Prop Size

[rjn cajun]

I`m in need of a new prop for my 8hp yamaha motor. The prop now is 8 1/2 x 7 1/2. I have this set up on a 10ft Livingston. I don`t use it for trolling as I`m a bass guy and have a trolling motor. So I use it from point A to B and in between on the smaller lakes. The reason I ask this is it takes a long time to get on plane with the prop I have now. Once on plane it`s fine. So I guess what I`m asking is what do I need to do to plane out faster without over loading the motor. Also replacing it because I hit a rock last time out. Thanks guys rjn cajun

[Amx]

There are rocks in our lakes?

[rjn cajun]

There are rocks in our lakes?

Thanks for the help Tom:joker: I`m sure you know which one. If your not careful you will hit it everytime you launch or load.

[The HAWG HUNTER]

Raise the motor an inch or more and see what it will do.:thumright The higher the pitch the faster you go, the lower the pitch the faster out of the hole but slower top end.

[G-Man]

There are a few things you need to figure out before you change the pitch of your prop. Any idea of how fast your top end is now? Top RPMs? There are a number of prop pitch calculating tools available on the internet. Try this one out: http://www.boatpropellers.com/propcalc.html

I ran the calculator using the following numbers:
RPM - 5500
Gear Ratio - 2.08
Pitch - 7.5
Boat Weight - 300 (I don't think that one is used by the calculator)
Boat Length - 10
Slip - .1

This gives a top speed of 16.9mph

Now if you already know the top speed and you know the RPMs, you can accurately calculate your prop slippage. Play with it and see what you come up with. You may be maxed out with your 8 horse as the Livingstons are not the most effecient planing hull available. As mentioned before, decrease the pitch and you will lose top end but get up on plane faster and vice versa.

[FishingFool]

I would search online for forums with owners of your boat and motor. That's what I did on my boat.

My boat came with a 17 pitch prop. I noticed at full throttle, i was only get ~4500 RPM, where as, it should be at 6000 RPM. And speeds were in the mid to high 20 MPH only. Slow to get in plane.

Found iboats with a bunch of owners with similiar setup. Most had 12 or 13" props. Got a 12" prop and it was like night and day.

Now hitting 6000 RPM at WOT, and max speed has been 34 MPH on GPS.


Are you getting reaching max RPM on full throttle?
Maybe just need to shift some weight around on the boat. Shift some weight towards the bow?

[rjn cajun]

Thanks for the info guys. Some of these things I don`t know speed,rpm etc. My planning ability with this set up is boarder line with weight. I have my rods and reels gas can and two batteries. With two batteries it takes a little longer to plan then with one. I never thought one battery would make that big a difference. But it does on a small boat. I really don`t know how to find out my speed or my rpm`s without the proper electronics. I`m thinking I need to raise the pitch on it. Need to research a bit more.

[rjn cajun]

I don`t see anything on the web and research I`ve been doing about diameter. Is this because you don`t need to change the diameter? What will changing the diameter of the prop do?

[bassboattech]

CAJUN i dont think your on the right path 1 because its a 10 foot livingston(heavy fiberglass)2 if you look at the coast guard rating i think your boat is rated for alot more and in the boat industry we never rig anything with less than 25 percent of the rated horse power. classic case of being under powered thats why it takes so long to plane out(its 8 horse power) if you go up in pitch it probably wont plane at all. if you go down in pitch you will be running this 8 horse power at full throttle just to go any where. remember yamaha ships its little motors with a prop that works the best all around. it is a trolling motor or at least its marketed as such. i would be really interested what a 10 foot liv is rated for....hope this helps ( this is not a bass boat with a jack plate, going up or down on the motor will not make little if any difference like some other posters recomended.

[Bodofish]

I gotta go with Basstech on this one. What comes to mind... tuning a trail 90 for the race course. Putting that header on the '62 bug. Can you do it? Sure. Is it going to make any difference? Probably not enough to measure. Want to go faster or plane a little easier? Save up some pennies and get the max rated engine for the boat. Or not, it is what it is, a 10 foot cat. It's never going to be fast, have a hole shot or carry that big load. It will give you many hours of pleasure putting and fishing. Crack another cold one and enjoy the day!