Jack Plate

[AGENT 37]

Does anyone have a jack plate that allows the motor to be lowered below the normal height of the transom, or are they all designed to raise the motor?

I have a recently purchased 22' aluminum Bayrunner with a 24.5' transom. It has a 90 HP long shaft Honda that sits too high and has a cavitation/ventilation issue and does not allow me to utilize trim to bring the bow up out of the water because it must be run in the full trim down position. I need to get the bow out of the water because it is throwing too much water and making for a very wet ride. It blows out any time that I hit the throttle for a quick hole shot and it always blows out in a turn regardless of trim. I am curious as to the mounting bolt pattern on a fixed jack plate; would it allow for installation with existing holes in the transom at a lower level? I don't really want to drill new holes in the boat. But would have no problem making them in the jack plate if there was room. Also, would one of the hydraulic units be able to lower the outboard 2-4 inches? What is the range of travel in the down direction when mounted normally, or do they only allow for upward travel above the height of the transom? I've attached a picture. Thanks for any feed back.

Lower units are so stinking expensive, I thought about extending this motor out to 25 inches but it would cost over $2000 for new parts and I haven't been able to find any used ones for the past few weeks.

 

[72SideWinderSS]

Re: Jack Plate

I think I would be looking for a better technology prop, if it were me.

You didn't say what year, model of motor you have, or WOT rpm's and Speed, or the dia. and pitch of the propeller.

You may find with a more advanced prop, you may not have to buy or need a jack plate.

Just a thought.

 

[tashasdaddy]

Re: Jack Plate

it really sounds like you need a engine bracket mount, that sets the motor further back. you could mount a jackplate low, but, i believe you will get into trouble, with having clearance, for the trim and tilt function.

 

[Gary H NC]

Re: Jack Plate

Give this place a call.I bet they have or can make what you need!
Aluminum brackets that bolt to the transom and then the motor bolts to it.You could drill lower holes in the bracket and there you go..
Bobs can hook you up..
Maybe a couple hundred bucks at most or spend a little more for the adjustable jack plate.
http://www.bobsmachine.com/

 

[jevery]

Re: Jack Plate

I?m not clear on the length of your motor. You say a 90 HP long shaft, then you say you would consider extending the motor to 25?. A long shaft motor is 25? and a short shaft is 20?. Picture looks like a short shaft from what I can tell. It also looks like the motor is already set in the lowest position or setting. Is this correct. Because the water coming off the bottom of the hull rises quickly as it leaves the hull, just having the motor set farther back, as a jack plate would do, would likely solve your problem. Though, if your motor is a short shaft, it may be cheaper to convert it to a long shaft as opposed to the cost of a hydraulic jack plate. A manual jack plate is considerably cheaper, however, and would probably be the most cost effective solution ? and would still give you a lot of adjustment options for fine tuning.

 

[stevewolverton]

Re: Jack Plate

A long shaft motor is 25? and a short shaft is 20?.

short shaft = 15"
long = 20"
extra long = 25"

Right?

 

[AGENT 37]

Re: Jack Plate

Prop won't help. It's a 1998 Honda BF90 that runs the boat 30+ opened up. The problem is the water displaced by the hull allows too much air to get under the anti-ventilation plate and prop so it spins out.

I don't want to build an offshore bracket/ extension to get the motor back 2 and a half feet because I'm looking at the cost of the bracket plus the cost of new control cables and wiring harness. I'm also concerned about the leverage that would put on the .10" aluminum that the boat is constructed with. I'd be looking at around $2000 for that solution.

It's not a short 15" shaft motor, it's a long 20" shaft motor. It would cost me nearly $2000 to turn it into an extra long 25" shaft motor.

I thought about the problems of having a fixed mount jack plate interfering with TnT would cause. That's why I was looking at a hydraulic one that I could raise up when I need to tilt the motor for $800-$900.

I'd like to know if one of these things has the range of motion that allows them to be lowered a few inches as well as being raised several inches.
There is definitely a benefit of being able to vertically raise your motor up when slowly cruising in shallow water. And I can see myself using this quite a bit.
But my goal is to get the best performance out of my boat but not unload 2k to convert the motor to an extra long shaft or build an offshore bracket.
I understand that for every 12 inches you move the outboard off of the transom you can raise it up 1 inch and maintain performance (out to an obvious measure of distance)

 

[AGENT 37]

Re: Jack Plate

Bob's machine was who I was looking at. They haven't sent me a reply on the same question that I asked here yet.

What's the range of down-travel (if any) that you can get from one of these hydraulic jacks?

 

[AGENT 37]

Re: Jack Plate

Does TH marine make a good quality hydraulic jack plate? I like the fact that there is no pump to mount in the boat. I'm thinking of just drilling new holes in the boat to mount the plate at a lower position on the transom, at the furthest down position that I will run the motor and use it to lift the motor above the top of the transom when I need to tilt the motor. I thought about mounting the plate backwards or upside down too. I guess that I'll just have to get one and see how I can make it work. Now I just need to decide which one..... any input?

 

[tashasdaddy]

Re: Jack Plate

the hydrolic TH plate is probably going to be you answer, you need to see if it has enough travel. you would have to mount it so that in the lowered position the motor is right for operation, and that it has enough travel up, to be able to tilt it. they also have different set backs.

 

[AGENT 37]

Re: Jack Plate

Bob's machine makes a plate with 12 inches of travel; I think I saw 5 inches for TH. Bob's uses a separate reservoir in the boat and runs the hydraulic lines to the plate. I'm not sure what is better.... anybody had experience with either one? I'll probably go with the shortest set back that I can get and hopefully won't have to replace all of my controls. I'll have to figure out how to re-route my steering cable to prevent rub anyhow with the up and down travel. I'm thinking about having it come straight out the back of the transom then bend around rather than coming out into the splash well. Ideally I should probably just replace it with a hydraulic unit. But I'm already broke.....

 

[jevery]

Re: Jack Plate

short shaft = 15"
long = 20"
extra long = 25"

That's why I frequent this board. Learn something everyday. Never even heard of a 15" shaft. Now have to add XXLong 30" shaft.

 

[AGENT 37]

Re: Jack Plate

I went ahead and converted my Honda motor to an extra long shaft, 25 inches. I needed 2.75 inches to get the motor lowered to the keel. The 5 inch extension made it so that I needed to raise the motor 2.25 inches to get it level with the keel. That's exactly what I got when I remounted the motor through the lowest bolt holes. Absolutely perfect now.