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View Full Version : Chine walk on the repowered 18



bigman
05-30-2002, 09:33 PM
The 300 mpi in the Donzi flys.The 23 prop gives it an awesome hole shot.I've got to try the 25.Problem is at about 62 to 65(don't have any idea how accurate the new Gaffrig speedo is)and still not WOT, I get some real chine walk out of it.I believe I need trim tabs.I don't know for sure.Any suggestions on what to do would be appreciated. Thanks for any help,Bigman.

MOP
05-31-2002, 06:46 AM
I have a buddie with a 383 SB in and 18, he had the same problem. He found almost no trim helped but what finally fixed it was a prop change not sure what he put on. I will try to call him and find out. There are alot of 18 owners up here I am very sure you will get an answer soon.

Ranman
05-31-2002, 08:02 AM
Bigman, I have an 18 with the 350MAG MPI and 1.65 Bravo. I'm running a 25p Mirage Plus. I also have trim tabs. My boat, if not careful can develop a serious chine walk at the speeds you have mentioned. I feel it has to do with the stock steering setup having a bit too much play in it. My guess is that full hydraulic steering would solve the problem. Since I won't be installing hydraulic steering anytime soon, I've learned to deal with it.

To combat the chine walking I have found two practices that help eliminate the problem.

1) Drive out of it. As the boat begins to rock side to side, you can learn to "bump" the steering wheel in the opposite direction of the rock. One or two bumps of the wheel will cause the chine walk to stop. If you're traveling in a straight line, it will act up again so you'll have to "bump" the wheel again. This is a continuous process. I've just learned how to drive the boat and keep it from chine walking at the same time.

2) Another tactic that seems to work for me is to always try to keep the steering wheel loaded up to one side. I do this by never really driving in a straight line. If I keep a bit of tension on the wheel (usually to the right against the drive rotation) allowing the boat to make a very gradual arc to the right, the chinewalk will nearly disappear.

Anyway, there's my two cents, hope it helps you out. Randy

PaulO
05-31-2002, 08:54 AM
I think all stern drive 18s will begin to setup a chine walk somewhere around 68 - 72 mph. Part of it is the hull design. The rounded bottom and the lack of any strakes in the last 2 feet of the bottom (that is in the water) do not allow the boat anything to balance on. Remember, water at that speed is a fairly hard surface. Imagine trying to balance your 18 on the last 1-2 feet of the bottom on your driveway. It would always flop side to side. Another contributing factor can be looseness in the steering. I would expect to be dissapointed if I were installing external hydraulic steering with the expectation that it would completely cure my chine-walking problems on an 18. What it may do is to raise the speed at which the chine-walking starts to set up if a portion is due to steering slop.
PaulO

Looped
05-31-2002, 09:56 AM
So Paul what are you saying, us Barrelbackers with the strakes that run all the way back to the transom and with a sharp "V" bottom we have a less of a chine walk issue?

Having not driven my 18 yet I have no idea.
Craig

CDMA
05-31-2002, 11:14 AM
I second the above question.

Chris

Attempting to out post Digger...mono e mono with a marine...good call Chris....real good

CDMA
05-31-2002, 11:18 AM
Transom of a Barrelback. Notice sharp keel and full length chines...

http://www.donzi.net/photos/callardrollsrear.jpg

ToonaFish
05-31-2002, 12:08 PM
I third the question... and wonder how much the full chines effect speed?

Chris, you've simply got to stop showing your rear so much. But your post challenge timing is great - the only time you should go hand to hand with a Marine is when he only has one functional arm. Does his handicap qualify him as a one armed Winni Bandit?

Bunches,

Celene 'would that be a transom note?'

Rich
05-31-2002, 04:08 PM
Now THAT'S a beautiful rear end

smokediver
05-31-2002, 04:49 PM
chris,toona, be nice , there is two of us !

