I think you won't be able to plane up 3 people and a dog with a 9.8. Maybe, but it will be iffy. I have had a 9.8 Nissan
4 stroke and a 9.8 Nissan 2 stroke
on a 9 foot Zoom and it planes up just fine with two people. I have not tried 3. I had a 13 foot Zoom with an 8 hp and it would plane up 2 people and a dog (Jack Russell). That same boat
with a 2-stroke 15 would plane up 3 people. I had a 130 pound aluminum
bottom 11 foot inflatable
with a 2-stroke 15hp and it would JUST barely plane up 3 people and a dog. Now I have an 11.5 aluminum inflatable
with a 2-stroke 25hp and it planes up 4 people and 4 whippets (35 pound dogs) no problem, although deck
space and windage becomes an issue at that point, (also dog slobber).
I know it sounds risky to buy a used motor, but I think for less than $1500 if you shop carefully, you should find a well cared for 15 hp 2 stroke. They are light, and easy to service
. Yamahas are KING in the Caribbean
Either way. DO NOT SCRIMP ON A DINGHY
MOTOR. The few extra bucks it costs initially to buy a bigger motor will pay for itself 100 times over in your ability to do some great long range exploring.