Prop Size

[robsd]

My little merc 9.8 has a 2 blade prop. I see other engines (some smaller...some 15hp) with 3 blade props. On the smaller engine the prop is smaller in diameter. <br /><br />So the question is why a 2 blade over a 3 blade and is there a 3 blade available for my 9.8 (merc 110) that may give me a little boost?<br /><br />Thanks,<br />Rob

 

[Bear]

Re: Prop Size

I'll give it a try. A 2 blade is more efficient, less drag, less blade area and faster for a light boat.<br /><br />A 3 blade has more thrust, better hole shot.<br /><br />But you can compensate by diameter and pitch. There is so many variables so you can't really generalize.<br /><br />It has to do with gear ratio and gear case size and max possible propeller diameter too.<br /><br />There is race boats with 2, 3, 4 and 5 blade prop. You can't say which is better. I depends.<br /><br />My "race engine" ('65 6HP Johnson) has a 2 blade too. Later models have 3 blades. I think they will fit my prop shaft. I think the gear ratio is the same. So, is there a 3 blade for your 9.8? I don't know yet. We'll see...<br /><br />(Sorry - no grammar or spell check.)

 

[rickdb1boat]

Re: Prop Size

Engine Serial # Please. Might be able to help if you have it.

 

[Bear]

Re: Prop Size

The '79 9.8 had a 3 blade according to this site and the exploded view. $90 here:<br /> http://www.mercruiserparts.com/select_docs3a.asp?doc_nbr=+13716+++ <br />I guess all 9.8 models 1979-86 had them. But how come your engine doesn't? <br />Is there older 9.8 models than that? Probably a Kiekhaefer Mercury 110 9.8 1962-66.<br />These are the serial numbers I've have:<br /> http://www.marinshopen.se/guide/mp/merc30.htm

 

[Bear]

Re: Prop Size

Propellers early Merc 110 and 1968-71:<br /> http://www.maxrules.com/oldmercs/Propellers/Props/6.PDF <br />Parts look up:<br /> http://www.mercruiserparts.com/partsByNumber.asp <br />"Part number not found" But the where 9"x7" for "Aux Power or Work Boat". So the answer is... I don't know. <br /><br />Check this site too:<br /> http://www.pfs-ware.com/kwast/ <br />Ask here too:<br /> http://www.pfs-ware.com/kwast/mercboard/index.htm <br /><br />I almost forgot. A boost you asked. I don't think so. Then you need to know rpm at WOT. What are you looking for, more thrust, hole shot or top speed? The 2 blade might be just fine.

 

[radsrh]

Re: Prop Size

If you go to Merc's web site, they have a option at the bottom of the screen called prop selector. You can enter your boat weight, motor size ect and it will give you the options avalable to you.

 

[robsd]

Re: Prop Size

Thanks for the replies. The boost was a little more speed when the boat is loaded. The boat is a 14' jon, with just me according to a gps I can get 12-13-14 depending on the current, a little faster down river. Add a person or 2 and it slows....a lot I know the boat isn't built for speed but if a few bucks gets me a little more it might be worth it (free boat so I have nothing invested in it now).<br /><br />The 9.8 is a 1970 model, don't have the serial number but I had to call Mercury for them to look it up, no local dealer could find it. The serial number is the old 6 digit if I recall. According to the links I have the 2 blade 9" or 10". The 3 blade indicates a 7" and is for a work boat...ie something that need more bottom end.<br /><br />Thanks,<br />Rob

 

[rickdb1boat]

Re: Prop Size

This sounds pretty much like what you found!<br /><br /> <br />Propeller Type: Outboard<br /> Manufacturer : MERCURY, SEA RAY<br /> HP / Model : MERC 9.8 - 8 SPLINE<br /> Year : 1968-79<br /> Boat Size : STANDARD REPLACEMENT<br /> Material : ALUMINUM<br /><br />Blades Diameter & Pitch Rotation Part number Style Comments <br />2 Blade 9" X 9" RH #032021 MICHIGAN MATCH <br /><br /> <br /><br />Propeller Type: Outboard<br /> Manufacturer : MERCURY, SEA RAY<br /> HP / Model : MERC 9.8 - 8 SPLINE<br /> Year : 1968-79<br /> Boat Size : LIGHT RUNABOUT - LIGHT LOADS<br /> Material : ALUMINUM<br /><br />Blades Diameter & Pitch Rotation Part number Style Comments <br />2 Blade 9" X 10" RH #032019 MICHIGAN MATCH <br /><br />--------------------------------------------------<br /><br />Propeller Type: Outboard<br /> Manufacturer : MERCURY, SEA RAY<br /> HP / Model : MERC 9.8 - 8 SPLINE<br /> Year : 1968-79<br /> Boat Size : 14'-16' BOATS - ALL LOADS, SKIBOATS<br /> Material : ALUMINUM<br /><br />Blades Diameter & Pitch Rotation Part number Style Comments <br />3 Blade 9" X 7" RH #032020 MICHIGAN MATCH