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Old 11-05-2021, 16:32   #31
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Re: Double Outboards on a Catamaran

From an economic perspective you’ll be lucky to sell a VGC 1GM for the cost of a new Yamaha 9.9.

I personally think a HT 26 would be an awesome canal boat but not much else. I know they’re super seaworthy, but any passage must just be constant slamming and lack of sleep.

I once saw on in Boot Key with a single outboard that had maybe 12” or bridgedeck clearance. So if you want a sailboat that’s the way to go. Otherwise, for motoring and calm seas motorsailing keep the diesels till they bust.
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Old 11-05-2021, 23:10   #32
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Re: Double Outboards on a Catamaran

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We’ve owned 3 catamarans with single outboards and 4 catamarans with twin outboards. I guess I probably have enough experience with both applications to comment and I also guess you’ve never owned or operated a catamaran with a single steerable out board?
Steerable would work on a 40 footer 20 feet wide, I didn’t mention steerable Charlie Brown, I talking fixed .
Is this the Jobie cat section?
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Old 11-05-2021, 23:37   #33
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Re: Double Outboards on a Catamaran

There is only one small outboard (high thrust) that is designed to push heavy loads, that is the 9.9 hp yamaha, It has a 3 to 1 gearbox ratio and a 12 inch prop and comes in 25 inch long shaft all the other 10/20 hp engines come with a 2 to 1 ratio and a 10 inch prop and are designed to push 3.5 to 4 metre tinnys around at 20 knots. Also worth considering is hull speed, pretty much all sailing catamarans because of there hull shape ( were designed to sail) are only good for 6 to 8 knots under power then they start to squat becoming much less efficient as a result. 2x 9.9 hp high thrust Yamaha’s will push you along at 6 knots easily using less than 4 litres an hour combined
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Old 12-05-2021, 04:01   #34
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Re: Double Outboards on a Catamaran

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Steerable would work on a 40 footer 20 feet wide, I didn’t mention steerable Charlie Brown, I talking fixed .

Is this the Jobie cat section?


You didn’t mention steerable or fixed you just stated a single outboard would be suicidal. Why wouldn’t it be steerable? Only makes sense.
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Old 12-05-2021, 04:03   #35
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Re: Double Outboards on a Catamaran

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There is only one small outboard (high thrust) that is designed to push heavy loads, that is the 9.9 hp yamaha, It has a 3 to 1 gearbox ratio and a 12 inch prop and comes in 25 inch long shaft all the other 10/20 hp engines come with a 2 to 1 ratio and a 10 inch prop and are designed to push 3.5 to 4 metre tinnys around at 20 knots. Also worth considering is hull speed, pretty much all sailing catamarans because of there hull shape ( were designed to sail) are only good for 6 to 8 knots under power then they start to squat becoming much less efficient as a result. 2x 9.9 hp high thrust Yamaha’s will push you along at 6 knots easily using less than 4 litres an hour combined


I was under the same impression until we bought a 38’ cat with a single Honda 15, the thrust that motor has is incredible!
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Old 12-05-2021, 15:29   #36
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Re: Double Outboards on a Catamaran

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I was under the same impression until we bought a 38’ cat with a single Honda 15, the thrust that motor has is incredible!
Yep, Honda's "Powerthrust" props do work well.

IMO, what's more important, and the reason I chose Honda 20s, is the available leg length.

The Hondas come with a 28 inch leg. (AFAIK this is only available on the 15 in the US for some reason.)

The biggest gearbox and prop on earth won't do you any good if it's not in the water.
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Old 13-05-2021, 14:04   #37
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Re: Double Outboards on a Catamaran

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Originally Posted by Bunji View Post
There is only one small outboard (high thrust) that is designed to push heavy loads, that is the 9.9 hp yamaha, It has a 3 to 1 gearbox ratio and a 12 inch prop and comes in 25 inch long shaft all the other 10/20 hp engines come with a 2 to 1 ratio and a 10 inch prop and are designed to push 3.5 to 4 metre tinnys around at 20 knots. Also worth considering is hull speed, pretty much all sailing catamarans because of there hull shape ( were designed to sail) are only good for 6 to 8 knots under power then they start to squat becoming much less efficient as a result. 2x 9.9 hp high thrust Yamaha’s will push you along at 6 knots easily using less than 4 litres an hour combined
Our 2002 Seawind 1000 had the Yamaha 9.9 high thrust motors, and they were very dependable. They lasted for about 12 years, and one of them suffered failure. At that age, it is very difficult to find head gaskets, and some parts, and it was more economical to just replace.

