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Hey everyone. I am going from a single 150 Yamaha to twin 70's using Jack Plates.
I have read up on this a bit and just want one last do or don't before I start drilling.
I want to use the Upper Single motor mount holes as the Outer mount holes for the twin motors.
1 this would save 2 more holes drilled in the transom.
2 if I moved the motors out more it would only be a inch or so. Between the boat ground wire and lifting eyes I am pretty limited.
3 This would also be a sure bet of not creating the dreaded Blind hole!
4 Ease of figuring out my hole pattern. I would use the existing hole and bolt my Jack plate to it, then level it out and bingo, the jack plate can be used as a template for the other holes.
I have seen a few photos of what looks like people already doing this and a few that went ahead and went right up against the lifting eyes.
Any comment or questions before I do this?
Thanks
Erick

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I believe the engines are supposed to be mounted a certain distance apart on centerline.

I do not have that info for Yamaha twins. Maybe someone else does.

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Interesting that you should bring this subject up.

I recently did the exact opposite re-rig that you are doing, going from twin Johnson 70's to a single Merc 150. Even more interesting, is that the Johnson 70's were installed exactly as you are contemplating, since this boat was originally rigged with a single Johnson 70. The owner wanted more power, so the installer used the upper holes of the single installation for the outer, upper holes of the twin 70 installation.

This gave a rather close engine centerline mounting of about 25-1/2". It worker OK on the old 19 Outrage hull, because of the non-vee transom shape, and the fact that both a single and twin installation on this hull uses the same 20" engines:

http://smg.photobucket.com/albums/v42...an0006.jpg.

I think you could use this method on an 18 Outrage, since you are using jackplates, but you first have to be sure the engines will be low enough. The deeper vee of the 18 Outrage requires twins spaced at 29-3/4" per Whaler's recommendation on this hull. So if you go closer, the engines are running higher.

I would personally fill the two holes and use Whaler's recommendation. That's what i did on my 18.

http://smg.photobucket.com/albums/v42...G_0454.jpg

If I can be of additional information, let me know. And if you use the closer mounting, I still have the original, like new tie bar for the closer mounting. I'll give you a good deal on it.

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Thanks Finnegan! I have In2Deeps setup from his 18 Outrage. I hope it will all just bolt in my 18 Ft outrage. I will let you know if that tie need bar.
The Jack Plates should give me a good up down on the motors and I will tune them in when I get going.
Still debating but Really I can only get 1 inch more on either side. Not sure this is even worth the hassle of aligning new holes. Once I get to actually doing the work i will rethink it. I really don't want a blind hole here.
Erick

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Are you saying that the Yamaha motor that is on there now is mounted using the bottom blind holes?

You say you are going to fill the bottom holes anyway, right?

Never drill any holes for any blind holes on the transom of an Outrage 18'...
These were never needed on this model hull.

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There is nothing wrong with your plan. When spacing twin engines there are two primary things to consider.

- Will there be sufficient space between the motors to avoid interference when the motors are turned?

- Will the transom be the appropriate height for the shaft length of motor chosen?

When using relatively thin inline outboards, like the Yamaha 70s, you can go as tight as 22" o.c. for the motor spacing, according the ABYC.

Whaler recommended a spacing of 29-3/4" o.c. presumably to accommodate twin 20" shaft length motors on hulls designed for a single 25" shaft length motor.

If you use the two upper holes you have now, you will end up with motor spacing of 25-3/4" o.c. which is more than enough clearance for the motors and only four inches less than the Whaler recommendation.

This will result in the motors being a little higher on the transom vis-a-vis the gearcases. Given that outboards have historically been set far too low on Whaler transoms, this is probably just fine. On the 18 foot hull that two inch difference in spacing per side will only result in a 5/8" difference in transom height; less than one bolt hole of spacing.

As far as the stern eyes/lifting eyes are concerned, if they are in the way, just move them. There is nothing to unscrewing them and drilling new 1/2" holes in a new location. You can do this anywhere in the reinforced (flat) part of the transom.

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The single motor does not have a blind hole. It is mounted pretty high like it should be. I am just concerned about the blind hole with the lower outer ones for the twin motors. The transom gets pretty shallow towards the sides and looks like if I move out as far as I can that the bolts won't come thru or will be right at the bottom where it will be hard to get too.
Oh one more thing I think I should tape up the transum before i drill thru to keep it from cracking the Gell coat.
thanks
Erick

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Thanks Tom, Duh, I did not think of just moving the eye/lifting holes. How about moving the ground wire? How is that connected?
thanks
Erick

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Erick,

The splashwell of the 18 is plenty deep enough to accommodate the mounting bolts of twin outboards. It was designed to accommodate them with the standard BIA pattern. Lay it out and you'll see.

Don't use tape when drilling the holes; clamp a block of scrap wood solidly to the transom and drill into it.

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The ground plate is secured with a single #12 screw. Just move that too if need be.

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Thanks Tom. You got me thinking too much now! LOL!

