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Comparables to the great Yamaha 9.9 high-thrust?


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Since I was a little kid, I've sailed on boats pushed by Yamaha 9.9 high-thrusts, and as surely as I remember lullabies, I remember my pops whispering in my ear that the 9.9 was the only outboard purpose-made to push a sailboat.

Fast-forward a couple decades. I have 6 percent more knowledge about sailboats than I did at age 10, and a credit card, and I need a new motor.

And of course, the high-thrusts are back-ordered till kingdom-come because of the 'rona, plus, even worse, it appears to be nigh impossible to find one without an integral power-tilt mechanism (which I am skeptical would raise as high as manual tilt, and of which I am also dubious of on general grounds, on the basis of the sailor's simplicity-is-golden philosophy).

I've heard about the tohatsu 2-sroke 9.9 (light, and will pass anything but a fuel dock) and the nissan sailpro (only available in 6 HP?) - but the closest thing has a 2.3:1 gear ratio rather than the yammy's 2.9:1 - and it seems like with a heavy slow sailboat, that probably matters?

Any thoughts on pushers that perform comparably turning a big prop made for a displacement boat?

For reference this is for a typically-overloaded 27 foot sloop that spends as much time under power as sail, pushing the family up into the islands (but also out to the west side) most summers. Reliability is paramount. Noise levels are also a priority on long (12+ hour) pushes to/from the fun zone.

 

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  • Breamerly changed the title to Comparables to the great Yamaha 9.9 high-thrust?

I believe that the Mercury ProKicker models will be the closest and likley the best option to replace a Yamaha in this regard. They are not manual tilt normally, but they do lift very high. I just installed a lease return 15 HP version on my commuter boat as a backup to the main engine, and it tilts way up and easily stays out of the water even with the 25" extra long shaft and the reverse sloping transom. They have EFI, decent sized alternators and most come setup for remote controls, so would be a good option for a sailboat as you don't need to hang over the back to tilt it, start it, or do anything to it during normal use.

Hard to come by used right now, but there are lease returns here and there that end up a couple grand less in purchase price while still having warranty and being an effectively new motor.

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14 minutes ago, Goatish said:

I believe that the Mercury ProKicker models will be the closest and likley the best option to replace a Yamaha in this regard. They are not manual tilt normally, but they do lift very high. I just installed a lease return 15 HP version on my commuter boat as a backup to the main engine, and it tilts way up and easily stays out of the water even with the 25" extra long shaft and the reverse sloping transom. They have EFI, decent sized alternators and most come setup for remote controls, so would be a good option for a sailboat as you don't need to hang over the back to tilt it, start it, or do anything to it during normal use.

Hard to come by used right now, but there are lease returns here and there that end up a couple grand less in purchase price while still having warranty and being an effectively new motor.

Is this the one (below)?

Looks like it has 2.42:1, but is purpose-built for a larger prop otherwise, they say? 

https://www.powerequipmentdirect.com/Mercury-Marine-1F10261KK-Engines/p97582.html?gclid=Cj0KCQjw3duCBhCAARIsAJeFyPVT6Hm8Hzt0uQvDEWyIxceCJYKAUSB9nejbpVJHclAILU5QCGWoUaAt6BEALw_wcB

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Poked around a bit. The mercury 9.9 pro-kicker is a little different from the mercury 9.9 Command Thrust, but they both have a 2.42:1 lower unit.

That's compared to the 2.9:1 lower unit in the Yamaha.

Aside from the lower unit they appear quite similar otherwise.

Yamaha displaces 212 cc, with a 2.2x1.69 bore/stroke — the Merc is 208 CC with a 2.16 x 1.73 bore/stroke. So the Yamaha has a slightly larger (2%) displacement, but the merc has a 2% longer stroke (long skinny cylinders produce more torque than short squat ones). But those are very small variations, and must to some degree cancel each other out. Both are available in a 25" shaft.

That leaves the prop and lower unit.

The merc specs a bigger prop: 10"X7" 4-blade VS. a 9.25"X(?) 3-blade on the Yamaha. But I see that SOLAS makes essentially the same 10x7 4-blade for the Yamaha, so if they have the same cylinder geometry and can fit the same prop, that means the main difference is the gear ratio in the foot.

So to the gear ratio....

To turn that 10X7 prop ten times, theoretically moving the boat 70 inches forward, the merc engine is rotating about 24 times, during which period it detonates (completes a single combustion stroke) 24 times (well 24.2 times, each, if you want to be precise).

To turn the same prop the same number of times, pushing the same boat the same 70 inches forward, the Yamaha engine is fully rotating 29 times, and detonating 29 times.

Or, over any given distance, the Yamaha is firing 12 times for every 10 times the Merc fires (29:24 = ~12:10).

Orrrrrrr..... if I can remember my high school physics.... assuming the same amount of fuel per combustion stroke (same throttle/mix setting), the Yamaha is capable of doing about 20% more work than the Merc per time unit, meaning it produces about 20% more power (which in rotational terms is... torque? I thinK?).

