5 blades vs 4 or 3 blade

[LubeDude]

Re: 5 blades vs 4 or 3 blade

Originally posted by BillP:<br /> Adding a doefin will let it trim even higher before blowout. It may not look "cool" but it is faster.

<br /><br />Finns are out of the water at WOT, (or should be) Therefore have no effect when trimming!

 

[BillP]

Re: 5 blades vs 4 or 3 blade

Originally posted by LubeDude:<br />

Originally posted by BillP:<br /> Adding a doefin will let it trim even higher before blowout. It may not look "cool" but it is faster.

<br /><br />Finns are out of the water at WOT, (or should be) Therefore have no effect when trimming!

Lubedude, <br /><br />I'm speaking from 15+ years of experience with and without the fin. My post is 100% accurate. Your comment is 100% inaccurate.<br />The fin deflects the rooster tail down and around the prop when trimmed high. I blowout at 5900-6000 without a fin and hit the rev limiter with the fin...the rev limiter is set at 6300. I have to pull the throttle back to keep it from bouncing off the rev limiter.

 

[walleyehed]

Re: 5 blades vs 4 or 3 blade

The idea here, guys, is to require the least amount of trim (positive) and still keep the nose up and free..the best way to do this is to raise the engine, let the prop maintain efficiency. It's NOT operating at it's best if it's throwing water, tail or no tail.<br />Engine heigth, set-back and prop diameter are most important for performance apps.<br />BiilP, that is an unusual situation you have there, and it baffles me as to what is going on.<br />the flow from the prop is going up and back at a much faster rate than your fwd speed, so I'm not understanding how it's putting water back in front of the prop....???<br />In the testing of props, jackplates and engine heigth issues...with and without fins, never have I seen a faster set-up with a fin.<br />I'd like to hear a little more about your set-up- Boat/engine, mounting heigth, prop...that kind a stuff. It sounds unique!

 

[LubeDude]

Re: 5 blades vs 4 or 3 blade

Originally posted by walleyehed:<br /> BillP, that is an unusual situation you have there, and it baffles me as to what is going on.<br />the flow from the prop is going up and back at a much faster rate than your fwd speed, so I'm not understanding how it's putting water back in front of the prop....???<br />In the testing of props, jackplates and engine heigth issues...with and without fins, never have I seen a faster set-up with a fin.<br />I'd like to hear a little more about your set-up- Boat/engine, mounting heigth, prop...that kind a stuff. It sounds unique!

Im with ya on this one, Goes against everything Ive learned over the years. Ill just sit back and listen. <br /><br />Oh, and by the way, What I said wasnt 100% inaccurate.

 

[Dhadley]

Re: 5 blades vs 4 or 3 blade

My boats have always been faster and quicker with the fin. <br /><br />Now -- keep in mind that there are lots of different designs of fins. Some are so small that they dont hurt even if they are under water.<br /><br />I use the larger ones we built. The whole idea is -- and this is the part most folks miss -- the fin is a tool. It simply allows you to raise the motor higher than you could without it. Higher = less drag. Less drag = a more efficient set up. Higher efficiency = better performance.<br /><br />The fin by itself means very little at best. What you do with the fin, as a tool, is where you gain.<br /><br />Yes, my fin is out of the water when the boats on plane. But it does capture and take advantage of water thats normally going right past the gearcase and lost. We get all the advantages of a better holeshot BUT we get more lift too. <br /><br />We've even seen more water pressure. The water thats normally going up past the gearcase is captured and "stacked up" and more gets into the stock water inlet. With our fin a low water pick up is sometimes needed to take full advantage of the opportunities the tool provides.<br /><br />We did a tripple engine boat once that without the fins would barely get on plane. Once on plane it was a rocket. We added our fins and could raise the motors so high on the jackplates the the low water pick up on the center motor was 2" out of the water. With the fins the boat launched so hard you could ski behind it. And it ran faster.<br /><br />Bottom line is that with the proper fin used the proper way the boat will indeed be faster, run shallower, get up quicker, be more stable and more efficient that without it.

 

[walleyehed]

Re: 5 blades vs 4 or 3 blade

School is in session....thanks for the explanation, DH.

