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Old 12-08-2009, 12:10   #1
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Why Big HP Difference in Sail/Power Cats?

Been looking into cats as they seem to offer some seriously good advantages over monohulls for long term cruising and liveaboard potential (e.g. space, stability, fuel economy, privacy with berths at opposite ends of hulls), but one thing that is puzzling me is that sail cats seem to have engines offering under 50 hp yet their power cat cousins have typically over 100 hp per engine.

Does this mean the sail cats only have engines intended for manouvering in/out of marinas etc, or are they powerful enough to use instead of sails for passagemaking or cruising when conditions may mean single-handed would be easier/safer using engines rather than sails?
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Old 12-08-2009, 12:35   #2
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Power cats are engined sufficiently to be at least equivalent in speed to semi-planing mono power boats. Fuel for boats like this is probably restricted to about 600nm

A sailing cat uses its sails however, the engines are used for in and out of harbours, for powering through calms, and for power generation. Some people will motor sail in order to maintain speed - Either way this has to be balanced against fuel supplies, and need to keep weight to manageable proportions. Thus a sailing cat will have a much smaller HP than a power boat.
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Old 12-08-2009, 13:47   #3
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The "small" engines on sail cats are perfectly capable of driving the boat at hull speed. All the extra HP will get it up on a plane.

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Old 12-08-2009, 15:53   #4
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All the modern Cats and trimarans have hulls that are fast displacement and non planing.
A friend of mine has a 40 ft Sailing Cat with two 160 hp Steyr diesels and has a top speed of 22 knots and cruising speed of 15 knots. The boat does not plane.
He sails most of the time but likes to have the ability to get someware in a hurry if necessary.
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Old 12-08-2009, 15:59   #5
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Power cats are meant to go a lot faster. To double a boats speed you roughly need to square to cube the horsepower. Power cats can plane with enough horsepower. I have one at work that planes that goes 35 knots.
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Old 12-08-2009, 16:17   #6
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For a boat to plane you need a minimum of 50 hp per ton.
The new generation of multihulls have Non planing hulls that require much less hp to reach speeds in excess of 20 knots.
They also have a much smoother ride as the hulls are wave piercing.
Most catamaran ferries use this technology.
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