Maximize plane with Honda 9.9 on 12' tinny, and 2 heavy guys :)

[tugcapitan]

~~Hi there, new to forums but not new to boating. Professional tugboater.
In the summer I run my grandpas old 12' tinny for a week of fishing in the gulf islands with a 9.9 Honda 4-stroke. Ripped us around great as kids, but now as we are older and fatter , two guys in the boat makes it more of a cruiser than a planer. Honda runs great and came with a 4 blade prop D 10 P 7.
Just wondering if anyone thinks we might get the little bit more that we need to plane by switching to a 3 blade, and if so what size? Would stainless make a difference on such a small set-up or no?
Perhaps we just have to be happy with what we got and lose some weight? lol
Not interested in re-powering, and its not a big deal, but if a new prop might make us go faster I'm into spending that money.
15kts on plane when I'm by myself, 11kts and not on plane when my bro is in the boat too.
Thanks much iboat community,
Tugcapitan

 

[steelespike]

Is this a Jon boat? Your 4 blade should get you on plane best. If its all beat up you need repair or replacement.
7" pitch is the smallest made good for heavy loads and there is a stainless available.
If your not close to planning, I don't think a prop change will help.
Try different trim settings.
​ Are we talking 150 lb. big guys or 300 lb. big guys? Your motor is about 102 lb. 6 gallons of gas about 35 lb.
Your boat's capacity is probably about 600 lb. for everything.
Be sure the motor is in excellent tune. Eliminate as much weight as possible.
3 gallon tank. A 9.9 will use about .9 of a gallon an hour at wot,
plastic paddle instead of 2 wood oars. Be sure your not dragging along a bunch of water in the stern.
A 9.9 is good for about 20 mph with a light load you might give it a test with a light load see what you get.
Some cells have a GPS app to check speed.

 

[tugcapitan]

~~Thx for reply. Prop was new last year no dings after someone else did ding it so that's not a concern. Did try different trim settings to no avail. 2-200lb big guys, wood oars, two fishing rods, tackle box, coffee thermos, snacks, jackets, small stereo, safety ect. I figure we are probably doing as well as we can. Just me test was also with rods and tackle, gear ect at 15kts or 17.3mph and planning nicely, although I have to put all my gear and the fuel up front and lean my body forward for the hole shot. I have the navionics chart app on my phone. I think added draft with my bro puts us near your 600lb capacity and just means we have to cruise to our spot instead of plane. It was maybe just a nice dream that a faster spinning 3 blade stainless prop would do the job only more hp could provide. The motor is already as big and heavy as you would want to put on it, sinks the transom down pretty good.
When you say make sure your not dragging along a lot of water in the stern I assume you mean in the boat? Yes of course not. Or do you refer to another phenomenon like dragging water between the leg and the transom due to trim?
As for motor tune, I had it pro done every year until last year. I'll do it myself this year so I picked up Honda engine oil, leg oil and a new spark plug, and was planning to spray carb cleaner in the carb and pull on the rope without the sparkplug in as I didn't get a chance to put fuel stabilizer in it when putting it down for the winter. Of course I always use fresh gas. Anything else I'm missing?

 

[jestor68]

Without a tachometer reading, you can't know if a different prop pitch might help.

Your little Honda needs to turn up to 6000 rpm at WOT. Is it?

You'd likely be better off using the 9.25 X 7 3 blade to reduce the load on the motor, allowing it to spin up faster and higher.

 

[Sea Rider]

Go for a wot spin with you alone and lightly loaded boat, check achieved wot rpm, Must necesarily install a ind tach to check as any advise here would be plain speculation and wild guessing. Once tach is installed will be able to maximize prop blade/pitch for boat to plane. If severely under powered could install a Jr Sting Ray doel fin, trim tabs to help boat plane faster.

Generally speaking a 9.9 is a detuned 15 HP, what parts would you need to upgrade that 9.9 to a 15 ? If not that costly go for it. Check Honda spare parts manul for physical differences.

Happy Boating