Tips for driving stepped bottom boats
04-25-2003, 09:19 AM
#31
Enjoy the show
VIP Member
Join Date: Feb 2001
Location: The Joisey Shore
Posts: 10,353
Likes: 0
Received 0 Likes
on
0 Posts
This was posted by T2x on the cat thread and I thought it really belonged here......
====================
From: T2x
Ron P.--My thoughts on "spinning" in..... Simple physics.... Right hand rotation propellers,torque (lean) the boat to the left. Left hand rotation propellers torque the boat to the right. In a twin engine boat spinning outboard or , RH on right side, LH on left, the torque of the propellers tends to return the boat to level when one side or the other leans outward. When props are spun inboard RH on left, LH on right, or counter rotated the torque tends to make the lean worse. This occurs because as a boat(Cat or Vee) leans to one side, the prop on that side buries deeper and exerts more force, while the prop on the other side rises (in some cases out of the water) and exerts less force. So...... If a RH prop is spinning on the right side of a boat leaning to the right, the prop tends to push the hull back over to the left. (spinning Outboard). If, however, the left hand prop is on the right side in a right hand lean , the prop tends to continue to roll the boat over. I submit that this is why there has been such a dramatic increase in barrel rolls (even in straight-aways) in races in recent years. When I flew over races for 16 years, I could always spot the counter rotated boats, because they behaved very differently (and definitely not better)than their properly spun (outboard rotation) competitors.
The reason that many people spin them "backwards" is the fact that on some hulls the boat may gain a mile or two per hour at top speed....or..... the boat has a bottom tune that needs more bow lift. The speed can generally be achieved in other ways without using an unnatural rotation as a "bandaid" (This is particularly problematical on stepped bottom boats that skid first, then catch suddenly, then roll outward......get the picture?)
One can re-tune most bottoms to add rocker to provide bow lift without resorting to ill advised prop rotation changes.
Counter rotation is adviseable on SINGLE engine race boats when the courses change from counter-clockwise to clockwise. LH props like right turns and handle better, RH props like left turns. Since the Bravo drive allows for a simple flick of a lever to reverse rotation, one would expect that Factory 1 racers would have a supply of left and right props depending on the course ....... up until this year most F1 racers don't...... I guess nobody has "invented" this yet.
====================
From: T2x
Ron P.--My thoughts on "spinning" in..... Simple physics.... Right hand rotation propellers,torque (lean) the boat to the left. Left hand rotation propellers torque the boat to the right. In a twin engine boat spinning outboard or , RH on right side, LH on left, the torque of the propellers tends to return the boat to level when one side or the other leans outward. When props are spun inboard RH on left, LH on right, or counter rotated the torque tends to make the lean worse. This occurs because as a boat(Cat or Vee) leans to one side, the prop on that side buries deeper and exerts more force, while the prop on the other side rises (in some cases out of the water) and exerts less force. So...... If a RH prop is spinning on the right side of a boat leaning to the right, the prop tends to push the hull back over to the left. (spinning Outboard). If, however, the left hand prop is on the right side in a right hand lean , the prop tends to continue to roll the boat over. I submit that this is why there has been such a dramatic increase in barrel rolls (even in straight-aways) in races in recent years. When I flew over races for 16 years, I could always spot the counter rotated boats, because they behaved very differently (and definitely not better)than their properly spun (outboard rotation) competitors.
The reason that many people spin them "backwards" is the fact that on some hulls the boat may gain a mile or two per hour at top speed....or..... the boat has a bottom tune that needs more bow lift. The speed can generally be achieved in other ways without using an unnatural rotation as a "bandaid" (This is particularly problematical on stepped bottom boats that skid first, then catch suddenly, then roll outward......get the picture?)
One can re-tune most bottoms to add rocker to provide bow lift without resorting to ill advised prop rotation changes.
Counter rotation is adviseable on SINGLE engine race boats when the courses change from counter-clockwise to clockwise. LH props like right turns and handle better, RH props like left turns. Since the Bravo drive allows for a simple flick of a lever to reverse rotation, one would expect that Factory 1 racers would have a supply of left and right props depending on the course ....... up until this year most F1 racers don't...... I guess nobody has "invented" this yet.
04-25-2003, 09:22 AM
#32
Enjoy the show
VIP Member
Join Date: Feb 2001
Location: The Joisey Shore
Posts: 10,353
Likes: 0
Received 0 Likes
on
0 Posts
I posted this from the Great Moments in Cat History.
I have spoken to many people about this and it seems that V bottoms will become a handful to drive with the props spinning inward.
If your manufacturer stuck the drives on with an inward direction, you might want to swap them to spin out for safety reasons. And yes, you might give up 1 mph if you do so. You might also enjoy a better handling boat.
I have spoken to many people about this and it seems that V bottoms will become a handful to drive with the props spinning inward.
If your manufacturer stuck the drives on with an inward direction, you might want to swap them to spin out for safety reasons. And yes, you might give up 1 mph if you do so. You might also enjoy a better handling boat.
04-25-2003, 09:37 AM
#34
Rough Seas Lie Ahead
Gold Member
Join Date: Feb 2002
Location: Virginia Beach, VA
Posts: 2,465
Likes: 0
Received 0 Likes
on
0 Posts
mlitefan glad to hear you got to go out and run it a bit. Can't wait to hear impressions/thoughts on the possibilities...
