Displacement power cat outboard choice

[Russell Brown]

I am building an outboard powered catamaran and would like some input on the my choice for an outboard motor. The boat I’m building is a slightly larger sister to a boat I own that is powered by a 15 hp Honda outboard.
The best way I can show what I’m building is to link to a video of the boat I’m using now.
https://www.youtube.com/watch?v=41qoqxMVkBU

The new boat is 3 feet longer, will weigh about the same, and is intended for long range camp cruising. The pod is long enough to be able to sleep aboard behind the driver & passenger seats and the hulls are made from 23 foot long Nigel Irens designed trimaran outrigger hulls.

The new boat is more than half complete and was designed around the Yamaha 20 hp long shaft.
The Yamaha was chosen because we have experience with it on our PT Skiff and a good friend has an unbelievable amount of trouble-free hours on one in a single outrigger motorboat I designed.
Reliability is paramount in the new boat as we intend some open water passages and almost always cruise in remote places. I have done many thousands of miles in the old boat with an old motor, but It’s a bit like flying a single engine plane. We hope to go farther in the new boat.

The downside to the Yamaha 20 is that it’s a bit of a gas hog, which is contrary to what the boat is all about.

On the PT Skiff with a Yamaha 20, we carefully measured fuel consumption.
At full throttle (6000 rpm’s) it burned very close to 2 gph.
at 5000 rpm’s it burned 1.35 gph.
at 4000 rpm’s, consumption was .9 gallons per hour.
This was a new motor when tested and possibly the fuel consumption got better, but I am used to much better economy with the Honda 15 on the old boat.

The Water Bug (in the video) burns just over 1 gallon per hour with the Honda 15 at close to full throttle (15 knots), but with the throttle backed well off the consumption is closer to 1/2 gallon per hour (at about 12 knots). The beauty of this kind of displacement hulled motorboat seems to be that the half throttle speed is quite high in relation to full throttle speed.

Unfortunately it seems that there is not much effort put into fuel efficiency for motors this small.
Fuel injection seems to kick in at 25 or 30 hp in most outboards and I don’t want that much power nor can I afford the weight of a bigger outboard.

Is there some kind of magic here that I’m missing? Is the Yamaha 20 about as good as I’ll find for fuel economy in a 20 hp outboard motor?

I can’t put an inboard in this boat and I’m not interested in hybrid power, but I would very much appreciate input about fuel consumption and reliability of outboards in the 20 hp range.

Thanks, Russell

 

[Mr Efficiency]

Doesn't look like a "gas hog" to me. It sounds as though you want what you see as lower fuel consumption from a Honda ( I think that is doubtful, or if is the case, won't be much different), but are attracted to what you see as greater reliablity from a Yamaha ( again, that is something that would be hard to establish as fact). So you want a Yamahonda, which isn't in production !

 

[rasorinc]

How does the new Yamaha 20 stats compare to a new Honda 20, a new Tohatsu 20, and a new Mercury 20 though I believe Tohatsu makes that size for Merc.
How about a pair of 8 hp or 10 hp, which would settle your possible 2nd engine needs.

 

[Russell Brown]

The twin engine choice doesn't look good from a weight or fuel consumption perspective and the boat was designed around a single engine.
It's pretty hard to find fuel consumption data on small outboards. The best data I found was a site called blue something, but it is no longer on the web. The Yamaha was shown using a bit more fuel than other 4 strokes.
Thanks,
Russell

 

[rasorinc]

I would call their US Headquarters and ask for those specs, and buy the very best fuel filter system.

 

[Mr Efficiency]

Suzuki 4-strokes have a good reputation for fuel economy, but you have to compare like with like, and outputs vary between engines of the same hp rating, and at different rpm.

 

[DCockey]

The Suzuki 20 HP and 25 HP engines have EFI which might result in higher efficiency.

 

[Russell Brown]

Does anyone have direct experience with the Suzuki 20 or 25? Could it be as reliable a motor as the Yamaha?
Have I posted in the right place on this forum for outboard experts or should I be in the outboard section?
Thanks,
Russell

 

[Mr Efficiency]

The bigger Suzuki motors are popular with commercial operators in Australia. In the past Suzukis had a reputation for using an alloy in the castings that wasn't up to scratch, but they seem to have fixed that nowadays.

 

[Mr Efficiency]

Do they offer 25" length in the 20 or 25hp ?

 

[whitepointer23]

google trailer boat fisherman. Its an aussie site which has an online library with test and consumption figures on most outboards.

 

[whitepointer23]

Parsons are worth a look to. Yamaha clones but they are gaining a good reputation here.

 

[Mr Efficiency]

Parsons are worth a look to. Yamaha clones but they are gaining a good reputation here.

Interesting (the yamaha bit). 2 or 4 stroke ?

 

[fishtigua]

Parsun outboards are indeed a cheap knock-off of old Yamahas. Do you really want a 15 year old engine made in China?

http://www.parsunmarine.com/products.asp

I'd go with a Mariner/Merc. Lighter than the Honda and less of a rot/ruster than the Tohatsu/Suzuki.

 

[Russell Brown]

Fish,
Why the Mariner/Merc over the Yamaha 20?
I know Mariner's are good, but I'm after ultimate reliability (as well as good fuel economy).
We spend a lot of time in BC, Canada and it seems the Yamaha's are the favorite for reliability, but it's so hard to get good information about the small outboards.
I want to learn as much as I can about the compromises before I buy.
Thanks for the feedback.
Russell