Hey guys I need a bit of advise. I have an older aluminum Lowe line flat bottom v nose boat that has a 15" transom. The motor is an 1979 25 hp evinrude with a 17 inch shaft. I purchased a th marine mini jacker jack plate to help me get a little more clearance in shallow water. I'm not looking to go crazy with all the bells and whistles a jack plate can do. I just want to mount it correctly so that I get a few more inches In shallow water clearance.

My question is exactly where should I mount the motor. I'm under the understanding that the bottom of the anti ventilation plate should be even with the bottom of the boat as well as parallel with it. Am I correct in that assumption? Also there are a number of ribs on the bottom that stick down about an inch below the bottom of the boat. Should the anti vent plate be even with the bottom of the boat or an inch lower with the bottom of the ribs?

I want to make sure I get this all right before I drill the holes and make it permanent. This jack plate isn't really adjustable after it's installed. So any mistakes are likely to be hard for to fix.

Thanks for any advise you guys can give me prior to drilling the holes.

See pics below.





Here are the ribs on the bottom



Here it is with the bottom of the boat lined up with the bottom of the anti ventilation plate.



Or should the plate actually happy be an inch lower lined up with the bottom of the rib?



The leading edge of the motor is about 9.5 inches from the transom



I want to make sure I mount this right so I don't have problems with cavitation or keeping the engine cool since my intake is on the tab shown here.

the whole idea behind a jack plate is so that the engine can be adjusted to different heights. can't you drill a series of holes so that you can set the engine at 4 or 5 different heights, untill you find the best location for your needs.

Yes actually you can. It has indentions every inch you can drill out so you can adjust it up or down by an inch at a time. It's not really a jack plate per se, but more of a block to adapt a long shaft motor to a shorter transom. I just want to get my initial setup correct.

I believe you get your mounting hight measuring from the prop shaft not the cavitation plate.

I don't know what they answer is but I know someone on here does. Do you have a short shaft motor you can use for reference? hand a short shaft motor on the transom and measure to prop shaft then adjust the mounting bracket/motor to achieve the same distance with your motor.

Red Chevy is correct--The proper way to get your height is to level the bottom of the boat and level the anti-cav plate, Then measure from the floor to the bottom of the boat and floor to centerline of the prop shaft. Then subtract the 2 giving you propshaft to bottom of the hull measurement. By doing what you trying to accomplish with such a small motor your prolly going to loose any hole shot and top speed. Behind every boat the water swells up a bit while running. The amount of swell depends greatly on hull design and loading, so this swell will very from boat to boat. Swell is less at WOT, more and slower speeds.---Never jack your motor up to where the top water intake holes will be out of the water. You will loose water pressure reducing cooling abilities which could lead to catastrophic engine failure. Without having a water pressure gauge, this will be impossible to check. Talk with any shop that deals with small motors/john-boats they should be able to give you a max height for that motor.

Drilling multiple sets of holes in your transom is not the smartest approach. Consult with someone who actually does this kind of work and take their advice instead of trying to figure out which out of all the responses you get here is the correct one.

I don't think he was referring to multiple holes in the transom but in the plate itself. That I know you can do because the instructions say you can.

A lot of what I've read online says the anti ventilation or cav plate should be in line with the bottom of the boat! Is this not correct? I'm not looking to raise the motor drastically. I'm looking to adapt a longer shaft motor that is 17 inch shaft to a 15 inch transom.

I will do the measurement technique you mention and see what I get as well