Our 2019 Seawind 1160 Lite has dual Yamaha 25 hp high thrust outboards, model T25XA. They were manufactured in 2018 and have 25 inch shaft, but I have not found them available in the US. In mid 2019, that same motor went from carb to EFI, with a significant weight savings in the new model. THAT is what I would look for.
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Old 13-05-2021, 21:25   #38
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Re: Double Outboards on a Catamaran

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Our 2002 Seawind 1000 had the Yamaha 9.9 high thrust motors, and they were very dependable. They lasted for about 12 years, and one of them suffered failure. At that age, it is very difficult to find head gaskets, and some parts, and it was more economical to just replace.

Our 2019 Seawind 1160 Lite has dual Yamaha 25 hp high thrust outboards, model T25XA. They were manufactured in 2018 and have 25 inch shaft, but I have not found them available in the US. In mid 2019, that same motor went from carb to EFI, with a significant weight savings in the new model. THAT is what I would look for.
Absolutely cheap enough to just replace every 10 years
OP has 26 ft catamaran, 25 hp x 2 would be overkill also much more expensive and heavier 70kgs / 45kgs
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Old 15-05-2021, 06:45   #39
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Re: Double Outboards on a Catamaran

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Absolutely cheap enough to just replace every 10 years

OP has 26 ft catamaran, 25 hp x 2 would be overkill also much more expensive and heavier 70kgs / 45kgs
Agreed.
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Old 15-05-2021, 08:05   #40
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Re: Double Outboards on a Catamaran

Most catamarans would do well with one engine. The additional engine would help with a small increase of speed but pay for gas usage.
One engine requires acquiring skills and is not forgiving. I have an EDELCAT33 with a 15 HP 2 cycle Yamaha and it does just fine. Is about the same dimensions as your boat.
Building and properly placing the motor mounts or sleds requires some thinking so not to aggravate hobby horsing with weight at the end. Then there is the question of how much money if any are you going to get from your old diesels. I am assuming cost constraints are a reality, otherwise you would have a modern Ir bigger boat. Ñ used 9.9 Hugh trust Yamaha may be the only thing you need. It does not need to be centered either. If you are concern about reliability, build two sled. Use only one, and in an emergency you can always use your dinghy’s out board on the second sled.
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Old 15-05-2021, 08:41   #41
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Re: Double Outboards on a Catamaran

Looking at your situation (two adults and 4 children) on a Heavenly Twins 27' catamaran, and your hope to gain more accommodation space by relocating the power to the back of the hulls TOGETHER with a look at the boat itself (https://sailboatdata.com/sailboat/heavenly-twins) my advice is:

It's not worth it.

You are going to add very little space and I think you will have poor performance with the engines at the extreme aft end of the hulls. Possibly a single engine in the middle of the boat, with a lowering mechanism would work better, but in either case you will embark on a major modification project. In the end you'll put in a lot of work and have a boat with less value and not much gain in interior space. It's still going to be crowded with 6 people.

I think there is a good chance that you have very little invested in this vessel. Don't invest a lot more. Best to use it as is for as long as you can stand it and then move on to something a little larger and more suitable for cruising with a large family.
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Old 04-06-2021, 08:29   #42
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Re: Double Outboards on a Catamaran

I have a Fountaine Pajot Louisiane 37 with twin 9.9 Suzuki outboards. I am happy with the set up. BUT they are only useful for docking, or light wind situations. They will not power the boat against wind over 15 knots, or choppy seas.
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Old 04-06-2021, 10:25   #43
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Re: Double Outboards on a Catamaran

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I have a Fountaine Pajot Louisiane 37 with twin 9.9 Suzuki outboards. I am happy with the set up. BUT they are only useful for docking, or light wind situations. They will not power the boat against wind over 15 knots, or choppy seas.


I don’t believe the Suzuki’s lower unit gearing or prop size is optimized for pushing a catamaran, the Yamaha T9.9 was designed for this purpose.
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Old 04-06-2021, 13:09   #44
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Re: Double Outboards on a Catamaran

AJ,

I was going to ask how he liked the Suzuki’s until I read his entire post.

The Vardo will go as well as he suggests with the Single T8 and 5 3/4” pitch prop.
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Old 04-06-2021, 17:00   #45
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Re: Double Outboards on a Catamaran

The FP L37 is a nice boat, but I also would think a little heavy for twin 9.9s. Even the Yamaha high thrust versions. My Seawind 1160 Lite (38 ft) came standard with twin 20 hp Hondas, but we went with optional Yamaha 25 HTs.
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