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HydroStream Viking Transom Braces
Daniel W. Rickey
Winnipeg, Manitoba Canada
drickey@mts.net
2002-10-08
Introduction
The HydroStream.org web site has shown the
articles documenting the (unexpected) restoration of my HydroStream
Viking. After driving around
for two years with a 115, I decided to move up in power. This article is about the work I did to my Viking in
preparation for its new, larger engine.
Problem
The built-in setback of the Viking is one of
the things that make it a high-performance boat. By removing a chunk of the pad & transom, the engine
weight helps to lift the bow, leaving more power to propel the boat.
However, the built-in setback has one disadvantage which is
illustrated here.
Here is a cross section schematic of the rear of a
Viking. The important thing
to note is that the two main structural parts of the boat, i.e. the
stringers and transom, are not connected.
This is a consequence of the built-in setback.
Now consider what happens when the boat lands after
launching off of a wave. The
heavy engine will press down on the transom while the water pushes up on
the pad. Because the transom
and pad aren’t well connected, we would expect there to be a fair amount
of flex. Since gel coat
doesn’t flex easily, any flex would result in cracks.
With this in mind, let’s crawl under the boat and have a look.
This photo shows the region aft of the pad.
As expected, stress cracks run from side to side just forward of
the transom. Because of the
built-in setback, there are no stringers in this region.
Thus the hull is a bit weak here.
This is a close-up view of the cracks.
They are actually difficult to see without a bright light.
The view is the bottom of the hull just forward of the transom.
Solution
The solution to this problem to add a set of large
braces to the boat. These are
to tie the transom and stringers together.
The philosophy here is to distribute the load of the heavy engine
and avoid regions of high stress. Unfortunately,
there is one problem with this plan.
Problem: the large braces would go through the fuel
tank. The fuel tank can’t
be moved since it is confined by the filler tube and rear seat.
The solution used here was to install smaller braces.
These should do a fair bit to help distribute the load.
The next few photos shows how this was done.
This is a view of the back of the boat with the rear
seat removed. The two round
holes are for ventilation and prevent the wood floor from rotting.
Visible here is the small amount of room available
between the fuel tank and transom. The
bilge is below the fuel tank. The
braces can’t interfere with the 1/2” thick aluminum washer plate.
Here it is with tank removed.
The plan is to install two small “knee” braces to help tie the
transom into the floor and stringers.
Because of the fuel tank, there isn’t enough room to have braces
extend directly from the transom to the stringers.
There is a gap between the floor and the top of the
stringers. This will be
filled with thickened epoxy and glassed.
The idea is to tie the floor, stringers, and transom together.
I used this sliding bevel tool to
duplicate the transom angle onto plywood.
Braces were cut from 1/2” marine-grade plywood that
is 7/16” thick. Two pieces
were epoxied together for each brace to give a thickness close to 1”.
Here the braces are epoxied in place using thickened
West System epoxy resin. Also
visible is the thickened epoxy filling the floor-to-stringer gap.
Here are the braces glassed in.
It’s not the nicest piece of work, but no one will see it behind
the fuel tank! The braces
don’t quite tie the transom directly to the stringers: there just
isn’t enough room in the back of this Viking. The idea is to help distribute the loads more evenly.
Discussion
The braces were quite easy to install.
Since they are hidden, the glass work is easy to do.
Since the fuel tank was out it was also a convenient time to tidy
up the wiring and bilge pump.
Keep in mind that this boat has a new floor.
If your boat has the original floor, there’s a fairly good chance
it is rotten near the transom. So if you are planning modifications like this, make sure the
wood is good first. The
easiest way to do this is to drill a few small holes in the floor. If the wood is good, the holes are easily filled with epoxy.
If the wood is bad then you have a big problem.
This section
features articles written by you guys. Submit whatever you would like - as long as
it applies to HydroStreams, motors, trailers, or towing vehicles. Please send it to
me in a form where I can just insert it into this page (some kind of Word processing
document would be good). It would be a good idea to check with me first to make sure
nobody else is working on the same topic. Everyone please consider writing
an article and sharing some information that will
help out your fellow Streamers.
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