How to properly install a outboard

[j_k_bisson]

I'm coming to the point where I need to install my new rebuilt/restored outboard and I am trying to figure out how to determine the correct height for the installation. Here is the pic of my question.



What is the "X" height that it needs.

The motor is a 1987 225hp Evinrude. The boat is a 1991 Bayliner Trophy. Boat transom height is made for a 25" shaft motor. The motor is a 20# but with a 5" Bay Mfg Extension kit making it a 25" motor. SO all this is good.

Just need to to figure out what the fine measurement is at the bottom of the hull.

 

[1979checkmate]

Re: How to properly install a outboard

There is no answer for you. The truth is, any combination of boat, motor, and propeller will have a different optimum height. Get a jackplate so you can fine tune it after testing.

 

[carholme]

Re: How to properly install a outboard

jk;

The reccomended cav plate position to begin with is per this:

http://www.boatmotors.com/ref/shaft_length.html

Have you determined that you actually have a cav plate that is lower than the bottom of the transom and if so by how much? I wouldn't be sweating a jackplate at this point until you have determined that X value.
Sometimes if you are trying to fine tune it for a small amount, some people use a small shim on top of the transom, using the slots in the clamp bracket to allow the engine to come up a bit.

If you haven't hung it yet, measuring the transom and the distance between the top of the transom bracket and the cav plate should give you a pretty close idea of what X will be on installation.

Not trying to counter 1979checkmate but I am just not a fan of jackplates unless there is a real need.

Gerry

 

[1979checkmate]

Re: How to properly install a outboard

The main reason i suggested a jackplate is i come from a performance boating background, now with a bayliner trophy, i do imagine the OP's main concern is not speed. However, having the optimum height does help economy a bit in most cases as well. Also, my main reason for running jackplates is actually not the adjustability in height (mine always stays at the same spot), it is for the setback. At least on my boat and other performance hulls, the setback makes a HUGE difference in handling.

 

[64osby]

Re: How to properly install a outboard

J K I'm not an expert on this, most of the info I have seen on this site calls for the starting point to be cavitation plate about 1" above bottom of hull. Fine tune from there.

Nice job on the boat by the way.

 

[j_k_bisson]

Re: How to properly install a outboard

Thanks Guys for all the help with this. I'll start with even if I can. Depends on the height of the transom and the true length of the drive/mid section. I have not started playing with the measurements yet. As the boat is at a buddies house and I still need to purchase the extention kit. The kit will be ordered tomorrow and when it comes in I'll get everyhting assembled and then we start playing with this issue.

Just wantes to get an understanding of how all this works.

I would think you would want to be 1" on the x dimension. That way the hull would not cause any cavitation into the prop at any speeds. Is this true?

The hull has trim tabs so adding the jack plate is not needed.

 

[carholme]

Re: How to properly install a outboard

j_k;

I am not an expert either but my own experience is to start with the plate just even with the lowest transom point and accounts for many of the variables with hull bottoms. This at least ensures that I have the best chance of a prop not coming out of the water in a turn as a result of the engine being too high.

However 64osby is correct that many start out with it set high.

I refer you to these articles which may assist you. If, when you get the extension kit and have a trial fit on the transom and are close to the position you feel is best, I would get it on the water and see what is happening.

http://outboard-boat.com/index.php?...-systems-and-set-ups&Itemid=53&layout=default

Gerry

 

[j_k_bisson]

Re: How to properly install a outboard

My only problem is that the "testing method" is a bit danting to me. Hell I have a 225 hp motor on a 21 trophy. That could most likely get 45+ mph. It's not really safe in my opinion to be doing high speed turns in it of 3/4 throtle. 30mph...... I'll go with the 1/2" to 3/4" like the recommend and call it a day.

 

[Bob_VT]

Re: How to properly install a outboard

Shoot dhadley a PM and ask him. I consider him the Pro in the X factor area