Need prop pitch help! (hwsii and others, i need you!)

[blorr]

OK, I posted stuff about my boat several weeks ago and was told that it seemed that the motor was low on power. I took it in and had them test everything and they said it all seems to be fine. So, I'm just going to go with the best rec based on what I have right now. I would really appreciate everyone's input!!

Iboats Boat and Motor Info

1. Year, make and model of boat
1993 Dynasty bowrider

2. Length, width and base weight of boat, look for boat decal on back of boat
18' long
7'1" width
1775 base weight

2a.What is the maximum recommended HP for your boat
not sure

3. Number of people and gallons of gas normally on boat
4 people, 14 gallons

4. What do you use the boat for
slalom skiing

6. Year, make. manufacturer and model of motor
1993 mercruiser 4.3 liter V6

7. HP and gear ratio of motor IMPORTANT
175 hp.
I think 1.83

8. Manufacturer?s recommended Wide Open Throttle (WOT) range
4400 - 4800

10. Is it a bass boat or does it have a pad bottom
NO

11. Does it have a hydrafoil, dolefin or trim tabs
It does have a hydrafoil

12. Make, model, diameter, pitch, number of blades and whether SS or aluminum prop
I have two:
15X19 pitch SS Solas
Also a 15 3/4 X 15 pitch Mecury mirage plus

13. WOT RPM and speed from your current prop and how much gas and how many people were in the boat for the test data and is the speed by GPS. Make sure you trim the prop up until it starts ventilating and then just trim in until it quits ventilating. If you do not have a tach you can buy a digital tachometer and hour meter here: http://cgi.ebay.com/ebaymotors/Tacho...Q5fAccessories
First prop (the 15 x 19 SS Solas)
RPM __4200_______ Speed __37____ GPS __Yes, 37 on GPS____ No. of people __1____ Gal. Gas __16______

Second Prop (the 15 3/4 x 15 SS mirage plus)
RPM __4800_______ Speed __35____ GPS __Yes, 35 on GPS____ No. of people __1____ Gal. Gas __16______

14. Are you at sea level or a higher elevation, give us the elevation in feet
600 ft. elevation

15. Has your motor been tuned up lately and have you checked that the carburetor butterfly is opening all the way, checked compression, and looked at the plugs and checked spark as well as timing and advance, all of the foregoing could be the reason your prop is not attaining full RPM
I think everything is working well. It has been checked.

16. How long has this prop been on the boat and why, at this time, do you think it is the wrong prop
Just for the summer. I feel like they both underperform

17. Does the prop show any damage that you can see
NO

18. What problems are you trying to cure or what are you looking for the boat to do that it is not doing the way you think it should or to your expectations
I need good hole shot and would like to be able to maintain a slalom skiier at 36mph if needed.

THANKS SO MUCH FOR ALL OF YOUR HELP!

 

[hwsiii]

Re: Need prop pitch help! (hwsii and others, i need you!)

Blorr, in another post you stated that the Mirage Plus was getting 39 MPH, so I am kind of lost.

Re: 4.3 Mercruiser Prop Questions

Ok, here is what I got.

Had a 15X19 stainless prop and got 4100 RPM at WOT and top speed of 37

Put a 15 3/4 X 15 Stainless mirage plus prop and got 4800 RPM at WOT and top speed of 39.

I have a 16' Flats boat with a 40 HP motor and I run a 14" SS Apollo prop with an all up weight with me only of right at 1,500 pounds and I am able to get a touch over 30 MPH, and your boat with just you in it weighs right at 2,300 pounds with a 175 HP engine, does the difference in speed seem right to you.
I can only tell you, that in my opinion you are developing only about 125 HP from your motor, if your top speed is 39. You will not get hardly any more speed out of your boat by changing props.


H

 

[blorr]

Re: Need prop pitch help! (hwsii and others, i need you!)

Sorry for the confusion. My first post was a misprint! It is 35mph with the 15 pitch. I honestly don't know what to do from here. I had everything on the motor tested and they said it looks good. I know the guy and he is reputable. So at this point I'm just wondering if there is some kind of flaw in the hull design. I'm just trying to get the best prop I can get with what I have. Thanks so much for taking some time for me!!!

