Donzi 2008 27ZR at 70mph+

[rsg69cpa]

Okay, so I finally took my new Donzi up to full throtle racing another Donzi (first time I'd seen him). Well, things were going fine until the boat felt like it was going to take off out of the water. No tabs and trim at 2. all I could do was slow down as the boat started dancing viciously.
Would I have benn better off trimming down a bit? Putting the tabs down? Both?? or was it too late by the time I started to react?
thanks!!

[Barry Eller]

Okay, so I finally took my new Donzi up to full throtle racing another Donzi (first time I'd seen him). Well, things were going fine until the boat felt like it was going to take off out of the water. No tabs and trim at 2. all I could do was slow down as the boat started dancing viciously.
Would I have benn better off trimming down a bit? Putting the tabs down? Both?? or was it too late by the time I started to react?
thanks!!

Define "dancing viciously"...side to side rocking back and forth is called "chine walking". High Performance boats take "seat time" to learn how to drive. "Racing" the first time you go to WOT probably was not a good idea. Increase your speed in safe water conditions gradually with a neutral to negative trim and a little bit of tab to get the feel of your boat...then gradually raise the tabs and then play with the trim. Also if the boat was already out of shape it was probably too late to try and lower tabs and trim until you are more experienced. Some propellers will handle better than others also. What prop are you running?

Again...SEAT TIME IN SAFE CONDITIONS...NOT RACING...

[rsg69cpa]

Barry:
Thanks for the advice. Let me explain, this is not my first rodeo and it is not my first performance boat. It is, however, my first step-hull/hydraulic steering setup.
With that in mind, and other advice?
thanks.

[rsg69cpa]

28" 4 blade.
when you say "neutral" on the trim, do you mean all the way down? the tabs were all the ay up, so I presume this would be a neutral stance?
thanks again!!

[VetteLT193]

Neutral trim is where the prop shafts are parallel to the bottom of the boat. i.e., they are not down all the way where they are tucked in and not aiming up at all.

One thing that got me when I went to the stepped hull is how flat they run. If you are trying to air your stuff out like a non stepped hull (i.e. bow high attitude) you are probably trimmed out too much and the drive can't carry the weight of the bow causing it to fall and bounce.

try it trimmed in a bit more. A different prop may really change that though... The 4 blade bravos on my 28 ZX like trim. the Mirage plus do not. But I have twins Vs. single engine so it is totally different for your boat.

[fasttrucker]

Hi,Ive found if you go with the wind and chop the zr doesnt need tabs down at all.If Iam running in the bay and it starts to chine I slow down then drop tabs down.Then hit the gas.It only slow the zr down a bit.Check my post out http://www.donzi.net/forums/showthre...highlight=27zr

[fasttrucker]

Also check out this discussion,I hope this helps. http://www.donzi.net/forums/showthre...highlight=27zr

[fasttrucker]

Okay, so I finally took my new Donzi up to full throtle racing another Donzi (first time I'd seen him). Well, things were going fine until the boat felt like it was going to take off out of the water. No tabs and trim at 2. all I could do was slow down as the boat started dancing viciously.
Would I have benn better off trimming down a bit? Putting the tabs down? Both?? or was it too late by the time I started to react?
thanks!!

I find that just a smudge under 1/2 on the drive trim gauge works best for me.If it gets real sloppy out in the bay I drop it down a bit more.The trick with the step hull design is that when you go into a turn you dont drop/trim the drive down.That can cause a spin out which has happened to some of the Donzi net. guys.Mostly on the 22zx.(Its never happened to me and I owned a 22zx).I think with a stock 496ho you dont have to worry about it so-much.

[rsg69cpa]

thanks for the advice. As I wasn't "porpoising", di you think some tabs for surface area and higher trim?

[VetteLT193]

I find that just a smudge under 1/2 on the drive trim gauge works best for me.If it gets real sloppy out in the bay I drop it down a bit more.The trick with the step hull design is that when you go into a turn you dont drop/trim the drive down.That can cause a spin out which has happened to some of the Donzi net. guys.Mostly on the 22zx.(Its never happened to me and I owned a 22zx).I think with a stock 496ho you dont have to worry about it so-much.

Does the 27 ZR have the flat spot on the bottom of the hull? Meaning, it doesn't come to a full V at the stern? My 28 has that and I think it helps the spin and roll effect. probably doesn't stop the spin but it sure seems to give notice before spinning out and probably won't hook and roll like a full V would.

[fasttrucker]

thanks for the advice. As I wasn't "porpoising", di you think some tabs for surface area and higher trim?

The 27ZR does not do "porpoising" thats for non-stepped hull designs.
Anytime you drop tabs you are draging something in the water and that will stablize you.Also anytime you drag something in the water you will lose speed and fuel mpg,s.

[DonZi 26]

Define "dancing viciously"...side to side rocking back and forth is called "chine walking". High Performance boats take "seat time" to learn how to drive. "Racing" the first time you go to WOT probably was not a good idea. Increase your speed in safe water conditions gradually with a neutral to negative trim and a little bit of tab to get the feel of your boat...then gradually raise the tabs and then play with the trim. Also if the boat was already out of shape it was probably too late to try and lower tabs and trim until you are more experienced. Some propellers will handle better than others also. What prop are you running?

Again...SEAT TIME IN SAFE CONDITIONS...NOT RACING...

I totally have to agree with barry!!

Its not just boats its with everything in life....you first have to get used to the object before you go hardcore!!

Its very imp that first you get to know the boat....for instance run it at various rpm (not anywere close to full throttle) at different trim angles, do some turns without touching any trims, then when you think that you know the boat well start aiming for full throttle. However start increasing the rpm bit by bit and trim as you go along and see how the boat reacts, but you would know what your boat can handle becuase you would have gotten used to it!

Stepped hulls are tricky though.....good luck

[tomahdonzi]

I also have an '08 27ZR with 496HO. I always run the trim tabs down about 1/2 way at WOT. I also have the drive trimmed just below 1/2 way (I have a guage, not manual indicators). I learned pretty quickly that at WOT, if I didn't have the trim tabs down enough, the boat wanted to chine-walk pretty significantly. With the tabs down 1/2 way, I don't seem to notice any loss in speed. I recently recorded 72mph at 5,050 rpms with this setup. I also have the Bravo I 28 pitch prop, as my gear ratio is 1.65, which I'm guessing yours is too (it will say on the drive).

In any event, try putting the tabs down more. That should eliminate the instability. Then play with the drive trim to maximize the rpm's given the conditions.

[rsg69cpa]

this is truly a valuable forum. I went back at it last weekend. slight chop, but otherwise a beautiful day. with some trim work (4.5-ish) and some tabs, i hit 70mph at 4800 rpms.
Could not have accomplished this without all the great advice.
Thanks to all. Have a safe off-season.

[Barry Eller]

Was it more stable using tabs?