Also Available: Cockpit Plans
Ideally suited for the Sport C
The Dillon Sport C tunnelboat was designed and built for racing in the APBA Sport C class.
Sport C is a national class which allows for several boat and motor options, but the typical rig is a tunnelboat approximately twelve feet long, powered by a two-cylinder, 40hp Nissan or Tohatsu outboard. More about Sport C racing HERE.
APBA rules require a reinforced cockpit in Sport C boats. I outfitted the original Dillon Sport C with a composite-built cockpit of my own making. Plans for the Dillon Composite Cockpit are now available, and since the Sport C was designed around it, it is perfectly suited to this boat.
The plywood cockpit described in the plans is perfectly suited to the non-racer, and also can be adapted for racing use (see the Construction Notes).
My first year racing the Dillon Sport C was not impressive in terms of race results -- I generally finished last. Nevertheless, I am very happy with the way the boat functioned, and I'm confident that further work on propeller and setup will improve performance and make my boat competitive.
Using a round-tipped cleaver from Ron Hill, I was able to run at speeds of 54-55 mph. The ultimate goal will be to run in the 58-59 mph range, and I believe my boat is capable of that -- but it will likely require a significant investment in a professionally-worked propeller.
The Dillon Sport C is my second attempt to build a Sport C racing boat. The first project did not work out in the end, but its failures (and successes) informed the design of the new boat and have lead me to this point. You can read about the earlier project HERE.
The Dillon Sport C was designed for speeds up to 60 mph using the lightweight (130 lbs.) Sport C motor. A heavier and more powerful motor would likely require some re-balancing; for instance, moving the seat forward a foot or so. Speeds much over 60 mph are not recommended. Because of the aerodynamic lift generated in a boat like this, hydraulic trim to keep it under control is virtually a requirement.
I built the original Dillon Sport C with white pine stringers and (mostly) 5mm (3/16") exterior-grade plywood. I recommend 5mm (marine or exterior) plywood for most of the hull plus 3mm marine for the deck and front cowling. Many will state that marine plywood is the only choice. But though I've seen failures in exterior plywood, I've seen virtually identical failures in marine. Exterior grade plywood requires good structure (stringers and bulkheads) behind it, but I would stipulate that marine plywood calls for exactly the same.
That said, you can hardly go wrong using okoume marine plywood. But you can save a few hundred dollars by using locally available, exterior grades. It's your choice.