Which Prop? A Typical Question

[Buster_boy]

The only thing I know about props is they're round, they spin, and they make my boat go. That out of the way, I have a Merc 9.9 Bigfoot four blade prop on a 16ft pontoon. What prop can I put on that will get me the most speed? I know it won't be an offshore speed but I want as much as I can get.

 

[steelespike]

You need to read the sticks at the top of the prop forum.
Get us the prop size(usually under the prop nut).
get us the lightly loaded wot(wide open throttle) rpm and gps speed.
The 16 foot pontoon is speed challenged. Just not enough surface in relation to weight.
While a toon doesn't plane the longer ones seem to do better for speed.
A 9.9 on a light planing hull might make about 21 mph.
On a pontoon you would be lucky to make half that.
Get us the prop size.
Eliminate any excess weight,be sure the motor is in excellent tune.
Try different motor trim and play with weight placement.

 

[Scott Danforth]

you need to know the RPM of the motor and gps speed like steelespike indicated

also, on a 'toon, motor setup (primarily height) has more effect on speed than on any other type of boat. make sure your motor is high enough that the anti-cav plate is just under water, however low enough it wont cavitate when you put a cooler of beer on the front of the 'toon deck. if your too deep, you go slow

my guess that you have a 9.9 on a 16' toon is that you are on a restricted lake? dont expect to go faster than say 8-10mph on your toon with a 9.9

 

[Sea Rider]

Being a 4 strokes would be impossible to bump it into a 15 HP due to having a much less CC powerhead, which had been ideal for more top speed along power while correctly propped.

Happy Boating

 

[Buster_boy]

Yeah, I have no idea the rpm. This motor is not hooked to the gauges so I can not answer that question. Thanks anyway guys!

 

[steelespike]

If you get us the speed by gps we can get a rough idea of the rpm.If you read up on the Induction tach
simple hookup and can be used on many motors.

 

[Buster_boy]

Ok next time I'm out I'll try to get that info.

 

[Silvertip]

Speed alone won't be of help. You need speed and WOT RPM. RPM can only be determined with a tachometer. You can probably rent a tune-up tach at your local auto store. But then Tiny Tachs are relatively inexpensive and easy to install.

 

[Buster_boy]

I downloaded a speedometer app. I went a breakneck speed of 5mph at WOT.

 

[Buster_boy]

I kicked in the afterburner last night and I broke 6mph wot. It may have been the breeze, I'm not sure but I was haulin ass!

 

[Sea Rider]

Now need the rpm reading at full hammer down, you could be already lugging that engine and not knowing a thing about that which is no bueno for the engine. Once wot revs are known and depending on the wot rpm run can maximize a prop to run at full wot revs, toon will perform much better with slight top speed increase if speed increase is something you are aiming for. Be aware that slight speed increase will only happen if already running engine at the lugging rpm side while achieving 6 mph.

Rpm and speed should be tested on flat calm no wind water cond...

Happy Boating

 

[Buster_boy]

I don't have a tach. The tach that is on the helm is attached to the 40hp I'm not using. No tach, no revs. No revs, no prop info. Poor Jim! :0(

 

[Sea Rider]

Buy an induction Hardline Hour/Tach model HR-8061-2 from Iboats, Amazon and tach that kicker, can get full ponies out of that 9.9 HP if going for a tach along a prop maximization...the way to go.

Happy Boating

 

[Buster_boy]

Realistically though, how much more mph would I gain from a 9.9?

 

[nanuk]

prolly none, but you'd extend the life of your engine.

have you looked into those laser tachs? they use a piece of reflective tape on the flywheel.... I use one to set throttle on my tractor for proper PTO rpms.

 

[Buster_boy]

Nope, never heard of them. I'm just tired of my little 16ft pontoon being passed by bigger boats with the same size motor. Granted it's a 9.9 not an offshore boat, but when I have 20-22ft boats with 9.9's pass me, something is wrong.

I read where three blade props provide more speed then four blade props yet no one on here seems to agree. I have people tell me to put on a 15hp carb and it'll go faster, again people say not so much. Why is that? It's five more hp. Doesn't that equate to something? It must do something if people do it?

I'm confused.

 

[Buster_boy]

OK so I bought a Hardline induction hour/tach like you said. It has one wire, my coil has two. Where do I wrap the induction wire? The motor is a 4 stk twin.

 

[Sea Rider]

Can wrap it at upper or lower plug cable, follow product instructions.When installed and OB is ON check idle rpm, should read low around 800-1000 revs if reads double will need to adjust firing sequence...report back if final tach instalation was successful.

Happy Boating

 

[Buster_boy]

OK thanks had to ask cuz instructions didn't say anything about two coil/plugs wires. Started to rain before I got back to it but I'll get it tomorrow.

 

[Buster_boy]

I put it on, got the boat in the water and took a ride. At idle it's 1100 +/-, WOT 5000+/-, 4-5 mph and the prop is four blade 10x7. It's kinda banged up too so a replacement is probably not a bad idea anyway.