 

[hwsiii]

Re: Need prop pitch help! (hwsii and others, i need you!)

Blorr, I wish I had an answer to what is going on, it could be the hull or something else but I will be dadgummed if I know what. I do not want to give up on you, I want us to find the problem and fix it.
Have you taken the hydrafoil off and tried it without it.
Bring the boat to a junkyard or to the highway scales and weigh the boat on the trailer, maybe it has excess water in the hull.
Push the throttle all the way forward at the dash and look inside the venturis and make sure that the butterfly valves are completely vertical inside and make sure the connection to the back butterflies is working as well.
I want to ponder on this a little while to see what I can come up with.

The Mirage 15" is showing less than 8% prop slip at this time, so there is no better prop you can put on it at this time with the horsepower the motor is producing.

I started searching back through my records I found someone else I helped with this same boat, and he has a 5 Liter 200 HP I/O.

http://forums.iboats.com/showthread.php?t=329431&highlight=dynasty

Destro1975 Destro1975 is offline
Cadet

Join Date: Jun 2009
Posts: 8
Default Re: Prop recomendations?
Alright Solas Amita 4 blade 14x21 = 45MPH 4500RPM with 450lbs of people a 2 big full coolers.

and 4100RPMs @ 40MPH with 6 adults, 1 very large same big coolers.

Huge wake, overall I think the prop will work well for me most of the time I had a full/heavy boat most of the day overall I like the way the 4 blade handles and feels turns better and it more stable. I think a 20p 4 blade may be in my future.

Thanks!
Reply With Quote

H

 

[steelespike]

Re: Need prop pitch help! (hwsii and others, i need you!)

Very good idea to weigh the boat.Observe how it sits in the water does it seem excesively low in the stern?Does it list one side or the other?
Also as suggested by H remove the foil.It could be causing a couple of mph loss could be fighting the trimming affect.Trim tabs would be a much better choice.Smart tabs are passive and easy to install and most have very favorable results.Excellent factory support.
Did you ask the tech to check specific things or just to check.
Did they do a compression check and report figures?check and report throttle open all the way?Did the check the timing advance?
It has been my experience that mechanical advance sometimes gets corroded and doesn't work right.
When you trim up does the hull respond or does it continue to lay down flat?

 

[blorr]

Re: Need prop pitch help! (hwsii and others, i need you!)

They tested the compression and it was good in all cylinders.
I'll check the butterfly.
I'll also try to get it weighed.

Thanks! Brent

 

[blorr]

Re: Need prop pitch help! (hwsii and others, i need you!)

Am I figuring my dry weight correctly?

Here is where I'm getting it:
http://www.nadaguides.com/default.aspx?LI=1-24-38-5694-0-0-0&l=1&w=24&p=38&f=5697&m=0508&y=1993&ml=D&gc=MR&gtc=MR&d=1600061195

It says net weight is 1775. Is that with or without the motor?
I was figuring that it was with the motor, but if it is without the motor my weight is closer to 2200 without any people or gear.

Thoughts?

 

[hwsiii]

Re: Need prop pitch help! (hwsii and others, i need you!)

Those numbers are with the motor Brent.


H

 

[Moodrid]

Re: Need prop pitch help! (hwsii and others, i need you!)

I have a 94 18 foot Monterey with about same weight and width as you.It has the 4.3 v6 190 with a 4 barrel all stock.I bought it 4 years ago and it had a stock 14x19 aluminum prop on it.With me the wife and kid and full tank of gas and ice chest it would run 50 and turn 5700 or so rpm.Motor says do not exceed 4800.ooops.Did not know that till this year.A buddy let me try and since buy his prop.It is a 15x23 stainless Mirage.With it same load I run 55 and turn 4800rpm.Probly hit 60 or so if I burn out some gas and drink all my beer lol.A 14 x21 Mirage would probly do you good.If you try a 23 dont get the Mirage plus because they are cupped more.