 

[LubeDude]

Re: 5 blades vs 4 or 3 blade

Well Walleyehed, would you like to take a walk together with our tails between our legs??<br /><br />If it were not comeing from Dehadley, I probably would have argued the point into the ground as I have never experienced this myself, quite the oposit.<br /><br />You are right Walleyehed, Life is indeed a learning experience.<br /><br />I have to ask though, "Why dont you EVER see race boats with fins"? Maybe I dont hang around race boats enough!

 

[walleyehed]

Re: 5 blades vs 4 or 3 blade

I think this may be the difference in our applications...most generally, we see the "common" items for standard power boats, however, when performance goes up, so do the tricks of the guys reaching the extra speed or RPM, and I can see where this would start to come into play on some of the faster Bass boats (Race-born performance tricks)and being incorporated into such boats as these.<br />I don't think I will ever be capable of that type of performance with my alum deep-V, but I must say it's got me thinking.......

 

[LubeDude]

Re: 5 blades vs 4 or 3 blade

I have never had a boat that even started to be what you might call a "performance boat" Untill the one I have, and it is reaching speeds of around 65 MPH with the right prop, I suppose with a jack plate, and different props, maybe this may come into play, But even if it would, NO FIN IS GETTING ON MY BOAT!!!, Man I hate those things. Maybe if someone would make a really nice polished aluminum one that actually looked like something, I MIGHT concider it. But where I am today, Its not going to happen.

 

[BillP]

Re: 5 blades vs 4 or 3 blade

Dehadly,<br />Thanks for relating your experience. <br /><br />walleyehed,<br />The idea with my setup was to trim as high as possible with a stock rig (no jackplate, no low water pickup, etc.) for shallow water runs. Fastest hull speed wasn't part of the equation. If going for speed I would go up about 2-3" pitch on the prop BUT it would make unacceptable performance at other speeds...therefore a fin works in this application. There is nothing unusual about the boat, it is a stock 17' Cobia semi-vee with 65hp commercial version OMC engine...a daily driver for casual boating. <br /><br />Where you are seeing ob race boats that don't run with rooster tails and/or engines trimmed up? Most racers trim the engine AND jackplate up to run fastest. They trim the engine up to lift the hull...there are exceptions but normally it isn't done any other way. <br /><br />I can't think of any race rig (or high performance sport boat)that doesn't throw a rooster tail either. The higher the prop, the longer the tail due to increased prop pitch for surface running. If you hang off the back of a boat setup this way you can see the individual blades throwing the tail when they break the surface. The water is also thrown up against the cavitation plate...and fin if installed. Watch the F1s and see how it is done. <br /><br />Like Dhadley says, fins are a tool. The trick is how, when and where to use the tool.

 

[walleyehed]

Re: 5 blades vs 4 or 3 blade

Bill, I understand the fins are a "tool".<br />In setting up for max performance of high-speed boats, 65hp on a 17ft'r isn't apples to apples.<br />F1s run with half of the prop out of the water to decrease prop load, by which they compensate by increasing pitch dramatically-2 different set-ups here. Yes, they throw one heck of a rooster tail, but again, only half the prop is below the water-line, not a "general" set-up.<br />The world speed record (150hp class)for stock engines is held by Merc with a Mazco prop and less than 3 degrees positive trim-stock lower unit, no fins, just a jack-plate and the best prop made by man, setting on the back of an Allison hull. Still yet, a different set-up than what we are looking at on a day-to-day basis.<br />Heck, Bill, I may try some fins on my stock 18ft'r with an OMC 200hp, and I may find some improvements, I don't know...I DO know every set-up is different, and may require different techniques to extract the best performance, and you have done just that, in your case...extracted the best performance for your needs. Good job.

 

[BillP]

Re: 5 blades vs 4 or 3 blade

I really wasn't comparing my rig to performance race boats even though methods are the same. My response was about the fin working to reduce blowout without a jackplate, which it does in spades. The side effect is higher rpms and more speed with a standard ss omc 3 blade prop...and a rooster tail. I believe water deflecting off the fin also provides lift. We are talking the same language as performance rigs, prop blades breaking the surface and positive trim.

 

[Dhadley]

Re: 5 blades vs 4 or 3 blade

<br /><br />OK. Heres a race boat with a fin on it. I couldnt find a really good picture of the fin itself but this will give you an idea of how high we ran the motor. And yes, its a 20" motor on a 20" transom.<br /><br />This was a drag boat so the launch was very very important.<br /><br />Theres better pics at ExtremeBoats@www.msnusers.com