Thread Tools Search this Thread Display Modes
Old 10-10-2011, 02:15 PM   #1
Join Date: Oct 2011
Posts: 1
Default 2005 1800MX Prop selection

Hi guys,

Reasonably new owner of a 2005 1800MX 3.0L 135hp Mercruiser and looking for a bit of advice regarding props.

Usage is pretty much wakeboarding all over so not too fussed with regards to top end.

Current prop (came with it) is a Laser II 19p....Current performance is around 35mph top speed (sorry dont know rpm - new to this!!) (which seems low) and seemingly an age to plane.

What Im looking for a low speed planing and good hole shot. Prop selector on Mercury web says recommends high 5 19p - whats all your lot opinion and is the 35mph speed normal or a symptom of issues?

I can get a SH high 5 21p but not sure if thats too much pitch?

When giving it full throttle I get a fair bit of vibration as well which seems a bit odd (like the prop is ventilating).

Thanks all in advance

BenBaron is offline   Reply With Quote
Old 10-10-2011, 02:47 PM   #2

seapuppy's Avatar
Join Date: Nov 2005
Location: Everett Wa
Posts: 4,681

welcome to the zoo...
well..there's a few things we need to verify before you go plopping down tons of money on a new where are you located so you can buy us all beer...........(might wanna introduce yersef some)...
2nd is ..what is your wot rpm?? when your out on smooth water..hit the throttle to wide open throttle and see where the top speed/rpm is...
how much gear and people do you have on board the will tell you which way to move the prop ....
to answer your other question about may well be doing that or it may be spinning the prop thing you need to find out is 1)wot should be between 4200-4800rpm....2) how heavy the boat is with gear..(take everything off you don't need)....and what the prop condition nicks, dents, out of true...etc....take it off and to a prop shop to have it tuned back up...

now to answer your question about props....if you go up in prop 19 to will loose about 400 rpm off the top end and will probably gain some mph if you go down in 19 to will gain 400 4200 rpm to 42400 rpm or roughly 4300 rpm(acct for gauge error).......
going down will decrease your hole shot time or time to plane....going up will increase it.....make sense???


Don't compare your life to others. You have no idea what their journey is all about.
SSN683 Association member
Par Excellence
2008 Bayliner 340 - "Wild Whim"
I live in my own little world....but it's okay-they know me here!!!

Avid practitioner of the martial art: KLIK-PAO.

Anyone that sez "Size doesn't matter" has never owned a boat!
seapuppy is offline   Reply With Quote
Old 10-21-2011, 12:52 PM   #3
Lt. JG
Join Date: Jul 2008
Location: Lee's Summit, MO USA
Posts: 32

If its any help, i have a 1900SR2 witha 4.3L, i use an 18P 3 balde when i pull skiiers or am on a small lake... she drives like a vette but only has a top in around 35-40 MPH. When we go to larger lakes an I know I'm going to be running around alot (poker runs, bar runs, etc.), i'll put on a 21P 3 balde aluminum and my top end moves to 45-50 MPH but a lot less responsive out of the hole. I also use Smart Tabs to help get her on plane more quickly in all scenarios (love them)

Some will recommend stainless steel props but if you boat in areas like i do in the midwest where there is often sumbergred timber and other obstacles in the water, i recommend Aluminum props for the one reason a lot of folks hate them, they break easy. I'd much rather replace a $100-110 prop than the gears in my outdrive . Not sure where you live but check the web for a place called "midwest prop", they have great prices and service.
jkcoon is offline   Reply With Quote
Old 10-21-2011, 04:04 PM   #4

Join Date: Apr 2008
Posts: 4,656

All great points. The only thing i can add is, I doubt the prop will dictate how slowly you can run while still staying on plane. Tabs and trim will really come into play here. I don't suggest a hydrofoil. While that will give the stern lift and allow you to run on plane at slower speeds, the lift is being placed on either the drive and transom assembly, or the outboard and the transom mount, depending on whether it is an I/O or OB. You're better off suing tabs and trim which obtains lift from the hull. The smart should have manual adjustments which are statically set. Possibly try setting at a more aggressive setting. Otherwise, adjustable tabs such as bennet (hydraulic) or Lenco (Electric) might allow you more control and adjustability over a smart tab.

One more thing to keep in mind. If you're goal is not top end, but rather hole shots and slower speeds for towing sports, make sure not to go too low in the pitch. While lowering pitch will lower top end speed and decrease the hole shot times, you want to make sure that the Max. RPM is not exceeding the Max. RPM rated for the motor. In testing, you should still test WOT and make sure you remain within the range of the motor.
shrew is offline   Reply With Quote
Old 10-22-2011, 01:51 PM   #5
Lt. JG
Join Date: Jul 2008
Location: Lee's Summit, MO USA
Posts: 32

Would agree with Shrew on use of tabs for planeing, however I think on smaller craft (<20'), on-the-fly adjustable tabs can be dangerous, so i highly recommend the SmartTabs. I isntalled the SX model with 60# pistons and am extremely pleased with the results... planes faster, no more chine walking, and bites into turns. When looking for solutions i also considered hydorfoils but after researchinn further, decided I didn't want to drill holes in or put the stress on the outdrive... not that drilling 16 holes in the transom was any less nerve-racking
jkcoon is offline   Reply With Quote
Old 11-10-2011, 10:26 PM   #6
Join Date: Nov 2011
Posts: 5

all good advice. As long as your motor is in good working condition, those advices are true for a straight forward answer.

If you have 500 bucks to spend, I would buy a redline weber carb to replace the stock one. I have a 2008 maxum 1800mx with the 3.0 and the weber. I run a 21 pitch prop and with 9 people (I know, too many people), I can pull up a heavy tuber. If I have just me, my 0-30mph is 3 seconds. Hope that helps

gbf is offline   Reply With Quote

Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off

Powered by vBadvanced CMPS v3.2.3

All times are GMT. The time now is 01:26 PM.

Powered by vBulletin® Version 3.8.8 Beta 4
Copyright ©2000 - 2020, vBulletin Solutions, Inc.