As far as the step driving goes, the Sunsation is a tad unique in that it's step is only partial and runs inboard only to the first strake. Sort of gives the best of both. I believe the Sunsation step is more for planing a little quicker than for WOT advantages. If you've ever seen a picture of a 288/32 running trimmed up you'll notice the "semi-steps" are running out of the water...
But the Sunsations do have a little nuance and that's bow steer. Their noses are long and therefore requires a tad trim up to cut it hard otherwise the nose will dig in and cut hard.....I learned this within the first few days of operating it while dialing in the operating envelope. If you lift the bow a tad she'll turn as hard you want it to...
As far as the step driving goes, the Sunsation is a tad unique in that it's step is only partial and runs inboard only to the first strake. Sort of gives the best of both. I believe the Sunsation step is more for planing a little quicker than for WOT advantages. If you've ever seen a picture of a 288/32 running trimmed up you'll notice the "semi-steps" are running out of the water...
But the Sunsations do have a little nuance and that's bow steer. Their noses are long and therefore requires a tad trim up to cut it hard otherwise the nose will dig in and cut hard.....I learned this within the first few days of operating it while dialing in the operating envelope. If you lift the bow a tad she'll turn as hard you want it to...
04-25-2003, 09:38 AM
#35
Registered
Join Date: Jun 2001
Location: Michigan
Posts: 3,345
Likes: 0
Received 0 Likes
on
0 Posts
you may want to test for yourself...again...stop looking for absolutes.
if the manufacture set it that way...ask them why...they may have just done some testing??what center are the drives at??...what percentage of the blades are exposed on what stroke??...how was the propeller designed...a boat that bow steers is EVERY bit a handful as a boat thats ass is too light.
if the manufacture set it that way...ask them why...they may have just done some testing??what center are the drives at??...what percentage of the blades are exposed on what stroke??...how was the propeller designed...a boat that bow steers is EVERY bit a handful as a boat thats ass is too light.
04-25-2003, 09:46 AM
#36
Allergic to Nonsense
Platinum Member
Join Date: Aug 2001
Location: Granite Quarry, NC
Posts: 5,011
Likes: 0
Received 17 Likes
on
17 Posts
Originally posted by audacity
...a boat that bow steers is EVERY bit a handful as a boat thats ass is too light.
...a boat that bow steers is EVERY bit a handful as a boat thats ass is too light.
T2x
Last edited by T2x; 04-25-2003 at 09:51 AM.
04-25-2003, 09:51 AM
#37
Allergic to Nonsense
Platinum Member
Join Date: Aug 2001
Location: Granite Quarry, NC
Posts: 5,011
Likes: 0
Received 17 Likes
on
17 Posts
Originally posted by audacity
the bottom line (pun intended)...get to know your boat and yourself...don't go out there and learn with passengers. if ya want to know more???...i'm sure there are some racers in your area that always love seat time and are more than happy to pass along knowledge. i know some race teams sell seat time in a race boat, as we do...the information is out there...you just have to ask!
people seem to want a absolute answer...like for turning X boat where do i set tabs, drive and throttles in a turn...i think we create more problems trying to answer ...again, EVERY boat will have a different feel! so get to know your boat and set up...know WHAT and WHY it's doing things...this will allow you to change with it dynamically, as we know the environment it is in does!
BE SAFE
the bottom line (pun intended)...get to know your boat and yourself...don't go out there and learn with passengers. if ya want to know more???...i'm sure there are some racers in your area that always love seat time and are more than happy to pass along knowledge. i know some race teams sell seat time in a race boat, as we do...the information is out there...you just have to ask!
people seem to want a absolute answer...like for turning X boat where do i set tabs, drive and throttles in a turn...i think we create more problems trying to answer ...again, EVERY boat will have a different feel! so get to know your boat and set up...know WHAT and WHY it's doing things...this will allow you to change with it dynamically, as we know the environment it is in does!
BE SAFE
I concur with all of the above except that there are a surprisingly large number of racers who don't have a clue.........and have a huge "show off" factor.
be selective of whom you trust in all things......and always Be Safe.
T2x
Last edited by T2x; 04-25-2003 at 10:31 AM.
04-25-2003, 09:59 AM
#38
Registered
Join Date: Jun 2001
Location: Michigan
Posts: 3,345
Likes: 0
Received 0 Likes
on
0 Posts
the end result maybe...but they are different...cg plays a part and the moment can work for or against you...also surface adhesion and laminar flow (in differnt areas of the hull) work themselves into he equation as well. the later is what we are working on now.
04-25-2003, 10:03 AM
#39
Registered
Join Date: Jun 2001
Location: Michigan
Posts: 3,345
Likes: 0
Received 0 Likes
on
0 Posts
"suprisingly large number of racers who don't have a clue.........and have a huge "show off" factor. "
i agree...but if your savvy enough to seek out good information and repeatable data...you maybe keen enough to sift through the bull **** too.
i agree...but if your savvy enough to seek out good information and repeatable data...you maybe keen enough to sift through the bull **** too.
01-11-2005, 01:12 AM
#40
Charter Member # 430
Charter Member
Re: Tips for driving stepped bottom boats
Thank God for these boards! I have a new Eliminator with steps and never really thought about it. I never turn hard tho. When I turn, I ALWAYS settle the boat slowing down get into the turn then throttle out. Guess I was doing right all along. I will be a lot more careful now.
THANK YOU ALL!
THANK YOU ALL!
