Installing transom backing plates on an M15

Discussion about the boats Jerry Montgomery created: sailing, maintenance, repair and renovation.
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scoob
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Installing transom backing plates on an M15

#1 Post by scoob » Tue Jul 03, 2012 5:55 pm

Backing plates are important if you install hardware to the Montgomery 15s transom (also applies to the M17 and M23). Jerry built the boats with balsa core to strengthen the transom where the motor mount and rudder gudgeons are installed.

Most of Jerry's M15s came with a fixed-height motor mount. Many folks retro-fit a adjustable height motor mount and add a transom boarding ladder.

I recommend you install backing boards to the transom to provide greater strength when installing a adjustable motor mount (these are much heavier than the fixed height bracket) and a transom boarding ladder. Why is this important? Take a look -
backing plates.jpg
(click on image for a larger version)


The above picture shows how a insufficiently backed boarding ladder can significantly damage the transom. The duct tape was used to keep water from getting into the boat when she was stored after the damage occurred. The tape residue was easily cleaned off using acetone. I will post details on how the transom was repaired in a few weeks.


When installing backing plates it is also important that you use stainless steel hardware (at least 18-8, or 304, or 316 grades) and sufficient bedding compound. If you don't you can get this -
backing plates.jpg
(click on image for a larger version)


Pictured above is RUST that comes from using non-stainless hardware and insufficient bedding compound.

The greatest challenge when installing a backing plate is gaining access to the M15's transom. Some M15s have the cockpit locker liners cut out allows access to the transom. If you prefer to keep your M15's locker liners you need to install access ports on the aft end of the cockpit seats.

Use cardboard to create a pattern of the interior of the transom where there the motor mount and/or boarding ladder will be installed.

Cut the backing board out of at least 1/4" thick marine grade plywood (greater than 1/2" is overkill in my opinion). After cutting out the plywood coat with epoxy.
backing plates.jpg
(click on image for a larger version)


Mix a batch of epoxy that is thickened to a mayonnaise consistency and coat the inside of the transom where the backing plate will be attached. also apply thickened epoxy on the transom side of the backing board. (You can also use 3M 5200 to bond/glue the backing plate to the transom.)

Press the backing plate in place and secure it in place. radius the squeeze-out epoxy around the edge of the backing plate.
backing plates.jpg
(click on image for a larger version)


After the epoxy has 'kicked' and cured (about 24 hours ... temperature depending) you can now install the transom hardware. (pictures and description on how to install transom hardware coming soon).
Attachments
broke.JPG
starboard side backing installed 2.JPG
failed bedding compound.JPG
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:: Dave Scobie
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JOE S
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Installing transom backing plates on an M15

#2 Post by JOE S » Wed Jul 04, 2012 11:27 am

I have owned 2 older M17s and the transom on both has been plywood not balsa core. Maybe different era boats are different.

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scoob
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#3 Post by scoob » Thu Jul 05, 2012 10:21 am

JOE S wrote:I have owned 2 older M17s and the transom on both has been plywood not balsa core.
Joe:

which version of M17? the first style with the transom cutout for the outboard motor?
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:: Dave Scobie
:: Sage Marine Sales and Promotion

:: “Integrity is being good, even if no one is watching”™
::
:: my boat's www-site - http://www.m17-375.webs.com

doug
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#4 Post by doug » Fri Sep 14, 2012 8:52 pm

i agree with joe s i have a 74 m 17 #079 and it has plywood backing in the upper half of the transom this boat has the cutout ,also my decks are not cored probably the only thing that saved this boat as it out in a field for 10yrs. full of water. unfortunetly the iron punchings caused a bunch of disasters .[ shame on jerry].scoob please suggest that owners list their boats # then we can form a better time line on changes in production. my boat also has a early 10in. wide rudder with 2 gudgeons on the transom and 3 pintles on the rudder so that has to be lifted off the gudgeons and remounted in the raised position using the lower & center piintles it's a hassle . i like S17 keep up the good work doug

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sal
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#5 Post by sal » Sat Sep 15, 2012 6:50 am

Hi Doug,

Welcome to the Sage forum and thanx for your suggestion on the numbers. Probably a good idea. Thanx also for your kind comments. We plan to make the Sage 17 the best of the best.

sal

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