New 2:1 Transmission

[DJ13]

Does anyone know the benefits and which boats it will be in? Thx

[UNSTUCK]

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.

[robricketts]

I believe the 2:1 is standard in the rzx boats with all motors other than the 575. Perhaps I’m wrong on the 575 but I believe it’s business as usual for the r z and rz series boats.


Sent from my iPhone using Tapatalk

[freeheel4life]

UNSTUCK,
The 2:1 are running an 1 1/4" shaft. Also has a bigger strut(longer distance from hull to cutlasss bearing) to get more angle allowing prop to be curther from the hull. Which in turn accommodates the larger diameter props. Had and rzx customer damage his prop and thought a regular ol ACME weekend saver kit would get him on the water. He realized quite quickly his weekend was over when he went to swap props.

[UNSTUCK]

Yes, I did know about the 1 1/4" being used. I guess my remarks are based on someone (me) wanting to try to upgrade their old drivetrain with a 2:1 system. I have been thinking about going this route instead of installing a supercharger, if I keep my boat.

I have been wondering what all was done on an RZX to make room for the bigger props. I figured they used a longer strut to get more angle. What are they doing on the other end? Does the V-drive have a different angle on the output or are they just raising the V-drive higher to allow the prop shaft to angle further down? With the new 1 1/4" prop shaft being used to prevent breakage, did the V-drive get beefed up too, or were they already strong enough? I doubt it was needed, but did they have to adjust the prop shaft through hull because of the shaft now sitting a bit lower? I realize a little movement at the V-drive would mean quite a bit of movement at the prop, so maybe very little adjustment was needed to make all this work. Especially considering the supercharged boats would still be using all the older parts (original shorter strut, etc.).

I need a 2:1 transmission that will bolt up to my GM engine. Who is using that combo, Nautique or maybe Malibu? I need to price out some parts!

[bsreid]

I may be wrong but I think Malibu is and maybe Supra... unstuck, what engine do you have in your mb that needs more power?

[Germaine Marine]

The only people I think currently using the 2-1 are nautique, Malibu, mastercraft and Tige to my knowledge.

[freeheel4life]

Yes, I did know about the 1 1/4" being used. I guess my remarks are based on someone (me) wanting to try to upgrade their old drivetrain with a 2:1 system. I have been thinking about going this route instead of installing a supercharger, if I keep my boat.

I have been wondering what all was done on an RZX to make room for the bigger props. I figured they used a longer strut to get more angle. What are they doing on the other end? Does the V-drive have a different angle on the output or are they just raising the V-drive higher to allow the prop shaft to angle further down? With the new 1 1/4" prop shaft being used to prevent breakage, did the V-drive get beefed up too, or were they already strong enough? I doubt it was needed, but did they have to adjust the prop shaft through hull because of the shaft now sitting a bit lower? I realize a little movement at the V-drive would mean quite a bit of movement at the prop, so maybe very little adjustment was needed to make all this work. Especially considering the supercharged boats would still be using all the older parts (original shorter strut, etc.).

I need a 2:1 transmission that will bolt up to my GM engine. Who is using that combo, Nautique or maybe Malibu? I need to price out some parts!

Havent got to dive into this stuff much because you usually find all this stuff out after someone runs aground and requires serious repairs. I doubt that angle would be changed at v drive coupler as Indmar has been doing a thru shaft where it couples at front of v drive not behind it like in years past. I believe all the angles are matched via motor mounts and entire engine trans and v drive are set at inverse angle to whatever shaft angle is. Again just a guess as this is all new stuff that is mostly either sitting in the parking lot waiting to be sold or just in service and hasn't had any reason to dive into it.
To retro a 2:1 I think you would have to pull the motor(obviously), drop out shaft, remove thru log and drill out glass to accommodate a larger log for the 1 1/4" shaft. Also you would possibly have to get Marine Hardware to cast you a one off strut depending on if you are going to mount strut in the same location as the old one. Plus a new shaft seal, new 1 1/4 shaft, and new prop, you are starting to really rack it up in costs. Oh ya and theres the cost of new gearbox. Wouldn't be surprised if this turned into a 40 hour project easily, on top of some serious $ in parts.
Would be a neat project, but I'm sure would involve some hair pulling and choice 4 letter words. Some actual math/engineering for the guys at Marine Hardware as well. Would have Precision Propeller tweak the cup on my prop dirst, but a bit late this year for that.

[UNSTUCK]

I have the GM L96 engine. (Indmar 410) At my elevation and 5000 pounds of ballast available, I just can't get it done. In order to run all the weight I had to use a 2937 prop, which had me surfing at over 4500 RPM. Just to fast for me. I now use a 2419 and run at or just under 4000. I can't fill all my ballast now. More like only 3000 pounds. I was thinking of adding a supercharger, but now I think this may be an easier way to do it as I'm stuck (see what I did there?) between getting the ECM tuned or maybe losing Zero-off.
I need to puts a parts list together and figure how to price them out. I estimate the SC to cost me about $6000 depending on what happens with the cruise control.

