how much set back is too much on a 20' runabout

[bleedblue94]

im doing a full restore on a 20' 1991 bayliner capri and have a 1983 175 johnson 90 degree motor i want to put on it. i need to know how much setback will be too much for this boat and motor. 6", 8", 10", 12"? thanks

 

[Texasmark]

Re: how much set back is too much on a 20' runabout

Rename your thread and address it to Mr. DHadley. He is the xpert on "setup". Don't PM him as what he has to say is for all to read and that can't happen with a PM.

Mark

 

[bleedblue94]

Re: how much set back is too much on a 20' runabout

thanks, im not sure how to rename the thread? do i need a mod to do that?

 

[Dhadley]

Re: how much set back is too much on a 20' runabout

There wasn't a 60* 175 in 83 but no matter. A lot depends on how it ran before with the motor on the transom. If you need a lot of bow lift I'd probably go with a 8" offset. You can always add 2" spacers so that will give you some options.

 

[bleedblue94]

Re: how much set back is too much on a 20' runabout

There wasn't a 60* 175 in 83 but no matter. A lot depends on how it ran before with the motor on the transom. If you need a lot of bow lift I'd probably go with a 8" offset. You can always add 2" spacers so that will give you some options.

truthfully im in the later stages of a full rebuild of this boat and swapping out the 5 cylinder force with this johnson. the main issue is the hull has built in swim platforms designed into it on either side of the motor that flare outward. the motor can not fully swing side to side as it is just hitting these platforms. if i use setback i will be able to gain the clearance i need though bc the gap between the platforms is a "V" shape. thats why im trying to find out how much set back would be the most i could safely get away with. i know there isnt an exact rule or anything but im asking more from people w experience for advice. would just getting the 10" plate be too much?

 

[Jlawsen]

Re: how much set back is too much on a 20' runabout

Typically a boat of that hull design can perform well with up to a 5-1/2" set back.

 

[JB]

Re: how much set back is too much on a 20' runabout

Swim ladders or platforms adjacent to an outboard scare the dickens out of me. The amount of setback might just determine how much of your child's leg you could amputate in a moment of distraction.

 

[bleedblue94]

Re: how much set back is too much on a 20' runabout

Swim ladders or platforms adjacent to an outboard scare the dickens out of me. The amount of setback might just determine how much of your child's leg you could amputate in a moment of distraction.

i guess if youre reckless and have the motor running while people are getting in and out of the boat, which i never do...

 

[JB]

Re: how much set back is too much on a 20' runabout

i guess if you're reckless and have the motor running while people are getting in and out of the boat, which i never do...

Nobody makes stupid mistakes on purpose.

 

[bleedblue94]

Re: how much set back is too much on a 20' runabout

Nobody makes stupid mistakes on purpose.

This I understand as many bad things are not meant to happen. But IF the key is not in the ignition while anchored or afloat and is sitting on the dash, then the only way for the motor to start would be divine intervention or one of the most fantastic series of electrical shortouts I could imagine.

Anyways back to topic. I think I'm going to have to go with either the 10" or 12" bc of clearance issues with molded swim platforms and my new motor being able to fully swing/turn. I think the 10" will work (clear the motor of hitting the swim platforms). I just would consider the 12" if it will not be deterimental. I am going to run stainless steel smart tabs as recommended by nauticus which should alieveate most of the issues of such a long bracket. The transom is rock solid. A nice sandwhich of three brand new 3/4" pieces of marine ply, new stringers of 3/4" clear pine and knee braces of the 3/4" clear pine w pieces of 3/4" marine ply wrapped on either side of the clear pine that will push on the transom. So strength in that way is not a concern.

I'm confident I can run the 10" setback, but would the 12" be too much?

And by the way thanks to people for commenting and adding info. It is appreciated

 

[Philster]

Re: how much set back is too much on a 20' runabout

At that setback, you need to raise the motor anywhere from 1-3" above it's starting point (of AV plate even with bottom).

You'll need to tinker with engine height for sure. You won't get it right from jump street.

 

[Jlawsen]

Re: how much set back is too much on a 20' runabout

10 and 12 are both too much. You have a V hull not a pad. Your motor is going to be in dirty water. You will cavitate with minimal trim up and have problems in turns. However, if your pockets are deep then go ahead.

 

[bleedblue94]

Re: how much set back is too much on a 20' runabout

At that setback, you need to raise the motor anywhere from 1-3" above it's starting point (of AV plate even with bottom).

You'll need to tinker with engine height for sure. You won't get it right from jump street.

I'm well aware I will have to raise it. I know it will take some tinkering to get it right. I'm just worried that the 10-12 will be unworkable. The feedback I've gotten is with that much power and the proper adjustments and tabs it should work out properly w adjustments if I have the patience. But patience will be needed with either the 10" or 12". I'm just wondering if the 12" will not be managable...

 

[bleedblue94]

Re: how much set back is too much on a 20' runabout

i went with the 10" plate from vance. should be here today. i think i have enough buoyancy to compensate, and the hull design along with the smart tabs should ensure things work well. my next issue will be routing the steering cable due to the molded swim platforms on the hull. i will post pictures of it all later