4.3LX on 18', prop questions

[93maxum4.3lx]

boat: 93 maxum 18' open bow
motor: 4.3 LX ~ 190 HP
drive: mercruiser alpha 1.81 ratio
has a stingray hydrofoil installed
prop: mercruiser "Vengeance" 14x19 SS
GPS speed: 42mph @ 5000 rpm (would go higher if allowed)
load: full gas, 2 people

my reason for posting is to get some prop advice on the above setup. The supposed "max rpm" for this motor is either 4600 or 4800, but as currently propped it will go past 5000. On the other hand, the boat gets up on plane very easily as presently set up.

now, I imagine this setup would be just fine with more than two people in the boat, and/or pulling a skier; or at altitude. But, with only two people in the boat (which is half of my use) it seems a bit under propped.

I was looking at options to lower the WOT rpm a bit, maybe gain some efficiency WITHOUT sacrificing the hole shot; and one option I found is the mercury Laser II prop series, they have a 13.875 x 21 prop with exhaust ventilation holes drilled to help the hole shot.

so, to get to the questions...

1) any guesses on how much holeshot i'd lose (if at all) going from a vengeance 14x19 to a laserII 13.875 x 21? The laserII is advertised as "bow lifting", does this mean that (when planing) the boat will ride at more of an angle and thus be harder to see directly forward?

2) any other advice or recommendations? any good 14x20 props out there?

I don't care so much about the top speed MPH, but if there is more efficiency to be had without sacrificing the holeshot then I"d like to explore that.

thanks!!

 

[Tail_Gunner]

Re: 4.3LX on 18', prop questions

boat: 93 maxum 18' open bow
motor: 4.3 LX ~ 190 HP
drive: mercruiser alpha 1.81 ratio
has a stingray hydrofoil installed
prop: mercruiser "Vengeance" 14x19 SS
GPS speed: 42mph @ 5000 rpm (would go higher if allowed)
load: full gas, 2 people

my reason for posting is to get some prop advice on the above setup. The supposed "max rpm" for this motor is either 4600 or 4800, but as currently propped it will go past 5000. On the other hand, the boat gets up on plane very easily as presently set up.

now, I imagine this setup would be just fine with more than two people in the boat, and/or pulling a skier; or at altitude. But, with only two people in the boat (which is half of my use) it seems a bit under propped.

I was looking at options to lower the WOT rpm a bit, maybe gain some efficiency WITHOUT sacrificing the hole shot; and one option I found is the mercury Laser II prop series, they have a 13.875 x 21 prop with exhaust ventilation holes drilled to help the hole shot.

so, to get to the questions...

1) any guesses on how much holeshot i'd lose (if at all) going from a vengeance 14x19 to a laserII 13.875 x 21? The laserII is advertised as "bow lifting", does this mean that (when planing) the boat will ride at more of an angle and thus be harder to see directly forward?

2) any other advice or recommendations? any good 14x20 props out there?

I don't care so much about the top speed MPH, but if there is more efficiency to be had without sacrificing the holeshot then I"d like to explore that.

thanks!!

GPS speed: 42mph @ 5000 rpm (would go higher if allowed)
load: full gas, 2 people........how much Higher...

By lx do you mean it as 4bl carb?

 

[93maxum4.3lx]

Re: 4.3LX on 18', prop questions

GPS speed: 42mph @ 5000 rpm (would go higher if allowed)
load: full gas, 2 people........how much Higher...

By lx do you mean it as 4bl carb?

how much higher, maybe 5200-5300. it was still climbing at 5000 when i pulled the throttle back; it was "almost" done but still noticeably climbing.

lx = 4bl carb yes. advertised power is 180hp propshaft.

 

[93maxum4.3lx]

Re: 4.3LX on 18', prop questions

a few other bits of info

brochure weight for the boat with the 3.0L is 2190lbs, but I have the 4.3L.

30 gal fuel capacity (about 180 lbs)

transom deadrise 19*

don't know if it has a rev limiter

no real feel for accuracy of tach, but 42mph at 5000 seems right at 15.5% slip. so perhaps the tach reads 100-150 high, and/or the vengeance prop on it isn't so hot (i understand it's just a basic aluminum mold filled with stainless, NOT an optimized stainless design). or perhaps the maxum hull isnt that great.

anyways, i am now leaning more to a 4-blade, perhaps a titan4 or a bay pro II. 20" pitch. should keep all my present holeshot, run more efficient and maybe give a few mph up top? still concerned about "too much" lift though, and reports of chine walk..

 

[93maxum4.3lx]

Re: 4.3LX on 18', prop questions

sorry for the multiple posts, but in summary, my goals are:

(in comparison to my 14x19 vengeance SS):
* NO reduction in holeshot
* INCREASE in top speed
* INCREASE in overall efficiency
* SLIGHT decrease in WOT RPM is ok (up to 200 rpm)

and in summary, my questions are:
* would a vented 21p 3-blade (laser II, stiletto advantage II, or ?) meet my goals?
* would a 19p or (vented?) 20p 4-blade (bay pro II, titan4, or ?) meet my goals?
* which would give me the most gain?

I tend to be inclined towards a 4-blader to decrease plane speeds (family / ski / tube use) but I don't want to end up going any slower than I do now.

 

[donnymac]

Re: 4.3LX on 18', prop questions

You remind me of me About 3 months ago I was asking the same questions.
I have the 4.3 fuel injected Volvo. Heavier boat but similar numbers. Could we tweek it one way or the other. Sure, a 100 rpm less here a couple of mph there. Long story short, I'm happy with the boat and unless the lottery comes my way, the money goes in the tank and the fun starts now.

 

[Tail_Gunner]

Re: 4.3LX on 18', prop questions

21 pitch 3 blade stilletto

20pitch 4 blade stiletto

22pitch merc enertia big bucks and who know's...