Could a 4 blade actually be faster?

[Winner1750]

I'm going out if my mind trying to figure out what prop I need. I have an 87 Winner Escape 1750 with the 130hp 3.0 Mercruiser and alpha 1 gen 1 1.98 ratio. I have always used 14.5x19p which is what came on the boat, but it always over revved at WOT to the tune of 5000-5300 RPM. This particular 130hp version has a WOT range of 4200-4600. The problem with that 5000 RPM is that I am only going 32 mph (GPS verified) and at 27mph at 4000 RPM. According to the 3 slip calculators I used that equates to between 25-30% slip. That seems really high to me. I did try a 14.25x21p. It was definitely faster but took for ever to get out of the hole and still revved up to 5000 RPM eventually, so I returned it (thank you Amazon).
So my question is, is a 4 blade the answer? Will it give me less slip/more grip, therefore giving me more speed. I know the common thinking is that 4 blades are slower but with that amount of slip I feel like grip is the answer. Any amount of advice will be appreciated.

 

[Scott06]

I'm going out if my mind trying to figure out what prop I need. I have an 87 Winner Escape 1750 with the 130hp 3.0 Mercruiser and alpha 1 gen 1 1.98 ratio. I have always used 14.5x19p which is what came on the boat, but it always over revved at WOT to the tune of 5000-5300 RPM. This particular 130hp version has a WOT range of 4200-4600. The problem with that 5000 RPM is that I am only going 32 mph (GPS verified) and at 27mph at 4000 RPM. According to the 3 slip calculators I used that equates to between 25-30% slip. That seems really high to me. I did try a 14.25x21p. It was definitely faster but took for ever to get out of the hole and still revved up to 5000 RPM eventually, so I returned it (thank you Amazon).
So my question is, is a 4 blade the answer? Will it give me less slip/more grip, therefore giving me more speed. I know the common thinking is that 4 blades are slower but with that amount of slip I feel like grip is the answer. Any amount of advice will be appreciated.

First verify your tach is accurate vs a shop tach or tach in a modern timing light. I would doubt a 3.0 will swing a 19" to 5300, so if tach is off there is some of your slip issue (rpms arent actually that high). Is the prop in good conditon?

Four blades generally are slower, I ran two pitches of michign vortex 4 blades on my sea ray 170/3.0 a 16" for skiing (would over rev) and an 18" for general use. I lost some top speed (3-4mph) but gained so much more in the more used rpm ranges like holeshot, lower planing speed and stern lift).

On my current boat sea ray 200 sport, a 4 blade is actually faster. I get slightly higher top speed with a revolution 4 than a enertia because I can trim out more and get more of the hull out of the water as the Rev 4 still has grip closer to waters surface. I doubt this is the case with your boat as it is much lighter and less beam... I suspect the tach is off otherwise the 21" would work ok...fix that before messing with props

 

[dingbat]

No getting around the physics of an extra blade. More surface = more friction

Ran a 4 blade for years. Switched to a Enertia prop 2 years ago. Hole shot, fuel economy and top speed all improved going to the 3 blade.

 

[Winner1750]

First verify your tach is accurate vs a shop tach or tach in a modern timing light. I would doubt a 3.0 will swing a 19" to 5300, so if tach is off there is some of your slip issue (rpms arent actually that high). Is the prop in good conditon?

Four blades generally are slower, I ran two pitches of michign vortex 4 blades on my sea ray 170/3.0 a 16" for skiing (would over rev) and an 18" for general use. I lost some top speed (3-4mph) but gained so much more in the more used rpm ranges like holeshot, lower planing speed and stern lift).

On my current boat sea ray 200 sport, a 4 blade is actually faster. I get slightly higher top speed with a revolution 4 than a enertia because I can trim out more and get more of the hull out of the water as the Rev 4 still has grip closer to waters surface. I doubt this is the case with your boat as it is much lighter and less beam... I suspect the tach is off otherwise the 21" would work ok...fix that before messing with props

I believe the tach is accurate. The reality is that whether or not it is, I'm still only going 32mph at WOT in a small boat with a 19p. It just doesn't seem right. I feel like it should be in the 38-42mph range. Am I wrong?

 

[racerone]

Have your boat weighed.----At one time " winner boats " used individual plastic containers for flotation.-----Not sure about yours.-----If boat is water logged it will be slow !----Note---Some high performance offshore boats use 5 blade props.-----Blades may not all be in the water all the time.

 

[Winner1750]

Have your boat weighed.----At one time " winner boats " used individual plastic containers for flotation.-----Not sure about yours.-----If boat is water logged it will be slow !----Note---Some high performance offshore boats use 5 blade props.-----Blades may not all be in the water all the time.

