Mirage Plus props on V6 Alpha One's?

[EricW]

I've currently got 13.75 x 21 Vengeance props on my twin 220hp 4.3 MPI Alpha One GenIIs. The boat is a 94 290 DA. I'm thinking about going to 15.25 x 19 Mirage Plus props.

Overall performance is currrently what I would call "good". WOT with the boat lightly loaded is 42 mph (gps) at almost 4800 rpms. Trim tabs full up and drives trimmed out slightly.

With a light load, the boat gets on plane nice and cruises relatively slowly -- I can keep it on plane nicely at about 3300 rpm and 26 mph. 3800 gets me 30 mph.

Loaded down, planing and cruising performance suffers quite a bit. The boat is VERY stern heavy with passengers and full fuel. The 130 gal fuel tank runs across the boat completely behind the aft cabin, right in front of the engines. The fresh water tank is right in front of the fuel tank, under the rear aft cabin bunk. The stern also has a generator, 4 batts, holding tank, plus the 2 FWC motors. This boat is very stern heavy even compared to other Sundancers. With 6 adults and full fuel, it takes a long time to plane, even with trim tabs down. With that load, the boat falls off plane below 3800 rpms.

I was thinking that larger diameter props with more surface area would hold the boat on plane better with a load. Maybe there would be less slippage and better overall performance since the boat is very stern heavy for a pair of little Vengeance props.

I've had good luck with SS 3 blade props on previous boats, so I thought larger 3 bladers might give better overall performance than switching to alum 4 blade props.

Any thoughts/opinions/experiences?

 

[390pi]

I have a '92 290DA w/ 4.3s.

I run 14x20 4 blade aluminum 48-834854A45 and 48-834855A45), which helps with the heavy stern. I can also run at slightly slower speeds/rpms and still plane.

With a fully unloaded boat, I used to be able to do 42mph, but as you add stuff, it slows down. Of course, I have the 4bbl/175hp 4.3's.

The stock props were probably 13.75x21, which is what you have.

I do not see a need fo SS props on boats like these.

Try the aluminums; they are around $100/ea.

 

[EricW]

I picked up a pair of 15.25x19 Mirage Plus props used at a good price. I just put them on and ran the boat. By myself, with between 1/2 and 3/4 tank of fuel.

So, I dropped 2 inches in pitch but went from smaller blade area Vengeance to larger area Mirage Plus.

Interesting results.

As soon as I put it in gear and moved forward, I noticed a difference. The boat responded quicker, and speed at idle rpm is at least 1/2 mph faster. Then, the boat planed a lot quicker and 3100 now gives 26 mph. 3500 gives 30 mph. 3800 gives 34 mph. Hopefully, I will be just as pleased once the boat is loaded down.

I slowed to 2800 rpm and the boat stayed firmly on plane at 22 mph with no tabs.

WOT was now only 4500 rpm, and top speed was 41.5 mph. My previous WOT was 4700 with 21p props, and one time before with very low fuel I hit 42 mph. I couldn't hit 42 today, but I would say that top speed is essentially the same, but turning 200 rpm less. I guess it all comes down to reduced prop slip ratio.

Overall, I'm very satisfied. Cruising RPMs are lower, and planing performance is significantly improved. Pretty interesting that dropping 2 inches in pitch dropped my WOT rpms by 200 rpm.

 

[sr330daguy]

I picked up a pair of 15.25x19 Mirage Plus props used at a good price. I just put them on and ran the boat. By myself, with between 1/2 and 3/4 tank of fuel.

So, I dropped 2 inches in pitch but went from smaller blade area Vengeance to larger area Mirage Plus.

Interesting results.

As soon as I put it in gear and moved forward, I noticed a difference. The boat responded quicker, and speed at idle rpm is at least 1/2 mph faster. Then, the boat planed a lot quicker and 3100 now gives 26 mph. 3500 gives 30 mph. 3800 gives 34 mph. Hopefully, I will be just as pleased once the boat is loaded down.

I slowed to 2800 rpm and the boat stayed firmly on plane at 22 mph with no tabs.

WOT was now only 4500 rpm, and top speed was 41.5 mph. My previous WOT was 4700 with 21p props, and one time before with very low fuel I hit 42 mph. I couldn't hit 42 today, but I would say that top speed is essentially the same, but turning 200 rpm less. I guess it all comes down to reduced prop slip ratio.

Overall, I'm very satisfied. Cruising RPMs are lower, and planing performance is significantly improved. Pretty interesting that dropping 2 inches in pitch dropped my WOT rpms by 200 rpm.

Great to hear, you have more blade surface and diameter ,which will decrease your RPM as will more pitch.Those props also had more cup added.

 

[CAGE RATTLER]

Hey Eric,

As much as you've helped me dial in my prop after the repower, I feel funny giving you suggestions.

But I'd be worried with the 4500 WOT rpm's. Once you get a heavy load in rough seas I'd be worried about lugging the engine to much.

Definately odd that the rpm's went down with a 2" lower pitch but i guess thats due to the different type of props.

Now go try some Rev 4's so i know what they will do for my setup :grin:

 

[sr330daguy]

With Eric's new mid range numbers I wouldn't be concerned,he well with in his engine operating range.Really who runs their engines wide open all the time?If he feels he needs the 200 Rpm he can have some of the cup taken out,as these props had more added in attempt to cure a slight cavitation problem.

 

[EricW]

Hey Rick ---

I do actually wish WOT rpms were a bit higher. 4500 WOT is still in the 4400-4800 recommended range, though. And I tell you, cruising performance at all speeds has improved. No signs of lugging/bogging when getting on plane. It really holds lower speeds well. We went to Canton last night, and came back today. There were 4 adults and gear on the boat. I slowed to 2800 rpm/22 mph and the speeds & RPMs just stay put. Bump up to 3300 rpms and speeds stay put right at 30 mph. The boat just didn't cruise as nice with the old props -- I used to feel like I had to move the throttle a lot. Before, if I tried to achieve about a 24 mph cruise, the boat would start to gradually keep slowing. Then, I slightly bump the throttle up and I would start going too fast.

Having a bit of cup or pitch removed is great option. So far, though, I haven't noticed the engines struggle with the props as they are.

 

[sr330daguy]

Don't forget your RPMs will go up as the air gets cooler and dryer,Its been a steam bath here in upstate NY.

 

[CAGE RATTLER]

Hey Rick ---

I do actually wish WOT rpms were a bit higher. 4500 WOT is still in the 4400-4800 recommended range, though. And I tell you, cruising performance at all speeds has improved. No signs of lugging/bogging when getting on plane. It really holds lower speeds well. We went to Canton last night, and came back today. There were 4 adults and gear on the boat. I slowed to 2800 rpm/22 mph and the speeds & RPMs just stay put. Bump up to 3300 rpms and speeds stay put right at 30 mph. The boat just didn't cruise as nice with the old props -- I used to feel like I had to move the throttle a lot. Before, if I tried to achieve about a 24 mph cruise, the boat would start to gradually keep slowing. Then, I slightly bump the throttle up and I would start going too fast.

Having a bit of cup or pitch removed is great option. So far, though, I haven't noticed the engines struggle with the props as they are.

I know what you mean. The 21P mirage plus i tried just felt fantastic too. I was also at 4500 WOT rpm but im still going to see what i get with a 19P next weekend. Still wish i could find a rev 4 to try before i make the final purchase.