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toddturowski
10-30-2000, 08:04 PM
Has anyone tried using a stern jack on an 18 classic? I have a 1999 18 classic with a 350 mag alpha one drive with the 23 pitch mirag plus. I run about 67-68 mph on the gaffrig 2 speedo, I know that I should use a radar gun, but I do not have one, nor a portable gps. I run wide open at about 53 to 54 rpm, then with a bit too much trim, I hit the rev. liminator. I think some of it has to do with it the fact that I removed the stock chrome exhaust baffels, and I have only rubber flaps on it now. I am sure this causes at least a 50 rpm increase, but granted, much better sound. I want to reach 70+++. I read in "Hot Boat" about thes Jack plate from "Land and Sea", just wanted to know if anyone has tried it.
Just a note, I had posted a question about a month ago and asked about an extension plate. I knew what I was talking about but I did not know that it was actually called a stern jack. My young and inexperienced brain needs knowledge!!!!!!!!!!!!!!!!!

GEOO
10-30-2000, 08:19 PM
Todd, I spoke to Two people who purchased the Land & Sea Stern Jack. One on an 18 the other on a 22 classic. Both said they gained 1 maybe 2 mph but the boat was alot more stable. They said it added more control then speed. GEOO

Tito
10-31-2000, 06:47 AM
Geoo is right we install them all the time and you gain control but very little speed, most customers feel it is not worth the expence. Because you are reaching maximum rpms you need a different prop, but before you buy one check your speed with gps or radar, otherwise you will not be able to compare differences and it become a guessing game.

Barry Phillips
10-31-2000, 07:08 AM
Pick up a copy of October's Trailer Boats.
Thier is a test copareing a Stainless
Maine Hi-Torgue exhaust system.
The boat tested was a 20' Sea Ray with
a 260 MerCruiser. The gained 4.2 MPH
and 100 rpm on the top end seems
impossible, but the stats don't lie.
Trailer Boat feels that loseing 113 lbs
off the stern, changed the point
of water contact giving the boat more
stern lift. The motor was stock otherwise.
Check it out.
SO-SLO

donzi86
10-31-2000, 03:53 PM
Todd I recently purchased a stern jack and put it on my 18' classic. I have a Merc small block with an Alpha Drive that has been bumped up to around 310 HP. Everyone is right, you don't gain much on extra speed, especially if you are already running in the high 60's. The handling you gain is amazing though. I feel it was worth it for that. The only thing is that I was turning 6300 RPM's with my 23 pitch Mirage prop after the installation. I had to go to a 25 pitch which dropped the R's back down to the 5400 area. That adds quite a bit to your expense if you have to go out and buy a new Mirage Prop. It's an easy installation with the exception of the fact that you have to cut the rams and have an 8" spacer welded in place. It is very important to have someone who knows what they are doing do this part. They need to stay very straight ofcourse. Bottom line is that if you plan on keeping your Donzi until the bury you in it...as I do...I would get the Stern Jack. The boat will ride better and higher out of the water. They do have a return policy also if you don't get out of it what you want, you can return the whole thing. Kind of hard to cut the spacers on the rams out though. Good luck Todd, let me know if I can be of any other help.

Shawn

PaulO
10-31-2000, 06:29 PM
Shawn,
Very interesting! Thanks for the info. I am considering a stern jack and/or Alpha SS over the winter. Let me ask you this; what was the RPM with the old mirage before the stern jack? If you gained considerable RPM from the Stern Jack install, how come that did not correspond to speed gains?
Thanks,
PaulO

Barry Phillips
11-02-2000, 07:45 AM
Todd: I to thought about a stern jack, not
much bann for the buck if top end is your
goal. I think they work better on lighter
flat bottom hulls. Land & Sea claims
that thier jack helped a Donzi 18 gain
6mph in an ad they ran a couple of years
ago. If they did indeed see an increase
on a test boat or a customer's, maybe
they can tell you the set up. I've noticed
all these bass boats running around
with jacks are useing 4 and 5 blade
blade props. I've seen the boat at
Lake George and it looked really cool
but at the time he was running a 3 blade.
Call Land & Sea, if they can't provide you
with setup spec.s than the claims aren't
real. I believe the improved control is the
result of drive being set back from the
stern not it's ability to go up and down.
With that in mind a simple extension box
might be the ansure, except your quest
is 70+mph. Take a look at that exhaust
compairson in Trailer Boat, the weight
savings alone well bump you 1 or 2 mph.
If you gain 4.2 mph as TB claims, all the
better.
SO-SLO

