Drive Rotation
 

Since the drives are off the boat for checking while it's getting painted (being de-graphic'd back to white) I was wondering if it would make any sense to consider having them put back on "backwards" for in-rotation. Boat is big, heavy, moderate power, smooth riding ... and slow. F-402, probably 12,000# normal running weight with fuel and people, 450HP or so a side, max speed right under 60 mph.

-Greg

O.K. : Not quite enough info. Boat length? Deadrise? C/L-engine seperation? Need to know more before giving bad advice. --- Jer

If they are BRAVO drives you can't change rotation by swaping the drives. You change rotation on a Bravo drive by switching the props and changing the cables on the shifters.

Yeah TB, I had my head stuck back in the middle ages and thinking TRS's. But as I said: "Not enough info. yet for good advice" --- Jer

no! you need all the sternlift you can get. it will only make you're boat hard to dock. the only boats that benefit from inward rotation are light steps,and,that takes proper testing by people that know what they are doing.

Based on the age, and that it's a Formula, I'll bet it does have TRS drives, like my '85 302. AudioFN tried reversing his TRS drives, and ended up putting them back. He kind of liked their handeling under power, but not around the docks. His engines are very close together, maybe 29 to 30 inches.

jpclear: the 302 is 6900 lbs dry, probably 8500 - 9000 actual weight, 24 degree deadrise, and 31" b/t c/l's (I think from memory!) Non-stepped hull. I THINK the 402 is the same stats on deadrise and c/l. What do you think the change would do on our boats?

my boat is faster with the props turning in for more bow lift and I don't see a difference in handling at the docks. I do have a raised X dimension.

Opie 272 reversed them on his 272 Formula and picked up (if I remember correcly) 2.5 mph by turning them in:eek:

Guess the F-402 is just too old for most people to know about it (plus I heard they built less than a dozen of them). It's a true 40' 2", 24* V, TRS drives, 35" centerlines. Currently running Bravo-1 4-blade props (1-2 mph slower than Mirage at top but about 6-7 mph faster at cruise).

The boats at Art Lillie's shop getting paint and "you might as well's". I'll talk with Art when he gets back (off racing again) but thought I'd ping the board as well.

-Greg

The only V hulls that I've seen gain much speed by turning them in were on high horsepower boats with boxes. And they're still a biotch to dock.
But if you've got the time, and a strong back to lift those TRSs, I guess it couldn't hurt to try.
My $0.02
Gary

With all the dinkin I've done
with switching prop rotation
on different boats, the best I've
seen is a little over 1 MPH.
And like Gary said, they handle
like crap around the dock,
( reverse seems less effective)
So, IMO, the 1 MPH or less,
isn't worth the pain and suffering
of poor docking maneuverability

my .02
jt

OK, here's the theory as I understand it.
Turning in digs the stern in deeper, raising the bow.
Less trim is therefore needed to raise the bow.
Higher X dimensions can then be used = faster.
Digging the stern in deeper can result in more wetted area = slower. Especially at lower speeds, and possibly at cruise speed.
UNLESS, you have A LOT of hp to get the whole boat out of the water.
OR, you are running a box to move the center of gravity and bouyancy back more resulting in less wetted area.
Anyone buy that?
BTW, I do know a 38 Top Gun, no steps, that got about 5 mph top end turning in. But he's running Vs, boxes, and a pair of 950s.
Gary

Gary,
I 'm with you on the "dig" theory.

What do you think causes the
poor docking maneuverability ???,
It seems to me, that whichever
drive is in reverse, has very little
thrust.

Is it the thrust being pushed
upward towards the transom,
( Keel side of drives)
the thrust of the inside swing
is the prop being, basically
cancelled out.

Do you buy that theory ???

jt

I have a 1984 Cigarette 38' flat deck, with twin 1100hp. PSI supercharged engines. I notched the transom 12" and have # 5 SSM drives on Stelling's box's.
Up until this summer I had the drives turing out. I talked to Tres Martin about the mid-range porpoising that I was having. He suggested 1) Turn the drive in 2) run 5 bbl props 3) put a "wedge" at the back of the lifting strakes 16" long and .125" high at the transom.
I turned the drives in, and spent $2500 getting the whole bottom " true'd " and the wedges glassed in. I havn't gone to 5 bbl. props yet, still running my 17.5x31 4bbl. props.
I put the boat in the h2o 3 days ago and it seems to porpoise worse than before. I'm going to play with drive height, as the bullet is now 1/2" above the bottom and I have 1" & 2" spacers that I can try.
The boat ran 101 mph on GPS, turning the drives in, before all these modifications, with 3" of spacers in ea. drive and 260 gal. of fuel on board, and the 950hp. pulleys on the blowers. I have 2 sets of upper pulleys that I can change to, to raise the boost aka. hp.
The boat has a full interior and is not a " cover-girl" Cigarette. If anyone has any suggestions- I'm open to listen and try.
I'm also running the 380 trim tabs, which will take out the porpoising, but wastes energy. If tucking the drives in and using the tabs is the only way to get rid of the mid-range porpoising- so be it.
Top end is fine, as the boat rides bow up at anything over 60-70 mph.

G.K.,
I take it you haven't ran it with the
drives turning out, since the bottom
work ??
Might be worth a try,
That should add back some stern lift.

jt