Honda 20hp versus Yamaha 9.9HP

[rodscat]

Need to replace my current motors which are twin 20HP honda 4 strokes and have been going strong for 10 years, without any issues.

just comparing the Honda motors which have not changed for 10 years to the Yamaha 9.9 hp high thrust motors.

Unable to get a lot of info from the dealers as they are just pushing there own brand of motors

38ft chamberlin catamaran approx 6 ton is what the motors are to be used on.

Look forward to your feedback and experience on these 2 type of motors.

[Chotu]

Basically, what I've learned is it's all in the props.

If you could fit the high thrust props on the Honda 20's at the right pitch for your boat you'd have something great.

However, the manufacturers make all that difficult.

You just have to figure out which props you can put on which engines that fit your boat. Not easy but it can be done.

[Sand crab]

The Honda 20s can be ordered as a "Power Thrust" unit with different props.

https://marine.honda.com/outboards/motor-detail/BF15-20

[billknny]

There is no magic...

A 9.9HP engine has 1/2 the available power of a 20HP.

As others have said, the issue is to match the prop to the application so the engine runs at the speed that allows it to generate the power it is capable of.

For a 6 ton boat, 40HP is more than enough, if the props allow the engines to develop full HP. If you installed the engines with the "stock" props the chances are that they are WAY off.

When you run your existing 20HP engines at full throttle, what RPM do they turn? Is that RPM within the range specified by Honda for the engine? If not, you will get way more bang for your buck re-propping than re-powering.

[rodscat]

Yes currently have the High thrust props on the Honda 20HP, i have been led to believe that the 9.9 perform better

[billknny]

Originally Posted by rodscat

Yes currently have the High thrust props on the Honda 20HP, i have been led to believe that the 9.9 perform better

You might have "high thrust props" but if the engines don't run at the right RPM then they can not generate 20 HP than you are paying for.

Properly set up, there is no way that a 9.9 will out push a 20HP, no matter what the salesman says. It's just math...

[44'cruisingcat]

Originally Posted by rodscat

Yes currently have the High thrust props on the Honda 20HP, i have been led to believe that the 9.9 perform better

Yes, many people say this. I think it's based on people comparing the 9.9 HT with the Honda running standard props. In that case the Yamaha would be better, particularly in reverse.

With the Powerthrust props on the Hondas they become far better suited.

The Hondas also have the advantage of having a 28inch leg available. The best prop on earth isn't much good if it's out of the water!

Friends of ours replaced Honda 20 Powerthrust motors with 9.9 HTs, due to cost.

They reported that the 9.9s were significantly inferior in performance, requiring both engines to be run to provide similar performance to a single Honda.

Low speed maneuvering may be better with the Yamahas though.

[Lippe]

Originally Posted by billknny

You might have "high thrust props" but if the engines don't run at the right RPM then they can not generate 20 HP than you are paying for.

Properly set up, there is no way that a 9.9 will out push a 20HP, no matter what the salesman says. It's just math...

Have you wondered why only 9,9 hp outboards have the output labelled so accurately. It is not standard mathematics but tax mathematics. In many countries there is taxes or registeration requested on 10hp engines and upwards. That is why it was developed a 9,9 hp engine that usually without any further adjustments gives about 15 hp.

[smj]

Originally Posted by Lippe

Have you wondered why only 9,9 hp outboards have the output labelled so accurately. It is not standard mathematics but tax mathematics. In many countries there is taxes or registeration requested on 10hp engines and upwards. That is why it was developed a 9,9 hp engine that usually without any further adjustments gives about 15 hp.

In the US it’s the fact quite a few lakes have regulations restricting outboards of 10hp and above.

[David M]

You are talking twice the horsepower. There is no propeller, pitch, diameter, number of blades, reduction ratio magic that will match the thrust developed by two 9.9's to the thrust developed by two 20 horsepower engines...even when you consider possible labeling inaccuracies. Just compare naturally aspirated engine displacements for engines of that size.

[Lippe]

Originally Posted by smj

In the US it’s the fact quite a few lakes have regulations restricting outboards of 10hp and above.

Yes but you get the same 9,9 hp engine that I get in Finland. It has 9,9 hp written on but in fact it has more power in it.

[Lippe]

Originally Posted by David M

You are talking twice the horsepower. There is no propeller, pitch, diameter, number of blades, reduction ratio magic that will match the thrust developed by two 9.9's to the thrust developed by two 20 horsepower engines...even when you consider possible labeling inaccuracies. Just compare naturally aspirated engine displacements for engines of that size.

9,9 labelled outboards give normally more than 10 hp. Some of them 15 hp and have same displacement than a 15 hp labelled has. This is the case for example with my Mercury 9,9 hp.

[Sinkers]

Hi, if it helps you to decide , I have a Seawind 1000xl with Yamaha 9.9s, so I can give you an idea of performance. Flat out in absolutely still conditions I get 7 kts.
Normal cruise is more like 6 knots in still conditions. Any headwinds or worse heading straight into a chop really hurts the speed. Punching into a 15kt headwind and chop would bring the speed back to about 4 kts and anything over 20 is just too hard. The solution of course is to motorsail with just the main up. My opinion is the boat would benefit hugely from larger engines with more thrust. The trick is which engine achieves this ? The Honda 20s are a possibility. How would your boats performance compare with mine? I am at CLEVELAND near BRISBANE if you would like to go for a run in my boat before you commit.
All the best
Greg

[Sparx]

I have twin 9.9 Yamaha High Thrust motors on a Maine Cat 38. Specs suggest 4 tons empty, mine is loaded for cruising. At wide open throttle we go 7.5 knots. Typically cruise at 6.5 knots burning less than a gallon per hour. Using a single engine the boat moves 5 to 5.5 knots using modest rpm. Low speed and reverse maneuverability is great. We have the extra long legs.

[44'cruisingcat]

Originally Posted by Lippe

9,9 labelled outboards give normally more than 10 hp. Some of them 15 hp and have same displacement than a 15 hp labelled has. This is the case for example with my Mercury 9,9 hp.

I doubt this, as manufacturers would be leaving themselves wide open for lawsuits in places where there are license restrictions on horsepower.

Manufacturers do often use the same motor for a couple of horsepower ratings, but they do make changes such as carburetors so the motors actually produce the rated power.

The current Yamaha 9.9 HT is an upgraded 8.