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I had twin Evinrude 70hp on my prior 1986 Outrage 18' and did not see that either the ground plate or the D-Rings had to be moved at all. They appeared to be in their original location and the engines were at the recommended distance apart.

http://users.sisqtel.net/jkriz/Outrag...age86.html

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Joe,

Are you *positive* your 70's were mounted 29-3/4" o.c.?

That last photo sure doesn't look like the two upper inside mounting bolts are 16-3/4" apart...

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Tom,

I spent $250 on a brand new OMC Twin Engine Tie Bar...
The engines were original to the boat and from what I remember I measured the distance before I bought the tie bar just to make sure...
These were 20 inch shaft motors mounted all the way down.

I still have the old tie bar but I think I took one of the ends off just to see how they were designed.

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The motors being original to the boat in no way means they were mounted 29-3/4" o.c.

Looking at the photo again, I am almost certain they are mounted much closer than that and I would bet money they are 25-3/4" o.c.

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Tom,

I was Not implying they were 29 3/4 inches apart.

I was implying that this was an original install rather than a conversion from a single motor to twin motors like the original posters question and install here.

Whatever the dealer used is what he used.

I went out and tried to measure the old tie bar but I had taken one end off as it was coming apart. This is why I replaced the tie bar and I unfortunately messed other threads up when taking it apart. That is why I had to spend the big bucks for an entire new one. Haven't had the heart to throw the old one out as there are still some good SS parts left on it and one good tie end...

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I can back Joe up on this one. I bought my 18 Outrage new and drilled the transom for the twin BIA bolt pattern Mercs myself, using the recommended 29-3/4". Everything fit between the D-Eyes, and all bolts came into the splashwell easily.

My boat is a 1986.
Front mount or side mount hydraulic cylinders require a minimum engine centerline spacing of 26" according to Teleflex. I would not recommend mechanical steering for twins.

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OK, so we have Joe's boat where the motors were NOT 29-3/4" apart and we have Larry's boat where they were 29-3/4" apart.

Both spacings work just fine.

Joe -- Did you have mechanical steering on your Outrage 18? Did it work well?

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I remember mine being very close to standard if not standard but cannot verify due to lack of memory...

I remember measuring for the toe-in according to the OMC Installation Instructions that I still have... 1/4" to 3/8" toe-in

See the photo below and click on it to enlarge it. The engines can't go out much further due to the Tow/Ski eyes so they are fairly wide apart.

I don't think there is anyway you could mount a single engine in the 2 inside holes of these twin motors. The distance seems too far apart to mount a single engine.

As a note to myself..
This photo is during testing and before I painted the mid and lower units.

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Tom,
Yes, I did have twin cable mechanical steering on my twin motor setup and it worked well for me. About the same as my single engine Evinrude 150 with the same twin cable steering setup which I still have.

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That is what I was thinking first that the only real problem with spacing is making sure that the motors don't hit each other. It would be nice to keep them as far apart as possible but the real thing is how close can you go. Nice discussion guys.
thanks
Erick

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My $0.02.

Since you're using jack plates mounting height really isn't a concern.

A wider spacing should give a bit more lateral stability and maneuverability while docking.

It's a large project and filling/drilling two more hole probably shouldn't be your deciding factor.

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Point taken. I wonder how wide I can go with moving the eyelets/ski hooks?

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I'm not sure about the specific set up on the 18 or if this would apply, but keep in mind not to mount either engine directly behind a clamshell/thru hull, strake, or anything else on the bottom or transom that produces turbulence, to avoid engine cooling issues.

Great project, keep the progress reports coming!

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I would mount them as close together as possible, as long as the height was still OK in relation to the cavitation plates to the bottom. The closer the motors are to the center, the less chance of prop blowout when turning.

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So really it is just do what you want! LOL! So many ideas. Wide close, blind hole, no blind hole. Move eyelets/ski hooks, don't. Whats a poor newbie to do! LOL! More coffee I say! More to ponder in this great debate. Have a great day and if you can get out and boat, please do enjoy!
later
Erick

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Well after all the great debate, I just went with what I had. I used the Upper single engine mount holes as the Upper inner holes for the twin’s motors and jack plates. I put a bolt in the upper holes and jack plate. I then pivot the Jack plate so it aligned evenly with the transom. Then I used a clamp to hold it in place. I then used a marker and marked where the holes were, pulled the jack plate off and drilled. Came out well. The extra bolts I bought were a little bigger than the ones from the single motor install so I will go out and get the right size bolts from a specialty bolt/fastener store. It took a little more doing than I thought but all in all I am happy with it. Looks good. I have 2 photos of the install that I will post sometime when I make a new project album of installing the motors, including mounting motors, aligning them, rigging and such. Time is hard to come by at my house to work on the boat. My main goal is to get her back in the water and enjoy while my kids are still around. When they leave then I can do a full resto but hopefully after many years of great boating.
Thanks guys,
Erick