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mphatc
05-12-2004, 07:39 PM
So if you were to put a Bravo I on an 18 Classic hull what would you use for an X dimension??

FWIW, power is Ford 302 with ~ 345 HP at 4800 rpm.

Looking for answers and thoughts as I've heard so many say that I should go higher than Donzi builds the new boats . . which if I am correct is 14 1/4" . . .

TIA,
Mario L.

Lenny
05-12-2004, 08:11 PM
14 1/16 on an Alpha/Bravo setup @ 12 degrees, 17" on a Blackhawk... that is what the MERC literature says. Our transoms fall in the middle-ish of 12-13 degrees...

Instead or raising the "X" if you need to, I would seriously consider the IMCO arrangement for about $4G. Keeping the low C of G would surely have its' rewards, and if you bought a 2" shorter unit and didn't like it, you could always space it back down in 1/2" increments.

Mr X
05-12-2004, 08:14 PM
Mario,
there are too many other issues to factor in.
You have to make sure that your engine hatch clearance
will not be a problem.
Also your stringers may not be high enough to go up much.
Then your transom/exhaust may be an issue.
You have to think EVERYTHING through and measure everything
several times to figure out how high you can go up.
Some classics came with 14 1/4. Others were 14 1/2

If you go too high cavatation and porpoising will be an issue.

I KNOW that 2" higher is good for 4-6 MPH, as I have done it.

Are you planning on completely re-glassing in a new transom,
that is really the only correct way to do it.

MOP
05-12-2004, 08:19 PM
Are the newer Alphas shorter than say 85-87 versions? Mine is longer and mounted higher than a late 22C W/Bravo I checked out locally?

mphatc
05-12-2004, 08:24 PM
Deck is a Corsican . . . . lots of room!

Transom exhaust holes don't need to change as there are 2 sections of flex pipe, 1 vertical, 1 horizontal . .

I don't want ANY porposing, and I want to retain the lively hadling the baot had before.

Lenny, please explain the 12 degrees . . . is this the transom angle that I need to factor into the equation to arrive at the correct X???

Mario

MOP
05-12-2004, 08:55 PM
The detractor is the raising of the CG, some boats get squirrelly. As a matter of course I would put the cav plate about 1 to 1-1/2 inches above the keel maybe even higher for better speed. Steves 18 with the BH drive has the engine way up and handles great, there has to be a bunch of 18's with a raised X. I would get more feed back and think this out awhile and cut once.

Phil

Lenny
05-13-2004, 01:17 AM
Mario, follow Teds' advise. That is what 12-12.5 degrees works out to on the transom measured AGAINST the actual surface. I would do AT LEAST the 14 1/2. This is a measured, on the transom, actual measurement that compensates for the transom angle. We are about 12 1/2 degrees I believe. That is what I come up with with a set of 24" dividers. 14 1/2" would be a very stock/like conservative placement and retain good balance imo.

A 15 degree transom get a recommended 14 1/4" "X" dimension from Merc, 16 3/8" for a Blackhawk so we are on the higher side of Merc stock recommendations. I have a copy from DONZI on "X" dimension placement for 18's and 350 MAG/MPI and it shows 14 1/2". Take it from there. By the way, Ted would know. ;)

DONZI
05-13-2004, 06:06 AM
Member Kent Perroux has done this to his 18/bravo also.If you can contact him.He could also provide some feedback.

DonCig
01-02-2006, 11:50 AM
I measured my 1997 Donzi Classic 18 with a stock Bravo 1 from the factory and my X dim. is 14.5" as measured by the "tape measure" method.
I had the 350 mag MPI Gen+ engine with the stock Merc. silent choice exhaust system and my transom tips are 14.25" apart and the exhaust hole centerline is located 1.5" above the Gimbal stud reference line.

Ted and Lenny, thanks for your help.

DonCig

Woodsy
01-03-2006, 10:03 AM
Mario...

Go with what Ted said... I wouldn't go more than 14.5" and then I would start playing with an IMCO shorty setup.

Tell me you are finally going to get rid of those log type risers!

Woodsy

mrfixxall
01-03-2006, 10:31 AM
I dont think mercury makes a ford late model bellhousing..If i remember correctly they made ford bellhousing in 1973,74,75,76 but the stans for the gimble housing were wider..
just a thought..

mphatc
01-03-2006, 10:31 AM
Guys,

Ancient thread here . . . back from 2004 . . .

I did install my drive at 14 3/4" and my engine came back to the exact same mounting location it was at originally as built with the Volvo and H&M 302!

Woodsy, Yes, I'm looking at something other than the H&M Logs , inspite of the loss of originality! Not a lot of options for the Ford 302 though ;-(

Happy New Year!

Mario