Jack plate on small boat questions

I have an aluminum V hull which has a 15" transom, but most all of my motors are 20" shaft. The boat is only a 14.5" V hull with a minimal deadrise at the stern, maybe 4" or so.
My question is, if I use a fixed jack plate, which raises the motor up, what is the correct setting or starting point? Most of the jack plates are 4" setback by 3.5" rise, making the measured height of my transom exactly 20". The boat has a max of 25 hp, and I have both a 25 and 10 hp motor which I'd like to switch back and forth as needed. Do I set the anti-cavitation plate as I would if the motor were directly on the transom?
Will I likely notice any adverse affects with the motor mounted on the plate?

I am guessing that I'll need to mount the plate at it's highest point to get the motor even with the bottom of the boat, and I think maybe it might need to be up a half inch or an inch which may be an issue. I use the same motors on another boat, so I don't want to convert them to 20" shafts and their perfect running motors as they are. (Usually if the 10hp is on this boat, the 25 hp is on my other boat or the opposite).

The boat is light, maybe 400lbs at best plus motor when in the water.
Is there any handling change or running characteristics associated with moving the motor back that little bit? Should I move it farther back? I can make my own jack plate if needed.

Anyone have any experience with a TH Mini Jacker?

http://www.iboats.com/T_H_Marine_Mi...14970563--**********.504744957--view_id.40133

I like the boat but would like to run my newer motors, which are all long shaft. I do have to say that I am a bit concerned about drilling the never drilled transom as well as the fact that the transom wood on this boat doesn't go to the bottom, so I will have to either only use the upper holes or add some sort of reinforcement to the lower transom?

Re: Jack plate on small boat questions

thr mini jacker is great, but a transom elevator or homemade mini jacker is much cheaper.

Re: Jack plate on small boat questions

i put TH mini jacker on a 15ft fiberglass boat last summer and it works great. i was mounting a johnson 28hp SPL and set the cav plate even with the bottom of the transom. i have had no problem with water pick up but do get a little bit of cavitation in rough water. if i was remounting it i would probably go a half or 3/4 in lower to hopefully get rid of the cavitation. i bought mine on ebay for $60 brand new. i bolted my motor on to the mini jacker. when i was testing the set up i just had the motor clamped on and had a little problem with it vibrating loose a liitle bit. it was a little tight to get to the clamp handles on the motor so i may not have had it clamped tight to start with. i assume it was operator error not jack plate error. the boat handles fine so if it made a difference in handling it was minor.

Re: Jack plate on small boat questions

Both motors I have will be clamp on, I don't want to go the bolt on route if I can help it since I don't keep the motor on the boat when not in use. Too many small motors walk away at night around here.
My larger motor is a Merc, so I don't have the folding handles, but from what I can see, to get the anti-cavitation plate level, The plate will be all the way up on the transom. So I should have plenty of room to tighten the clamps. The Merc motor has bolt heads, the smaller Evinrude has toggle type levers.

I was thinking about making the jack plate but I figured the Mini-Jacker would be lighter. than using the four pieces of heavy angle iron, and since the motor will only clamp on, I'd have to make up a mounting plate as well. I'd rather not rely on just plywood. I like the fact that the Mini-Jacker is all one piece. Adjustability isn't a concern, once it's set for the bigger motor, that's where it will stay, if the transom was 20" in the first place, I'd not have the option to adjust it anyway.

Not getting good water to the smaller motor was something I was concerned about, I have that problem with my other boat since it's transom is a bit taller for some reason, motor sits about 1 3/4" above the bottom of the boat. I borrowed the same motor in a 25" sailboat edition and that problem went away but I lost all sorts of speed with the extra long shaft which put the anti-cavitation plate below the bottom of the boat by about a half inch.
So that wasn't the cure. The best situation I have is with a lower pitch prop than I would normally run and take it easy. I get the best all around performance that way even though I can border on over revving if I'm not careful. I don't abuse it anyhow, and it works better that way when loaded too. I'd like to be able to run that same motor on this boat as well, hopefully without any changes. My concern is with the larger motor, as we only have one lake with a 10HP max hp limit and I rarely fish there, but I'd like the ability to do so with either boat.

Re: Jack plate on small boat questions

I got a look at one of those TH Mini Jacker plates today which was installed on a similar boat, I didn't like how much of the plate's mounting surface stuck up above the transom to get a full 5" of lift. About 1/4 of the plates mounting surface was above the transom's top edge. Leaving only the bottom 2/3 or so to bolt it secure to the transom. It looks like a custom jack plate is in order.

Is there any advantage of going farther back? If I'm going to build it, I can make it even a farther set back. I was told by a local shop here that the farther I get the motor back, the higher I can run the motor, and the easier it will be to get up on plane?
Does any of this sound right? Keep in mind its only a small aluminum boat.

Re: Jack plate on small boat questions

on that size boat i don't think you will see a lot of difference. i would just make a transom elevator, which is what a Mini Jacker is. it is not a jack plate. home depot sell 1 1/2 inch aluminum angle, that is all you need for a transom elevator.

Re: Jack plate on small boat questions

TD, what did you use for the motor panel itself? Just plywood or did you back it with something?

I was also thinking that maybe since the boat is so small, and that I'm dealing with such a small prop and motor, it may react even more so to a set back motor?

I have some 4" angle here I can use and I've also got some 3" C channel that I've considered using but I like the idea of the wider flange I'll get with the angle iron. The C channel has only a 1 3/4" flange. I was thinking of running a 4 stroke 25hp which adds some weight, but right now, my 2 stroke Evinrude 25 and my Honda 10hp 4 stroke are nearly the same weight. I have concerns also about the leverage effect of adding the weight too far back too.
The transom is single wall, no splashwell and only one knee brace. The boat is rated at 25hp max.

Re: Jack plate on small boat questions

Check out these products.

http://www.iboats.com/Transom_Eleva...7787572--**********.882173635--view_id.168950

made by this company -

http://www.trmarine.com/cat.html

For an adjustable jack plate -

http://www.thesportscenterstore.com/proddetail.php?prod=241206

Re: Jack plate on small boat questions

I am currently running a 35hp 3 cylinder johnson long shaft on a short transom boat using the th marine jack plate. My jack plate mounting holes also sit pretty high above the transom, probly a 1/4 of the total length, but I have yet to have any ill effects. Motor still isn't quite level with the bottom of the boat, but thats as high as i was willing to go. If it hasn't broke under all that torque Im pretty sure your 25 and 10 will be fine.