Slip

[spdracr39]

What are reasonable slip numbers for 3 blade aluminum vs stainless? Also if a 4 or 5 blade reduce slip why don't they make you go faster if you are turning the same rpm? Just trying to get a better understanding of how this works. according to my calculations I am getting about 16% slip with an average load ( three large adults plus gear and fuel) using my solas rubex three blade alum 14x19 and that seems high to me but maybe normal I just don't know. If I go to my 14x21 three blade solas new saturn stainless ( which is too much prop for my boat ) I get only 11% slip and go faster but can't get the rpm's up.
Here are my numbers:

14x19 alum 3 blade solas rubex
rpm 4200
gear ratio 1.47
speed 44mph gps
slip 11%
hole shot is good

14x21 3 stainless 3 blade solas new saturn
rpm 4000
gear ratio 1.47
speed 48 mph gps
slip 11%

I was thinking about maybe a 17p 4 blade stainless (undecided on brand) or a three blade stainless enertia 19p
The dealer recommended a 17p high 5. I don't really want to lose any more top speed than necessary but want to get a better pull for the kneeboard and tubing.

 

[QC]

Re: Slip

I'm confused about a few things . . . The 5.0 MPI uses a 1.62 gear ratio, so that's one. Also seems light on power. What altitude? Can you make her porpoise? Load? Trimming out etc?

If the 1.47 is right, then I understand the low RPM and speed. Yes sounds like you need a 17, tha thing is supposed to spin between 4600 and 5000 RPM.

To answer your question about slip with 4 blades, RPM goes down with a 4 or 5 blade so you lose speed with the RPM loss pushing the extra blade(s).

 

[spdracr39]

Re: Slip

We are only a few hundred feet above sea level. I will look again and make sure of the ratio but I am pretty sure. I was thinking 17 also so you think a 17p three blade is the way to go?

 

[QC]

Re: Slip

1.47s were for the 350 Mag, so someone would've had to swap the drive.

 

[spdracr39]

Re: Slip

So if it is the 1.47 would a 15P be too much ? I had another person in the boat yesterday and the rpm's would only hit 4200. I am not interested in top speed as much as just running it in the proper range with the optimum load on the motor. It is sensitive to porpoising and the tabs help but the trim settings still don't seem right. I have to stay trimmed way down compared to my last boat ( same model just a few years older ).

 

[coopin87]

Re: Slip

I have a 1.62 I would be willing to trade you for that 1.47 lol

 

[spdracr39]

Re: Slip

Thanks for the offer if you were next door maybe
I seem to have gotten away from my original question. With an average load what is a reasonable slip percentage ?

 

[QC]

Re: Slip

Well a WAG from me would be 8 - 15% . . .

 

[spdracr39]

Re: Slip

Thanks. I am going to try a 17p three blade stainless Apollo and see how it goes. They have a great sale here and it will make a good spare if nothing else

 

[QC]

Re: Slip

Good plan. I am still very interested in what your gear ratio is. Please post up results on the 17 too. Good luck!

 

[spdracr39]

Re: Slip

I will post that ratio and s/n tonight maybe you can tell me the vintage of the outdrive. I noticed when I bought the " only 70hours" boat the corrosion plates looked very corroded for a 4 year old boat but over all it was in great condition. It also had an aftermarket prop that looked like new which also was a flag. The gear lube looked good and everything functioned perfectly so I bought it and love it. I bet they ruined the outdrive and traded it in.

 

[spdracr39]

Re: Slip

The drive is a 1.47 s/n 1a201471 and has these stickers on it.

the ratio is stamped on the side.

 

[QC]

Re: Slip

Well that explains/confirms it. I think I'd like to see numbers with the 17. Good luck!! She can't get worse that way. Hole shot should definitely improve, even over the Aluminum, so give it a rip.

 

[spdracr39]

Re: Slip

Is there anyway to know the year the outdrive was made? I'm just curious how old it is compared to the boat.

 

[QC]

Re: Slip

Checking for some help on that.

 

[Fun Times]

Re: Slip

Is there anyway to know the year the outdrive was made? I'm just curious how old it is compared to the boat.

Your boat came with engine serial number 1A051639 Model # 4M4102LUS MERCRUISER 5.0L MPI ALPHA W/DRAIN 5.0L ALPHA MPI Manufacture Date:05/09/2007

But swapped to engine serial number 1A348745, Model # 4M4122LUU MERCRUISER 5.0 A EO 5.0L ALPHA MPI Manufacture Date: 07/17/2009. Note on 07/23/2009 the MOTOR WAS BLOWN, A dealer SWAPPED WITH NEW MOTOR S/N 1A348745.

DRV: 1A201471, Model # 5121200TS MERCRUISER ALPHA 1.47:1 Manufacture Date: 10/15/2007
TRN: 1A120553, Model # 6111001LS MERCRUISER ALPHA TRANSOM Manufacture Date: 05/08/2007

 

[QC]

Re: Slip

Thanks Fun Times, that's backwards as to what I thought. Figured the drive had been swapped. Is it typical that they would use the 1:47 in that boat? I understood the 5.0 was mated with a 1.62.

 

[spdracr39]

Re: Slip

Wow a plethora of Information !!!! Thanks !!
And that also makes me curious, are you magic ? How did you get all that about the engine from the drive serial number ????

 

[Fun Times]

Re: Slip

Thanks Fun Times, that's backwards as to what I thought. Figured the drive had been swapped. Is it typical that they would use the 1:47 in that boat? I understood the 5.0 was mated with a 1.62.

No problem QC.

On average it appears as though the 20 & 21 ft tahoes are using the 1.47R with the 5.0 mpi 260 hp and their 22 ft boats with the 5.0 mpi 260 hp are using the 1.62R.

Mercs alpha gear ratio cut off between using the 1.62 & the 1.47 seems to be the horsepower rating of 260 hp on smaller boats as you can tell by looking at the bottom of this chart for example,
http://www.seilermarine.com/info/mercruiser-drive-ratio-chart.php
5.0 Liter 230 5.0/305 8 1.61 24-24 1991-2005
5.7 Liter 260 5.7/350 8 1.47 20-22 1991-2005

The gear ratio is an option for the boat manufacturers to choose but you're right QC, The 1.62R would be a better fit for this particular boat especially if spdracr39 is going to load the boat down with the big boy's, etc, etc. Possibly the reason the boat needed a new engine from what i had read.

Primary gear ratio for the 5.0 mpi alpha 260 hp should be the 1.62
The optional ratio would be 1.47
high altitude would be 1.81:1
As noted below
http://www.lakeconroemarine.net/Mer...0L_MPI_Engine/mercruiser_5_0l_mpi_engine.html

No magic spdracr39, In some cases, Mercruiser dealers are able to look up some basic information using serial numbers is all. Computer technology nowadays.

 

[QC]

Re: Slip

Made that gear ratio chart into an Excel file (Open Source Document, ods) if anybody wants it.

Thanks Fun Times!!!