I have had this Saturn 12' inflatable catamaran for about a year now and have been getting it ready for the summer season here in Arizona with some healthy upgrades .. have put in some hours recently and would like to share my thoughts on this rig.
Last year I took it out a few times with a 2.5hp Suzuki long shaft and no other modifications .. the little zuke was just too underpowered and the drag from the long shaft motor was not helping. I had picked up a 1996 Johnson 20hp 2 stroke (big 521cc block that they used for the 20hp --> 35hp engines since the late 70's) over the winter and got it going on the hose after some new plugs and a carb rebuild. Unfortunately I think it needs a base gasket under the powerhead so that motor is on hold for now and has not hit the water on the Saturn Cat yet.
So fast forward to a couple weeks back and I picked up a brand new Mercury 9.9 four stroke to play with in short shaft. Got it broken in and now and I am starting to really dig into the issues that come with this hull.
The pros and cons of this boat are pretty equal all things considered -- Here's my take so far:
Pros:
Cheap!
Great platform for swimming .. really easy re-entry without a ladder needed
Big & Comfy interior space
Decent ride - stays pretty dry
Cons:
Airfloor - Causes prop cavitation and or ventilation
Slow Hull - much slower than I was expecting it to be
Not very rigid even when maxed out on air pressure
Hard to keep full pressure after dropping in the water
Short transom is about 3" too short for a short shaft
While taking it out with the new 9.9 Merc I was fairly disappointed (stock 3 blade 8.5 pitch prop) .. I didn't have a GPS with me on that break in run however I am fairly sure I was not getting over about 10 mph with just myself and a light load in the boat. Maybe barely getting on plane and It was ventilating at almost all speeds and the motor was not getting up to the proper RPM range. You could hear the burble sounds coming from the prop and the wake out the back did not look good at all .. kind of looked like a SPA or Jacuzzi
Got home and ordered up a Solas Amita 4 blade prop in 7 pitch along with a Permatrim plate from New Zealand, got them mounted up and headed back out.
Huge difference! Now the boat is on plane in about 3-4 seconds and I am hitting around 14mph top speed. The wake looks like a proper boat wake now. It is still getting the cavitation / ventilation issue just not near as much, I credit 90% of this to air floor at this point. I am happy with it and had fun running 3 gallons thru it and covering about 30 miles.
The next week I picked up a 4' x 8' piece of 1/2" plywood and decided to put a floor below the air floor to try and keep the bottom more flat to curb the issues with prop hook up. Cut it to fit and sanded it down smooth and put on 3 coats of varthane sealer to keep it dry. Then added some rubber stripping to the edges just to keep it locked in and prevent any chafing and thru it all back together and inflated to full pressure. Headed back to the lake for some testing last night. The downside to this modification is that I did add about 40lbs to the boat, although it is spread out evenly across the whole floor. If I did it again I would aim to keep the weight of the floor piece down under about 25lbs.
At the same time I also added a 1" wood block on the transom to lift the motor up .. I do think this has brought my Rpms up a couple hundred and brought the splash down off the back of the boat -- After checking my permatrim plate going wide open / top speed .. it needs to come up about another 2"
The results are amazing! No more cavitation issues and the boat jumps on plane fast. It now likes to cruise at 13-14mph and tops out just over 15mph. Really had a good time last night with the boat finally feeling like a boat vs a sloppy floatable toy.
Next up I am considering building a 3" rise on the transom and connecting it to the wood floor piece with some heavy duty L brackets to tie everything together .. I think this would be needed for anything heavier than my current motor @ 84lbs.
Here's some pics so far -- Any suggestions on future mods are greatly appreciated!
