Re: Trailering with Outboard on Transom

From: Jim Nolan (panache426@hotmail.com)
Date: Wed Feb 09 2000 - 21:33:21 PST


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        West Wight Potter Mailing List maintainer
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The shock loading is a very valid point and if the shock is greater than
4g's it will exceed the loading of the engine when running. So if the shock
loading of the motor is enough to crack the transom, what does the keel do
to the trunk? Remember the keel is unrestrained and resting only on two
bolts. By rough estimates the keel must put a force in excess of 400 psi
vertically on the keel trunk. The same force that makes the motor exceed 4 g
will likely cause the same to the keel, giving it a force on the order of
1600+ pounds. Has anyone experienced keel trunk damage when towing? A
further consideration then would also be the force on the leaf spring of the
trailer.

Jim Nolan P-19 #426 Panache

>From: Kent Crispin <kent@songbird.com>
>To: wwpotter@tscnet.com
>Subject: Re: Trailering with Outboard on Transom
>Date: Wed, 9 Feb 2000 17:48:19 -0800
>
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> West Wight Potter Mailing List maintainer
> dfarrell@ridgecrest.ca.us
> List hosted by www.tscnet.com
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>On Wed, Feb 09, 2000 at 06:03:11PM -0700, Jim Nolan wrote:
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> > West Wight Potter Mailing List maintainer
> > dfarrell@ridgecrest.ca.us
> > List hosted by www.tscnet.com
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> > A 4hp motor has roughly 200 pounds of thrust. This force is directed
>normal
> > to the surface of the transom, in this mode the transom is the weakest.
> > Trailering a 50 lb motor puts the forces mostly in shear on the
>transom. In
> > this mode the transom is the strongest. For concerns about moment
>forces,
> > when the motor is down propelling the boat this has a much greater
>moment
> > than when the motor is raised in the trailing position (400 ft lbs vs 50
>ft
> > lbs roughly). If you are concerned about the transom when trailering you
> > should also be more concerned about the transom when motoring the boat.
>
>You are overlooking shock loads, and the lever arm of the motor mount.
>The thrust of the motor in operation is, relatively speaking, a quite
>smooth force...
>
>--
>Kent Crispin "Do good, and you'll be
>kent@songbird.com lonesome." -- Mark Twain
>

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