Engine well offset

[Marc Paulais]

Hello,

I understand that offsetting the engine well to the right in a scale hydro puts weight on the right for better cornering. At the opposite, offset to the left helps to counteract prop torque.

But, when I go through pictures of scale boats, it appears that some are offset to the right, some others to the left. And some others are not at all... Also, when I look at R Newton's plans, the Miller High Life hull (# 146) is offset to the left while the Miss Budweiser T-3, -5 or -6 (# 172) has no offset.

Finally, I just read in another recent post a Don Ferrette comment saying that engine well should be offset to the right....

So, my question is : is there a rationale behind offsetting engine well in a scale boat or is that a matter of personal choice or does that depend on hull type?

Thanks a lot for your advice.

Marc

 

[P THOMAS]

Most of the models are built with an offset to the inside (right). the full scale boats run CCW and have the engine cowl set off to the inside of the turns. The models run CW so it follows that the weight should be to the inside.

Some models cowls can be offset but the drive line can be run down the center. My Atlas Van Line is built that way because of the asymmetrical design of the stripes and lettering on the left and right. it is only 1/2 inch offset and the cowl is wide enough to cover that.

The Bud T5 I have is offset to the inside, cowl and drive line. The plans do have the offset built into the bulkhead drawings. maybe the paint drawing doesnot show this.

PHIL T

 

[Marc Paulais]

I got it.

I went through the R Newton Bud T-5 plans, and you are right. The engine well is centered but le left sponsom is wider than the right one. So the engine well is indeed offset to the right.

Great thanks Phil

Marc

 

[Don Ferrette]

I got it.I went through the R Newton Bud T-5 plans, and you are right. The engine well is centered but le left sponsom is wider than the right one. So the engine well is indeed offset to the right.

Great thanks Phil

Marc

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Marc your comparing 2 different things. The non symetrical Jones style sponsons are in fact different sizes with one being wider than the other. The tub or engine well is still offset, look closely at the deck width, measure both sides between the tub & the inside edges of the front sponsons.

 

[Mark Anderson]

Given a choice I would always offset to the left. Watch a sport or scale boat blow off, it first lifts the left sponson then rolls as it goes over. This is more evident in the turn. Really watch what is going on. We used to have a pond that was only three feet deep. you did not use a chase boat, just pulled up your hip boots and waded out. I used to go out in the middle of the turn (I know really stupid) and learned alot about what makes these things go around a corner by turning around myself. I not only want the weight to the left but also the cowl and belly pan to move the aerodynamic lift more to the right. Tune the weight balance so the boat lifts straight without rolling then work with the fin to get it to turn. You will have a much better handling boat that is alot more forgiving. Even if it does not blow off, when it lifts the left sponson first think about all the stuff that is now going through the water sideways, then the effect of the boat slapping back down.

 

[Don Ferrette]

Given a choice I would always offset to the left. Watch a sport or scale boat blow off, it first lifts the left sponson then rolls as it goes over.............

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I don't totally agree with offset having any effect on why the left sponson lifts first. What I have found is that at the beginning of the front lifting, the turn fin, which will either be angled or curved in will try to hold the right sponson down. The angle or cup of the fin initially fights that sponson lifting hence the left, not having the same level of resistance comes up faster, especially if it occurs in a turn as the fin is pulling the right side down.

 

[Preston_Hall]

Left trim only aides in the left lift as well. Maybe some of the fly aways are happening with a little left turn.

I really doubt you would see much difference in offsetting the motor. Offsetting the strut is a different story.

 

[Mark Anderson]

Everybody has there own theory. You just have to go with what works for you. My boats are off set to the left that works for me. I use little to no left trim, the boats can be turned left very well for a turnfin boat, and run the same trim wise with or without the turn fin.

 

[Mark Anderson]

An improperly set up turn fin can pull the right sponson down.

No matter what we do all boats slide some through the corner. When you turn the boat sideways you open the left non trip and sponson side to the on comming air which acts to lift the left side of the boat. Watch at a race how many boats lift off 20 feet into the corner even though they appear to have a good ride attitude. Another key factor in this is rudder pivot angle. But that is another subject.

 

[Hurricane]

Motor off set to the left and rudder on the left, and we use the fuel from the right tank before the fuel in the left with saddle tanks. That seems to be the winning combination here in RCU land. I'm not saying that we are the fastest or the anything else but the RCU champ was also the NAMBA champ a couple of years ago. Like Mark said to each there own but this combination does win! I know this works well with the 8255 hull also evan when it weighs a little more than most (20#).

 

[Bob Howard]

Tried to email Mie McKnight but they were returned. I would like to know if NAMBA allows mirroring of these boats like the other org.s. I can not find anything on it in the rule book and would sure like to know before I start building.

Bob :huh:

 

[Mike McKnight]

Hi Bob,

Sorry for the delayed response but between work, district stuff and getting ready for the Nationals I'm not up on here as much lately.

The reason you see boats with offsets one way or the other is that some boats were molded to look exactly as the real boats and they had offsets ot the left as they turned left. The direction of the offset is determined from looking from the transom forward as the direction of travel goes. Since we go fast turn right "mirroring" has been allowed for performance purposes. As long as it still resembles the real boat you're fine.

The NAMBA rule book doesn't specifically mention the offset in the measurements but it has been accepted that as long as it still falls in the 10% variances allowed in other dimensions it's ok. The one problem I have is that there are some instances where a boat didn't have an offset and the model does...in my opinion that does not resemble the real boat.

I have a couple of hulls that offset left and they have Lucero sponsons and a couple that offset right and those are asymetrical Jones sponsons. Both types lift occasionally but I've never had any of them blow off. Either way I still balance the boat the same way and make sure the power train is as close to center of the airtrap not the center of the tub. When I say "balance" the boat that means down the long axis and laterally at trailing edge of the ride pads. If you can do that well any weight issues from an offset will be minimalized.

 

[Bill Brandt]

I've come to find that getting lane one, holding it and going like a bat outta Haiti at the horn is the way to win races. Engine offset? I agree with all of you. Optimum engine and prop set-up to allow the fastest cornering and accelleration has been what has benefited me the most.

I must admit though, I'm impressed with the discussion.