Obviously, the corollary is that the Yam will hit its powerband/redline at a lower boat-speed, since the Yamaha is having to run at a higher engine RPM to achieve the same prop RPM, but it can do so against more resistance  (ie, a heavier boat, more chop/headwind, etc). 

I'm thoroughly confused, and probably fucked some part of all that up completely, because I barely understand any of this, but in general so far I am getting the impression that the yamaha wins out for pushing my family and all our junk into confused chop and a 10 kt headwind at point wilson on our way up to watmo for the tenth time in the last two years.

Very open to any corrections or suggestions about my thinking here.

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I owned a Tohatsu 6 HP "Sailpro" - 25" shaft, manual tilt. It would push our 40' catamaran at 3.5-4 knots flat out. Same motor as the Nissan 6 Sailpro but Nissan is now out of the outboard business.

But it truly sucked. The carb would foul if you looked at it sideways. It seemed so unhappy to start and to run. And I've owned a lot of outboards. None were anywhere close to how bad it was.

I'm assuming you realize that new 2 strokes are not available and are considering used.

Mercury Prokicker 15  bore x stroke:  61 x 57 mm (2.40 x 2.24 in), 108 lbs

https://www.mercurymarine.com/en/ca/engines/outboard/fourstroke/prokicker-99-15/

Tohatsu 9.9 has exactly the same bore and stroke. This is not a coincidence but rather Tohatsu makes them for Mercury

https://www.tohatsu.com/marine/int/outboards/MFS9.9E.html

https://www.tohatsu.com/marine/int/outboards/MFS8B.html  has a bore x stroke of 55 x 44mm. Also exactly the same as the Mercury 9.9. Weird huh?

Neither of these will have the same efficiency as the Yamaha 9.9 due to its high gear reduction ratio and big prop. But they will be enough for your boat. The Yamaha uses a much bigger 11-3/4" diameter prop.  If you found a lower prop diameter it is probably the "regular" Yamaha 9.9 outboard that likely has about a 2.2:1 gear ratio.

https://www.defender.com/product.jsp?id=6898376#  - show prop diameter

 

 

 

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2 hours ago, Zonker said:

I'm assuming you realize that new 2 strokes are not available and are considering used.

Who said anything about a two-sroke? My first choice is a new Yamaha T9.9, which is a four-stroke. The only thing that has kept me from clicking 'buy' already is the fact that Yamaha appears to have shifted almost entirely to manufacturing these motors with power tilt, which is a feature that I really don't want, extra complication being the source of misery that it is on a sailboat.

2 hours ago, Zonker said:

But they will be enough for your boat.

Since I use the boat for a lot of mini-cruising (gunkholing),  I end up under power a lot. Two summers ago we powered something like 40 hours out to the west side. I try to avoid doing that much usually, but in summer calm, 30 hours under power including bashing through the rips at point wilson and out into the straight on a 5-day islands trip is par for the course. Given that, it seems like it would make sense to have a solid pusher, not the "it'll do in a pinch" version.

So that's it. I'm an otherwise ready buyer, just taking a cursory look around to convince myself I haven't overlooked something like an equivalent Merc., which I would go for in a heartbeat. Honestly the CommandThrust 9.9 is tempting, with that 2.42, but when I did the numbers it seems just a little lighter on the torque side than I'd like, ideally.

I have to admit I'm a bit confused about the two-stroke option though. My understanding was that they are more powerful because they fire twice as many combustion strokes in a given number of engine revolutions as a 4. Does that mean a two-stroke running at the same RPM as a comparable-displacement 4 just produce double the power?

And wouldn't that mean that a two-stroke rated for X HP would only need to have roughly half the displacement of a 4-stroke rated for the same HP? Yet Tohatsu's advertised 2S's are comparable or greater displacement than 4 strokes of the same rated HP.

I still don't think 2S is really an option given A) how loud they are, B) how much more gas they eat (small boat, limited tankage), and C) the fact that I'd have to buy used (and I'm looking to increase my reliability, not decrease it). But I'm interested to know more about them I guess.

 

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New 2-strokes are being made, just not sold in the US. I have personally seen both Merc and Yam in the Bahamas. Their market is sail cruisers who buy them  for dinghy use. They sell out, too.

The newer 2S are much quieter, get better fuel economy and recommend lower oil ratios after break-in although most pax apparently ignore and continue the higher ratios

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12 hours ago, Breamerly said:

Who said anything about a two-stroke?

you did! In your first post.

On 3/20/2021 at 10:57 PM, Breamerly said:

I've heard about the tohatsu 2-sroke 9.9...

2 strokes are lighter and cheaper because they have no valve train, just ports in cylinder walls. But no, they don't produce double the power for a given displacement. A 9.9 is still a 9.9 HP. They do have different shaped torque curves; the 2 stroke has more torque at low RPMs; good for getting a boat on plane like an overloaded dinghy.

Yamaha 9.9 4 stroke, regular & high thrust - 212 cc

Yamaha 9.9 2 stroke - 246 cc

(That is probably more a case of the block sharing differing between the 4 and 2 stroke models. The 4-stroke 8 and 9.9 are the same block, while the 2-stroke 9.9 and 15 are the same displacement.)

