View Full Version : Optimal Jet OB transom Height 60/40 Merc

06-09-2009, 11:43 PM
Just bought a 60/40 Merc Jet for my Alumaweld jet boat.
Season is short here in Winter Park, Colorado, so I need to make sure
I get the height right the first time.

Dealer advised that the Shoe should be 1/8 inch above the bottom of the boat. The owners manual isn't much help (or I just can't find the ref)

Anyway, the motor was sold as having a 15" shaft. The actual length between the top of the motor clamp and front lip of the shoe is very close to 25". I have built the transom up to 25", but can lower or raise it if needed.

Anyone know the best height range for the transom?

Any help would be appreciated.


07-29-2009, 06:15 PM
probably late for this thread.

I use a straight edge comming off the bottom of boat. and set my motor where the straight edge hits exactly in the middle of the leading edge of jet unit (shoe) and the start of the grates.

60/40 mercs made two different sizes of shafts. a 15in midsection and a 20in section. the 15in midsection requires a 22 in transom. a 20 inch midsection requires a 25 in transom

08-03-2009, 02:13 AM
22.5" for 15" motor, 28.5" for 20" and 32.5" for 25" motor.... if you have alumawelds stock 20'' transom its basically the top holes of the mounting bracket, with the 15" mid..

the base of the shoe( leading edge lip) needs to be 1/8" below bottom of hull the lip is a total of just over 1/4" tall and the difference needs to be split in order to properly run clean and not spray, yet still maintain bite in the bouncing a jet does and not free rev the motor all the time..

08-03-2009, 02:14 AM
and with a jet, there is no second chances.... if your low it gets you wet and sprays like hell, and runs like total crap.... if its 2 high it goes no where and free revs once the boat comes on plane...

08-03-2009, 12:13 PM
River ratj40 & 150aintenuff:

Pretty new to the forum so I'm just learning how to respond to your comments.

Thank you very much for your time and help!

River ratj40:
you mentioned sharpening the impeller and polishing it. My dad used to have that done on his Alumaweld. He was running a 427CU and I don't know if that would have more of an effective on my smaller motor. I have a stainless impeller and have not worked much with that metal. what tools are best for sharpening and polishing?
Is there a firm like Solas that sells polished impellers or a firm that specializes in the sharpening and polishing? The concept makes great sense. I just want to make sure I do it right.

The Hull plate is stamped Alumaweld, but was made by "Xpress" out of Hotsprings, Arkansas. The reason I bring that up is that the transom slopes back at 73 degrees on my boat (My brothers Alumaweld has a 90 degress transom) It looks like the configuration of my hull allow the water to fill in behind the boat until it hits speed (found this out when running a larger engine with prop) I see you use a jack plate. Do you think the Jack plate in my garage (5" set back) would help or hinder the performance? Also, I see you work at a shop. What are the most feasible performance enhancing mods that can be done to a 09 Merc 60/40? Plugs, wires, legal fuel blending?

Thanks again!


08-03-2009, 07:23 PM
do not use a jackplate. water comes off the bottom of boat and loads pump. the more room that water has it doesnt load the pump properly(especially in rough water)

as far as polishing...i use a local machine shop.. they do great work...pm and ill get you their number.

08-03-2009, 09:33 PM
Thanks for the feed back and I'll put the jack in the back for another application

08-03-2009, 09:45 PM
jets can use a plate... but they dont gain any thing.. just bolt to transom

08-04-2009, 01:56 AM
90.6 MPH and I wouldn't have much left either.
Way to Go! That is moving in the water.

Thanks for your feed back.

When do you plan to be running again?