Prop Slip Test

212rowboat

my contention is that during your transition between displacement to plane, you're not getting completely up on the 'pad' step... 

212rowboat

in that last pic, as viewed from underneath while on plane, you can see the entry is behind the entry angle of the bow on all three planes- and you can imagine the force is directed to the 'pad'...

if you look closely you can see vertical lines in the pic in the yellow of the boats hull... third from the left is where the water is cutting the water, but not where the majority of the force is... but where that cuts is behind where the angle transitions to a flatter region... that doesn't complete it's transition until it's where the center line of the hull (keel) intersects the 4th vertical line... the 'whisker spray' is completely above the water line for all practical purposes, only touching it from time to time to make that spray... the weight of this hull is from the sixth vertical line back... it is firmly on the 'pad'... 

Dream_Inn

I'd often wondered if SS props would be a good way to go for me on my B-2s as well.  @alswagg?  How about 4 blade?  The boat does perform well and decent hole shot for the load I'm pushing I guess.  She also seems to stay steady with a buddy's 2007 400 with B-3 drives.  I've tried to do some direct comparisons with his boat, but he tends to run his generator a lot, so haven't had exact numbers to compare yet.

212rowboat

Handymans342

Dream, you dont have SS blades? What do you have?

Dream_Inn

Handy, if ain't SS, then it's gotta be aluminum.  I have a couple big AL props (17.5 X 23P)

Michael T

At higher RPMs aluminum blades will actually changetheirs pitch but not at cruiser speeds. That happens at 60 MPH+. One thing I haven't read about is whether or not aluminum blades might flex under LOAD and change their pitch? Hmmmmmm

randy56

@ Handy, off topic, there is a 2002, 342 for sale on e-bay with BB, if you want another one, read what it says about top speed, wot, you could have one for week days and one for week ends.

rasbury

I would have thought all the boats, especially the cruiser boats, would come with at least the optimum pitch with the design of a hull- why issues mow?

Handymans342

Nevermind

Dirtythirty

Alswagg Posts: 903Member ✭✭✭✭

March 4

Stainless is thinner blades which cut or pull better than aluminum. Yes alum will flex some but not sure the amount on B 2 blades.  Most Rinker cruisers had B3. The 420 only had B 3 XR drives.  

My 420 has Nibral props which came as standard for the IPS drives. I replaced the origials, and they weren't cheap.  But I'm being told they are extremely rigid, strong and durable.

Dirtythirty

Cableguy Greg

Now that is a prop!!!

Handymans342

My slip test was 33. I don't get it. What should it be???????

jmichels

Hey Stranger! Glad to see you are living the dream in the diesel torque monster !

Back to the OP.  It is not uncommon for any engine gas or diesel to have a set rev limiter to not allow it to redline when at idle or no load. In fact I have never seen any engine gas or diesel that you could rev to redline that was computer controlled.  This protects the engine from over revving or "running out" . The easiest way to blow a engine would be revving it hard to redline and then letting out. The rods, crank, piston and bore in that Yanmar are probably massive and the rapid deceleration on a engine with no load can spin a bearing pretty easily and or over rev as well. I would not be surprised one bit if Yanmar has set a governor to protect the motor under no load. Whether or not you are reaching maximum rpms or desired maximum rpms under load at WOT is another story. What are you using to obtain the maximum rpm reading? 

Further more. I learned today that the props pitch can be fine tuned by a good prop shop and increased or decreased to give you those rpms you are looking for without replacing the props. Pretty neat.  It could also be the props simply need to be trued back to factory spec and rebalanced. 

Looking forward to following the results on this......

Handymans342

Josh, I dont need more RPM. I cant get any more speed without more RPM out of the motors. I may be able to go to a 4 blade prop but thats about all I can do. I was just trying to understand this formula. Why do I have a 1.67 outdrive? ETC. 

raybo3

Handy if I am not mistaken you have Bravo 2's. What would happen if you spent some of your $$$$$$$ and changed over to BravoIII's?...... Just say'n....

Handymans342

Ray, if I did that, I would install Yanmar Drives. How would you know what to install gear ratio wise???? What prop? Guess I need a marine engineer.

raybo3

Handymans342 said:

Ray, if I did that, I would install Yanmar Drives. How would you know what to install gear ratio wise???? What prop? Guess I need a marine engineer.

I am sure Al would know.......

Dream_Inn

Ray, I'm not sure what switching to B-3s would do (except cost a lot more money).  I have B-2s and I believe had better pickup and top end compared to the identical boat with B-3s.  The two of us did a 10-day trip together this summer and performance and efficiency were same, maybe a tad better on my boat.

Handymans342

Yes, nothing wrong with B2 drives. They are a beast

raybo3

Just thinking that maybe with the 2 props there would be less "slippage". I totally understand that the B2 is a "beefy" drive. Now I am really thinking. If there was no noticeable difference between the drives then why do the use the B3 if the B2 is beefier???????? Just say'n......... 

Michael T

On most applications the B3 blows the B2 out of the water, performance wise. I have seen side by side comparisons of Rinker EC 340s with B3 and B2 drives. The B3 was better in every category. When Volvo first introduced the counter-rotating duoprop 10 years before Mercury, there were so many tests that proved that point it isn't worth debating. When Volvo's patent expired mercury had its B3 ready to go and again mercury's B3 beat its own B2 and B1 hands down.

My guess would be that on a very large application, one that would be the outer limits of a gas/stern drive application - and an EC 400 would be exactly that - imo, the B2 might perform better. Where I boat they call the B2s "barge drives".  

Handymans342

I hear all you guys but how is the drive ratio and prop determined for a particular motor?? It has to be engineered. I have a 1.67 drive, why not a 1.8 or a 2.1  What difference would it make?

Michael T

I posted a formula a couple of years ago, when a similar conversation took place, to determine slippage. It should be in the archives?

Handymans342

19 diameter 23pitch

Handymans342

And its a Diesel X Bravo 2. If that makes any difference 

Handymans342

Michael T said:

I posted a formula a couple of years ago, when a similar conversation took place, to determine slippage. It should be in the archives?

Find it MT please

Michael T

Steve, I'll try. I have gotten rid of a lot of files. I may still have a binder of formulae.

randy56

@Handymans342, I'm keep trying to figure out what you are trying to accomplish. I thought your boat ran great, plane time was short, plenty of power. Strong on torque, you can feel it. You can run all day on a small amount of fuel. so here is my opinion, don't fix it, it's not broke, The Rinker guys studied all this before they put it together. you have a wonderful 342 that is in excelant condition and will out last most, because of the set up you have. I would take longevity over speed any day. Since its not that much differance in speed . Most others will be swaping engine's or boats, and your just broke in good. Ok I'm off my soap box.
   Now if the ole guy still has a need for speed, get ya one of those jet ski's with 300 hp. Those things go so fast you cannot were your hat. LOL