I'm looking for two (or maybe three?) hulls to make a power displacement cat, powered by an electric motor.
I know... this is heresy, converting a sailboat to power. But here I am. At least I am planning on converting to quiet electric power! I want it to go at least 6 mph, and 10 mph would be nice.
I'd *like* to be able to support 8 adults, and I know that is alot for most beach cats. I was looking at the Hobie Getaway and thinking I could maybe find a third hull to make a trimaran with the central hull forward.
Most of the specification sites focus on racing with 2 or 3 people so it is hard to find what hulls can support this. I may start with old hobie 18 hulls and keep it to only 4 adults until I find something larger or make my own.
I like the looks of the hobie 21 hulls. Just not sure what kind of capacity is reasonable to expect.
Thanks for any help you could give!
-Jeff
Recommendations for hulls for power displacement cat
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Posted: Sep 13, 2020 - 11:59 AM
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Posted: Sep 13, 2020 - 01:28 PM
Lots of buoyancy, fine entry the entire length of the hull and front trampoline are what you are looking for. It's been done before. Go to G-Cat's Facebook page and you'll see what you want to do.
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Bill Townsend
G-Cat 5.0
Sarasota
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Posted: Sep 13, 2020 - 05:12 PM
Thanks! Great stuff on that page! -
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Posted: Sep 13, 2020 - 06:58 PM
There's a guy in Hawaii that has some posted some interesting dual motor mods to a Getaway. His pics are on Instagram under the name Willdesignsandbuilds.
As far as capacity is concerned, 8 adults plus an electric power system would be a stretch for the standard 21' hulls. The addition of a third hull would fix that problem.
In regards to speed, I've done a bunch of gas powered motoring with a Hobie 21sc. A 2.5hp Suzuki will easily push the boat at 4-5mph at less than 20% throttle. After 5mph its really diminishing returns from a power standpoint. My max speed is 12mph with no sail rigging and perfectly flat water.
I'm guessing the hull speed is around 5-6 mph which is also the max that most trolling motors are going to do with standard propellers. A 24volt trolling motor with 100 Ah lithium batteries would be great for 5mph cruising in protected waters.
There's some 48volt electric outboards that will reach the speeds you are searching for, however the investment is pretty steep.
For the money, a four stroke 9.9hp to 15hp with a third hull is probably the lightest and quietest(non-electric) way to reach your goals. -
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Posted: Sep 14, 2020 - 11:39 AM
Some of the Hobies have curved curved cross tubes which are problematic if you are adding a third (center) hull. Avoid asymmetrical hulls (original Prindle 18) because of the unnecessary drag. If the hulls you choose are board less they will track better without rudders and you will probably be able to steer much better with just the motor. This is an interesting project. I once had a G-Cat 5.7 that I used as a fishing platform. It had a Cheeta motor bracket and a 3.5 two stroke. The Cheeta was limited to 30 lbs but back in the two stroke days this wasn't a problem. It went fast with that little motor. It was amazing how I could hit a steep wake and not even feel it. Displacement hulls are easily driven with little power and remember how heavy 4 strokes are. You won't find a huge difference in speed if you double your hp. You'll have to put some kind of board between the hulls with a vertical piece to clamp the motor if you use two hulls. If you use three, you may have to saw off the stern of the middle hull and fashion a transom strong enough for the motor plus you would be getting the tiller of the motor closer to you. When I was using my boat for fishing, the trampolines were uncomfortable to stand on. A solid deck made of plywood with stringers underneath might be a good idea, the added weight shouldn't matter with what you are trying to do.
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Bill Townsend
G-Cat 5.0
Sarasota
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Posted: Sep 15, 2020 - 06:16 AM
So your requirements are 8 adults, 10 MPH and electric only?
I looked into this very seriously a few years back trying to achieve similar requirements. Trolling motor(s) will only push you 5-6mph at full throttle and use a lot of electricity. Torqueedo and Elco are the major manufacturers of electric outboards. If you really need 10MPH I think you have to go this direction.
I dont think 21 ft is enough, maybe 23 probably 27 to 30. Mostly because to have any kind of range you will need lots of batteries and batteries are heavy. In my test boat I needed a total of 8 golf cart batteries at 60 lbs each to get a 4 hour range at 6MPH. At that point I shelved the project. Not enough speed, not enough range, and way too heavy.
Not a lot of choices for hulls in those sizes but here are a few to look out for:
Stiletto 23, 27, 30 are obvious choices because of the high freeboard, decent hull space, and extreme light weight hulls.
Seawind 24
MacGregor 36
Crowther
C/S/K
Probably a few others I cant think of right now.
As a frame of reference my Stiletto 27 will do 13MPH at full throttle with a 15HP 2 cycle Yamaha outboard and 10MPH at 75% throttle (cruising speed) using about 1.5 gal/hr. Outboard and 5 gal of fuel is under 100 lbs.
Brad in Jacksonville, FL
2x Stiletto 27s, one for racing, one for cruising. -
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Posted: Sep 15, 2020 - 10:06 AM
You can now cut the weight down on the batteries a LOT with Lithium Iron Phosphate batteries, however...there's a price. $500 for 54 AH @ 17 pounds and $900 for a 100 AH @ 32 pounds. They are the ticket, but man are they $$$$
In the end, I kept looking and found a used, but very much like new and running like new Suzuki DT-2 for something like $300 @ 26 pounds. Haven't felt the need to open it up yet, either.
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Chuck C
NACRA 500 Mk2
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Posted: Sep 15, 2020 - 10:18 AM
here is the solution:
get a bit of a dock - add a 3.5 tohatsu
done
(our friend's powerboat and jetski were broke and he wanted to get his tent up for our thanksgiving island camping)
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