how do I find a prop that fits

[sergioy]

I need to find a prop for my my boat.I've got a 1975 Mark Twain with a 165 hp strait six I/O.At this time i've got a 15X21. From wht I can make out on the bumbers on it, they are:4 79576A 4 21P By the way is that Greek or Egyptian hieroglyphics? Last time I went to the marine shop they gave me that prop, not the same numbers that where on the last one either. So how do I choose a prop by just looking at the numbers? Would it be possible to get a SS prop for this age boat? Your input would be greatly apreciated.

 

[KaGee]

Re: how do I find a prop that fits

You can start by calling Iboats... they have a prop specialist and very competitive prop prices.

 

[stevens]

Re: how do I find a prop that fits

This site and tool might also be useful:<br /><br />www.mercruiser.com/propellers<br />www.mercurymarine.com/prop_selector<br /><br />You might want to compare prices at, say, iboats.com, propline.com, propellersonline.com, etc.

 

[Silvertip]

Re: how do I find a prop that fits

Finding a prop that fits is only one part step in the process of buying a prop. The first numbers on that prop are the manufacturers part number. 24P stands for 24-inches of pitch. Theoretically (without slippage) the prop moves through the water 24 inches with each revolution. Before you go further, you need to determine the maximum recommended wide open throttle rpm range for the engine (which is probably in the range of 4200 - 4500 for yours). If with a normal load you cannot achieve those rpms, your boat is overpropped and you need to drop back to say a 21 which will raise rpm to more favorable level. If it revs higher than recommended, you need to increase pitch. Diameter has less effect on performance than pitch. And before you make your benchmark runs, make sure the engine is properly tuned. Buying props to take care of engine performance problems is a terrible waste of money. Stainless steel props generally perform better (all else being equal) but again, the price may not outweigh the benefit.

 

[sergioy]

Re: how do I find a prop that fits

Well, I went ahead and ordered a propeller from iboats. And I must say that I am very happy. Their prop selector worked very easily. I had tried using another sites web interface and I must say that I was intimidated by it. But iboats has a good web interface to help select a prop. Plus their price was very competetive. The last prop I got was a rebuilt one for $70. I paid iboats $110 for a brand new one. Not bad, if I do say so myself.

 

[walleyehed]

Re: how do I find a prop that fits

W.S., what part of the state are ya in?????

 

[sergioy]

Re: how do I find a prop that fits

Actually, I am now in Dallas Texas. I am about 3 miles away from the lake. I think my wife will devorce me in about a year. If I am not at the lake fishing, then we are out on the ski boat cuttin' up with the kids. It is really awesome.