Performance check..........is this about right?

[geoff-nz]

I have a cx-19 Glastron with mcm130 mercruiser and alpha1 drive. The drive is a new SEI replacement but there is some confusion at the shop where the work was done as to what ratio drive was fitted. He thinks it was a 1.61 from memory. I have used the mercury prop claculator and if I programme it as a 1.98 drive I get 9% slip which sounds too good to be true. At 1.61 ratio it claculates 26% which is horrible.

The boat came with a stainless 21" propeller but would only rev out to 3600rpm when I brought it, and barely make it onto plane so I fitted a Solas Rubex 14 1/2x 17" 4 blade aluminium. I intend to buy a 3blade as well for a bit more top end when lightly loaded.

I now get 4200rpm WOT at 31mph with 4 POB, 31gal fuel and heaps of gear for an overnight fishing mission.

I'm pretty happy with that as its a heavy lump of a boat, but thought I would get on here and ask if thats what I should expect performance wise for this boat/engine combination.

This question isnt really about props but more I am trying to get a gauge on the performance/condition of my Mercruiser engine. Economy is real good, almost on a par with my 60hp 2 stroke outboard on a much smaller boat.

What are your thoughts?

Cheers Geoff

 

[86 century]

Re: Performance check..........is this about right?

Your speed doesn't seam to be to far off.

Have you tested the new prop with a lighter load to see what your Max rpm is.

Just for reference our 19.5' searay would run 34mph with the same prop at around 4800rpm.

 

[Don S]

Re: Performance check..........is this about right?

The 3.0L engines use a 1.98 gear ratio.

 

[geoff-nz]

Re: Performance check..........is this about right?

Your speed doesn't seam to be to far off.

Have you tested the new prop with a lighter load to see what your Max rpm is.

Just for reference our 19.5' searay would run 34mph with the same prop at around 4800rpm.

Hi 86 . thanks for your reply. Thats the kind of info I was looking for.
I'm thinkin with only 2pob and a large humminbird transducer removed as well as no bedding, cooker, food etc that 34 may be achievable.

I just wanted to make sure it was running in the performance ballpark that it should be.


Hi Don.

I knew that 1.98 is the correct ratio but when I asked the mech who did the leg change for the previous owner he said he thought (going by memory as it was a year ago) that he had supplied a 1.61.
I thought it strange that the boat came with a 21" prop which the previous owner said performed well but when I finally got it on the water just struggled and barely planed. I had to put this down to one of two things........ the wrong ratio supplied or, the engine has issues. Thats why I asked for replies from people with similar rigs. Based on 86's reply I am thinkin I am on the right track and the mechanic has fitted a 1.61 drive in error (which is ok with me), I just need to get the correct prop sorted.Or it has the correct drive and 17" is the correct pitch for this setup. Either way is a win/win for me as mercruiser stuff costs big money over here and no way can I afford a new 3.0L engine for $12K

Does that sound logical. Sorry for the long winded post.

Any one else running a 19/20ft boat with mcm 130 mercruiser please feel free to chime in with your performance figures so I can get a baseline idea of what mine should be able to acheive.

Cheers Guys!

Geoff

 

[HT32BSX115]

Re: Performance check..........is this about right?

I programme it as a 1.98 drive I get 9% slip which sounds too good to be true. At 1.61 ratio it claculates 26% which is horrible.

You may still be over propped with a 4blade 17. You might try a 3 blade 17p and see what happens. Don't expect a huge improvement though. A 3.0L engine is not a super "power house"

I believe Mercruiser rates the 3.0L engine 4400-4800. They also recommend (as do most all engine mfrs) propping for the upper end of the range meaning you should be turning 4800 at WOT (when loaded with a typical load of people/gear/fuel/etc) to get best performance.

It might also be good to just check the ratio of that drive so you know for sure.

Good luck,


Rick

 

[fishrdan]

Re: Performance check..........is this about right?

I fitted a Solas Rubex 14 1/2x 17" 4 blade aluminium.... I now get 4200rpm WOT at 31mph with 4 POB, 31gal fuel and heaps of gear for an overnight fishing mission.

For the load, that sounds about right to me. I have an older 140HP Mercruiser in a heavily loaded 18'er turning an 18P 4 blade prop and run around 35MPH at 4600RPM. With a bunch of people/gear on board and it will drop to 30+ at 4200RPM. I think you need a lower pitched prop to get the RPM's up, 4200 is below Mercruiser's recommended WOT RPM for your 3.0L engine. (4200 is within spec for my older engine)

 

[geoff-nz]

Re: Performance check..........is this about right?

Awesome guys, thanks for the feedback. I will be going out in the next couple of weeks with much less weight onboard so I will see what I get and judge my future prop choice from that.

Thanks agin

Geoff