Tabs down or drives in???
 

Would someone help explain a comment Teague made in Powerboat regarding tabs and drive setting. He mentioned that for step bottom boats you are better off setting the tabs down a little and the drives at neutral trim for flying level and running in rougher water.

My question is why is this better than leaving the tabs up some or all the way and trimming the drives in. Assuming you can trim the drives so that you run level. Does this effect speed and or ride comfort?


Thanks,
Rick

I belive the reasoning behind leaving the drives out is to prevent burying the bow and causing a bow steer problem, which could be a problem with a step bottom boat.

I understand you don't want to drive the bow down so hard that you get bow steer. However, in rougher water I thought you wanted the bow down to cut through the wave instead of bouncing on the top of it. Don't you get a more comfortable ride cutting through than pounding on top.

Tabs that are level or slightly down actually extend the boats running surface. Flying level from wave top to wave top is a much smoother ride then busting through waves or going up and down if the boat speed isn't fast enough to fly.

Does the fact that neutral drive position, keeps the prop at optimum thrust angle have anything to do with this??? I really dont know, just another aspect though.....

They way ive been told a few different times is that in a step bottom boat you dont want to tuck the drives cause you will get bow steer and during a turn you can hook or even worse roll the boat. I guess that where alot of people get in trouble switching from a non-step to a step hull...
As for the tabs....like it was mentioned above...it increases the running surface of the boat :)

Someone please set me straight if this is wrong.. :D

As it was explained to me, bow steer and wrong pivot point are pretty much one in the same thing in a step bottom boat. In a single step boat, the pivot point when steering is exactly that one step. When you are in a multi-step boat, and you are in an other than ideal postion in the water, the bottom of the boat can pick a different spot to pivot on for a turn or an unexpected maneuver.
BT's comments make sense to me, that you would want to keep the drives constant, for obvious consistancy, and try to control flight/ride level with the tabs.

My experience has been similar. depends on the waves, but usually I do not trim the drives in all the way, I leave them out and use a little tab. Rides smoother and the bow doesn't tend to nose dive as much. Plus I run a little faster that way:)

"Ideally" one wants to find the balance that provides for the boat to, for lack of better words, "skip" across crest to crest of each wave. This involves tuning the right amount of tab/trim and, let's not forget, THROTTLE. Too little or much of either will put you in the pounding scenario. Is this true for every outing you make? Not even. Wave heights, span, consistency, winds, boat loading, etc. will demand a slightly different approach each time. But one could say the tab/trim setup described by Teague is a good starting point...

Thanks guys for all of the input. Like stated above, it is a good starting point. Then tweek from there by feel.

Rick

It's nice to see a good topic like this...

I'll throw a wrench into the works here...since the transom is the last part of the hull to leave the water when taking flight, wouldn't the tabs have a tendency to push the attitude of the bow down since they are lowered a bit? Or does the fact that the drive is basically neutral and the tabs aren't down that far negate any tendency to drive the bow down?

What you don't want to have happen is for the stern to land first. This is the first step in creating a stuff situation. AND YOU DON'T WANT TO STUFF IT!!!!!!!!!!

Plus it unloads the drive so you are not at a bad driveshaft angle. The engine does not labor as much.

Ron P...
What part do you want to land or re-enter the water with?
I'm just trying to picture all of this.
But haven't I seen in magazines statements about step bottoms of in racing or high speed turns to just tuck the drives alittle and then raise them as you come out of the turn? The problem has been that steps are loose and thats the reason for tucking in a turn.
??????

I always though "stuffing" was caused from something like too much tab, and when you launch the stern of the boat is abnormally forced down and not left for the motion to carry it upward off the wave, bringing the bow down and the bow hitting first into the rise of the next wave.

Hitting the stern first, causing the bow to slam down on the water, well, I'd call that just one hard ass landing:) But there is probably a name.

BUt I agree, you don't want the stern or the bow to hit "first", you want the middle center point of gravity of the boat to hit first for a decent landing. Or in effect, the boat to land level, or all at the same time.

And what are you guys doing launching boats? Why don't you slow down and not get any air? (that's what my wife asks anyway...) LOL!

Mark

I agree with 32 Fever, you should land on the center of gravity. I would also watch tucking in the drives too much in a turn on a step boat. The ass is loose enough and the pivot point is already very far foward so you don't want to give the bow any more bite than it has. I'd say nuetral to slightly up in a turn.

A stuff happens when you fly off one wave top, and then with the bow raised in the air, you land stern first on the top of the next wave. This now trips the transom of the boat higher than the bow and it goes into the third wave nose first. Watching those freeze frame slow motion shots will show ya how it's done.

If the boat was flying level the ass hitting first wouldn't make much of a difference. It would just skip off the wave and onto the next.

The other danger is since the bow is being slammed down at a greater than normal speed, the passengers feel the boat falling faster than they are, so when it finally hits, thier feet are off the ground.

Finally, if you run a stepped hull I would strongly suggest you follow T2Xs advice and spin your props outward. This will aid in keeping things in order when going around a turn.

See the greatest moments in V bottom history thread for this topic about prop rotation theory.

Understand I'm speaking about running at race speeds. It's hard to make a boat fly level at 45mph. You need to be moving better than that for level flight.

TTT

Any more thoughts?

Just a thought?!
This could be related to the whole idea of the longer the boat the smoother the ride. If you are riding a rocking horse it will beat the (#%)%( out of you. If you are LONG ENOUGH it will be nice and smoooooth.
Nose level, drives level, tabs level,(creating the longer waterline) skimming the tops of the waves, you will be faster.
Did I get it right?

Ron,
You mentioned it is hard to fly level at 45mph. What speed do you need to be at before that starts to happen?

Rick

Opie bigger is better. It helps the span the waves. A 40' footer could have the bow on one wave and the stern on another. In these same seas a 24' boat would be going up and down, unless its going fast enough to fly from wave top to wave top.

RV, I'd say this happens around 55 or 60 for most hulls. The faster you go the smoother it gets. This also means that you know how to read the water and throttle the boat so you don't get yourself into trouble.

Some great info here.

What would you do???

Running in moderate seas and need to tuck in a LITTLE drop drives slightly or tabs slightly? Assuming you dont need to do both.

I think Ron has a good point...at 45 my 28' is just loping around and the hull isn't getting on top of much if it's choppy, however, as I approach 53-55mph, there is a whole different feel to it and it rides much better. You really need to start paying closer attention to things as you reach that speed and higher.

Buy a big boat, trim the drives to just before blowout, AND LET HER BUCK, Between 80-90 they seem to fly real level! Tabs, I didn't even know I had tabs.:D Midnight:cool:

Always leave the tabs level with the bottom and use the drives to change your trim angle. Tabs are used when the drive movement is not enough.

When I raced, the throttles never came off the stops (unless we were in flight) regardless of conditions. The difference in speed was in the trim settings. Granted we had a canopy and five point harnesses, but you get the point. Our best trick for trimming the boat was the bow ballast tank that would hold 40 gallons of water. We also had electric pumps to move the fuel from the back tank to the front tank to change the center of gravity. We also could choose which tank we suck gas from. Mr Technology, had all the toys.

Doesnt keeping your tabs level require you to use more drive trim? By using the tabs to extend the running surface further back, its like the oposite of having an extension box. Your bringing the end of the hull closer to the prop thereby reducing the leverage the drive has on the hull. Just thoinking out loud and the truth is likely the same as props...test cause every boats different.