woodsy32
11-02-2000, 09:43 AM
I don't know what your budget is, but instead of spending $2000 for a stern jack, if it is speed you want, find someone who will raise your engine & sterndrive, and thus shorten your "X" dimension. I was talking to a guy who races APBA Offshore, (I am not too sure what class he runs, but it is a triple outboard powered catamaran of some sort, probably a Skater), about improvements to my 22 Classic. It was his opinion that the Donzi's run out of hull, (the boat is too small in length) for an extension box to be cost effective speedwise. It was his recommendation to shorten the X dimension by raising the motor/sterndrive and redo the transom. He estimated the cost to be right around $2500.00 plus/minus a little. He was doing that to a 24' Checkmate when I stopped by to talk to him. I discussed all sorts of ideas for my 22' Classic, and to be truthful, he shot down most of them. It was his opinion that everything looks awesome in a magazine, but is rarely cost effective on a boat. I talked to him about what I was thinking about doing to my boat: the IMCO extension box with external steering… shot that idea down. He shot down the IMCO shortened Bravo too... didn't like the ProCharger idea either... way too many reasons to list here! He even had a pair of modified Stellings extension boxes lying around the shop. Did not think they were a good (cost effective) idea for the Donzi. He did have an aluminum head 502/550HP rat motor, (I assume it was for the Checkmate, the customer was looking to hit 80+), he thought that WAS a good idea for the Donzi. For the record, he did not say that the above mentioned products would not work, he just said they were not cost effective for the amount of speed you may gain. Anyway, to get to the point the basic premise of his recommendations was if you want more speed, raise the X dimension, and get more HP. His recommendation for my boat was as follows... Get a good exhaust; he mentioned Stainless Marine, EMI, IMCO & Gil. I have the 385Hp 454 Mag MPI, he suggested I get the Vortex kit for it, it coupled with the new exhaust will give me a little boost now, and be transferable to another motor later. He also suggested the Bennett Sport Tabs (12 X 16), I have some small (cheap) from the factory trim tabs, those have to go! That was the end of the low cost suggestions. Then he started with the whole speed = $$$ suggestions. Raise the motor and sterndrive, 2" to 3", he would have to measure it. I guess Mercruiser sells spacer kits to fine tune the drive height to the hull. The final recommendation is to get one of those 502 crate motors and massage it a little... good exhaust, maybe a different cam, get to about 550-600HP. ($7000) He seems to think that combination should break 80mph with the right prop. If there are any racers in your area, try to drop by and see them to get their opinion on what works and what doesn't. They have been there/ bought that/broke that! Anyway, just my $.02 worth.

Dave

BigGrizzly
11-02-2000, 09:44 PM
I just priced all the stuff that guy said you need and it comes to $21000. The vortex kit comes to 7500 for the 454mpi. The 502 crate motor comes to $75300(new). ETC.
The 22 runs out of hull at 80 mph without the jack. So what is next? IDEA sell wife kids and corvette and buy a 28ZX.

CDMA
11-02-2000, 10:45 PM
Big G,

Tell us more about your boats...

What do they run and what have you done to them...

Chris

GEOO
11-03-2000, 05:49 AM
"Running out of Hull". It's a matter of set-up. A 18 Donzi with 300hp run's out of hull at 65. The boat is fully trimmed and running out of the water, it get's loose. Put more power in the boat don't trim as much and 65 mph is stable. Set-up, is the key to a stable fast ride. With the right power and setup a 18 Donzi can go 90 and still be stable. GEOO

woodsy32
11-03-2000, 06:37 AM
Grizz...

