Does it have to be REAL CLOSE?

[Teammuir1]

OK everyone I am new to this forum but not really new to boating but
I now have a fixer upper and I want to install another motor on my JON BOAT
I have been told that you want a motor's decavatation plate even with the bottom of the boat..
PLEASE anyone Educate me on this subject......

 

[Barnacle_Bill]

Re: Does it have to be REAL CLOSE?

The anti cavitation plate should be with 1" of being even with the bottom of the boat for best performance. If it is too high the motor could run hot. If too low poor performance.

 

[bowman316]

Re: Does it have to be REAL CLOSE?

i would rather have it 4 inches too low, than 1 inch too high

 

[Teammuir1]

Re: Does it have to be REAL CLOSE?

OK now I understand about it being to High... the motor would not get
enough water to allow for good cooling
but what about to low.. you mentioned that it would have poor performance... PLEASE explain more....
in the mean time let me tell you what I have and what I want to do.
I dont have any pictures able to be uploaded just yet but they
will come soon.
I have an Alumacraft Jon Boat that has been extreamly modified
to be used as a Deck fishing boat....well I have a Johnson 33 2 stoke on it now
but I want more ( power, speed, performance ) lol.
so I have heard of short shaft and long shaft....
my 33 is a short shaft... I want to install a Johnson 70 hp on it
my 33 is an electric start ( by the way ) I know pics tell a thousand words..
but tell me more about this difference... if any from a 33 to a 70 in the length of the motor.

 

[tx1961whaler]

Re: Does it have to be REAL CLOSE?

I have an Alumacraft Jon Boat that has been extreamly modified
to be used as a Deck fishing boat....well I have a Johnson 33 2 stoke on it now
but I want more ( power, speed, performance ) lol.
so I have heard of short shaft and long shaft....
my 33 is a short shaft... I want to install a Johnson 70 hp on it
my 33 is an electric start ( by the way ) I know pics tell a thousand words..
but tell me more about this difference... if any from a 33 to a 70 in the length of the motor.

A 70 could be a long shaft. Post the model number to be sure. What is the boat rated for in HP? You're doubling the HP and really increasing the weight and that can make for some pretty squirrelly handling (read:dangerous) if you're not careful.
A long shaft motor on a 15" transom will drag the lower end in the water and slow the boat down and maybe cause handling issues.

 

[Teammuir1]

Re: Does it have to be REAL CLOSE?

I do not have the 70 motor yet... I want to get one.
I was told that they make a short shaft 70....
I am not sure as the hp rating on the boat...
the boat is a 16 ft'r
as far as the weight I am not worried to much about that
I am going to install these guys on the back of the boat
boat tanks to give me 250 lbs more buoyancy ......

 

[Teammuir1]

Re: Does it have to be REAL CLOSE?

Looking at the picture I posted it appears that the boat has
a Jack Plate to raise the motor up......
I guess If I found a 70 motor long shaft then I could
add a Jack Plate.... that would get me maximum adjustments for
better performance!!!
If I have to I can always make a new Transom one that's thicker and stronger than the one that came on the boat.

 

[d.boat]

Re: Does it have to be REAL CLOSE?

First things first, you're getting ahead of yourself.

1. What is the HP rating of the boat. Don't procede until you know. Then, stick within it. The HP rating has to do with the strength of the boat sure, but it is mainly based on the length, width and height of the gunwales. If your boat doesn't have a capacity plate on it, contact the manufacturer (look for hull serial number), or there is a formula on the US Coast Guard website.

2. What is the transom height of the boat? That will tell you what length shaft to get. The thing in your photo does not look like a jack plate to me, it looks like an aftermarket trim/tilt unit. The jack plate will look similar but won't tilt up like that. If you do get a jack plate, you will have some flexibility with your shaft length, but only within the travel of it.

You can fairly easily adjust upwards and inch or so if necessary w/o a jack plate, but not alot more than that.

Good luck.

 

[tx1961whaler]

Re: Does it have to be REAL CLOSE?

An Alumacraft MV1648 is rated for 40 hp. A regular 1648 (flat bottom) is rated for 35 HP.

A 1650AW welded is rated for either 60 or 75 HP

 

[bowman316]

Re: Does it have to be REAL CLOSE?

you can take out the 5 inch extension on the lower unit, and swap out the drive shaft and shift shaft for a short shaft

 

[Teammuir1]

Re: Does it have to be REAL CLOSE?

WOW
I am thrilled to get alot of interest in helping me out..
THANKS ALOT GUYS...
so let me try to answere what I know.....
I just walked out and took some pictures.. and looked for the Id
tag.... and then Measured the Transom.
so I have enclosed 2 pics of the ID tag on the back of the Transom
The Transom measures 16 inches
I know my 33 johnson is a short shaft
I am not sure how to decifer the ID tag... I see there is a 78 on the end
so I suspect that the boat is a 1978???
I hope you guys can help me figure this out.

 

[Teammuir1]

Re: Does it have to be REAL CLOSE?