In your case the Yamaha 9.9 is probably the best choice, given that you motor a lot. I don't think the Mercury/Tohatsu ones are "do in a pinch". They'll be fine in 90% of conditions; it's when punching into a sea that the Yamaha will be superior.

 

 

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Something worth looking into if you plan to motor a lot is what HP and prop pitch is actually best for your vessel.

There is a free calculator here that I find quite helpful and have used when sorting out how to best re-prop my 5HP 2 stroke for my race boat: https://www.vicprop.com/free-propeller-sizing-calculators

I don't know what your displacement or waterline dimensions are, but if you do, you may find that a 9.9 is not ideal for your vessel in the long run, and if you are looking to buy new, knowing that in advance of a purchase may save some headaches down the road.

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15 hours ago, Breamerly said:

And wouldn't that mean that a two-stroke rated for X HP would only need to have roughly half the displacement of a 4-stroke rated for the same HP? 

 

2 hours ago, Zonker said:

2 strokes are lighter and cheaper because they have no valve train, just ports in cylinder walls. But no, they don't produce double the power for a given displacement. A 9.9 is still a 9.9 HP. They do have different shaped torque curves; the 2 stroke has more torque at low RPMs; good for getting a boat on plane like an overloaded dinghy.

Yamaha 9.9 4 stroke, regular & high thrust - 212 cc

Yamaha 9.9 2 stroke - 246 cc

I apologize in advance about the thread drift, but I raced motocross when I was young and foolish.

My ride was the 2-stroke Honda CR250R, which displaced 249cc and produced about 55HP - five times as much as an outboard with the same displacement!

In 1996 the rules changed to allow 450cc 4-strokes to compete against 250cc 2-strokes. Yamaha made the first 4-stroke that could compete with a 2-stroke in terms of power delivery, although it did weigh about 30 pounds more, and had nearly twice the displacement. Even so, the 2-strokes still dominated for several years before being phased out due to emissions.

Point being, in a very high state of tune, a 2-stroke can produce much more power than an equivalent displacement 4-stroke. Honda's current 249cc 4-stroke "only" makes 39.4HP, about 30% less than their 2-stroke of the same displacement from 25 years ago.  

Small outboard engines are certainly not in in this highly tuned category, and as @Zonker noted, the horsepower rating is still the horsepower rating. 

End of thread drift. 

 

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11 hours ago, Zonker said:

you did! In your first post.

haha guilty as charged! I meant to just use it as kind of. a figure of speech or a signpost that I was really trying to think outside the box, but I could have been clearer that a 2S was never seriously in the running for the noise and fuel consumption reasons.
 

10 hours ago, Goatish said:

Something worth looking into if you plan to motor a lot is what HP and prop pitch is actually best for your vessel.

There is a free calculator here that I find quite helpful and have used when sorting out how to best re-prop my 5HP 2 stroke for my race boat: https://www.vicprop.com/free-propeller-sizing-calculators

This is a great resource, I will definitely check it out, thank you. I do also think that I have been pushing a bit too small of a prop for the application, after doing all this reading.


 

11 hours ago, Zonker said:

In your case the Yamaha 9.9 is probably the best choice, given that you motor a lot. I don't think the Mercury/Tohatsu ones are "do in a pinch". They'll be fine in 90% of conditions; it's when punching into a sea that the Yamaha will be superior.

This is the direction I am leaning. interesting insight about the Merc. not having used anything really aside from the yamaha, I. get they're only a little less perfect for the task, but it's hard to really grock how much less perfect.
 

9 hours ago, Kenny Dumas said:

The power lift on my yammy has been reliable, going on 6 years now

good to hear this from a sailor. some of the mechanics know their stuff, and the odd salesman, too, but christ some of the guys at the yamaha dealerships are useless. One guy spent five minutes telling me how I 'need a bigger engine, because it turns faster.' Swear to god he hadn't the foggiest notion of what a gear ratio was, or the difference between planing and displacement. Also have basically been politely told I'm crazy for not wanting auto lift, including with the golden lines of "they hardly draw any power" and "they never break." Real numbnuts material.

 

8 hours ago, gspot said:

Point being, in a very high state of tune, a 2-stroke can produce much more power than an equivalent displacement 4-stroke. Honda's current 249cc 4-stroke "only" makes 39.4HP, about 30% less than their 2-stroke of the same displacement from 25 years ago. 


This makes a lot of sense as kind of the far pole on the spectrum of possible scenarios. They do, after all, get to do twice as many boom-booms per spin-spin.



Overall good info here folks, thank you.
 

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Do the other options have something like Yamaha's "dual thrust" prop, with a hollow ring in the center for the exhaust in reverse? I found that made a huge difference in maneuvering power - reverse worked almost as well as forward, unlike most other outboards I've used.

 

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4 hours ago, Zonker said:

So don't approach a dock as quickly if you go with another brand.

A good note but in general I'm not in the habit of relying on reverse while docking. Boat's so small (27) I usually just step off and belay my spring on the nearest handy cleat, with the stern in hand to check any pivot. Might be different if I often had to dock in a crosswind, but marinas around here are so often so well protected...

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