The Troyer Horizontal is one of my favorite and most successful commercial plastic gourds. This gourd is opaque (non-translucent) and provides a deep safe cavity for purple martins. I use Troyer Horizontals with cling plates and ones with add-on tunnels/porches and raise many martins in them each season.
Horizontal gourds need venting, particularly in the Deep South where our high temperatures and humidity can create potential problems for martin nestlings. Though Troyer gourds are opaque and white, heat can still be an issue under extreme conditions.
Troyer Horizontals can be easily vented in several ways. The easiest way for me is to drill two vent holes in the upper back indention bumps which are there for that purpose. I use ¼ and 3/8 inch diameter holes and you can use holes up to ½ inch. If you use larger holes, then you may have a rainwater problem. However, this can be mitigated by using extended rain canopies over the vents just like you can do over a gourd entrance hole. Aluminum canopies could be installed over the vent holes using adhesive.
The Troyer Horizontal gourd indentions are located in the upper back of the gourd to help vent rising hot airflow out and possibly reduce humidity build up inside. Also, the entrance hole and the vents are at opposite directions of the gourd and this may help to create a cross ventilation effect relative to airflow movement.
You can also install PVC elbows in the upper backs on Troyer gourds for venting. These elbows come in various diameters I believe. The elbows could be attached with adhesive. The downward pointing elbow would help prevent rainwater intrusion into the gourd. I have not used the elbow approach yet.
I have included two photos of one of the backs of my Troyer Horizontal gourds showing how I drill the vent holes in the two upper indentions. In these photos, I am using 3/8 inch diameter holes that are drilled directly under the indention bumps. The bumps function somewhat as a canopy. I also am using ¼ inch holes in other gourds. Both diameters seem to work well though I probably get a little better airflow with the 3/8 inch size. You need to drill your holes at a slight downward angle at the lower edge of the indented middle of the bump so that the slope of the bump will help to provide protection from rainwater. Also create a channel that will allow any rainwater to run downward rather than inside the vent hole. You do this by holding the drill down at an angle toward the back of the gourd as you create the vent hole. My pictures show the channel. It can be difficult to hold the drill in place while drilling on slick plastic.
The upper indentions on the Troyer Horizontal gourds seem to work well in minimizing rainwater inflow into the gourds from the vent holes. Of course, if there is a deluge with winds, then possibly rainwater could be blown under the sloping indention and overcome the downward rain channel. All my Troyer Horizontals have adequate drainage holes in the bottoms and I build thick pre-nests from pine needles. Pine needles tend to shed water well. As mentioned previously, you could attach small rain canopies with adhesive over the vent holes and have them extend out maybe an inch. The canopies could be made from aluminum and that would probably keep nearly all water from entering.
This photo shows the back of a tunneled/porched Troyer Horizontal gourd with two 3/8 inch diameter vent holes cut under the indention bumps.
This photo shows a close-up of the vent holes. You can see how the holes are at a slight downward angle just under the indention bumps.
Steve