I meant the Vortex MPI Kit... it only runs about $1000 - $1200. It includes a new flame arrestor with a K&N filter, a new MSD spark box and a fuel pressure regulator that allows you to increase the fuel pressure to the injectors. It's supposed to give you about 20-30 extra HP with the 454 Mag MPI. I should not have used the word "boost". This racer did not recommend a supercharger for any motor, unless the motor was built specifically for that purpose. I added up the cost of the improvements, and came up with about 1/2 of the 21,000. The breakdown was as follows... Bennett Sport Tabs $800, Good Exhaust System $2500, Raise the X dimension $2500, GM 502/500HP crate motor with 575HP Cam $7500, total = $13,300.00 subtract the sale of the 454 Mag MPI (-3000) and it totals about $10,300. So, I don't have to sell the Buell or the truck, but I think the girlfriend might have to go!! I can probably do the whole boat if I don't have to buy the engagement ring!! http://www.donzi.net/ubb/smile.gif I think if I do this in stages over the next few years, with the 502 being the last improvement, it will not be too tough on the budget. Of course by then GEOO will have the new turbine ASD drive/engine combo that will make his 18 go 150mph. GEOO, you are right about your hull setup. I called the racer yesterday, and he totally agreed with you, although he thought chine walk would become a serious issue at any speed much past 80-85mph. I know your Arneson setup is pretty fast, how is the chine walk with that setup? Of course, adding an Arneson to my wish list would bring me up to Big Grizzly's original estimate. I wonder what I can get for the Buell??? Hmmmmmm...

Dave

Dave

Barry Phillips
11-03-2000, 07:31 AM
I know of three 22s that can run in excess
of 80mph one with a procharger on a
502, one with warmed up HP 500 and
orther with a built up 502 not shure of
the details. I do know they are fast and
do not run out of hull at 80mph. If I had
the cash I would trade in my 250hp
350 for a 377 Scorpian, mayby when
I repower. My point is if you want to go fast
in a 18 or a 22 or anything, any
hotrodder is going to tell you thier is no
replacement for big HP. How you gain
that is really a matter of much do want
to spend and how reliable you want your
ride to be. A stern jack for my Bravo
would be in the 3,500 range installed,
I would rather spend that money on
the motor. In my case a cam, 4 barrel
carb and intake and a good exhaust .
On MPI motor it gets a more complicated
I would start with the exhaust and then
look at the injection itself how can it
be modified? The Magnums make
nice HP as they are, but thier is always
room for improvement if your goals
modest. But if you want to go really fast
your going have to find big HP like Geoo.
or get a 22 with a 502 and start from
their.
SO-SLO

PaulO
11-03-2000, 10:33 AM
Although I just re-did the transom last winter when I switched from Volvo to Merc, I would gladly do it again to raise the X-dimension. The problem with a non-barrelback 18 is that there is no room to raise the engine any further. The hatch can be modified but, there is no good place for the thru-transom exhaust. I will continue to search for an SS and some Hi-Po exhaust.
PaulO

roadtrip
11-03-2000, 05:22 PM
I beg to differ on this set-up determines how much hull you got arguement.
In my quest a couple of years ago to be the fastest v-hull boat on the lake, I built up a Fountain 32 with twin 800SCs. Top radar speed was 115mph and believe me that boat ran out of hull long before it ever saw top end. This boat was rigged and balanced properly, but believe me it was spooky at anything over about 100 mph. The hull ran out at 100 and the driver's ability(or stupidity) and water conditions kicked in after that.
I would be interested in hearing what top speed is on a 22 Classic, before it does run out of hull and egos and story telling cut in. I would guess 80 mph is about it, except in rare water conditions with the proper moon phase and nutcake at the wheel....

doug
11-03-2000, 08:13 PM
I have a 2+3 with a SBC and SS drive CLE case
it runs 78 on GPS so you don't need the
set back to get into the 80s just more motor
and a short drive. It seems to me most of
the top speed problems posted here are hamperd by a
short X dim. and to deep of a drive. To much gearcase drag ill handling is the result at speed. The guy at the dealer near here said
that the setback work great on the 18 and 22
He claimed to have gone 100 in a 18 with the blown BB he showed me in his shop.
Thanks Doug
I love this place!!!

------------------
old Yeller

BigGrizzly
11-04-2000, 12:07 AM
Geoo wish I could agree with you on the hull thing, but I can't. Your use to your boat, the drive makes your boat think it is a 26 footer. When my Corsican is two feet out of the water so is prop and all. When yours is the same your prop and t-fin is still there. check with Rick ask him how much hull is in the water at 72mph and where are his trim tabs are. Your boat is special-it is a great set up, you just forget how it use to be.
Woodsy, the vortex kit won't give you 20-30 hp, if the origional system is set up right to begin with. Check on a eariler post by Geeo, he put a carh on his injected engine and got an increase in hp. This is not a mistake ,the man who builds his motors knows his stuff. Keep the Buell, Erric spent his life trying to design a real American sport bike,and he did it! This cost him his wife and a factory road race sponsorship. He started like Chris,with a mission. I raced with him for a long time and he never lost sight of his goals. Well get a good exhaust, good cam, and head work, see you at 75.

