Author Topic: Holes in motor boards  (Read 1887 times)

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Todd j

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Holes in motor boards
« on: March 25, 2021, 08:04:06 AM »
Brian, what is your stance on drilling scupper holes through the motor boards.  In my case it would be one each just outside the foot print of the jack plate mount.  I bought 8”x4” ss and plan on using a glass tube that requires 1 3/4”x5” hole.  In my case with raised decks the hole pretty much centers on the router slot
   It’s pretty much exactly what Chuck is doing, except my transom is structural meaning no hull extension
« Last Edit: March 25, 2021, 08:07:23 AM by Todd j »

Brian.Dixon

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Re: Holes in motor boards
« Reply #1 on: March 25, 2021, 08:41:21 AM »
Brian, what is your stance on drilling scupper holes through the motor boards.  In my case it would be one each just outside the foot print of the jack plate mount.  I bought 8”x4” ss and plan on using a glass tube that requires 1 3/4”x5” hole.  In my case with raised decks the hole pretty much centers on the router slot
   It’s pretty much exactly what Chuck is doing, except my transom is structural meaning no hull extension

It's OK, but reinforcement is never bad.  I'll explain...

When the 2 LVL motor boards are glued onto the transom plywood, and the forward face glassed (even if slotted for drywell), the motor boards effectively become a really wide beam on it's face.  The LVL that's used is rated to have (if I recall) 2" holes through it ... if they are 2" or more from the edge of the 'beam'.  In your case, your scupper 'ovals' are close enough to that rule and a long way from any edges of the 'beam' and fine if the rest of the transom is built as-is.  THAT said, if you're going to put larger holes through the transom for larger scuppers, an extra layer of 10-oz or even biaxial plus woven (wet on wet, 6+ oz biax covered by 6+ oz woven) wouldn't hurt.  I'd run the reinforcement glass the full length of the transom, inside and out, and about 8-10 inches wide, centered vertically over the scupper holes.  The reason for inside and outside is that fiberglass is only strong in tension... when the transom tries to flex outward, the outside glass takes the strain, and vice versa for the inside glass.  BUT, this is somewhat overkill and optional.  If caught early enough in the build process, I'd do it.  If not, then I wouldn't worry about it.  Don't forget that the bottom of the drywell gives the transom a lot of stiffness too ... not to worry.

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Todd j

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Re: Holes in motor boards
« Reply #2 on: March 25, 2021, 09:23:42 AM »
Thank you.  For-me it is too late to add glass as you describe.  I will incorporate my splashwell drains into the scupper tubes as to not further weaken the motor boards.  It’s getting busy back there

Brian.Dixon

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Re: Holes in motor boards
« Reply #3 on: March 25, 2021, 03:41:32 PM »

You can move deck scuppers inward toward the middle of the boat 2 or 3 inches if you're concerned.  It'll leave a little water in the corners now and then, but would still serve their purpose.
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Todd j

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Re: Holes in motor boards
« Reply #4 on: March 25, 2021, 03:49:24 PM »
Right now I have them laid out just to the sides of the footprint of the jackplate.  I have too many pipes and crud stubbed up in the corners.  would this still be Okay?
« Last Edit: March 25, 2021, 03:52:16 PM by Todd j »

Brian.Dixon

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Re: Holes in motor boards
« Reply #5 on: March 26, 2021, 06:28:49 AM »

That'll work ... I'd also drain the aft corners of the deck into the bilge and have a bilge pump right over the keel.  What water doesn't make it out the scuppers will find its way out via the pump.

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Todd j

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Re: Holes in motor boards
« Reply #6 on: March 26, 2021, 01:25:30 PM »
I’m planning on something wry similar to your suggestion
« Last Edit: July 23, 2021, 11:46:08 AM by Todd j »

Brian.Dixon

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Re: Holes in motor boards
« Reply #7 on: March 26, 2021, 03:06:36 PM »
I’m planning on something wry similar to your suggestion

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Todd j

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Re: Holes in motor boards
« Reply #8 on: July 23, 2021, 11:54:05 AM »
For over drilling motor boards for the purposes of mounting outboards I’m curious if a standard has been developed.  My jack plate requires 1/2” bolts.   My thought is to drill a minimum of 3/4”  hole and fill the holes and redrill to 17/32”.  Or something similar

Brian.Dixon

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Re: Holes in motor boards
« Reply #9 on: July 23, 2021, 05:19:12 PM »

That should work as long as the holes are in the right place so you can drill through the epoxy fill without cutting into the wood.  If you DO hit wood, then soak that end grain with epoxy until it won't take more, then sand and wipe, then rub a silica-thickened peanut-butter thick layer of epoxy over the exposed wood ... cure, sand, final coat of epoxy.  You can always use removable (REMOVABLE - can be sliced with a putty knife!) caulk as back-up.
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Todd j

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Re: Holes in motor boards
« Reply #10 on: July 23, 2021, 08:42:02 PM »
great