As I said on the first post, I'll be discussing in phases...
1. Overview of the Aquacat and My own Boat's Design Specifications
Obviously, the weapon of choice when it comes to surf bait boats is the Aquacat Dinglehopper. I want to discuss why/how I thought it could be improved on, and what my motives were for building my own boat instead of splashing on an Aquacat.
The Aquacat's been around for a while (not sure exactly how long..) and comes as either a standard or turbo model. In terms of pricing, R12-16k are the figures that normally get tossed around when the Aquacat is discussed. We can have a look at the sales specs of a typical Aquact turbo, straight off their website:
- Dimensions: L 103cm, W 29cm, D 27cm (excl. antennae)
- Weight: 14kg with batteries loaded
- Motor Transmission: Geared 1kw Brush-less Motor(fan cooled)
- Speed Control: Electronic Speed Control
- Battery Requirement: 2 X 9amp/hr 12v Lead Acid Gel Cells
- Maximum Distance (Range): Power Prop: 1600m at full throttle (On one charge)1800m at 2/3 throttle
- Maximum Speed: 170m / min (or +-2.8m/second) on the "Power prop"
From what I've read on Sealine, the common issues people have with the Aquacat are as follows:
- The thing is seriously heavy: 14 kgs is a lot to haul around, especially with all your other gear, rods..etc
- Poor life of the batteries: For a solid day of fishing, you going to need a serious amount of spare batteries. More weight and more inconvenience! In general, I've read guys get 2-3 trips behind the back-line on a set of batteries.
- Water, working itself into the hull: Obviously, all down to how well the hatch is closed.
From a technical point of view, I find some of the Aquacat's claimed performance credentials slightly hard to believe, particularly when one starts factoring in the poor performance of gel type Lead acid batteries in high current-draw type applications. In short, the more current you draw from these batteries, the less efficient they become. Typically, lets assume you use your Aquacat full speed to the back-line. According to the figures above (1600m range @ 170m/min) your batteries are drained in just under 10 minutes run time. Neglecting drive train power losses and stuff, your 9Ah batteries are actually ONLY giving you 4.3Ah of capacity (refer to typical lead acid gel battery performance data). This is the reason why so many guys are complaining about all the spare batteries they need to haul along. Although this has more to do with the batteries than the boat itself, its definitely worth your while to consider using high performance batteries in your DIY boat build (Lithium ion, Lithium Polymer..etc). We can't fault the Aquacat here, like I said, its the batteries that under perform.
Working back from the claimed specs, you can also see what a bait boat of the Aquacat's size is going to need in terms of Power to work its way through the surf. Yes, they claim it has a 1kW motor, but the motor actually only draws about 550W-580W at full throttle (the motor is probably rated to supply a maximum of 1kW). There is nothing wrong with that though. A lot of how much power you manage to work from your motor depends on how you gear it (Prop-shaft's rotational speed)as well your propeller selection (pitch and diameter)...etc.
If you going to build your own bait boat, there are plenty of good aspects that can be sponged off of the Aquacat. The Aquacat's weight actually works to its benefit once its in the water, with most of the weight low down in the hull giving it a low center of gravity. This makes the boat inherently stable and allows it to self right once toppled over. The yellow and pink round orientation buoy that's positioned up top also helps in this regard. The Aquacat's weight also gives it a lot of directional stability once its in rough water, not being easy to be thrown about or turned around is a huge benefit. Its physical dimensions also serve as a good guide line of what size boat you should be looking at building.
So, after doing my homework, I could put together a set of specs that I wanted to target for my build. They were as follows
- Physical hull size: 1000mm long x300mm wide x250mm deep
- Weight: Around 10kg (Looking for something lighter)
- Motor: Brushless, Nominal Power draw, 500W. Ample power reserve if required
- Batteries: Lithium Polymer Batteries, 11.1V +-35Ah capacity.
- Tow out Speed, +-2.5m/s
- Operational time on a charge: 50 minutes
The boat was designed to be used primarily to tow out large baits for in-eds. There is no complicated hatch or bait compartment, only a release mechanism allowing you to attach your tackle to the back of the boat. The bait,sinker..etc all get towed out behind the boat in the water. I figured trying to stash away a whole chokka or mackerel, let alone larger baits, would take up far to much space and complicate the build.
I wanted to make a boat that could go out for a whole day of fishing and do over 15 bait drops all on a single charge. Hence the ridiculously large battery capacity above. I also wanted the boat to be capable of handling very rough surf conditions such that we could make use of most fishing spots, thus a large power reserve is required.
Once built and on the water this last December, The boat performed within all the above specs.
Next up... The internal bits of the boat
rather, welcome back. 