KRAVEN
05-31-2002, 06:33 PM
I have a 2002 18ft scorpion powered classic with hydraulic sterring and tabs.I also develope chine walk at aprox 76mph on flat water.I think it has to do with the rounded bottom.It does seem to be better when running in chop.I am running a lab finished 25 mirage. :D

Doug L.
05-31-2002, 07:00 PM
Bigman
Check all the pivit points on the gimble ring.
Don't forget the tiller arm and pins for the cable
and power steering the movements should be smooth
with no play you will see some movement in the steering control valve most of which will be before the power steering or cable side of the system.
If you are running your drive deep in the water
( stock X dim.) the faster you go the more the drive wants to surface lifting the back of the boat makeing it fall from chine to chine, this
with some play in the steering can be a handful.
A good prop shop should be able to set you up
with a prop that has little transom lift.
Just my thoughts on this I am sure someone has some others to add.
I don't get any chine walk through those speeds
but I do have external steering.
Doug

PaulO
06-03-2002, 12:01 PM
Can't opine based on experience since I have not been in a sharp-keeled 18 above 70mph but, theoretically, if the strakes are in the water and they are of sufficient size to support the boat from side-to-side, it should be an improvement.
PaulO

turbo2256
06-03-2002, 12:45 PM
2CENTS MORE: At the higher speeds sooner or later too much boat is out of the water a four blade prop that reduces bow lift is necessary to improve handling of the boat this reduces speed but with enough power the top speed still increases (thats what over powering is all about) good tabs and hyd steering are still needed. I usually use off the shelf Hydromotives to start get vidios of the boat running at speed and lab them up...oh yea once in awhile it just wont work

Rootsy
06-04-2002, 07:05 PM
ahhhhh such a wonderful topic this is, i could probably ponder this for days on end... so many good thoughts, theory and ideas! now someone just needs to unscramble the whole danged puzzle! eventhough someone told me once to give up on trying to figure it out wink

now one or two of my scrambled thoughts which probably make absolutely no sense, hold no water and are probably just pointless...

has anyone gotten a 16 to not walk above say 58 - 60, what is the fastest 16 out there that is actually in control that doesn't have a semi surface drive (alpha ss, etc etc etc)? if i look at photos of my boat running at say 45 - 50 trimmed out there are no strakes really touching the water, the hull is out of the water reward of the inner strakes and MAYBE the outer strakes touch lightly til i pour on some power and it really gets light and nothing but smooth rounded bottom is riding on top. actually i punch it from 2500 and it can get quite exciting through 4000 rpm with over 400 lbs of torque going to the prop, it almost feels like the whole boat is riding on nothing but the prop (although i highly dount it is that drastic) sometimes while accelerating full tilt, and it starts to chine walk much sooner than just easing into it!. i know sam and i really have to have it squirrly to get into the low to mid 60's but what fun is that??? i have enough torque goin with the 21 mirage to get 4700 untrimmed and 59 mph, 60 1/2 with just a tad of trim beginning to get squirrly but still under control and 61.9, 4800 rpm developing a really nasty case of chinewalk, i haven't really held onto it to see what i can get top end, don't really want to take a chance on hurting the boat or ejecting myself... just can't trim it out and hang onto it is the problem.. nose gets high and the boat gets light and you feel like you are trying to balance on one toe... more than 2 or maybe 3 taps of the trim and it's all over, unless you can hang on for a bit with the steering... i'd be very interested in knowing how the fully straked 18's run at high speeds with standard depth drives. what do you all think of maybe partial strakes or balancing pads for say the last foot of the hull? too much stern lift? i'd be willing to give up a mph or two in return for stability beyond 65, i can always make more hp... or maybe an idea or two that i have pondered but i reckon has been tried... hmmm i might need to model this...

compared to a 16 is the x dimension higher in an 18 from the factory? sorta seems like it is with the bubble on most of the hatches and eyeballing the rear of a few boats but then again my motor sits high in the rear and low in the front.

anyway.. i'll shuddup now that i ahve wasted everyones time and probably made you all dumber for reading this :rolleyes: ....

MOP
06-04-2002, 07:39 PM
Boy I can just hear the belly roll laughs at this tilt on things! On the old light plywood stuff we ran many ago I and a few others added bronze fins which reall straightened the boats out alot. But we were running darn near flat bottoms with very little rocker, I'm saying about one inch bow in 16 feet. Mine were six inch very thin sort of like an old water ski fin. Has any one tried something like this?

