Low RPM's and slightly slow speeds: 1994 Sea Ray 180 4.3L

zul

Petty Officer 1st Class
Joined
Aug 24, 2015
Messages
235
Had my "New to me - Used boat" out twice now. Here's what I've got so far:

14x19 pitch 4 blade, cupped VenSura.
1.84R gear ratio on Alpha 1

41 mph @ 4400 rpm's (trimmed up) - one person and half tank of gas.
This is using dash info and GPS.

Thinking that I should get some more speed out of this setup (most similar boats are getting around 45 or better). Shows great power in pulling skiers but the bow rides high on take-off, boat takes it's time to plane and it's sorta slow outta the hole. The power is there for skiing but hopeful to improve the take-off / hole shot?

It does want to cav when trimmed up high at WOT, so I've gotten best results by backing off the trim a bit to get these results. I've gotten it up to 4500 rpm's but it was cav'ing and squirly and lost some speed.

Prop seems in fairly good condition, very few and very small pits or dings. So 'fairly' new condition prop, not perfect.

I'm not a speed freak but I do barefoot waterski and have a need for that extra 2-3 mph. With this setup, I'm only getting 37 mph with 2 people in the boat and me skiing on back. Not quit fast enough for barefoot.

SO - Would changing prop help my top end speed? And which direction to go? Those RPM's are already on the low end (4400-4800 recommended)

Thanks in advance!

zul in AZ
 

alldodge

Moderator
Staff member
Joined
Mar 8, 2009
Messages
40,581
I would suggest trying a 21x3 blade prop. You won't get the same lift but should get more speed. Everybody seems to want a 4 blade, but they can also hurt performance
 

Chris1956

Supreme Mariner
Joined
Mar 25, 2004
Messages
27,036
I had an '88 SR 19 foot bowrider with the 4.3LX motor. It had similar performance to what you are seeing. Trim Tabs will help you get on plane faster, and with less bow lift. Obviously put them down for take off and up for cruising. I would therefore not recommend non-adjustable tabs.

A bow lifting prop might give you some better speed, but barefoot skiing speed will be a stretch.
 

steelespike

Supreme Mariner
Joined
Apr 26, 2002
Messages
19,069
Your gear ratio 1.84 seems to indicate a 190 hp 4.3. Alldodge is on to something Your prop is cupped and being a 4 blade it may be holding you back.
Cup adds about 1" in pitch when calculating..
I second the 21" 3 blade.
I think that a 4.3 should be close to 50 mph Your 41 mph is about what a 3.0 would do in a 180.
but it would lack power for water sports.
 

Sea Rider

Supreme Mariner
Joined
Sep 20, 2008
Messages
12,345
You should be trimmed for combo to run parallel to water level while on plane, check if this set up betters top speed.

Happy Boating
 

jimmbo

Supreme Mariner
Joined
May 24, 2004
Messages
12,944
I'm really partial to the Mercury Enertia props. A 20 inch should be about right for you uses
 

zul

Petty Officer 1st Class
Joined
Aug 24, 2015
Messages
235
So I will purchase a Mercury Enertia prop and it looks like I have 2 options for $540:

1. 13.8 x 21
2. 13.75 x 20

Can anyone guess where the RPM's might end up considering I'm at 41mph @ 4300 rpms with my current 4 blade 14 x 19 cupped?

Also, with the Flo Torq II: Will this hub protect the outdrive if I hit sand at slow speed or cruising hard strike? Sad to imagine damaging an expensive prop and more sad to wreck the out drive. My boating friend swears by aluminium props but thinking SS is the way to go ... ?!?

Thanks again for the help. I'll report back in a few weeks when the new prop is set and tested. I'll be saving up for the hydro trim tabs as that looks like a $1,000 project, maybe next year...
 
Top