Any experts on Yamaha high thrust outboards around?

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NealB

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We use our 32 foot Comanche catamaran for coastal cruising.

She has a Yamaha 9.9hp high thrust outboard as an auxilliary engine.

It's a great engine: reliable, quiet, smooth and very economical.

Just one problem: in strong headwinds, it is underpowered, and we go sideways.

eg Last year, we moved out from the quay at Weymouth, in gusty conditions, to anchor overnight in Portland, ready to take the inshore passage round Portland the next morning (and avoid the hassles of getting out from the inside of a raft at 0500). As we poked our bows into the entrance between the walls of Portland, a really strong gust from the west hit us, and we spent several nervous moments wondering whether we'd get through the entrance.

So, we're thinking about fitting a bigger engine.

Fitting an inboard diesel is too much hassle, plus I quite like the outboard option.

I wonder if anyone here knows much about Yamaha's 15 or 25hp high thrust versions?

Any thoughts on whether either would be a good set-up on a Comanche (the engine is in a closed locker ahead of the cockpit)?

Which should we go for?

Any recommendations about good dealers? I've emailed two so far, and, over a week later, no reply from either.

Any pearls of wisdom gratefully received.
 
Interesting. I was just about to order a Yamaha high thrust 9.9 for our 35' cat. What does your boat displace ? Ours is a light (2,000 Kg) Wharram with much less windage than most and I would have expected plenty of drive from that engine provided we can get the prop deep enough.

We will also mount the engine in a well that is ahead of the cockpit. This will inevitably make close quarters manoeuvring a challenge in a cross, wind. But we can live with that.

I am really reluctant to go for a bigger engine because of weight and cost penalties. Do you think I will regret that ?
 
I reckon the 9.9 Yam is too small for a 35' cat.

The Dragonfly 920 has the 9.9 as standard, and it's 30' and probably a lot less displacement than a 35' cat would be. Even so, some owners of the DF 920 go a size up.

The 15 is 10 kg heavier than the 9.9. Not a lot on a 35' cat.
 
Interesting indeed!

I reckon in cruising trim we must be 4 to 5 tons (ish), plus we've a lot more windage than your Wharram.

We used a Yam 9.9 high thrust outboard on our old Pahi 31 very successfully. It was mounted on the stern beam, and gave wonderful close quarters handling.

I also remember bobbing up and down in a swell, for hours and hours, in windless conditions south of Tusker Rock, with the prop out the water most of the time.

We found the 9.9 ideal on that boat: mounting it foreward more would have been better though.
 
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The Dragonfly 920 has the 9.9 as standard, and it's 30' and probably a lot less displacement than a 35' cat would be. Even so, some owners of the DF 920 go a size up.

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Thanks, that's a useful benchmark. The DF920 turns out to weigh almost exactly the same as our Wharram, so I am somewhat reassured.
 
most of the Yamaha 9.9's are the same block/bore etc as the 15hp - all that is needed normally is a carb jet change to uprate to 15hp. I helped a friend do this on a 9M catalac and his view after a season use was that it made a big difference to his power. I think that these motors are a higher gear ratio than the general 2:1, must be as the prop is bigger than my 25HP tohatsu 2 stroke, which is brilliant but I only average 0.7 galls per hr@ 6knots.
 
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most of the Yamaha 9.9's are the same block/bore etc as the 15hp

[/ QUOTE ]

That may have been true once, but they look like different beasties now...

9.9 Bore x Stroke 56mm x 43mm, 40kg, 0.8l oil sump
15 Bore x Stroke 63mm x 58mm 51kg 1.6l oil sump

Looking at the figures, it's the 15 and 20 that are the same basic engine now
 
Yes...twin engines has strong appeal.

The problem is where to mount them, with our particular layout.

We've got a long keel on each hull, rather than Iroquois type daggerboards.
 
I have an older 9.9 yamaha on my 22 foot etap.

I thought it was the prop that made it 'high thrust'

I thought the pitch & blade area etc of the prop was set up to compensate for the gearing of the motor, which was designed more with higher speed boats in mind than a little sailing boat.

I know I have a 'high thrust' prop on mine (has bigger blades that looks a bit like 'mickey mouse ears' as someone once told me on here when I was trying to identify it)

Did they also do a 'high thrust' engine with different gearing as well then?
 
NealB said:
Yes...twin engines has strong appeal.

The problem is where to mount them, with our particular layout.
Click to expand...
Hi Neal,

I am gathering as much info I can get on the Comanche...
So after a quick scroll through my folders looking for the engine setup on 'Nokoni' I found a possible answer to your question above:
10455.zijdroog.jpg

I know it is preferred to have the engines central as they will not lift clear of the waves...
But they are easy accessible and the construction to lift them out of the water seems straightforward...
This empties your central well which you can use for extra stowage, fueltank, genny or other goodies...

Hope this helps :D
 
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Thanks djeeke....I've sent you a pm.

I don't like the arrangement on 'Nokoni' because:

- as you say, the props will cavitate really badly
- the engines are very vulnerable to being nicked
- I can very easily use the tilt mechanism on my engine to lift the prop clear of the water: much easier, I would think than standing right at the stern to lift the whole engine.
- to my eye, they look all wrong.

Ease of fitting/ removal seems to be the only advantage.

Since this thread started, I've bought a pair of secondhand, extra-long shaft, Yamaha 9.9 hp hi thrust outboards. I know how I want the new pods arranged - I just need someone to do the grp work.

I've cruised this summer with just one of the 'new' engines. The old engine was the standard long shaft. Who'd have thought that an extra six inches of shaft would make such a difference (cue predictable double entendre jokes)?


Psssst.....whisper.......anyone interested in a good Yamaha 9.9 hi thrust outboard......pm me!
 
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How old is your 9hp? they certainly used to share the 15hp platform so worth looking in to if it's teh right age as it's cheap easy horse power, My local yamy dealer told me how to do it when we were lucking, but ended up buying a 15 as that was available at the time...
 
In answer to one of your earlier questions, there are different props available for the 9.9. I fitted a coarser prop on our Iroquois to give better cruising speed at lower revs as we never needed the ultimate power of the finer prop. It was made from some sort of composite, rather than ally, and was a lot cheaper than the ally version. Unfortunately, I can't remember where I bought it.
 
Moonshiners said:
How old is your 9hp? they certainly used to share the 15hp platform so worth looking in to if it's teh right age as it's cheap easy horse power, My local yamy dealer told me how to do it when we were lucking, but ended up buying a 15 as that was available at the time...
Click to expand...

From memory, I think it's around 1998 vintage (as are the secondhand ones I've now bought).

Easy, cheap extra horses would be very acceptable, so any more info on this welcomed.
 
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