Better prop choice?

[PatinIdaho]

Boat is a open bow V hull 18.5F, loaded normal is about 2200lbs, 190HP(470), 1.84 GR Alpha 1,
Prop is a 14.25X21P Black Max(new)
WOT is 4600@34mph(gps)
25mph(gps)@3200 rpm. Prop slip using the calculators out there say 28% slip!
I don't think i have any numbers wrong. Tach was verified up to 2K using a hand held tach and they both matched. Speed was measured with GPS.
Seems like i could do better with a different prop but unsure where to start and would appreciate the advise.
Thanks.

 

[jimmbo]

A Pre 83 Mercruiser 470 is 170 HP with a WOT range of 3800 - 4200 rpm, in 84 or 85 the spec was still 170 HP with WOT range becoming 4200 - 4600

Your numbers aren't adding up.

 

[PatinIdaho]

Ok. Maybe im wrong on what im calling it. It is a 1986. Here is the tag

 

[jimmbo]

Having the right info makes a big difference. OK it's not a 470, it is a 190. I and maybe others, wouldn't have been chasing info down for the 470.

4600 rpm with a 21 inch prop assuming the gear ratio is still 1.84:1(what does it say on the Outdrive?)... That should move the boat about 44mph, assuming 12% slippage.
3200 rpm, 30mph 12% slippage.

You compared the tach reading with another, but only to 2K.

GPS speed. Where you checked the speed, does that lake or RIver have a Current?

Have you actually weighed the Boat?

 

[PatinIdaho]

Speed is on a very slow moving LARGE lake
the other tach I checked the boat tach with is a dwell/tach gauge that only reads rpm to 2k
The GR stamped on the outdrive says 1.84.
I have not weighed the boat but all transom and core samples are dry solid wood.
After thinking about it I'm thinking weight distribution could be the problem.
I have 2, 65 pound batteries for the trolling motor mounted in the ski locker. Starting battery at rear
And there were 2, 250 pound guys sitting near the rear.

 

[PatinIdaho]

Should add. 3 ppl total. Me and the other two guys
So maybe total weight was 2800? Lbs

 

[jimmbo]

Are you trimming the outdrive out as the speed goes up after getting on plane?

 

[PatinIdaho]

Yes I did.
this weekend I'll have time to test again with just me and wife.
ill try to find a scale also but small town and no truck stop.

 

[nola mike]

Similar numbers on my '86 3.7L as far as the boat/weight, #1700 unloaded. I hit upper 40's easy by myself, and 35 without any sweat in a boat loaded like a refugee escape...Currently using 23p aluminum.

 

[PatinIdaho]

Yeah im pretty sure having 5 or 600 pounds near the stern is the problem. Had zero weight up front to balance things out. May need to figure out how to move batteries forward. All just a guess at this point till i get to the lake this weekend again.

 

[QBhoy]

Every day is a school day on here. I honestly didn’t know the 4 pot 470 had a 190hp version. Thought they all 165 or 170.

 

[nola mike]

Only for a year or two I think. Had a 4bbl carb, pretty rare.

 

[PatinIdaho]

Yeah 4bbl carb. Quadrajet.

So today i was able to hit 28.5(gps) 2Adults(380lbs) and a full tank gas. 25 gallons(155lbs)
For the life of me i can't remember for sure but at 4200 rpm i think i was at 36/37mph. Wound it out to 4600 rpm but forgot to check speed before i backed out of it :facepalm:
I could wind it out to 4800rpm as that's max but i don't wanna push it that hard. Trimmed all the way in it gets up on plane easy with out much bow rise at all and then trim it out so i think i can go with a 23P prop with out a problem?.
Might order one and see how it acts with that on it.
Also the two trolling batteries(120lbs) in the ski locker sit about 3/4 of the way back from the front. Wonder if i moved them as far forward as i can about 1/4 of the way back from the front would make much of a difference?

Should also ad the boat is a 1986 Blue Water 18.5 Executive open bow. IBoats spec says 2300 pounds dry. How accurate i dunno?

 

[Bikestdy]

In order to be able to help you choose a better prop you will need to push it as hard as it goes with a normal load (gear and people). If it will go over 4800rpm we need to know how much over (don't hold it there long, just long enough to see how high you rpms get), also need to know how your using the boat ex water sports, general cruising, goals of max speed or hole shot.

 

[danieljkramer]

Following this - New boater, got a 1986 Wellcraft 192 American with MCM 170. It feels underpowered, only getting up to about 3500 RPM and about 25 mph. I am trying to work through throubleshooting the engine (timing, fuel delivery, compression), but also doing propeller research. After forum searching, this thread has some of the most comparable boat/engine setups.

I originally wanted to reduce my pitch to get my RPM's up, but I'm also seeing people with 23" pitch props (@nola mike) doing just fine and reporting 40+mph. Is is possible my diameter is too big?

Also note: my goal is a better/healthier/faster cruising speed to get from place to place quickly / efficiently. Not doing any hole shots or pulling skiers.

Thanks!

 

[GA_Boater]

Following this - New boater, got a 1986 Wellcraft 192 American with MCM 170. It feels underpowered, only getting up to about 3500 RPM and about 25 mph. I am trying to work through throubleshooting the engine (timing, fuel delivery, compression), but also doing propeller research. After forum searching, this thread has some of the most comparable boat/engine setups.

I originally wanted to reduce my pitch to get my RPM's up, but I'm also seeing people with 23" pitch props (@nola mike) doing just fine and reporting 40+mph. Is is possible my diameter is too big?

Also note: my goal is a better/healthier/faster cruising speed to get from place to place quickly / efficiently. Not doing any hole shots or pulling skiers.

Thanks!

This thread ended over a year ago.

Closed.