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Old 27-03-2017, 19:34   #1
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Twin outboard motor alignment

Hi

The OB slides vertically on rails straight up and down (in and out of the water) close to, but outward of the centreline of each hull.

Right now there is a much oversized opening in the bottom of the hull for the OB's which I intend to reduce to a snug fit and fit a trap door to close off when sailing.

Before doing the work I want to make sure the OB is orientated for best performance at cruising speed with one outboard running.

Has anyone done testing to see if there is much to be gained by changing the toe and/or the tilt especially when running one engine only.

Thanks
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Old 29-03-2017, 07:00   #2
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Re: Twin outboard motor alignment

You may be overthinking this. Not saying good alignment is not important, just that any boat is subject to wind and wave action that normally has a much larger affect on performance than any small misalignment. I have noticed that filling my water tank and and the five five gallon gas cans affects my boat speed and probably how the tilt as well.

Not to mention sailboats are suppose to be sailed as much as possible and motored as little as possible.
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Old 29-03-2017, 07:17   #3
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Re: Twin outboard motor alignment

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You may be overthinking this.
My thoughts too. On a runaround with big beefy outboards yes its worth considering along with counter rotating props, but on a yacht with what 10hp perhaps? it isn't going to alter much. That assumes you have the prop down far enough to be in clean water and not ventilate by drawing air in to the prop when charging into the waves.

Yes to blocking off the excessive cut outs and ensure that the exhaust gasses can escape and not choke the crew in the cockpit.

Looks a bit odd doesn't it, but apparently works:
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Old 29-03-2017, 15:34   #4
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Re: Twin outboard motor alignment

I considered it briefly toeing the motors in, but decided since I'd only be guessing at how much I'd be just as likely to hurt as help.

If you really wanted to you could fit an adjustable link to the steering arm, and experiment.

While there may be gains to be had, I'd think they'd be pretty small.
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Old 29-03-2017, 15:58   #5
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Re: Twin outboard motor alignment

I would put more effort into getting the outboards tucked under a bit, not vertical but with the prop a little forward. That will help reduce aeration of the prop, or another way put, pulling air down into the prop. That to me is a bigger issue than direction of thrust.
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Old 31-03-2017, 02:23   #6
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Re: Twin outboard motor alignment

Thanks all.

I definitely do think about all these things more than most. I prefer "all consideration" than "over think" :-).

But I bet there is something worth having to be had in getting it right. I'll think of a test procedure and give it a go.

If I don't add a write up on it you'll know you were right :-)

I don't want to even think about leaning them in or out........................ Oh too late....... It would give lift on the outside and negative lift on the inside motor. The boat would lean more in turns, if that's what you want?
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Old 31-03-2017, 02:54   #7
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Re: Twin outboard motor alignment

Have you given much thought to Ackerman geometry for the rudders?
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Old 31-03-2017, 04:54   #8
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Re: Twin outboard motor alignment

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Have you given much thought to Ackerman geometry for the rudders?
Yep, checked it. It has it built into the design. I haven't measured it. For now I just assume Schionning did the math, I'll check it one day. I have noticed though on full lock to port, the port rudder almost goes over centre and sticks a bit coming back, I'll have to adjust the stop.
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