Hi Randy,
The exhaust boot was made in three sub components that were then bonded together.
First, I made a model of the boot shape itself from cardboard and tape. The upper part of the boot slips over the existing exhaust deflector, with extra clearance all around, then extends twards the bottom of the hull in a "dog leg" shape to get around the trim tab. As the boot curves around the trim tab the shape becomes eliptical so that it cuts thru the water like the lower unit on an O/I would. I made the model extend further below the hull than required to allow for trimming later. I then covered the whole thing with plastic shrink wrap (the same stuff used to cover the boat for winer storage) then fiberglassed over it with heavy roving and West System epoxy resin. After this had cured, I soaked the whole thing in a bucket of water to soften up the cardboard then pulled it all out. Since the resin does'nt stick to plastic the shrink wrap pulled out easily as well.
Secondly, I used a Tupperware lid as a mold to form the flange that would join the boot to the existing exhaust deflector flange. Using a lid that is the same diameter as the existing flange, I filled it with layers of roving and resin. Once cured it poped right out of the plastic. Then using a jig saw & drill I cut the hole out of the center and drilled the bolting holes.
Thirdly, I layed out some roving and resin flat on some plastic shrink wrap. I then once cured cut out the shape of the cavitation plate and front deflector from this.
Lastly, I joined all of these components together with a mix of resin, thickener and chopped glass. Once cured I installed it on the boat then trimmed the length about 4 inches below the hull on the leading edge with a taper up to the trailing edge of about 30°. Under way this taper creates a void or a vacuum in the water to help draw out the exhaust. I also added one extra bolt thru the transom about 1 1/2 " from the bottom into th main body of the boot to help hold it against the force of the water rushing by it.
There is no "tell tail" hole for two reasons. Where it's located you could'nt see any water flow and it back pressure is not a problem. This thing dumps the exhaust at about the same level below the waterline as an I/O dumps it thru it's gimbal housing. I did however add one extra safety feature, just below the cavitation plate I used a die grinder and cut a groove into half the thickness of the glass all the way around then filled it with resin only. This created a shear point just in case it hits somthing in the water, this way only a small piece of it will require repair instead of damaging the whole thing. And yes this does work since i've had to replace it once already.
I'll try to get out to the marina this weekend and take some pictures of it and send them to your e-mail address.
Hope this helps,