Here is a picture of my boat!
I have not yet seen a pic of someone else's boat fixed up
like this one.
I have googled jon boats looked at alot different ones
but not really like mine.
If some one has a pic for ideas please post them,,,, would really like to see
other guys boats..... ( Jon Boats ) lol

 

[tx1961whaler]

Re: Does it have to be REAL CLOSE?

WOW
I am thrilled to get alot of interest in helping me out..
THANKS ALOT GUYS...
so let me try to answere what I know.....
I just walked out and took some pictures.. and looked for the Id
tag.... and then Measured the Transom.
so I have enclosed 2 pics of the ID tag on the back of the Transom
The Transom measures 16 inches
I know my 33 johnson is a short shaft
I am not sure how to decifer the ID tag... I see there is a 78 on the end
so I suspect that the boat is a 1978???
I hope you guys can help me figure this out.

See if you can get some paint remover and get the rustoleum off of the sticker that is painted over above the stamped plate. The pictures of the boat looks like a regular 1648 flat bottomed, riveted hull.

 

[Teammuir1]

Re: Does it have to be REAL CLOSE?

tx1961whaler

The sticker does not have anything on it..
I removed the paint. but the sticker is actually scratched
before it was painted...
sooo that was a bust.

the tag thats in the pic reads

ACBF4876M78F

I am not so sure how to determine whats what though....

 

[Teammuir1]

Re: Does it have to be REAL CLOSE?

Did Alumacraft make 1648's? I only found LOWE'S for the 1648

Mine is a Alumacraft

 

[tx1961whaler]

Re: Does it have to be REAL CLOSE?

They currently make a modified-vee hull MV1648:
http://alumacraft.com/jon-boats/mv-1648-ncs.php
Looks like yours has the flat front, which would make it a flat bottom. The MV's have the point up front.

 

[F_R]

Re: Does it have to be REAL CLOSE?

Why don't you simply call Alumacraft's customer service guy and ask him? You scare me to death, thinking of putting a 70hp on a flat bottom jon boat. Suicide, unless the factory says it is ok.

 

[tx1961whaler]

Re: Does it have to be REAL CLOSE?

Why don't you simply call Alumacraft's customer service guy and ask him? You scare me to death, thinking of putting a 70hp on a flat bottom jon boat. Suicide, unless the factory says it is ok.

I was waiting to see who was going to pipe and and be the bad guy here.
I was just tap dancing around it and pushing specs showing that no flat bottom from Alumacraft has more than a 35 hp rating...
I put a 50 HP force on my 13 foot Whaler for one day at the time when I had no dependents. That was a stupid-scary thing to do, as it was very unpredictable as to what it was going to do. I think the hull was just running on the little skegs at about 50 mph......needless to say the 40 went back on the next day, and I think it is slightly overpowered with the 40....

 

[Teammuir1]

Re: Does it have to be REAL CLOSE?

OK I get what you guys are saying....
so there has to be some kinda problem with my 33 then.
I dont have a speedo nor a GPS for the water..
I have a GPS for my Truck.. ( if it will work I should try it )
I dont know how fast the boat is actually going.....
( SLOW ) I know that ... lol
1.) I know the hull needs cleaning...
2.) I dont know what RPM the motor is turning..
but I had my son of 21 yrs old drive it while I had the cover off
and tried tuning it while he was driving and I got maybe what sounded
to be 300 more Rpms..... but then it wouldnt idle correctly.. so I adjusted
it back......
the boat was built in 1981 from there it was kept in a garage for
its entire life I know some wood needs replacing.. but the wood thats rotted
is not WATER LOGGED.... just rotted.... ( over time )
MY GRAND FATHER is the person that built this boat.. it has alot of
sintamental value to me... My son and I fish alot off of it.....
so I wanted to make this boat go faster.....
I LOOK on U TUBE and guys in there Jon BOATS are going alot faster than I am .. but they dont have the PAY LOAD as I do either....
any more thoughts......
I really am appreciative for all your all's comments...
I know the transom has some VERY STRONG braces in the back for support....
I am not sure as far as the weight for my 33 johnson... but I did look up the weight for a 70 johnson.. and its 250 pds..... thats why I was thinking of adding the boat floats to the rear.....
I Am lost here my Grandfather said he actually pulled a SKI'er
with this boat the way that it is presently... I AM TELLING HIM there is NO WAY IN HELL... I dont even get the boat up off to PLANE OUT......
never mind pull a ski'er.....
THE MOTOR.... is running GREAT.. starts immediatly idles SUPER....and takes off just fine.. but just does not PLANE OUT... nor go fast enough to.
any more thoughts?

 

[Teammuir1]

Re: Does it have to be REAL CLOSE?

Check out the Jon Boat in the video
THATS ONE BIG MOTOR...... lol
cant tell the size of the transom but
it sure looks small.. LOL

http://www.youtube.com/watch?v=SaLb0-y0Fvg&feature=related