looking for +70 in a 96 18c

[tice652]

I just purchased a 96 Donzi 18c. 350mag mpi and bravo 1. I am 100% satisfied with the boat. It consistantly hits 68 gps and I love the sound of low 70's better than high 60's At WOT it runs at just over 5000 rpms. The engine's high end range is 4800 and the simple solution is going from a 23 pitch to a 24. I'm looking for some pro's and con's on this and ideas for upping HP a little to help compensate. Acceleration right now is great- will the 24 kill it? Any speed decrease with installing tabs?
Thanks for your time
Dan

[mrfixxall]

I just purchased a 96 Donzi 18c. 350mag mpi and bravo 1. I am 100% satisfied with the boat. It consistantly hits 68 gps and I love the sound of low 70's better than high 60's At WOT it runs at just over 5000 rpms. The engine's high end range is 4800 and the simple solution is going from a 23 pitch to a 24. I'm looking for some pro's and con's on this and ideas for upping HP a little to help compensate. Acceleration right now is great- will the 24 kill it? Any speed decrease with installing tabs?
Thanks for your time
Dan

Put a 25pitch turbo prop on it and it will bring down your rpm's to 4800 and you should hit 71+..if your going to install tabs mount them 1/2'' above the leading edge of the transm but they wont make it any faster,just more stable..

[tice652]

Thanks for the input. Skip the 24 all together? As far as tabs go are the twin ram bennets the best way to go?
Thanks
Dan

[marcdups]

SINGLE RAMS SHOULD BE MORE THAN ENOUGH,sorry I aws shoutihg, but on a serious note single rams are all you need, as a mobile marine mech I an looking for someone to fix my boat, any help ?

[mrfixxall]

[QUOTE=tice652;414729]Thanks for the input. Skip the 24 all together? As far as tabs go are the twin ram bennets the best way to go?
Thanks
Dan[/QUOi


If you plan on using your tabs above 50 mph then its a good idea to get a twin ram system, their stronger and will last longer..single rams will brake at higher speeds..

[tice652]

Yes they will be used at 70 to keep the chine walk to a minimum - im not planning on pushing the bow down but just a little stability. My top end is the same with 2 or 4 people in the boat- less chining with 4. My speed increases with 2 untill it walks and i have to back off. So tabs are a must - Now i just need a prop shop with a loaner 25 pitch turbo to test.
thanks
Dan

[mrfixxall]

Yes they will be used at 70 to keep the chine walk to a minimum - im not planning on pushing the bow down but just a little stability. My top end is the same with 2 or 4 people in the boat- less chining with 4. My speed increases with 2 untill it walks and i have to back off. So tabs are a must - Now i just need a prop shop with a loaner 25 pitch turbo to test.
thanks
Dan

merc has this thing call ''try before you buy'' find a local auth mers dealer and they will lend you a prop before you buy it...

[RedDog]

if you drop the tabs you're not going to hit 70. Practice and you should be able to counter-act the walking. Keep the wheel with a slight tension to left or right or gentle counter-steers to work through it. Hard - yes! I'm not comfortably there consistently myself.

Only time I find the tabs of benefit is it towing a wake-boarder or in a mid cruise speed of 2800 - 3300 rpm. The less fuel I have the less the tabs are needed

[ThunderMarineDave]

I think the nicest trim tabs on the market are the PHC type. These are nearly exact copies of Mercury K-Planes, but 1/4 the price. They use Oildyne type pumps (similar to Mercury trim pump).

However, the smallest set they have are 22", and that is quite a bit too big for you application.

Bennets are ok - avoid Lenco...

-David
THUNDER MARINE

[tice652]

I just smoked a 65mph gps sea-doo off the line. Beat him top end too, It was close at first but slowly pulled away. Maybe the 23 pitch isn't that bad.
Dan

[blackhawk]

if you drop the tabs you're not going to hit 70. Practice and you should be able to counter-act the walking. Keep the wheel with a slight tension to left or right or gentle counter-steers to work through it. Hard - yes! I'm not comfortably there consistently myself.

My Unlimited chine walked when trimmed out for the last one or two mph. Some props were better than others. I counter steered at the right time with a slight "bump" to the left. It took me two weeks and quite a few hours to get it down. But once I did it was second nature

[BigGrizzly]

No offense but seat time, part of the problem is the driver. I have been driving the Donzi since 66 and it takes time to learn the boat characteristics. Steering goes a long way. Tabs won't do anything for that issue.

[tice652]

I understand that practice will help me a great deal. Grizzly Just out of curiosity what speed are you hitting with a 18 C? Up to 65 I can correct a wake induced walk but its at upper 60's when its almost like resonant frequency . It keeps escalating untill you back off. I Keep slight pressure on the steering wheel which I learned from a previous post and that keeps it from ever starting at most speeds. Looks like a good day for windshield time today so its to the launch ramp for me.

Dan

[BigGrizzly]

My own Corsican will not relate. I have a old Volvo with internal Teleflex power assist hydraulic steering. On this particular combination I run on a good day 67 GPS. Chine walking is because your trying to balance the boat on a very narrow basket ball shape. On my particular boat, The photos say, I run on the last 20 inches of the hull at about 18 inches wide. take a yard stick to your boat and measure this and what I said will become clear. This is a balancing act. Any sudden movements or over corrections will set it off. With the wrong props or over working the tabs will only aggravate the situation. I was with Poodle in his X18 at over 70 MPH (on my GPS) and it was not a issue. His boat has the power to just drive through it. Driving through is another discussion and is better in person than in print. When we go to rally these discussion take place after the oos and ahahs of the boats. This is why the board members are so close"like going to a family reunion with just the family you like. ". Look at and study the bottom of your hull and you will see. Handling of a Donzi id like eating an Elephant, one bite at a time.