How to tell what Prop i need

[Superbee]

The Prop thats on the boat is a Michigan SMC-805<br />3 fin is this what this boat should have? It also had another Prop in the boat 2 fin I'm going to guess it's a Michigan 787 it does not say Michigan anywhere<br />1968 Mark Twain<br />merc 327 V-8<br />II Drive<br />Thanks

 

[Laddies]

Re: How to tell what Prop i need

Dave, first props are kinda hard the come by for that II unit. If you need when I get a few minutes I can dig in the attic and get a old mich. catalog and ck the pitch of those props, basicly you need to get 4200 to 4400 RPM at WOT. I remember some guys turning 5200, but that was not on old iron---Bob

 

[Superbee]

Re: How to tell what Prop i need

will that book tell ya what it takes to pull those RPM's? I guess my next question is if i find one How much do they run, and if i find one New for $25 should i jump on it? It's a SMC809, or even do i need to replace this?<br />When i took it out Sunday the Tach was not working<br />i only ran it around the Lake once because of the Stern is leaking oil and didn't want to fry it<br />I got this fix today no more leaky So next time i can keep it out longer and the tach will be fixed<br />Any help would be Great<br />Thanks

 

[pvisser]

Re: How to tell what Prop i need

I had a similar question last season. The jist of the solution is to find out your engines suggested WOT RPM, and pla with the pitch until you achieve it.<br /><br />A prop for $25.00 is a bargain anytime, may not be the right one, but always good for a spare?

 

[Superbee]

Re: How to tell what Prop i need

Ya thats what i'm thing i will get it if i can.<br />Newbie Question looking at the motor what way should it turn Clockwise or counter clockwise<br />I was told Merc motors run backwards?

 

[QC]

Re: How to tell what Prop i need

All modern sterndrive Mercruiser Engines are left hand (standard, counterclockwise) rotation.<br />Most single engine boats use a right-hand rotation drive unit meaning that<br />the propeller rotation is right-hand (standard, clockwise) rotation.<br /><br />This is viewed from the flywheel i.e. engine is running on a stand and you are looking at the flywheel while standing in the back.<br /><br />This doesn't mean that your setup follows this as it is older and who knows its history?<br /><br />Also, prop discussions must begin with the tach. See the Engine FAQ's section there are two subjects you need to look over. Prop selection and Wide Open Throttle RPMs.

 

[Superbee]

Re: How to tell what Prop i need

I do beleave that the prop is Left Hand Prop<br />If i stood in the back of engine and looked at the flywheel it would be going Counterclock wise

 

[Superbee]

Re: How to tell what Prop i need

I took this back out today with the speedo and tach working the boat top out at 38mph and 3000rpm Full throttle<br />if these Gauges are right the tach is new.<br />Should i leave it or try a new prop<br />I found another PRop it's a Michigan 16.75X19 LH<br />I beleave what i have now is a 15x19 LH<br /><br />Just asking

 

[Bondo]

Re: How to tell what Prop i need

Your rpms are Extremely Low...... Are you SURE the tach is Right ????<br /><br />If it is,.. You're going to need atleast a 15" pitch prop to get them back up to the 42/4400rpm range.......

 

[Superbee]

Re: How to tell what Prop i need

Well i don't know, it has 4 6 8 it was on 8 when i put it to 6cyl it went to 4000RPM and when i put it to 4cyl it went to 6000rpm the Tach is new it didn't seem to me it was a high RPM was just kinda smooth<br />i heard the 4 barrel open<br />Does more RPM Mean faster boat it topout at 38mph<br />that gauge is about 40 years old, next time i go out a freind is going to bring his GPS

 

[tommays]

Re: How to tell what Prop i need

i would recomend a shop tack to check the RPM as to low or to high will both damage the motor<br /><br />i dont no of to many stock motors that make enough HP to go 38 mph at 3000 RPM <br /><br />its one of those things that really needs to be in the right range or it gets expensive quick<br /><br />tommays

 

[Superbee]

Re: How to tell what Prop i need

Laddies,<br />Have you had time to check that Prop info?<br />I bought one off eBay today for $25 i beleave it's about the same thing i have, but now i have a Spare.<br />SMC-805 Mine<br /><br />SMC-809 is the one i pickup up off eBay <br />Thanks

 

[Superbee]

Re: How to tell what Prop i need

I also took this back out today with a GPS it said that i was moving 36mph Engine was still at 3000 Rpm<br />Full Throttle i took 2 extra tachs with same thing.<br />So i do know that the Speedo is off 2mph.