Author Topic: New tach, new prop!!! (Read 24101 times)

MarkS · « **on:** June 12, 2010, 02:08:12 PM »

A 21P may be too much, but I LIKE IT!
http://www.youtube.com/watch?v=5nKLPX-_xVA

Hyperacme · « **Reply #1 on:** June 12, 2010, 02:26:29 PM »

I'm I seeing 46 mph at 4300 rpm's ?
Speedo is hard to see.

MarkS · « **Reply #2 on:** June 12, 2010, 02:56:41 PM »

It looked like 39mph, but you're right Gregg, it was hard to see. Haulin' the mail, that's all I can tell for sure! I don't care about turning MAX rpm, (5500) unless it's bad turning less for the old Johnson, what do you think? I was told the "sweet spot" was about 3500, and the 21P is sweet right about there.

Hyperacme · « **Reply #3 on:** June 12, 2010, 03:38:54 PM »

OK ..
When I'd freeze the video, speedo was very hard to read.

My understanding about props/rpm's/mph is to run a prop that gets your rpm's at WOT some where in the middle of your max. rpm range.
I have heard that proping your motor for under max rpm's is not good for it. ( but that was off a Merc forum )

"Sweet spot" would be your motor would be running 5250 rpm's at WOT and when you throttled down to 3500 rpm's it would run at it's best mpg range of powerband.

If that all makes sence ?

Rich_V174SS · « **Reply #4 on:** June 12, 2010, 05:21:11 PM »

Marks speedo may be reading in knots and if that's the case 39 knots is about 44.8 mph.

MarkS · « **Reply #5 on:** June 13, 2010, 05:18:51 AM »

It makes sense on the sweet spot Gregg, I'm just trying to sort out my best cruising range without hurting the motor. I don't like running WOT, I mean she is 37 years old! (Do like a blast now and then, gotta be honest though.) Think I need to put the 19P four blade back on and see what that does now that I have a tach that reads right. I would be happy with the 21P at 3500 for cruising, it just "feels better".

Update: 19P back on, anybody need a three hour old 21P?

Hyperacme · « **Reply #6 on:** June 13, 2010, 09:27:09 AM »

I got a new Michigan Wheel Vortex XHS 13x19 prop to test, thinking the newer style could get me a few more 10th of a mph but lost over a half mph.
Have also tried a 13 x 19 SST prop and got the same mph as my old style OMC prop.
If I can find a 21P locally for cheap I might give it a try, but think I'll try other brands of 19P.

By old style I mean the old OMC with the convergence hub on the end ... see picture...to hard to explane ...LOL
Dave found it for me, $35 rebuilt and the fastest prop I have tried to date.

What brand is your 21P ?

First picture is rebuit OMC 19P with convergance hub , best one so far.
Second picture from left to right, OMC 17P alm. with convergance hub , OMC 19P alm. with convergance hub and last is a OMC 19P SST.

MarkS · « **Reply #7 on:** June 13, 2010, 11:11:55 AM »

It's a Solas Amita 3. It has pretty good cupping on the blades, solid rubber hub. Might be just what you're looking for, I don't know?

And the four blade 19P I'm going back to.

How does $75 and I'll pay the shipping sound?

Hyperacme · « **Reply #8 on:** June 13, 2010, 11:21:57 AM »

I think the 21P would pull my rpm's down to low, I'm getting 5400 rpm's with the 19P props ( my rpm range is 5000 to 6000 rpm's ).
HUMMM... Your 19P is a four blade ... some thing else to try ...LOL

Got my 19P for sale also ...

Michigan Wheel Vortex XHS 13x19 prop - $85 (Woodbury)
http://minneapolis.craigslist.org/wsh/boa/1788110417.html

MarkS · « **Reply #9 on:** June 13, 2010, 11:30:09 AM »

Yes, it probably would. If you hear of anybody looking for one, you know who to refer them to right? The four blade is 1/2" smaller diameter (12.5) than the three blades, hurts top end but what a holeshot!!!

The Simpsons were sitting out by the lake yesterday.

Hyperacme · « **Reply #10 on:** June 13, 2010, 11:33:32 AM »

OK ...
Four blades out ..
Would rather have top end.
Is your prop on Craigslist ?

MarkS · « **Reply #11 on:** June 13, 2010, 01:26:45 PM »

Just posted it: http://atlanta.craigslist.org/sat/boa/1789866891.html

74 Carlson · « **Reply #12 on:** June 13, 2010, 07:05:40 PM »

You should always prop your boat for WOT. After you get all your normal running gear like life jackets, anchors, batteries and what ever else you like to bring along in the boat thats where you should prop it at. You will do more harm than good being over propped, you end up putting more strain on the motor being over propped

MarkS · « **Reply #13 on:** June 13, 2010, 08:18:44 PM »

Thanks for the advise, I should be back up well within the operating range now. I didn't get a chance to re-test today, but the 19P four blade is back on the boat, will report back next weekend after doing so with the accurate tach. Guess that "need for speed" thing kinda snuck up on me, don't ya just hate it when that happens!?

V153 · « **Reply #14 on:** June 13, 2010, 10:59:06 PM »

Quote from: 74 Carlson on June 13, 2010, 07:05:40 PM

You should always prop your boat for WOT. After you get all your normal running gear like life jackets, anchors, batteries and what ever else you like to bring along in the boat thats where you should prop it at. You will do more harm than good being over propped, you end up putting more strain on the motor being over propped

Ideally. For top end. You should be propped a couple/few hundred rpm above the factory recommended 'redline' @ wot. Talking 2 stroke outboards that is. Rpm = hp.

Do not try this with your 4 stroke I/O.

MarkS · « **Reply #15 on:** June 14, 2010, 03:42:42 AM »

I appreciate the input and advise guys, thanks. I should be fine with the 19P four blade, we'll find out next Sat.! If it does go too high, I'll be in touch about that Vortex Gregg. (Wanted to prop test again yesterday, but worked on domestic chores to keep the better half happy.) I go boating by myself most of the time (NOT complaining), and pretty much have the same equipment on board, so the load in my boat rarely changes. Guess I gotta just get used to letting her sing full song to me back there!

74 Carlson · « **Reply #16 on:** June 15, 2010, 12:26:14 AM »

Unless you have done good mod work to your motor I would not recommend exceeding the factory WOT RPM. Bad things can happen to a stock engine being over reved and if the stock motor is not tuned properly and you exceed the factory RPM redline on a regular basis it's not the matter if, it's a matter of when it blows up on you. On stock motors everything has to be set up perfect like timing, carbs, fuel and air flow to the motor all the time to be able to run maybe at the most 300 rpm's above factory rcommendations. I have seen what happens to a stock motor when you constantly over rev, it destroys everything including the engine block so when it goes dont try to fix it just go buy another motor.

MarkS · « **Reply #17 on:** June 15, 2010, 03:43:23 AM »

I understand about not over-revving, I sure don't want to "implode" this great old motor. Now that I have a tach that actually works, it WON'T see anything over 5500! Guess I should have worded my statement a little more clearly. What I should have said, is if I still have throttle left at 5500, I'll be in touch about the Vortex.

The 21P sold last night (thanks Sean), and will be on it's way to MN today.

V153 · « **Reply #18 on:** June 15, 2010, 03:34:03 PM »

Quote from: 74 Carlson on June 15, 2010, 12:26:14 AM

Unless you have done good mod work to your motor I would not recommend exceeding the factory WOT RPM. Bad things can happen to a stock engine being over reved and if the stock motor is not tuned properly and you exceed the factory RPM redline on a regular basis it's not the matter if, it's a matter of when it blows up on you. On stock motors everything has to be set up perfect like timing, carbs, fuel and air flow to the motor all the time to be able to run maybe at the most 300 rpm's above factory rcommendations. I have seen what happens to a stock motor when you constantly over rev, it destroys everything including the engine block so when it goes dont try to fix it just go buy another motor.

Not trying to say you should rush out & run 2 -300 rpm above the redline all day long. 'Specially with a stock motor. But for bursts of top end and/or cruising @ higher speeds that's where I've always tried to prop my outboards. In a perfect world we'd all have a prop that could pull 10 skiers, cruise 35mph @ 3000rpm, and max out a lil over the redline @ wot. Sadly we live in an imperfect world ...

If you're looking for top end you need to lose the 4 blade Mark. Great holeshot yeah but not a top end prop. Step up to a 3 blade stainless say 13 1/2 or 13 3/4 by 19 or 20 for starters. Raising the motor a hole would probably help too. With no ill effects.

Now the prop testing fun begins ... !

MarkS · « **Reply #19 on:** June 15, 2010, 08:12:24 PM »

Quote

If you're looking for top end you need to lose the 4 blade Mark. Great holeshot yeah but not a top end prop.

Yeah, I should have gone with a 3 blade 19P as a starting point, just had a "bonehead moment" when I bought it. At least the 4/19P will get me out of the lugging issue, I'll just have to see where my RPM's are this weekend, and be careful not to over-rev of course. I'll also try moving the trim pin up a notch, I'm only one hole up from bottom now. I'm leaving the proceeds from selling the 21P in my Paypal account to start saving for a new 3 blade, would love to go stainless but we'll see how it goes....

Quote

Now the prop testing fun begins ... !

Absolutely, it's all part of the learning process right!? My next motor WILL have PT&T! I've had two hernia operations in the last two years, (work injuries), and lifting/tilting the V4 is the only part of the whole thing I Don't like.