prop size/pith selection

[sosstangs]

hey guys, i recently piked up a 16 ft sea n sport skiff that has a
93 40 hp yamaha motor. Ive taken it out 2x and its not running as well as id like it to...... after some investigating it looks like one of the blades is bent almost at a 90 degree angle to the prop.... i am looking at getting a 4 blade prop for good hole shot and midrange cruising...... my questions lies in what size prop (diameter) and what pitch should I look at getting? I would like to achieve good hole shot as well as decent cruising, and top end speed is always good, but efficiency and fuel economy are more important at this point.Any input would be greatly appreciated!


Danny

 

[Silvertip]

Re: prop size/pith selection

Check your existing prop for a part number or numbers like 12x17 (12 inch diameter and 17 inches of pitch). Not knowing what you have now means we would be guessing what you need. The best prop is one that allows the engine to rev at or near the top its recommended rpm band. There is no such thing as a standard prop since the manufacturers have no idea what kind of boat the engine will get installed on. Your motor on a pontoon for example would take a very different prop than on the skiff you have. Lastly, you said it's not performing as well as you'd like. Before buying a prop, make sure the engine is making full power (tune up tiime maybe). Make sure the throttle is opening fully. Leave fuel economy out of the equation since no matter what you do you will not save enough fuel to begin paying for a prop. That's just the way it is. You can save fuel by running slower, carrying less stuff, going on a diet, leaving the dog at home, and taking a six pack of adult beverage rather than a case (although I know that's hard to do).

 

[sosstangs]

Re: prop size/pith selection

Check your existing prop for a part number or numbers like 12x17 (12 inch diameter and 17 inches of pitch). Not knowing what you have now means we would be guessing what you need. The best prop is one that allows the engine to rev at or near the top its recommended rpm band. There is no such thing as a standard prop since the manufacturers have no idea what kind of boat the engine will get installed on. Your motor on a pontoon for example would take a very different prop than on the skiff you have. Lastly, you said it's not performing as well as you'd like. Before buying a prop, make sure the engine is making full power (tune up tiime maybe). Make sure the throttle is opening fully. Leave fuel economy out of the equation since no matter what you do you will not save enough fuel to begin paying for a prop. That's just the way it is. You can save fuel by running slower, carrying less stuff, going on a diet, leaving the dog at home, and taking a six pack of adult beverage rather than a case (although I know that's hard to do).

Ok, will have to check to see if there are any numbers on it.... the motor revs excellent in neutral and is very responsive..... however when on the water. she seems to take forever to pick up rpms and also doesnt seem to be making top power...... i am getting the carbs rebuilt but i also want to get a new prop has seen better days...... my boat load is always the same.... just me and a pal some fishing gear and a cooler for the fillets..... not much of a drinker on the boat, unless doing the sandbar thing.....
anyone recommend a 3 blade vs 4 blade? or vice versa?

 

[K.P.]

Re: prop size/pith selection

I don't believe you will see any benefit from a four blade prop on a skiff powered by a 40 HP motor. Four blades work better on v-hull boats that are heavy in the rear. Niether matches your rig. Stick with a 3 blade and maybe consider stainless for better hole shot and cruising. You'll be able to raise the motor higher with a stainless prop that will result in better overall performance.

You will not get any idea of performance from an existing prop that has a bent blade. See if a prop shop can fix it and use it as your baseline performance indicator to select your next prop. I also would ask other owners of similar rigs what they are running for props and what RPM they are getting.

 

[sosstangs]

Re: prop size/pith selection

well, my skiff actually is stern heavy...... its a flat bottom v hulled boat..... you dont think a 4 blade wold offer me better hole shot? I will get the measurements tomorrow....

 

[K.P.]

Re: prop size/pith selection

The correct prop pitch is what will get you the best hole shot. A four blade has a certain cool factor. Unfortunately the rotaional resistance of the additional blade will require you to drop at least one inch of pitch from whatever 3 blade works best. So do you want cool or performance?

Getting your motor properly setup on your rig and operating in the correct RPM range is what will get you out of the hole and planning well. We don't even know where to begin because your current prop is bent and you have no performance measurment to go by. If I were to guess at prop pitch it would be 13...maybe 12...I doubt 14.

 

[sosstangs]

Re: prop size/pith selection

The correct prop pitch is what will get you the best hole shot. A four blade has a certain cool factor. Unfortunately the rotaional resistance of the additional blade will require you to drop at least one inch of pitch from whatever 3 blade works best. So do you want cool or performance?

Getting your motor properly setup on your rig and operating in the correct RPM range is what will get you out of the hole and planning well. We don't even know where to begin because your current prop is bent and you have no performance measurment to go by. If I were to guess at prop pitch it would be 13...maybe 12...I doubt 14.

ok, took my prop off today to find a 10 1/4 x 14-g
what does the "g" mean? also, is this pitch too high for my motor?

 

[sosstangs]

Re: prop size/pith selection

ttt... help me out guys, i want to get her done for this upcoming weekend!!!

 

[steelespike]

Re: prop size/pith selection

Really can't make a decision without your present max rpm and speed.
Also a description of the boat,all the bells and whistles or basic tiller steer
fishing boat. That G may be a C for clockwise rotation.
I think the economic way to go is fix the prop, run it and get the specs.
Then decide what prop based on the performance.
Alternately get another 14 and get the specs,decide if its worth it for a different prop.
Don't operate the motor permanently wthout knowing if it is operating within its rpm range.

 

[sosstangs]

Re: prop size/pith selection

ok, the boat is a 16 ft sea n sport skiff.... it is a v hull but flat bottomed boat. The motor is a 93 40 hp yamaha tiller motor. I would say the boat weighs around 500-700 lbs plus gear and a cooler, your looking at about 800.... then myself and another guy, your looking around 1150 and motor is approx 150.... so were looking at about 1400-1500 lbs of weight with a full tank of gas (9 gallons). from time to time, i will have a livewell running with 5-10 gallons of water..... up to this point i have not had any additional water in the boat.....

 

[sosstangs]

Re: prop size/pith selection

ttt.....

 

[steelespike]

Re: prop size/pith selection

ok, the boat is a 16 ft sea n sport skiff.... it is a v hull but flat bottomed boat. The motor is a 93 40 hp yamaha tiller motor. I would say the boat weighs around 500-700 lbs plus gear and a cooler, your looking at about 800.... then myself and another guy, your looking around 1150 and motor is approx 150.... so were looking at about 1400-1500 lbs of weight with a full tank of gas (9 gallons). from time to time, i will have a livewell running with 5-10 gallons of water..... up to this point i have not had any additional water in the boat.....

Good job; now get that prop fixed and give us the max rpm and speed.
Loaded and un loaded would be excellent.

 

[sosstangs]

Re: prop size/pith selection

Good job; now get that prop fixed and give us the max rpm and speed.
Loaded and un loaded would be excellent.

ok, may seem like a stupid uestion... but if i want to figure out the rpms i am running on my tiller motor, how am i suppossed to do that? it does not have any guages.... is this just something a motor shop will do>.... with going rates of 90-100 per hour labor, what are my other options?

 

[steelespike]

Re: prop size/pith selection

You can get a tiny tach, they have a web site.Reasonable price,easy to install fits any similar motor without regard to stator poles.
If you make noises about thinking you need a prop your marina might let you borrow a shop tach.Personally I'm eventually going to get a tinytach for my 65 Merc 500 tiller steer so I can fine tune things.