New 2:1 Transmission

[Bakes5]

o

[IDBoating]

@IDBoating - So by weighting down the stern of the boat when we are surfing, this compounds the issue even further. The boat starts trying to lift itself out of the water rather than going forward.

Exactly the point that Senior Engineer was making. "Are we giving up the benefits of a larger prop by increasing the propshaft angle?" A darned good question which will vary boat by boat.

I assume engineers somewhere are pondering all of this and trying to figure out the best angles.

As with everything else, it's all tradeoffs and compromises. Ideally you'd have a zero degree propshaft, but imagine what the drivetrain would look like.

[IDBoating]

putting the broom end on a box and the handle end on a 1" block my "prop shaft" angle was 7*. I then removed the 1" block so the handle was sitting on my workbench. My new prop shaft angle was 8.5*. 1.5* is not much at all.

I agree, you're well within the "industry standard" specs from that article and the increase you're considering isn't big a percentage of what you have now. That said, I suspect the authors of that material were thinking "traditional" boats and not inboards built for surfing, so I have no idea if their standard angles apply to this industry.

Might be interesting to visit the various manufacturer websites and eyeball the propshaft angles they show on their "Build a Boat" pages. Those give you a pretty decent side view, you ought to be able to guess within 10% or so using a protractor. See what the industry average is. If you're within that, I'd say you're golden for a DIY project of this magnitude!

Seems like I remember you saying one time that autowake tries to keep the boat around 6* attitude so I assume that is the ideal angle

There is no single ideal angle, it varies hull to hull and also with ballast amounts and roll angle and your wave preferences and.... The point of AutoWake is to make it easy to get BACK to your preferred wake or wave. Only you can decide what that is!

[Germaine Marine]

As I understand it, the bigger diameter prop you can run the better your boat will perform. That bigger prop will also suck up all your HP. So the 2:1 will put your engine back in the RPM sweet spot and you will have way more performance with that nice, large prop. All of this only works if you can fit a larger (16-17") prop under your boat. The other thing to consider is all the leverage that bigger prop will put against your prop shaft. I don't think I'd want to run the standard 1 1/8" shaft with that big of a prop.

To paraphrase Jason in a conversation we had, the 2:1 is supercharger performance on a poorman's (me) budget.

That Jason guy rules...

[DJ13]

Thanks guys this has turned a bit technical but very good information. Can anyone confirm it will only be in the RZX’s and not the Z or R’s?


Sent from my iPad using Tapatalk

[freeheel4life]

I'm not in sales, am pretty sure it's on rzx line only. No need for it on anything except maybe z3 and r23 for guys that want to run serious weight. Not even sure Tige would even let you option it onto an r or z series boat..

[KoolAid]

Only for the RZX2/3 models.

[UNSTUCK]

When I asked "sales" about that they seemed to think it could be done at least in the Z. Didn't ask about R, but if they can do it in a Z they can do it in an R. Now if they will or not.....

[TigeFamily]

Is the whole point of a 2:1 transmission to be able to get the power that you need out of a smaller engine? Guess I just don't know enough about how this all works together.

Haven't props come a ways in last few years to allow great low end torque without sacrificing all your top end? I have a 24ft boat with ZR409 engine and 1.48 trans and even tho I can fit a 15" prop....I run a #1433 (14.25x14.25) since I have gotten best results with it. I have 5000lbs of ballast and use a suck gate and rpm is 3400 @ 11-11.2mph. Even with 6-8 people the boat does not struggle and will go 13mph pretty easy at 4000rpm (tested one day just to see how close it was to maxing out on power)....empty ballast the boat will hit 40mph. Guess the only benefit I can see from being able to run a 17" prop may be lower rpm's, but in mine at least I don't see the point of that either since I average 4.5GPH surfing. I am only at 800ft elevation tho and may think differently if I was at 5000ft like some of you guys.

In this situation I could see it...I have a friend with a 2006 Malibu 247. He has bigger engine than me (8.1 with 450HP) and runs at lower rpm (under 3000) when ballasted with 5000lbs and surfing at 10.8-11mph, but he cannot go any faster than that at all, it basically flatlines.....so he decided to change his trans over the winter. He has a 1:1 now and is going to a 1.48. From his research, he is pretty sure that will increase his power. I am sure he is correct since he is in the racing industry. Told him I want to help him with the swap so I can learn something about this stuff.

[Bakes5]

I predict we will be having this same conversation in 2020 regarding 2.5:1 or 3:1 transmissions and 8000 pounds of ballast.

[UNSTUCK]

Is the whole point of a 2:1 transmission to be able to get the power that you need out of a smaller engine? Guess I just don't know enough about how this all works together.

Pretty much. Think of a rock crawler needing bigger tires to crawl over larger rocks. The tire size is the final gear ratio in the drivetrain. When they get bigger it brings down the engine rpm's (ie HP) at a certain speed compared to before the tire swap. To overcome the added load and lower RPM's the driver has to go to lower gears in the axles (or transmission/transfer case). With the lower gears he now has the mechanical advantage that he had before and things stay equal, for the most part. So to answer your question, but to take it a bit further, the whole point of a 2:1 trans is to be able to get the power (not really more power, but more mechanical advantage) out of a smaller engine in order to spin a larger prop. The larger prop gives you the pulling power you need and still be able to cruise at a higher MPH. Whereas on my big boat now with a 15" prop, I can have all the pull I want, but it falls way short on cruise speed. But I don't have the "power" to spin a larger prop right now so I have to choose between pull and top end speed.
The two ways to overcome my problem would be to go 2:1 or add more HP to the engine.

Someone correct me if I got it all wrong.

[chpthril]

@tigefam,

Moving a heavily ballast boat not only takes engine power, but takes traction. That traction comes from the prop. Larger prop means better traction due to more surface area. Lower pitch also helps with traction and improved performance, but we can only go down so far in pitch, before the negative effects outweigh the gains. Same with going up in diameter. We can only go up so much before we get a negative effect. The main ones are prop burn or just can physically fit the larger dia prop, loss of engine power to turn the large wheel and too much drop in engine rpm, putting then engine on the low side of the power band. The 2 later go hand in hand kind of.

So no enters the gear reduction drive. Up until a few years ago, we had about 1.5:1 gear and these could spin a 14.5" prop real well and some 15" props depending the engine HP/Torque and the prop's pitch. Then a couple years ago, we saw a jump to a 1.7ish to 1 and now we are seeing the 2:1 gear. All the while, seeing larger and larger wheels. So, larger wheel = better traction, gear reduction needed to prevent robbing all the engine power to turn said larger wheel. As a package deal, the boat pushes the ballast, has a decent rpm and can still hit a respectable cruising speed.

[TigeFamily]

gotcha, thanks

[Germaine Marine]

You wont see higher then 2:1 the physics behind it have simply capped that side.

To be honest, I really think a 1.75:1 with the strut change etc for clearance would have been the home run. The angle Tige could squeeze out while adequate , was not enough in my opinion. I think they could only get so much before the negative aspects started creeping in.

The money prop diameter with the 2:1 is 18 inches.... you slide the pitch way down and let it rip. Problem is, we just dont have enough room. The 17 inch props are working great im just being ultra picky about what I think would have been ideal. A few Makers run that setup and the performance is incredible.

The 17 runs great it just doesent maximize the reduction to its full potential.

Acme is tooling for an 18 diameter prop just for that reason.

1.75 with a 16.5-17 inch wheel I can only imagine would have been dynamite.

[bsreid]

What about acme 5 blade props, anything good there?