I agree with road trip a 22 will run out of hull at 80-83,even the Black Hawk except on smooooooth water. Yes a 22 can do 90, with alot of hair and brass.

Chris, my boats are a 18 Corsican with a 351 Ford Cleveland with CMI exhaust. I have 8 different cams for this motor that I played with untill I got what I wanted. What is in it now is not the fastest, but the most fun. It will pull up three skiers, and will rev. 5600 rpms if I let it. I keep it about 5200 unless I have to prove a point. I run a 23 Hill prop and have a Volvo 270 drive with a 290 trans plate ( for power trim). The cam I use now has 106 lobe centers and 232 duration at 0.050 and is a dual profile cam,, more at 11:00. The hp, well this depends what scale you use. On the bar scale the hp goes to 550hp with 4 Miller Lites and two Baha owners. It really has 425+ hp. The 22 Criterion has a TRS drive a Merc11 trans and a 330?? /454 engine at present.

[This message has been edited by BigGrizzly (edited 11-04-2000).]

[This message has been edited by BigGrizzly (edited 11-04-2000).]

Owen
11-04-2000, 07:00 PM
Geoo, the top end handling problems - running out of hull, is exactly what I've run into with my Jr and its 351. It starts to crab walk to starboard on the prop and I feel like I lose steering. There's more speed there, its just not controllable speed.
This is one reason I was interested in that Saro Drive I saw at the Annapolis Show. What I can't wrap my brain around is how these drives (arneson et cetera) vector force in any way but to lift the stern and plow the bow. I know that currently there isn't enough room for a transmission but I found another dirt cheap hull that I could chop out the back seat, make the front a bench and add the room needed. But no sales lit tells me what the actual handling of a surface drive is like. Does it suck down the stern like a jet and does it have greater or less of a torque effect on the hull than a Stern Drive?

RickR
11-04-2000, 07:56 PM
The Classics with the rounded keel have a handleing problem when the hull is running so dry it gets above the inside lifting strakes. Around 68 GPS(BBC/18 Classic). At that speed there is not a platform for the hull to ride on (like trying to stand on a basketball)

On my 18, at speed, the platform is created with the keel and the left trim tab (the tab also counteracts the right hand prop).

Tab placement is very important. Thats why for very high performance, with a rounded keel, Classic I reccomend placing the tabs as close as possible to the keel (without interfering with the drive) 1/4" above the wetted surface.

------------------
RICKR
mailto:riggerb@aol.comriggerb@aol.com</A>

GEOO
11-06-2000, 05:37 PM
Owen,
What size and type prop do you have? How much do you have to trim to get to top speed?
You are correct, surface drives and/or shallow X-dim gives little if any bow lift. You'll need to shift the CG back or build rocker into the hull. I've even heard of people putting wedges under the hull in the midship to ad in bow lift.
I run a horizontal fin on the bottom of my skeg set at neg 4 degrees, to dig the drive in, to create bow lift. When I get back in to the water, I will try and move the CG back and reduce some of the fins drag by setting it level.

RoadTrip,
I disagree. I believe set-up is the key to control. An Allison 18 or 20 footer can run 100 (set up with off-set jack plates ect.), many river racing jet boat's run over 100 and are controllable. Donzi doesn't design their boat's for a certain speed. They make a hull and do some fine tuning to get rid of any bad handling charateristics.
By changing drive height, prop size and style, center of gravity, tab location, etc. you can make a once uncontrollable boat drivable. Don't get me wrong, I'm not saying a 18 Donzi can go 120. But I think it could run 100 and still be controlled. Controllablity (new word?) and dangerous are different. My 18 is rock solid at 85 in 1-2 foot chop. Hit a cross wake or blink, and miss the yacht's wake and you could have a hairy situation. My 18 was scary at 68 with my original set-up (1975), and with alot of luck and trial and error, now one could drive with your hand's off the wheel at 80.
Usually you gain in one area and lose in an other. If you run a small diameter prop the boat might sit lower in the water at high speeds and be more controllable, however coming on plane will be difficult. Same with weight, if you move the CG back the boat will ride bow high at speeds,(you'll need less positive trim) but may porpoise at cruise. GEOO