So:

2:1 transmission
V-drive (unless I can reuse mine, unlikely)
1 1/4" prop shaft and coupler to v-drive
Prop shaft seal
Longer strut with bearing
17" prop

If all that is cheaper than 6k it would be worth looking into to see if it would work.

[freeheel4life]

Also the log. Its the piece where shaft passes thru actual hull of boat. Believe you would have to upsize it, and if you did you may not have the room on the glass to mount a new one depending.....

[IDBoating]

I'll toss this in here....

I had a discussion with the Senior Engineer at a prominent inboard company about 2:1 transmissions and (especially about) larger props. The big deal on their side is the angle of the propshaft. As you enlarge the prop, you need more clearance from the hull. The "easy" way to get that is to increase the angle of the propshaft, by lowering the back end (i.e. the longer strut folks here are talking about). Then remember that the stern is often lower than the bow while underway, which further increases the propshaft angle.

Why does this matter? Because of the angle of thrust coming off the prop. Theoretically you'd like the prop pushing straight back, the propshaft level with the water's surface. But that's not practical in an inboard so we tolerate some down angle, recognizing that as that vector changes from purely horizontal to having some vertical component the system is getting less efficient. Now, take it to the extreme: A vertical propshaft would give you zero forward propulsion as the prop tried to lift the hull straight up. You can see that as the propshaft angle goes more and more away from truly horizontal, things get less and less efficient.

If you retrofit a larger prop by just increasing the propshaft angle, you decrease the efficiency. Then the hull angle while underway increases the angle even more, reducing efficiency yet again. Somewhere in this the benefit of that larger prop is lost in water churned at the wrong angle (that vertical component of the vector, toward the bottom of the lake).

The "less easy" way to get more prop diameter without increasing the propshaft angle is to lower the front of the propshaft too. Trouble is, the v-drive cannot be lower than the hull. So the last variable in the geometry would be to shift the v-drive farther forward in the hull. If you draw this out as a right triangle you'll see that moving the v-drive forward gives you a reduction in propshaft angle. However, it has to move a LONG way forward to get much of a change in that angle, and the whole point of v-drives is to keep the weight and bulk toward the stern. I guess if you were really crazy you could do an old skiboat-style midengine design but use a v-drive orientation instead of direct drive. But that defeats the purpose of the whole exercise.

I wonder if something could be done with the profile of the hull near the transom. Maybe a semicircular recess that projects forward so the prop sees uninterrupted water flowing toward it, but the propshaft doesn't have to drop. Basically like the transmission hump on the floor of a car.

[freeheel4life]

All great points IDboating. Some '12ish Sangers ran a drive shaft from trans to v-drive and vdrive was mounted further toward bow with its own brackets. Always wondered why, maybe that was it. also some manufacturers did a prop bubble to allow clearance for a larger wheel without prop burn

[IDBoating]

Here's an excerpt on the topic:

What is the proper shaft angle to use? A shaft angle between 10 and 14 degrees is common, with 12 degrees sometimes considered as "standard". In many cases, however, a 16-degree shaft angle is used, especially in shorter boats. While shaft angles steeper than this are permissible (assuming that the engine can handle this inclination), sacrifices will be made to efficiency at the propeller. Therefore, it is best to avoid a shaft angle exceeding 16 degrees. However, the key word here on the boat and conditions of use, operating conditions could increase the angle of the motor, such as could occur when encountering rough seas, or if the boat trims down or "squats" by the transom while underway. Obviously, these factors could effectively increase the "operating" shaft angle and perhaps impair the lubrication capabilities of the engines. So whenever possible, the lower shaft angles are desirable.

In very fast boats, especially those used in competition, such as the vee drive type, or those with the motor forward of the driver, shaft angles will often be at much less than 12 degrees. Theoretically, the thrust of the propeller resolves itself into two forces; one giving the lift, and the other imparting the forward motion. If the angle is at a minimum, there will be a greater force forward than if the angle were steeper. However, for normal boats at normal operating speeds under normal conditions, shaft angles between 10 and 16 degrees have shown through years of experience that there is little practical variation in speed and efficiency in this range of shaft angles.

[JohnnieMo]

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

[UNSTUCK]

ID, good points. I've spent some time thinking about this as well. I just grabbed my 5' long test prop shaft (ok a broom handle) for a little experimenting. I need the end of my prop shaft to sit 1" lower than it does now in order to fit a 17" prop (I have a 15" prop now). So 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*. I don't know how long my real prop shaft is, but I bet it's close. 1.5* is not much at all. I really think the biggest issue would be lining up the new shaft position in such a way that it doesn't bind at the V-drive couple. I'm sure it would be a mix of dropping the engine mounts and raising the V-drive mounts. And that's good to do anyways as it would sit more level during surfing with ballast at slow speeds. Now I'm curious to see what my current prop angle is during surfing. 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, plus my current prop angle then add 1.5ish and hope all that's less than 16*. I'll have to look at my boat when I get home.