Back4More

2 years later and still nobody knows....

T2x

Let me make this real simple.

A boat tends to rotate in the opposite direction from prop rotation...Therefore a single engine RH drive boat tends to lean left and a single engine LH drive boat tends to lean right.... simple physics. In twin engine boats one drive tends to counter act the other and lateral balance is improved..... whether spinning in or spinning out......... simple physics.

However!!!!!!

In a twin engine application, if one propeller is deeper in the water than another...while turning or as a result of simple lateral oscillation induced by an uneven water surface (waves)...the deeper propeller transfers more torque than the shallower prop. So if you are spinning "Out" (RH on Starboard/LH on Port) the deeper propeller will tend to drive the shallower (opposite) prop back down into the water.....levelizing the craft. If you are spinning "In" the deeper propeller will tend to lift the shallower propeller further out of the water.....increasing the outward roll of the hull....... simple physics. These forces do not change with steps, 6 blade props, bottom tweaks or any other bandaids.

Now....... As I said many of the current performance boat builders have not built sufficient bow lift into there hulls, added too much constant section or have balanced them too far forward for a given application. In some cases this is due to the builder having years of reverse rotation and compensating accordingly. Spinning out will increase stern lift in some of these hulls...... spinning in will increase bow lift ( actually reduce stern lift) in some of them as well. To me that means that there is something wrong with the boat...... not the prop rotation.

No matter how much speed you think you may be getting from reverse rotation.....the reality is your lateral stability has been forever compromised.....and some of your hull recovery in high speed turns and oscillations has been reduced.

This doesn't mean that hulls set up to spin out never barrel roll and hulls that are set up to spin in always do. It simply means that there is more of a tendency to barrel roll and roll out ward at the wrong time with a backward rotaion than with the traditional right on right/left on left set up.

In the years (decades) that I covered Offshore racing from a helicopter, I got to the point where I could spot propeller rotation from a distance simply by the added oscillations in straightaways and awkward turning machinations of the hulls spinning in. At least one World Champion thanked me for telling him to reverse his rotation from in to out before setting a World record on a particular race course. He lost a mile an hour on top end but reduced his time around the course dramatically.

There are some who will fight this simple fact to their graves and a particular era of 36 Skater that may have been tweaked to run counter rotation ( interesting that MTI's have this "tendency" too.....wonder where they came from? )

But as I said.... The facts is the facts.

T2x

Coolerman

Hey Rich, I got everything you said, and it makes perfect sense.

BUT, in high speed vee-bottoms (100mph+ or more), the boat doesn't have a wide foot-print like most cats, and spinning out creates even more stern lift leaving even less of a footprint (width wise) for the boat to run on, making it a handfull to balance (drive). In other words, at high speed in a vee, there is more lateral stability lost from the smaller footprint of the hull than there is lateral stability gained from spinning the props out.

The BT's actually have a more than normal amount of bow lift (lack of stern lift), and still, we couldn't make them work spinning out. I guess OL, Statement, and Fountain haven't either.... On our boat, from 30-80mph, outward rotation hands down wins. 80-100mph is a toss up, and 100+ no question that spinning in works better. From 30-60 or so, we do experience some roll as you had mentioned will happen.

I will agree though that spinning out would seem to be the way to go on cats. It just doesn't work on a high speed vee unless you were to have an abnormally shallow deadrise, but then that wouldn't make for a great rough water boat.
-Jason Parvey

JaayTeee

On cats, how much does drive placement in relationship
to how near the inside half of the drives were to
the edge of tunnel have on this ?

I would think that if they're wide, the dynamics
would be just like a V bottom.

But if they're close to the tunnel, where the inside half of the rotation is exposed to the water coming thru the tunnel,
that might make that half of the blade rotation be running
in deeper water, than say what the outside is.

Just thinking out loud here

Indy

You're serious?

glassdave

iTrader: (1)

Thanks, this is what i have always gone by. "Compromised ability to recover" is a grood way to put it and i was trying to find those words earlier. I started racing in 02 and started keeping track of prop rotation on various boats on the course in about 05 and i know what I've seen since then. This thread is an eye opener on V hulls for me as well, hate to say it but i did not know it applied to them as well (not sure why i didnt just assume).

TWIN-SPINS

i like the three man bolster seating in the Jet-Cat 16http://www.offshoreonly.com/forums/a...honyb61002.jpg

kap328

Reply:
I am not sure what you disagree about I did not find the answer to the question and have a hard time deciphering your post.

Sure a lot of nice photos of vintage, one off, and old time race boats of the past were posted... but they were irrelevant to the question posed by the author of this thread.

I can only assume from your post that the Glenn Curtiss & Company produced the first stepped V-Bottom. If so where did you get the information?

Where can I read about it and how they developed their hull from merely having chines to stepping the bottom.

KAP

P.S. Spin in or out depends on what hull you have, driving style and your set-up it's not like a master key or one size fits all conclusion.

Are you!

Back4More

So that why my non step with outward rotation rides and handles like a dream. Thanks T2x, I learned something today.

rlj676

Please elaborate on how you find a step to improve the ride in the ocean/rough? I am sure you've been in a step that rode better than a traditional V in the rough, but I would be nearly positive that would be due to other factors.