonna guess: is it because the water further back is "cleaner" in an aerodynamic sense?

-peter

You might be a noob, but your very perceptive. In the final analysis, prop shaft height to the pad is meaningless, only used as a comparative reference. The most important height is propshaft to water surface.

I also believe that too much is made of "cleaner" water. Our sufacing props are all splashing around half out of the water anyway, and when you change engine position, so many things happen, I don't know any way to determine a benefit from cleaner water.

As Jeff said, the greatest benefit will be from changing balance, and the results can be pretty amazing.

[Jay R.]

Like its already been said, Balance is better to fly the hull. This means that you have more surface area out of the water causing less drag. also, a jack plate is usually recommended with a nose cone/ LWP. So with a jackplate and nose cone, you can get the gear case out of the water, again causing less drag. Supposedly the cleaner water argument stands because its more efficient. Aerated water will compress under the force of the prop pushing forward, weither this is actually happening or not I can't comment on. but its less likely to happen farther back and in cleaner water.

[Wizard]

Correct. I'll only add an anology. Think of your boat as a teter toter. The hull is one end, the engine is the other. Somewhere near the transom is the pivot point. THe closer the motor is to the transom the farther forward the pivot point the harder it is for the prop to lift the hull. Moving the weight of the engine back moves the pivot point farther back making it easier for the prop to lift.

There's alot more too it like prop slip and trim. The more trim you use to lift the hull the more the prop slips and you lose effeciency. Moving the engine back allows you to run the prop higher in the water using less trim because it's easier to lift the ligher hull. I agree the cleaner water thing is over sold but what does happen is the water flowing off the transom rises and is higher the farther back you go. This raised water column allows you to run the propshaft higher gaining rpms.

Higher rpm + less slip = faster speeds.

Hope this helps. :cheers:

[pcrussell50]

thanks, guys. especially riverman/jeff, because you have also been forthcoming with helpful answers when it comes to my v4 crossflow questions. jay, you too. oh, heck. all of you, really. :smiletest:

-peter

[transomstand]

thanks, guys. especially riverman/jeff, because you have also been forthcoming with helpful answers when it comes to my v4 crossflow questions. jay, you too. oh, heck. all of you, really. :smiletest:

-peter

Oh sure, bond with the OMC guy:p:D:D

[pcrussell50]

Oh sure, bond with the OMC guy:p:D:D

hey, a brotha's gotta go where his bread gets buttered :D

-peter

[Jay R.]

Us OMC guys are a lower class around here! we gotta stick together!!

[Riverman]

Yer welcome but remember I'm a bit of a noob too. To my knowledge everyone has offered good advice to you so far.

Don't forget about the huge advantage jackplates give - adjust-ability! The more you can mess with your setup the more fun you'll have.

[FlatSleek]

Yer welcome but remember I'm a bit of a noob too. To my knowledge everyone has offered good advice to you so far.

Don't forget about the huge advantage jackplates give - adjust-ability! The more you can mess with your setup the more fun you'll have.

Riverman over 5,000 posts hardly qualifies you as a noob:D I don't mean to sidetrack your thread Peter, I've read most boats do gain top speed with some setback and was wondering what are the negative effects or poor handling characteristics caused by too much setback, on certain hulls like on most Streams I've read no more than 6 inches is best but on hulls like my Sleek more is better, does the length of the hull have much to do with it or mainly just comes down to design?

[Riverman]

Look at Wizard's teeter-totter analogy above, it answers your question.

Longer heavier hull + light motor = most setback needed

Light hull + heavy motor = least setback needed

[400hpV8johnrude]

and a noched transom counts as part ov the setback.....the end of the pad is the pivot point not the transom

[BADTROLL]

Awsome thread! Im not new to boating by any means but im sure new to this hot boat stuff. Its nice to have an understanding of what makes these things so fast.and do it safe. Good info! IS A NOOB SAME AS A NEWBIE?

[tj309]

A Noob is the same as a Newby. Setback is dictated by the type of boat, the desired result, weight distribution in the hull, how much gas you have in the tank... and a whole lot of other factors. Every boat is different in this forum because we all try to milk every MPH out of what we have. This is not your father's bayliner.

Having said all of that if you have a hi-perf boat setback is usually desireable for the many reasons stated in previous posts. When you drive a high perf boat you are really flying it. You may have 3' of boat in the water at speed. Trim is really important here. The best combo will allow you to run at about neutral trim and fly your boat. Neutral trim = less drag in the water.

There are so many variables involved in getting that last MPH out of your boat and that is why there is no "set" formula to do it.

Try this experiment: Trim your motor in for a quick take-off - give it the throttle - get on plane - find a slow planing speed between 25 and 40 MPH, and then fine tune the trim. You will see an immediate increase in speed. If you have a hydraulic jack plate then you raise it up until WP drops and put it back down just a bit to regain WP - and then you open her up!