Tomahawk
06-05-2002, 06:33 AM
Bigman, and others running 18's with Mirage props. Here's my theory, and it is just that but based upon experience. The Mirage is a great prop but has a little too much diameter for a light boat at speed. Mirage is 14 5/8" diameter. My 22 even starts to wobble a bit in the high 60's. If you can, try a Precision Turbo prop, which is a different design and a smaller diameter at 14 1/4". You also might be able to go up one size on pitch. I would bet that your boat would stabilize and go faster.
Same thing with the big Bravo 4-blades on 18 and 22 Classics. Some of these things make Tomahawk careen across the water like a beserk marshmellow. Went from 23 pitch props to a 25 turbo. Boat is now solid and hauls butt for a basically stock 454 Mag. Chris may have a take on this theory. I just know it works for me. :)

GEOO
06-05-2002, 08:22 AM
I have had the same results as Tom. (when I ran an outdrive).
I liked to run the smallest diameter I can without to much slippage. The larger diameter props seam to lift the rear of the boat more and have more leverage; regarding the torque of the prop on the hull. I have found that by using a smaller prop and adding a little cup to help lift the bow works well. I also like to use a prop with smaller surface area, smaller blades (less transom lift). If carrying the bow is a problem use a prop with more rake.
GEOO

bigman
06-05-2002, 06:56 PM
Hey everybody can't tell ya all how much I appreciate all the advice thanks alot.Lots of things to try.I'll check for play in the steering,the outdrive and power steering are new.I know I have considerable play in the steering box.I spent all the $ I can this year so hydraulic steering has to come next year(that's if I don't screw my self into the lake this year).I've got the 25 to try.Chris thanks for the great deal on the 23, it is just like new.The boat does do better with almost no trim.Like Jamie if I really thump it I get some chine walk at lesser speeds.Ranman I'll try to load the steering and see what happens,but as far as bumping the wheel you've got a bigger set of %#@s than I do.Mop I don't think your idea is so off the wall, I think I even read something on the same lines in Classic Boating. Thanks again everyone Bigman.

CDMA
06-05-2002, 07:13 PM
Well unfortunately prop design is senior year so I am not extraordinately voiced in the technical aspect at this point however I do have some general thoughts. First of all my thoughts follow almost word for word Geoo’s. That aside I have in the past used a decidedly low tech method to choosing a prop for my boat. When I had the Volvo I ran a 3 blade ultra, the alpha a 21 mirage, and now with the Bravo I have a 25 lab mirage waiting. Maybe by trying a slew of different props and experimenting I could do a little better but prop testing can become very expensive. In the future as I keep a power package for longer then a year I might try some other things but for now I have always just gone with what I know will work well enough and stuck with it. I am pretty confident with the 25 lab and in the future if I was to do anything I would build my own. There is a guy on the island here that casts his own props and can work with you to make one to order. That would be cool. An Allard Engineering prop.

On another note Bigman you need to keep in mind there is a significant difference between a mirage and a mirage +. They are related in design but quite different. The + has thicker blades, more cup and more of a parabolic shape. You might have different results with it.

Chris

bigman
06-05-2002, 08:23 PM
Thanks Chris for the imfo. The prop I got with the package is a 25 x 14 1/2 Mirage plus.I test in 2 weeks, I'll keep you posted,Thanks again,Bigman

CDMA
06-05-2002, 08:27 PM
Bigman,

If the 23 isn't enough that would be the next step. I have a 25+ lab I am hoping will work well on my new stock 350...

Rootsy
06-06-2002, 11:35 AM
hmmmmm with it said that lighter boats may like smaller diameters at speed i wonder what a sub 14 inch prop - 13 1/2 - 13 3/4 dia (outboard land) would do for stability? would you just pitch it up to compensate? would the smaller blade area help appreciably? yep i don;t know jack bout prop selection... someone clue me in on all the tips and tricks and stuff eh...

Digger
06-06-2002, 12:18 PM
awesome thread! somehow I lost track of it, hadn't checked it since it first posted. CDMA, you should know that I am able to type with TWO hands now. :D still a ways off from flying tho :mad: