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Author Topic:   Another prop question
Lars Simonsen posted 06-03-2003 08:10 PM ET (US)   Profile for Lars Simonsen   Send Email to Lars Simonsen  
I finally got around to raising my motor two holes (it was on the lowest hole). My 6 year old son and I raised the motor using an ancient family secret handed down by my egyptian ancestors.

I have a 1998 18' Dauntless (with the transom notch) and a 1998 Optimax 135. The prop is a stock Mercury aluminum 3 blade prop with the numbers "010378" printed on it. I have no idea what the pitch is.

Even with the motor set in the lowest hole, I could easily get the motor to 6000 rpm (and it would probably rev higher if I were an idiot and the throttle didn't hit the stop). Max speed was somewhere around 40 give or take 2 mph.

With the motor now raised two holes, the boat no longer throws the v-shaped rooster tail. It also stays on plane at lower RPMs. The cavitation plate is about midway between the bottom of the hull (before the transom notch) and the top of the hull in the transom notch. The transom notch is about 4 inches deep, so that puts the cavitation plate about 2 inches above the lowest point of the hull, and 2 inches below the top of the notch.

I just took it out this afternoon after work for the first time since raising the motor (it's been blowing a gale since this weekend, and it finally died down to 10 to 15 this afternoon). But it was still too rough to get the boat to WOT.

The one thing I noticed is that in the rough water (it was 3'-4' chop and some white caps), if I was going slow and gave it some throttle with the motor trimmed up any at all, the prop would break loose. It was fine with the motor trimmed all the way down, and actually seemed to be smoother in the rough water than before (mostly because I could keep it on plane at a lower speed, I'm sure).

Before I raised the motor, I figured that I might find that my prop would slip some since even at the lowest setting, I could get beyond redline on this motor (which I believe is 5500).

I'm not sure I've provided enough information for anyone to give me any advice on a different prop, but until the wind dies down and I can get out and give it a real test, this is the best I can do.

I'm not looking for top speed. I mostly fish with the boat, and am just looking for the prop that is the best all around and takes full advantage of the power of the motor.

Any suggestions? If the weather and my schedule cooperate any time soon, I'll provide more information. I'm hoping to go fishing Saturday a.m., and should have some more info after that.

Lars

lhg posted 06-03-2003 08:34 PM ET (US)     Profile for lhg    
With the engine now lifted up 1 1/2", you will need a Mercury performance line prop, as you are too high for an aluminum to function properly. They're no good anyway on a V-6.

I would recommend the 4 blade "Performance Offshore" prop for your boat. This will give you great holding, and bow lift for better performance. It doesn't sound like you're describing a Mercury prop, as they ALWAYS have the pitch on them, usually hyphenated after the part #, as in XXXXXXX-17P. Your speed wil definitely increase over aluminum.

YOu will need to determine what pitch the aluminum is, as it was turning 6000 fully submerged. I would go up 2" pitch for the SS model, and because you have raised the engine at the same time. I wild guess would be either a 19 or 17" pitch for your engine. Check out the Mercury web site prop selector.

Lars Simonsen posted 06-03-2003 09:02 PM ET (US)     Profile for Lars Simonsen  Send Email to Lars Simonsen     
Thanks!

Yes, I figured a four blade prop would be part of the solution. I'll look more carefully at my prop and see if it's got any more numbers on it.

I'll check on the prop selector, too.

Sal DiMercurio posted 06-03-2003 11:12 PM ET (US)     Profile for Sal DiMercurio  Send Email to Sal DiMercurio     
Thats just the part number, not the size, look a little harder & you will see something like 14 x 15 or 17 , thats the size of the prop.
Ihg is right, a normal aluminum prop is worthless on that engine & being raised it makes it worse, s/s is the only way to go.
I doubt theres only 4" between the bottom of the boat & top of the transom, your engine bracket is closer to 8 - 10" alone, from what your describing, the bottom cylinders would be under water with the engine off.
We really can't give you the correct prop size until you tell us the size of your present prop & what kind of rpms she's twisting.
Sal
Lars Simonsen posted 06-04-2003 01:10 PM ET (US)     Profile for Lars Simonsen  Send Email to Lars Simonsen     
It's 4" from the top of the transom notch (or pocket or whatever it's called) which is sort of a tunnel in the hull. The plate is much further down from the top of the transom.

This evening I'm going to check to see whether there are any other numbers on the propeller.

bsmotril posted 06-04-2003 03:32 PM ET (US)     Profile for bsmotril  Send Email to bsmotril     
I have the same year and horsepower Optimax. Mine definetly will run up against the rev limiter and not go higher than 5600 rpm. The alarm horn sounds each time you do. A four pladed prop will help with the slippage on the higher motor, but I think the offshore series has too much diameter for your size and weight of boat. The downside to that is you loose a little top end. You might try a Stilleto brand 3 bladed prop with cup. Probably a 17" pitch is what you need. They hold well and give great speed on midweight boats. They are smaller diameter than the Merc props which might let you even go with a 19" .They are also a lot less expensive than the Merc props. The least expensive solution would be to have a local prop shop add some 2" equivalent cup to your existing prop. That would help with both the high rpms and slippage.
BillS
Lars Simonsen posted 06-04-2003 09:56 PM ET (US)     Profile for Lars Simonsen  Send Email to Lars Simonsen     
The mystery of the numbers is revealed. The 010378 number is something that the prop shop stamped onto the prop according to my local boat shop. When they painted the prop, the other numbers became less visible. I can't make out all of the numbers, but it starts with a 48, and ends with 17P. I assume the 17P is the number of significance. If the others have any value, I can try harder to decipher those.

My local boat shop said they can probably get me a good used stainless steel prop at a decent price, which sounds good to me.

Since I was reaching 6000 rpm with the 17 pitch prop with the motor all the way down, I'm quite certain that I'll hit that same rpm with the same prop and the motor raised two holes.

Sounds like a 19 pitch stainless steel would be a step in the right direction. As I said, I'm looking for best all around performance. I don't want the boat to go any slower (~40 mph is slow enough for the top speed), but I'm not trying to break any speed records either. Raising the motor has already had made one very noticeable improvement in allowing me to stay on plane at a lower speed. Sounds like a new prop will help even more.

BTW, are Ballistic props any good? That's what the guy at the boat shop recommended as a good and less pricey SS prop.

Thanks for everyone's help!

Lars

Sal DiMercurio posted 06-04-2003 10:42 PM ET (US)     Profile for Sal DiMercurio  Send Email to Sal DiMercurio     
Whoa a second, your going to gain about another 200 rpms by raising the engine, so the same size prop, [ i think your running a 13.25 x 17 ] is going rev a whole lot more as you raise the engine.
You can get a s/s Stiletto for $259 delivered to your door in a couple days from Aftermarket.
Ballistic props are ok but cost more then the Stiletto.
Sal
Lars Simonsen posted 06-04-2003 10:49 PM ET (US)     Profile for Lars Simonsen  Send Email to Lars Simonsen     
What size stilleto would you recommend?
Sal DiMercurio posted 06-05-2003 01:00 AM ET (US)     Profile for Sal DiMercurio  Send Email to Sal DiMercurio     
Lars, before you buy a new prop, you must borrow one from a prop shop [ they wont have a Stiletto, but we can get an idea of which way to go ].
I would start with a 13.25 x 19 performance type prop, run it, come back here & if it needs fine tuning, we can then do it, but not until you try a 13.25 x 19 first.
I feel the 19p might run a little over the recommended max rpms but thats ok as long as you don't run her wide open all the time.
If it's to much over, then we have to go to a 21p to bring the Rs down.
Sal
Lars Simonsen posted 06-05-2003 07:27 AM ET (US)     Profile for Lars Simonsen  Send Email to Lars Simonsen     
Sounds good. I'll see if I can find a place to borrow a prop and report any results!
Lars Simonsen posted 06-05-2003 08:22 AM ET (US)     Profile for Lars Simonsen  Send Email to Lars Simonsen     
Here's some more information.

As best I can tell the numbers on the prop are: 48888828 A15 17P

The A15 could be an A13, but it does look more like a 15 than a 13.

I measured the prop as best I could and it appears that the blades are about 5 1/8 inches, and the hub is 4 1/2 inches. Is there such a thing as a 15 inch diameter prop?

Bigshot posted 06-05-2003 11:25 AM ET (US)     Profile for Bigshot  Send Email to Bigshot     
Yes and most 17" Pitch are 15x17. I would try a 14.25 or whatever by 19" like sal said. If you are a 100 or so over redline have it double cupped which will bring you down 100-200rpm. If you are still hitting 5700+ then step up to a 20 or 21"
lhg posted 06-05-2003 03:14 PM ET (US)     Profile for lhg    
Mercury's current aluminum 17" pitch prop for a V-6, with fixed hub is, #48-832838A45-17P.
Diameter, which should be ignored when choosing a prop, is 15", 2100-3600 total load. Speed range shown is 35-41 on a 135 Optimax.

Also of interest, as long as I have the Mercury propeller book out, regarding 4-BLADED PROPS: "they" state

4-bladed props usually:

1. plane the boat faster the 3-blade props

2. keep the boat on plane at a lower speed

3. give improved mid-range speed at the same PRM as a 3-blade propeller

4. provide quicker acceleration than most 3-blade propellers

5. run smoother than 3-blade propellers

6. have better holding power in rough conditions

7. are less likely to ventilate in sharp turns

8. provide better low speed handling

9. are not quite as fast on the top end as a comparable 3-blade propeller.

bsmotril posted 06-05-2003 04:03 PM ET (US)     Profile for bsmotril  Send Email to bsmotril     
After running Merc's 4 blade offshore 17" against a Mirage 3 blade 17", I can tell you where my experience differs from Merc's points. This is factual data as measured by GPS.
1. plane the boat faster the 3-blade props
True by my seat of the pants feel

2. keep the boat on plane at a lower speed
True, by about 2mph on a 3500# boat with a Merc 175. But the engine is running 300-400 rpm higher at any given speed in the midrange

3. give improved mid-range speed at the same PRM as a 3-blade propeller
Found this to be absolutley FALSE. Prop acted more like a 15" than a 17" RPMS wree higher at all speeds.

4. provide quicker acceleration than most 3-blade propellers
Seat of the pants says this is true, but the difference is not great.

5. run smoother than 3-blade propellers
To me, this was the biggest difference. The boat now felt turbin powered versus Piston powered. Very nice....

6. have better holding power in rough conditions
Did not notice any difference here at all. Maybe the engine needed to be raised to take advantage of this ability of the 4 blade. But then, the 3 blade did not really have any problems hooking up.

7. are less likely to ventilate in sharp turns
Noticed no difference here, probably for same reasons as #6 above.

8. provide better low speed handling
No noticable difference on my deep V, still wanders at idle speed

9. are not quite as fast on the top end as a comparable 3-blade propeller.
Yup, 4-5 mph slower than the Mirage 3 Blade

I did not buy the 4 blade because I could not justify the almost $500 price for the benefit over my Mirage 3 Blade.
For an additional reference data point, my spare prop was a Michigain Wheel 17" Aluminum with Cup added. Planing the boat with thqt prop was an excercise in throttle control and frustration. It would ventilate if you did not gradually increase throttle to match boat speed. Let loose on turns, and would not plane under 4000rpm, and slipped even then. So the Mirage had a lot of benefits over a 3 blade aluminum of the same 17" pitch. With Lars lighter boat, I agree with Sal and think he'll get the most bang for the buck with a Stilleto three blade. If his rig was pushing 4000lbs loaded, then I'd look to the four blade.
BillS

Lars Simonsen posted 06-05-2003 04:40 PM ET (US)     Profile for Lars Simonsen  Send Email to Lars Simonsen     
At $250, the Stilleto blade is the most attractive alternative I've seen. I think I may have a line on a 19" pitch SS prop that I can borrow (and buy for fairly cheap if it fits the bill).

I'll let you know!

Thanks again for all of the suggestions and advice. I have certainly learned a lot about props as a result (at least enough to be dangerous)!

Lars

Lars Simonsen posted 06-05-2003 08:59 PM ET (US)     Profile for Lars Simonsen  Send Email to Lars Simonsen     
Everything miraculously fell into place. The local boat shop (that sells Johnsons) happened to have a mercury 14 x 19 SS prop back in their warehouse, which they loaned to me. It also happened to fit my motor, even though it is a mercruiser prop.

The weather also cooperated. I got in about 20 minutes of boating and here are the results:

With just me on board and not much equipment, the RPMs at WOT were around 5500, although I was able to get the RPMs up to about 5800 with the motor trimmed way up. Top speed was about 48 mph (about 8 MPH higher than with the other prop). The boat easily stayed on plane at 3000 rpm. No big change in how fast I could get the boat on plane.

The one thing that I found that may became slightly annoying is that the prop breaks loose pretty readily in a turn. But I was also out to check top speed, and had the motor trimmed up pretty high. Trimming the motor down in turns solved the problem.

The one question I have is that this propeller is substantially heavier than the original aluminum prop. The aluminum prop seems to have all excess metal removed (it has a cone like hole bored into the back of the hub, whereas the stainless steel one is solid). Exhaust ports are the same on both props. Do I risk damaging my motor by using a prop that is so much heavier (I assume since it's balanced, the weight doesn't really matter, but what do I know).

I think I can get this prop for a bargain. What do you think?

Sal DiMercurio posted 06-05-2003 09:18 PM ET (US)     Profile for Sal DiMercurio  Send Email to Sal DiMercurio     
Yes, the s/s prop weighs about 11 - 12 lbs compared to the 4-lb aluminum prop.
No it wont hurt your engine, they are built to twist either aluminum or s/s.
I would get a performance prop, not that one the dealer let you use, because that prop is breaking loose in the turns & will also break loose in rough water.
Get a Stiletto of the same size, you will love it.
Heres the 800 number for Aftermarket.
1 800 349-2628
I think the prop you want is either $249.00 or $259.00......no tx
Plus they are nice & shiny in case you need to shave in the fresh.
The stiletto will make your boat ride completely different, much higher on the water.
Sal
Lars Simonsen posted 06-05-2003 09:24 PM ET (US)     Profile for Lars Simonsen  Send Email to Lars Simonsen     
That sounds good. After reading your post about lowering your engine to run in the ocean, I started having second thoughts about this prop, particularly with the blowing out in the turns. Like I said, high speed is not really my goal; all around good performance is, and that to me means be able to run WOT without exceeding redline.

I found the Aftermarket.com website earlier today, so I'll probably go ahead and order the prop.

Thanks for your help!

Sal DiMercurio posted 06-05-2003 09:38 PM ET (US)     Profile for Sal DiMercurio  Send Email to Sal DiMercurio     
The Aftermarket web site has been changed, I think it's AFTA.com, not sure but call on the 800 number & ask them for the correct web address & they will give it to you 24 hours a day.
I think the web address Aftermarket.com is only automobile parts.
Lars, try the DStiletto up high, if she breaks loose drop her down a hole, she will bite much better then a standard prop.
Sal
Lars Simonsen posted 06-05-2003 10:56 PM ET (US)     Profile for Lars Simonsen  Send Email to Lars Simonsen     
In a few days, I'll be "twisting a stiletto"!

I went ahead and ordered it. I'll let you know how it performs.

Yeehaw!

Thanks again to everyone who responded!

Lars

Lars Simonsen posted 06-11-2003 09:27 PM ET (US)     Profile for Lars Simonsen  Send Email to Lars Simonsen     
I got my stiletto today. I even got a brief boat ride in. It was a little choppy today, but was still able to get a good run in. I was able to get to 5400 RPM and about 45 mph (I wasn't using my gps, so that was just based on the speedo on my depth finder). No problem with the prop breaking loose in turns. I can probably squeeze 200 more rpm and a couple more miles per hour on a less windy and choppy day, so the prop and motor height seem to be just right. (I might could even raise the motor one more hole, but I'd be making a trade off for a little more speed, and I'd rather have the prop more submerged. The approx. 48 mph I think I can get out of it is plenty fast, and I'm glad to have a prop that isn't breaking loose all the time.

I noticed a strange spray behind my boat at one point, which turned out to be caused by the transducer on my depth finder. The transducer is mounted on the transom and hangs down just a little below the bottom of the hull. It can pivot vertically on its mount, and had pivoted with the front completely down so that it was "scooping" water, and throwing up enough of a spray to spray the cowling on the motor. I pivoted it back to horizontal, and that corrected it.

The boat doesn't get up on plane quite as quickly as with the other prop, but I'm glad to be able to use the full RPM and power range of the motor.

So the modifications were a success!

Lars

Sal DiMercurio posted 06-11-2003 11:00 PM ET (US)     Profile for Sal DiMercurio  Send Email to Sal DiMercurio     
Lars, did you notice your boat riding higher then before ?
Glad she performs to your liking.
Sal
lhg posted 06-12-2003 06:05 PM ET (US)     Profile for lhg    
It's interesting here to see how much better a good performance SS prop performs over a conventional aluminum prop.

It sounds like the SS Mercury prop you tried was a standard elephant ear "Vengeance" prop, which is why you had the slippage. They still run well, however, and are far superior to aluminum on any rig that will do over 30mph.

Lars Simonsen posted 06-12-2003 09:25 PM ET (US)     Profile for Lars Simonsen  Send Email to Lars Simonsen     
It wasn't the perfect day for a test run (at least not a day for a fair comparison to the day I ran with the mercruiser prop). There was a pretty good breeze blowing, and about 1.5-2 foot chop; I could get to WOT, but I don't think it was optimum conditions for testing top speed.

The boat was definitely higher on the water than before raising the motor, but again, it'll take a longer boat ride to tell how much difference the stiletto prop makes. The biggest noticeable difference was the "grip" of the prop, and the conditions were pretty good for putting that to the test.

All in all, I'm pleased with the results.

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