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bentpole
02-01-2007, 07:59 AM
Can any of you tell me if there is a web site I can go to that will tell me what size of prop I need? I had a 30 hp yamaha on my boat changed it over to a 40 yamaha,It don't seem as fast as my 30 & LOVES the gas,I use to could fish 2 days on a tank of gas. now I'll do good to make it a full day on the same tank????:( Was told it may need a diff- size prop.

must buy my fish
02-01-2007, 08:10 AM
What size is on it now? I have a merc. 30 hp with a 13 pitch prop .If you get too much pitch it can cause overheating & lugs your motor too much.

papasage
02-01-2007, 08:20 AM
try this site .
http://www.themarinedoctor.com/cgi-bin/YaBB.pl

drill instructor
02-01-2007, 08:30 AM
be very carefull going to a bigger prop. i cracked my gearcase doing just that. I will definetly ask a pro. I sure wish i had asked a mechnic. Boat weight and size has a lot to with.

Jerry Blake
02-01-2007, 08:33 AM
Can any of you tell me if there is a web site I can go to that will tell me what size of prop I need? I had a 30 hp yamaha on my boat changed it over to a 40 yamaha,It don't seem as fast as my 30 & LOVES the gas,I use to could fish 2 days on a tank of gas. now I'll do good to make it a full day on the same tank????:( Was told it may need a diff- size prop.

Hey bentpole:

It's real important to have the right prop for your set-up. Every boat is different depending on how much weight you carry and how it is distributed in the boat.

Ideally you want to just reach the maximum recommended RPMs for your motor at wide open throttle with a light load. If you can't reach maximum RPMs you have too much pitch and if you reach maximum RPMs below wide open throttle you have too little pitch.

Too much pitch and you're working your motor too hard and too little pitch your wasting horsepower and have the potential of damaging your engine by running at too high of RPMs. Going to a stainless steel prop and having it "tuned" by a prop rebuilder that knows what he is doing will give you more efficiency.

You also want to make sure your motor is installed as high as possible on your transom without causing excess slipage or "ventilation". If you have to raise your motor past horizontal to reach maximum speed at a given throttle position you may want to try raising the motor one or two holes. Throwing up a "Rooster Tail" is real pretty but isn't as efficient as pushing water straight behind you. On the other hand, if you have to keep your motor trimmed below horizontal to keep from slipping then your motor is mounted too high.

ky-slabseeker
02-01-2007, 08:33 AM
The biggest thing you want to keep an eye on is your RPM:cool

Barnacle Bill
02-01-2007, 08:54 AM
Here is everything you ever wanted to know about a prop. http://boatfix.com/how/props.html

grubby
02-01-2007, 08:55 AM
I was told by a reputable dealer here in okla. that you want your prop at only 4 to 6 inches below the bottom of your boat for best fuel economy. rpms are very important to watch. lower number on the pitch gives better hole shot. the higher number gives you top end speed but less hole shot. yamaha should be able to tell you the ideal prop for your boat.

robbor
02-01-2007, 02:14 PM
You also want to consider how much you load the boat down and how rough the water normally is. I would not hesitate going 1 or 2 steps faster than factory to a 15-16". Also try not to gun it from a dead stop, just ease it up to speed. I wish I could go 1 day on a tank of gas.

Marshrat
02-01-2007, 03:42 PM
Can any of you tell me if there is a web site I can go to that will tell me what size of prop I need? I had a 30 hp yamaha on my boat changed it over to a 40 yamaha,It don't seem as fast as my 30 & LOVES the gas,I use to could fish 2 days on a tank of gas. now I'll do good to make it a full day on the same tank????:( Was told it may need a diff- size prop.

Check out this site. You should be able to find what you need, just answer the questions.

http://appcenter.mercurymarine.com/propSelector/home.do;jsessionid=05ae3b9b49184db69e579833b4705bc 4.n6XIsAyIpkjMmQPvqAzIngTxpQOUaN0Ka3D3lN4RawSMaMSK-x8L-x8Kn6bycgTAn38Lb65Abx4M-wOSa30K8Nzta5WN-AfJpBDD-APzqAbHml9DpAiImQXH8N4QaxmQbMbCpQPz8QvJpkixn6jAmlj Gr5XDqQLvpAe_


Warren

FishnLine
02-01-2007, 06:54 PM
While on the subject of props, how much difference will you see between a 3 blade and a 4 blade prop?

Barnacle Bill
02-01-2007, 09:03 PM
A 4 blade the same size as the 3 will give you a better hole shot but take alittle off the top end.

FishnLine
02-02-2007, 08:35 AM
A 4 blade the same size as the 3 will give you a better hole shot but take alittle off the top end.

Thanks for the info. I didn't know that.

DRPEPPER
02-02-2007, 10:16 AM
I am definetly not a pro on this subject so I will tell you my experience and you be the judge.

My previous fishing boat had a 40hp mariner with a 14 when I bought it. When I mangeled that one, I was talked into downsizing to a 13. I didn't like it. My current boat came with a 40 hp merc and a 13. I was satisfied with the performance. I also mangeled this prop and was forced to buy a 14 due to supply and my need to get back on the water. I can tell a favorable difference in reguards to speed. I like it. Can't tell if it helped milage or not. But I am sure it did when I stay on bigger water.
DP

Cane Pole
02-02-2007, 09:33 PM
try this site .
http://www.themarinedoctor.com/cgi-bin/YaBB.pl

Good article papa.

TITELINE
02-02-2007, 10:41 PM
I would look at setting up power trim if u dont have it. smaller pitch gives u a better hole shot but higher top end rpm. bigger pitch more hi end torque. the trim is the biggest factor. i would go with the bigger pitch with trim to unload the gear on top and run at a much lower rpm with good speed. unload the motor and dont worry about speed. you'll save alot of fuel and your engine.

papasage
02-05-2007, 06:31 AM
http://www.themarinedoctor.com/Propellers.htm