Cobra1

I just added 800 HP to my 27' Cobra V bottom. I am seeing a little chine walk at about 80 mph 4200 rpm. I have a lot of power left but I keep backing out when i feel a little chine walk. My question is how much chine walk is ok before i back out? I have trim tabs and full hyd steering. I have been driving boats for 15 years but never a V bottom over 80 mph. Can a 27' V bottom do over 90 mph without chine walk?Thanks for the advice.

LarryD

at over 80 in a 27 you are going to get alittle chine walk as long as it stays gentle just drive through it however there are a few things that help you mentioned that you have tabs if they are not already put the long ones ( mercury or =) but the long 30 inch ones don't bury the tabs but run them about parallel or up alittle ( in flat water) also what prop do you run ? you can have the trailing edge eased to settle the stern talk to matt at throttle up he can help. where are your tabs mounted?
at some speed all v's will tend to start chining
good luck
Larry svl #51 wild ride

articfriends

iTrader: (1)

How much prop are you turning? My 272 baja v-hull has 950 hp and runs low to mid 90's with a 32 pitch labbed. It used to chinewalk from 70-75 mph when it had 750 hp but the full hyd steering got rid of 95 % of it. It will torque steer/roll from 60 to 80 now if I try to run with no weight in the boat or gas but 1/2 tk of gas or one passenger eliminates it. I'm sure your running a 4 blade prop,it makes it much worse but like my boat you probably could break a 3 blade loose at any speed with the kind of power your talking about. Labbed props seem to help too,I think the thicker blades on a non-labbed prop lift the transom more. Your steering is definately full hydraulic to the helm? Is it twin ram? I added external twin ram at first to my boat and it still chine walked terrible,the full to helm cleaned it up. What is your beam?How long are your tabs,I had cheap bennets and made stainless replacements that are twice as long. Even though I don't run with my tabs very far into the water if the boat twist back and forth they are close to the water and help to neutralize the chine walking.You might have to run with your tabs dug in hard until you reach a certain speed or find that you have to "drive thru it" because of design of your hull,Smitty

Cord

iTrader: (2)

Chine walk can kill. There is a board member who several years ago added that kind of power to his Baja against the recommendations of his engine builder. I remember that builder saying "This boat is going to kill somebody." I recommemded that he not build the engine, but it was a rich contract and he needed the money. Well his prediction turned out to be pretty accurate. The members best friend spent the next couple of years in a coma and the boat was sold for it's parts-after it's second time out.

The ability to control a chine walk has as much to do with the driver as the boat. Do you just steer the boat or are you in tune with the boat? Focus on the bow. You'll see the point start to waver as the boat drops off it's pad. The boat will always drop to the right so you can twitch the wheel to the left. High speeds will result in you shooting glances to the water and back to the bow trying to read everything at once. If you get out of synch and tweek the wheel at the wrong moment you will throw the boat into a severe chinewalk that can only be corrected by chopping the throttle and puckering. This is super dangerous because it will be very easy to hook a chine. Please wear a impact vest and keep the passengers out of the boat until you master it.

There are some things that can be done to help reduce the chinewalk. Do the lifting strakes go all the way to the transom? If so, then removing a couple of them will help kill the lift and perhaps ballance the boat. How tight is the steering? You have FULL hydraulic, right? How tight is your gimble? That gimble had better be like a virgin, any slop will result in a chine walk at your speeds. How high is your x-dim? Lowering it will help create more bow lift and help ballance the boat. What do you use for a prop? Yea the Bravo's are fast, but a Hydromotive is super smooth. How much trim do you dial in? If you are overtrimming for the speed, you could be driving the boat out of the water. The final easy fix is to drag tab. This will slow the boat, but it provides a larger area for the boat to ballance on. Just don't attempt to adjust the tabs at speed. A errant adjustment could result in the loss of control.

The ultimate fix? Pull your engine out and stab it into a cat. You'll go 10mph faster and can do it one handed while talking to your passengers. Believe me, cats are that good. They really are.

GOODT

Or a Fountian.......

Griff

That tragic accident was in a 25 Sunsation and had nothing to do with chine walking. He hit a big wave wrong going to fast and hooked the boat.

Cobra1

Thank you all for the info. I do have dual ram full hyd steering. I will check for play. i am running a 4 blade 28 pitch prop. I haven't had a chance to run to my max rpm so I'm sure i will be changing props. I have victory trim tabs but I'm not sure of the size. they look at least 20". The tabs follow the bottom of the hull about 4" in from the outside edges. (Cord )I will check my X dimension and get back to you. if i start to chine walk to hard and i back off the throttle to hard what will happen? if i drop the tabs to much what will happen (besides loss of speed) I am only getting a slow rocking back and forth but before i hurt someone i want to ask all the questions. PS: I will be putting this motor in a cat next year.

Cobra1

Larry, Are you saying to not drop my tabs at all? How do they keep you stable if they aren't down? by the way i was testing on water like glass. I would hold the steering wheel stable. maybe thats my problem. maybe i should play with the steering a little.

Cord

iTrader: (2)

I wouldn't be too concerned about a slow rocking motion, so long as it stays slow. Glass water will bring out the worst in chine walking. So will holding the wheel still. Before you do anything, try steering the chine walk, get a feel for it and slowly push the throttle forward. See my above post for the steering. Your later posts make the problem sound better than your first one.

Dropping the tabs too far won't cause anything too dramatic - so long as you are not going fast. Don't drop the tabs at speed because you could loose control if something isn't just right. Back off and adjust them and then speed back up and see what happens. Later when you are very familiar with the new power and how the boat reacts to it you can try adjusting the tabs at speed.

Boatally Insane

iTrader: (1)

I have a Checkmate 230 Enforcer with about 550 hp in it and it starts to chinewalk BAD at 75 mph so I just end up counter-steering against the chinewalk to kep the boat balanced on the keel... It took a little practice but eventually I did get the hang of it

I've heard that Throttle up can also modify your prop to help some also...

Doug