 

[craze1cars]

Re: Need prop pitch help! (hwsii and others, i need you!)

These performance numbers sound identical to my "old" boat, which I still own...

1992 Rinker 181 bowrider, same length/width as yours. I believe this to be basically the same weight and setup as your Dynasty. The biggest difference being mine has a 3.0L 4 cylinder and a small one at that...rated at only 115 hp. And mine is a 1.98 ratio outdrive if I recall. NADA rates my weight at 2,000 pounds.

That boat with 3 people and full fuel/gear always gets 37mph GPS top speed with a 14.25 x 17 pitch Turning Point aluminum Hustler at about 4,600 rpm. Going to a 19 pitch of the same model resulted in exactly the same top speed at 4,200 rpm. So your boat is rated at 60 horsepower more than mine, with similar design, is listed as being 225 pound lighter, and we're at the same elevation. Yet they have nearly the exact same performance numbers? Not right. Your boat should easily destroy mine in a race...

You still sound very underpowered for a 4.3, or maybe very overweight as has been discussed if the boat happens to be completely waterlogged...but I would think it would need to have well over 500 pounds of water on board to slow it THAT much, which I don't think is even possible. And even with 500 pounds of full ballast bags in my wheezy boat and 3 or 4 people on board, I can still get it to 35 gps with no problem. So I do not believe excess weight is the problem.

Who did the "check" of your boat when you took it in? Steelspike asked much of this earlier, but I think it needs to be asked again...can you find out what were the actual results of the compression test? Did the place who tested this stuff provide you with any actual numbers? How many PSI in each cylinder? Did they check your ignition timing? What exact figure did they set it at? If your timing is retarded it will cost HUGE horsepower while the engine will run fine. If they tested it, did they test it CORRECTLY? Many Mercruisers of this vintage MUST have some wires disconnected to set the motor into a 'base' timing mode before checking timing...while some others can just be allowed to idle without setting a mode first. It depends on the ignition system. If yours has electronic advance (and I think it probably does) and he didn't follow proper procedure to set it in base mode, your ignition timing is WAY late, and this will definitely create the exact problem you are experiencing.

And while he was doing this, did he test your boat's tach also while he had a shop tach hooked up, or do you know for sure your boat's tach is accurate? Tachs in older boats are NOTORIOUS for being off significantly...you may be over-revving quite a lot and not even realize it? If it planes out nice and quickly I would suspect this is a possiblity. Or is it slow planing out too? You say you slalom...I do to...a lot. Does this boat pull deep-water slalom starts rather easily or do you drag a long ways? Please share the skiier's approximate weight when if you answer this...

While you're looking at the throttle butterflies in your carb, also see if the choke is open fully (straight up and down) when the engine is warm (with the understanding that it is supposed to be mostly or partially closed when the engine is cold). A stuck/partially closed choke will kill airflow thru a motor and will rob a ton of HP. Make sure you recognize that the choke butterfly is up top, and the throttle butterfly is down deeper in the throat, and that the deeper one should move directly with the throttle from wide open to fully closed at any engine temp. The choke one won't normally move much with the throttle being moved...it moves very slowly on it's own accord, depending on engine temp.

Maybe this was already discussed in your previous post which I haven't found or read, but are you trimming the motor out for max speed after it planes? Trim position can have a HUGE impact on speed...leaving it trimmed all the way down will literally shave off 10mph or more on many boats, depending on how the boat is designed. Trim it out and your RPMS and speed should both climb very steadily and noticably.

Is the bottom clean? I've had friends boats absolutely refuse to plane after they sat in a slip for a few months and grew their own "green carpet"...simply trailer them to the power washer, blast off the "carpet", drop them back in the water, and they go like rockets! So I have seen bottom grime from sitting in slips easily rob 10mph or more.

I'm obviously just shotgunning this, but it sure seems something just isn't adding up completely...I figured a few ideas might help just a little bit.

Good luck in honing in on the problem. But from what I see here, I do not believe the biggest part of the problem is in your prop.