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Old 22-01-2016, 10:20   #16
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Re: Can you add more hp to a Gemini

If you need to travel at 15 knots, you need a powerboat. Not a sailboat. The Gemini 105Mc is a sailboat, it has auxiliary power. It will sail faster than the motor can push it. It will also motorsail faster than the engine alone. If the wind is light, put up a spinnaker or the screacher, it will still sail faster than the motor can push it.

The boat sails faster when it is loaded lightly. For coastal cruising, you will want the extra loading capacity for supplies, not engine and fuel weight. Just my 2cents, YMMV.
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Old 22-01-2016, 11:27   #17
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Re: Can you add more hp to a Gemini

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Originally Posted by lindabarzini View Post
I am thinking about a Catamaran, but don't know much about them.

Unlike a displacement monohull, the stability of a catamaran is generated from the width which allows cats to hydroplane, thus cats can go 10-12 knots or more in 20-30kts of breeze where a monohull is limited by hull speed.

So, couldn't you replace the engine/engines on a catamaran with more powerful engines. For example, I see many Gemini 105MC cats with about 30 hp motors. Couldn't this be replaced with a 150 hp motor? Shouldn't a cat theoretically be able to motor at 15kts with a bigger motor?

Since I have never seen this nor heard of this, what am I missing?
Yep! Put in a gas turbines.
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Old 22-01-2016, 11:35   #18
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Re: Can you add more hp to a Gemini

Thanks for the input. I hadn't realized the fuel consumption would be so significant.

I spoke with a Gemini dealer who said the manufacturer replaced the dual 15hp Yanmars with dual 29hp motors on the new Legacy, but they didn't gain more than a knot, so they went back to the 15s.

I watched this of a Fountaine Pajot powercat that used 10 liters/hr only going 7.5 kts.

The have dual 175hp outboards and you can buy dual 250hp motors with a top speed of 46kts and cruising speed of 27kts, but with a fuel consumption of 13gph.

So, it is possible, but its really a different boat. Powercats are not long distance cruisers primarily because of the fuel consumption rate.
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Old 22-01-2016, 15:12   #19
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Re: Can you add more hp to a Gemini

We have a 3400 Gemini. We swapped out the original 40hp for a 25hp. Top speed is barely impacted but you never go at top speed. It just makes a lot of noise and doesn't go much faster in exchange for drastically increasing fuel consumption. Figure around 7.5kts as top speed and 6.5kts as a nice cruising speed.

Reality is the Gemini and most production cats are still displacement vessels. They will go a little faster than the same length mono but unless you get into truly high performance model, don't count on beating hull speed except in rare situations.

Except for a few of the early 105's, they use diesel with a special I/O unit that can't handle much more HP. Plus the motor wouldn't fit in the current hatch requiring major fiberglass surgery.

If you get one of the older outboard models, you could increase the HP but since it's not designed for it I wouldn't put more than 40hp on the sled. I have heard of a couple guys glassing the sled in place to make it stronger but then the sled is permanently deployed taking away one of the big benefits of eliminating drag under sale.

The gemini is a great boat but I think you will be disappointed if you try to make it something that it isn't. The fact you didn't understand that sail cats can't plane suggests you should really look to buy a boat that does what you want and not rebuild one to do it.
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Old 22-01-2016, 16:07   #20
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Re: Can you add more hp to a Gemini

A number of us own or have owned Gemini catamaran converted to use outboards. The factory Westerbeke and Stelete sometimes hold up forever, but several of us have reported extensive expense and reliability problems.

That said, there are a number of single and twin engine Gems with 25 hp and a few with 40 hp. Much above that, I don't think the boat would take the strain.

If you want a power cat, buy one. If you convert a Gem, you have a sailing cat with a big engine - not a satisfactory combination.,
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Old 23-01-2016, 05:51   #21
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Re: Can you add more hp to a Gemini

you are looking at this the wrong way around...................... buy a power cat, then add a mast and sails.........
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Old 23-01-2016, 10:21   #22
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Re: Can you add more hp to a Gemini

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you are looking at this the wrong way around...................... buy a power cat, then add a mast and sails.........
I see some power cats that appear to be the reverse. The sail boat sold without rigging and called a power cat.
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Old 29-01-2016, 10:20   #23
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Re: Can you add more hp to a Gemini

Gemini's don't need more HP they need more beam.
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Old 30-01-2016, 08:44   #24
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Re: Can you add more hp to a Gemini

If you need more beam, you need a different catamaran. It's really as simple as that.......................
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Old 30-01-2016, 21:18   #25
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Re: Can you add more hp to a Gemini

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Gemini's don't need more HP they need more beam.
Good luck getting a 20' beam cat in a standard 35' slip. One of the key design criteria of the Gemini is to be able to use standard marina facilities (slips, travel lifts, etc...)
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Old 31-01-2016, 08:53   #26
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Re: Can you add more hp to a Gemini

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Good luck getting a 20' beam cat in a standard 35' slip. One of the key design criteria of the Gemini is to be able to use standard marina facilities (slips, travel lifts, etc...)
The birth and also the hail out. I've had to tris so ask me how I know.
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Old 31-01-2016, 18:13   #27
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Re: Can you add more hp to a Gemini

[Good luck getting a 20' beam cat in a standard 35' slip. One of the key design criteria of the Gemini is to be able to use standard marina facilities (slips, travel lifts, etc

Maybe I'm wrong but shouldn't a sailboat be designed to sail well, not dock well?
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Old 01-02-2016, 07:00   #28
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Re: Can you add more hp to a Gemini

And I'm sure you will want to tell us about your vast experience sailing aboard a Gemini.................
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Old 01-02-2016, 11:37   #29
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Re: Can you add more hp to a Gemini

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[Good luck getting a 20' beam cat in a standard 35' slip. One of the key design criteria of the Gemini is to be able to use standard marina facilities (slips, travel lifts, etc

Maybe I'm wrong but shouldn't a sailboat be designed to sail well, not dock well?
Who said it doesn't sail well?
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Old 29-01-2017, 17:24   #30
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Re: Can you add more hp to a Gemini

I installed a 50 HP Honda on my 2000 Gemini Catamaran. The conversion took me and my friend approx. 2 days.

My YouTube link:

https://youtu.be/2uWn8JqBrvs
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