Advice? 8 hp vs 9.9 Yamaha 4 stroke

[Musicaltrees]

I’m about to purchase my first 4 stroke engine for my trusty 9.5’ ribbed AB Dinghy. Can anyone weigh in on the difference in performance of the Yamaha 8 vs 9.9 hp? I just want to be sure the 8 will plane the inflatable. Is there THAT much difference in the two? I like the fact the 8 hp is 10#s lighter and $400 cheaper. Thanks!

[a64pilot]

Many times the same engine block is used for different HP levels.
In that case I want the most HP for the same weight. However your choices are obviously different blocks as the weight is different.
If your buying from a dealer, I’d talk to them and tell them you want the smallest motor that will plane the boat at average load and see if they will let you try both.
It can’t hurt to ask, if they are guaranteed a sale, they might say yes.

Yes, sometimes the extra 2 HP will get you on plane easily, while you’ll just wallow around on 8 leaning way forward etc to crawl onto plane, or not quite make it.

[smj]

Both the Yamaha 8hp and 9.9hp use the same 212cc block. They both weigh the same, 87lbs. If your unsure if the 8hp will plane your dinghy then no doubt buy the 9.9hp.

[a64pilot]

Just as reference, you can get 20 HP for 99 lbs. in the Suzuki.
87 lbs sounds awful piggy for 8 HP.

[james247]

Originally Posted by Musicaltrees

I’m about to purchase my first 4 stroke engine for my trusty 9.5’ ribbed AB Dinghy. Can anyone weigh in on the difference in performance of the Yamaha 8 vs 9.9 hp? I just want to be sure the 8 will plane the inflatable. Is there THAT much difference in the two? I like the fact the 8 hp is 10#s lighter and $400 cheaper. Thanks!

I agree with the comments below. 20percent more power is significant. The difference is more about what you intend to carry.

[akprb]

Same weight, bigger motor. No brainer :-)

The 400.00 will quickly be forgotten. Dragging yourself up on plane with three in the boat or bombing from Stocking Island to G Town won’t ;-)

[jslayton321]

I bought a new Nissan 9.9 in 2914 - went thru same analysis. For Nissan the 8 hp and 9.9 hp were the same weight, same engine as best I could tell - it must have been carburetors. Get the 9.9, it quickly planes my little Avon 8'-6" with 2 passengers, slowly with 3.

[mnh]

Hi,
I used the 8 HP for years on a 10 ft. RIB. Planed easily with 2 people and groceries. The 8 was less expensive than the 9.9. Weight was considerable though when pulling it up from the dinghy. I lucked out and got the 2 cycle in the last year they were sold in the US. Advantage? + It started every time. No clogged carbs. You can buy a 2 cycle version of the 8 or 9.9 in the Bahamas (Marsh Harbor, Abacos for Ex.) and ship back to the US. Or, ask someone on SSCA if they would bring it back bring it back your way in the Spring, from say Green Turtle or Hopetown.
Bottom line, the 8 hp did just fine for getting up on a plane quickly with 2 people and a load. Hope this helps...

[Cheechako]

In 2 stroke I had a 15 Yam on a 10 ft AB RIB. Heavy RIB with double floor. I would want 15 hp again on that boat. I had the same engine on an AB 9 ft RIB and it was too much really. That is telling me you want the 10 HP likely.

[Scrimshaw4]

FYI Tohatsu makes a 9.9 4 stroke OB that is branded as Tohatsu, Nissan and Mercury. There are minor changes in the controls. Check with your RIB company on what HP they recommend. Lifting fins may help low power but I think are a when stowing. JMHO

[Cadence]

I'd go with the highest HP on the label, placard whatever, probably on the inside of the transom. They are conservative.

[Caliber40]

Both motors are two small....you’ll not be happy with either. If you can’t pull off buying a 2 stroke from the Bahamas find a used one. Even my 2 stroke 15 sometimes struggles to plane with a load.

A good fast inflatable is a must for cruising!

[Scaramanga F25]

Mercury 15HP 2 stroke, 74 lbs and available.

[hobopacket]

I have lots of experience with smaller engines in my old job. A dingy doesn’t idle that often making a two stroke attractive. A two stroke 9.9 or 15 would be ideal.

[SailFastTri]

I used to own an AB 310 (10') dinghy. AB has a deeper V hull than some other companies and a higher bow. That makes for a bit less pounding and a bit drier ride, but more difficult to plane than a flatter bottom. My 9.9 would struggle to get it on plane with 2 people (about 300lbs total), and you had to move some weight toward the middle to help it get up. So if you want to plane, 9.9 is the minimum.

Also, I agree with others about power-to-weight.