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Old 29-01-2018, 06:04   #1
DRL
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Gemini 105mc conversion Deisel to gas??

I am thinking about converting my Gemini 105mc from the Westerbeke/Sonic Drive leg to a gas Yamaha. Has anyone made such a conversion? Or, can share any resources?
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Old 29-01-2018, 06:51   #2
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Re: Gemini 105mc conversion Deisel to gas??

I don't have any experience with it, I did see this video of installation of 50hp Suzuki with a jack plate:


The only think that I would think about is what might the swap do to the resell price of the boat. Personally I would prefer the diesel.
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Old 29-01-2018, 09:13   #3
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Re: Gemini 105mc conversion Deisel to gas??

Thank you! Resale is Something to consider.
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Old 30-01-2018, 21:11   #4
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Re: Gemini 105mc conversion Deisel to gas??

New gas is far better for resale than old Diesel, especially on a Gem with an old driveleg.

Several on the Gemini yahoo blog including mine, Shearwater III and Grouchy Turtle, a better job with a jack plate.
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Old 30-01-2018, 23:56   #5
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Re: Gemini 105mc conversion Deisel to gas??

Go to the Yahoo Group. Several have done this.

At some point we will probably get another Gemini and would definitely prefer an outboard model. The only trick with resale is you have to do a decent job. If it looks all hinky, I would probably avoid it.

The jack plate video looks like a nice installation but a couple of comments:
- 50hp is a bit high for a Gemini. We originally had a 40hp and had trouble with it fouling plugs (2 stroke) because there was never was run hot enough to keep them clean. We replaced with a 25hp 4 stroke and that was a nice balance. Enough load to get the engine up to temp but some reserve for tough conditions. Some have gone down to 15hp and like it but there are times, we would have used all 15hp and wanted more. If you feel the need for a 25" shaft, they make extension kits for the 25hp motors.
- I assume they spent the time properly reinforcing the area where it mounts. The outboard Gemini's had a separate bucket that could be raised or lowered, so you will need to consider the structure.
- I would consider fairing the bottom leading edge of the jack plate so water flows under it smoothly.
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Old 31-01-2018, 05:57   #6
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Re: Gemini 105mc conversion Deisel to gas??

There is no doubt that modern outboards are more reliable and quieter than ever. However, I would not want to carry gasoline onboard.

If I had to search for a new Gemini, personally, I would avoid boats with a gasoline outboard.
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Old 31-01-2018, 06:13   #7
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Re: Gemini 105mc conversion Deisel to gas??

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Originally Posted by Davy J View Post
However, I would not want to carry gasoline onboard.
So does you dinghy motor run on diesel, or battery?

Maine Cat, Seawind and others have been building gasoline outboard propelled boats for a long time. Successful lines. No issues.
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Old 31-01-2018, 06:23   #8
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Re: Gemini 105mc conversion Deisel to gas??

Quote:
So does you dinghy motor run on diesel, or battery?
Dink has Honda 2hp outboard. We carry a 2 gallon gas can that stays in the dinghy. No gasoline below decks on the Gemini.
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Old 31-01-2018, 06:25   #9
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Re: Gemini 105mc conversion Deisel to gas??

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There is no doubt that modern outboards are more reliable and quieter than ever. However, I would not want to carry gasoline onboard.

If I had to search for a new Gemini, personally, I would avoid boats with a gasoline outboard.
Are you paranoid about gasoline powered cars blowing up? Just like a car, the gas tanks on a Gemini are bottom vented and with an outboard, the engine is completely clear of the hulls. So the issues with inboard powered gas engines are largely eliminated.
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Old 31-01-2018, 06:34   #10
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Re: Gemini 105mc conversion Deisel to gas??

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Are you paranoid about gasoline powered cars blowing up?
No, but your are missing the point. I'm saying that some people will not consider the boat with a modified power plant. Thus, possibly affecting resale.

Since I would prefer the original diesel motor, I wouldn't consider boats that didn't have one. YMMV
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Old 31-01-2018, 06:38   #11
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Re: Gemini 105mc conversion Deisel to gas??

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So does you dinghy motor run on diesel, or battery?

Maine Cat, Seawind and others have been building gasoline outboard propelled boats for a long time. Successful lines. No issues.
Gasoline fuel stays in the dinghy, maybe carried outside near the stern so any leaks drain to the ocean. Keeping gasoline in a boat that is not equipped with gasoline safety equipment, bilge blowers, sniffers etc is a risk I don't like having.
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Old 31-01-2018, 06:57   #12
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Re: Gemini 105mc conversion Deisel to gas??

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Gasoline fuel stays in the dinghy, maybe carried outside near the stern so any leaks drain to the ocean. Keeping gasoline in a boat that is not equipped with gasoline safety equipment, bilge blowers, sniffers etc is a risk I don't like having.
People are missing the point. The problem with inboard gas engines on monohulls is any leak or fumes from the tank or engine wind up in the bilge where they have no way to escape, so you can have a risk of them catching fire. Hence the need for blowers and sniffers.

On a Gemini the gas tanks are in the bridge deck with vents on the bottom that lead under the bridge deck (not into the hulls), so any leaks or fumes DO DRAIN TO THE OCEAN. Furthermore with an outboard, if there are any leaks at the motor, those also drain to the ocean.

It's an apples and oranges comparison.
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Old 31-01-2018, 07:12   #13
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Re: Gemini 105mc conversion Deisel to gas??

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People are missing the point. The problem with inboard gas engines on monohulls is any leak or fumes from the tank or engine wind up in the bilge where they have no way to escape, so you can have a risk of them catching fire. Hence the need for blowers and sniffers.

On a Gemini the gas tanks are in the bridge deck with vents on the bottom that lead under the bridge deck (not into the hulls), so any leaks or fumes DO DRAIN TO THE OCEAN. Furthermore with an outboard, if there are any leaks at the motor, those also drain to the ocean.

It's an apples and oranges comparison.
Couple of items here.

1. A Gemini factory built with a diesel engine, does it's fuel tank vent and have same safety systems as a gasoline designed one?

2. The point re the dinghy was sailjumanji post asking if the dinghy ran on gas, then implied that if you carry gas for the dinghy why comment that having gas on board was unsafe. I would suggest the same in your outboard powered Gemini if you carried spare gas below decks, or in a non draining un-vented storage locker.


I used to have a twin outboard powered cat with fuel tank that if it leaked would fall to the ocean, all fine and good. I was still paranoid about fuel handling/transfer at the dock or refilling at sea, static, sparks etc and where to carry spare fuel. It obviously is all manageable but higher risk than diesel.
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Old 31-01-2018, 07:22   #14
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Re: Gemini 105mc conversion Deisel to gas??

I remember looking at a gem a while back- you’ll free up a whole locker, and the diesel set up in the gem is probably a lot louder than a 4 stroke new OB... and I have heard the silette drive leg is a PITA?
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Old 31-01-2018, 07:45   #15
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Re: Gemini 105mc conversion Deisel to gas??

There are no blowers, sniffers, etc on Maine Cat and Seawind gas tanks. They are vented, and drain overboard. They are not tied to cabin in any way. It's pretty much the same system as on your automobile! It's pretty darn simple.

I have seen one SW 1160 deluxe converted from diesel engines to outboard motors. Very professional job and I suspect it actually increased resale value. That said, a sloppy conversion of a Gemini or one that looks DIY will certainly impair resale, IMO.
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