Update on a 3 blade to 4 blade prop switch

[truckermatt]

Just wanted to let people know my experience with change from a 3 blade to a 4 blade prop.

Engine is a 4.3L 175hp and alpha one drive.

I started with a 14.25x21p 3 blade Alum. 46mph and 4700rpm @ WOT

I went with a 14x20p 4 blade alum. 45mph and 4500rpm @ WOT


I knew my rpms would drop a little, so I guess I could have used a 4 blade 18p prop.

I have happy with the prop after my first run yesterday, didn't feel much different, but we only had to people on board, so time will tell when we load it with 6 and go skiing.

 

[Texasmark]

Re: Update on a 3 blade to 4 blade prop switch

I knew my rpms would drop a little, so I guess I could have used a 4 blade 18p prop.

I have happy with the prop after my first run yesterday, didn't feel much different, but we only had to people on board, so time will tell when we load it with 6 and go skiing.

That's what your data is saying. You may be disappointed when you add the extra load of more bodies and water toys. Also with the 18 your hole shot and ability to get up skiers and all will be greatly enhanced. You probably won't believe you are in the same boat. So what if you loose a little top end, right. You can't tell the difference between 40 and 45 anyway if you don't look at the speedometer.

 

[truckermatt]

Re: Update on a 3 blade to 4 blade prop switch

That's what your data is saying. You may be disappointed when you add the extra load of more bodies and water toys. .

So your saying that I may not have gained anything in reality by going with the 20p ?

 

[Texasmark]

Re: Update on a 3 blade to 4 blade prop switch

I'm saying the extra blade made for more drag....takes power to spin it. With a limited amount of engine power, your data shows that you are into your reserve. Therefore additional load, like when you fill the boat with folks and water toys, will pull your rpms down even faster than they did with the 3 blade.

Dropping your pitch, as you mentioned, will take that load back off the engine and give it some room to perform.

It is a trial and error thing. Every situation is unique but the data is there and it has had meaning in other similar applications. You may have noticed in other threads on the subject that folks in the know do recommend dropping pitch when you add the 4 blade for the reason you are experiencing.

Personally, I'd get the 18P prop.

Mark

 

[truckermatt]

Re: Update on a 3 blade to 4 blade prop switch

I will see if I can try the 18 pitch prop. hope i can get to around 4700-4800 rpms

 

[truckermatt]

Re: Update on a 3 blade to 4 blade prop switch

Well i tried a new prop today. My top speed went down a little but rpms stayed about the same. do you think this is OK?


Michigan Wheel 14.5x18p 4 blade 4600rpm @ 42mph

Hole shot was better (with 2 people) still have to try it with a full load. I dont really run WOT much, but my crusing speed increased, 2500rpm @ 25mph

 

[fishrdan]

Re: Update on a 3 blade to 4 blade prop switch

I started with a 14.25x21p 3 blade Alum. 46mph and 4700rpm @ WOT

I went with a 14x20p 4 blade alum. 45mph and 4500rpm @ WOT

Michigan Wheel 14.5x18p 4 blade 4600rpm @ 42mph

Something doesn't sound right as your RPM's should have been changing more with the prop swaps. I just read this and thought you were going to overshoot the WOT RPM going to a 18P 4 blade, but the engine only gained 100RPM by dropping 2" of pitch, it should have been +300-400RPM. Are you dealing with loss of engine performance due to atmospheric conditions (hot/cold/humid/dry) or engine tune (plugs/wires/filters/fuel)?

My engine runs far better and turns more RPM in February's 40-60* temps, than it does in August's 100+ temps.

 

[truckermatt]

Re: Update on a 3 blade to 4 blade prop switch

the test of the 20p 4 blade was 75 and no humidity and the 18p was about 83 and pretty humid... engine runs flawlessly

I would have thought i would get more rpms also.

Maybe my little v-6 doesnt have the power to turn the 4 blade

 

[fishrdan]

Re: Update on a 3 blade to 4 blade prop switch

The weather conditions were pretty close, but 83* with high humidity will make less power than 75 and dry, probably insignificant... Our last trip out I came back when the monsoon's were rolling in, high humidity, 108* temps, the boat was down on power a tad.

Maybe my little v-6 doesnt have the power to turn the 4 blade

The extra blade isn't the issue, pitch maybe, but not the extra blade. I'm running a 18P 4 blade Alpha4 prop on my 140HP Mercruiser, 1:98 ratio drive. My boat was a slug with a 19P 3 blade and the 18P 4 blade turned it into a completely different boat.

I wonder how good of a design the MW 4 blade props are? I have one as a backup, but haven't tried it yet. I'd venture to say, if you did a side-by-side test with Michigan wheel, Quicksilver, Solas and Turning Point 4 blade props, one of them would perform better than the others, on "your" boat. For as good as the Alpha4 prop works on my boat, I think I dumb-lucked into selecting it.

 

[truckermatt]

Re: Update on a 3 blade to 4 blade prop switch

I wonder how good of a design the MW 4 blade props are? I have one as a backup, but haven't tried it yet. I'd venture to say, if you did a side-by-side test with Michigan wheel, Quicksilver, Solas and Turning Point 4 blade props, one of them would perform better than the others, on "your" boat. For as good as the Alpha4 prop works on my boat, I think I dumb-lucked into selecting it.

