wrote in message
...
My boat has a 20" transom height, my motor Johnson 120hp. has a 25"
shaft. Should I convert the motor back to a 20" or install a Jack plate
or an adapter plate to raise the motor? Or should I swap/trade the
motor for a 20" long shaft? Or should I get a boat hull with a 25"
transom? How common is a 25" transom, were their many made? Which
models and manufacturers made 25" transoms? What to do? What to do?
Any help or advice appreciated. Thanks. Tom.

Perhaps you could fill in a little more information like what it is
you are trying to accomplish. Are you buying a boat at one place
and a motor at another - have a motor and are looking for a boat?

It's always better to match the motor to the transom - anything else
like jack plates and the like are patches. 25" transoms are common
so if you have a motor but not a boat, that isn't a problem.

My opinion.

Later,

Tom

Ok I'll give some more info, I have a 16' 4winns Marquis with a 75hp.
Mercury 20" transom on it. The problem is that the 75 is not enough
power for slalom skiing starts so I bought a 120hp. Johnson, the 4winns
is rated @ 125hp. Maximum. Then I found out that the Johnson has the
extra longshaft, after I bought it of course. So now I am trying to
decide what would be the best way to go in terms of cost and
performance. Any advice? I was concerned about the extra stress (if
any) on the transom from lifting the motor an extra 5" on a jack plate,
or any possible performance improvement from the Prop being further back
and away when trimmed up at speed if anyone has done this. I was also
planning on mounting the jack plate on the pre-drilled mercury transom
mounting holes thereby eliminating the need to drill more holes in the
transom. Or would it just be easier/better to find a decent used hull
with a 25" transom. Who made a 25" transom in a 16'-18' ski/fish open
or closed bow V-hull boat? If any one knows. Thanks. Tom.

Ok I'll give some more info, I have a 16' 4winns Marquis with a 75hp.
Mercury 20" transom on it. The problem is that the 75 is not enough
power for slalom skiing starts so I bought a 120hp. Johnson, the 4winns
is rated @ 125hp. Maximum. Then I found out that the Johnson has the
extra longshaft, after I bought it of course. So now I am trying to
decide what would be the best way to go in terms of cost and
performance. Any advice? I was concerned about the extra stress (if
any) on the transom from lifting the motor an extra 5" on a jack plate,
or any possible performance improvement from the Prop being further back
and away when trimmed up at speed if anyone has done this. I was also
planning on mounting the jack plate on the pre-drilled mercury transom
mounting holes thereby eliminating the need to drill more holes in the
transom. Or would it just be easier/better to find a decent used hull
with a 25" transom. Who made a 25" transom in a 16'-18' ski/fish open
or closed bow V-hull boat? If any one knows. Thanks. Tom.








I'd say your only hope is to buy a used lower unit. I had that problem and the
guy at the local salvage place traded me for $200. A good used one goes for
about $300. It's not a big deal to replace them. Shouldn't take more that a
couple of hours. If you do you might as well replace the two seals and the
water pump impeller.

Barry

wrote in message
...

Ok I'll give some more info, I have a 16' 4winns Marquis with a 75hp.
Mercury 20" transom on it. The problem is that the 75 is not enough
power for slalom skiing starts so I bought a 120hp. Johnson, the 4winns
is rated @ 125hp. Maximum. Then I found out that the Johnson has the
extra longshaft, after I bought it of course. So now I am trying to
decide what would be the best way to go in terms of cost and
performance. Any advice?

I know that there is a company that makes a conversion kit
for long-to-short and vice versa, but I can't find the information
at the moment. I'll email you when I find it.

Chances are you would need more than a lower unit to convert to a shorter
shaft. The tower housing (part of the mid section) has to be changed also.

I would install a jack plate that is capable of being set for 2" of setback.
Use the same mounting holes on the transom. Mount the jack plate as high as
possible. Then mount the engine as high as possible. Then adjust so the
cavitation plate is 1" above the bottom of the boat w/ the motor trimmed
flat. The extra stress is not a concern.

More setback will increase top end speed but will cost you on hole shot for
skiing.

Since you will have to change props anyway, I would recommend a good 4 blade
SS prop for extra hole shot performance.
You want your rpms right at max for best hole shot. Try a few props before
you buy. Guess is you will need a 21 or 22 pitch but that is a guess.

Tony
My boats and autos - http://t.thomas.home.mchsi.com



wrote in message
...
Ok I'll give some more info, I have a 16' 4winns Marquis with a 75hp.
Mercury 20" transom on it. The problem is that the 75 is not enough
power for slalom skiing starts so I bought a 120hp. Johnson, the 4winns
is rated @ 125hp. Maximum. Then I found out that the Johnson has the
extra longshaft, after I bought it of course. So now I am trying to
decide what would be the best way to go in terms of cost and
performance. Any advice? I was concerned about the extra stress (if
any) on the transom from lifting the motor an extra 5" on a jack plate,
or any possible performance improvement from the Prop being further back
and away when trimmed up at speed if anyone has done this. I was also
planning on mounting the jack plate on the pre-drilled mercury transom
mounting holes thereby eliminating the need to drill more holes in the
transom. Or would it just be easier/better to find a decent used hull
with a 25" transom. Who made a 25" transom in a 16'-18' ski/fish open
or closed bow V-hull boat? If any one knows. Thanks. Tom.

Ask your questions here www.screamandfly.com


wrote in message
...
My boat has a 20" transom height, my motor Johnson 120hp. has a 25"
shaft. Should I convert the motor back to a 20" or install a Jack plate
or an adapter plate to raise the motor? Or should I swap/trade the
motor for a 20" long shaft? Or should I get a boat hull with a 25"
transom? How common is a 25" transom, were their many made? Which
models and manufacturers made 25" transoms? What to do? What to do?
Any help or advice appreciated. Thanks. Tom.

Why. When was the last time a drag racer worked on a Johnson 120 hp 25"
shaft engine.

Maybe all the OT posters could go there.

--
Tony
my boats and autos - http://t.thomas.home.mchsi.com


"Woodchuck" wrote in message
...
Ask your questions here www.screamandfly.com


wrote in message
...
My boat has a 20" transom height, my motor Johnson 120hp. has a 25"
shaft. Should I convert the motor back to a 20" or install a Jack plate
or an adapter plate to raise the motor? Or should I swap/trade the
motor for a 20" long shaft? Or should I get a boat hull with a 25"
transom? How common is a 25" transom, were their many made? Which
models and manufacturers made 25" transoms? What to do? What to do?
Any help or advice appreciated. Thanks. Tom.

Thanks for the replies. I think I will try the Jack/lift plate and see
how it looks and performs, if it's no good then I can always search the
salvage yards or E-bay for a 20" motor with a blown powerhead, or if I
can find a bargain hull with a 25" transom. Thanks again for your
input. Tom.