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 arenít well connected, we would expect there to be a fair amount of flex.  Since gel coat doesnít flex easily, any flex would result in cracks.  With this in mind, letís 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 canít 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 canít interfere with the 1/2Ē thick aluminum washer plate.
 
Here it is with tank removed.  The plan is to install two small ďkneeĒ braces to help tie the transom into the floor and stringers.  Because of the fuel tank, there isnít 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 1/2Ē marine-grade plywood that is 7/16Ē thick.  Two pieces were epoxied together for each brace to give a thickness close to 1Ē.
 
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.  Itís not the nicest piece of work, but no one will see it behind the fuel tank!  The braces donít quite tie the transom directly to the stringers: there just isnít 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, thereís 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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