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Old 23-02-2017, 09:11   #1
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Double Outboards on a Catamaran

I have a Heavenly Twins Catamaran Mk111 with double Yanmar 1 GM Engines.
My plan is to do some extensive sailing on it possibly Mediterranean, Red Sea, Indian Ocean.

There is going to be two adults and 4 children so space is going to be precious.
My thoughts possibly would be to remove the two Yanmar's and have two Outboards, possibly Yamaha 9.9 XL Shafts instead to create more space and another for a back up.
Which i would like to put on stern mounts.

Has anybody on here done this to their Catamaran? All feed back would be appreciated on this idea.

I am going to have 4 x 65 watt Solar panels and two wind turbines to charge the house batteries. I will also carry a 1000W Generator as a back up. So not worried about using outboards to charge batteries.
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Old 23-02-2017, 09:21   #2
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pirate Re: Double Outboards on a Catamaran

Do you have the OB well/s in the cockpit already..???
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Old 23-02-2017, 09:33   #3
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Re: Double Outboards on a Catamaran

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Do you have the OB well/s in the cockpit already..???
I would like to put them on Stern Mounts.
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Old 23-02-2017, 09:42   #4
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Re: Double Outboards on a Catamaran

Are the inboards in fine working order?
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Old 23-02-2017, 10:50   #5
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Re: Double Outboards on a Catamaran

I have talked to a guy sailing a twin o/b cat in the West Indies. He was 100% happy with this application. His engines were mounted just inboard of each hull.

You probably want to investigate the XL shafts (I have seen them on e.g. Tohatsu).

BTW if your cruising is serious, get o/b that are somewhat above the i/b rating for your design AND make sure your manufacturer provides 'sailing' props.

Cheers,
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Old 23-02-2017, 17:15   #6
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Re: Double Outboards on a Catamaran

Are you doing this to make more room or to replace unreliable motors? If it's to make more room, I would think that there are many other strategies you could employ to solve that. If it's unreliable motors, wouldn't think that a pair of outboards would not give you the longevity and the reliability that you might need for the long journeys that you're suggesting. It also means that you will be carrying large volumes of petrol and that has risks associated with it.
Given the costs and complexities of adding a pair of o/bs, I would think that the yanmars are a much better choice. Think about adapting the throttle linkages and putting the motors into reverse. If you currently have a throttle/gear linkage for each motor, you might lose significant maneuverability when mooring.

A 1000w gennie sounds great, but I suspect that you will have to adapt your high voltage system to accept it and even then, it will only charge as well as your current charger can do. Most small gennies have a 12v outlet but it's only designed to work at a few watts. This might mean that you will have to run the gennie for many hours to fully charge your batteries

A brand new, complete 1GM costs 4000 euros. That's with gearbox, control panel etc,etc. You might get a bare engine for much less. The changeover is a simple DIY
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Old 23-02-2017, 17:29   #7
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pirate Re: Double Outboards on a Catamaran

Quote:
Originally Posted by philipmclaren1 View Post
I would like to put them on Stern Mounts.
Ouch..!!! I'd look at a single 15hp XL shaft mounted central under the rear cockpit seating area.. it'd be sufficient to power her nicely and a lot easier to operate.. with no cavitation.
HT's have a tendency to hobby horse.
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Old 23-02-2017, 17:37   #8
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Re: Double Outboards on a Catamaran

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Originally Posted by boatman61 View Post
Ouch..!!! I'd look at a single 15hp XL shaft mounted central under the rear cockpit seating area.. it'd be sufficient to power her nicely and a lot easier to operate.. with no cavitation.

HT's have a tendency to hobby horse.

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Old 24-02-2017, 04:12   #9
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Re: Double Outboards on a Catamaran

Totally agree that two large OB's on the stern is a bad idea.
Single engine mounted in the cockpit with a small aux OB on
a stern bracket would be better. You need to consider manoeuvring
if you intend to use marinas etc. Turning the main engine is one option. The route we went was to add a bow thruster (HT27).
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Old 24-02-2017, 07:38   #10
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Re: Double Outboards on a Catamaran

A single outboard well in cockpit is the outboard option for a HT.


Outboards can be a great option for a cruising boat (bottom vent the tanks below the bridge deck and 99% of the concerns go away). For such a small boat, twin engines is likely overkill.


Putting the engines at the far ends of the hulls is a bad idea unless the boat is designed for it. In calm conditions, it will work OK but when the sterns lift off waves, the props are likely to come out of the water. Extra Long Shaft engines will help but not entirely.


I suggest googling the HT websites as they have already considered the options.
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Old 24-02-2017, 08:01   #11
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Re: Double Outboards on a Catamaran

The fuel economy with the outboards will be much worse than with the inboards so you need to allow a lot of space for extra fuel so you may not gain there. Also diesels seem much more reliable, to me at least, than outboards, especially in an exposed location.
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Old 24-02-2017, 08:12   #12
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Re: Double Outboards on a Catamaran

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The fuel economy with the outboards will be much worse than with the inboards so you need to allow a lot of space for extra fuel so you may not gain there. Also diesels seem much more reliable, to me at least, than outboards, especially in an exposed location.
You are thinking old school.

Modern 4 strokes do pretty good. We had a Gemini and got within 20% of what the diesel versions boats were getting. If range is critical, we could get 10-12 miles per gallon but usually, we accepted around 6mpg and made better time.

As far as reliability, we installed the motor (25hp Merc EFI) in 2007 and sold it last year with over a 1000hrs on it. Other than fluid/filter changes, a set of spark plugs (probably not needed) and a new water pump impeller...zero maintenance.
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Old 24-02-2017, 13:10   #13
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Re: Double Outboards on a Catamaran

If it's extra bedrooms, consider enclosing the cockpit area. you can easily put demountable beds in there.
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Old 26-02-2017, 15:03   #14
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Re: Double Outboards on a Catamaran

Look at this setup on a Seawind 1000. Powered by dual Yamaha 9.9 high thrust long shaft outboards. These pics are of the original 2002 motors, which I replaced with same Yamaha 9.9's in 2012 - which are smaller and lighter power head. The motor swings up on a large stainless steel bracket - not the Yamaha bracket. Lift is by a 3:1 pulley attached to motor cavitation plate. The hull cowling protects the motor while it is down and motoring. The motor boxes are probably about 6-8 ft forward of the stern. Spread apart like this, the boat can just about turn in its own length. This is a very good system.

If the motors were instead mounted on the sterns, I am afraid that you'd be cavitating/aerating the props in short choppy waves. Plus the motor would be in the way each time you wanted to board the dinghy. As much as I am a fan of dual outboards, if stern were my only choice, I would probably stick with the inboard diesels.
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Old 27-02-2017, 09:46   #15
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Re: Double Outboards on a Catamaran

Hi to all.

I have a 35ft-5,60mt beam-Richard Woods design, 3tons due to pvc foam hull material, with one VolvoPenta 2001-1cyl. (9hp) + the other engine, new Vetus M2-06 2cyln.s (16hp) inboard diesels with both saildrives.

Because without any movement, after 4 years at a harbour, no idea about zincs at all, l expect serious damages at saildrives.

I plan to get out a shipyard within 2 months, l dont plan to spend "lots of" money for repairing saildrive gearboxes... Total 25hp is not enough for me.

We will be at Ionian and Egean sea, not a ocean passage..

Fuel economy is not very important.

I plan -ok l dream- about 2*50hp modern 4stroke O/Bs.

With half throttle, 12kts...



Any advices welcome.

Thank you.
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