I was wondering the same thing also, When I used the Quicksilver 14x20p, the blades were about 3/4 away from the anode on the drive,

but this Michigan wheel prop sits way forward of that and has about 2 inches of clearance. and its 14.5" diameter

In my almighty quest I may try a quicksilver 14x18p 4 blade

 

[Texasmark]

Re: Update on a 3 blade to 4 blade prop switch

I was wondering the same thing also, When I used the Quicksilver 14x20p, the blades were about 3/4 away from the anode on the drive,

but this Michigan wheel prop sits way forward of that and has about 2 inches of clearance. and its 14.5" diameter

In my almighty quest I may try a quicksilver 14x18p 4 blade

If you are talking about the trim tab when you say "the anode on the drive" then you have just described a bass boat prop with a high rake with the short dimension and a prop more made for an I/O with the 2" gap. First one is for bow lift on a BB. They run on a "pad", long flat surface at the rear of the hull. Getting the bow up helps to remove the boat from the water helping the pad be the only water contact hence decreasing drag and increasing speed. An I/O, especially a deep V rides pretty much in the water and I have been told that you do better without the high rake on them. Mr. DHadley can instruct you.

Mark

 

[fishrdan]

Re: Update on a 3 blade to 4 blade prop switch

I was wondering the same thing also, When I used the Quicksilver 14x20p, the blades were about 3/4 away from the anode on the drive,

but this Michigan wheel prop sits way forward of that and has about 2 inches of clearance. and its 14.5" diameter

I had to bust out the grinder and modify the trim tab (anode) on my MC1 drive to make the 14.5x18p Alpha4 prop fit, otherwise the prop was hitting the trim tab. There are different shaped trim tabs, so yours might have more or less prop clearance than mine. I haven't had the 18P Alpha4 and 18P MW 4 blade side-by-side to compare the blade geometry and the height of the props, so I'm not sure how they compare to each other.

 

[theBrownskull]

Re: Update on a 3 blade to 4 blade prop switch

I had a 1997 Starcraft with a Mercruiser 4.3 190 V6 in it with a basic Mercury SS 19 pitch three blade Vengeance prop. on it. That thing would turn 4800 RPM all day long and would practically throw you out of the back of the boat when you canned the throttle from a dead start. If you are unhappy with the four blade try something else.

 

[truckermatt]

Re: Update on a 3 blade to 4 blade prop switch

I had to bust out the grinder and modify the trim tab (anode) on my MC1 drive to make the 14.5x18p Alpha4 prop fit, otherwise the prop was hitting the trim tab. There are different shaped trim tabs, so yours might have more or less prop clearance than mine. I haven't had the 18P Alpha4 and 18P MW 4 blade side-by-side to compare the blade geometry and the height of the props, so I'm not sure how they compare to each other.

when i had the quicksilver 14x20p 4 blade I had too change out the anode to a "racing" one by mercury in order to have the clearance.

 

[truckermatt]

Re: Update on a 3 blade to 4 blade prop switch

I had a 1997 Starcraft with a Mercruiser 4.3 190 V6 in it with a basic Mercury SS 19 pitch three blade Vengeance prop. on it. That thing would turn 4800 RPM all day long and would practically throw you out of the back of the boat when you canned the throttle from a dead start. If you are unhappy with the four blade try something else.

I started with a 3 blade alum. 14.25x21p and it ran 4700 rpm WOT I am happy with the prop, I just wanted to see if I could get more holeshot because the majority of what I do is ski/ tube

 

[jestor68]

Re: Update on a 3 blade to 4 blade prop switch

I have a Solas Rubex 4 (aluminum) that I use for serious skiing.

Since you're starting with a 21", the Rubex 4 14-3/10 X 19" seems the logical step (-2") when going to a 4.

 

[truckermatt]

Re: Update on a 3 blade to 4 blade prop switch

I had to bust out the grinder and modify the trim tab (anode) on my MC1 drive to make the 14.5x18p Alpha4 prop fit, otherwise the prop was hitting the trim tab. There are different shaped trim tabs, so yours might have more or less prop clearance than mine. I haven't had the 18P Alpha4 and 18P MW 4 blade side-by-side to compare the blade geometry and the height of the props, so I'm not sure how they compare to each other.

Well I now know that the Michigan wheel prop has blade that dont extend past the rear pf the exhaust hole. while the quicksilver prop I had the blade extended a little past that point. It might be called rake or something like that.

 

[truckermatt]

Re: Update on a 3 blade to 4 blade prop switch

double post :-(

 

[86 century]

Re: Update on a 3 blade to 4 blade prop switch

I went from an unknown make 14x19p to a 14x17p solas amita or however they spell it.
Made a huge difference in over all performance only lost about 2mph off the topend.

 

[truckermatt]

Re: Update on a 3 blade to 4 blade prop switch

Ok, Well here is another update for another prop test.

This time a Quicksilver 14.5x18p 4 blade.

43mph @ 4800rpms 90% trimmed out

Hole shot is very nice and noticeable but if I trim further I can rev it to 5000k and 44 mph obviously too much.

If quicksilver made a 14 x19p 4 blade alum I would be great I think.

But I think I am going to keep this prop because my cruise speed is nice and if i gun it from a stop it doesnt over rev. Only at higher speed which i rarely go.