I think mine has foam. I don't believe that to be the issue as it has been this way for the 8 summers I've owned this boat. Although I guess it could have always been waterlogged. I have considered this in the past, but my gut is telling me that is not the issue.

 

[Scott06]

I believe the tach is accurate. The reality is that whether or not it is, I'm still only going 32mph at WOT in a small boat with a 19p. It just doesn't seem right. I feel like it should be in the 38-42mph range. Am I wrong?

I think 38 is probably about the realstic top end for a 3.0 .that is what I saw in my 170. Might be worth weighing your boat or seeing if water is under the floor given the age of it.

The slip numbers are really high, so would think either the boat is way heavier or tach is wrong. Easy to double check tach but its your call

 

[Scott Danforth]

I hit 41 in a 16.5 foot long boat with total weight in the 1800# range with a 3.0 spinning a 19p prop at 4600 RPM with light chop and only 1 person on board.

no way a 3.0 can spin a 21p prop at 5300 RPM without nitrous or a blower. no way a 3.0 can live above 5000 RPM for very long. first, the head warps, then the pistons come out and swap bores. no way the 3.0 loaded can spin that fast under load because the head wont allow it to breath enough to spin that high.

your tach is way way way off. most likely your tach is set to 6 cylinders or the tack is simply whacky. if your tach is set to 6 cylinders so your RPM would be 3533. 5300/(6/4).

looking at your boat, at near zero slip, you would be spinning 3530 RPM at 32mph with a 19p

so go back and check your tach.

 

[Winner1750]

I hit 41 in a 16.5 foot long boat with total weight in the 1800# range with a 3.0 spinning a 19p prop at 4600 RPM with light chop and only 1 person on board.

no way a 3.0 can spin a 21p prop at 5300 RPM without nitrous or a blower. no way a 3.0 can live above 5000 RPM for very long. first, the head warps, then the pistons come out and swap bores. no way the 3.0 loaded can spin that fast under load because the head wont allow it to breath enough to spin that high.

your tach is way way way off. most likely your tach is set to 6 cylinders or the tack is simply whacky. if your tach is set to 6 cylinders so your RPM would be 3533. 5300/(6/4).

looking at your boat, at near zero slip, you would be spinning 3530 RPM at 32mph with a 19p

so go back and check your tach.

It will spin the 19 up to 5300 if I'm light 5000 heavy. The 21 maxed out at 5000. I forgot to GPS the speed with the 21, but the seat of my pants told me it was faster for sure. I used it once and promptly returned it because it took about a year get out of the hole. I am starting to question my tach now though. Again I still feel like 32 with a 19p at WOT seems slow to me no matter what the RPMs are. I'm concerned about the weight now too. It doesn't sit any lower in the water than it ever did. Would that be affected by being waterlogged?

 

[QBhoy]

Check your speed with gps first. I’d think.
I’d also suggest that a 19” ally generic prop will certainly see you under propped and over revving here.
a 21” would be better. But depends what 21”
To answer the question around will a 4 blade be faster. It’s a tough one to answer. But simply…will it be faster…the answer would be yes…if you were to compare a 4 blade bravo or 4 blade Rev 4 to a same pitch 3 blade solas ally or any other cheap ally prop. Would a 4 blade be faster than a like for like pitch tempest or enertia 3 blade ?…almost certainly not. Physics are usually not to be argued with. Mostly !

 

[QBhoy]

Can I be a little cheeky perhaps ? Apologies and disregard if it’s not the case or relevant…
Are you fairly new to boating ? If you aren’t, don’t read any further. If you are, it may be the case that you are trimming up too high and having a detrimental effect on things. An ally prop won’t take too much trim before it loses grip. When this happens…you sound as if you are going faster…but the reality is that you actually drop speed and will over rev. This would explain all and the horrendous prop slip too.
with a good stainless prop…it will take so much more trim and keep a hold of the water better before losing a hold of it.

 

[Scott Danforth]

It will spin the 19 up to 5300 if I'm light 5000 heavy. The 21 maxed out at 5000. I forgot to GPS the speed with the 21, but the seat of my pants told me it was faster for sure. I used it once and promptly returned it because it took about a year get out of the hole. I am starting to question my tach now though. Again I still feel like 32 with a 19p at WOT seems slow to me no matter what the RPMs are. I'm concerned about the weight now too. It doesn't sit any lower in the water than it ever did. Would that be affected by being waterlogged?

put a certified laser tach on that motor to verify your RPM's. you may want to do some reading on the GM inliners over at http://inliners.org/ if you want to understand why these motors dont go above 5k without serious valve/lifter/cam/head/intake work