Hiya
Skippy, that open transom is one of THE best safety features you can have on a butt-cat!!
Let me explain. I also started out fishing on monohulls, like most Cape anglers. Having owned Billfish's, Cape Craft's, Calibre Cabin Boat and having fished off a mulititude of different vessel, the first time i fished off a open transon butt-cat, i had the EXACT same sentiment as you!! It freaked me out that water would come onto the deck. After asking why the need for an open transom, i was told that when they surf launched this particular vessel in Durban, should you get a wave over the front, the water will simply run out of the back.
Took me a while, but i got used to the idea of an open transom, and my current boat is designed this way.
We don't surf launch here in Cape Town, so WHY would an open transom be advantages?
Let me explain with a story. A few seasons back, we had 3 Cape Crafts ALMOST sink out in the deep. Two were 28'ers and the other a 25'er. All three are commercial boats with VERY, VERY experienced skippers onboard. They were all coming home from the deep, in a particularly nasty NW'erly wind with some swell. The one boat took 2 swells over his bow and the skipper was standing WAIST DEEP in water INSIDE his cabin!! The water level was FLUSH with the top of the boat gunwhale!! Needless to say, he sent out a MAYDAY, but luckily maganed to turn the boat around and get the water to drain out. EXACTLY the same happened to the 2 other boats mentioned. Note, these are Cape Crafts, which are used by the majority of the commercial fleet and are VERY, VERY sea-worthy vessels.
What happens is that you come over a very large swell in the NW'erly, then fall into the hole behind the swell. Before you can accelerate, the next swell breaks over your bow, putting a few hundred litres of water on your deck. Your boats now a bit heavier and the VERY next swell does the same thing!! You now have over half a ton of water on your deck!! Your boats now VERY heavy, which means your scuppers are now UNDER the water. To get them to work, the boat has to keep moving!! NOW, the problems you face:
i) Your boats too heavy and could sink. This is more applicable to commercials, as we have at least 1000kg's of ice on board PLUS anything from 500kg to 2000kg of fish as well. This severely compromises ones flotation. Add another 1000kg's of water on your deck and you are seriously in danger of sinking!!
ii) Assuming your batteries don't short out and both your motors are still running, you need to clear the water off your deck. Your scuppers are underwater and will not clear the water quick enough at very slow speed. You need to turn around and run WITH the swells. NOW, this is VERY, VERY dangerous!! Should you turn and a swell catches you broadside, you WILL CAPSIZE!! If you can get the boat turned it'll still take QUITE a while for your scuppers to clear that volumes of water. Thats why MANY commercial tuna anglers with Cape Crafts have MONSTEROUS bilge pumps in their bloodbox's in the rear of the boat. Just to assist in getting water out of your boat in that scenario.
This is primarily applicable to centre console and walk-around style boats. Full cabin boats offer more protection, BUT, i have had numerous swells crash OVER my cabin, so it can still flood your boat. I've also seen widows smashed out by the NW'erly, which now also will allow water to get onto your deck.
The open transom on the butt-cat eliminates this danger. Any swell breaking over the bow will simply wash out the back. No danger of sinking or capsizing. Open transoms on butt-cat style boats is simply more boaters should be made aware of and understand WHY and how they work. This will make for safer boating!!
Some pic's of my boats open transom:
